新型骨修复材料可降解哌嗪基聚氨酯脲的研究
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摘要
修复骨缺损是这几个世纪以来人们一直深入探索研究的重点课题之一。骨是自然界中一种活的生物材料,当其受到损伤或者损坏时,仅依靠骨自身的修复能力是无法愈合的,需要通过骨移植,将合适的骨材料替代品填充于缺损部位,以便新骨生成。以生物材料为基础的人工骨替代材料成为研究开发热点,其具有广阔的发展潜力和应用前景,有望成功解决临床上骨缺损的难题。基于骨组织工程材料的要求,本文设计并制备了新型骨修复材料生物可降解哌嗪基聚氨酯脲(P-PUU),采用傅立叶变换红外光谱仪(FTIR)、凝胶色谱-多角激光光散射仪(GPC-MALLS)、核磁共振仪(NMR)、示差扫描量热仪(DSC)、高精度原子力显微镜(AFM)以及常规化学分析方法对所制备材料化学结构及化学物理性质进行系统表征;然后采用拉伸实验、动态力学分析以及弯曲试验对P-PUUs力学性能以及形状记忆行为性能测试进行考察;接着详细考察了P-PUUs材料的亲/疏水性、体外生物降解性以及热降解性能;最后对P-PUUs材料的细胞相容性进行了全面评价。主要研究内容和结论如下:
1.以辛酸亚锡(Sn(Oct)2)为引发剂,小分子二胺哌嗪(PP)为助引发剂构成共引发体系,引发D,L-丙交酯熔融开环聚合,制备作为P-PUU材料原料之一的羟基封端聚乳酸基大分子醇(PDLLA diol)。优化了胺类物质作为助引发剂D,L-丙交酯熔融开环聚合的反应条件;重点考察了助引发剂用量对PDLLA diol分子量的影响;并对PDLLA diol的结构及热性能进行表征。
①FTIR和1H NMR的结果表明,通过哌嗪作为引发剂成功制备了羟基封端聚乳酸;以端羟基聚乳酸的分子量和收率为目标,单因素优化胺类物质助引发PDLLA diol合成条件:最佳反应温度为150℃,最佳反应时间为24h。
②羟值分析、1H NMR及GPC-MALLS的检测结果表明,调节D,L-丙交酯单体和助引发剂PP的比例关系,可以获得不同分子量的羟基封端聚乳酸。③DSC分析表明,PDLLA diol材料的玻璃化转变温度(Tg)具有分子量依赖性,随分子量的增加,玻璃化温度可由15.95℃增至32.15℃。
2.以PDLLA diol为软段,1,6-六亚甲基二异氰酸酯(HDI)和PP为扩链剂,在无水甲苯溶剂体系下,以Sn(Oct)2为催化剂二步法扩链,制备了一系列嵌段P-PUUs材料。研究了软硬段比例、反应温度及扩链剂类型等因素对P-PUUs合成的影响。并对P-PUUs材料的结构与热性能进行了表征。
①FTIR、1HNMR及13C NMR的分析结果表明,羟基封端聚乳酸大分子醇与异氰酸酯发生反应,并经PP扩链,成功制备高分子量的P-PUUs材料。其中最佳的PP扩链温度为:30℃。
②调节软段分子量和软硬段比例可以获得一系列梯度哌嗪含量的P-PUUs材料,其理化性能也不同。
③检测交联度的重量分析法结果表明,与丁二胺作为扩链剂相对,哌嗪作为扩链剂能避免P-PUUs材料制备过程中的交联现象。
④DSC热分析结果表明,其Tg与软硬段组分关系密切,随着硬段含量升高,Tg呈上升趋势;同时在P-PUUs材料的DSC曲线上观察到两个温度转变区:一个为软段分子温度转变(20℃附近),另一个为材料的玻璃化温度,表明P-PUUs具有典型软硬段热不相容性现象。
⑤高精度AFM对P-PUUs单分子膜层进行扫描结果表明,观察到P-PUUs材料的分子结构,证实P-PUUs材料成功制备,同时也明显观察到聚氨酯脲类材料的典型软硬段结构分离现象。
3.采用拉伸以及动态力学分析(DMA)实验,考察了软段分子量和软硬段的比例对P-PUUs材料力学特质行为的影响,同时运用拉伸试验来考察P-PUUs材料形状记忆特性行为。
①机械拉伸试验试验结果表明,P-PUUs材料呈现良好的机械力学特性。随着硬段含量增加,弹性模量和弹性强度呈上升趋势,断裂伸长率呈相反趋势;随着软段分子量的增大,P-PUUs材料的弹性模量和弹性强度呈下降趋势,断裂伸长率则上升;扩链剂的选择对聚氨酯材料的影响也较大,PP具有刚性的六元环,既能增加材料的力学性能,同时通过较低交联度也能提高材料的力学特性。
②DMA结果表明,P-PUUs材料的硬段含量增加,DMA的存储模量随着上升,内摩擦(Tanδ)转变温度也随之上升,所得的Tg也上升。
③P-PUUs材料拥有良好的形状记忆性能,形状固定率均大于95%,形状回复率(Rr)可以达到93%以上;形状固定率随着硬段含量的增加而上升,而固定率则相反。
4.考察了P-PUUs材料的亲/疏水性及降解行为。亲/疏水性的评价指标为静态水接触角和24h材料的整体吸水率;降解行为包括生物降解行为和热降解行为,前者的评价指标为失重率、吸水率、pH值变化以及样品表面形貌的变化,后者考察其热稳定性及降解活化能;另外本研究重点研究了扩链剂的选择对聚氨酯脲材料降解性能的影响。
①亲疏水性研究表明,P-PUUs的静态水接触角小于对照组PDLLA,吸水率大于PDLLA组,硬段的引入能改善材料的亲疏水性质,同时P-PUUs的亲水性随着硬段含量的增加,呈上升趋势;但亲水性随着软段分子量的增加呈下降趋势。
②体外降解实验表明,P-PUUs材料与PDLLA对照组相比,在降解前期,失重率和介质pH值下降较大,但是随后降解减缓,失重率和介质的pH值下降缓慢,没有加速阶段出现,表明材料降解过程受其亲疏水性和降解产物两方面的影响,P-PUUs降解过程中释放的碱性物质能够中和PDLLA片段降解产物中的酸性物质,避免酸致自催化现象。
