【EI 会议投稿模板】 Mechanical Properties of Poly (Ɛ-caprolactone)/ Polyethylene Terephthalate Composite Small Diameter Vascular Graft Mohammed Abedalwafa, Li Chao-Jing, Wang Fu-Jun, Wang Lu*, Lian Ming-qiang, Jia Hao Key Laboratory of Textile Science and Technology, Ministry of Education College of Textiles, Donghua University Shanghai, P. R. China
[email protected] Abstract—The purpose of the vascular graft prostheses or implantation is not only to keep a patient alive, but for the patient to continue with their normal lives. Polyethylene terephthalate (PET) has been successfully used in large diameter grafts; unfortunately, small diameter grafts were failures. Due to surface forces, blood plasma proteins are adsorbed by the graft, resulting vessel reclosure. Poly (Ɛ-caprolactone) (PCL) is a promising biodegradable polymer with a longer degradation time. The mechanical properties of the pure PCL cannot meet up with the requirement. The aim of this study is to develop new vascular graft from PCL reinforced with PET monofilament weft-knitted tube fabric. The PET fabrics were knitted using small single jersey knitting machine. Then PCL solution was coated outside and inside of the weft-knitted fabric with a PTFE rod, and the pure PCL tube was taken as a control. The samples were dried by freeze drying method. The results have shown that the new vascular grafts have good porosity. In addition the tensile properties, elastic recovery and the suture retention strength of the new vascular grafts were improved compared with pure PCL vascular graft, which could be used in clinical application. Keywords- Polyethylene terephthalate, monofilament, weftknitted tube fabric, Poly (Ɛ-caprolactone) (PCL), mechanical properties, vascular graft.
I.
INTRODUCTION
Atherosclerosis is a sickness of arteries that causes more deaths and disability than any other disease in the world, more than all types of cancer combined [1,2]. Vascular grafts are special tubes that serve as artificial replacements for damaged blood vessels, which are already commercially available, mainly produced from polyester knitted or woven fabrics [3, 4] or the expanded polytetrafluoroethylene (PTFE) [5-8]. Knitted constructions are made from interloping yarns in horizontal rows and vertical columns of stitches. Knitting constructions account for more than 50% of the structures available, due to softer, more flexible and easily comfortable, and have better handling characteristics than woven graft designs [9]. PET is mostly recognized in biomedical application due its
biocompatibility, resilience, flexibility, durability and resistance to biodegradation and sterilization. PET has been successfully used in large diameter grafts; however, small caliber grafts still show an unacceptable high percentage of failure. Due to surface forces, blood plasma proteins are adsorbed by the graft, resulting in inflammation, infection, thrombus formation and ultimately vessel reclosure [10]. Unfortunately knitting structure cannot use directly due to high porosity, leakage of blood and low biocompatibility property. Composite vascular grafts consist of PET weft-knitted tube fabrics coated with polyurethane (PU) were studied, to improve the mechanical properties, elasticity and blood-proof properties [11-13]. The disadvantage of application of the PU vascular graft is the toxicity of PU, which produces lethal monomers upon degradation. So that’s why the use of PU was stopped for in vivo and vitro applications. PCL is a promising biodegradable polymer with a longer degradation time, and has been widely used both in vivo and vitro [14-18]. Small-diameter PCL grafts represent a promising alternative for the future because of their better characteristics such as biodegradability, biocompatibility, flexibility and easy to manufacture [19,20]. PCL was used as raw material to make small diameter blood vessel scaffold by electrospinning but the mechanical properties cannot meet up with the requirement of vascular grafts [21,22]. The main aim of this study is to improve the mechanical properties by developing composite vascular grafts, from PCL reinforced with PET monofilament weft-knitted tube fabric. And to characterize it by using scanning electron microscopy, textiles multi strength tester, water permeability device and filament mightiness instrument. II.
EXPERIMENTAL
A. Materials PET monofilament (30D) and density (1.39g\ cm-3) was used for knitting tubular fabric. PCL with density (1.145g\cm-3) was purchased from Shenzhen Brightchina Industrial Co., Ltd. Acetic acid used as a solvent was purchased from Sinopharm Chemical Reagent Co., Ltd.
B. Methods The PET tube fabrics were knitted using small single jersey knitting machine modified by our lab, which has 10needles/inch. The knitting process was done by inserting glass rod which has a diameter of 6 mm, to control the diameter of the vascular graft, as shown in Fig.1 (A). After that 15 wt% PCL solution was dissolved in Acetic acid, the mixtures were stirred continuously at room temperature until a homogeneous solution was formed. Then PCL solution was coated outside and inside of the weft-knitting fabric with a PTFE rod and the pure PCL tube was taken as a control. After coating, PCL composite vascular grafts and pure PCL vascular grafts were put in the refrigerator for 12 h for drying preparation. Finally the samples were dried by freeze drying method in the temperature -60oC and pressure below 20 Pa for 3h. Fig.1 (B) shows PCL/PET composite small diameter Vascular Graft.
according to standard ISO 7198: 1998 [23]. The strain rate is 50 mm/min. The results were average of 5 times testing. D. Water Permeability A water reservoir was connected to a polyethylene tube. The graft of 5 cm in length was joined to the other end of polyethylene tube. The water reservoir was put in high places about 165 cm. The pressure transducer was used to make sure that the distal end of the graft was exposed to 120 mm Hg pressure constantly. The permeated water through the graft wall was collected over time (min) in a graduated cylinder in order to calculate in mL cm-2 min-1, according to Standard ISO 7198: 1998 [23]. E. Elastic Recovery The elastic recovery property after the compression was tested in the (YG061) filament mightiness instrument, Laizhou Electronic Instrument Co., Ltd. with renovation, and could be used to test pressure elasticity of man-made tubes. Similar to crush resistance test referred in ISO 25539 [24]. The strain rate is 10 mm/min, and the samples pressure to 50% of them diameter. The results were average of 3 times testing. The elastic recovery of each sample calculates from (2) according to the Figure 2. E% = [(E1+E2)/ET]*100
(2)
Figure 1. (A) An optical microscope images show the structure of the weftknitting fabric (X2) (B) Optical image of PCL/ PET composite small diameter vascular graft.
