polymers Article
Shape Memory Polyurethanes Based on Zwitterionic Hard Segments Shuqin Fu 1,2,3 , Huanhuan Ren 3 , Zaochuan Ge 3 , Haitao Zhuo 1, * and Shaojun Chen 3, * 1 2 3
*
Shenzhen Key Laboratory of Functional Polymer, College of Chemistry and Environmental Engineering, Shenzhen University, Shenzhen 518060, China;
[email protected] Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province, College of Optoelectronic Engineering, Shenzhen University, Shenzhen 518060, China Guangdong Research Center for Interfacial Engineering of Functional Materials, Shenzhen Key Laboratory of Polymer Science and Technology, Shenzhen Key Laboratory of Special Functional Materials, Nanshan District Key Lab for Biopolymers and Safety Evaluation, College of Materials Science and Engineering, Shenzhen University, Shenzhen 518060, China;
[email protected] (H.R.);
[email protected] (Z.G.) Correspondence:
[email protected] (H.Z.);
[email protected] (S.C.); Tel./Fax: +86-755-26534562 (S.C.)
Received: 2 September 2017; Accepted: 18 September 2017; Published: 21 September 2017
Abstract: This work aimed at elucidating the influence of zwitterionic hard segments on the structures and properties of shape memory polyurethanes (SMPUs). A series of zwitterionic SMPUs was successfully prepared with N-methyldiethanolamine (MDEA), 1,3-propanesultone (1,3-PS), 1,6-hexamethylene diisocyanate (HDI) and polyethylene glycol (PEG6000). The influence of MDEA-PS-based zwitterionic hard segment on structure, morphology, thermal property, shape memory property and cytocompatibility were systematically investigated. The results demonstrated that the PEG-based zwitterionic SMPUs (PEG-ZSMPUs) formed phase separation structure consisting of crystalline soft phase and amorphous hard phase. The MDEA-PS zwitterionic segments showed a tendency to form ionic clusters in hard segments, which served as reinforced net points. Shape memory analysis showed that zwitterionic PEG-ZSMPUs containing a high content of zwitterionic segments had thermal-induced shape memory effects. Finally, cytotoxic assays demonstrated that MDEA-PS zwitterionic segment improved the biocompatibility of PEG-ZSMPUs. The zwitterionic PEG-ZSMPUs could thus have a promising application in smart biomedical fields. Keywords: shape memory; polyurethane; N-methyldiethanolamine; zwitterionic polymer; biocompatibility
1. Introduction Polyurethanes are a general segmented copolymer comprising of hard and soft segments [1]. In the past several decades, polyurethanes possessing shape memory effects (SMEs) have been widely studied due to their capabilities to fix temporary shapes upon cooling and recover to the original shapes upon heating [2,3]. So far, many kinds of polyurethanes have been found to show various SMEs, including thermal-induced SMEs, moisture-sensitive SMEs, and multi-SMEs [4]. In the shape memory polyurethanes (SMPUs), the hard segments generally determine permanent shapes and serve as physical net points, while the soft segments control the fixing and recovering of temporary shapes, and serve as switches [5,6]. Adjusting the structure and content of either hard or soft segments can cause SMPUs to have quite different morphologies and properties. Thus, various kinds of soft and hard segments have been used to control the shape memory properties [7], and in order to meet such complex requirements in the practical applications, SMPUs with more functionalities have been rapidly developed. More attentions are drawn in particular to the recent developed multi-functional SMPUs [8–10].
Polymers 2017, 9, 465; doi:10.3390/polym9100465
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Generally, the design and synthesis of multifunctional SMPUs require key functional monomers, which can be further functionalized or triggered to have various properties, such as biocompatibility, electrical conductivity, and self-healing properties [11–13]. The biocompatibility is the key factor influencing the biomedical applications of SMPUs. Polyethylene glycol (PEG), which has good biocompatibility, is a good candidate of soft segment for the synthesis of biomedical SMPUs [12]. Bonfil et al. synthesized a series of polyurethane films that were composed of PEG and castor oil by using the one-shot polymerization method [14]. They have shown that not only do PEG-based SMPUs have excellent thermal-induced shape memory effects, but they also have some interesting properties, such as water-triggered shape memory effect. In addition, our recent investigation has found that a higher content of hard segments might influence the biocompatibility of SMPUs [12]. Therefore, it is necessary to further modify the hard segments of SMPUs in order to meet the need in biocompatibility. Recently, N-methyldiethanolamine (MDEA), which contains tertiary amine, has been used in the design of stimulus-responsive polyurethanes to have temperature and pH dual-responsive characteristics [15]. It is well known that the tertiary amine in the MDEA segment can be protonated to become ionic form [16,17]. The polyurethane-containing MDEA segment can thus be ionized with acetic acid or 1,3-propanesulonate (PS) to zwitterionic polyurethanes, which has been widely reported to have a good biocompatibility [18,19]. Our recent work has confirmed that the zwitterionic polyurethanes based on HDI and MDEA showed not only moisture-sensitive SMEs, but also had good biocompatibility and antibacterial properties [20,21]. To date, it is known that the thermal-induced SME is greatly influenced by the MDEA-PS-based zwitterionic segments; however, its influence when served as hard segments is still unclear. Aimed at designing SMPUs to have both good biocompatibility and shape memory properties, this work designed a new kind of zwitterionic SMPUs by incorporating PEG soft segments and MDEA based zwitterionic hard segments. Based on our previous communications on PEG-based SMPUs, zwitterionic SMPUs, and amide-containing SMPUs [22], a series of PEG-based zwitterionic SMPUs (denoted PEG-ZSMPUs) were synthesized from MDEA, HDI, PEG and 1,3-PS by adjusting the molar ratio of 1,3-PS and MDEA. The influence of zwitterionic hard segments on the structure, morphology, thermal properties, shape memory properties and cytocompatiblity of PEG-ZSMPUs were then systematically studied. 2. Experimental 2.1. Materials Dibutyltindilaurate (DBTDL; analytical reagent), 1,6-hexamethylene diisocyanate (HDI; analytical reagent), N-methyldiethanolamine (MDEA; analytical reagent), polyethylene glycol (number-average molecular weight of 6000, PEG6000; premium grade), 1,3-propanesultone (1,3-PS; analytical reagent), and dimethylformamide (DMF; analytical reagent) were purchased from Aladdin Chemical Reagent Co. Ltd. (Shanghai, China), and used without further purification. 2.2. Synthesis of PEG-ZSMPUs A series of PEG-ZSMPUs were synthesized from different molar ratios of 1,3-PS and MDEA by polyurethane polymerization and ring-opening reactions according to the composition shown in Table 1. The procedure in preparation of PEG-ZSMPUs is presented in Scheme 1. The preparation was conducted in an argon-filled and a mechanically stirred 250-mL three-neck flask. First, chemicals including MDEA (3.32 g, 0.0279 mol), HDI (5.01 g, 0.0297 mol), and DMF (10 mL) were mixed at 60 ◦ C. After purging and stirring for 15 min, DBTDL catalyst (0.15 wt % of polyurethane) was added to the mixture [22]. When the temperature was increased to 80 ◦ C under vigorous stirring, the reaction mixture became violent and its viscosity was significantly increased. At 1.5 h into the reaction, DMF was added to the reaction to control its viscosity, followed by PEG6000 (11.67 g, 0.0019 mol), and then left for an additional 3 h. After that, 1,3-PS (3.40 g, 0.0278 mol) was added, and the reaction
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◦ Cfor (11.67 g, 0.0019 mol), and then left 3 h. After 1,3-PSand (3.40 g, 0.0278 mol) was was conducted hermetically at 75 foran12additional h. The molar ratiosthat, of 1,3-PS MDEA were adjusted added, and the reaction was conducted hermetically at 75 °C for 12 evaporated h. The molarfrom ratios 1,3-PS according to composition presented in Table 1. Finally, DMF was theofresulting and MDEAsolution were adjusted according to composition in 12 Table 1. Finally, DMF was SMPU/DMF in a Teflon pan and in a vacuumpresented at 80 ◦ C for h. The target zwitterionic evaporated from the resulting SMPU/DMF solution in a Teflon pan and in a vacuum at 80 °Cof for 12 SMPU were coded “#PEG-ZSMPU”, where “#” is the number representing the molar ratio 1,3-PS h.MDEA. The target zwitterionic SMPU were coded “#PEG-ZSMPU”, where “#” is the number and representing the molar ratio of 1,3-PS and MDEA.