③扩链剂的选择和聚氨酯材料降解行为密切相关,考察的降解行为包括生物降解和热降解,在生物降解方面,胺类扩链剂能提高聚氨酯材料的稳定性,能起到控制生物降解的速率作用;而在热降解方面,醇类扩链剂获得的氨基甲酸酯键比胺类扩链剂获得的脲基稳定;运用Ozawa-Flynn-Wall法计算出三种不同扩链剂制备的三种不同聚氨酯脲材料的热降解活化能,也进一步证明上述结论。
5.基于大鼠成骨细胞与PDLLA及P-PUUs膜材的相互作用的评价模型,从细胞前期形态、细胞黏附、铺展和增殖及后期的分化、矿化等几个方面入手,对PDLLA及P-PUUs材料的细胞相容性进行了系统地分析比较。
①与PDLLA对照组相比,P-PUUs不利于早期黏附与铺展,成骨细胞对P-PUU表面的适应期较长;但P-PUUs材料随着硬段含量的增加,细胞在其上的粘附与铺展能力呈增强趋势。表明材料和细胞之间的相互作用是一个复杂的过程,并不完全依赖于材料的亲疏水性。
②从细胞在P-PUUs上的增殖行为来看,相比于PDLLA组,P-PUUs材料更能促进成骨细胞增殖,同时随着硬段含量的增加,细胞在材料上的增殖行为也增强。采用波尔兹曼函数S模型对细胞增殖行为数据进行拟合比较,进一步证实上述结论。并提出采用生物群体生长的逻辑斯谛方程来对细胞在材料上生命行为进行评价。
③通过检测蛋白质含量、碱性磷酸酶含量、无机钙分泌量以及定量PCR检测目标基因等方法来考察成骨细胞在材料上的分化、矿化能力,结果表明,P-PUU材料具有促进成骨细胞分化及矿化能力,而且并不缩短细胞的生长分化周期;同时随着硬段含量的增加,促进作用更加明显。
Last centuries, bone repair engineering is one of the most important topics for us to explore. Bone, a live biomaterial in the nature, is a good example of a dynamic tissue, since it has a unique capability of self-regenerating or self-remodeling to a certain extent throughout the life. However, many circumstances call for bone grafting owing to bone defects either from traumatic or from non-traumatic destruction. In the case of severe defects and loss of volume, bone cannot be healed by itself and grafting is required to restore function without damaging living tissues. So far, the grafting based biomaterial was attracted more and more attention and had potentiality to solve this clinical puzzle. In the repair, the suitable biomaterial scaffold is need with many excellent properties, such as biodegradablity, appropriate mechanical properties and biocompatibility and so on. In my present, a novel biodegradable piperazine-based poly (urethane urea) (P-PUU) is synthesized to meet the requirement of scaffold material in bone repair. Some methods of fourier transform infrared spectrometry (FTIR), Gel permeation chromatography with multi angle laser light scattering (GPC-MALLS), differential scanning calorimeter (DSC), nuclear magnetic resonance spectrometer (NMR), high resolving capability atomic force microscope(AFM) and classical chemical analysis were used to characterize its structures. Then mechanical tensile testing and dynamic mechanical analysis (DMA) were used to explore mechanical and shape memory properties of P-PUUs. Thirdly, the hydrophilicity/hydrophobicity, biodegradation and thermal degradation of the P-PUUs were investigated. Thereafter, the cell biocompatibility of P-PUUs was systemically evaluated. The main works and conclusions are included as follows:
