Robust adhesion between solid-state hydroxyapatite and bone tissue through surface demineralization

Objective: Current bone adhesives typically lack adequate mechanical strength, long-term stability, or biocompatibility. To address these limitations, we designed a new adhesion strategy using a solid-state hydroxyapatite (HAp) adhesive in combination with bone surface demineralization.
Methods: Solid-state HAp adhesives were synthesized via wet chemical precipitation and heat treatment. Cortical bone specimens were partially demineralized with phosphoric acid (H3PO4) or ethylenediaminetetraacetic acid (EDTA), and characterized using scanning electron microscopy (SEM) and attenuated total reflectance–Fourier transform infrared spectroscopy (ATR-FTIR). Shear adhesion strength of HAp to demineralized bone was measured over time. In vivo fixation was assessed in rats using micro-computed tomography and histology. Statistical analysis used Tukey-Kramer tests after normality and variance checks.
Results: Although the HAp adhesive failed to adhere to non-demineralized bone, effective adhesion was achieved on the surface-demineralized bone tissue. Shear adhesion strength was significantly higher in EDTA-treated samples (238.4 kPa at 10 h) compared to H3PO4-treated samples (102.9 kPa at 1 h), with performance correlating with demineralization depth. ATR-FTIR and SEM analyses revealed that EDTA preserved collagen's triple-helix structure and free water content, both enhancing adhesion. Animal experiments confirmed stable fixation of HAp adhesive to demineralized bone tissue.
Conclusions: Surface demineralization enabled strong adhesion of the solid-state HAp adhesive to bone by exposing collagen swollen with water. Adhesion strength was influenced by structural changes in the demineralized layer, and the adhesive provided stable in vivo fixation, supporting its potential for bone-anchored biomedical applications.