Assessing hard X-ray photoelectron spectroscopy as a new evaluation method for studying protein adsorption on anisotropic hydroxyapatite ceramics model

Abstract

Despite the growing interest in hard X-ray photoelectron spectroscopy (HAXPES) due to its deeper probing depth and potential for investigating bulk properties, studies exploring its application for understanding the interface between biomaterials and biological substances (such as proteins) remain limited. The adsorption abilities of proteins on hydroxyapatite (HAp) ceramics with preferred orientation to the a-plane (aHAp), together HAp ceramics without an anisotropic structure (iHAp) were evaluated using two complementary methods: Bradford-based quantification of adsorbed proteins and HAXPES-based analysis of their chemical binding states. aHAp had a significantly higher amount of adsorbed bovine serum albumin (BSA), normalized for a specific surface area, than iHAp from commercially-available HAp powder. The integrated intensity of C1s HAXPES spectra of HAp ceramics with and without anisotropic structure before and after BSA adsorption increased after BSA adsorption. This increase in integrated intensity was more significant for aHAp. This increase in integrated intensity was more pronounced for aHAp. Moreover, the C1s spectra of BSA-adsorbed aHAp ceramics attributed chemical information derived from COO and COOH, which are specific to proteins such as BSA, by peak fitting. The finding that aHAp specifically adsorbed BSA corroborated the results obtained from protein quantification. Overall, this study demonstrates the validity of HAXPES as a novel evaluation method for examining protein adsorption on biomaterials, particularly HAp ceramics.