1. Hydroxy group ended poly (D, L-lactide) (PDLLA diol) was synthesized by melt ring-opening polymerization of D, L-lactide using Sn (Oct) 2 as initiator and piperazine as coinitiator. Then, the conditions of ring-opening polymerization of D, L-lactide with piperazine as coinitiator were optimized. An extensive investigation effort was expended in understanding the effects of dosage of coinitiator on the molecular weight and the structure and thermal properties were characterized.
①FTIR, 1HNMR revealed that PDLLA diol was successfully obtained by using above-mentioned system. The optimization conditions of ring-opening polymerization of D, L-lactide with piperazine as coinitiator were as follows: reaction time, 24h; reaction temperature, 150℃.
②Hydroxyl value, 1H NMR and GPC-MALLS analysis indicated that PDLLA diol with different molecular could synthesized by varying the ratio of D, L-lactide/PP.
③The results of DSC indicated that the glass transition temperature (Tg) depended on its molecular weight and the Tg increased from 15.95 to 32.15℃with the increasing of molecular weight.
2. A series of P-PUUs materials were prepared based on PDLLA diol as the soft segment, hexamethylene diisocyanate (HDI) and piperazine (PP) as the chain extender. The effects of the reactive temperature and ratio of hard segment/soft segment were discussed, and the structure and thermal properties of P-PUUs were characterized.
①FTIR, 1H NMR and 13C NMR exhibited that, PDLLA diol have successfully reacted with HDI, and then P-PUUs with high molecular weight could obtained by chain extending reaction with PP as the chain extender. The optimization extending reaction was 30℃, nearby the room temperature.
②By varying the molecular weight of soft segment and the ratio of soft segment/hard segment, the P-PUUs with gradient contents of piperazine could be synthesized. Therefor, those materials would have different physicochemical properties for application in bone repair.
③The weight analysis for the degree of cross-linking showed that comparing with BDA as the chain extender, PP as the chain extender can make the synthesis process of polyurethanes easier to control and lead the polyurethanes with low or no degree of crosslinking, which lays a solid foundation for physical properties of the P-PUUs.
