Biocompatible and biodegradable photopolymers for microstereolitho- graphy

The fabrication of geometrically well defined 3-dimensional scaffolds offering good cell adhesion is still an important topic in tissue engineering. Microstereolithography (µSLA), which is based on the photopolymerization of a liquid resin using a laser, turned out to be especially suitable because accessible resolutions of about 5 μm allow the fabrication of cellular structures for a number of biomedical applications. In order to find suitable materials the biocompatibility, determined by cell adhesion and cell proliferation of osteoblast-like cells, the photoreactivity, mechanical properties and cytotoxicity of several commercially available acrylate based monomers and polymers have been tested. Despite the high rate of polymerization and the easy accessibility of a large number of monomers, the main drawback of these acrylate containing resins is the high cytotoxicity of residual unreacted acrylate groups. Therefore a new class of pho-toreactive monomers based on vinyl ester, carbonates and carbamates were synthesized. These materials showed lower cy-totoxicity by a factor of 100 compared to similar acrylates the biocompatibility and mechanical properties of the polymers were evaluated, indicating the suitability of this new class of biophotopolymers for a number of applications in tissue engineering. Further tests regarding biodegradability of these polymers were performed. 1. Introduction Additive Manufacturing Technolgy (AMT) techniques allow a material fabrication with defined geometry and pore structure. Microstereolithography (µSLA) has gained increasing interest over the last two decades and is often considered as one of the most innovative AMT techniques [1]. Therefore, it has become a very appealing methods for the production of three-dimensional scaffolds for several tissue engineering applications in the recent past [2],[3]. It is based on a layer-by-layer curing of a light-sensitive resin via photopolymerization. Radicals are being formed upon excitation of a photoinitiator by an UV-laser inducing po-lymerization and therefore, a phase transition of the resin from liquid to solid occurs. Materials solidification, through radical polymerization is most commonly based on acrylate or methacrylate chemistry [4]. Suitable biocompat-ible spacers for these type of reactive groups are based on alcohols like poly(ethylene glycol)[5],[6] and amines like chitosan.[7] It has to be noted that the main disadvantage of methacrylates is their limited reactivity due to the sterical hindrance and inductive stabilization of the formed radical of the additional methyl group. Acrylates are considerably more reactive but also show a significant tendency towards Michael addition side reactions with amino groups of proteins or DNA giving hydro-lytically non-cleavable aliphatic adducts. This frequently