Preparation and Characterization of Hydroxyapatite

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Ministry of Higher Education and Scientific Research University of Technology Department of Production Engineering and Metallurgy

Preparation and Characterization of Hydroxyapatite/ Yttria Partially Stabilized Zirconia Polymeric Biocomposite

A Thesis Submitted to: Department of Production Engineering and Metallurgy- University of Technology In a Partial Fulfillment of the Requirements for the Degree of

Doctor of Philosophy In Metallurgy Engineering Submitted By

Jenan Sattar Kashan Supervised By

Prof. Dr. Amin D.Thamir

Prof. Dr. Jafar T. Al-

Haidary

February 2014

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……….

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Acknowledgment

I would like to thank Prof. Dr. Amin D. Thamir, and Prof. Dr. Jafar T. Al-Haidary for initiating this project, and for the great freedom they gave me to take my own decision in the course of this research and for their helpful advice and directions during my work. Immense thank go to all the staff in the Department of Production Engineering and Metallurgy especially Assistant

Prof. Dr. Ahmed Ali

Akbar the Head of the Dept. and for all help and support . Very special thanks for Prof.Dr. Animesh

Jha

in IMR/ SPEME/

University of Leeds/ UK for all his support and genres advices during my staying in UK within Research Scholarship Program. Many thanks are extended to Yotamu Auhara, Mohammed Javed, Mrs. Mare Gray, Diana and Mrs. Shielagh Ogden in IMR/SPEME/University of Leeds for kind help and advice . Finally I would like to acknowledge the generosity of the Ministry of Higher Education and Scientific Research for financial support within research scholarship program, for the University of Technology /Baghdad, and University of Leeds/ UK for all help during the course of my research.

Jenan Sattar

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‫بسم هللا الرحمن الرحيم‬

‫ْ‬ ‫اسْ‬ ‫ِّ‬ ‫ك الَّ ِذي َخ َل َق َخ َل َق‬ ‫ب‬ ‫ر‬ ‫م‬ ‫ب‬ ‫أ‬ ‫ا ْق َر ِ ِ َ َ‬ ‫ِْ‬ ‫ك‬ ‫ان ِمنْ َع َلق ا ْق َر ْأ َو َر ُّب َ‬ ‫اْل ْن َس َ‬ ‫ْاْلَ ْك َرم الَّ ِذي َعلَّ َم ِب ْال َق َل ِم َعلَّ َم‬ ‫ِْ‬ ‫ان َما َل ْم َيعْ َل ْم‬ ‫اْل ْن َس َ‬ ‫صدق هللا العظيم‬

‫‪4‬‬


Abstract Hydroxyapatite

reinforced

high

density

polyethylene

bioactive

composite, has been suggested since 80s in the last century as an implant and bone analogue materials. Unfortunately, the strength of this composite material is below the lower bounds

for cortical bone. In this thesis, two types of nano sized fillers

have been used; 3 mol %Y-PSZ and HA in HDPE polymeric matrix. Both of the filler particles size and type effect on the mechanical, physical and biocompatibility for the bioactive composite have been investigated by using hot pressing technique to shape the samples at different compression pressures (56, 84, 112, and 140 MPa) at a compounding temperature of 140 °C for 30 min as a compounding time. Scanning electron microscopy with energy dispersive X-ray spectrometer, X-ray diffraction, differential scanning calorimetry, Raman spectroscopy, andFourier Transformation Infrared Spectroscopytechniques have been used in characterization and analysis process. The results showed that the properties achieved for composite samples containing Y-PSZ are very close to that belongs to natural bone. Highest density obtained at 20 volume fraction of both HA and Y-PSZ at 84 compression pressure. Furthermore, highest fracture strength was reported at the same composition but at 140 MPA compression pressure. The biocomposite with Y-PSZ showed less degradation during immersion in Ringer solution. The chemical bonds formed between organic-inorganc phases in the composite are very similar to that of natural bond. These results showed that nano sized Y-PSZ/HA/HDPE composite can be considered as a promising material in bone disease therapies. 5


Abbreviations

CHAp

Carbonate apatite

CCD

Charge-coupled device

FST

Fully stabilized zirconia

FTIR Spectroscopy

Fourier

HA

Transformation

Infrared

Hydroxyapatite

HDPE

High density polyethylene

HAPEXTM

HA-reinforced (up to40 vol %) HDPE

LDPE

Low density polyethylene

LLDPE

Linear low density polyethylene

PSZ

Partial stabilized zirconia

PLLA

Poly-L-lactic acid

SCORIM injection

Shear controlled orientation in Moulding

Tg

Glass Transition Temperature

TZP

Tetragonal zirconia polycrystalline

UHMWPE polyethylene

Ultra high molecular weight

ZTC/ZTD ceramics

Zirconia toughened /dispersed

6


Contents Number

1.1 1.2 2.1 2.2 2.2.1 2.2.2 2.2.3 2.3 2.4 2.5 2.5.1 2.5.2 2.5.3 2.6 2.7 2.7.1 2.7.2 2.7.3 2.8 2.8.1 2.8.2 2.8.3 2.9 2.10 2.10.1

Title Dedication Acknowledgments Abstract Contents Abbreviations Chapter 1 Introduction Objective of the research work Chapter 2 Introduction Biomaterials Interaction with Human body Bioinert Biomaterials Bioactive Biomaterials Bioresorbable Biomaterials Bone Structure Hydroxyapatite Ceramics Polymers Classification of polymers Structure of Polymers Glass Transition Temperature High Density Polyethylene (HDPE) Zirconia Ceramics Crystal Structure Transformation Toughening in Zirconia Ceramics Partial Stabilized Zirconia Requirements for Biomaterials Biocompatibility Sterilizability Functionability Hydroxyapatite–Polymer Nanocomposites Chemical Bonds Characterization methods Laser Raman Spectroscopy 7

Page. No. I II III IV VII 1 3 4 7 7 7 7 8 11 12 13 13 14 16 18 18 19 19 22 22 23 23 23 24 24


2.10.2 2.11 3.1 3.2 3.2.1 3.2.2 3.2.3 3.3 3.4 3.4.1 3.4.2 3.4.2.1 3.4.2.2 3.4.3 3.4.4 3.4.5 3.4.6 3.4.7 3.4.7.1 3.4.7.2 3.4.7.3 3.4.8 3.4.8.1 4.1 4.2 4.2.1 4.2.2 4.3 4.3.1 4.3.2

Fourier Transformation Infrared Spectroscopy (FTIR) Literature Survey Chapter 3 Introduction Materials Hydroxyapatite Yttria Partially Stabilized Zirconia HDPE Powder Composite Synthesis Method Characterization Methods Density and Porosity Mechanical Testing Vickers Micro –Hardness Test Fracture Strength Test XRD characterization Scanning Electron Microscopy (SEM) and Energy Dispersive X-Ray Spectroscopy (EDX) Laser Raman Spectroscopy Fourier Transformation Infrared Spectroscopy (FTIR) Thermal analysis by DSC Non-isothermal Measurements at Different Heating Rates and Constant Cooling Rate Non-isothermal Measurements at Different Heating and Cooling Rates Specific Heat Measurement Biocompatibility Test Ringer Solution Preparation Chapter Four Introduction Physical Properties Measurements Density Porosity Mechanical Properties Vickers Micro-Hardness Fracture Strength Measurements by Diametrical 8

25 27 32 32 32 32 33 34 35 35 36 36 37 38 38 39 39 40 40 40 41 41 41 44 44 44 44 46 46 47


4.4 4.5 4.6 4.7 4.8 4.8.1 4.8.2 4.8.3 4.9 5.1 5.1.1 5.1.2 5.2

Compression Test XRD SEM Imaging Raman Spectroscopy Fourier Transform Infrared Spectroscopy (FTIR) Thermal analysis Determination of Kinetics Parameters Melting and Crystallization Behavior Specific Heat Calculation Bio-Test Chapter Five Conclusions Nano HA /HDPE system Nano YSZ/ HA /HDPE System Recommendations References

9

48 50 58 62 66 66 68 71 83 103 103 104 105 106


Committee Certificate We, hereby, the examining commission, certify that after reading this thesis and examining the student (Jenan Sattar Kashan) in its content, we think it is adequate for award of the degree of Doctor of philosophy in Metallurgy engineering.

Signature: Name: Dr. Thekra Ismael Hamad Title: Assist Professor Member Date: / /2014

Signature: Name: Dr. Bahaa Fakhri Title: Assist Professor Member Date: / / 2014

Signature: Name: Dr. Alaa Abdulhasan Atiyah Ataiwi Title: Assist Professor Member Date: / /2014

Signature: Name: Dr. Ali Hussein Title: Professor Member Date: / / 2014

Signature: Name: Dr. Mohammed JasimKadhim Title: Professor Chairman Date: / / 2014 Signature: Name: Dr. Jafar Al-Haidary DawayThamir Title: Professor Supervisor Date: / /2014

Signature: Name: Dr. Amin Title: Professor Supervisor Date: /

/ 2014

In review of the available recommendation, I forward this thesis for debate by the Examining committee.

Signature: Name: Dr. Ahmed Ali Akbar Title: Assist Professor Head of Department of Production Engineering and Metallurgy Date: / / 2014

10


1 11


1.1 Introduction Bone fractures among the aged mainly among women, is a common phenomenon in patients above 40 years. Low back pain and cervical pain is also a big problem in the society [1]. The bone grafts field has been developed to increase the quality of life of a patient who suffers from a bone disease, (e.g. osteoporosis, osteomalacia, osteogenesis, imperfect) or bone defect (e.g. bone fracture) [2]. Bone disease is a serious health condition that directly impacts on the quality of life of sufferers, particularly among the aged. For this resins, many researchers had taken the challenges to develop new biomaterials for bone grafts applications [3-5]. In the last few decades, substantial research efforts were invested to develop bioactive composites as bone analogue replacement by reinforcing high-density polyethylene (HDPE) matrix with bioactive hydroxyapatite (HA) ceramic particulates [6 -10]. Bonfieldet al. was the first to develop HA-reinforced (up to40 vol %) HDPE biomaterial for skeletal applications and coined a trade name HAPEXTM for HA/HDPE composite [11]. Unfortunately, Bonfield researches could not improve the mechanical strength for this composite system to make it suitable for load bearing bones applications. These results gave a significant induction for other researchers to modify this biocomposite to improve the mechanical properties especially fracture strength which was reported that it is less than cortical bone bonds [12]. Many approaches have been adopted by different researchers to modify this composite which is very similar to the structure of natural bone (inorganic hydroxyapatite in collagen matrix). Hydroxyapatite reinforced polyethylene (HA-HDPE) composite was investigated as a skull reconstruction implant to repair skull defects. HA-HDPE composite is a proven biomaterial as bone substitute, which has been used clinically as 12


middle ear prostheses and orbital floor implants since 1980’s [13]. Partial stabilized zirconia (PSZ) offer ideal filler mechanical and biological properties for this type of biomaterials other than; it has been recorded as bio-inert materials in orthopedic and dentistry applications [14-16]. Superior mechanical properties for PSZ belong to the phase transformation phenomenon as reported by previous studies [17, 18]. Furthermore, the effect of using nano sized hydroxyapatite on the properties of bioactive composites has been studied by several researches as an approach to enhance mechanical and biocompatibility [3, 19, 20]. This thesis consists of five chapters, chapter one give an introduction, and objective of work. Chapter two contains the theoretical part of thesis and literature survey, while chapter three explain the experimental work that has been done to achieve the results. All results and data analysis are reported in chapter four. Finally, conclusions and recommendations for future work have been reported in chapter five.

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1.2 Objective of the research work The aim of this thesis is to modify and characterize mechanical and physical properties for Y-PSZ/ HA/ HDPE nano composite as bioactive material

for bone graft applications as new therapies during bone

fracture in a patient who suffers from a bone disease.