④The results of DSC showed that Tg could be regulated by the ratio of hard segment/soft segment and with the content of hard segment raising, Tg of P-PUUs rose. In addition, two temperature transitions in DSC curves of P-PUUs were obviouly observed: the slight transition was cosed to the Tg of PDLLA diol, could be attributed to the internal loosening of soft segments, the other one represented the Tg of P-PUUs. This implied that typical phase separation of P-PUUs due to the thermodynamic incompatibility of the two segments might occur.
⑤The results of high resolving capability AFM for scanning the monomolecular layer of P-PUUs indicated that the P-PUUs were successfully obtained with typical phase separation.
3. The mechanical properties of P-PUUs were characterized by mechanical tensile testing and DMA, and the influences of molecular weight of soft segment, the ratio of soft segment/hard segment were investigated. The shape memory behaviors were also studied by the tensile testing.
①The results indicated that P-PUUs have nice mechanical properties. The tensile modulus and tensile strength increased with the increasing of the hard segment content, while the elongation at break had the opposite trend. With the raising of the molecular weight of soft segment, the tensile modulus and tensile strength decressed, but the elongation at break increased. PP as chain extender could improve the mechanical properties with two methods: one is that PP has a six-atom rigid ring, which was introduced into the backbone of the P-PUUs to improve tensile modulus and tensile strength, the other one is that PP as chain extender can reduce the dregree of crosslinking.
②The results of DMA showed that the storage modulus and the transitions of Tanδincreased with the hard segment content rising.
③P-PUUs had good shape memory properties with large shape fixation ratio (Rf, all above 95%) and shape recovery ratio (Rr, all above 93%). Meanwhile, the shape memory properties were affected by the components and the hard segment content. Rr decreased with the increasing of the hard segment content, however, Rf had the opposite trend.
4. The hydrophilicity/hydrophobicity, biodegradation and themal degradation of P-PUUs were investigated. The evaluation indicators of hydrophilicity/hydrophobicity were static water contact angle and water absorption ratio, while the evaluation indicators of degradation behavior were the weight loss ratio and pH value changes, surface topography, moreover, the themal degradation were studied by thermogravimetric analysis and activation energy. In addition, the effect of different chain extenders on degradation properties of segmented polyurethanes was investigated.
①The static water contact angle of P-PUUs was smaller than PDLLA controls and the water absorption ratio was more than PDLLA controls. This is mainly due to the fact that the hydrophilic PP segment could form more hydrogen bond with water molecules and improved the hydrophilicity of P-PUUs. Meanwhile, the hydrophilicity had an uptrend with the increasing of hard segment content.
②Data of hydrolytic degradation of the polymers during 12 weeks indicated that the in vitro degradation stability of P-PUUs was more than PDLLA control, because the alkaline substance during the degradation of P-PUUs could eliminate or weaken the acid induced auto-catalysis.
③The results revealed that chain extender played an important role in biodegradation and thermal degradation of polyurethanes. During the biodegradation, polyurethane with amine style chain extender had more stability than those with hydroxyl chain extender, however, during thermal degradation the carbamate revealed more stability than urea bond. The results of the thermal degradation of polyurethanes were confirmed by the activation energy, which was calculated from the TGA data according to Ozawa-Flynn-Wall method.
5. The cytocompatibility of P-PUUs was evaluated by employing primary SD rat osteoblasts as the model cells and poly (DL-lactic acid) (PDLLA) as the control. The osteoblasts morphology, cell attachment and spreading, cell proliferation, cell differentiation and mineralization ability were systemically detected to indicate the cytocompatibility of P-PUUs.
①Initial morphology, adhesion, spreading of osteoblasts on all P-PUU films is no better than those on PDLLA film. Furthermore, with the increased amount of hard segments in P-PUUs, both cell doubling rate and migration rate correspondingly increased. Those results revealed that the interaction between cell and material was a complicated process, not only completely depended on the hydrophilicity of matetials.
