High Aspect Ratio Fatty Acid Functionalized Strontium Hydroxyapatite Nanorod and PMMA Bone Cement Filler

Abstract

High aspect ratio strontium hydroxyapatite nanorod significant enhances the mechanical strength of bioactive bone cement, due to its fiber like nature. However, incompatibility between resin matrix and strontium hydroxyapatite (Sr-HA) reduce the maximum filler loading and excessive strontium release leads to cytotoxicity problem. The aim of this study is to design a high aspect ratio hydroxyapatite nanorod with good resin compatibility and acceptable strontium release rate. In this study four C-18 fatty acids with different degree of unsaturation on nanorod morphology were investigated. These include stearic(n=0), oleic(n=1), linoleic(n=2), and linolenic acid(n=3). Functionalized strontium hydroxyapatite nanorod was synthesized by Liquid Solid Solution Method at 160°C for 15 hours. From TEM analysis, the aspect ratio of linoleic (22.00±11.86) and oleic acid (22.47±6.20) were larger than linolenic(4.76±1.73) and stearic acid (6.14±2.57). Hydrophobic FTIR pattern was shown in linolenic, linoleic and stearic acid functionalized nanorod. The reinforced bone cement has lower setting temperature than PMMA counterpart. Based on MTT and BrdU assay on mouse fibroblast (L929), proliferation rate of linoleic acid> linolenic acid> oleic acid> stearic acid. Exclude oleic acid all functionalized nanorod has higher relative growth rate than untreated strontium hydroxyapatite nanorod. From Hank immersion study and rat implantation study, the reinforced bone cement showed good bioactivity. In this study, high aspect ratio strontium hydroxyapatite nanorods can be fabricated by using linoleic and oleic acid. Linoleic acid functionalized strontium hydroxyapatite showed optimal aspect ratio, proliferation rate, cytotoxicity profile and good resin compatibility. New bone cement has lower setting temperature, better match stiffness and high bioactivity; these properties enhance the safety of vertebroplasty application.