14


2

2.1 Introduction

15


Developing and improving orthopedic biomaterials presents unique challenges given the complexity of the human body and the unique requirements for implanted materials [21]. While biomaterials are not required to wholly resemble bone itself, they must provide functional similarity, since the composition, microstructure, and mechanical properties of the biomaterial affect the surrounding environment [22]. In the past, the goal was to implant an inert biomaterial with adequate mechanical properties, but this approach typically leads to encapsulation of the implant by fibrous tissue. Currently, the most accepted approach is that the ideal bone substitute must sustain and promote cellular function including attachment, proliferation and differentiation, in addition to promoting tissue ingrowth and possessing adequate mechanical properties [23]. Biomaterials interaction with human body has different behavior depending on the type of biomaterials, so that we can classify biomaterials as listed below: i) Biological biomaterials. ii) Synthetic biomaterials. Furthermore, biological biomaterials are classified into soft tissue and hard tissue, while synthetic biomaterials can be classified into [22]: a) Metallic. b) Polymeric. c) Ceramic . d) Composite biomaterials.

16


Table 2-1 shows classification of biomaterials [22]. Table 2-2 shows the mechanical properties of some biomaterials as a comparison with natural bone [22].

Table 2-1 Classification of biomaterials [22]. Biological Biomaterials

Synthetic Biomaterials

1.Soft Tissue:

1.Polymeric

Skin, Tendon,

 Ultra High Molecular Weight

Pericardium, Cornea

Polyethylene (UHMWPE).  Polymethylmethacarylate(PMMA).

2.Hard Tissue:

 Polyethyl ether ketone (PEEK).  Silicone, Polyurethane(PU).

Bone, Dentine, Cuticle

 Polytetrafluoroethylen (PTFE). 2.Metallic Stainless Steel, Cobalt-based Alloy(Co-Cr-Mo), Titanium Alloy (Ti-Al-V), Gold,Platinum. 3.Ceramic  Alumina(A1203),  Zirconia(Zr02), 

Carbon,Hydroxyapatite [CalOPO4( OH)6]

 ,Tricalcium Phosphate [Caj(PO4)2]  ,Bio glass [Na20( CaO)(P203)(Si02), 

Calcium Aluminate [Ca(A1204)]

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Table 2-2 Mechanical properties of some biomaterial and natural bone[22]. Young Modulus GPa

Copressive Strength MPa

Tensile Strength MPa

Density g/cm3

Fracture Toughness MPa.m1/2

Metals (Ti-6Al-4V)

114

450-1850

900-1172

4.43

44-66

Cr-Co-Mo

210

480-600

400-1030

8.3

120-160

Stainless Steel (316 L)

193

-

515

8.0

20-95

Ceramics Alumina

420

4400

282-551

3.98

3-5.4

Zirconia(TZP)

210

1990

88-1500

5.74-6.08

6.4-10.9

Silicon Nitride (HPSN)

304

3700

700-1000

3.3

3.7-5.5

Hydroxyapatite (3%Porosity)

7-3

350-450

38-48

-

3.05-3.15

Human Tissue Cortical Bone

3.8-11.7

88-164

82-114

1.7-2.0

2-12

Cancellous Bone

0.2-0.5

23

10-20

-

-

Cartilage

0.002-0.01

-

5-25

-

-

48-72

-

1.19

38-48

0.94

-

Others Bone Cement (PMMA)

2.24-3.25

UHMWHD polyethylene

0.69

80 20

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2.2 Biomaterials Interaction with Human body Biomaterials show different behavior during implantation within human body, depending on their interaction with living environment, so that we can classify biomaterials depending on this interaction into: 2.2.1 Bioinert Biomaterials Maintain their physical and mechanical properties while in the host. They used as structural- support implants. Examples of bioinert biomaterials are zirconia ceramics, alumina, UHMWPE. Some of their applications are some of these are bone plates, bone screws, and femoral heads [24]. 2.2.2 Bioactive Biomaterials Bioactive refers to a material, which upon being placed within the human body interacts with the surrounding bone and in some cases, even soft tissue. This occurs through a time – dependent kinetic modification of the surface, triggered by their implantation within the living bone. An ion – exchange reaction between the bioactive implant and surrounding body fluids – results in the formation of a biologically active carbonate apatite (CHAp) layer on the implant that is chemically and crystallographically equivalent to the mineral phase in bone. Prime examples of these materials are synthetic hydroxyapatite [Ca10 (PO4)6(OH) 2], glass ceramic, and bioglass[25]. 2.2.3 Bioresorbable Biomaterials Bioresorbable refers to a material that upon placement within the human body starts to dissolve (resorbed) and slowly replaced by advancing tissue (such as bone). Common examples of bioresorbable materials are tricalcium phosphate [Ca3(PO4)2] and polylactic–polyglycolic acid copolymers. Calcium oxide, calcium carbonate and gypsum are other 19


common materials that have been utilized during the last three decades [26]. Fig. 2.1 shows the different types of biomaterials according to their interaction within human body [22].

Fig. 2.1 Classification of bioceramics according to their responses at the boneimplant.interface:

(a)

bioinert

alumina

dental

implant;

(b)

bioactive

hydroxyapatite (Cal0(P04)2(OH)2) coating on a metallic dental implant; (c) surface

active

bioglass;(d)

bioresorbabletricalcium

phosphate

implant

(Ca3(P04)2) [22].

2.3 Bone Structure Bone is a tough and rigid form of connective tissue. It is the weight bearing organ of human body and it is responsible for almost all strength of human skeleton [27]. Natural bone is an innate example of inorganic-organic bio composites. It consists in composition of inorganic crystals and organic matrix which are Mainly represented by hydroxyapatite and Type I collagen, respectively. 20


Bones consist of organic (30%) and inorganic compounds (70%). Mineral parts of bones provide their stiffness and proper mechanical properties [28]. The inorganic phase of bone is a ceramic crystalline-type mineral that is an impure form of naturally occurring calcium phosphate, most often referred to as hydroxyapatite: Ca10(PO4)6(OH)2.Bone hydroxyapatite is not pure hydroxyapatite because the tiny apatite crystals (2 - to 5-nm-thick ×15-nm-wide × 20- to 50-nm-long plates) contain impurities such as potassium, magnesium, strontium, and sodium (in place of the calcium ions), carbonate (in place of the phosphate ions), and chloride or fluoride (in place of the hydroxyl ions). The organic phase of bone consists primarily of type I collagen (90 percent by weight), some other minor collagen types (III and VI) [29]. Microstructure of bones consists of two types of bones: 1. Cortical (Compact bone). 2. Trabecular (Spongy bone). Bone is considered to be a responsive material.

The formation and

resorption of bone occur continuously. Stress level is a very important factor that affect directly on bone, because the body responds to stress level in different areas of bone to ensure the right amount of healthy bone tissue is maintained and bone can be continually reshaped [30]. Stress level defer from bone to another depending on bone position and loadbearing effect on the bone. Fig. 2.2 a and b shows two types of bone structure [31, 32].

21


Fig. 2.2a: Crosse section showing two types of bone[31].

Fig. 2.2b: shows longitudinal section in bone [32].

22


2.4 Hydroxyapatite Ceramics Hydroxyapatite (HA) ceramics have long been recognized as substitute materials for bones due to their chemical and biological similarity to human hard tissues [33]. Hydroxyapatite (HA) is one of the most-widely used biomaterials in hard tissue repair and regeneration, and because it is considered a bioactive ceramics. Because of its chemical composition, which is similar to that of Inorganic part of natural bone, an excellent bone forming ability has been reported in many experimental models.Moreover, HA has been developed as a scaffolding material for the recruitment of bone-associated cells in bone tissue engineering applications [34]. The most important function for using HA in bone regeneration and repair applications is due to it is ability to reduce bone loss, improve osteoblast proliferation ,enhance bone formation , and improve the osseointegration of the implants [35], that’s why HA is used extensively in dental, orthopedic, and maxillofacial application duo to excellent long term clinical outcome [36]. Hydroxyapatite have a stoichiometric chemical formula Ca10(PO4)6(OH)2 with atomic ratio of Ca / P of 1.67, and have a hexagonal crystal structure with cell parameters of a = b= 9.418 A° and c = 6.884 A°. [37]. Table 2-3shows various calcium phosphates with their res pective Ca / P ratios [38].

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Table 2-3various calcium phosphate with their Ca/P ratios [37]. Ca/P

Name

Formula

Acronym

2.0

Tetracalicum Phosphate

Ca4O(PO4)2

TetCP

1.67

Hydroxyapatite

Ca10(PO4)6(OH)2

HA

1.50

Tricalcium Phosphate

Ca3(PO4)2

TCP

1.33

Octacalcium phosphate

Ca8H2(PO4)65H2O

OCP

1.0

Diacalcium phosphate dihydrate

CaHPO4.2H2O

DCPD

1.0

Diacalcium phosphate

CaHPO4

DCPA

1.0

Calcium pyrophosphate

Ca2P2O7

CPP

1.0

Calcium pyrophosphate dihydrate

Ca2P2O7.2H2O

CPPD

0.7

Heptacalcium phosphate

Ca7(P5O16)2

HCP

0.67

Tetracalicumdihydrate Phosphate

Ca4H2P6O20

TDHP

0.5

Monocalcium Phosphate monohydrate

Ca(H2PO4)2.H2O

MCPM

0.5

Calcium metaphosphate

Ca(PO3)2

CMP

2.5 Polymers Macromolecule that is formed by linking of repeating units through covalent bonds in the main backbone. Properties are determined by molecular weight, length, backbone structure, side chains, and crystallinity. Resulting macromolecules have huge molecular weights [39]. Polymers consists of long chains with high molecular weight composed of repeating units called (mer).They can be either amorphous or semicrystalline, or can exist in a glassy state.amorphous glassy state are hard, brittle no melting point, while semi-crystalline glassy state are hard, brittle crystal formation and when cooled exhibit a melting point [40].

24


2.5.1 Classification of polymers Polymers can be classified depending on their properties into: 1. Thermoplastic: Polymers that flow when heated; thus, easily reshaped and recycled. This property is due to presence of long chains with limited or no crosslinks. (Polyethylene, polyvinylchloride) 2. Thermosetting: Decomposed when heated; thus, can not be reformed or recycled. Presence of extensive crosslinks between long chains induces decomposition upon heating and renders thermosetting polymers brittle (Epoxy and polyesters). 3. Elastomers: Intermediate between thermoplastic and thermosetting polymers due to presence of some crosslinking. Can undergo extensive elastic deformation (natural rubber, silicone) [41]. 2.5.2 Structure of Polymers Polymers have a structure differs from other structural materials like ceramics and metal duo to its macromolecular nature .Polymers consists of covalently bonded long chains. The average molecular weight, considered very important property in polymeric materials which have direct effect on their properties, especially mechanical one. High molecular weights are beneficial for properties like strain-to-break, impact resistance, wear, etc. [42]. Polymers structure can be classified depending on the chain complexity into: 1. Linear 2. Branched or Cross-linked 25


3. Ladder 4. Network polymers. The structure of polymers has a significant effect on their properties, especially mechanical properties. 2.5.3 Glass Transition Temperature (Tg) The glass transition temperature (Tg), is the temperature at which the amorphous phase of the polymer is converted between rubbery and glassy states. (Tg) constitutes the most important mechanical property for all polymers. Upon synthesis of a new polymer, the glass transition temperature is among the first properties measured [44]. At temperature above Tg, a non-crystalline polymer material behave rubbery, or like a viscous fluid, depending on the molecular weight and how much the temperature exceeds the glass transition temperature. Below Tg, a bulk polymer is describe as a glass that is more or less brittle , depending on the structural complexity and how much it is cooled down [45,46]. The main properties that undergo a drastic change at the glass transition Temperature of any polymer: a) Hardness b) Volume c) Modulus (Young’s module) d) Percent elongation-to-break

26


Fig.2.3 shows volume –temperature curve which shows the glass transition temperature [44]. Figure 2.4 shows relationship between molecular weight and temperature for thermoplastic materials [44].

Fig.2.3 Glass transition temperature in polymers [44].

27


Fig. 2.4: Relationship between molecular weight and temperature [44].