②The results of cell proliferated behaviors on different films showed that P-PUUs could promoted the proliferation of osteoblast, and with the the increasing of the hard segment content, the positive regulation was more and more obvious. These results were confirmed by Boltzmann function sigmoidal fit. Based on it, we hypothesized that the interaction between cell and material could be ascribed to biocenose growth Logistic model.
③Osteoblast on different P-PUUs films all exhibited lower physiological functions compared to those on PDLLA films within the first 10 days after seeding. Thereafter, however, the osteoblasts on P-PUUs demonstrated better differentiation and mineralization than those on PDLLA films, and P-PUU-3 > P-PUU-2 > P-PUU-1.
1.以辛酸亚锡(Sn(Oct)2)为引发剂,小分子二胺哌嗪(PP)为助引发剂构成共引发体系,引发D,L-丙交酯熔融开环聚合,制备作为P-PUU材料原料之一的羟基封端聚乳酸基大分子醇(PDLLA diol)。优化了胺类物质作为助引发剂D,L-丙交酯熔融开环聚合的反应条件;重点考察了助引发剂用量对PDLLA diol分子量的影响;并对PDLLA diol的结构及热性能进行表征。
①FTIR和1H NMR的结果表明,通过哌嗪作为引发剂成功制备了羟基封端聚乳酸;以端羟基聚乳酸的分子量和收率为目标,单因素优化胺类物质助引发PDLLA diol合成条件:最佳反应温度为150℃,最佳反应时间为24h。
②羟值分析、1H NMR及GPC-MALLS的检测结果表明,调节D,L-丙交酯单体和助引发剂PP的比例关系,可以获得不同分子量的羟基封端聚乳酸。③DSC分析表明,PDLLA diol材料的玻璃化转变温度(Tg)具有分子量依赖性,随分子量的增加,玻璃化温度可由15.95℃增至32.15℃。
2.以PDLLA diol为软段,1,6-六亚甲基二异氰酸酯(HDI)和PP为扩链剂,在无水甲苯溶剂体系下,以Sn(Oct)2为催化剂二步法扩链,制备了一系列嵌段P-PUUs材料。研究了软硬段比例、反应温度及扩链剂类型等因素对P-PUUs合成的影响。并对P-PUUs材料的结构与热性能进行了表征。
①FTIR、1HNMR及13C NMR的分析结果表明,羟基封端聚乳酸大分子醇与异氰酸酯发生反应,并经PP扩链,成功制备高分子量的P-PUUs材料。其中最佳的PP扩链温度为:30℃。
②调节软段分子量和软硬段比例可以获得一系列梯度哌嗪含量的P-PUUs材料,其理化性能也不同。
③检测交联度的重量分析法结果表明,与丁二胺作为扩链剂相对,哌嗪作为扩链剂能避免P-PUUs材料制备过程中的交联现象。
④DSC热分析结果表明,其Tg与软硬段组分关系密切,随着硬段含量升高,Tg呈上升趋势;同时在P-PUUs材料的DSC曲线上观察到两个温度转变区:一个为软段分子温度转变(20℃附近),另一个为材料的玻璃化温度,表明P-PUUs具有典型软硬段热不相容性现象。
⑤高精度AFM对P-PUUs单分子膜层进行扫描结果表明,观察到P-PUUs材料的分子结构,证实P-PUUs材料成功制备,同时也明显观察到聚氨酯脲类材料的典型软硬段结构分离现象。
3.采用拉伸以及动态力学分析(DMA)实验,考察了软段分子量和软硬段的比例对P-PUUs材料力学特质行为的影响,同时运用拉伸试验来考察P-PUUs材料形状记忆特性行为。
①机械拉伸试验试验结果表明,P-PUUs材料呈现良好的机械力学特性。随着硬段含量增加,弹性模量和弹性强度呈上升趋势,断裂伸长率呈相反趋势;随着软段分子量的增大,P-PUUs材料的弹性模量和弹性强度呈下降趋势,断裂伸长率则上升;扩链剂的选择对聚氨酯材料的影响也较大,PP具有刚性的六元环,既能增加材料的力学性能,同时通过较低交联度也能提高材料的力学特性。
②DMA结果表明,P-PUUs材料的硬段含量增加,DMA的存储模量随着上升,内摩擦(Tanδ)转变温度也随之上升,所得的Tg也上升。
③P-PUUs材料拥有良好的形状记忆性能,形状固定率均大于95%,形状回复率(Rr)可以达到93%以上;形状固定率随着硬段含量的增加而上升,而固定率则相反。
4.考察了P-PUUs材料的亲/疏水性及降解行为。亲/疏水性的评价指标为静态水接触角和24h材料的整体吸水率;降解行为包括生物降解行为和热降解行为,前者的评价指标为失重率、吸水率、pH值变化以及样品表面形貌的变化,后者考察其热稳定性及降解活化能;另外本研究重点研究了扩链剂的选择对聚氨酯脲材料降解性能的影响。
①亲疏水性研究表明,P-PUUs的静态水接触角小于对照组PDLLA,吸水率大于PDLLA组,硬段的引入能改善材料的亲疏水性质,同时P-PUUs的亲水性随着硬段含量的增加,呈上升趋势;但亲水性随着软段分子量的增加呈下降趋势。
②体外降解实验表明,P-PUUs材料与PDLLA对照组相比,在降解前期,失重率和介质pH值下降较大,但是随后降解减缓,失重率和介质的pH值下降缓慢,没有加速阶段出现,表明材料降解过程受其亲疏水性和降解产物两方面的影响,P-PUUs降解过程中释放的碱性物质能够中和PDLLA片段降解产物中的酸性物质,避免酸致自催化现象。
③扩链剂的选择和聚氨酯材料降解行为密切相关,考察的降解行为包括生物降解和热降解,在生物降解方面,胺类扩链剂能提高聚氨酯材料的稳定性,能起到控制生物降解的速率作用;而在热降解方面,醇类扩链剂获得的氨基甲酸酯键比胺类扩链剂获得的脲基稳定;运用Ozawa-Flynn-Wall法计算出三种不同扩链剂制备的三种不同聚氨酯脲材料的热降解活化能,也进一步证明上述结论。
