High strength polyisobutylene based structures : synthesis, characterization and suitability for biomedical applications

Abstract

In this study, there are two main focuses: (i) increasing the strength of polyisobutylene structures via interpenetrating network and polyurethane (PU) formation. Specifically, the latter strategy involves strengthening polyurethanes with the additional hydrogen-bonding sites in PIB soft domain and nanolayers, (ii) investigating the suitability of these high strength PUs for biomedical applications by comparing them with the commercial one. In this context, PIB primary network was synthesized by using Thiol-ene (click) chemistry, in which HS- PIB-SH, prepared from HO-PIB-OH via esterification, reacted with a trifunctional allyl compound as a crosslinker. Sequential IPN method were preferred to be used for successful and controllable PIB/PS based IPN formation. The fundamental network characteristics, which are homogeneity of primary network, increased crosslink density and decreased mesh size, proved the successful IPN formation resulting in enhanced dimensional stability in solvents, tensile strength, thermal stability as well as creep resistance. Newly synthesized high strength PIB-based PUs all showed that inert PIB barriers enhanced the protection of hydrolytically and oxidatively vulnerable carbamate bonds. Among them, sulfur addition aiming extra H-bonding sites in PIB soft phase of PUs was not very affective on static mechanical properties but improved thermal stability and surprisingly increased creep resistance of sulfur-containing PIB based PU (PIBS-PU) via H-bonded S atoms (N-H…S) between hard and soft phases. Nanolayers addition to PIBS-PU, on the other hand, enhanced elongation, tensile strength, creep resistance and hydrolytic-oxidative stability since as a co-chain extender/reinforcing filler, organically modified montmorillonite (OmMMT) covalently integrates hard PU segments, shields the vulnerable urethane linkages, and prevents the sulfur oxidation in soft segments. Besides, suitability of these high strength PIB based PUs for biomedical applications were evaluated in terms of first preliminary surface properties including surface stiffness, charges, roughness, wettability, chemical functionalities, and dimensional stability in water medium. Then, calcification resistance, protein adsorption, cell attachment, cell viability and bacterial resistance of them were investigated. It has been found that these properties of high strength PUs were superior to clinically widely implanted PDMS-based polyurethane, Elast- Eon®, in the biomedical applications due to (i) increased hydrolytic and oxidative stability (ii) higher dimensional stability in PBS medium. In short, the commercial one was found to have lower in vitro biocompatibility as well as higher cytotoxicity than newly synthesized PIB based PUs.