Introduction:
Regenerative medicine in orthopedic surgery demands advanced materials capable of mimicking the dynamic properties of native tissues. Hydrogels based on collagen, a natural extracellular matrix component, and polyvinylpyrrolidone (PVP), a versatile synthetic polymer, provide a unique combination of biocompatibility and mechanical stability. This project focuses on developing functional hydrogels using 4D printing technology to address the challenges of tissue repair in orthopedic applications.

Methods:
Collagen–PVP hydrogels were synthesized using collagen (5% w/v) and PVP (10% w/v) to form a hybrid polymer network with tunable mechanical and biological properties. Scaffolds were fabricated using 4D printing, enabling stimuli-responsive behaviors such as shape-memory and swelling. Mechanical testing revealed a compression modulus, and the swelling capacity reached from 150 ± 25% to 375 ± 25% in physiological conditions. Biodegradation analysis indicated a 15% mass loss over 30 days. Cellular studies using osteoblasts and chondrocytes assessed biocompatibility (>90% cell viability after 7 days) and differentiation.

Results:
The collagen–PVP hydrogels demonstrated excellent mechanical strength and elasticity, suitable for load-bearing orthopedic applications. The 4D-printed scaffolds exhibited dynamic shape adaptation in response to temperature and hydration changes. Cellular studies confirmed high biocompatibility, with a significant proliferation and differentiation of osteoblasts and chondrocytes. The hybrid hydrogels also showed controlled degradation profiles, aligning with tissue healing timelines.

Conclusions:
Collagen–PVP hydrogels fabricated using 4D printing represent a promising solution for orthopedic regenerative applications. Their combination of adaptability, biocompatibility, and mechanical performance positions them as advanced materials for cartilage and bone repair. Further studies will focus on in vivo evaluations and the integration of bioactive agents to enhance therapeutic outcomes.

Acknowledgments: This research was carried out within the SMART-MAT Functional Materials Scientific Club of the Faculty of Materials Engineering and Physics at Cracow University of Technology and as part of the project entitled "Functional Hydrogels Fabricated Using 4D Printing" financed by the FutureLab organization operating at Cracow University of Technology.