Carbon-centered radicals in γ-irradiated bone substituting biomaterials based on hydroxyapatite

Area of Science:

• Biomaterials Science
• Materials Science
• Biophysics

Background:

• Synthetic hydroxyapatite materials are used as bone substitutes.
• Understanding their structural integrity post-irradiation is crucial for clinical applications.
• Electron paramagnetic resonance (EPR) spectroscopy is a sensitive tool for detecting radical species.

Purpose of the Study:

• To compare radiation-induced radical formation in synthetic bone grafts (NanoBone®, HA Biocer) and human compact bone using EPR spectroscopy.
• To investigate the stability and molecular structure of radiation-induced radicals.
• To infer differences in microscopic structures based on EPR and FT-IR spectral analysis.

Main Methods:

• Gamma irradiation of synthetic hydroxyapatite (NanoBone®, HA Biocer) and human compact bone.
• Electron paramagnetic resonance (EPR) spectroscopy to detect and analyze radiation-induced carbon-centered radicals.
• Fourier-transform infrared (FT-IR) spectroscopy to analyze molecular structures.

Main Results:

• All irradiated samples exhibited carbon-centered radicals, but with differing structures and concentrations.
• CO(2)(-) anion radicals were stable in compact bone and synthetic hydroxyapatite, while CO(3)(3-) radicals dominated NanoBone® and HA Biocer immediately after irradiation.
• Storage led to the appearance of CO(2)(-) signals in NanoBone® and HA Biocer.
• FT-IR spectra showed HPO(4)(2-) and CO(3)(2-) in synthetic materials, contrasting with collagen dominance in compact bone.

Conclusions:

• EPR spectroscopy reveals significant differences in radiation-induced radical behavior between synthetic bone grafts and human bone.
• The observed radical differences suggest distinct microscopic structural characteristics of NanoBone®, HA Biocer, and natural bone.
• These findings have implications for the characterization and application of synthetic bone-substituting materials.