Reinforcement of polyvinyl alcohol hydrogels with calcium ions and iron oxide nanoparticles: Effects on morphology, swelling, and mechanical properties

Abstract

• Simultaneous reinforcement strategy to enhance PVA-based hydrogel performance. • Dual incorporation of reinforcements increases crosslinking density and mechanical properties. • Developed hydrogels exhibited controlled morphology and significantly reduced swelling rate. • Mean pore area decreased and swelling resistance improved by the synergistic action of reinforcements. • Tensile strength improved by up to 241 %, demonstrating a strong structure–property relationship. Polyvinyl alcohol (PVA) hydrogels are attractive materials for biomedical, soft robotics, and sensing applications due to their flexibility, water retention, and biocompatibility. However, achieving simultaneous improvements in mechanical strength, morphology, and swelling control remains challenging. In this study, nanocomposite PVA hydrogels were developed by incorporating calcium ions and iron oxide (Fe₂O₃) nanoparticles as reinforcing agents. The hydrogels were characterized using FE-SEM, XRD, FT-IR, swelling tests, and tensile testing. Results showed that both Ca²⁺ and Fe₂O₃ promoted network densification, as evidenced by FT-IR peak shifts and enhanced crystallinity in XRD patterns. The mean pore area decreased from 2.77 μm² in pure PVA to 0.476 μm² with Ca and 0.338 μm² with Ca + Fe₂O₃, while swelling rates reduced from 5.63 % min⁻¹ to 5.41 % min⁻¹ and 2.57 % min⁻¹, respectively. Mechanical testing revealed a 241.3 % increase in tensile strength compared with the unreinforced hydrogel. These findings demonstrate that dual reinforcement with Ca²⁺ and Fe₂O₃ produces structurally robust hydrogels with superior durability and controlled swelling, offering a practical strategy for advanced biomedical and soft robotic applications.