Lithography based additive manufacturing technologies (AMT) like stereolithography or digital light processing have become appealing methods for the fabrication of 3D cellular scaffolds for tissue engineering and regenerative medicine. To circumvent the use of (meth)acrylate-based photopolymers, that suffer from skin irritation and sometimes cytotoxicity, new monomers based on vinyl esters were prepared. In vitro cytotoxicity studies with osteoblast-like cells proofed that monomers based on vinyl esters are significantly less cytotoxic than (meth)acrylates. Photoreactivity was followed by photo-differential scanning calorimetry and the mechanical properties of the photocured materials were screened by nanoindentation. Conversion rates and indentation moduli between those of acrylate and methacrylate references could be observed. Furthermore, osteoblast-like cells were successfully seeded onto polymer specimens. Finally, we were able to print a 3D test structure out of a vinyl ester-based formulation by l-SLA with a layer thickness of 50 lm. For in vivo testing of vinyl esters these 3D scaffolds were implanted into surgical defects of the distal femoral bone of adult New Zealand white rabbits. The obtained histological results approved the excellent biocompatibility of vinyl esters. V V C 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6941-6954, 2009

Rapid prototyping by means of stereolithography using different types of photopolymers has gained increasing interest because cellular structures can be built at a high resolution with sub-lm feature sizes. Structures made with digital light processing and microstereolithography and rapid prototyping based on two-photon absorption photopolymerization techniques are presented. Soluble photopolymers were developed to substitute crosslinked photopolymers as mold materials and to extend the variety of materials which can be cast. With these molds, the processing of 'bio-inspired' ceramic composites with a controlled architecture from a macroscopic scale down to the nanometer range is possible. Another example is the development of biophotopolymers that are based on commercially available reactive diluents and modified gelatin for the fabrication of cellular bone replacement materials. Biocompatibility was investigated by seeding with osteoblast-like cells.

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Monomers for radical photopolymerization based on vinyl esters (VEs) have recently been identified as suitable alternatives to (meth)acrylates on account of their low irritancy and cytotoxicity. The drawback of most VEs with abstractable hydrogens is their relatively low reactivity compared with (meth)acrylates. Within this article, we proved by photo-differential scanning calorimetry measurements and real-time Fourier transform infrared spectroscopy that the thiol-ene concept is able to improve the photoreactivity of these VEs to a large extent to a level between those of acrylates and methacrylates.Other VEs have now a reactivity of at least the level of similar acrylates. Mechanical properties as determined by Dynamic Mechanical Analysis and Charpy impact tests showed significant toughening of these materials. Furthermore, we were able to confirm low toxicity of all components by osteoblast cell culture experiments.

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