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R. Gmeiner, B. Steyrer, A. Samusjew, A. Mautner, R. Liska, J. Stampfl:
"Stereolithographic Manufacturing of Biodegradable Photopolymers";
Poster: Polymer Processing Society Conference 2015, Graz; 09-21-2015 - 09-25-2015.

Biocompatible photopolymers based on vinyl-ester monomers are showing minimal cytotoxic behaviour during in-vitro tests1 and can be processed by stereolithographic additive manufacturing techniques2. By addition of functional thiols, even biodegradable formulations with non-toxic degradation products were achieved3. The biological characteristics (e.g. degradation time) as well as the mechanical properties (e.g. flexural strength and modulus, impact strength) can be tailored in a wide range, making these polymers high promising candidates for medical implant materials in the field of soft tissue replacement or -support, even in load-bearing applications. In combination with a high-precision production technique, called stereolithographic manufacturing and also used for the fabrication of bioactive ceramics4, 5, we succeeded in creating delicate scaffold structures with an accuracy of 50x50x50µm³ as well as bulk structures for mechanical tests. For this purpose, we used an active mask technology based on the Digital Light Processing (DLP) technique, implemented in the Blueprinter stereolithographic production machines of the TU Wien. In addition to unfilled polymer structures, we also added micro-fibres of biodegradable glass into our formulations, showing that we can as well process fibre-filled biopolymers.
In this study, we tested different formulations of the vinyl-ester - thiol system in terms of mechanical properties. We used adipic acid divinyl-esters (AVE) as a photo-curable polymer matrix structure and added pentaerythritol tetrakis (TT) to modify the mechanical behaviour of the resulting polymer as well as its biological degradability. Beside these beneficial biological properties, the material class shows very useful mechanical characteristics. We have investigated the flexural bending strength using DMA techniques as well as the Charpy impact strength of selected AVE/TT polymers. To simulate the possible thermal environment when used as an implant material, DMA tests were conducted at room temperature (20°C) as well as at 37°C. Anyway, only `fresh´ and undamaged samples have been tested so far, not investigating their structural losses in a degradable biological environment. For an AVE formulation with 20% functional content of TT a flexural modulus of 811MPa was measured at 37°C (3pt-bending test, 1000MPa at 20°C). The flexural strength was identified to be around 27MPa (20°C). By adding 7,7wt% of glass microfibers, the flexural modulus was raised to 1045MPa at 37°C (respectively 1420MPa at 20°C) and the flexural strength was around 34MPa (20°C). The Charpy impact test of the unfilled AVE/TT shows a very promising impact strength of 15kJ/m² but significantly went down when the polymer was filled with glass microfibers (5kJ/m² for AVE/TT formulations with 10wt% filler content).

additive manufacturing, biodegradable polymers, stereolithography, photopolymers, bioactive, vinyl-ester, thiols

http://publik.tuwien.ac.at/files/PubDat_244978.pdf