Table 1. Composition of Polyethylene glycol (PEG)-ZSMPUs. Table 1. Composition of Polyethylene glycol (PEG)-ZSMPUs. Soft segment Hard segment Soft segment Hard segment ZHSC *ZHSC * # SamplesSamples R# R HDI (g) PEG6000 (g) (g) HDI (g)(g) MDEA MDEA(g) (g) 1,3-PS 1,3-PS (wt %) (wt %) HDI (g) PEG6000 HDI (g)(g) 0PEG-ZSMPU0.33 0.33 4.68 3.32 0 0 0 0PEG-ZSMPU 11.6711.67 4.68 3.32 0 40 40 0.2PEG-ZSMPU 0.33 11.67 4.68 3.32 0.68 0.2 0.2PEG-ZSMPU 0.33 11.67 4.68 3.32 0.68 0.2 42 42 0.4PEG-ZSMPU 4.68 3.32 1.36 0.4PEG-ZSMPU 0.33 0.33 11.6711.67 4.68 3.32 1.36 0.4 0.4 44 44 0.6PEG-ZSMPU 4.68 3.32 2.04 0.6PEG-ZSMPU 0.33 0.33 11.6711.67 4.68 3.32 2.04 0.6 0.6 46 46 0.8PEG-ZSMPU 4.68 3.32 2.72 0.8PEG-ZSMPU 0.33 0.33 11.6711.67 4.68 3.32 2.72 0.8 0.8 47 47 1.0PEG-ZSMPU 0.33 0.33 11.6711.67 4.68 3.32 3.40 1.0 1.0 49 49 1.0PEG-ZSMPU 4.68 3.32 3.40 # R#isRthe is molar the molar ratio of 1,3-propanesultone (1,3-PS) and methyldiethanolamine (MDEA); * ZHSC: ratio of 1,3-propanesultone (1,3-PS) and methyldiethanolamine (MDEA); * ZHSC: zwitterionic hard segment content.hard segment content. zwitterionic
Scheme1.1.The The synthesis synthesis route route of Scheme of PEG-ZSMPUs. PEG-ZSMPUs.
2.3. Characterization of PEG-ZSMPUs 2.3. Characterization of PEG-ZSMPUs Fourier transform-infrared spectroscopy spectra (FT-IR, Thermo Nicolet FT-IR 6700, Nicolet, Fourier transform-infrared spectroscopy spectra (FT-IR, Thermo Nicolet FT-IR 6700, Nicolet, Madison, WI, USA) of PEG-ZSMPUs were scanned from 4000 to 400 cm−1 wavelengths. The spectra Madison, WI, USA) of PEG-ZSMPUs were scanned −1from 4000 to 400 cm−1 wavelengths. The spectra were the average of 32 scans at a resolution of 4 cm−1. were the average of 32 scans at a resolution of 4 cm . 1H-nuclear magnetic resonance spectra (1H-NMR, Avance III 400MHz, Bruker, The 1 The H-nuclear spectra (1 H-NMR, Avance III 400MHz, Bruker, Switzerland) Switzerland) were magnetic recorded resonance using DMSO-d 6 as the solvent and tetramethylsilane (TMS) as the were recorded using DMSO-d6 as the solvent and tetramethylsilane (TMS) as the internal standard. internal standard. Elemental analysis (EA, Vario EL III, Elementar Analysen-systeme GmbH, Hanau, Germany) was conducted to determine the weight percentage of S, N, C, and H of PEG-ZSMPUs.
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The XPS analysis (XPS, VG multilab2000, Thermo Electron Corporation, Waltham, MA, USA) was carried out using anode voltage and current of 15 kV and 10 mA, respectively. The elemental composition was determined on the basis of peak areas and sensitivity factor from C1s , N1s , O1s , and S2p peaks using advantage software. All of the binding energy values were confirmed with reference to carbon (C1s = 284.6 eV). X-ray diffractometry (XRD, D8 Advance, Bruker, Billerica, Germany) was performed to measure the crystallization of PEG-ZSMPUs. The XRD data were recorded in Bragg’s angle 2θ ranging from 5 to 90◦ with a scanning step size of 0.02◦ /s. The crystalline morphology and polarizing optical patterns of PEG-ZSMPUs were observed at 25 ◦ C by using a polarized optical microscope (POM, MP41, Mshot, Guangzhou, China), which was equipped with a hot stage (Mettler Toledo FP90 Central Processor & FP82 Hot Stage), and a camera was used to observe and record the strain recovery behaviors upon heating and cooling at a rate of 2 ◦ C/min. Atomic force microscopy (AFM, Nanonavi E-Sweep, SII Nanotechnology Instrument, SEIKO Co. Ltd, Tokyo, Japan) was used in tapping mode for morphological characterization of PEG-ZSMPUs. PEG-ZSMPUs were dissolved in DMF at a concentration of 5 mg/mL, which was then spin-coated on oxidized silicon substratesat 400 rpm for 10 s, followed by 4000 rpm for 60 s. The resulting spin-coated films were kept in a vacuumed oven at 50 ◦ C for 48 h to allow for the evaporation of the solvent. The morphology of PEG-ZSMPUs was examined using scanning electron microscopy (SEM, NGB4-DXS-10AC, Hitachi, Hitachi, Japan). Prior to SEM scanning, PEG-ZSMPUs were coated with a thin layer of gold. All of the measurements were repeated three times. Differential scanning calorimeter (DSC, Q200, TA universal, New Castle, DE, USA) was conducted in a purge gas, nitrogen to measure the glass-transition temperature (Tg ) and the melting temperature (Tm ) of PEG-ZSMPUs. PEG-ZSMPUs were first heated from −50 to 150 ◦ C at a heating rate of 10 ◦ C/min. The temperature was kept constant at 150 ◦ C for 1 min before cooling down to −50 ◦ C at a rate of 10 ◦ C·min−1 . After that, the samples were reheated and scanned from −50 to 150 ◦ C, at which the Tg and Tm were recorded. Thermogravimetric analysis (TGA) and derivative thermogravimetric analysis (DTG) were recorded with Q50 (TA universal, New Castle, DE, USA) at a heating rate of 10 ◦ C/min from 100 to 600 ◦ C in platinum crucibles under nitrogen flow (60 mL/min), and the sample weight of approximately 10 mg. Dynamic mechanical analysis (DMA, Q200, TA universal, USA) was determined in tensile mode with tension clamps under nitrogen at a heating rate of 3 ◦ C/min from −50 to 180 ◦ C. The rectangle specimens for DMA tests were prepared by film casting with approximate dimensions of 20 mm × 6 mm × 0.4 mm. Specimens were determined under 1.0 Hz. Shape-memory behaviours were also determined qualitatively with thermo-mechanical analysis using a TA Instruments DMA800 (TA universal, New Castle, DE, USA) (using tension clamps in controlled force mode). All of the samples were dried at 100 ◦ C in vacuo for 24 h and cut into rectangular pieces of approximately 10 mm × 2.0 mm × 0.5 mm. The detailed test setup for the shape-memory cycles is provided herein: (1) heating to approx. 55 ◦ C, followed by equilibration for 20 min; (2) uniaxial stretching to strain (εload ) by ramping the force from 0.001 N to 1 N at a rate of 0.25 N/min, followed by equilibration for 3 min; (3) fixing the strain (ε) about 100% by rapidly cooling to approx. 20 ◦ C with q = −10 ◦ C/min, followed by equilibration for 10 min; (4) unloading an external force 0 N at a rate of 0.25 N/min; (5) reheating to approx. 55 ◦ C at a rate of 4 ◦ C/min, followed by equilibration for 40 min; and finally, the recovery strain (εrec ) was recorded. The cytocompatibility of PEG-ZSMPUs was evaluated with regard to cell viability. Murine macrophage RAW264.7 cells (Shanghai Institute of Biochemistry and Cell Biology, Shanghai, China) were cultured at 37 ◦ C in RPMI-1640 medium supplemented with 10% fetal bovine serum, 100 IU·mL−1 penicillin, and 100 µg·mL−1 streptomycin in a humidified atmosphere with 5% CO2 . The cytotoxic effects of PEG-ZSMPUs were assessed with regard to cell viability of RAW264.7 cells, measured by tetrazolium salt (WST-8) based colorimetric assay according to Cell Counting Kit 8 (Dojindo,
