Preparation of a partially calcified gelatin membrane as a model for a soft-to-hard tissue interface

Cartilage and/or bone tissue engineering is a very challenging area in modern medicine. Since cartilage is an avascular tissue with limited capacity for self-repair, using scaffolds provides a promising option for the repair of severe cartilage damage caused by trauma, age-related degeneration, and/or diseases. Our aim in this study was to design a model for a functional biomedical membrane to form the interface between a cartilage-forming scaffold and bone. To realize such a membrane gelatin gels containing calcium or phosphate ions were exposed from one side to a solution of the other constituent ion (i.e., a sodium phosphate solution was allowed to diffuse into a calcium-containing gel and vice versa). The partially calcified gels were analyzed by XRD, ATR-FTIR spectra, E-SEM, and EDX. Thus, we confirmed the existence of a gradient of crystals, with a dense top layer, extending several micrometers into the gel. XRD spectra and Ca/P atomic ratios confirmed the existence of calcium deficient apatites. The effect of different experimental parameters on the calcification process within the gelatin membranes has been elucidated. It was shown that increasing the gelatin concentration from 5 wt % to 10 wt % retards calcification. A similar effect was observed when glycerol, which is frequently used as plasticizer, was added to the system. With increasing calcium concentration within the organic matrix, the quantity and density of calcium phosphate crystals over/within the gel increased. The possible explanations for the above phenomena are discussed.