Composites of polylactide and nano-hydroxyapatite created by cryomilling and warm isostatic pressing for bone implants applications

Abstract

Abstract This paper describes a bioresorbable composite for orthopaedic implants that has mechanical properties similar to those of natural bone. Nano-hydroxyapatite used to produce the nanocomposite was synthesised to achieve a structure similar to natural hydroxyapatite. Its mean particle size and specific surface area were 8\u202fnm and 260\u202fm2/g respectively. The second key component in the nanocomposite was a biodegradable polymer (polylactide). Prior to further processing, the nano-hydroxyapatite particles were annealed at temperatures from 100\u202f°C to 1200\u202f°C to reduce structural and surface absorbed water. The first step in obtaining the composite was cryomilling a mixture of nano-hydroxyapatite and polylactide at the temperature of liquid nitrogen. Each material provided 50\u202fvol% of the composition. Cryomilling enabled the formation of composite granules that had a uniform dispersion of the ceramic in the polymer. The granulate was subsequently poured into elastic forms and pressed at an isostatic pressure of 65\u202fMPa at 165\u202f°C. This process is called warm isostatic pressing. The composite properties depended on the quantity of structural water included in the HAP nanopowder. A maximum compressive strength of 110\u202fMPa and Young’s modulus of 6\u202fGPa were obtained.