ABSTRACT
Important issues in developing hydroxyapatite (HAp)- and titanium (Ti)-based composite biomaterials for orthopedic or dental devices include the dissociation of HAp during fabrication and its influences in the microstructure and biocompatibility of the final composite. During the densification by sintering of HAp/Ti composites, Ti reacts with -OH freed from HAp to form TiO2 thus dissociated HAp into Ca3(PO4)2, CaO, CaTiO3, TiP, and so forth. To inhibit this reaction, composites were fabricated with Ti and 30, 50, and 70 vol % ß-tricalcium phosphate (ß-TCP) instead of HAp by spark plasma sintering at 1200°C. It has been observed that after sintering at 1200°C, Ti also reacted with TCP, but unlike HAp/Ti composites, the final TCP/Ti composites contained significant amounts of unreacted TCP and Ti phases. The initial 70 vol % TCP/Ti composite showed compressive strength of 388.5 MPa, Young's modulus of 3.23 GPa, and Vickers hardness of 361.9 HV after sintering. The in vitro cytotoxicity and proliferation of osteoblast cells on the composites surfaces showed that the addition of a higher amount of TCP with Ti was beneficial by increasing cell viability, cell-composite attachment and proliferation. Osteopontin and collagen type II protein expression from osteoblasts cultured onto the 70% TCP-Ti composite was also higher than other composites and pure Ti. In vivo study verified that within 3 months of implantation in an animal body, 70% TCP-Ti had an excellent bone-implant interface compared with a pure Ti metal implant.
Subject(s)
Bone Substitutes/chemistry , Calcium Phosphates/chemistry , Titanium/chemistry , Animals , Bone Substitutes/metabolism , Calcium Phosphates/metabolism , Cell Line , Cell Survival/drug effects , Elastic Modulus , Femur/surgery , Hardness , Hot Temperature , Humans , Male , Materials Testing , Osteoblasts/cytology , Osteoblasts/drug effects , Prostheses and Implants , Rabbits , Titanium/metabolismABSTRACT
Hydroxyapatite (HA) coating was carried out by plasma spraying on bulk Ti substrates and porous Ti substrates having a Young's modulus similar to that of human bone. The microstructures and bond strengths of HA coatings were investigated in this study. The HA coatings with thickness of 200-250 microm were free from cracks at interfaces between the coating and Ti substrates. XRD analysis revealed that the HA powder used for plasma spraying had a highly crystallized apatite structure, while the HA coating contained several phases other than HA. The bond strength between the HA coating and the Ti substrates evaluated by standard bonding test (ASTM C633-01) were strongly affected by the failure behavior of the HA coating. A mechanism to explain the failure is discussed in terms of surface roughness of the plasma-sprayed HA coatings on the bulk and porous Ti substrates.
