Dynamic Creep and Fatigue Properties of Novel Elastomeric Biomaterials

• Applicant: Professor Dr.-Ing. Volker Altstädt
• Subject Area: Polymer Materials
• Term: from 2007 to 2009
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 30492292

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.

• DFG Programme: Research Grants