Mechanical Properties of Architectured Gelatin-Based Hydrogels on Different Hierarchical Levels

Preparation of three-dimensionally architectured porous biomaterials can be achieved in a one-step process by stabilizing gelatin with L-lysine diisocyanate ethyl ester (LDI) in water. The reaction of gelatin with LDI in presence of water leads to the formation of oligourea bridges between gelatin molecules and oligourea chains grafted on gelatin. The number and the length of the bridges, as well as of the grafted chains strongly depend on the concentration of the LDI used for the stabilization, and this has huge influence on the mechanical properties of the material on different hierarchical levels. Higher LDI concentrations yield materials with increased deformation resistance in tensile tests due to the higher number of covalent and physical netpoints in the material. However, mechanical properties determined on the micro-level by AFM indentation showed the opposite trend, i.e. a decrease of Young's modulus with increasing LDI content. This was interpreted by a decreasing number of shorter oligourea bridges between gelatin chains with decreasing LDI content.