Synthesis and Cytocompatibility of Bacterial Nanocellulose–Hydroxyapatite Biocomposites with Mg, Cu, Zn, and Sr Substitution

Abstract Bacterial nanocellulose (BNC) combined with hydroxyapatite (HAp) forms biocomposites that exhibit biomimetic properties favorable for bone regeneration. Moreover, incorporating trace elements naturally present in bone, such as Mg, Cu, Zn, and Sr, has been reported to enhance osteogenic activity and support vascularization. Despite these advantages, BNC’s resistance to enzymatic degradation in vivo remains a critical limitation. To address this, BNC-based biocomposites containing cation-substituted hydroxyapatite (at varying concentrations of Mg2+, Cu2+, Zn2+, or Sr2+) were synthesized and bioactivated in simulated body fluid (SBF). These materials were characterized using scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS), Fourier transform infrared/attenuated total reflectance (FTIR/ATR), X-ray diffraction (XRD), thermogravimetric analysis (TGA) and in vitro cytotoxicity assays. The most promising compositions were further evaluated for osteoblast (MC3T3-E1) adhesion and enzymatic biodegradation. SEM confirmed the uniform distribution of HAp crystals across the BNC network, while TGA revealed a high residual mass (51.9–65.6%), indicating effective HAp incorporation. Cytotoxicity results showed that the BNC/ZnHAp 1% and BNC/SrHAp 1% samples maintained cellular metabolic activity at approximately 90%, indicating biocompatibility. Additionally, these biocomposites promoted superior cell proliferation compared to the nonsubstituted BNC/HAp control at all time points. Overall, the incorporation of selected cations enhanced the biological performance of BNC/HAp biocomposites, suggesting their suitability for further investigation in bone tissue repair and implantable biomedical applications.