5.基于大鼠成骨细胞与PDLLA及P-PUUs膜材的相互作用的评价模型,从细胞前期形态、细胞黏附、铺展和增殖及后期的分化、矿化等几个方面入手,对PDLLA及P-PUUs材料的细胞相容性进行了系统地分析比较。
①与PDLLA对照组相比,P-PUUs不利于早期黏附与铺展,成骨细胞对P-PUU表面的适应期较长;但P-PUUs材料随着硬段含量的增加,细胞在其上的粘附与铺展能力呈增强趋势。表明材料和细胞之间的相互作用是一个复杂的过程,并不完全依赖于材料的亲疏水性。
②从细胞在P-PUUs上的增殖行为来看,相比于PDLLA组,P-PUUs材料更能促进成骨细胞增殖,同时随着硬段含量的增加,细胞在材料上的增殖行为也增强。采用波尔兹曼函数S模型对细胞增殖行为数据进行拟合比较,进一步证实上述结论。并提出采用生物群体生长的逻辑斯谛方程来对细胞在材料上生命行为进行评价。
③通过检测蛋白质含量、碱性磷酸酶含量、无机钙分泌量以及定量PCR检测目标基因等方法来考察成骨细胞在材料上的分化、矿化能力,结果表明,P-PUU材料具有促进成骨细胞分化及矿化能力,而且并不缩短细胞的生长分化周期;同时随着硬段含量的增加,促进作用更加明显。
Last centuries, bone repair engineering is one of the most important topics for us to explore. Bone, a live biomaterial in the nature, is a good example of a dynamic tissue, since it has a unique capability of self-regenerating or self-remodeling to a certain extent throughout the life. However, many circumstances call for bone grafting owing to bone defects either from traumatic or from non-traumatic destruction. In the case of severe defects and loss of volume, bone cannot be healed by itself and grafting is required to restore function without damaging living tissues. So far, the grafting based biomaterial was attracted more and more attention and had potentiality to solve this clinical puzzle. In the repair, the suitable biomaterial scaffold is need with many excellent properties, such as biodegradablity, appropriate mechanical properties and biocompatibility and so on. In my present, a novel biodegradable piperazine-based poly (urethane urea) (P-PUU) is synthesized to meet the requirement of scaffold material in bone repair. Some methods of fourier transform infrared spectrometry (FTIR), Gel permeation chromatography with multi angle laser light scattering (GPC-MALLS), differential scanning calorimeter (DSC), nuclear magnetic resonance spectrometer (NMR), high resolving capability atomic force microscope(AFM) and classical chemical analysis were used to characterize its structures. Then mechanical tensile testing and dynamic mechanical analysis (DMA) were used to explore mechanical and shape memory properties of P-PUUs. Thirdly, the hydrophilicity/hydrophobicity, biodegradation and thermal degradation of the P-PUUs were investigated. Thereafter, the cell biocompatibility of P-PUUs was systemically evaluated. The main works and conclusions are included as follows:
1. Hydroxy group ended poly (D, L-lactide) (PDLLA diol) was synthesized by melt ring-opening polymerization of D, L-lactide using Sn (Oct) 2 as initiator and piperazine as coinitiator. Then, the conditions of ring-opening polymerization of D, L-lactide with piperazine as coinitiator were optimized. An extensive investigation effort was expended in understanding the effects of dosage of coinitiator on the molecular weight and the structure and thermal properties were characterized.