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cytotoxic effects of PEG-ZSMPUs were assessed with regard to cell viability of RAW264.7 cells, salt (WST-8) based colorimetric assay according to Cell Counting 5Kit 8 of 15 (Dojindo, Kumamoto, Japan) [23]. The morphology cells grown on PEG-ZSMPUs films were observed by optical microscopy (ZEISS Axio Imager A1 m). Kumamoto, Japan) [23]. The morphology cells grown on PEG-ZSMPUs films were observed by optical microscopy (ZEISS Axio Imager A1 m). 3. Results and Discussion
measured tetrazolium Polymers 2017,by 9, 465
3. Results and Discussion 3.1. Structures of PEG-ZSMPUs 3.1. Structures PEG-ZSMPUs To verifyof the success in preparation of PEG-ZSMPUs, structures of PEG-ZSMPUs were investigated by the FT-IR (Figure and 1H-NMR S1, see supporting The FT-IR To verify success in 1)preparation of (Figure PEG-ZSMPUs, structures information). of PEG-ZSMPUs were −1, which could be spectrum of 1.0PEG-ZSMPU exhibited absorbance at 3324, 1691 and 1533 cm 1 investigated by FT-IR (Figure 1) and H-NMR (Figure S1, see supporting information). The FT-IR assigned and C=O stretching vibration and C–N deformation groups, −1 ,urethane spectrumtoofN–H 1.0PEG-ZSMPU exhibited absorbance at 3324, 1691 andvibration 1533 cmof which could be respectively. The low stretching vibration frequency of C=O group suggested that strong hydrogen assigned to N–H and C=O stretching vibration and C–N deformation vibration of urethane groups, bonds were The formed among both soft frequency and hardofsegments. comparing withhydrogen that of respectively. low stretching vibration C=O groupWhen suggested that strong 0PEG-ZSMPU (Figure 1A),both the soft FT-IR of 1.0PEG-ZSMPU showed additional peak at bonds were formed among andspectrum hard segments. When comparing withan that of 0PEG-ZSMPU −1, which could be attributed to the absorption of S=O group of sulfonic acid group (Figure 1). 1035 cm − 1 (Figure 1A), the FT-IR spectrum of 1.0PEG-ZSMPU showed an additional peak at 1035 cm , which In addition, intensity peak enhanced increasing molar 1,3-PS 1). andInMDEA in could be attributed to of thethe absorption of S=Owith group of sulfonic acidratios groupof(Figure addition, −1 PEG-ZSMPUs 1B). Moreover, the absorbance of isocyanate at 2272 cm was not intensity of the(Figure peak enhanced with increasing molar ratios of 1,3-PSgroups and MDEA in PEG-ZSMPUs 1H-NMR spectra of 0PEG-ZSMPU and observed in HDI-MDEA-PS hard segment. A comparison of − 1 (Figure 1B). Moreover, the absorbance of isocyanate groups at 2272 cm was not observed in 0.8PEG-ZSMPU further confirmed that chemical shift atspectra 3.10 ppm (Figure S1e) could be assigned to HDI-MDEA-PS hard segment. A comparison of 1 H-NMR of 0PEG-ZSMPU and 0.8PEG-ZSMPU + proton signals of that –N –CH 3. Proton signals corresponding to the –CH2– of sulfonic acid were further confirmed chemical shift at 3.10 ppm (Figure S1e) could be assigned to proton signals observed from 0.8PEG-ZSMPU at 1.70, 2.77, to and ppm (Figure S1c,d,f, respectively). When + of –N –CH3 . Proton signals corresponding the3.67 –CH 2 – of sulfonic acid were observed from 1 comparing with the H-NMR spectrum of 0PEG-ZSMPU, chemical shifts inWhen reference to –CHwith 2– of 0.8PEG-ZSMPU at 1.70, 2.77, and 3.67 ppm (Figure S1c,d,f, respectively). comparing MDEA were observed in 0.8PEG-ZSMPU (from 3.98 ppm in 0PEG-ZSMPU to 4.16, and 4.36 ppm in 1 the H-NMR spectrum of 0PEG-ZSMPU, chemical shifts in reference to –CH2 – of MDEA were 0.8PEG-ZSMPU). In addition, chemical shift associated with the N–H of 0.8PEG-ZSMPU were also observed in 0.8PEG-ZSMPU (from 3.98 ppm in 0PEG-ZSMPU to 4.16, and 4.36 ppm in 0.8PEG-ZSMPU). found (from 7.0 ppm 0PEG-ZSMPU 7.2–7.4 ppm in 0.8PEG-ZSMPU). elemental In addition, chemical shiftinassociated with thetoN–H of 0.8PEG-ZSMPU were also foundThe (from 7.0 ppm composition of PEG-ZSMPUs was determined by using an elementalanalyzer and found that the in 0PEG-ZSMPU to 7.2–7.4 ppm in 0.8PEG-ZSMPU). The elemental composition of PEG-ZSMPUs actual content of elemental S in PEG-ZSMPUs was close to its theoretical weight percentage (Table was determined by using an elementalanalyzer and found that the actual content of elemental S in S1, see supporting information). Additionally, X-ray photoelectron spectroscopy (XPS) of PEG-ZSMPUs was close to its theoretical weight percentage (Table S1, see supporting information). 0PEG-ZSMPUX-ray and 1.0PEG-ZSMPU further confirmed the presences of and S2s (binding energy, 230 eV) Additionally, photoelectron spectroscopy (XPS) of 0PEG-ZSMPU 1.0PEG-ZSMPU further and S2p (binding energy, of 168 orbitals in 1.0PEG-ZSMPU, which wereenergy, absent168 in 0PEG-ZSMPU confirmed the presences S2seV) (binding energy, 230 eV) and S2p (binding eV) orbitals in (Figure 2A). The N 1s spectrum of 1PEG-ZSMPU showed two peaks at 402.2 and 399.6 eV, indicating 1.0PEG-ZSMPU, which were absent in 0PEG-ZSMPU (Figure 2A). The N1s spectrum of 1PEG-ZSMPU the presences of ammonium in MDEA-PS segment and nitrogen of either in urethane or showed two peaks at 402.2 and nitrogen 399.6 eV, indicating the presences of ammonium nitrogen MDEA-PS un-reacted MDEA monomer, 2B). These confirmed that the designed segment and nitrogen of eitherrespectively urethane or(Figure un-reacted MDEAresults monomer, respectively (Figure 2B). PEG-ZSMPUs were successfully prepared. These results confirmed that the designed PEG-ZSMPUs were successfully prepared.