2.6 High Density Polyethylene (HDPE) High-density polyethylene (HDPE) with density range between (0.941 < density < 0.965) consider a thermoplastic material which is composed of carbon and hydrogen atoms joined together forming high molecular weight products. Methane gas is converted into ethylene, then, with the application of heat and pressure, into polyethylene [46, 47]. High density polyethylene (HDPE) has a wide range of applications duo to its low processing cost and good processability. Furthermore, HDPE is a biocompatible polymer [48] so that, it can be used in biomedical application especially in bone. Polymeric materials used in bone repair applications , should have high moldability so that they can be processed into porous scaffolds which could allow nutrient

28


and waste diffusion.The polymeric materials should also exhibit mechanical properties similar to those of native bone [49]. There are different types of polyethylene depending on the molecular weight, polymerization method, and chain complexity, for example, LDPE (low density polyethylene), LLDPE (linear low density polyethylene, and UHMWPE (ultra high molecular weight polyethylene. Molecular weight considers a very important factor that effect directly on the polymers behavior, for polyethylene, molecular weight equal to 28. Typical properties for different grades of polyethylene are listed in table 2-4 [50].

Table 2-4 Typical properties for polyethylene [50]. ASTM

UNITS

TEST

LDPE

HDPE

UHMWPE

Tensile strength

psi

D-638

1,400

4,000

3,100

Flexural modulus

psi

D-790

30,000

200,000

110,000

D-256

no break

1.3

18.0*

ºF

D-648

122

172

-

ºF

-

-

-

180

%

D-570

0.10

0.10

slight

Izod impact (notched) Heat deflection temperature At 66 psi

ft-lbs/in of notch

Maximum continuous service temperature in air Water absorption (immersion 24 hours)

29


Coefficient of linear thermal

in/in/ºFx10-

expansion

5

D-696

-

7.0

11.1

2.7 Zirconia Ceramics 2.7.1: Crystal Structure Zirconia (ZrO2) exhibits three distinct crystallographic phases with increasing temperature: a monoclinic stable from ambient temperature to 1170 °C, a tetragonal phase stable from 1170 to 2370 °C, and a cubic phase, stable above 2400 °C [51]. Cubic phase exhibit a face centered cubic (FCC) fluorite structure, while tetragonal and monoclinic polymorphs are distorted versions of this structure as shown in Fig. 2.5[52].

Fig. 2.5

Crystal structure of monoclic (a), tetragonal (b) and cubic

zirconia(c)[52].

The transformation from tetragonal to monoclinic upon cooling is a thermal, martensitic transformation which is associated with volume expansion of 4-5%. This leads to detrimental fracture of sintered pure 30


zirconia ceramics. The addition of oxide dopants such as ceria, yettria, calicia, and magnisa are needed to stabilize the high temperature tetragonal and/ or cubic phases [53]. 2.7.2 Transformation Toughening in Zirconia Ceramics Transformation toughening is a mechanism by which the fracture toughness of a material increases as a direct result of a phase transformation occurring due to the stress field a head of the tip of an advancing crack in a material [54]. The tetragonal to monoclinic (Tt-m) phase change that is detrimental to the structural integrity of undoped zirconia is the same phenomenon that increases the toughness of doped zirconia. Transformation toughening of zirconia was first discovered by Garvei, Hannink, and Pascoe [35],who demonstrated that (Tt-m)phase transformation in partially stabilized zirconia (PSZ) improved the mechanical strength and toughness of zirconia ceramics. Fig. 2.6 to (2.8) show transformation toughening and phase changes in zirconia [56, 57]. 2.7.3 Partial Stabilized Zirconia Zirconia containing ceramics are generally classified into four categories: 1. Tetragonal zirconia polycrystalline (TZP). 2. Partially stabilized zirconia (PSZ). 3. Fully stabilized zirconia (FST). 4. Zirconia toughened /dispersed ceramics (ZTC/ZTD) [58]. TZP consists of stabilized tetragonal single phase at room temperature. The PSZ microstructure contains dispersed particles of metastable tetragonal phase in a stable cubic matrix, and it can be consists of a mixture of c, t, and m phases depending on the doping oxides wt% [59]. 31


Fig. 2.9 shows the Y2O3- ZrO2 phase diagram after scott [60].

Fig. 2.6 Phase change from a tetragonal-shaped crystal to a monoclinic form of crystal[56].

Fig. 2.7 Closing of microcracks because of the crystal volume increase caused by the phase change [56].

32


Fig. 2.8 Stress induced transformation toughening in partials stabilized zirconia (Source: Piconi et al. 1999)[59].

Fig.2.9 The Y2O3-ZrO2 phase diagram after scott [60].

33


2.8 Requirements for Biomaterials A biomaterial is "a material that interacts with human tissue and body fluids to treat, improves, or replaces anatomical element(s) of the human body" [61]. All materials that are used as biomaterials should have specific properties which consider the main properties for biomaterials; we can list these properties as below: 2.8.1 Biocompatibility Biocompatibility is the primary characteristic that a medical device should Have in any orthopedic application; that is, it must not adversely affect the local and systemic host environment of interaction (bone, soft tissues, ionic composition of plasma, as well as intra- and extracellular fluids) [61]. Biocompatibility is a surface phenomenon depending on the interaction between biomaterials surface and host environment (Fig. 2.10) [62].

34


Fig. 2.10 Biomaterials surface –host interaction [62].

2.8.2 Sterilizability Biomaterials when used in human body must undergo sterilizing with suitable technique: gamma radiation, gas sterilizing, or steam autoclaving. These techniques have different effects on the materials properties [63], so that we must take care when we select sterilizing method, for example polyacetal will depolymerize and give off the toxic gas formaldehyde when subjected under high energy radiation by gamma [64].

2.8.3 Functionability The ability of the material to be shaped to suit a particular function.The material must therefore be able to be shaped economically using engineering fabrication processes [22]. 2.9 Hydroxyapatite–Polymer Nanocomposites Hydroxyapatite [(Ca10(PO4)6(OH)2 ] has received a lot of attention for use as a bone graft material,because of its excellent resorbable and osteoconductive properties, which is related to its crystallographic and chemical similarity with various calcified tissues in vertebrates. [65] Hydroxyapatite microstructure is very similar to inorganic phase in natural bone that is why it has been used by many researchers to modify and synthesis different composites systems that are used in repair and replacement of natural bone.

35


Inorganic phase in bone is nano sized structure; this is lead to many researches that deals with producing of nano-fibrous scaffolds [66]. Polymer matrix has been used to replace collagen in natural bone structure. Several kinds of polymers used for this purpose as a matrix for different composition composites depending on their behavior when implanted in vertebrates body, for examples, Poly-L-lactic acid (PLLA), High density polyethylene(HDPE),ultra high molecular weight polyethylene(UHMWPE), and many other polymers [66]. The progress in contemporary skeletal surgery enlarged the possibilities of joint replacement as well as skeletal repair in bone. But the reconstruction of bone often needs to bridge large size bone defects. For this reason treatment approaches with biomimetic ceramic materials seem to be the most suitable alternative and became an interesting and widely used substitute to fill bone defects [67]. For this reason, nano hydroxyapatite in polymer matrix composite considers robotic materials for such application. Chemical bonding between ceramics particles and polymer matrix consider a very important factor which have direct influence on this composite system. 2.10 Chemical Bonds Characterization methods Most effective characterization methods used to indicate chemical bonds within components of composite materials are: 2.10.1 Laser Raman Spectroscopy Raman Spectroscopy is a technique used to study vibrational, rotational, and other low-frequency modes in a system .Therefore, molecules in compounds can be identified since the vibrational information is specific for the chemical bonds within the molecules [68]. 36


The scattering process may occur either elastically (Rayleigh scattering), or inelastically (Raman scattering).Thus, Raman spectroscopy measures the wave length and intensity of inelastically scattered light from molecules. The laser light interacts with phonons, which are in macroscopic vibrational modes, or other excitations on the system, making the phonons shift up or down. This shift in energy from the molecular vibrations gives information about the phonon modes in the system [69]. Consequently, the Raman shift corresponds to the energy difference between the incident light and scattered photon .The mechanism of Raman scattering is different from that of infrared absorption, and Raman and IR spectra provide complementary information about the sample. Generally, when a sample is illuminated with a laser beam, light will be reflected from the illuminated spot and collected using lenses then sent to a monochromater. Wave lengths close to the laser line, due to the Rayleigh scattering, are filtered out while the rest of the collected light is dispersed onto a CCD (charge-coupled device) detector [70]. 2.10.2 Fourier Transformation Infrared Spectroscopy (FTIR) Fourier Transformation Infrared Spectroscopy (FTIR) is an absorption technique used to identify chemical bonds and molecular structure of compounds. The FTIR is based on the interferometer designed by Nichelson and a mathematical procedure developed by Fourier that converts respose from the time to the frequency domain [71]. Infrared (IR) radiation is an electromagnetic radiation in the range of wavelength between the visible and microwave regions of the 37


electromagnetic Spectrum. The IR region can be divided into 3 smaller regions: near-IR (14000-4000 cm-1),mid-IR(4000-400 cm-1) and farIR(400-20cm-1). Changes in fundamentals vibrational levels of most molecules occur in the mid-IR. Therefore, the spectra in this study were obtained in the midIR region. Infrared energy is emitted from a source; this beam passes through an aperture which controls the amount of energy presented to the samples (and, ultimately, to the detector). The beam enters the interferometer where the encoding takes place. The resulting interferogram signal then exits the interferometer .The beam then passes through the sample. Some of the infrared radiation is absorbed by the sample and some of it passes through (transmitted) .The absorbed frequencies of energy are characteristics of the sample since the frequency of vibration is determined mainly by masses of atoms and the strength of the bond between them, which is only slightly altered by atoms in the vicinity [72]. The IR beam finally passes to the detector to quantify the interferogram signal. The measured signal is digitalized and sent to the computer where the Fourier transformation takes place. Thus, the resulting spectrum represents the molecular absorption, creating a molecular "fingerprint" of the sample. The absorption peaks represent the frequencies of vibrations between the bonds of the atoms of materials [71]. In addition; the heights of the peaks in the spectrum indicate the relative amount of the materials present. 2.11 Literature Survey 38


A variety of hydroxyapatite (HA), Ca10 (PO4)6(OH)2, reinforced polymer composites have been investigated as orthopedic biomaterials over the last two decades, including HA-reinforced polyethylene [73, 74]. This composite material was first investigated by W. Bonfield within 80 th decade in the last century. The significance of HA reinforced polymer composites is based on mimicking the mechanical and biological properties of bone tissue because the composition of these composite is very similar to that for natural bone which composed from organicinorganic phases [75]. The strength of this composite was found to be less than that for natural bone, so that its clinical application was limited to bones with low load bearing strength such as middle ear or orbital floor implants. Modification for HA/HDPE composite was focusing on two approaches: 2.11.1 Composite Synthesis Methods Several researchers studied the effect of synthesis method for this composite material, M. Wang and W. Bonfield [76] investigated a method that depends on chemical roots, Silanation of hydroxyapatite and acrylic acid grafting of polyethylene were employed to improve bonding between hydroxyapatite and polyethylene. This method was shown to promote chemical adhesion between hydroxyapatite particles and the polymer. The use of the silane coupling agent also facilitated the penetration of polymer into cavities in individual ceramic particles, which resulted in enhanced mechanical interlocking at the matrix-reinforcement interface. This finding was similar to that found by R.A. Sousa and his research team [77].

