Hexagonal-to-Monoclinic Phase-Modulated HAp Nanofibers for Enhanced Piezoelectric and Biocompatible Performance.

Area of Science:

• Materials Science
• Nanotechnology
• Biomaterials

Background:

• Hydroxyapatite (HAp) is crucial for biomedical applications due to its biocompatibility.
• Controlling HAp's crystal structure, particularly its phase, is key to optimizing its functional properties.
• Investigating phase transitions in HAp nanofibers synthesized via hydrothermal methods is essential for tailored material design.

Purpose of the Study:

• To investigate the influence of reaction time on the hexagonal-to-monoclinic phase transition in hydroxyapatite (HAp) nanofibers.
• To elucidate the role of the monoclinic P2₁/b phase in HAp's structural and piezoelectric properties.
• To assess the biocompatibility of HAp nanofibers with varying monoclinic content.

Main Methods:

• Synthesis of HAp nanofibers via a modified hydrothermal method at 100 °C.
• Characterization using X-ray diffraction (XRD) with Rietveld refinement, FTIR, Raman spectroscopy, and Transmission Electron Microscopy (TEM).
• Piezoelectric properties evaluated using resonance-tracking piezoresponse force microscopy (RT-PFM); biocompatibility assessed via in vitro MTT assays.

Main Results:

• A time-dependent phase evolution from hexagonal to monoclinic HAp was observed.
• Nanofibers synthesized for 48 h showed ~98% monoclinic phase with enhanced piezoelectric response (d_eff = 19.85 pm/V).
• High monoclinic content did not affect biocompatibility, meeting ISO 10993 and ASTM F895 standards.

Conclusions:

• Reaction time is a critical parameter for controlling the hexagonal-to-monoclinic phase transition in HAp nanofibers.
• The monoclinic phase significantly enhances the piezoelectric properties of HAp nanofibers.
• These findings highlight a promising strategy for developing advanced piezoelectric biomaterials.