REPAIRING OF RABBIT SKULL DEFECT BY TGF-β1-INCORPORATED COLLAGEN SPONGES OF DIFFERENT THICKNESS

Abstract

We have recently demonstrated that a collagen sponge incorporating TGF-β1 was effective in inducing bone repair at the skull defect of rabbits. In this study, the bone repairing of rabbit skulls was tried by TGF-β1-incorporated collagen sponges of different thickness to assess the influence of the size of osteoinductive materials on the bone repairing. The collagen sponge used was prepared by foaming and freeze-drying 1 % aqueous solution of pepsin-processed porcine atelo-collagen, followed by dehydrothermal crosslinking for 6 hr in vacua. Collagen sponges with different thickness were prepared by changing the volume of collagen solution for freeze-drying and changing the number of sponges piled up. An aqueous solution of TGF-β1 or 125 I -labeled TGF-β1 was dropped onto the freeze-dried sponge to prepare collagen sponges incorporating TGF-β1 or 125 I -TGF-β1, respectively. Collagen sponges were also radioiodinated with Bolton Hunter Reagent. Following implantation of the collagen sponges incorporating 125 I -TGF-β1 and the 125 I -labeled collagen sponges into the mice subcutis, each radioactivity remaining was measured to compare the time profile of in vivo retention of TGF-β1 with that of the sponge. The TGF-β1 incorporated collagen sponges of different thickness were implanted into full-thickness defects of rabbit skulls with 6 mm in diameter. The bone repairing at the defect was evaluated in terms of histological and DEXA examinations 6 weeks later. The remaining radioactivity of 125 I -labeled collagen sponges and 125 I -labeled TGF-β1 incorporated in collagen sponges decreased with time. The remaining periods of radioactivities of the sponges prolonged with an increase in the sponge thickness, but those of TGF-β1 were independent with the sponge thickness. The collagen sponge with 2 mm thickness was the most effective in increasing the bone mineral density at the bone defect. This finding indicated that the sponge thickness is one of the key factors contributing to successful bone repairing.