(A) 1,3-PS
0PEG-ZSMPU 3324
1691
2864
1533 1464
1342
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Wavenumbers (cm ) Figure 1. Cont.
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(B) (B) 1.0PEG-ZSMPU 1.0PEG-ZSMPU 0.8PEG-ZSMPU 0.8PEG-ZSMPU 0.6PEG-ZSMPU 0.6PEG-ZSMPU 0.4PEG-ZSMPU 0.4PEG-ZSMPU 0.2PEG-ZSMPU 0.2PEG-ZSMPU
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Wavenumbers (cm ) Figure 1. Fourier transform-infrared spectroscopy spectra (FT-IR) spectra of samples, (A) for Figure Fourier transform-infrared transform-infrared spectroscopy spectroscopy spectra spectra (FT-IR) (FT-IR) spectra spectra of of samples, (A) for Figure 1. 1. Fourier samples, (A) for comparisions of 1,3-PS, 0PEG-ZSMPU and1PEG-ZSMPU; (B) for PEG-ZSMPUs with different comparisions of 1,3-PS, 0PEG-ZSMPU and1PEG-ZSMPU; (B) for PEG-ZSMPUs with different comparisions of 1,3-PS, 0PEG-ZSMPU and1PEG-ZSMPU; (B) for PEG-ZSMPUs with different zwitterionic hard segments. zwitterionic zwitterionic hard hard segments. segments.
(A) (A)
S2P
O1S O1S
S2P
C1S
C1S
164
N1S
1.0PEG-ZSMPU
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402 400 Binding energy (eV)
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404 402 400 and N 398spectra of 396 Figure (XPS) 0PEG-ZSMPU and 1s Figure2. 2. X-ray X-ray photoelectron photoelectron spectroscopy spectroscopy (XPS) Binding energy (eV) and N1s spectra of 0PEG-ZSMPU and 1.0PEG-ZSMPU. ((A) Full spectra; (B) N spectra). 1s 1.0PEG-ZSMPU. ((A) Full spectra; (B) N1s spectra).
Figure 2. X-ray photoelectron spectroscopy (XPS) and N1s spectra of 0PEG-ZSMPU and 1.0PEG-ZSMPU. ((A) Full spectra; (B) N1s spectra).
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3.2. Morphology of PEG-ZSMPUs
3.2.The Morphology of PEG-ZSMPUs morphology of PEG-ZSMPUs was investigated by XRD, POM, AFM and SEM. Figure 3 shows The the XRD curves withinvestigated different molar ratios of 1,3-PS The XRD morphology of of PEG-ZSMPUs PEG-ZSMPUs was by XRD, POM, AFMand andMDEA. SEM. Figure 3 patterns demonstrated PEG-ZSMPUs had two obvious crystallization peaks nearThe 2θ XRD = 18.7◦ shows the XRD curves that of PEG-ZSMPUs with different molar ratios of 1,3-PS and MDEA. and 22.8◦ , demonstrated indicating that crystal has had hightwo integrity large size.peaks Moreover, patterns thatthe PEG-ZSMPUs obviouswith crystallization near 2θ =intensities 18.7° and of crystallization peaks decreased first and then increased, with the increased molar ratio of 1,3-PSofand 22.8°, indicating that the crystal has high integrity with large size. Moreover, intensities crystallization peaks decreasedthe firstintensities and then increased, with the peaks increased molar ratio of 1,3-PS MDEA. As could be observed, of crystallization of 0.4PEG-ZSMPU wasand lower MDEA. As0.6PEG-ZSMPU, could be observed, thethe intensities of of crystallization peaks of 0.4PEG-ZSMPU waswas lower than that of while intensities crystallization peaks of 1.0PEG-ZSMPU lower than thatofof0PEG-ZSMPU. 0.6PEG-ZSMPU, while the isintensities of crystallization peaks of 1.0PEG-ZSMPU than that The reason that the aggregation of zwitterionic hard segmentwas firstly lower than of 0PEG-ZSMPU. that the too aggregation of zwitterionic promotes thethat crystallization of PEGThe softreason phase,iswhereas much higher content ofhard hardsegment segments firstly the phase crystallization of PEG softthe phase, whereas too much higherit content of hardthat result in promotes the soft-hard mixing, destroying crystallization. Furthermore, was observed segments in the soft-hard phase values mixing,when destroying the crystallization. Furthermore, it was positions ofresult the peak shifted to higher the molar ratio of 1,3-PS and MDEA increased. observed that positions of the peak shifted to higher values when the molar ratio of 1,3-PS and to The peak positions of 0PEG-ZSMPU, 0.2PEG-ZSMPU, 0.4PEG-ZSMPU and 0.6PEG-ZSMPU shifted MDEA increased. The peak positions of 0PEG-ZSMPU, 0.2PEG-ZSMPU, 0.4PEG-ZSMPU and higher peak values, while those of 0.8PEG-ZSMPU and 1.0PEG-ZSMPU shifted to lower peak values, 0.6PEG-ZSMPU shifted to higher peak values, while those of 0.8PEG-ZSMPU and 1.0PEG-ZSMPU which however were higher than that of 0PEG-ZSMPU. This indicated that the crystallization ability shifted to lower peak values, which however were higher than that of 0PEG-ZSMPU. This indicated of PEG-ZSMPUs decreased and then enhanced, which may be ascribed to the grafting of 1,3-PS on that the crystallization ability of PEG-ZSMPUs decreased and then enhanced, which may be to the main chain of PEG-ZSMPUs as well as the formation of branched chain that could destroy the ascribed to the grafting of 1,3-PS on to the main chain of PEG-ZSMPUs as well as the formation of regularity of molecular chain so that the crystallization ability of PEG-ZSMPUs was weaken. The POM branched chain that could destroy the regularity of molecular chain so that the crystallization image provided a direct visual-proof of the crystallization of PEG-ZSMPUs. As shown in Figure 4, ability of PEG-ZSMPUs was weaken. The POM image provided a direct visual-proof of the PEG-ZSMPUs many “+” polarizing optical patterns of the spherical indicating that crystallizationhad of PEG-ZSMPUs. As shown in Figure 4, PEG-ZSMPUs hadcrystals, many “+” polarizing PEG-ZSMPUs have good crystallinity. Moreover, the crystallization rate of PEG-ZSMPUs decreased optical patterns of the spherical crystals, indicating that PEG-ZSMPUs have good crystallinity. and then enhanced, with the increasing 1,3-PS content,decreased which was consistent with the with resultthe from Moreover, the crystallization rate of PEG-ZSMPUs and then enhanced, XRD analysis. increasing 1,3-PS content, which was consistent with the result from XRD analysis.
