Biocompatible and biodegradable photopolymers by additive manufacturing: from synthesis to in-vivo studies

Abstract

Designing a 3D scaffold with defined pore sizes offering good cell adhesion is still an important topic in tissue engineering (TE).<br />One approach to manufacture these scaffolds is by the curing of photosensitive resins by the means of Additive Manufacturing Technologies (AMTs) like microstereolithography (µ-SLA), Digital Light Processing (DLP) and two-photon induced photopolymerization (TPIP). With these techniques feature resolutions down to 10 µm (µ-SLA and DLP) or even 200 nm (TPIP) are obtainable.<br />The use of (meth)acrylate based photopolymers as biomaterials has gained increasing interest recently because of their easy access, tailorable mechanical properties and their ability of being structured by AMT techniques. However, methacrylates suffer from poor photoreactivity and acrylates show high affinity to side-reactions with amines like proteins causing adverse effects in the human body, making them less suitable for biomedical applications.<br />Therefore, new monomers based on vinyl esters, vinyl carbonates and vinyl carbamates, potentially giving water-soluble and biocompatible poly(vinyl alcohol) upon hydrolytic degradation, were synthesized. The materials exhibit similar properties compared to (meth)acrylate references regarding their photoreactivity, mechanical properties and degradation behaviour. Basic investigations concerning their biocompatibility, measured by their cytotoxicity towards osteoblasts and osteoclasts, revealed that the new monomers were about two orders of magnitude less toxic compared to acrylates. Cellular 3D structures were printed by AMT and were then tested in rabbits to prove their in-vivo biocompatibility. These results show the suitability of vinyl esters, vinyl carbonates and vinyl carbamates as starting materials for several scaffold-mediated TE applications.