①FTIR, 1HNMR revealed that PDLLA diol was successfully obtained by using above-mentioned system. The optimization conditions of ring-opening polymerization of D, L-lactide with piperazine as coinitiator were as follows: reaction time, 24h; reaction temperature, 150℃.
②Hydroxyl value, 1H NMR and GPC-MALLS analysis indicated that PDLLA diol with different molecular could synthesized by varying the ratio of D, L-lactide/PP.
③The results of DSC indicated that the glass transition temperature (Tg) depended on its molecular weight and the Tg increased from 15.95 to 32.15℃with the increasing of molecular weight.
2. A series of P-PUUs materials were prepared based on PDLLA diol as the soft segment, hexamethylene diisocyanate (HDI) and piperazine (PP) as the chain extender. The effects of the reactive temperature and ratio of hard segment/soft segment were discussed, and the structure and thermal properties of P-PUUs were characterized.
①FTIR, 1H NMR and 13C NMR exhibited that, PDLLA diol have successfully reacted with HDI, and then P-PUUs with high molecular weight could obtained by chain extending reaction with PP as the chain extender. The optimization extending reaction was 30℃, nearby the room temperature.
②By varying the molecular weight of soft segment and the ratio of soft segment/hard segment, the P-PUUs with gradient contents of piperazine could be synthesized. Therefor, those materials would have different physicochemical properties for application in bone repair.
③The weight analysis for the degree of cross-linking showed that comparing with BDA as the chain extender, PP as the chain extender can make the synthesis process of polyurethanes easier to control and lead the polyurethanes with low or no degree of crosslinking, which lays a solid foundation for physical properties of the P-PUUs.
④The results of DSC showed that Tg could be regulated by the ratio of hard segment/soft segment and with the content of hard segment raising, Tg of P-PUUs rose. In addition, two temperature transitions in DSC curves of P-PUUs were obviouly observed: the slight transition was cosed to the Tg of PDLLA diol, could be attributed to the internal loosening of soft segments, the other one represented the Tg of P-PUUs. This implied that typical phase separation of P-PUUs due to the thermodynamic incompatibility of the two segments might occur.
⑤The results of high resolving capability AFM for scanning the monomolecular layer of P-PUUs indicated that the P-PUUs were successfully obtained with typical phase separation.
