Advancing universal dental adhesives: Biomimetic strategies for enhanced hybrid layer remineralisation and bond durability

Resin-dentine bonds degrade when water-rich, resin-sparse collagen persists within the hybrid layer. This study evaluated biomimetic remineralisation strategies that aimed to enhance adhesive durability: polyacrylic acid-stabilised amorphous calcium phosphate-loaded mesoporous silica nanoparticles (PA-ACP/MSN) incorporated at 15 vol% into the primer phases of two commercially available two-step universal adhesives (G2 Bond Universal and OptiBond eXTRa Universal) applied in etch-and-rinse mode, with or without phosphorylation pretreatment (5% PA + 5% sodium trimetaphosphate). Adhesive-dentine specimens were characterised using microtensile bond strength (µTBS), confocal Raman microscopy (Phosphate peaks; Resin CH₂ peaks; Mineral-Matrix ratio MMR), nanoindentation across the hybrid layer and dye-assisted micropermeability assays. The incorporation of PA-ACP/MSN did not adversely affect the immediate µTBS of either adhesive. After ageing, the biomimetic treatment group demonstrated enhanced phosphate content, improved micro-mechanical properties, preservation of resin characteristics, a higher elastic modulus across the hybrid layer and a marked reduction in permeability relative to the control group. Adding the phosphorylation pretreatment step conferred no additional benefit over PA-ACP/MSN alone. These findings indicated that embedding PA-ACP/MSN in universal-adhesive primers promoted remineralisation, stiffened and sealed the hybrid layer, and preserved bonding effectiveness without adding clinical complexity, supporting a practical path to durable, bioactive/biomimetic resin-dentine interfaces.