Surface energies and the bone induction principle.

The macroscopic and histologic sequence of events in the induction of ectopic bone formation by porous demineralized bone and by synthetic porous sponges of poly-hydroxyethylmethacrylate (poly-HEMA) is described and reviewed. The observed relationship between the yield of new bone generated, and in vitro calcification, with the zeta potential, seems to parallel the connection between general adhesion in biologic systems and the critical surface tension. Consistent with experimental findings over the years, the bone induction principle (BIP) is probably associated with porous, mechanically suitable, hydrophilic materials with a high polar surface energy. It can be inferred that such surfaces are exposed when bone is suitably demineralized and treated, as has been reported. The discovery of noncollagenous proteins that are important to the BIP may be viewed in this light. Local heterogeneities on cellular surfaces are known to be important but are not detected by macroscopic techniques. It is suggested, following Lerchental, that induced stresses in the cell membranes cause a redistribution of surface charges that increases the local surface energy. This may lead therefore to an agglomeration and alignment of cells, as a response to the stress, accompanied by differentiation, as well.