Developing Biosensors for Monitoring Orthopedic Tissue Growth
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0950-D15-04
Developing Biosensors for Monitoring Orthopedic Tissue Growth Sirinrath Sirivisoot, Chang Yao, Xingcheng Xiao, Brian W. Sheldon, and Thomas J. Webster Division of Engineering, Brown University, Providence, RI, 02912
ABSTRACT The objective of this in vitro 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 not only in regenerating tissue necessary for orthopedic implant success, but also to aid in informing an orthopedic surgeon whether 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 Ti, developed by chemical etching and passivation treatments. Carbon nanotubes (CNTs), because of their electrical and mechanical properties, are essential to consider 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 Ti by a chemical vapor deposition process. Lastly, these sensors will be 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 Ti. This conductive, biodegradable polymer consists of polypyrrole (which is conductive) and poly-lactic-co-glycolic acid (which is biodegradable). Preliminary in vitro results suggest that osteoblast functions (specifically alkaline phosphatase activity and calcium deposition) on CNTs grown on anodized Ti are significantly enhanced when compared to anodized Ti and currently-used Ti; thus, it is anticipated that bone growth could be enhanced on these novel biomaterial sensors. INTRODUCTION In the human body, bone matrices are roughly 90% type-I collagen and mineral phase consisting of calcium phosphate-based apatite mineral. Collagen fibrils are impregnated with inorganic carbonate apatite nanocrystals (tens of nanometers in length and width, 2-3 nm in thickness) [1]. Bone consists of major living cells: osteoblasts, osteocytes, and osteoclasts, which are located in bone’s nanostructured mineralized organic matrix [2]. Osteoblasts form the organic matrix of bone, and produce alkaline phosphatase, which plays a critical role in the mineralization of bone. When they are trapped in the bone, which they formed, osteoblasts differentiate into osteocytes. While osteoblasts make bone, osteoclasts break it down, releasing acid that decomposes calcium phosphate-based apatite minerals [3]. Undoubtedly, implants require the functions of osteoblasts to create new bone growth in situ. However, in orthopedics, many kinds of materials are used (such as CoCrMo, Ti6A
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