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.

A study of biologically active peptide sequences (P-15) on the surface of an ABM scaffold (PepGen P-15) using AFM and FTIR.

Cellular response to any biomaterial surface is governed by a number of factors including topography, surface chemistry, surface charge, structural heterogeneity, and physiological conditions. Understanding these factors at the nanoscale level is crucial to develop improved biomaterials. Any changes in these properties due to surface modifications need to be addressed properly, as they could have significant impact on the cellular interaction with biomaterials. In this study, the topography and surface chemistry of commercially available tissue engineered xenograft, PepGen P-15 [comprised of a synthetic peptide P-15 irreversibly attached to anorganic bovine bone mineral (OsteoGraf/-N)] was studied using Atomic Force Microscopy (AFM), and Fourier Transform Infrared Spectroscopy (FTIR). FTIR confirmed the presence of the peptide on the surface of PepGen P-15. Changes in the peptide conformation, which includes a decrease in the beta-strand accompanied by an increase in unordered structures/random coil structures after attachment on OsteoGraf/-N is observed. Specific functional groups, which are involved in the binding mechanism, are identified. The results suggest that the attachment of the peptide on OsteoGraf/-N occurs via a specific surface docking ionic interaction involving the C-terminal carboxylic group on the peptide with positive domains generated by hydroxyl vacancies on the apatite surface.