3D-printed scaffolds use shape memory to heal infected bone defects

Infected bone defects arise in conditions such as osteomyelitis and post-traumatic bone infections, where microbial persistence and immune imbalance prevent effective healing. Standard treatments rely heavily on surgical debridement and high-dose antibiotics, but these methods face growing challenges from antibiotic resistance, cytotoxicity, and incomplete defect filling. Conventional bone graft materials often lack the ability to conform to dynamically changing defect geometries and cannot actively regulate infection-driven inflammation. Moreover, excessive pro-inflammatory macrophage responses suppress osteogenic differentiation, further hindering repair. Based on these challenges, there is a critical need to develop advanced biomaterials capable of adapting to complex defect shapes while sequentially controlling infection, inflammation, and bone regeneration.

Researchers from Chongqing Medical University and Chengdu University in China reported their findings in Burns & Trauma, published (DOI: 10.1093/burnst/tkaf072) online in 2025. The team developed a body-temperature-responsive, 3D-printed shape-memory scaffold coated with a metal-polyphenol network to treat infectious bone defects. Using a combination of low-temperature 3D printing and surface biofunctionalization, the scaffold was designed to adapt to irregular bone defects while providing antibacterial activity, immune regulation, and osteogenic support. The study demonstrates both in vitro and in vivo efficacy in controlling infection and promoting bone regeneration.

The newly developed scaffold is composed of a biodegradable shape-memory polymer blended with citric acid-modified hydroxyapatite, producing a porous structure that closely mimics cancellous bone. At physiological temperature (37 °C), the scaffold rapidly recovers its original shape, allowing it to tightly fill irregular bone defects and improve mechanical integration after implantation. This adaptive behavior directly addresses the mismatch issues common in traditional rigid implants.

To combat infection, the scaffold surface is coated with a tannic acid-magnesium metal-polyphenol network. This coating exhibits strong antibacterial activity against common pathogens, including Staphylococcus aureus and Escherichia coli, while enabling pH-responsive release in acidic, infection-associated microenvironments. Beyond pathogen clearance, the coating also plays a crucial immunomodulatory role by shifting macrophage polarization away from a pro-inflammatory state and toward a regenerative phenotype.

Importantly, the scaffold supports robust osteogenic differentiation. Enhanced mineral deposition, elevated alkaline phosphatase activity, and increased calcium nodule formation were observed in stem cell cultures. In an infected rat bone defect model, the scaffold significantly reduced bacterial burden, suppressed inflammatory cytokines, and promoted new bone formation, as confirmed by micro-CT and histological analyses. Together, these results demonstrate a coordinated, multi-stage healing process driven by a single intelligent implant.

"This work represents a major step forward in the treatment of infected bone defects," said one of the senior investigators involved in the study. "Instead of relying on separate interventions for infection control and bone regeneration, we designed a scaffold that adapts to the defect, clears bacteria, regulates the immune response, and actively supports new bone growth. The ability to respond to body temperature and the local inflammatory environment makes this system especially attractive for complex clinical cases where conventional implants are insufficient."

The shape-memory, bioactive scaffold offers broad potential for clinical translation in orthopedic trauma, chronic osteomyelitis, and revision surgeries following implant-related infections. By reducing dependence on high-dose antibiotics and improving defect integration, this approach may lower complication rates and accelerate patient recovery. Beyond bone repair, the design principles demonstrated in this study—combining structural adaptability with environment-responsive bioactivity—could be extended to other regenerative applications, including soft tissue repair and implantable drug-delivery systems. As smart biomaterials continue to evolve, such multifunctional scaffolds may redefine how clinicians manage complex, infection-compromised tissue regeneration.