Photocrosslinkable Hyaluronic acid
Hyaluronic acid (HA), or hyaluronan, is a versatile building block of novel biomaterials for tissue engineering and regenerative medicine. As the major component of extracellular matrix (ECM), HA is widely distributed in most connective tissues (skin, cartilage, etc.) and plays an important role in wound repair process. However, the native HA is far beyond the direct use in certain preclinical studies (e.g., articular cartilage regeneration) because it lacks of mechanical strength and long-enough duration in vivo. To address these problems, researchers have explored the (meth)acrylated HA as polymerizable hydrogel precursors which are injectable and biomechanically robust.
We are particularly interested in developing cytocompatible and (photo)polymerizable HA derivatives that are injectable and suitable for potential clinical applications. Specifically, we focus on the synthesis of low toxicity derivatives of HA by introducing cell-friendly functional groups (e.g., vinyl esters). Compared to acrylate, the vinyl ester chemistry shows much more promise due to its unique degradation products (FDA-approved poly(vinylalkohol) and easy-removable acetaldehyde) 
Gelatin is a cost-effective natural protein which is derived from denatured collagen type-I. Like collagen, the major drawback of gelatin-hydrogels are their poor mechanical properties, which could be optimized via varying chemical cross-linking approaches.
One of our aim was to develope photocurable gelatin-based materials for bone replacement with similar mechanical properties. To achieve such high strength and modulus highly crosslinked systems and therefore additional crosslinkers, are necessary. As gelatin is only water soluble, we solved the monomer-miscibility problem by introducing long polyethyleneglycol spacers. These cytocompatible materials were able to be processed by digital-light-processing (DLP) techniques to give arbitrary shaped cellular structures .
Furthermore we are interested in hydrogel scaffolds that can be printed by two photon induced photopolymerization . As the 3D writing in the presence of cells is one of our targets, reactive groups on gelatin with low toxicity e.g. vinylesters are of interest. Therefore, multiple vinyl ester groups were introduced to gelatin (GE-VE) through a facile aminolysis reaction with divinyladipat while reduced albumin (BSA-SH) were selected as macrothiols to donate multiple cysteine residues for thiol-ene photo-click reactions. By using the two photon induced polymerization technique, we were able to recapitulate a 3D hydrogel scaffold with complex geometry within the modified proteins. The robust radical-mediated thiol-ene polymerization was supposed to promote the high-writing speed (max. 50 mm/s).
 X.H. Qin, J. Torgersen, R. Saf, S. Mühleder, N.U Pucher, S. Ligon, W. Holnthoner, H. Redl, A. Ovsianikov, J. Stampfl, R. Liska, Journal of Polymer Science Part A: Polymer Chemistry, 51 (2013), S. 4799 - 4810.