Development of machinable hydroxyapatite-lanthanum phosphate composite for biomedical applications

• Development of machinable bioceramic composite for tailor made dimensions useful as biomedical implants.
• Synthesis and use of lanthanum phosphate as weak interphase material in synthetically prepared hydroxyapatite.
• Machinable (drillable) character was found in the compositions as long as the sintered ceramic remained as composite.
• Positive biocompatibility and bioactivity were found in the sintered composites.

To develop a bioceramic composite that can be machined to any shape and dimension will be of great importance and demanding material as an implant. Calcium phosphate (CaP) ceramics have high hardness that restricts the machinability of these materials and limits the wide applicability due to dimensional restrictions. Development of a machinable bioceramic composite by incorporation of a weak interphase material is done in the present study. Hydroxyapatite (HAp) and lanthanum phosphate (LP) powders were prepared chemically, mixed and pressed to form composites (LP, 10–50 wt.%) followed by sintering up to a temperature of 1200 °C. The products were characterized by phase analysis, densification, mechanical behavior, bioactivity, and biocompatibility. Machinability study of the sintered composites was done by using solid carbide (SC) drills in a conventional radial drilling machine. Phase analysis showed no reaction between the reactants and confirms the composite character till 1150 °C. Increasing LP content resulted in reduced densification, flexural strength, hardness with the incorporation of machinability. Positive bioactivity and biocompatibility were observed for the composites sintered up to 1150 °C. Sintering at 1200 °C results in a reaction between HAp and LP and formation of a new compound in the system Ca-P-La-O, hampering composite nature and destroying machinability.

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