Lipid-induced degradation in biocompatible poly(Styrene-Isobutylene-Styrene) (SIBS) thermoplastic elastomer

• Published in: Journal of the mechanical behavior of biomedical materials Vol. 68; pp. 80 - 87
• Main Authors: Fittipaldi, Mauro, Grace, Landon R.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier Ltd 01.04.2017
• Subjects: Biocompatible; Biocompatible Materials - chemistry; Degradation; Diffusion; Elastomers - chemistry; Lipids; Lipids - chemistry; Materials Testing; Polymer; Relaxation; Styrenes - chemistry; Degradation; Biocompatible; Relaxation; Lipids; Polymer; Diffusion
• ISSN: 1751-6161; 1878-0180; 1878-0180
• DOI: 10.1016/j.jmbbm.2017.01.031

The thermoplastic elastomer Poly(Styrene-block-Isobutylene-block-Styrene) (SIBS) is highly biocompatible, which has led to its use in several commercially-available implants. However, lipid-induced degradation has been previously identified as a primary cause of failure in long-term SIBS implants subject to mechanical loading. Thus, understanding the mechanisms and extent of lipid-induced damage and the role of styrene-isobutylene ratio and molecular weight is critical to improving longevity of SIBS-based implants in order to fully exploit the biocompatibility advantages. Samples of four different SIBS formulations were fabricated via compression molding, immersed to lipid saturation contents from 5 to 80% by weight, and tested in uniaxial tension, stress relaxation, and dynamic creep modes. Degradation mechanisms were investigated via infrared spectroscopy, chromatography, and microscopy. No evidence of lipid-induced chemical interactions or chain scissoring was observed. However, a decrease in tensile strength, loss of dynamic creep performance and faster relaxation with increasing lipid content is attributed to strong internal straining. The magnitude of these losses is inversely proportional to both molecular weight and styrene content, suggesting that selection of these variables during the design phase should be based not only on the mechanical requirements of the application, but the expected degree of lipid exposure.