Photoelectron-Triggered Immunomodulation: Spray-Modified Titanium Implants Promote Macrophage M2 Polarization and Osseointegration

The compromised regulation of osteoimmune homeostasis poses a critical challenge for titanium implant osseointegration as conventional surface strategies lack dynamic responsiveness to postoperative microenvironmental evolution. Here, we developed a near-infrared (NIR)-responsive biointerface with photoelectronic immunomodulation fabricated via ultrasonic spray. By controlling the deposition of NIR-active gold/rare earth nanocomposites (Au@RE) on sandblasted acid-etched titanium (annotated as Au@RE/SLA Ti), we achieved NIR-triggered photoelectron generation for noninvasive macrophage polarization control. XRD, TEM, and phototransient spectra confirmed the synthesis of Yb/Er-doped NaYF₄ coating with Au nanoparticles as nanocomposites, which exhibited photoelectric properties on SLA Ti under NIR irradiation. Biological evaluations indicated that NIR-activated photoelectronic signals effectively triggered M2 macrophage polarization in RAW 264.7 cells, which in turn facilitated osteogenic differentiation of MC3T3-E1 preosteoblastic cells in coculture systems. In vivo studies using a mouse femoral implant model showed significantly improved osseointegration with Au@RE/SLA Ti compared to conventional SLA Ti surfaces, accompanied by increased M2 macrophage infiltration and accelerated bone formation. This work thus integrates surface engineering using ultrasonic spray with photoelectronic immunomodulation, providing a foundation for dynamic regulation of the bone-implant interface.