III.
CHARACTERIZATION TECHNIQUES
A. Geometric Characteristic The geometrical characteristic was determined according to Standard ISO 7198: 1998 [23], the results were average of 10 times testing. Calculate and record the porosity (P %) of each sample from (1). P = 100 [1 – (M/1000hd)]
(1)
Where: M is mass per unit area of the sample (g m-2)
Figure 2. Calculate the elastic recovery.
F. Suture Retention Strength The suture retention strength was tested using a (YGB026H) textiles multi strength tester, Wenzhou Darong Textile Instrument Co., Ltd. according to Standard ISO 7198: 1998 [23]. The strain rate is 50 mm/min. Any sample was tested in 4 directions and the results were average of 3 times testing.
h is sample thickness (mm), d is density (g cm-3). B. Microstructure The surface morphology and cross section of PCL/PET vascular grafts were assessed using a JSM-5600LV scanning electron microscope (SEM) Japan JEOL. Before the examination, samples were gold sputter under nitrogen at an excitation voltage of 15 kv. C. Tensile Strength The strength of the samples (along the longitudinal and radial direction) was tested using a (YG-B026H) textiles multi strength tester, Wenzhou Darong Textile Instrument Co., Ltd.
Sponsoring fund: supported by Fundamental Research Funds for the Central Universities (NS2012), NNSF (31100682 and 30972942), 111 Project (B07024) and Engineering Research Center of Technical Textiles Ministry of Education. Corresponding author: College of Textiles, Donghua University, Shanghai 201620, P. R. China. E-mail:
[email protected]
IV.
RESULTS AND DISCUSSION
A. Geometric Characteristic PCL vascular graft reinforced with PET weft-knitted tube fabric is shown in Fig 1. (B) These composite vascular grafts combine the good elasticity and blood-proof properties of PCL with the strength and stability of a knitted structure. TABLE 1 is shown the thickness, the weight, PCL content and the porosity of the weft knitted tube fabric, composites and pure PCL vascular graft. In addition show that the porosity of PCL reinforces with weft-knitting tube fabric was increased compared to pure PCL, which has poor mechanical properties when the porosity is higher [21].
TABLE 1. GEOMETRIC CHARACTERISTIC Sample Thickness No* mm 0.104 1 0.260 2 0.211 3 *1 is PET weft-knitted tube graft and 3 is pure PCL
Weight g/m2 12.610 135.93 137.72
PCL Content % 0.00 90.72 100.00
Porosity % 91.28 55.62 42.89
fabric, 2 is PCL/PET composite vascular
E. Elastic Recovery The elastic recovery rate of PCL/PET composite vascular grafts was better than pure PCL vascular grafts, which can be easily returned to its original state with blood pressure. However the stop and relaxation strength were lower. Figure 5. shows the elastic recovery curve of the PCL/PET composite vascular graft and pure PCL vascular graft.
B. Microstructure Fig. 3. shows a typical SEM microstructure for surface section and a cross section of PCL/PET composite vascular graft, they were shown that the PCL/PET composite has a good porosity and it can be used in the clinical applications.
Figure 5. The elastic recovery curves of: (A) PCL\PET composite vascular graft and (B) pure PCL vascular graft.
Figure 3. SEM images showing the microporous structure of the PCL/ PET composite vascular graft (a) the surface section and (b) the cross section.
C. Tensile Strength of PCL/PET Composites 1) Longitudinal Tensile Strength Tensile curves of the PET weft-knitting tube fabric, pure PCL vascular graft and PCL/PET composite vascular graft, which are shown in Fig. 4. (A), specified that the PCL/PET composite has a much higher strength, excellent dimensional stability.
F. Suture Retention Strength Figure 6. shows the stress - strain curve of suture retention strength, three declines were observed on the stress-strain curve. The first decline was steep; it indicated the instant when the longitudinal cut began to form. The second decline was gradual; indicated the process by which the cut advanced longitudinally. The third decline was again steep and reached the zero point (the point when graft breakage ended). Fig. 6. shows that PCL/PET composite vascular grafts have much higher suture retention strength when compared with the pure PCL vascular graft.
2) Circumferential Tensile Strength Tensile curves of the PET weft-knitting tube fabric, pure PCL vascular graft and PCL/ PET composite, which is shown in Fig. 4. (B) Appeared that the PCL/ PET composite is much higher in strength and elongation. Figure 6. Suture retention strength curve
V.
Figure 4. Tensile curves of the weft-knitting tube fabric, pure PCL vascular graft, and PCL\PET composite vascular graft. (A) Longitudinal direction and (B) Circumferential direction.
D. Water permeability The water permeability of PCL/PET composite small diameter vascular and pure PCL vascular graft have zero water permeability, as generally we have to say the water permeability of all the samples are very good for the biomedical application, according to standard ISO 7198: 1998 [23].
CONCLUSION
New vascular grafts of small diameter have been developed by reinforcing PCL with PET weft-knitted fabrics. The tensile properties and the elastic recovery of new vascular grafts were increased compared with the pure PCL vascular graft. In addition the new composite vascular grafts have shown good porosity. The new vascular grafts are promising and it can be used in the clinical applications. ACKNOWLEDGMENT REFERENCES [1]
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