Effect of carbon fiber content on the structure, physicochemical properties and cytotoxicity of hydroxyapatite/glass/carbon fibers composites

Biogenic hydroxyapatite (BHA) is a promising material of natural origin for bone tissue replacement due to its good biocompatibility and close similarity to the mineral component of bone. The combination of hydroxyapatite with bioactive glass enhances both its bioactivity and mechanical properties. Carbon fibers (CFs), which are nanostructured materials prepared from hydrated cellulose fiber cloth, also have a natural origin and can be used in biomedical applications. This study investigates the structure, physicochemical properties, immersion behavior, and cytotoxicity of BHA/glass/CFs composites containing 10, 30, and 50 wt% activated CFs, prepared by closed sintering at 800 °C. The phase composition was analyzed using X-ray diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FT-IR), indicating the preservation of CFs in the composite structures. As the CFs content increases, the fibrous phase becomes more dominant, forming an interconnected network that contributes to the development of a hierarchical porous structure. Microstructural studies also confirmed the presence of CFs in the composite structures. The composite skeleton density ranges from 2.44 to 2.83 g/cm 3 and decreases with increasing CFs content. Immersion tests in saline demonstrated that higher CFs content leads to increased pH variation and solubility, attributed to the significant increase in the specific surface area. Post-immersion characterization of the composites after immersion in saline was examined to simulate their interaction with biological media, including XRD and microstructural analysis, was performed to simulate their interaction with biological media and confirmed the stability of the phase composition. Cytotoxicity evaluation using the MTT assay with MDCK and MDBK cell lines revealed no toxic effects for any of the compositions.