title: Comparison of clinical explants and accelerated hydrolytic aging to improve biostability assessment of silicone-based polyurethanes.
abstract: Although silicone-based polyurethanes have demonstrated increased oxidative stability, there have been conflicting reports of the long-term hydrolytic stability of Optim™ and PurSil(®) 35 based on recent temperature-accelerated hydrolysis studies. The goal of the current study was to identify in vitro-in vivo correlations to determine the relevance of this accelerated in vitro model for predicting clinical outcomes. Temperature-accelerated hydrolytic aging of three commonly used cardiac lead insulation materials, Optim™, Elasthane™ 55D, Elasthane™ 80A, and a related silicone-polyurethane, PurSil(®) 35, was performed. After 1 year at 85°C, similar losses in Mn and Mz were observed for the poly(ether urethanes), but an increase in Mz loss as compared to Mn loss was observed for the silicone-based polyurethanes. A similar trend of increased Mz loss as compared to Mn loss was observed in explanted Optim™ leads after 2-3 years; however, no statistically significant Mn loss was detected between 2-3 and 7-8 years of implantation. Given this preferential loss of high molecular weight chains, it was hypothesized that the observed differences between the polyurethanes were due to allophanate dissociation rather than backbone chain scission. Following full dissociation of the small percentage of allophanates in vivo, the observed molecular weight stability and proven clinical performance of Optim™ was attributed to the well-documented stability of the urethane bond under physiological conditions. This allophanate dissociation reaction is incompatible with the first order mechanism proposed in previous temperature-accelerated hydrolysis studies and may be the reason for the model's inaccurate prediction of significant and progressive molecular weight loss in vivo. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 1805-1816, 2016.
authors.affiliation: Department of Biomedical Engineering, Texas A&M University, College Station, Texas, 77843.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Cosgriff-Hernandez
authors.affiliation: St. Jude Medical, Sylmar, California, 91342.
authors.forename: Ekaterina
authors.initials: E
authors.lastname: Tkatchouk
authors.affiliation: Department of Biomedical Engineering, Texas A&M University, College Station, Texas, 77843.
authors.forename: Tyler
authors.initials: T
authors.lastname: Touchet
authors.affiliation: Department of Biomedical Engineering, Texas A&M University, College Station, Texas, 77843.
authors.forename: Nick
authors.initials: N
authors.lastname: Sears
authors.affiliation: Department of Biomedical Engineering, Texas A&M University, College Station, Texas, 77843.
authors.forename: Alysha
authors.initials: A
authors.lastname: Kishan
authors.affiliation: St. Jude Medical, Sylmar, California, 91342.
authors.forename: Christopher
authors.initials: C
authors.lastname: Jenney
authors.affiliation: St. Jude Medical, Sylmar, California, 91342.
authors.forename: Ajay D
authors.initials: AD
authors.lastname: Padsalgikar
authors.affiliation: St. Jude Medical, Sylmar, California, 91342.
authors.forename: Emily
authors.initials: E
authors.lastname: Chen
mesh_terms: D001672:Biocompatible Materials / Q000737:chemistry*; D006868:Hydrolysis; D008422:Materials Testing / Q000379:methods*; D008970:Molecular Weight; D011140:Polyurethanes / Q000737:chemistry*; D012212:Rheology; D012828:Silicones / Q000737:chemistry*; D013696:Temperature; D013718:Tensile Strength; D013997:Time Factors; D014783:Viscosity; D014867:Water / Q000737:chemistry
chemical_list: D001672:Biocompatible Materials; D011140:Polyurethanes; D012828:Silicones; D014867:Water
keywords: allophanate; biodegradation; hydrolysis; in vitro-in vivo correlations; polyurethane