39


Rui A. Sousa and co-workers studied the effect of using a nonconventional injection moulding technique known as shear controlled orientation in injection moulding (SCORIM) technique to induce a strong anisotropic character to the processed composites for both biodegradable and bioinert polymeric composites. Results for this approach showed that it was possible to produce, both biodegradable and bioinert matrix composites, with properties that might allow for their application in the orthopaedic field [78]. Another synthesis method was adopted by Sukasem Kangwantra kool [59], who had study the mechanically dynamic coating technique as a new technique to produce nano HA/ HDPE composite. He investigated the effect of particle size and operation variables (the rotor speed, the total treatment time, the number of preparation steps and the total volume fraction of HA). it was found that the embedment besides uniform coating and dispersion of HA nanoparticles onto the surface of HDPE core particle was easily achieved by rotational impact blending due to high impact energy to yield the relatively high properties. In 2008, L. Hao, etal studied the selective laser sintering process to produce HA/HDPE composite [80].They used this technique as a rapid manufacturing of customized implants. Different vol % of HA (30 and 40 vol %) composite samples were prepared using CO2 laser, they studied the effect of process parameters on the degree of particle fusion and porosity. They indicate that this technique

has the potential not only to fabricate HA/HDPE composite

products, but also produce appropriate features for their application as bioactive implants and tissue scaffolds. 40


2.11.2 Effect of filler morphology and properties Hydroxyapatite particles in HA/HDPE composite is the bioactive phase in this composite system, and is responsible for biological interaction (osteoconduction ) with living tissue, that is why many researchers have studied the different issues about filler material : morphology, mechanical and physical properties, and bonding with polymeric matrix. K.E. Tanner and group of researchers focused in their research on the morphology and surface area of HA particles on the rheology and processability for HA/HDPE composite. Different particles morphologies have been used; the results showed that low surface area HA filled composite exhibited better injection processing characteristics through improved rheological responses [81]. J.O. Eniwmide and co-workers have studied the effect of HA particle morphology and polyethylene molecular on

fracture toughness for the

composite material in 2004 [82]. They used 40 vol % of three different particle size of HA in HDPE matrix, Compact tension test was performed at room temperature and at 37. °C. Their results showed that the increasing in test temperature and decreasing the surface area of reinforcing HA particles caused an increasing in fracture toughness for the composite. In another study by a group of researchers [83], the effect of reinforcement morphology on the fatigue properties for HA/HDPE composite has been studied. They used two vol% of HA (20, and 40 vol%)of either HA whiskers or an equiaxed HA powder, and tested in four-point bending fatigue under simulated physiological conditions. The 41


results showed that HA whisker reinforced HDPE was more tolerant of fatigue damage due to either microcracking or polymer plasticity. 2.11.3 HA/ZrO2 Composites Several researches have studied HA/ZrO2 ceramics as a biomaterial in orthopedic and scaffold applications. In 2003, Rajendra Kumar and his collies [84], studied Radio frequency (RF) suspension plasma sprayed technique as a synthesis methods to prepare HA/ZrO2 ultrafine composite. They used different techniques as characterization methods like the Zeta potential nano-particle size analyzer, SEM, TEM, FEM, and DSC. Results indicated that nano-size, spherical HA/ZrO2 composite powders were produced with varying morphological features that depend on the thermal treatment. Results also showed that the HA decomposed into α and β-TCP due to decreasing Ca/P ratio with the formation of CaZrO3. Strength of bond to bone has been studied by T. Matsuno and co-workers [85], they prepare HA/Y-PSZ composite by covering the surface HA particles with 3 mol %Y-PSZ particles. The strength of bond between a sintered body and bone was evaluated by measuring the shear strength at the interface between them. Their results showed that as the period of implantation increased, the shear strength of the sintered body/bone interface intended to increase. Another

group

of researchers

Characterization of Ca

[86],

studied

Development

and

-PSZ /HA Composites for Orthopedic

Applications.

42


Composite was synthesis by co-precipitation process of precursor reagent solutions. The composites were evaluated using XRD, FT-IR and TGDTA, SEM, and EDAX They concluded that the structural features of HA phase is greatly influenced by the higher content of PSZ phase in the composites. Those results were similar to that belongs to A. Volcenvov etal [87]. A. Yari and co-workers [88], studied the effect of Ca-PSZ on mechanical properties of HA/HDPE composite. Twin screw extruder has been used as a samples synthesis method. Their results showed that increasing vol % of HA in the composite caused a decrease in fracture strength and fracture toughness, while replacing some HA amount with Ca-PSZ was beneficial in the improvement of both fracture strength and fracture toughness.

43


3 44


3.1 Introduction This chapter covers the materials used to produce the hybrid nano-bio composite used in this study with their characteristics, and the procedure for samples preparation, testing and evaluation. The composite materials samples were prepared in the Department of Production Engineering and Metallurgy/ University of Technology/ Baghdad/ Iraq, all specimens testing and evaluations were done in the Institute of Materials Research/SPEME/Faculty of Engineering/University of Leeds/UK. 3.2 Materials 3.2.1 Hydroxyapatite Hydroxyapatite powder of 99% purity with average particle size of 20 nm and a nodular shape with real density of (3.140 gm/cm 3) supplied by M.K. Nano (Toronto, Canada )has been used in this study, the chemical analysis is found in Table 3-1 . Table 3-1 Chemical analysis of nano HA powder HA 99% purity

Sulfate

Chloride

Heavy metals

(0.048%max):0.025 (0.05%max):0.02 (10ppm max):7.0

Loss on drying (1.0% max):0.75

3.2.2 Yttria Partially Stabilized Zirconia 3mol % Y-PSZ (5.2 wt% Y-PSZ) powder with average particle size of 40 nm having a spherical shape with a real density of ( 5.88gm/cm 3) supplied by M.K Nano (Canada, Toronto ) was used in this study. Its chemical analysis is found in Table 3-2.

45


Table 3-2 Chemical analysis of nanoY-PSZ powder.

Y2O3 5.2+0.2%

HfO2

Chloride

Fe2O3

SiO2

Ti02

≤3

0.0016

0.0053

0.004

0.0042

3.2.3 HDPE Powder HDPE powder with particle size of 5 µm and real density of (0.95 gm/cm3) supplied by Right Fortune Industrial Limited (Shanghai, China )was used as a matrix for the composite material. The specifications of HDPE are listed in Table 3-3.

Table 3-3 Specifications of HDPE

HDPE Material Property

Typical value

Mass Density g/cm3

0.941-0.959

Melt flow Rate(190 °C/2.6 Kg)g/10 min

≤1.0

Tensile Yield Strength MPa

≥19.0

Flexural Modulus MPa

≥965

Elongation at break %

≥400

Impact Embrittlement Temperature °C

MAX-118

46


3.3 Composite Synthesis Method In this study, hot compression method was adopted as approach for preparing the composite samples. Previous studied by other authors indicated that best mechanical, physical , and biological properties for HA/ HDPE composites within the micron particles size for both filler and matrix phases were achieved at 20 and 40 volume fraction values, so that we studied all measured properties for the nano particles sized filler for the same volume fractions as a comparison between our finding and the previous ones. Another composite system was prepared by adding 5.2 wt% of Y-PSZ at volume fraction of 10 and 20 respectively. Table 3-4 shows all compositions used to prepare the composites samples for this work. Table 3.4 shows the composite samples compositions prepared in this study

HDPE,

Composites Samples

HA, vol%

Y-PSZ, vol%

1st group

20

-

90

2nd

40

-

60

3ed

20

10

70

4th

20

20

60

vol%

Dry mixing by ball mill was used to produce homogenous particles distribution within the composites. Many experiments were done to find the most suitable for mixing by take different times and then examined for samples under optical microscopy. Best homogeneity was at 12hr mixing time, so that all samples prepared using this mixing time. 47


Four compression pressures have been used to fabricate the samples, 56, 84, 112, and 140 MPa for each composite system. All samples were prepared by heating temperature of 140 °C for 30 min. A hot pressing system has been designed especially for this study as shown in Fig. 3.1.

Fig. 3.1 Hot Pressing System

Disk shaped samples with diameter of 15 mm and 7 -10 mm in high were prepared using this hot pressing system. 3.4 Characterization Methods 3.4.1 Density and Porosity Bulk density for all samples was measured using pycnometer instrument of type AccuPyc1330 Pycnometer (AccuPyc Instrument Corporation, Holland).

48

from Micromeritics


The Occupy 1330 Pycnometeris easy-to-use, fully-automatic gas displacement pycnometer . Analyses are initiated with a few keystrokes. Once an analysis is initiated, data are collected, calculations performed, and results displayed without further operator intervention [89]. Sample testing Procedures: 1. Drying the samples in oven at a temperature of 60 °C for 48 hr. to remove moisture. 2. Weighting the samples using 4 digit balances. 3. Loading the sample into pycnometer cell, and sealing it carefully. 4. Opening the helium gas valve and programming the instrument to start analysis. Apparent porosity for the samples has been calculated using Archimedes principle. This method is based on soaking the samples in kerosene for 2h in evacuated desiccator to saturate their open-pore structure with the latter. The weight of saturated sample suspended in kerosene (Wi) and its weight in air, after removal of kerosene film from outer surface, (Ws) were recorded, while W is the dray samples' weight. Apparent porosity (P) is calculated according to the following equation [90]:

(3.1)

3.4.2 Mechanical Testing 3.4.2.1 Vickers Micro –Hardness Test Vickers micro hardness test has been used to measure hardness for all samples that are prepared with different compositions and different compression pressures. Several loads were used to measure the diameters 49


of the tetragonal indent; non-deformed indent shape with suitable size has been performed at 50 gm load, so that this value was adopted in all hardness measurements in this study. Microhardness tester (Digital Micro-Vickers Hardness tester TH714 )for Beijing TIME High Technology Ltd./China ) was used ,at a load of 50gm and testing time 15sec. 3.4.2.2 Fracture Strength Test The diametrical compression test is also known as: the diametrical tensile test, Brazilian disk test, indirect tensile test, compact crushing test, or compact hardness test was used to measure the fracture strength for all samples. This test is used for for materials which are too difficult to process or machine into the ASTM standard “dogbone” shaped specimen, which is pulled in tension [91, 92]. Fracture strength can be measured using the following equation [91]: σf= 2P/π Dt

(3.2)

Where:

σf : Tensile fracture strength (MPa) P: Cross head load (N) D: Specimen diameter (mm) t:Specimen thickness(mm) Tensile machine ( Instron machine/IMR/UK ) was used to test the samples , with a crosshead speed of 5 mm min -1.

50


3.4.3 XRD characterization: The XRD of the hybrid nano-composite pellets, were done using Philips X-Ray diffractometer Xbert -type with nickel filtered Cu Kα radiation (λ = 1.5406 A° ) at 40 kV and 30mA having a scan range ( 2 θ) of 10-80° at a step size of (o.o5 )degree. XRD charts have been

plotted using Origin Pro 8.1 and analysed by

using High Score JCPDS database software. The quantitative phase analysis has been done using the following equation [93]:

(3.3)

(3.4)

where Im and It are integral intensities which are represent the area under curve for each peak belonged to atomic planes in the equation 3.3, Note that, depending on whether the primitive tetragonal cell or the facecentred tetragonal cell (derived from the cubic polymorph, which has fluorite structure) is taken as the unit cell, the tetragonal (111) peak is sometimes denoted by (101)[94,95]. 3.4.4 Scanning Electron Microscopy (SEM) and Energy Dispersive XRay Spectroscopy (EDX) LEO-SEM 1530 scanning electron microscopy has been used to study the morphology of the samples was studied using, at an accelerating voltage of 5kV and a working distance of 6 mm. 51


The samples were prepared using silicon carbide papers with grids of 1000, 2500, and 4000within surface grinding step. After that, samples have been polished using diamond foam with suitable cloth disk. After surface preparation process, the samples were secured onto specimen holders by conductive carbon cement and coated with 5 nm layer of Pd-Pt (20:80) by CVD technique. The imaging process was controlled using Smart SEM software .The Ca /P ratio was calculated using energy dispersive X-ray spectroscopy (EDX) which is connected to SEM machine by using a working distance of 8 mm and accelerating voltage of 15 Kv. 3.4.5 Laser Raman Spectroscopy In this study, the vibrations, C=C and CH2, and the ionic groups, PO4-3 (phosphate), from the treated HDPE, and HA were detected using a Renishawin Via Raman spectrometer . A liquid nitrogen cooled CCD 2D array detector was used for measuring the Raman signal. The Raman spectra were stimulated by Ar-Ion laser beam with 521nm wavelength and a diameter of (1um).The spectra were obtained in the range of 3500 to 100 cm-1 at 10 sec exposure time and 1 cm-1 resolution ,Wire2.0 software used to control the scanning process, and the result charts were plotted using Origin Pro 8.1 software. 3.4.6 Fourier Transformation Infrared Spectroscopy (FTIR) Chemical bonding between the components within the composite samples has been indicated using FTIR technique. The ionic groups, CO32

