Injectable biodegradable hydrogels with tunable mechanical properties for the stimulation of neurogenesic differentiation of human mesenchymal stem cells in 3D culture

We report an injectable hydrogel scaffold system with tunable stiffness for controlling the proliferation rate and differentiation of human mesenchymal stem cells (hMSCs) in a three-dimensional (3D) context in normal growth media. The hydrogels composed of gelatin-hydroxyphenylpropionic acid (Gtn–HPA) conjugate were formed using the oxidative coupling of HPA moieties catalyzed by hydrogen peroxide (H2O2) and horseradish peroxidase (HRP). The stiffness of the hydrogels was readily tuned by varying the H2O2 concentration without changing the concentration of polymer precursor. We found that the hydrogel stiffness strongly affected the cell proliferation rates. The rate of hMSC proliferation increased with the decrease in the stiffness of the hydrogel. Also, the neurogenesis of hMSCs was controlled by the hydrogel stiffness in a 3D context without the use of any additional biochemical signal. These cells which were cultured in hydrogels with lower stiffness for 3 weeks expressed much more neuronal protein markers compared to those cultured within stiffer hydrogels for the same period of time.