Intensity (Counts)
0PEG-ZSMPU 0.2PEG-ZSMPU 0.4PEG-ZSMPU 0.6PEG-ZSMPU 0.8PEG-ZSMPU 1.0PEG-ZSMPU
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O
40
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2θ( )
Figure3.3.X-ray X-ray diffractometry diffractometry (XRD) Figure (XRD)curves curvesfor forPEG-ZSMPUs. PEG-ZSMPUs. 0PEG-ZSMPU
0.2PEG-ZSMPU
0.4PEG-ZSMPU
AFM technology provides a persuasive evidenceto visually study the morphology of PEG-ZSMPUs. The AFM images of PEG-ZSMPUs showed a phase separation structure comprising of hard and soft phases. The 3D phase AFM images showed some clear cuspidal outshoots (Figure 5), which may be due to HDI-MDEA aggregates and ionic 5mm bond serving as 5mm hard phase and some pot holes 5mm resulted from HDI-PEG6000 soft phase. The result shown in Figure 5 demonstrated that the amorphous 0.6PEG-ZSMPU 0.8PEG-ZSMPU 1.0PEG-ZSMPU hard phase (HDI-MDEA) was separated by soft phase and divided into small hard domains. The hard domain increased with increasing molar ratio of 1,3-PS and MDEA from 0.2 to 0.8 (Figure 5). When the molar ratio of 1,3-PS and MDEA was greater than 0.8, the hard phase of 1PEG-ZSMPU became continuous with the soft phase5mmembedded in 5mm it (Figure 5). This 5mm aggregation of zwitterionic polymers has been widely investigated previously [24]. The surface morphology of PEG-ZSMPUs was Figure 4. Polarized optical microscope (POM) images (magnified 100 times) of PEG-ZSMPUs.
0PEG-ZSMPU 0.2PEG-ZSMPU 0.4PEG-ZSMPU 0.6PEG-ZSMPU 0.8PEG-ZSMPU 1.0PEG-ZSMPU
Intensity (Counts)
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systematically investigated. Figure 6 displays SEM images of PEG-ZSMPUs films with different molar ratio of 1,3-PS and MDEA. The SEM images showed that 0PEG-ZSMPU had a smooth surface without Polymers 2017, 9, 465 8 of 15 any holes, those of 0.2PEG-ZSMPU, 0.4PEG-ZSMPU, 0.6PEG-ZSMPU and 0.8PEG-ZSMPU Polymers 2017,whereas 9, 465 8 of 15 were rough and appeared to have a series of bending wave patterns. As observed in 0.2PEG-ZSMPUs, AFM technology provides a persuasive evidenceto visually study the morphology of 0.4PEG-ZSMPUs, 0.6PEG-ZSMPUsaand 0.8PEG-ZSMPU, numbers of bending increased with AFM technology persuasive evidenceto visually study waves the morphology of PEG-ZSMPUs. The AFMprovides images of PEG-ZSMPUs showed a phase separation structure comprising the increase of The molar ratio of 1,3-PS and MDEA (Figure 6). Results from thestructure fracturecomprising surface of PEG-ZSMPUs. AFM images of PEG-ZSMPUs showed a phase separation of hard and soft phases. The 3D phase AFM images showed some clear cuspidal outshoots (Figure 5), PEG-ZSMPUs demonstrated thatphase they AFM had typical ductile fractures. However, the fracture (Figure surface 5), of of hardmay and be soft phases. The 3D images showed some clear cuspidal outshoots which due to HDI-MDEA aggregates and ionic bond serving as 60 hard phase and some pot 10 20 30 40 50 1.0PEG-ZSMPU wastorough and irregular multilayer, indicated that it was the brittle fracture. whichresulted may be from due HDI-MDEA aggregates bond serving as hard phase and some O which holes HDI-PEG6000 soft phase. and The2θ(ionic result shown in Figure 5 demonstrated that pot the ) These results indicated that the increased molarThe ratios of 1,3-PS and MDEA weakened the toughness holes resulted from HDI-PEG6000 soft phase. result shown in Figure 5 demonstrated thathard the amorphous hard phase (HDI-MDEA) was separated by soft phase and divided into small Figure 3. X-ray diffractometry (XRD) curves for PEG-ZSMPUs. but enhanced the brittleness of PEG-ZSMPUs. amorphous hard (HDI-MDEA) was increasing separated molar by softratio phase and divided into from small 0.2 hard domains. The hardphase domain increased with of 1,3-PS and MDEA to domains. The hard domain increased with increasing molar ratio of 1,3-PS and MDEA from 0.2 to 0.8 (Figure 5). When the molar ratio of 1,3-PS and MDEA was greater than 0.8, the hard phase of 0PEG-ZSMPU 0.2PEG-ZSMPU 0.4PEG-ZSMPU 0.8 (Figure 5). When molar ratio of 1,3-PS MDEA was greater than 0.8, hard phase of 1PEG-ZSMPU becamethe continuous with the softand phase embedded in it (Figure 5).the This aggregation 1PEG-ZSMPU became continuous with the soft phase embedded in it (Figure 5). This aggregation of zwitterionic polymers has been widely investigated previously [24]. The surface morphology of of zwitterionic was polymers has been widely investigated surface of PEG-ZSMPUs systematically investigated. Figurepreviously 6 displays[24]. SEMThe images of morphology PEG-ZSMPUs PEG-ZSMPUs was molar systematically investigated. Figure 6 SEM displays SEM imagesthat of 0PEG-ZSMPU PEG-ZSMPUs films with different ratio of 1,3-PS and MDEA. The images showed 5mm 5mm 5mm films with different molar ratio of 1,3-PS and MDEA. The SEM images showed that 0PEG-ZSMPU had a smooth surface without any holes, whereas those of 0.2PEG-ZSMPU, 0.4PEG-ZSMPU, 0.6PEG-ZSMPU 0.8PEG-ZSMPU 1.0PEG-ZSMPU had a smooth surface without any were holes,rough whereas those of 0.2PEG-ZSMPU, 0.4PEG-ZSMPU, 0.6PEG-ZSMPU and 0.8PEG-ZSMPU and appeared to have a series of bending wave 0.6PEG-ZSMPU and 0.8PEG-ZSMPU were rough and appeared to have a series of bending wave patterns. As observed in 0.2PEG-ZSMPUs, 0.4PEG-ZSMPUs, 0.6PEG-ZSMPUs and 0.8PEG-ZSMPU, patterns. As observed in 0.2PEG-ZSMPUs, 0.4PEG-ZSMPUs, 0.6PEG-ZSMPUs and 0.8PEG-ZSMPU, numbers of bending waves increased with the increase of molar ratio of 1,3-PS and MDEA (Figure numbers bending waves increased with the increase demonstrated of molar ratio that of 1,3-PS 