Archaeal tetraether lipid coatings—A strategy for the development of membrane analog spacer systems for the site-specific functionalization of medical surfaces

The primary goal of our investigation was the development of a versatile immobilization matrix based on archaeal tetraether lipids that meets the most important prerequisites to render an implant surface bioactive by binding specific functional groups or functional polymers with the necessary flexibility and an optimal spatial arrangement to be bioavailable. From this point of view, it appears obvious that numerous efforts made recently to avoid initial bacterial adhesion on catheter surfaces as an important prerequisite of material associated infection episodes have shown only a limited efficiency since the bioactive entities could not be presented in an optimal conformation and a stable density. A significant improvement of this situation can be achieved by highly specific biomimetic modifications of the catheter surfaces. The term “biomimetic” originates from the fact that specific archaeal tetraether lipids were introduced to form a membrane analog monomolecular spacer system, which (1) can be immobilized on nearly all solid surfaces and (2) chemically modified to present a tailor-made functionality in contact with aqueous media either to avoid or inhibit surface fouling or to equip any implant surface with the necessary chemical functionality to enable cell adhesion and tissue integration. Ultrathin films based on tetraether lipids isolated from archaea Thermoplasma acidophilum were used as a special biomimetic immobilization matrix on the surface of commercial medical silicon elastomers. A complete performance control of the membrane analog coatings was realized in addition to biofunctionality tests, including the proof of cytotoxicity and hemocompatibility according to DIN EN ISO 10993. In order to make sure that the developed immobilization matrix including the grafted functional groups are biocompatible under in vivo-conditions, specific animal tests were carried out to examine the in vivo-performance. It can be concluded that the tetraether lipid based coating systems on silicone have shown no signs of cytotoxicity and a good hemocompatibility. Moreover, no mutagenic effects, no irritation effects, and no sensitization effects could be demonstrated. After an implantation period of 28 days, no irregularities were found.