Hydrogels with water contents of 85, 90, 95, and 98 wt% were prepared through chemical crosslinking of acidic gelatin with varied concentrations of glutaraldehyde. In vivo release test of the gelatin hydrogels incorporating 125I-labeled transforming growth factor (TGF)-β1 revealed that the period of TGF-β1 release in the mouse subcutis prolonged with the decreased hydrogel water content. When the skull defect of rabbits (6 mm diameter) was treated by the TGF-β1-incorporating gelatin hydrogels, significant bone regeneration at the defect was observed at TGF-β1 doses 0.1μg or higher per defect, in marked contrast to free TGF-β1. The most efficious bone regeneration was induced by the hydrogels with water contents of 90 and 95 wt%. This water content dependance is ascribed to balance of TGF-β1 release and hydrogel degradation. Shorter TGF-β1 release from fastest degraded hydrogel (98 wt%) will not be enough to induce its osteogenic effect, while the slowest degradation of hydrogel (85 wt%) will physically impair bone regeneration at the skull defect. It is concluded that our biodegradable gelatin hydrogel functioned not only as a release matrix of TGF-β1 but also as a barrier for making space to prevent ingrowth of soft tissues to the bone defect.
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