Developing Biosensors for Monitoring Orthopedic Tissue Growth

The objective of this present study was to create a biosensor which can monitor in situ orthopedic tissue growth juxtaposed to a newly implanted orthopedic material. This biosensor has unique properties including the ability to sense, detect, and control bone regrowth. Such a biosensor is useful to not only regenerate tissue necessary for orthopedic implant success but it also aids in informing an orthopedic surgeon if sufficient new bone growth occurred. If the sensor determines that insufficient new bone growth occurred, the sensor can also act in an intelligent manner to release bone growth factors to increase bone formation. The primary biomaterial in this biosensor is anodized titanium, developed by chemical etching, and passivation treatments. Carbon nanotubes (CNTs), in terms of their electrical and mechanical properties, are imperative considerations when designing such biosensors since they will be used to apply and measure conductivity changes as new bone grows next to the implant. For this, parallel multiwall CNTs were grown from the pores of the anodized titanium by the chemical vapor deposition process. Lastly, this sensor is composed of a conductive, biodegradable, polymer layer that degrades when bone grows and, consequently, undergoes a change in conductivity that can be measured by the CNTs grown out of the anodized titanium. This conductive, biodegradable polymer consists of polypyrrole (which is conductive) and polylactic-co-glycolic acid (which is biodegradable). Preliminary in vitro results suggest that osteoblast functions (adhesion and proliferation) on such a biosensor is not significantly compromised when compared to currently-used titanium, yet, retains the ability to potentially measure new bone growth juxtaposed to an implant. In addition, although not tested here, it is anticipated that bone growth could be enhanced on these biosensors electrically.