3. The mechanical properties of P-PUUs were characterized by mechanical tensile testing and DMA, and the influences of molecular weight of soft segment, the ratio of soft segment/hard segment were investigated. The shape memory behaviors were also studied by the tensile testing.
①The results indicated that P-PUUs have nice mechanical properties. The tensile modulus and tensile strength increased with the increasing of the hard segment content, while the elongation at break had the opposite trend. With the raising of the molecular weight of soft segment, the tensile modulus and tensile strength decressed, but the elongation at break increased. PP as chain extender could improve the mechanical properties with two methods: one is that PP has a six-atom rigid ring, which was introduced into the backbone of the P-PUUs to improve tensile modulus and tensile strength, the other one is that PP as chain extender can reduce the dregree of crosslinking.
②The results of DMA showed that the storage modulus and the transitions of Tanδincreased with the hard segment content rising.
③P-PUUs had good shape memory properties with large shape fixation ratio (Rf, all above 95%) and shape recovery ratio (Rr, all above 93%). Meanwhile, the shape memory properties were affected by the components and the hard segment content. Rr decreased with the increasing of the hard segment content, however, Rf had the opposite trend.
4. The hydrophilicity/hydrophobicity, biodegradation and themal degradation of P-PUUs were investigated. The evaluation indicators of hydrophilicity/hydrophobicity were static water contact angle and water absorption ratio, while the evaluation indicators of degradation behavior were the weight loss ratio and pH value changes, surface topography, moreover, the themal degradation were studied by thermogravimetric analysis and activation energy. In addition, the effect of different chain extenders on degradation properties of segmented polyurethanes was investigated.
①The static water contact angle of P-PUUs was smaller than PDLLA controls and the water absorption ratio was more than PDLLA controls. This is mainly due to the fact that the hydrophilic PP segment could form more hydrogen bond with water molecules and improved the hydrophilicity of P-PUUs. Meanwhile, the hydrophilicity had an uptrend with the increasing of hard segment content.
②Data of hydrolytic degradation of the polymers during 12 weeks indicated that the in vitro degradation stability of P-PUUs was more than PDLLA control, because the alkaline substance during the degradation of P-PUUs could eliminate or weaken the acid induced auto-catalysis.
③The results revealed that chain extender played an important role in biodegradation and thermal degradation of polyurethanes. During the biodegradation, polyurethane with amine style chain extender had more stability than those with hydroxyl chain extender, however, during thermal degradation the carbamate revealed more stability than urea bond. The results of the thermal degradation of polyurethanes were confirmed by the activation energy, which was calculated from the TGA data according to Ozawa-Flynn-Wall method.
5. The cytocompatibility of P-PUUs was evaluated by employing primary SD rat osteoblasts as the model cells and poly (DL-lactic acid) (PDLLA) as the control. The osteoblasts morphology, cell attachment and spreading, cell proliferation, cell differentiation and mineralization ability were systemically detected to indicate the cytocompatibility of P-PUUs.
①Initial morphology, adhesion, spreading of osteoblasts on all P-PUU films is no better than those on PDLLA film. Furthermore, with the increased amount of hard segments in P-PUUs, both cell doubling rate and migration rate correspondingly increased. Those results revealed that the interaction between cell and material was a complicated process, not only completely depended on the hydrophilicity of matetials.
②The results of cell proliferated behaviors on different films showed that P-PUUs could promoted the proliferation of osteoblast, and with the the increasing of the hard segment content, the positive regulation was more and more obvious. These results were confirmed by Boltzmann function sigmoidal fit. Based on it, we hypothesized that the interaction between cell and material could be ascribed to biocenose growth Logistic model.
③Osteoblast on different P-PUUs films all exhibited lower physiological functions compared to those on PDLLA films within the first 10 days after seeding. Thereafter, however, the osteoblasts on P-PUUs demonstrated better differentiation and mineralization than those on PDLLA films, and P-PUU-3 > P-PUU-2 > P-PUU-1.
引文
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