(carbonate), PO4-3(phosphate), and OH-(hydroxyl) from the treated

HDPE ,and HA samples were detected using Affinity-1 FTIR by Shimadsu

Corporation

Analytical

and

Measuring

Instruments

Division/Japan at the nano- centre / University of Technology. 52


3.4.7 Thermal analysis by DSC DSC technique has been used to study thermal parameters and kinetics parapets as approach to understanding the effect of nano sized fillers on both of melting behaviour and crystallisation for HDPE matrix. DSC measurements were made using a Perkin–Elmer DSC-8000 thermal system purged with nitrogen. Its temperature scale was calibrated from the melting characteristics of indium. The experiments were conducted non-isothermally using two different heating and cooling programs: 3.4.7.1 Non-isothermal Measurements at Different Heating Rates and Constant Cooling Rate 10 to 12 mg weight of samples ,weighted by 4 digit accuracy electronic balance, were sealed in aluminium pan , then heated from 30 to 170 °Cat heating rates of 10,15, 20, 25, 30, 35, 40, and 80 °C/min and maintained at this temperature for 5 min in order to erase any previous morphological history which the sample might have, then the samples were cooled none isothermally at a fast cooling rate of 150 °C/min down to

room

temperature . 3.4.7.2 Non-isothermal Measurements at Different Heating and Cooling Rates 10 to 12 mg weight of samples were sailed in aluminium pan , then heated from 30 to 170 °Cat heating rates of 5,10, 20, 40,and 80 °C/min and maintained at this temperature for 5 min in order to erase any previous morphological history which the sample might be carrying, then the samples were cooled none isothermally at cooling rates of 5, 10, 20, 40, and 80 °C/min respectively down to room temperature .

53


All the calculations were done depending upon heat flow-temperature curves obtained from the DSC test. 3.4.7.3 Specific Heat Measurement In order to measure the specific heat of a sample, the sample holder temperature was programmed with the same program as that used for heating and cooling for the samples. The program was carried out with no sample present; however, empty aluminium foil sample containers were placed in the sample holders to establish a base line for DSC curves, then the base line was subtracting from the heat flow-temperature curve, and by using the Pymer software the single curve specific heat have been obtained . All DSC results have been plotted using Origin Pro 8.1 software. 3.4.8 Biocompatibility Test Biocompatibility took place in a bio-cell (Fig. 3.2) which is composed of:  Pyrex container with well fitted cover containing holes to insert the thermometer and pH-meter probes.  PH-meter type Jenway.  Thermocouple (R-type).  Hot plate magnetic stirrer type Corning PC-402D.  High vacuum silicone grease to seal the cell fitting.  Ringer Tablets. 3.4.8.1Ringer Solution Preparation Ringer tablets supplied by Merck Company, Germany have been used to prepare the SBF for biocompatibility test.

54


The solution was prepared by dissolving one tablet in 500 ml of distilled water autoclave at 121 °C for 15 min. Ringer solution composition is shown in Table 3-5.

Table 3-5 Composition of Ringer solution sodium ion

chloride ion

lactate

potassium ion

calcium ion

130 mmol/L

109 mmol/L

28 mmol/L

4 mmol/L

1.5 mmol/L

Lactated Ringer's has an osmolarity of 273 mOsm/L. The lactate is metabolized into bicarbonate by the liver, which can help correct metabolic acidosis. The solution is formulated to have concentrations of potassium and calcium that are similar to the ionized concentrations found in normal blood plasma. To maintain electrical neutrality, the solution has a lower level of sodium than that found in isotonic saline or plasma. Generally, the sodium, chloride, potassium and lactate come from NaCl (sodium chloride), NaC3H5O3 (sodium lactate), CaCl2 (calcium chloride), and KCl (potassium chloride).Although its pH is 6.5, it is an alkalizing solution.

55


Fig.3.2 Bio-cell used for biocompatibility test / IMR/ University of Leeds / UK.

56


4 57


4.1 Introduction This chapter consists of the results and data analysis which have been obtained from the experiments and the different testing's results, discusses the results in a comparison is made with the previous studies in the field of nano bio materials for bone repair and substitution. 4.2 Physical Properties Measurements 4.2.1Density The relationship between the compressive pressure and the bulk density is shown in Fig. 4.1. These results indicate that the filler volume fraction has a significant enhancement on bulk density value because both of HA and Y-PSZ powders have a real density values much higher than that for pure HDPE powder. For the same composite samples, the effect of compression pressure has no remarkable effect on the densities value and this behavior can be considered an indication for the homogenies mixing of component powders together during dry mixing step. Furthermore, nano sized fillers particles tends to coat the micron size polymer particles during dry mixing step as reported by previous authors [96]. 4.2.2 Porosity Results for apparent porosity for different compositions samples can be shown in Fi. 4.2.The porosity values increased with increasing the filler volume fraction because the nano particles tends to coat the polymer micron sized particles during dry mixing process and this effect create a micro-sized agglomerates which will caused and increasing in porosity value. The compression pressure has a significant effect on the porosities values for all composites samples used in this study, because of the 58


interconnecting between nano sized fillers particles with polymeric matrix micro-sized particles and between nano particles when compression pressure was applied during samples shaping process.

2.0 20 vol% HA 40 vol% HA 20 vol% HA -10 vol% Y-PSZ 20 vol% HA /20 v0l% Y-PSZ

1.9 1.8 1.7

3

Bulk Density (g/cm )

1.6 1.5 1.4 1.3 1.2 1.1 1.0 0.9 0.8 0.7 0.6 0.5 40

50

60

70

80

90

100

110

120

Compression Pressure( MPa)

130

140

150

Fig. 4.1 The relationship between compression pressure and bulk density for nano HA/HDPE and nano HA/ nano Y-PSZ /HDPE systems.

55 20 40 20 20

50

vol% vol% vol% vol%

HA HA HA /10 vol% Y-PSZ HA /20 vol% Y-PSZ

Apparant Porosity %

45 40 35 30 25 20 15 10 5 40

50

60

70

80

90

100

110

120

Compression Pressure (MPa)

130

140

150

Fig. 4.2 The relationship between compression pressure and porosity for nano HA / HDPE and nano HA / nano Y-PSZ / HDPE systems.

4.3 Mechanical Properties 59


4.3.1 Vickers Micro-Hardness The effect of compression pressure and the filler volume fraction and the effect of Y-PSZ addition to the nano HA/HDPE are shown in Figure4.3. For the nano HA/HDPE composite samples, the values of micro-hardness increase with increasing the compressive pressure due to interconnection and bonding between the filler and the polymer matrix which increase with increasing the pressure. For the HA/Y-PSZ/HDPE composite system, a significant enhancement in hardness values has been recognized which can be attributed to the zirconia mechanical properties and toughening mechanisms in zirconia. These finding commensurate with previous studies [97-100] that indicated the stress- induced phase transformation phenomenon in zirconia ceramics on the mechanical properties for all system containing partial stabilized zirconia. This phenomenon was recorded in XRD results in section 4.4 within this chapter.

200

20 40 20 20

180

vol% vol% vol% vol%


Vickers Micro-Hadrness (Hv)

160 140 120 100 80 60 40 20 0 40

50

60

70

80

90

100

110

120

Compressive Pressure (MPa)

130

140

150

Fig. 4.3 The relationship between compression pressure and Vickers micro-hardness for nano HA /HDPE and nano HA /nano Y-PSZ /HDPE systems.

60


4.3.2 Fracture Strength Measurements by Diametrical Compression Test Results of the diametrical compression test are shown in Fig. 4.4. These results indicate the effect of compression pressure and filler content as well as Zirconia effect on the fracture strength for the composite materials samples. The tensile strength results show a significant increasing in strength values with increasing both of the compression pressure and filler volume fractions, especially when adding nano-sized Zirconia. Interpretation of mechanical performance variation of polymer matrices upon particulate filling should consider the influence of the filler on the crystallization kinetics of the matrix as reported in previous references [101]. Mineral particles can act as nucleating agents of the polymeric matrices, which may affect the semi -crystalline structure of the polymer matrix and consequently the mechanical behavior of the composite [102, 103]. For the hybrid composite system of nano HA/ nano Y-PSZ/HDPE the crystallinity is decreased in comparison

with pure HDPE and nano

HA/HDPE system , but the mechanical properties

still increase with

compression pressure due to stress-induced transformation toughening for zirconia particles under stress field which is complies with previous studies [104,105].

61


20 40 20 20

Fracture Strength (MPa)

120

vol% vol% vol% vol%


100

80

60

40

20 40

50

60

70

80

90

100

110

120

Compressive Pressure (MPa)

130

140

150

Fig. 4.4The relationship between compression pressure and fracture strength for nano HA/HDPE and nano HA/ nano Y-PSZ /HDPE systems.

4.4 XRD Fig. 4.5 show the XRD results for starting powders for all components and for HA/HDPE, Y-PSZ/HA/HDPE samples. The effect of compressive pressure on the phase transformation of Zirconia is well recognized from the change in the amounts of tetragonal and monoclinic phases (Table 4-1), as the pressure increases, the amount of monoclinic phase increase due to phase transformation under external stress condition and the increasing in mechanical properties is an evident on this transformation. These results are complies with previous studies [106108]. The amounts of both (m) and( t) phases have been calculated for the same compositions and compression pressure but before and after diametrical 62


compression test too, an increasing in the amount of monoclinic phase recognized in this case too ,which is again an indication of stress-induced transformation toughening phenomena . The main peaks of monoclinic phase are (111 -), and (111),and the main peak for tetragonal phase is (101) which is considered as (111) during phase measurements as mentioned in chapter 4,have been detected in the samples containing zirconia. For pure HA powder, the major characteristic peaks they were located at 2ϴ:25.8, 31.7, 33, and 49.57. For the 20 vol% nano HA/HDPE and 40 vol % nano HA/HDPE samples,the analysis of the XRD peaks of starting HA powders reveals the presence of three major characteristic peaks of pure HA, located at 2ϴ: 32,40, and 47. The sharp peaks of HDPE powder at 2ϴ: 21 and 24 clearly indicate higher degree of crystallinity which is in line with other studies [109,110]. Table 4.1 Xm % and Xt % from area under peaks Sample composition Y-PSZ powder

Compression Pressure -

Xm% 10

Xt% 90

States -

20 vol% HA/10 vol% Y-PSZ

140 MPa

35.32

64.78

Before fracture


140 MPa

49.5

51.5

After fracture


140 MPa

40.6

59.4

Before fracture


140 MPa

54

46

After fracture

63


10 8000

15

20

25

30

35

40

45

50

55

60

65

70

75

80

10 vol% Y-PSZ/20 vol% HA

P

6000 4000

P

2000 0 10000

20 vol% HA

8000

P

t

t m

t

m tm

H

H

H

H

HH

t

P

6000 4000

H

Relative Intensity

2000 0 30000

Y-PSZ Powder

t m

20000

m m

10000 0 15000

t t t

HA Powder

H

10000

H

H

H

5000

H H

0 HDPE powder

200000

P P P

100000

P 0 10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

2Theta

Fig.4.5 XRD plots for starting powders and composite materials samples,H: Hydroxyapatite, P: polyethylene, t: tetragonal zirconia, m: monoclinic zirconia.

