Molecular forces governing tight contact between cellular surfaces and substrates.

M y dental visits over recent years alerted me to the importance of intermolecular forces as they act between biologic materials. My dentist recognized my professional interest and urged me to think more about forces acting at surfaces and to relate this to the vexing problems of designing and firmly incorporating artificial materials into dental structures. Recently, my interest increased when I encountered the work of Branemark et al.’ and Albrektsson et al.2 on metal implants and their reported apparent integration of metal with growing bone tissue. For quite different reasons, I had wondered about which properties of a molecule in solution would allow it to make a stable association with a particular kind of moIecule while eschewing virtually all other molecular species. This thinking was partly in the context of the more difficult question of why biologic cells will be selectively attracted to particular substrates, or to particular species of cells, but not to others. The electron micrograph of bone tissue clinging to a titanium surface in preference to all the mediums around it provided striking evidence for specific attraction. What was it about an artificial surface that provided such attraction? Consideration of the problem suggests that association in osseointegration is physically strong and that it requires molecular contact between physically rigid bodies. Simple attraction between bone tissue and substrate is not enough. Other materials must not be as strongly attracted to the substrate. Whatever first touched the implant material must have been displaced by the growing bone. The question becomes one of how to characterize an implant the surface of which is probably modified by whatever touches it before its integration. The most important thing to keep in mind is that the