Hyaluronic acid vinyl esters: A toolbox toward controlling mechanical properties of hydrogels for 3D microfabrication

In this study, a thorough exploration of constitutional parameters of thiol-ene photocrosslinkable hydrogels based on hyaluronic acid vinyl ester was conducted in order to decipher their impact on material properties. These constitutional parameters originated from the process of synthesis (macromer size and degree of substitution) and from the process of formulation (photoinitiator concentration, macromer content, and thiol-to-ene ratio). Various macromers were obtained with a broad variety of degrees of substitution. Photorheology measurements were performed in order to determine the influence of the structure parameters on photoreactivity and the physical properties of hydrogels. Final crosslink densities and photoreactivities dramatically increase with increasing number of functional groups, macromer concentrations as well as with photoinitiator concentration. Swellabilities of the hydrogels were determined as complementary reference values. Mass swelling ratios as well as mass loss increased with decreasing degree of substitution as a result of increased mesh size and hydrophilicity. Finally, hyaluronic acid vinyl ester formulations were used to encapsulate fluorescent-labeled immortalized human adipose-derived mesenchymal stem cells in 3D via UV and by high-resolution two-photon polymerization. Cell-survival was successfully studied via confocal laser scanning microscopy during the course of 2 weeks.