6). Resultsoffrom the fracture surface of PEG-ZSMPUs they and had MDEA typical (Figure ductile 5mm 6). ResultsHowever, from the the fracture surface of demonstrated thatand theyirregular had typical ductile 5mmPEG-ZSMPUs 5mm fractures. fracture surface of 1.0PEG-ZSMPU was rough multilayer, fractures. However, the fracture surface of 1.0PEG-ZSMPU was rough and irregular multilayer, which indicated that it was the brittle fracture. These results indicated that the increased molar Figure 4. Polarized optical (POM) images images (magnified 100 times) of PEG-ZSMPUs. PEG-ZSMPUs. whichofindicated that it was themicroscope brittle These results indicated that the molar Figure Polarized optical microscope (POM) 100 of ratios 1,3-PS4.and MDEA weakened thefracture. toughness but (magnified enhanced the times) brittleness of increased PEG-ZSMPUs. ratios of 1,3-PS and MDEA weakened the toughness but enhanced the brittleness of PEG-ZSMPUs. 0PEG-ZSMPU
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Figure 5. Atomic force microscopy (AFM) images (3D phase) of PEG-ZSMPUs. Figure Atomic force force microscopy Figure 5. 5. Atomic microscopy (AFM) (AFM) images images (3D (3D phase) phase) of of PEG-ZSMPUs. PEG-ZSMPUs. 0PEG-ZSMPU 0PEG-ZSMPU
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Figure 6. Scanning electron microscopy (SEM) images of PEG-ZSMPUs. of PEG-ZSMPUs. PEG-ZSMPUs. Figure 6. Scanning electron microscopy (SEM) images of
3.3. Thermal Properties of PEG-ZSMPUs 3.3. Thermal Properties of PEG-ZSMPUs The thermal properties of PEG-ZSMPUs, synthesized from different molar ratios of 1,3-PS and Thewere thermal propertiesby of using PEG-ZSMPUs, different molar ratios of 1,3-PS and MDEA, characterized DSC and synthesized TG. Figure 7from shows the DSC curves of PEG-ZSMPUs MDEA, were by usingand DSC and TG. Figure process. 7 shows the curves PEG-ZSMPUs obtained fromcharacterized the second heating cooling scanning TheDSC second DSCofheating curves obtained from the second heating and cooling scanning process. The second DSC heating demonstrated that PEG-ZSMPUs had a crystalline phase at the low temperature range, whichcurves could demonstrated PEG-ZSMPUs had phase a crystalline phase the zwitterions low temperature range, which could be ascribed tothat PEG crystalline soft (Figure 7B).atThe tended to improve the
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3.3. Thermal Properties of PEG-ZSMPUs The thermal properties of PEG-ZSMPUs, synthesized from different molar ratios of 1,3-PS and MDEA, were characterized by using DSC and TG. Figure 7 shows the DSC curves of PEG-ZSMPUs Polymers 2017, 9, 465 9 of 15 obtained from the second heating and cooling scanning process. The second DSC heating curves demonstrated that PEG-ZSMPUs had a crystalline phase at the low temperature range, which could be crystallization c) of (Figure the soft7B). phase. The Tc of tended PEG-ZSMPUs increased with the ascribed to PEGtemperature crystalline soft(Tphase The zwitterions to improve the crystallization increase of molar ratios of 1,3-PS and MDEA, which could be due to an increase of ionic interactions temperature (Tc ) of the soft phase. The Tc of PEG-ZSMPUs increased with the increase of molar (Figureof7A). Theand influence of which ionic interaction wastoalso TG interactions curves and DTG curves ratios 1,3-PS MDEA, could be due an shown increaseonofthe ionic (Figure 7A). (Figure 8A), demonstrating that was PEG-ZSMPUs higher decomposition The influence of ionic interaction also shownhad on the TG curves and DTGtemperatures curves (Figurewhen 8A), compared withthat thatPEG-ZSMPUs of their precursor (0PEG-ZSMPU). The maximum degradation temperatures of demonstrating had higher decomposition temperatures when compared with that PEG-ZSMPUs, defined by the temperature at which the maximum decomposition rate occurs, were of their precursor (0PEG-ZSMPU). The maximum degradation temperatures of PEG-ZSMPUs, defined higher than that of their precursor in the first stage (i.e., the maximum decomposition rate occurs a by the temperature at which the maximum decomposition rate occurs, were higher than that of their ◦ temperature of 256 °C in 1.0PEG-ZSMPU, compared with that of 248 °C in 0PEG-ZSMPU) (Figure precursor in the first stage (i.e., the maximum decomposition rate occurs a temperature of 256 C ◦ C inof 8B). TG curves further demonstrated that residues PEG-ZSMPUs(Figure above 8B). 500 °C with in 1.0PEG-ZSMPU, compared with that of 248 0PEG-ZSMPU) TGenhanced curves further ◦ increasing molar ratios of 1,3-PS and MDEA, implying that MDEA-PS zwitterionic hard segments demonstrated that residues of PEG-ZSMPUs above 500 C enhanced with increasing molar ratios of had a and good thermal-stability. Therefore, MDEA-PShard segment had had a tendency to enhance the 1,3-PS MDEA, implying that MDEA-PSthe zwitterionic segments a good thermal-stability. thermal-stability of PEG-ZSMPUs. Therefore, the MDEA-PS segment had a tendency to enhance the thermal-stability of PEG-ZSMPUs. (A)
Heat flow (mW/g)
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Figure 7. 7. Differential Differentialscanning scanningcalorimeter calorimeter(DSC) (DSC) curves of PEG-ZSMPUs: cooling curves curves of PEG-ZSMPUs: (A)(A) the the cooling curves and andthe (B)second the second heating curves. (B) DSCDSC heating curves.
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Temperature ( C) Figure (TGA curves curvesofofPEG-ZSMPUs: PEG-ZSMPUs: curves, DTG Figure8. 8.Thermogravimetric Thermogravimetric analysis analysis (TGA (A)(A) TGTG curves, andand (B)(B) DTG curves). curves).
