Dynamic Creep and Fatigue Properties of Novel Elastomeric Biomaterials

对于生物医学应用，使用中的材料，如硅橡胶和聚氨酯橡胶，需要具有生物相容性，并在严格的生理应力条件下保持良好的机械和动态性能。本研究项目旨在研究各种新型纳米结构热塑性弹性体(TPE)，它们有可能在合适的生物医学应用中取代硅橡胶和聚氨酯橡胶，并研究网络结构对其动态蠕变和疲劳性能的影响。这些生物相容的TPE在室温下的行为类似于交联橡胶，但可以在高温下加工成塑料，这是医疗设备制造中的一个重要优势。然而，非晶态嵌段型热塑性弹性体的蠕变性能不如交联型橡胶。为加强热塑性弹性体的蠕变性能，将引入不同的网络结构，并评估其改进效果。七种具有不同网络结构的橡胶将被研究：硅橡胶(具有共价键的网络结构)；聚氨酯，一种多嵌段半结晶共聚物(PU，氢键增强的物理网络结构)；线型聚苯乙烯-b-聚异丁烯-b-聚苯乙烯共聚物(PS-PIB-PS，无定形嵌段热塑性橡胶的物理网络结构特征)；树枝状或树状的聚异丁烯-聚苯乙烯共聚物(ARB-PIBPS，物理网络结构叠加在共价支化上)；新型ARB-PIB-PS-H(物理网络结构和共价支化氢键)；具有脂肪族二酸软段的嵌段多嵌段半结晶共聚酯(PED，半结晶多嵌段聚酯弹性体的物理网络结构特征)；以及最后，电子束交联的PED(PED-C，物理网络结构和共价键合)。硅橡胶(a，硅橡胶®)，PU(b，Pellethane®)和PS-PIB-PS(c，Translute用于药物冠状动脉支架，由合作者之一共同发明)是经FDA(美国食品和药物管理局)批准的生物材料，在本研究中用作参考材料。ARB-PIB-PS(D)和PED(F)是相对较新的材料，其生物相容性已得到证实。ARB-PIR-PS-H(E)和电子束交联型PED(G)是本研究中考虑的新型弹性体体系，将相应地进行合成和表征。ARB-PIB-PS-H合成方法的开发得到了普斯卡斯教授为期三年的补充NSF(美国国家科学基金会)项目的支持。目前正在寻求研究资金，以支持El Fray博士在FED交联剂方面的工作，以及教育和科学部对ARB-PIB-PS-H和PED-C的生物兼容性测试。在本项目中，将研究材料在空气和模拟生理条件下的动态蠕变和疲劳性能，并将数据与各种网络结构相关联。同时，研究了不同的网络结构对纳米结构材料的体相和表面相形态的影响。通过该项目，可以了解网络结构对软材料动态疲劳和蠕变性能的影响，为寻找性能优于医用级硅橡胶的新型生物材料提供基础知识。

For biomedical applications, materials in use, like silicone and polyurethane rubbers, need to be biocompatible and sustain good mechanical and dynamic performance under the rigor of physiological stress conditions. This research project intends to look at various novel nanostructured thermoplastic elastomers (TPEs), that have the potential to replace silicone and polyurethane rubbers in suitable biomedical applications, and study the effect of network structure on their dynamic creep and fatigue properties. These biocompatible TPEs behave similarly to crosslinked rubbers at room temperature but can be processed as plastics at elevated temperatures, an important advantage in medical device fabrication. However, the creep performance of amorphous block-type TPEs is known to be inferior to crosslinked rubbers. To enhance the creep behaviour of TPEs, various network structures will be introduced and assessed their effectiveness for improvement. Seven rubbers with different network structures, will be investigated: Silicone rubber (network with covalent bonds); Polyurethane which is a segmented multiblock semicrystalline copolymer (PU, physical network structure reinforced with hydrogen bonding) A linear polystyrene-b-polyisobutylene-b-polystyrene copolymer (PS-PIB-PS, physical network structure characteristic of amorphous block-type styrenic thermoplastic rubbers); An arborescent or tree-like polyisobutylene-polystyrene copolymer (arb-PIBPS, physical network structure superimposed on covalent branching); A novel arb-PIB-PS-H (physical network structure AND covalent branching AND hydrogen bonding); A segmented multiblock semicrystalline copolyester with aliphatic diacid soft segments (PED, physical network structure characteristic of semi-crystalline multiblock-type polyester elastomer); and, finally, An e-beam crosslinked PED (PED-C, physical network structure AND covalent bonding).Silicone rubber (a, Silastic®), PU (b, Pellethane®) and PS-PIB-PS (c, Translute¿ used on medicated coronary stents, co-invented by one of the collaborators) are biomaterials approved by the FDA (Food and Drug Administration in the US) and shall be used herein this study as reference materials. Arb-PIB-PS (d) and PED (f) are relatively new materials, whose biocompatibility has been confirmed. Arb-PIR-PS-H (e) and e-beam crosslinked PED (g) are novel elastomeric systems considered in this research and will be synthesized and characterized accordingly. The development of the synthetic procedure for arb-PIB-PS-H is supported by a complementary three-year NSF (National Science Foundation of the USA) project of Prof. Puskas. Research funding has currently been sought to support work on FED crosslinking and the biocompatibility testing of arb-PIB-PS-H and PED-C from the Ministry of Education and Science by Dr. El Fray. Herein this project, the dynamic creep and fatigue properties of the materials will be investigated in air and under simulated physiological conditions, and the data will be correlated with various network structures. Simultaneously, the effect of the various network structures on the bulk and surface phase morphology of the nanostructured materials will be investigated. From this project, good fundamental knowledge can be gained to understand the effect of network structure on dynamic fatigue and creep properties of soft materials in the pursuit of new biomaterials with properties superior to medical grade silicone rubber.