Chapter 33. Fabrication of Composite for Bone Repairing from α-Tricalcium Phosphate and Hydroxypropylcellulose

Summary

Tricalcium phosphate (TCP) ceramics is known as bioresorbable bone substitute in orthopedic field. Porous body of TCP has also high potential for application of drug delivery system in bony defect. Porous body of α-TCP can be easily fabricated through sintering β-TCP by conventional process, since α-TCP is thermodynamically stable phase at higher temperature than 1100°C. The problem is, however, that solubility of α-TCP is much higher than that of β-TCP. Therefore dissolution of the porous α-TCP ceramic is liable to progress much faster than bone repair. In the present study, we attempted to reduce dissolution rate of the porous α-TCP ceramic by coating with an organic polymer. We fabricated α-TCP porous body with continuous pores of 10-50 μm in diameter through conventional sintering process. The obtained porous body was coated with hydroxypropylcellulose (HPC). Several heat treatments were then applied for the HPC-coated porous α-TCP to increase mechanical strength and chemical durability. Chemical durability was examined in some buffer solutions with various pH by measurement of Ca²⁺ ion. Changes in crystalline phases are also analyzed with powder X-ray diffraction. The results on dissolution of α-TCP in buffer solutions showed that chemical durability increased by coating with HPC, followed by drying at 60°C and heat treatment at 100°C. Compressive strength of the porous α-TCP was also improved by coating with HPC. Thus prepared porous α-TCP is expected to be useful as a novel bone substitute by incorporating with drugs or osteoinductive factors.