3.4. ShapeMemory MemoryProperties PropertiesofofPEG-ZSMPUs PEG-ZSMPUs 3.4. Shape Thezwitterions zwitterionscan canaffect affectthe the dynamic dynamic mechanical Figure 9 shows The mechanicalproperties propertiesofofPEG-ZSMPUs. PEG-ZSMPUs. Figure 9 shows DMA curves of PEG-ZSMPUs with different molar ratios of 1,3-PS and MDEA, representing phase DMA curves of PEG-ZSMPUs with different molar ratios of 1,3-PS and MDEA, representing phase transitionsofofPEG-ZSMPUs. PEG-ZSMPUs. In In addition, addition, tan went transitions tan δδ curves curvesdemonstrated demonstratedthat thatthe thePEG-ZSMPUs PEG-ZSMPUs went about glass and crystal melting transitions at a low temperature range (e.g., below 100 °C). The ◦ about glass and crystal melting transitions at a low temperature range (e.g., below 100 C). The storage storage (E’) modulus curvesthat showed the E’ of PEG-ZSMPUs changedinslightly in state. a glassy state.the modulus curves(E’) showed the E’that of PEG-ZSMPUs changed slightly a glassy During During the crystal melting transition process, a sharp decrease in the modulus occurred in all of the crystal melting transition process, a sharp decrease in the modulus occurred in all of the PEG-ZSMPU PEG-ZSMPU samples. At the rubber state, the rubber modulus increased with the increase of molar samples. At the rubber state, the rubber modulus increased with the increase of molar ratios, indicating ratios, indicating the reinforcement of zwitterionic hard segments. The results showed that grafting the reinforcement of zwitterionic hard segments. The results showed that grafting of the 1,3-PS onto of the 1,3-PS onto the main chain of 0PEG-ZSMPU influenced main chain’s mobility. It is possible the main chain of 0PEG-ZSMPU influenced main chain’s mobility. It is possible that the degradation that the degradation and creep relaxation of sulfobetaine side chain may cause glass transition of and creep relaxation of sulfobetaine side chain may cause glass transition of the polymer to become the polymer to become wider when heated. Moreover, the elevated molar ratio of 1,3-PS may break wider when heated. thehard elevated molarinratio of 1,3-PS may break hydrogen bondratios among the hydrogen bondMoreover, among the segments PEG-ZSMPUs. While thethe higher modulus thebetween hard segments in and PEG-ZSMPUs. Whilewere the higher ratios between the glassy andwith rubber the glassy rubber modulus found modulus in PEG-ZSMPUs, their ratios increased modulus were found in PEG-ZSMPUs, their ratios increased with the increasing ratios of 1,3-PS the increasing ratios of 1,3-PS and MDEA. These results suggested that PEG-ZSMPUs with a higherand MDEA. suggested withSMEs, a higher of1.0PEG-ZSMPUs. 1,3-PS and MDEA might ratio ofThese 1,3-PSresults and MDEA might that showPEG-ZSMPUs thermally induced e.g.,ratio in the show thermally inducedSMEs SMEs, in the 1.0PEG-ZSMPUs. Thermal-induced ofe.g., PEG-ZSMPUs were analyzed by thermal-mechanical analysis using Thermal-induced SMEs ofThe PEG-ZSMPUs were analyzed thermal-mechanical analysis using a TA Instrument DMA Q200. results shown in Figure 10Abydemonstrated that 1.0PEG-ZSMPU a TA Instrument DMA Q200. The results shown in Figure 10A demonstrated that 1.0PEG-ZSMPU could be deformed to nearly 90% strain when it was heated to 55 °C; and, after being cooled down could be deformed to nearly 90% strain when it was heated to 55 ◦ C; and, after being cooled down
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◦ C, more to to aa temperature temperature below below 20 20 °C, more than than 94% 94% strain strain could could be be fixed. fixed. When When the the sample sample was was reheated reheated to 55 °C, nearly 79% of the deformed strain was recovered. Although all of the samples ◦ to 55 C, nearly 79% of the deformed strain was recovered. Although all of the samples showed showed good shape fixation, those without or less zwitterionic segment (e.g., samples 0PEG-ZSMPU good shape fixation, those without or less zwitterionic segment (e.g., samples 0PEG-ZSMPU and and 0.2PEG-ZSMPU) 0.2PEG-ZSMPU) showed showed aa very very low low shape shape recovery. recovery. These These demonstrated demonstrated that that the the zwitterionic zwitterionic hard hard segment could improve improvethe theshape shaperecovery recovery promoting aggregation of hard the hard segment to segment could byby promoting the the aggregation of the segment to serve serve as physical netpoints. as physical netpoints.
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Figure 9. The The Dynamic Dynamicmechanical mechanicalanalysis analysis(DMA) (DMA) curves of PEG-ZSMPUs PEG-ZSMPUs (A) storage modulus Figure 9. The Dynamic mechanical analysis (DMA) curves storage modulus Figure 9. curves of of PEG-ZSMPUs (A)(A) storage modulus and and (B) tan δ curves. and (B) δtan δ curves. (B) tan curves.
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n(1,3-PS)/n(MDEA) Figure 10. 10. Thermal-induced Thermal-inducedshape shape memory memory effects effects (SMEs) (SMEs) of of PEG-ZSMPUs: PEG-ZSMPUs: (A) (A) shaped shaped memory memory Figure curves of sample 1.0PEG-ZSMPU and (B) shape recovery and shape fixity of PEG-ZSMPUs with curves of 10. sample 1.0PEG-ZSMPU and (B) shape recovery shape fixity of with Figure Thermal-induced shape memory effects (SMEs)and of PEG-ZSMPUs: (A)PEG-ZSMPUs shaped memory various molar ratio of 1,3-PS/MDEA. various molar ratio of 1,3-PS/MDEA.and (B) shape recovery and shape fixity of PEG-ZSMPUs with curves of sample 1.0PEG-ZSMPU various molar ratio of 1,3-PS/MDEA.
3.5. CytocompatibilityAnalysis CytocompatibilityAnalysisofofPEG-ZSMPUs PEG-ZSMPUs 3.5. 3.5. CytocompatibilityAnalysis of PEG-ZSMPUs In vitro vitro biocompatibility biocompatibility ofofPEG-ZSMPUs PEG-ZSMPUswas wasstudied studied through adhesion proliferation In through adhesion andand proliferation of of RAW264.7 cells on PEG-ZSMPUs films. RAW264.7 cells were seeded on 0.2PEG-ZSMPU, In vitro biocompatibility of PEG-ZSMPUs was studied through adhesion and proliferation of RAW264.7 cells on PEG-ZSMPUs films. RAW264.7 cells were seeded on 0.2PEG-ZSMPU, RAW264.7 cells on PEG-ZSMPUs films. RAW264.7 cells were seeded on 0.2PEG-ZSMPU, 0.4PEG-ZSMPU, 0.6PEG-ZSMPU, 0.8PEG-ZSMPU and 1PEG-ZSMPU films, and then cultured at 0.4PEG-ZSMPU, 0.6PEG-ZSMPU, 0.8PEG-ZSMPU and 1PEG-ZSMPU films, and then cultured at 37 ◦ 0.6PEG-ZSMPU, 0.8PEG-ZSMPU andevaluated. 1PEG-ZSMPU films, and the then cultured at 37 37 0.4PEG-ZSMPU, C for Cellviability viability andproliferation proliferation were investigate cell adhesion and °C for 24 24 h. h. Cell and were then then evaluated.ToTo investigate the cell adhesion °Cviability, for the 24 h. Celllive/dead viability andof proliferation were on then evaluated. Tosubstrates investigate theconducted. cell adhesion viability, live/dead staining RAW264.7 cells different substrates was conducted. The results and the staining of RAW264.7 cells on different was The and viability, the live/dead staining of RAW264.7 cells on different substrates was conducted. The showedshowed that most RAW264.7 cells were viable (indicated by green color stain)color and displayed results that most RAW264.7 cells were viable (indicated by green stain) and sphere-like displayed resultsmorphologies showed thatmorphologies most RAW264.7 cellsresults were (indicated by green color stain) and displayed shaped (Figure 11). These demonstrated PEG-ZSMPUs possessed a good sphere-like shaped (Figure 11).viable These resultsthat demonstrated that PEG-ZSMPUs sphere-like shaped morphologies (Figure 11). These results demonstrated that PEG-ZSMPUs biocompatibility showed no while effectsshowed on cell adhesion morphology. possessed a good while biocompatibility no effectsand on cell adhesion and morphology. possessed a good biocompatibility while showed no effects on cell adhesion and morphology. Blank control Blank control
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Figure 11. The inverted micrographs RAW264.7 cells after after incubatingwith with samplePEG-ZSMPUs PEG-ZSMPUs Figure The invertedmicrographs micrographsofof ofRAW264.7 RAW264.7 cells cells Figure 11.11. The inverted after incubating incubating withsample sample PEG-ZSMPUs forfor 48 48 h. h. for 48 h.
