Bioactive chitosan scaffolds reinforced with hydroxyapatite and nickel tungstate for bone tissue engineering

Current bone tissue engineering (BTE) scaffolds often fail to simultaneously provide adequate mechanical performance, controlled ion release, and multifunctional biological activity, particularly when incorporating inorganic antimicrobial agents that may induce cytotoxic effects. Addressing this limitation requires bioactive additives capable of modulating cellular responses without compromising structural integrity. In this work, chitosan/hydroxyapatite composite scaffolds produced by freeze-drying were functionalized with NiWO₄ nanoparticles for BTE. Hydroxyapatite was incorporated at 10 wt%, while NiWO₄ was added at 2.5, 5, and 10 wt%. Structural analyses confirmed that the incorporation of inorganic phases did not induce structural changes in the polymeric matrix. However, thermal analyses revealed that these fillers modulated chitosan-water interactions, promoting a morphological transition from lamellar structures to a more interconnected porous network, which directly impacted the mechanical properties of the scaffolds. Ion release studies showed that NiWO₄ did not affect Ca²⁺ leaching, whereas Ni²⁺ release was enhanced by hydroxyapatite at higher NiWO₄ contents. Biological assays using MC3T3-E1 and L929 cells indicated cytotoxicity only for scaffolds containing 10 wt% NiWO₄ after 14 days. Although NiWO₄ induced elevated intracellular oxidative stress within the first 24 h, this effect was mitigated over time, particularly at lower concentrations. The scaffold containing 2.5 wt% NiWO₄ synergistically enhanced MC3T3-E1 migration, osteogenic differentiation, and mineral deposition, while hydroxyapatite improved cell adhesion. Additionally, NiWO₄ imparted antimicrobial activity, achieving up to 90% bacterial reduction against E. coli and S. aureus via controlled Ni²⁺ release and ROS generation. Overall, this hybrid scaffold represents a promising platform for BTE.