Biodegradation mechanisms of polyurethane elastomers

Abstract

After over 40 years of use in biomedical applications, polyurethanes remain one of the most popular biomaterials due to their exceptional biocompatibility, mechanical properties and versatility. However, failure of polyurethane based pacemaker leads and breast implant coatings in the late 1980s brought the long term stability of these implants under scrutiny. The biomedical device industry was faced with the need to find replacement polyurethane compositions that were biostable and maintained excellent biocompatibility and mechanical properties. The design of replacement biomedical polyurethanes is dependent on the mechanistic understanding of polyurethane biodegradation and the biological processes that govern these mechanisms. This review summarises the efforts of the authors' lab and others to elucidate the biological mechanisms of polyurethane biodegradation and evaluate promising new elastomers based on poly(carbonate urethane) and silicone copolymer chemistries. Several of the new classes of polyurethanes reviewed here show great promise; however, attenuated total reflectance Fourier transform infrared spectroscopy analysis of explanted samples provided evidence of chain scission and cross-linking in all of the polyurethane specimens. Therefore, it was concluded that the chosen soft segment modifications were insufficient to fully inhibit biodegradation. Potential biodegradation mechanisms were explored using oxidative and hydrolytic enzyme systems. Although cholesterol esterase initiated polyurethane degradation, the effect was minimal compared to the oxidation of these polyurethane elastomers. The in vivo and accelerated degradation studies supported oxidation as the dominant mechanism of biodegradation of PEU and PCU. The H 2 O 2 /CoCl 2 system remains an excellent choice to accelerate oxidative biodegradation for the prediction of long term biostability in quantitative comparison with current clinical poly(ether urethanes). The biostability ranking of these four materials based on statistical comparisons of chain scission and surface pitting is as follows: PEU,PEU-S(PCU,PCU-S. The more biostable PCU elastomer was concluded to be a suitable choice to replace PEU in medical applications. Furthermore, the silicone modification was shown to increase the biostability of the PEU and PCU elastomers while maintaining the thermoplastic elastomeric properties.

In vivo biostability of polymeric spine implants: retrieval analyses from a United States investigational device exemption study

“…Polyurethanes have been used in medical devices since the 1970s and the literature has reported on the biostability of polyurethanes [20][21][22][23][24][25]. Generally, the biostability of polyurethanes is strongly affected by multiple factors.…”

“…Generally, the biostability of polyurethanes is strongly affected by multiple factors. For example, polycarbonate soft segments are chemically more stable than either polyether or polyester counterparts and the biostability of a Shore 55D polyurethane is quite different from that of Shore 80A one [25]. The annealing process reduces environmental stress cracking (ESC) [20][21][22][23] while appropriate sterilization methods maintain the biostability of polyurethanes [20].…”

“…(3) The study of Ianuzzi assumes certain bands are related to degradation of PCU. This band assignment was originally proposed by Christensen [8,25] based on in vitro and in vivo rat studies. The present study did not reveal the appearance of any such bands and a previous study [32] suggested that these bands may overlap with the bands from tissue and body fluid residues (mainly for protein content).…”

Silk‐inspired polyurethane containing GlyAlaGlyAla tetrapeptide. II. physical properties and structure

“…As one subclass of the polyurethane family, segmented polyurethanes have found a number of biomedical applications due to the unique combination of excellent physical, mechanical and biological properties, besides the wide ranging applications in furnishings, textiles, paper making, packaging, adhesives, and sealants. 1 On the other hand, mankind has farmed Bombyx mori silkworms for thousands of years. The natural production of silk fiber looks easy for silkworms in contrast to the man-made spinning of chemical fiber commonly demanding high temperature and pressure.…”

“…In our previous work, we presented silk-inspired polyurethane biofiber by wet-spinning of biomedical PU/silk proteins blend solution. 31 Then the silkinspired PU containing GlyAlaGlyAla tetrapeptide was synthesized and its primary structure was qualitatively identified by means of elemental analysis (EA), 1 H nuclear magnetic resonance ( 1 H-NMR) spectroscopy and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). 32 Currently, we describe herein our efforts in investigating its physical properties and hierarchy structure of more importance.…”