Role of exchanged ions in the integration of ionomeric (glass polyalkenoate) bone substitutes

Ionomeric (glass polyalkenoate) implants are synthetic materials which can be used for repairing bone defects. It has been suggested that ions are leached from these implants during healing and that they influence cellular activity in the surrounding tissues. Morphological, immunohistochemical and microanalytical techniques were used to compare the osteogenic capacity of implants which eluted aluminium ions with implants which did not elute aluminium ions. The extracellular matrix molecules fibronectin and tenascin were located upon the surface of both implanted materials. Thick seams of lamellar bone were apposed to implants containing labile aluminium ions, but the bone was poorly mineralized. At the same time, transient increases were apparent in osteoblast activity on periosteal and endosteal surfaces and in chondrocyte activity in the growth plate and articular cartilages. In contrast, small amounts of mineralized lamellar bone were apposed to substituted implants (without aluminium) and the growth plate and articular cartilages remained normal in thickness and morphology. These results suggest that exchanged ions can influence the amount and quality of bone apposed to the implant. They also suggest that the effect of the ions depends upon their concentration and the state of differentiation of osteogenic cells.