4.5 SEM Imaging Figs. 4.6, and 4.7 show SEM images for HA/HDPE composites at different volume fractions of HA. While Figs.4.8 and 4.9 shows the SEM images for samples containing different volume fractions of Y-PSZ. These figures explain the homogenous distribution for HA particles in the polymer matrix for HA/HDPE system which can be considered as indication of homogenous distribution of filler particles within polymeric matrix during dry mixing step. For the Y-PSZ/HA/HDPE system, the SEM images show different microstructure for samples containing zirconia (Fig. 4.10). This 64


microstructure may be attributed to the effect of zirconia nano particles on the melting and crystallization behavior of polymeric matrix. Figure 4.11 shows cross section in sample sample containing 10 vol % of zirconia. Fractures surface for samples containing zirconia is shown in Figure 4.12. The fractured surface of samples containing zirconia, shows a simulated structure as the bone structure for both cortical bone (solid bone shell), and fibrous structure for the trabecular bone (cancellous sponge fibrous structure) is achieved here. This structure has not been recognized in samples containing only hydroxyapatite as filler materials which can be considered a new phenomenon by produce a biomimetic structure to the natural bone. 4.6 Raman Spectroscopy Figs. 4.13 to 4.16 show the Raman spectrum for nano HA/HDPE and nano HA/nano Y-PSZ/HDPE respectively. The analyses of these spectrums are given in Tables 4-2, 4-3.The characteristic peaks of HDPE are located in four zones .The features present at 1063 -1130 cm-1 are due to C-C stretching vibrations ,the feature observed at 1170 cm

-1

is CH2

rocking ,this observed at 1290 cm-1 is CH2 twisting vibration ,and peaks at 1413-1440 cm-1 are attributed to CH2 bending vibrations. These results comply with other studies [111].

65


Fig. 4.6 SEM images for 20 vol%, HA /HDPE samples.

66


Fig. 4.7 SEM images for 40 vol%, HA /HDPE samples.

67


Fig. 4.8 SEM images for 20 vol%,Y-PSZ/20 vol%, HA /HDPE samples.

68


a

B

69


c Fig. 4.9 Cross section SEM Images for 10 vol%Y-PSZ/20 vol%HA / HDPE composite at different magnifications.

a

70


b

c Fig.4.10

Fractured

surface

of

10

vol%,Y-PSZ/20

vol%,HA/HDPE composite at different magnifications .

71


The peak present at 960 cm -1 is a symmetric stretching mode which is often observed in hydroxyapatite and carbonated apatite as denoted in previous studies[112- 114]. The features at 2719 -2928 cm-1 are observed only in natural bone (Trabecular and Cortical bone)[111] so, the existen ce of these characteristic peaks in synthetic nanoHA is an indication that this composite system gives a very similar structure and bonding to that belonging to natural bone because the HAin natural bone is in nano size and this give a good explanation for enhancement in the mechanical properties for nano sized composite system. For nanoHA/HDPE composite samples, increasing in HAvol% caused an increase in Raman intensity because of increase in number of stimulated atoms, with higher intensity (HA as compared to HDPE) by laser beam. Increasing the compression pressure for the same composition samples causes a slight shift in peaks positions because of the strong mechanical interlocking between atoms.FornanoHA/nanoY-PSZ/HDPE composite system, samples with higher Y-PSZ content reflected higher Raman Intensities because they had higher densities which led to higher vibrations by the laser beam-atoms interactions.

72


140000

40 vol% HA 20 vol% HA

130000 120000 110000 100000

Raman Intensity

90000 80000 70000 60000 50000 40000 30000 20000 10000 0 -10000 0

500

1000

1500

2000

Raman Shift cm

2500

3000

3500

-

Fig. 4.11 Raman spectrum for 20, 40 vol% nanoHA/HDPE at 56 MPa compression

pressure.

130000 20 vol% HA 40 vol% HA

120000 110000 100000

Raman Intensity

90000 80000 70000 60000 50000 40000 30000 20000 10000 0 -10000 0

500

1000

1500

2000

Raman Shift cm

2500

3000

3500

-

Fig. 4.12 Raman spectrum for 20, 40 vol% nano HA/ HDPE at 140 MPa compression pressure.

73


140000 20 vol% HA /20 v0l% Y-PSZ 20 vol% HA /10 v0l% Y-PSZ

130000 120000 110000 100000

Raman Intensity

90000 80000 70000 60000 50000 40000 30000 20000 10000 0 -10000 0

500

1000

1500

2000

Raman Shift cm

2500

3000

3500

-

Fig. 4.13 Raman spectrum for 20 vol%HA/10 vol% Y-PSZ/HDPE and 20 vol% HA/20 vol% Y-PSZ/HDPEat 56 MPa compression pressure.

140000 20 vol% HA / 20 vol% Y-PSZ 20 vol% HA /10 vol% Y-PSZ

130000 120000 110000 100000

Raman Intensity

90000 80000 70000 60000 50000 40000 30000 20000 10000 0 -10000 0

500

1000

1500

2000

Raman Shift cm

2500

3000

3500

-

Fig. 4.14 Raman spectrum for 20vol% HA/10 vol% Y-PSZ/HDPE and 20 vol% HA/20 vol% Y-PSZ/HDPE at 140 pressure.

74

MPa compression


Table 4.2 Vibrational assignments and biomolecules involved in the Raman scattering process for nanoHA/HDPE bio-composite. Raman peaks (cm−1)

Vibrational assignments

Features

960

νs(P–O)

Hydroxyapatite

1063

C—C stretching

C, N

1130

C—C stretching

C, N

1163

CH2 rocking

C

1298

CH2 twisting

C, N

1406

CH2 bending

C

1446

CH2 bending

C

2719

CH stretch

Trabecular bone, and Cortical bone

2840

CH stretch


2881

CH stretch


2928

CH stretch


νs: symmetric stretching mode, A: amorphous; C: crystalline; N: anisotropic Table 4.3 Vibrational assignments and biomolecules involved in the Raman scattering process for nanoHA/nanoY-PSZ/HDPE bio-composite.

75


Raman peaks (cm−1)

Vibrational assignments

Features

982

νs(P–O)

Hydroxyapatite

1063

C—C stretching

C, N

1130

C—C stretching

C, N

1170

CH2 rocking

C

1292

CH2 twisting

C, N

1413

CH2 bending

C

1440

CH2 bending

C

2719

CH stretch


2848

CH stretch


2902

CH stretch


2928

CH stretch


νs: symmetric stretching mode, A: amorphous; C: crystalline; N: anisotropic

4.7 Fourier Transform Infrared Spectroscopy (FTIR) For nano HA/HDPE samples, FTIR spectrum reflects many characteristic peaks so that it is possible to explain the highest intensity peaks. For samples with 20 vol% nano HA/HDPE composition, Figs. 4.17 to 4.20 show the characteristics bonds for different compositions samples, while table 4-4 summarized the main chemical bonds within the structure for 20 vol %HA/HDPE sample.

76


Fig. 4.15 FTIR results for 20vol% HA/HDPE sample at 56 MPa compression pressure.

Fig. 4.16 FTIR results for 40 vol% HA/HDPE sample at 56MPa compression pressure.

77


Table(5-3)FTIR spectrum results of samples with 20 vol% nanoHAp/HDPE.

Fig. 4.19 FTIR results for 20 vol% HA/10 vol% Y-PSZ/HDPE sample at 56 MPa compression pressure.

Fig. 4.20 FTIR results for 20 vol % HA/20vol% Y-PSZ / HDPE sample at 56 MPa compression pressure.

78


Table4.4FTIR spectrum results of samples with 20 vol% nano HA/HDPE.

Slandered wave number, cm –1

Frequency shift , cm –1

567-607

590.22

600-650

Functional group Molecular motion PO4-3

Phosphate

634.58 653.87

C-H bend

Alkynes

735-770

738.74

C-H bend(Ortho)

aromatics

800-850

808.17

C-H bend(Para)

aromatics

810-1090

1020.04

PH bend

phosphines

=

1062.78

=

=

1160-1210

1163.08

C-C(O)-C stretch

esters

1210-1320

1242.16

C-O stretch

Carboxylic acids

1400-1440

1444.68 1714.14 1730.15 2308.79

O-H bend

=

C=O stretch

=

P-H stretch

phosphines

2868.15

=C-H stretch medium, two peaks

Alkynes

3640–36 10

3624

O–H stretch

alcohols, free hydroxyl phenols

3500-3700

3560.59

O –H stretch

alcohol

=

3664.75

=

=

=

3792.05

=

=

1700-1730 2270-2320

2820-2850

2835.36

FTIR analysis of biomaterials shows typical absorption bands at 3560 and 3441 cm–1 that correspond to the stretching mode of the OH group, The O - H groups are hydrogen bounded [115]. The hydroxyl vibration mode is found to be present near 634 cm –1, other absorption bands at 3163.26 and1643.35 cm–1 also correspond to the

79


presence of hydroxyl groups in HA. The band at 2393.66 cm–1 may be attributedto the trace amount of ambient water and carbon dioxide. The band at 1371.39 cm–1 reveals the presence of –CH2 asymmetric bending, and bands at 1020.06 and 590.22 cm –1 reveal the presence of phosphate group in the composite system. The band at 1768.72 cm–1 is for the C=O group , a shift from the 1714.72–1730.15 cm–1 wave number range may be attributed to a chemical bond formation across the inorganic-organic interface which is compline with other reported results [116, 117]. Aromatic compounds commonly exhibit multiple weak bands in the region3100–3000 cm−1 due to aromatic C–H stretching vibrations. The C- H asymmetric stretching observed in the region at 3080 cm-1 and the C-H symmetric stretching are assigned to 3008, 2982 cm -1.The strongest absorptions for aromatic compounds occur in the region 650– 900 cm−1 due to the C–H vibrations out of the plane to the aromatic ring. The C-H bending vibrations are assigned to 1120.34 cm -1 [118, 119]. Changing in compression pressure causes a shifting in peaks positions due to strong mechanical connection between atoms, while adding Y-PSZ nano particles leads to decrease in the number of characteristic peaks since the absorbing ability of the samples decreases with increase in YPSZ vol%. 4.8 Thermal Analysis 4.8.1Determination of Kinetics Parameters Thermal stability parameters have been investigated based on onset of melting To, peak of melting Tp, and heat of fusion obtained from single non-isothermal DSC scan.

80


The peak melting temperature and extrapolated onset melting temperature are calculated from the peak position and intersection of the extrapolated linear section of the falling peak edge with the baseline extrapolated from temperatures below the peak, while heat of fusion (∆H) is calculated by integrating the area under the DSC endothermic peak [116]. Several methods have been proposed to study the kinetics of crystallization and melting of HDPE with different types of filler [117, 120], but these kinetics for HDPE with nano HA and nano Y-PSZ have not been proposed before. The non-isothermal melting and crystallization process may be assumed to be comprised of infinitesimally small isothermal melting and crystallization steps. Therefore, the variables of the Avrami equation under a non-isothermal condition for the entire process will represent average values of all the corresponding constituents of isothermal melting and crystallization steps[114], so that we can use Avrami exponent can be used to describe melting and crystalline phase for non-isothermal DSC scan. Melting reaction factor (K) can be calculated based on Arrenius relationship [121]:

(1)

Where k° is a frequency factor, Ec is activation energy, and R is the gas constant. Ozawa-Chen equation [121-123] enables the evaluation of E c and k° from the shift of Tp to higher temperatures with increasing the heating rate in accordance with Kissinger method [121,124]: (2)

81


Plotting ln(Tp/β) vs.1/Tp (Figure 4.21)yield a straight line with gradient equal to Ec/R which has been used to calculate the activation energy of melting.

