Chemical Bonding Between Organic Matrix and Mineral in Human Bone Evidenced by X-ray Photoelectron Spectroscopy

Bone, a hierarchically organized composite, derives its strength and fracture toughness from its organic matrix and mineral building blocks. Although interfacial interactions affect bone mechanics, evidence of interfacial chemical bonding has been lacking. Using X-ray photoelectron spectroscopy (XPS), we provide new evidence of a chemical bond between the organic matrix and mineral in human bone. Analysis of femoral tissue with varying bone mineral density (BMD) revealed a calcium-nitrogen (Ca-N) signature, with 2.4-fold higher frequency of this interaction in normal bone compared to osteoporotic bone. We propose that this interaction originates between Ca ²⁺ in the extrafibrillar mineral and an iminic (N = C) moiety in the "glue" composition between mineralised fibrils. Our findings suggest that an increase in these bonds could strengthen bone, while their reduction in osteoporosis may weaken it. This study provides new insights into bone chemistry and its potential effects on mechanics in diseased tissue.