Sustained Release of Catechin from Gelatin and Its Effect on Bone Formation in Critical Sized Defects in Rat Calvaria

The potential of plant-derived polyphenols in bone tissue engineering has not been fully realized owing to difficulties in maintaining their stability in affected parts. Catechins, such as epigallocatechin gallate (EGCG), are not fully utilized in bone regenerative medicine. Here, we demonstrated that chemical and non-chemical modifications of gelatin with EGCG resulted in distinct bone-forming abilities in critical-sized bone defects (9 mm) in rat calvaria. We prepared two EGCG-containing gelatin sponges: vacuum-heated gelatin sponges modified chemically with EGCG (AC-vhEGCG-GS) and vacuum-heated gelatin sponges with EGCG (no chemical modification; NC-vhEGCG-GS). Both sponges were characterized using scanning electron microscopy and degradability and EGCG-retention tests. The bone-forming ability of the sponges were estimated using micro-computed tomography and hematoxylin-eosin staining; the quality of newly formed bone (collagen maturation) was determined using picrosirius red staining and polarized microscopy. Both sponges had a spongy and soft texture with macropores ranging 50-150 mu m with negligible differences in degradability. The NC-vhEGCG-GSs released all their EGCG content within 1 h, whereas AC-vhEGCG-GSs retained 75% of the EGCG for up to 24 h. In addition, AC-vhEGCG-GSs resulted in a significantly greater bone formation than NC-vhEGCG-GSs 4 w after implantation, with negligible differences in collagen maturation. These results suggest that the chemical modification of gelatin with EGCG might be a promising strategy to fully utilize the pharmacological effects of EGCG for natural polymer-based sponges. Moreover, the release rate of EGCG from gelatin is possibly a screening parameter affecting the function of EGCG in vivo.