Optically induced nonlinear piezoelectric response in nano-Hydroxyapatite ceramics for biotechnological applications

The field of tissue regeneration has advanced significantly through the development of biocompatible materials capable of promoting healing and cellular growth. Nano-hydroxyapatite (nHAp), which closely mimics the structure of bone minerals, has attracted considerable attention for its biocompatibility and osteoconductive properties. This study investigates the nonlinear opto-mechanical behavior of nHAp, focusing on its activation by optical pulses and its potential integration into ceramic coatings. A theoretical thermo–elastic–electro–optical model was developed to describe the coupling between optical irradiance, temperature rise, and piezoelectric activation in nHAp matrices. The model predicts maximum opto-mechanical efficiency for thin films below 4 μm and diameters near 0.5 cm, where near-infrared nonlinear absorption enhances the induced voltage up to 5.7 V μm⁻¹under an irradiance of 1 MW/cm². Experimentally, nHAp powders and thin films were synthesized with nanorod-like morphology and a stoichiometric Ca/P ratio of 2.2, confirming structural fidelity. Photothermal analyses revealed that laser fluence between 17 and 63 kJ/cm²progressively altered the surface morphology, from intact nanostructures to ablated and microfractured regions, establishing a safe operational limit below 10 kJ/cm². These results provide quantitative evidence of the opto-mechanical coupling in nHAp and define key parameters for the future development of light-activated, biocompatible piezoelectric coatings and devices.