⁄ ssinger method

Once Ec has been determined n can be evaluated using relationship proposed by Piloyanet al [121,125]: (3)

Where ∆Y is the displacement of the non- isothermal DSC trace from the base line. Plotting ln ∆Y vs 1/T(Fig. 4.22) gives a straight line wit h a slope of nEc/R from which n can be calculated. The percentage of crystallization was calculated by normalizing the heat of melting to that of 100% crystalline PE (290 J/g),by following equation [126, 127]:

(4)

WhereXc is the degree of crystallinity,∆Hm is the specific enthalpy of melting,∆Hm+

is the specific enthalpy of melting for 100% crystalline

PE. 4.8.2Melting and Crystallization Behavior Effect of different filler types on the rheological and thermal properties of polymer matrix had been investigated by several authors [127-129], in this study we focuses on the role of nano sized fillers on the melting and crystallization kinetics for HDPE as an approach to understanding the particulate filler -polymer matrix interaction

82

because it is an important


factor that affects thermal, mechanical, and biological properties for this composite system. This section, we report the melting and crystallization kinetics behavior of HDPE, nano HA/HDPE, and nano Y-PSZ/HA/HDPE samples. The kinetics parameters like the Avrami exponent and the activation energy have been evaluated from differential scanning calorimetry (DSC) melting endotherms by using the approach listed in experimental part . In general, typical HDPE, HA/HDPE, and Y-PSZ/HA /HDPE samples showed a single melting endotherm. The peak melting temperature and extrapolated onset melting temperature and heat of fusion were affected significaly by both of heating-cooling conditions and nano filler type and volume fraction. Tp,To, and ∆H obtained at different heating and cooling conditions for samples are reported in Tables 4.5,and 4.6. The values of Ec, n, K, and Xc% for DSC curves at different heatingconstant cooling rates and different heating-cooling rates are listed in Tables 4.7,4.8 respectively . All DSC scans show a single endothermic peak for melting, in some researches [128,130] existence of the single peak in the endothermic and exothermic curves has been attributed to the occurrence of cocrystallization. However as mentioned by some authors, existence of single peak is not only a reliable reason to confirm the occurrence of co-crystallization. In such cases, the analysis on the melting and crystallization temperature is inadequate and the other sensitive parameter in such situations is the halfwidth of the endotherms [130]. Larger half-width is expected if two or more components form separate crystals, although the melting or crystallization peaks may be located in close proximity.

83


By increasing the heating rate, the melting peak is shifted to higher values and this may be related to rheological properties which change with changing the viscosity with increasing the heating rates and with the presence of nano fillers which will affects the melting behavior for the composite. Crystallization is increased by adding nano HA particles, because of the nano particles role as nucleation site for the crystalline phase, and the crystallization was judged via the heat of fusion ∆H. As the heat of fusion increases, so did the crystallization and this finding agrees with previous literature [116,128]. Adding nano Y-PSZ tonanoHA particles caused more shifting for melting peaks for higher values and the crystallization process is decreased. However, nano particles at higher loading restrict the mobility of the molecules, hence the crystallinity decreased. Avrami constant values was vibrated around 1(Table 4.7) for all DSC thermograms at different heating rates-constant cooling rate(high cooling rate) ,and this can be attributed to the melting phase behavior and geometry by the presence of nano particles which encourage the one direction phase geometry ,Ec value was decreased with increasing filler vol%. As observed in Table4-8the obtained values of n at different heatingcooling rates,n had higher values and was ranged from less than 1 to more than 4 especially by the presence of nano Y-PSZ particles compared with neat HDPE. In the Avrami expression, the Avrami exponent n provides qualitative information on the nature of nucleation and the growth processes.

84


They should be integer and from 1 to 4. The values of nof heterogeneous nucleation should be less than that of sporadic nucleation under the same crystal growth mechanism [120]. The value of Ec decreased sharply with increasing the filler content for the DSC scans at different heating-cooling rates in spite of increasing the crystallinity when adding nano HA and this give an indication that the activation energy is depending on the melting phase and melting process factorsis not just affected by the crystallization process. The Tp values are more sensitive to the heating and cooling rates than To values for both DSC non-isothermal programs, but for different heatingcooling rates the Tp values shifted to higher values than that for different heating-constant high cooling rate thermograms. Figure4.23 shows the corresponding DSC thermograms for pure HDPE obtained in the different heating rates and constant cooling rate heating processes, while the DSC curves for pure HDPE at different heatingcooling rates are shown in Figure 4.24. Fig. 4.25 shows the DSC curve for the nano composite: (a) at nano HAp as a filler additive (b) at nano HA/nanoY-PSZ filler additive at different heating rates and constant cooling rate. Fig. 4.26 shows the DSC curve for the nano composite :( a) at nano HAp as a filler additive (b) at nano HA/nanoY-PSZ filler additive at different heating –cooling rates. 4.8.3Specific Heat Calculation Figs. 4.27, and 4.28 show the relationship between heating rate-specific heat at different heating rates-constant cooling rate , heating rate-specific heat at different heating- cooling rates respectively. The value of specific heat decreases with increasing the ceramic filler vol%.

85


Tables 4.9, and 4.10 list the specific heat values for all samples at different heating rates-constant cooling rate, and different heating-cooling rates respectively. The specific heat is an indication of the heat required to add to the system to increase the temperature, so that when the heat transfer has been restricted by nano ceramics particles, the value of specific heat decreases as well as the crystalline structure% decreases. a 0.40 Equation Weight Residual Sum of Squares Pearson's r Adj. R-Square

0.35

ln(Tp/B)

0.30

Book1_D

Equation W eight Residual Sum of Squares Pearson's r Adj. R-Square

y = a + b*x No Weighting 5.75736E-4 0.987 0.96986 Intercept Slope

Standard Error 0.3218 0.1325

y = a + b*x No W eighting 0.00124 0.97535 0.9432 Intercept Slope

Book1_B

Value -4.53912 1.99305

Value -5.45421 2.34727

Standard Error 0.53078 0.21679

Equation Weight Residual Sum of Squares Pearson's r Adj. R-Square

0.25

0.20

Book1_F


Value Standard Error -6.1792 0.31785 2.6568 0.13035

HDPE 20 vol% HAp 10 vol% YSZ/20 vol% HAp Linear Fit of Book1_F Linear Fit of Book1_D Linear Fit of Book1_B

0.15 2.36

2.38

2.40

2.42

2.44

2.46

2.48

2.50

1000/Tp

b 0.40 0.38 0.36 0.34

Equation Weight Residual Sum of Squares Pearson's r Adj. R-Square Book1_F

y = a + b*x No Weighting 0.00593 0.89308 0.73011 Intercept Slope


ln(Tp/B)

0.32


0.30 0.28

Book1_D

0.26


0.24 0.22 0.20 0.18

HDPE 20 vol% HAp 10vol% YSZ/20 vol% HAp Linear Fit of Book1_B Linear Fit of Book1_F Linear Fit of Book1_D

Book1_B

y = a + b*x No Weighting 0.00412 0.92392 0.80483 Intercept Slope




0.16 2.40

2.42

2.44

2.46

1000/Tp

86

2.48

2.50

2.52


ln Y

Fig. 4.21 Relationship between ln(Tp /β) vs 1000/TP: a)at different heating rates-constant cooling rate , b ) at different heating-cooling rates.

5.2 5.0 4.8 4.6 4.4 4.2 4.0 3.8 3.6 3.4 3.2 3.0 2.8 2.6 2.4 2.2 2.0 1.8

-1.67 -1.32

o

-1

10 C min o -1 20 C min o -1 30 C min o -1 40 C min o -1 80 C min o -1 linear fit 10 C min o -1 linear fit 20 C min o -1 linear fit 30 C min o -1 linear fit 40 C min o -1 linear fit 80 C min

6.8

7.0

7.2

-1.99

-2.15

-2.35

7.4

7.6

1000/Tp(K)

7.8

8.0

8.2

8.4

-1

b 5.0 4.5

-3.42

4.0

ln Y

3.5

o

-1

10 C min o -1 20 C min o -1 30 C min o -1 40 C min o -1 80 C min o -1 (10 C min ) o -1 (20 C min ) o -1 (30 C min ) o -1 (40 C min ) o -1 (80 C min )

3.0 2.5 2.0 1.5

-1.82 -3.47

-1.89

-2.23 1.0 7.0

7.2

7.4

7.6

7.8

1000/Tp (K)

8.0

8.2

8.4

-1

Fig. 4.22 Relationship between ln ∆Y vs 1000/Tp for 10 vol% YPSZ/20 vol % HA /HDPE composite :a) at different heating ratesconstant cooling rate, b) at different heating cooling rate.

87

Heat flow (mW)


260 240 220 200 180 160 140 120 100 80 60 40 20 0 -20 -40 -60 -80 -100

10 20 30 40 80

30

40

50

60

70

80

90

100

110 120 130 140 150 160 170 0

Temp. (C )

Fig. 4.23 The corresponding DSC thermograms for pure HDPE obtained in the different heating rates and constant cooling rate heating.

5-5 20-20 40-40 80-80

200 150

Heat flow (mW)

100 50 0 -50 -100 -150 -200 30

40

50

60

70

80

90

100 110 120 130 140 150 160 170 0

Temp. (C )

Fig. 4.24 the DSC curves for pure HDPE at different heating-cooling rates.

88


a 220

20 30 40 80

200 180 160

Heat flow (mW)

140 120 100 80 60 40 20 0 -20 -40 -60 30

40

50

60

70

80

90

100

110 120 130 140 150 160 170 0

Temp. (C )

b 20 30 40 80

140 120 100

Heat flow (mW)

80 60 40 20 0 -20 -40 -60 -80 -100 30

40

50

60

70

80

90

100 110 120 130 140 150 160 170 0

Temp. (C )

Fig. 4.25 The DSC curve for the nano composite: (a) at nano HA as a filler additive (b) at nano HA/nano Y-PSZ filler additive at different heating rates and constant cooling rate.

89


a

150

5-5 20-20 40-40 80-80

Heat flow (mW)

100

50

0

-50

-100

30

40

50

60

70

80

90

100 110 120 130 140 150 160 170 0

Temp. (C )

b 5-5 20-20 40-40 80-80

150

Heat flow (mW)

100

50

0

-50

-100

-150 30

40

50

60

70

80

90

100 110 120 130 140 150 160 170 0

Temp. (C )

Fig. 4.26 shows the DSC curve for the nano composite :( a) at nano HA as a filler additive ( b) at nano HA/nano Y-PSZ filler additive at different heating –cooling rates .

90


34

20 vol% HA 20 vol% HA /10 vol% Y-PSZ HDPE

32 30 28

24

0

Cp (J/g*C )

26

22 20 18 16 14 12 10 8 0

10

20

30

40

50 0

60

70

80

90

Heating rate (C /min)

Fig. 4.27 Relationship between heating rate-specific heat at different heating rates- constant cooling rate.

35

HDPE 20 vol% HA 20 vol% HA , 10 vol% Y-PSZ

30

0

Cp (J/g*C )

25

20

15

10

5 0

10

20

30

40

50

60

0

70

80

90

Heating-cooling rates (C )

Fig. 4.28 Relationship between heating rate-specific heat at different heating-cooling rates.

91


Table 4-5 Thermal data for DSC curves at different heating rates and constant cooling rate.

Sample ID

HDPE

20 vol% HA

20 vol % HA -10 vol % YPSZ

Heating rate C°/min 10 15 20 25 30 35 40 80

Tp C0≠

T onset *C°

Heat of fusion for melting J/g

131 132 133 134 134 136 138 143

125 126 126 126 126 126 128 131

153 138 202 151 138 155 194 191

10 15 20 25 30 35 40 80

134 135 136 137 138 138 142 149

127 127 127 128 128 128 128 132

140 143 153 131 165 130 138 145

10 15 20 25 30 35

133 134 134 137 137 138

126 126 127 128 128 128

106 99 92 102 94 95

40

138

129

93

80

144

132

100

≠: Melting peak temperature *: Start melting temperature

92


Table 4-6 The thermal data for DSC curves at different heating –cooling rates .

Sample ID

HDPE

20 vol% HA

20 vol% HA-10 vol% YPSZ

Heating – cooling rate °C/min

0≠

Tp C

T onset °C*

Heat of fusion for melting J/g

5 10 20 40 80

132 133 133 136 139

125 125 126 127 129

153 146 127 121 129

5 10 20 40 80

132 134 136 140 146

126 126 127 128 131

132 153 166 151 95

5 10 20 40 80

132 134 136 140 146

126 126 127 129 133

92 94 100 87 93

≠: Melting peak temperature *: Start melting temperature

93


Table 4-7 The values of Ec, n, K, and Xc at different heating rates-constant cooling rate.

