Bioactive silica and titania coatings on implant materials

Abstract

A major goal of the current research on implants is the generation of a sustainable positive interaction of the implant with the body, accompanied by minimal side effects. Hence, the focus of many studies lies on the integration of implants in the surrounding tissue, often supported by implant-associated drug delivery, thus reducing the need for systemic medication usually associated with strong side effects. When the surface of an implant is bioinert or bioincompatible due to its physical or chemical properties, this can be improved by a suitable coating. Such coatings change the surface properties chemically and/or structurally. Additionally, they can provide reservoirs for an implant-associated drug delivery. This thesis focusses on the development of bioactive silica and titania coatings on different types of implant materials like polymers, bioglasses or metals. These systems were chosen with regard to applications on middle ear or cochlea implants. The thesis was carried out as a part of the D1 project in the Collaborative Research Centre 599 “Sustainable bioresorbable and permanent implants of metallic and ceramic materials” of the German Research Foundation and of the Cluster of Excellence “Hearing4all”. The first part of the thesis presents comprehensive investigations on the properties of periodic mesoporous organosilica (PMO) coatings as a novel biomaterial. PMOs are materials with a high surface area and structured mesopores that can be synthesized by condensation and hydrolysis from organosilica precursors in combination with structure-directing agents. PMO coatings on implant materials have not been studied so far. In this work, it was demonstrated that PMO coatings could store and release large amounts of active substances like the antibiotic ciprofloxacin and the neuroprotective agent rolipram. Furthermore, cell culture experiments showed that PMO coatings were cytocompatible and could influence the cell growth positively. The second part of the thesis deals with the functionalization of PEEK (polyether ether ketone) surfaces. The polymer PEEK possesses favourable properties for application as a biomaterial and can, for example, be applied in middle ear prostheses. However, although PEEK is biocompatible, it is also bioinert. Hence, for some applications as an implant material, its surface has to be functionalized before implantation. The objective of the present work was to coat PEEK with differently modified titania films by the dip-coating method to produce mechanically stable thin films. The developed coatings were based either on super-hydrophilic porous titania and or on titania modified with titania nanoparticles. They displayed excellent results in cell culture tests and led to an enhanced cell compatibility of the PEEK material.