addition,the theviability viability of of treated treated RAW264.7 RAW264.7 cells saltsalt In In addition, cells was was studied studiedusing usingaaatetrazolium tetrazolium In addition, the viability of treated RAW264.7 cells was studied using tetrazolium salt (WST-8)-based colorimetric assay according to the Cell Counting Kit-8 (CCK-8) [20] and calculated (WST-8)-based colorimetric assay according to the Cell Counting Kit-8 (CCK-8) [20] and calculated (WST-8)-based colorimetric assay according to the Cell Counting Kit-8 (CCK-8) [20] and calculated by normalization in reference to the untreated cells [21]. The results shown in Figure 12, viability of by normalization normalizationininreference referencetotothe theuntreated untreatedcells cells[21]. [21].The The results shown in Figure viability by results shown in Figure 12,12, viability of RAW264.7 cells treated with PEG-ZSMPUs of different molar ratios of 1,3-PS and MDEA, of RAW264.7 cells treated with PEG-ZSMPUs ofdifferent differentmolar molarratios ratiosofof1,3-PS 1,3-PS and and MDEA, MDEA, RAW264.7 cells treated with PEG-ZSMPUs of demonstrated that more than 90% cell viability were observed in 0.2PEG-ZSMPU, 0.4PEG-ZSMPU
demonstrated that more than 90% cell viability were observed in 0.2PEG-ZSMPU, 0.4PEG-ZSMPU
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Polymers 2017, 9, 465 of 15 and 0.6PEG-ZSMPU (Figure 12). Whereas, the higher molar ratios of 1,3-PS and MDEA13slightly demonstrated that moreas than 90% cellby viability were observed in 0.2PEG-ZSMPU, 0.4PEG-ZSMPU and reduced cell viability, indicated cell viabilities of 0.8PEG-ZSMPU and 1PEG-ZSMPU, which and 0.6PEG-ZSMPU (Figure 12). Whereas, the higher molar ratios of 1,3-PS and MDEA slightly 0.6PEG-ZSMPU (Figure 12). Whereas, the higher molar ratios of 1,3-PS and MDEA slightly reduced were slightly lower than the control. Analysis ofofresults above demonstrated that all of the reduced cellasviability, asby indicated by cellof viabilities 0.8PEG-ZSMPU and 1PEG-ZSMPU, which cell viability, indicated cell viabilities 0.8PEG-ZSMPU and 1PEG-ZSMPU, which were slightly PEG-ZSMPUs biocompatibility, andof this is highly consistent with previous were slightly have lower good than the control. Analysis results above demonstrated that our all of the lower than theon control. Analysis of results above demonstrated that all of the PEG-ZSMPUs have investigations zwitterionic polyurethanes [21]. PEG-ZSMPUs have good biocompatibility, and this is highly consistent with our previous good biocompatibility, and this is highly consistent with our previous investigations on zwitterionic investigations on zwitterionic polyurethanes [21]. polyurethanes [21].
Figure 12. The cell activity of RAW264.7 cells incubated with the PEG-ZSMPUs films and Figure RAW264.7 cells cellsincubated incubatedwith withthe thePEG-ZSMPUs PEG-ZSMPUs films Control Figure12. 12.The The cell cell activity activity of of RAW264.7 films andand Control Control sample. sample. sample.
Furthermore, the biocompatibility ofof polymers and bioactivity of treated RAW264.7 cellscells werewere also Furthermore, polymers and bioactivity treated RAW264.7 Furthermore,the the biocompatibility biocompatibility of polymers and bioactivity ofof treated RAW264.7 cells were observed in SEM images. The SEM images of RAW264.7 cells treated with PEG-ZSMPUs are shown in also SEM images imagesofofRAW264.7 RAW264.7cells cellstreated treated with PEG-ZSMPUs alsoobserved observedin inSEM SEM images. images. The SEM with PEG-ZSMPUs are are Figure 13 demonstrated that cells had many clear filopodia so that they were able to adhere well to shownininFigure Figure 13 13 demonstrated demonstrated that that they were ableable to to shown that cells cells had hadmany manyclear clearfilopodia filopodiasoso that they were PEG-ZSMPUs substrate. Thus, it could be concluded that PEG-ZSMPUs have good biocompatibility. adherewell welltotoPEG-ZSMPUs PEG-ZSMPUs substrate. substrate. Thus, PEG-ZSMPUs have good adhere Thus,ititcould couldbebeconcluded concludedthat that PEG-ZSMPUs have good It has been shownItIt that enhanced bioactivity macrophages promotes phagocytosis of promotes invasive biocompatibility. has been shown that enhanced bioactivity of ofmacrophages promotes biocompatibility. has been shown that of enhanced bioactivity macrophages particles, tumour cells and bacteria.tumour On thecells other hand, weak bioactivity reduces thebioactivity loss of drug phagocytosis invasive particles, and bacteria. On the hand, weak phagocytosis ofofinvasive particles, tumour cells and bacteria. On theother other hand, weak bioactivity carriers and implanted devices. Thus, PEG-ZSMPUs may have high potential application in smart reduces the loss of drug carriers and implanted devices. Thus, PEG-ZSMPUs may have high reduces the loss of drug carriers and implanted devices. Thus, PEG-ZSMPUs may have high biomedical fields [25]. potential application in smart biomedical fields [25]. potential application in smart biomedical fields [25]. Blank control Blank control
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1.0 PEG-ZSMPU
1.0 PEG-ZSMPU
Figure 13. SEM images of RAW264.7 Cells incubated with PEG-ZSMPUs and the control sample. Figure 13. SEM images of RAW264.7 Cells incubated with PEG-ZSMPUs and the control sample. Figure 13. SEM images of RAW264.7 Cells incubated with PEG-ZSMPUs and the control sample.
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4. Conclusions In this work, zwitterionic PEG-ZSMPUs were synthesized using polyurethane polymerization from MDEA, HDI and PEG6000, followed by a ring-opening reaction with 1,3-PS. The structure and properties of zwitterionic PEG-ZSMPUs were systematically investigated. The results demonstrated that PEG-ZSMPUs formed phase separation structure that was composed of crystalline soft phase and amorphous hard phase. The zwitterionic hard segment greatly influenced their structures and properties. The MDEA-PS zwitterionic segments had a tendency to form ionic clusters in hard segments. Shape memory analysis showed that zwitterionic PEG-ZSMPUs had thermal-induced SMEs. 1.0PEG-ZSMPU had >78% and >94% of shape recovery and shape fixity, respectively. Finally, the cytotoxic assays demonstrated that MDEA-PS zwitterionic segment improved the biocompatibility of PEG-ZSMPUs. The zwitterionic PEG-ZSMPUs are thus expected to have promising application in smart biomedical fields. Supplementary Materials: The following are available online at www.mdpi.com/2073-4360/9/10/465/s1, Figure S1: The 1 HNMR spectra of 0PEG-ZSMPU and 0.8PEG-ZSMPU, Table S1: Elemental analysis results of PEG-ZSMPUs. Acknowledgments: The authors gratefully acknowledge the financial support from the Natural Science Foundation of China (Grant No. 51773120), the Natural Science Foundation of Guangdong (Grant Nos. 2014A030313559, 2016A030313050 and 2017A030310045), the National Natural Science Foundation of Guangdong Province for Vertical Coordination Project (No. 201642), the Nanshan District Key Lab for Biopolymers and Safety Evaluation (No. KC2014ZDZJ0001A), the Science and Technology Project of Shenzhen City (Grant Nos. CYZZ20150827160341635, ZDSYS201507141105130 and JCYJ20170412105034748), the Guangdong Graduate Education Innovation Program for Postgraduate Demonstration Base of Joint Training, the Research Project of Shenzhen University (No. 201518), and the Top Talent Launch Scientific Research Projects of Shenzhen (827-000133). Author Contributions: Haitao Zhuo conceived and designed the experiments; Shuqin Fu and Huanhuan Ren performed the experiments; Shaojun Chen analyzed the data; Zaochuan Ge and Haitao Zhuo contributed reagents/materials/analysis tools; Shaojun Chen and Shuqin Fu wrote the paper. Conflicts of Interest: The authors declare no conflict of interest.
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