Improving Bone Implant Technology

Orthopedic, dental, and other bone implants are becoming commonplace, but they are not yet trouble-free. John Brunski, professor of biomedical engineering, and co-researchers Jill Helms and Celine Colnot at UC San Francisco and Antonio Nanci at the University of Montreal have been awarded a new $1.9 million, four-year grant from the National Institutes of Health. The scientists are studying such implants to discover how weight loading influences blood supply, cell differentiation, and bone healing around these increasingly common devices.

	Images of molecular markers at a bone/stainless steel implant interface show genetic activity indicating new bone formation (orange, green, and yellow) compared with the lack of genetic activity that indicates cartilage development (red) (image courtesy of J. Helms and C. Colnot, UCSF)

Many people who receive implants recover well as healthy tissue regenerates to lock the implanted material to the surrounding bone. Through a process of cell differentiation, the new tissue eventually becomes normal bone. In some cases, however, and for unknown reasons, the interfacial tissue that grows back at the implant site never progresses to become normal bone. Clues are now emerging about how force on the implant can create conditions in early healing that prevent differentiation of stem cells into bone cells.

Immediately placing weight-bearing pressure (“loading”) onto an implant can lead to the formation of anomalous “fibrous tissue” instead of normal bone at the implant site. Fibrous tissue can impede an implant’s performance; knowing what causes it can help prevent it from forming. To do this, bioengineers need to determine the optimal biomechanical situation (for example, amount and timing of weight loading) for bone healing around implants.

“The cellular and molecular rules that govern how bone adapts to a loaded or unloaded implant have not been as clearly determined as we would like,” said Brunski. Resolving this issue will increase the success rate of implants.