Sample ID

Heatingcooling rate 10

HDPE

Ec *kJ/mol

n≠

Kᶱ

Xc%**

19

0.7

3.97*10-3

52

15

1.4

=

47

20

0.78

=

69

25

0.87

=

52

30

0.96

=

47

35

0.9

=

53

40

0.77

=

66

80

0.77

=

65

1.17

11*10-3

48

15

1.12

=

49

20

1.07

=

52

25

1.07

=

45

30

0.64

=

56

35

1

=

44

40

0.97

=

48

80

0.78

=

50

0.84

2*10-3

48

15

1.1

=

34

20

1.28

=

31

25

0.91

=

35

30

1.31

=

32

35

0.75

=

32

40

0.72

=

48

80

0.71

=

34

10

20 vol% HA

10

20 vol % HA-10 vol % Y-PSZ

17

22

*: Activation energy, ≠: Avrami constant, °: Constant of reaction **:Crystallinity %

94


Table 4-8 The values of Ec, n, K, and Xc at different heating-cooling rates.

Sample ID

Heating-cooling rate

Ec* kJ/mol

n≠

K°

Xc%**

5-5

47

0.74

1.18*10-6

39

HDPE

10-10

0.61

50

20-20

0.52

43

40-40

0.41

41

80-80

0.35

44

5-5

20 vol% HA/ HDPE

3.21

0.12

45

10-10

3.01

53

20-20

2.23

57

40-40

1.77

52

80-80

1.66

32

5-5 20 vol% HA, 10 vol%Y-PSZ /HDPE

8

6

4.68

0.27

31

10-10

4.23

32

20-20

3.38

34

40-40

3.18

30

80-80

2.77

32

*: Activation energy, ≠: Avrami constant, °: Constant of reaction **: Crystallinity %

95


Table 4-9 Specific Heat value at different heating rates-constant cooling rate.

Sample ID

HDPE

20 vol% HA

20 vol% HA/10 vol %YPSZ

Heating rate C°/min

Cp J/g*C°

10 15 20 25 30 35 40 80

33 31 26 23 22 21 19 18

10

22

15 20 25 30 35 40 80

21 18 17.5 17 15 12.5 10

10

19

15 20 25 30 35 40

17.5 17 15 13 12.9 12.5

80

10

96


Table 4-10 Specific Heat values at different heating-cooling rates.

Sample ID

Heating –cooling rates °C/min

Cp J/g*°C

5-5 10-10 20-20 40-40 80-80

32 28 23 15.5 13

5-5 10-10 20-20 40-40 80-80

29 24 22 15 7.6

5-5 10-10 20-20 40-40 80-80

20 16.5 14.5 9.8 8.5

HDPE

20 vol% HA

20 vol% HA/10 vol % Y-PSZ

4.9Bio-Test Phase's stability during immersion in Ringer solution has been studies extensively within this work. The Ringer solution used as a biological environment similar to the natural blood plasma. Different immersion times (5, 10, and 15 days) have been used. Characterization methods were, XRD to study the phase's degradation as a function of time, SEM to explain surface changes after immersion in the solution, and EDX quantitave analysis to measure the Ca /P ratio in the samples before and after exposure to Ringer solution. The XRD charts for HA/HDPE system after immersion in SBF for different exposure time are shown in Figs. 4.29, and 4.30. Reference 97


spectrum charts for monotite and drushite phases in HA/HDPE samples are shown in Figs. 4.31 and 4.32. For 20 vol% HA samples, the main phases before immersion in SBF were hydroxyapatite( Ca10(PO4)6 (OH)2 and polyethylene(C2H4)n with a trace of monotite phase (CaHPO4) and calcium phosphate hydrate (Ca2P2O7.4H2O) . After 5 days exposure in SBF, the same phases still existed but the amount of crystalline polymer decrease duo to the degradation in polyethylene. After increasing the exposure time to 10 days, the brushi te phase (CaHPO4.2H2O) started to appear in the sample with a trace of monoclinic calcium phosphate hydrate phase (Ca3(PO3)6 ·10H2O). The montite and brushite (CaHPO4.2H2O )phases existence in the samples complies with previous studies [131-133].After 15 days in SBF most of the polymer degraded and the amount of hydroxyapatite decreased with increasing the trace of brushite phase .Figures (4.33) and (4.34) show the SEM images for the 20 vol% and 40 vol% HA samples at different exposure times respectively. Brushite and monotite are important intermediate phases to produce high pure hydroxyapatite [134]. Brushite is a relatively high solubility calcium phosphate compound and is known to convert into apatite like calcium phosphate when soaked in SBF solutions at the human body temperature for about one week [135].

98


10

15

2500

20

25

30

35

20 vol% HA

40

45

50

55

60

65

70

75

55

60

65

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80

before

2000 1500 1000 500 2000

5Days

1500

Relative Intensity

1000 500

1500

10 Days

1000 500 15 Days 1200 1000 800 600 400 200 15 20 0 10

25

30

35

40

45

50

75

80

2Theta(degree)

Fig. 4.29 XRD results of 20 vol% HA samples at different exposure times.

10

15

20

25

30

40 vol% HA

20000

35

40

45

50

55

60

65

70

75

80

45

50

55

60

65

70

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before

10000 5000 0 8000

5 Days

6000

RelativeIntensity

H

15000

4000 2000 0 4000

10 Days

3000 2000 1000 1500

15 Days

1000 500 010

15

20

25

30

35

40

2Theta(degree)

Fig. 4.30 XRD results of40 vol% HA samples at different exposure times.

99


Hydroxyapatite

Ca2P2O7 •4H2O

CaHPO4(Monotite) Fig. 4.31 Reference spectrum for 20 vol% nano HA after 5 days in Ringer solution.

100


CaHPO4.2H2O(Brushite)

monotite Fig. 4.32 Reference spectrum for 40 vol% nano HA after 5 days in Ringer solution.

101


a

b Fig. 4.33 20 vol%HA samples: a: before immersion in Ringer solution, b: after 5 days exposure.

102


c

d Fig. 4.33- 20 vol% HA samples: c: after 10 days exposure, and d: after 15 days exposure.

103


a

b Fig. 4.34- 40 vol% HA samples: a: before immersion in Ringer solution, b: after 5 days exposure.

104


c

d Fig. 4.34- 40 vol%HA samplesc: after 10 days exposure, and d: after 15 days exposure.

EDX quantitative results of 20 and 40 vol % HA samples before and after emersion in SBF for different exposure times are listed in tables 4 -11 and 105


4-12 respectively, where the Ca /P ratios have been calculate at different positions on the samples surfaces. Table 4-11 Ca/P ratio in 20 vol% HA sample before and after immersion in Ringer solution for different exposure time. Exposure time Before immersion 5 days 10 days

15 days

Locations

Ca/P

Spectrum 1 Spectrum 2 Spectrum 1 Spectrum 2 Spectrum 1 Spectrum 2 Spectrum 1 Spectrum 2 Spectrum 3 Spectrum 4

2 2.13 2.2 2.3 1.81 1.98 1.8 2.3 2.32 1.99

Table 4-12Ca/P ratio in 40 vol% HA sample before and after immersion in Ringer solution for different exposure time. Exposure time Before immersion 5 days 10 days 15 days

Locations

Ca/P

Spectrum 1 Spectrum 2 Spectrum 1 Spectrum 2 Spectrum 1 Spectrum 2 Spectrum 1 Spectrum 2

2.1 2.13 2 1.98 1.87 1.85 1.68 1.69

The microstructure of 20 vol% HA shows the formation of distinct Ca-P precipitate on its surface after 5 days exposure in Ringer solution (Fig. 4.33-b). After 15 days of Ringer solution treatment, distinct morphological changes of Ca-P precipitates were observed (Fig. 4.33106


d).The precipitates were present in large quantity and were visible even at low magnification as compared to that of five days Ringer solution treated samples. The apatite formation on the surface of composite is confirmed by EDX spot analysis of a number of such globules, which confirmed the presence of Ca and P. Thus, the Ringer solution study demonstrated the increase in precipitation of Ca-P with soaking time. For 40 vol% HA samples, more Ca-P precipitates formation have been recognized after immersion in Ringer solution as shown in Fig. 4.34. For nano-zirconia contained samples, the zirconia caused less degradation in the polymer matrix and more stability in Ringer solution, XRD results of samples containing different amounts of zirconia are shown in Figs. 4.35 and 4.36.

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

25

30

35

40

45

50

55

60

65

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80

before

15000 10000 5000 0 8000

15 Days

6000

Relative Intensity

4000 2000

0 12000

10 Days

10000 8000 6000 4000 2000 0 15000

5Days

10000 5000 0 10

15

20

2Theta(degree)

Fig. 4.35 XRD results of 10 vol% Y-PSZ/20 vol% HA samples at different exposure times.

107


10 15 20 12000 Before

25

30

35

40

45

50

55

60

65

70

75

80

25

30

35

40

45

50

55

60

65

70

75

80

10000 8000 6000 4000 2000 0

15 Days

6000

Relative Intensity

4000 2000

0 10000

10 Days

8000 6000 4000 2000 0 5Days

12000 10000 8000 6000 4000 2000 0 10

15

20

2Theta

Fig. 4.36 XRD results of 20 vol% Y-PSZ/20 vol% HA samples at different exposure times.

Reference spectrum for samples containing zirconia is shown in Figure4.37. Ca/P ratios for Y-PSZ/ HA/ HDPE composite samples at different compositions and at different exposure times in SBF are listed in Tables 4-13, and 4-14. Microstructure for samples containing Y-PSZ is shown in Figs. 4.38 and 4.39.

108


Tetragonal Phase( zirconia)

Monoclinic Zirconia

109


(C2H4)n

Brushite

110


Monetite Fig. 4.37- 10 vol% nano Y-PSZ / 20 vol% nano HA /HDPE sample after 10 days in Ringer solution.

Table 4-13 Ca/P ratio in 10 vol% Y-PSZ /20 vol% HA sample before and after immersion in Ringer solution for different exposure times. Exposure time

Locations

Ca/P

Before immersion

Spectrum 1

2.3

5 days

Spectrum 2 Spectrum 1

2.44 2.89

10 days


2.34 1.97

15 days

Spectrum 1

2

111


Table 4-14 Ca/P ratio in 20 vol% Y-PSZ/20 vol% HA sample before and after immersion in Ringer solution for different exposure times. Exposure time

Locations

Ca/P

Before immersion

Spectrum 1

1.7

5 days

Spectrum 1

1.6

10 days

Spectrum 1

2.02

15 days


2.15 2.03

Spectrum 2

1.56

The value of Ca/P increases after exposure to Ringer solution proves the formation of Ca P precipitates which give a good bonding to bone during implantation. These results give an indication that zirconia nano particles gave more stability for phases within composite system which will give more time for hydroxyapatite to form bioactive bonding to natural bone cells during implantation in living host. Furthermore zirconia nano particles had affect the polymer matrix dissolution and degradation during exposure to biological solution , so we can concluding that the toughness for the biocomosite product- bone bridge will enhanced by nano Y-PSZ filler existence because the polymer matrix toughen the composite side by side with zirconia. From Ca/P ratio measurements at different exposure times for both composite systems, we can conclude that the calcium amount increase after immersion in Ringer solution which an indication about the chemical interaction between calcium ions in Ringer solution and the hydroxyapatite in the composite samples. This ratio was shown to increase in samples containing zirconia because improvement in composition stability which is an evident that zirconia enhanced the biocompatibility of the composite by given of more time to biological 112


bonding between bioactive composite and natural bone during implantation which will take place in future works related to this composite system.

a

b Fig.4 .38 -10 vol% Y-PSZ/20 vol%HA samples: a: before immersion in Ringer solution, b: after 5 days exposure.

113


A

B

C

Fig. 4.39 20 vol% Y-PSZ/20vol%HA samples: a: before immersion in Ringer solution, b: after 10 days exposure, c: after 15 days exposure.

114


5 115


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