Surface energetics of bone mineral and synthetic hydroxyapatite using inverse gas chromatography

Surface energy is one of the important factors that govern protein adhesion and cell attachment on biomaterial surfaces. Inverse gas chromatography (IGC) provides an excellent method to measure the surface energetics of rough and porous biosurfaces. In this study IGC was used to characterize and compare the surface energetics of synthetic and biological hydroxyapatites (natural bone mineral). IGC experiments were performed on three samples: synthetic hydroxyapatites with two levels of purity (99% and 90%) and natural biological hydroxyapatite obtained from bovine trabecular bone. The Lifshitz-Van der Waals component of the surface free energy (γ(S)(LW)) and specific interaction parameter (ɛ(π)) were determined by using homologous series of n-alkanes and alkenes as IGC probe molecules, respectively. The synthetic hydroxyapatite had values of γ(S)(LW) of 33.4 mJm⁻² at 99% purity and 53.3 mJm⁻² at 90% purity. Biological hydroxyapatite had a value of γ(S)(LW) of 45.7 mJm⁻². For the synthetic hydroxyapatite, the values of π-bond specific interaction parameters, ɛ(π), were 0.95 mJ (99%) and 3.01 mJ (90%). The biological hydroxyapatite sample had a value of 2.44 mJ for ɛ(π). The results suggest that, as compared to the synthetic compounds, the biological apatite has considerable surface heterogeneity, either chemical (impurities) or structural suggesting a scaffold surface that is more conducive of protein adhesion and cell attachment.