Ca-deficient hydroxyapatite/polylactide nanocomposites with chemically modified interfaces by high pressure consolidation at room temperature

Hydroxyapatite (HAP) is a close synthetic analog of the bone mineral and is often considered as a material for bone graft substitutes and tissue engineering scaffolds. Despite its attractive bioactive properties low-fracture toughness limits the use of HAP ceramics to a number of non-load-bearing applications. To obtain a more adequate mechanical behavior, HAP is often combined with polymers based on lactic and glycolic acids or polycaprolactone using hot pressing. In such composite materials, the compatibility and bonding strength of HAP–polymer interfaces are critical parameters that must be controlled and improved. This may be achieved, for example, by covalent immobilization of organic moieties on the ceramic particles surface. In this work, the surface of calcium-deficient hydroxyapatite (CDHAP) was modified by reaction with hexamethylene diisocyanate (HDI) in a non-aqueous suspension. Composites of CDHAP–HDI with polylactide (PLA) were high pressure consolidated at room temperature at 2.5 GPa yielding up to 90% theoretical density. The effects of total organic fraction and modification extent on compression strength were studied. Materials with high extent of modification and high organic content exhibited compressive strength of ~295 MPa, much higher than reported in other studies. These materials are suitable candidates for load bearing orthopedic applications.