Low-temperature plasma effect-induced enhancement of osteogenic activity in calcium phosphate ceramics

Calcium phosphate (Ca-P) ceramics are promising bioactive material that can be used for the remodeling and regeneration of bone tissue. However, it's sintering temperature-dependent mechanical strength, which is negatively correlated with its bioactivity, causes difficulties in improving the comprehensive performance of Ca-P ceramics. Here, the femtosecond laser (FSL) with low-temperature plasma effect was adopted to modify the hydroxyapatite (HA) ceramics after high temperatures (1250 °C) sintering, pursuing higher mechanical strength along with better osteogenic activity. The changes in the physicochemical properties of the materials and the osteogenic activity were characterized and investigated. Cell evaluations and in vivo experiments were performed to assess and verify the effect of FSL processing on the osteogenic capability of HA ceramics. The results indicated that α- and β-tricalcium phosphate (TCP) multiphase components were formed on the HA ceramic surfaces after laser treatment, simultaneously bringing about surface micro-nano porous structure, accelerated release of calcium (Ca) and phosphate (Pi) ions, enhancement of roughness, hydrophilicity and surface energy. Their synergistic effect facilitated apatite precipitation on the HA surface, promoted osteogenic differentiation and osteogenic/angiogenic gene expression. In vivo results also confirmed the enhancement of HA ceramic osteogenic activity by FSL treatment. This study presents an effective strategy of introducing FSL etching to high-temperature sintered Ca-P ceramics to improve the bone regeneration of HA ceramics and attain satisfactory mechanical strength at the same time. It will further promote the clinical application of HA ceramics in the field of bone regenerative repair. STATEMENT OF SIGNIFICANCE: This study introduces a method that uses the low-temperature plasma effect of the femtosecond laser (FSL) to modify the surfaces of high-temperature sintered hydroxyapatite (HA) ceramics, enhancing their osteogenic activity while maintaining the original mechanical strength. FSL processing induces the formation of bioactive multiphase of tricalcium phosphate (α-TCP and β-TCP) on the surfaces, creates micro-nano topographies, improves hydrophilicity and surface energy, promoting osteoblast differentiation and osteogenic gene expression for faster bone regeneration. This method overcomes the issue that high-temperature sintered HA ceramics have high strength but low osteogenic activity. It provides a modification method for HA ceramics with well-characterized performance enhancements, offering a convenient and effective strategy for high quality bone regenerative repair.