The role of stiffness of gelatin–hydroxyphenylpropionic acid hydrogels formed by enzyme-mediated crosslinking on the differentiation of human mesenchymal stem cell

We report the stimulation of neurogenesis and myogenesis of human mesenchymal stem cells (hMSCs) on the surfaces of biodegradable hydrogels with different stiffness. The hydrogels were composed of gelatin–hydroxyphenylpropionic acid (Gtn–HPA) conjugate were formed using the oxidative coupling of phenol moieties catalyzed by hydrogen peroxide (H2O2) and horseradish peroxidase (HRP). The storage modulus of the hydrogels was readily tuned from 600 to 12800 Pa. It was found that the stiffness of the hydrogel strongly affected the cell attachment, focal adhesion, migration and proliferation rate of hMSCs. The hMSCs on stiffer surfaces have a larger spreading area, more organized cytoskeletons, more stable focal adhesion, faster migration and a higher proliferation rate. The gene expression related to the extracellular matrix and adhesion molecules also differed when the cells were cultured on hydrogels with different stiffness. The differentiation of hMSCs on the surface of the hydrogel was closely linked to the hydrogel stiffness. The cells on a softer hydrogel (600 Pa) expressed more neurogenic protein markers, while cells on a stiffer hydrogel (12000 Pa) showed a higher up-regulation of myogenic protein markers.