Optimization of Hydroxyapatite Bone Cement Properties

Calcium phosphate based cements have become useful biomaterials for the repair of bone defects. Our work has focussed on optimization of handling characteristics to improve the physical-chemical and biological properties of hydroxyapatite cements (HAC, Morio et al, 2000, 2001). Objectives:The objective of the current study was to determine the handling properties of HAC (BoneSource®, Howmedica-Leibinger, Inc.) when mixed with a combination of sodium phosphate (SP) and hydroxypropyl methylcellulose (HPMC) compared to water (W), SP or HPMC alone. Methods: The handling properties (working time, WT; setting time, ST) of HAC-SP-HPMC mixtures were evaluated in conjunction with specific mechanical and biological properties. Results: SP alone decreased working (WT) and setting times (ST) (7 + 1 min, 19 + 2 min), while HPMC alone increased WT and ST (17 + 4 min, 54 + 4 min), compared to W (11 + 1 min; 29 + 5 min) or SP-HPMC (13 + 2 min, 41+ 4 min) mixtures. For each mixture there was a significant (P<0.05) increase in diametral compression strength (sdc) from 1 to 24 hr (<1.0 MPa to > 2.5 MPa), with SP-HPMC demonstrating the highest sdc (3.7 MPa). All HAC mixtures demonstrated overall biocompatibility and osseoconductive properties in vivo. SP and HPMC mixtures helped stabilize the HAC, which led to significant levels of osseointegration with simultaneous implantation of endosseous implants (68-70 % bone contact at 6 months) in intra-oral canine bone defects. Conclusions: When SP and/or HPMC are used to alter the setting reaction, the physical-chemical properties and overall biological usefulness of the HAC cement for repair of bone defects are enhanced.