The influence of nacre surface and its modification on bone apposition: A bone development model on rats

Background: Bone graft substitutes are currently used individually or in various combinations in reconstructing bone defects. Nacre, marine mineralized structure, was recently proposed as a very biocompatible and osteoinductive material for use in periodontal and implant surgery. Our aim was to investigate the interaction between natural nacre and fresh bone marrow, during bone development, in an ectopic site of DA rats. Surface modifications of nacre were tested. Methods: Demineralized bone matrix (DBM) cylinders (demineralized cortex of diaphysis) prepared from rat femurs were filled with fresh marrow, which was removed from other 2-month old DA rat femurs. Natural nacre particle or nacre which was treated with HCl, phosphate buffer saline (PBS), and Ca(OH)(2) to modify its surface was placed into the DBM cylinders. The cylinders were implanted subcutaneously at the thoracic region of growing DA rats. After 4 weeks the cylinders were surgically removed, fixed in buffered formalin, and x-rayed. Scans of the microradiographs and histological evaluation of the DBM cylinders including bone developed at the interface of nacre and its surface modifications were compared to marrow controls. Results: The results show that natural nacre is a poor conductive biomaterial in a bone developmental environment. Nacre surface treated with Ca(OH)(2) and PBS was found to be most biocompatible. In this group, new bone was apposed directly on the nacre surface and the total amount of bone was highest in comparison to other treatment groups. Conclusions: This study does not support previous observations that nacre is osseoinductive. Our model system seems to be very sensitive and capable of testing interaction between surface modifications of biomaterials and fresh marrow in the process of new bone development.