In vitro oxidation of high polydimethylsiloxane content biomedical polyurethanes: Correlation with the microstructure

Abstract

The resistance to in vitro metal ion oxidation of a polydimethylsiloxane (PDMS)-containing thermoplastic polyurethane elastomer (Elast-Eon) is compared with that of a polyurethane consisting of the same hard segment chemistry and content, but with aliphatic polycarbonate soft segments (PCU). Scanning electron microscopy and attenuated total reflectance Fourier transform infrared spectroscopy were used to assess changes in surface morphology and chemistry. The extent of bulk degradation was assessed indirectly by dynamic mechanical analysis and small-angle X-ray scattering experiments. The findings indicate that Elast-Eon is more resistant to oxidation than the PCU, because of the presence of the PDMS soft segments as well as its phase separated microstructure. The PCU exhibits a rather high degree of intermixing between hard and soft segments, rendering the hard segments dissolved or trapped in the soft phase more susceptible to oxidative conditions. By contrast, we propose that the existence of a completely phase separated PDMS soft phase in Elast-Eon protects the remainder of the segments from oxidation.

Aliphatic polycarbonate-based thermoplastic polyurethane elastomers containing diphenyl sulfide units

“…were visible, corresponding to the nonbonded carbonate carbonyl groups and H-bonded urethane carbonyl groups in ordered hard-segment domains, respectively [24]. With the growth of the soft segment content, a progressive increase in the intensity of the peak at the higher wavenumber, with a simultaneous decrease in the intensity of the peak at the lower wavenumber, was observed.…”

Limitations of predictingin vivobiostability of multiphase polyurethane elastomers using temperature-accelerated degradation testing

“…11 Several in vitro and in vivo studies have shown that PDMS-based polyurethanes (E2A and PurSilV R 35, the latter containing both polyether and a smaller fraction of PDMS soft segments) have improved biostability compared to 80A durometer PEUs and either equivalent or improved biostability compared to 55D durometer PEUs. [13][14][15][16][17] In a 2-year sheep study, strained E2A demonstrated biostability equal to that of 55D durometer PEU. 13 Ward et al reported that strained PurSilV R 35 tubing specimens were significantly more biostable than 80A durometer PEUs in a 2-year rabbit study.…”

“…11 This in turn leads to a high degree of biostability as both PDMS and well-formed hard blocks are resistant to biological degradation mechanisms. [12][13][14] The third phase forms a "shell" around the hard domain "core" and consists of a mixed phase of polyhexamethylene oxide (PHMO), PDMS end-groups, and some short hard segments. 11 Several in vitro and in vivo studies have shown that PDMS-based polyurethanes (E2A and PurSilV R 35, the latter containing both polyether and a smaller fraction of PDMS soft segments) have improved biostability compared to 80A durometer PEUs and either equivalent or improved biostability compared to 55D durometer PEUs.…”

Cure kinetics and modeling the reaction of silicone rubber

“…Silicone rubbers generally, based on polydimethylsiloxane (PDMS), have special properties such as low toxicity, physiological inertness, good blood compatibility, and good thermal, oxidative, and mechanical stabilities, as well as flexibility and reliability over a wide range of temperatures and humidity [1][2][3][4]. These unique properties have allowed silicones to be used in various applications, from aerospace applications to medical devices, such as seals for the automotive industry; artificial skin, blood pumps, drug delivery systems, and implants for medical purposes; packaging and baking pans for the food industry; and connectors and cables for appliances and telecommunications [4][5][6][7][8][9][10].…”