Hybrid Chitosan/PCL Shape Memory Scaffolds – A Novel Approach for Bone Regeneration and Infection Prevention
The treatment of complex bone defects, particularly in the cranio-maxillofacial region, remains a major clinical challenge. Autologous grafts are considered the gold standard, but they are associated with limitations such as resorption, insufficient fit, and infection risks.
Synthetic materials such as bone cements or putty masses often fail to convince as well, since they cannot be adequately adapted to complex defects, exhibit low porosity, and tend to be brittle. In addition, implants carry the risk of microbial biofilm formation on their surface, which is difficult to treat and may ultimately necessitate explantation.
Shape memory polymer (SMP) scaffolds based on poly(ε-caprolactone) (PCL) have gained attention in recent years as an innovative alternative. They can be softened by heating, press-fitted into the defect, and then hardened again upon cooling, allowing for a customized fit without additional shaping. PCL also provides mechanical stability within the range of trabecular bone. However, its slow degradation rate and lack of antimicrobial properties remain significant limitations.
Chitosan as a Key Component
To overcome these weaknesses, a recent study by Dixon et al. (2025) integrated chitosan as a complementary component. The researchers used chitosan powder with a molecular weight of approximately 15 kg mol⁻¹ and a degree of deacetylation of 86 %, determined by ¹H-NMR.
Chitosan is a biopolymer derived from chitin and is characterized by biocompatibility, biodegradability, antimicrobial activity, and its ability to promote cell adhesion and proliferation. Combining PCL with chitosan therefore enables the development of stable, shape-memory scaffolds with enhanced biological functionality and additional infection protection.
Fabrication of the Hybrid Scaffolds
The researchers developed semi-interpenetrating networks (semi-IPNs) consisting of PCL-diacrylate and chitosan-graft-PCL copolymers. The copolymers were synthesized via ring-opening polymerization of ε-caprolactone onto the chitosan backbone. Depending on the composition, the scaffolds contained between 0.8 and 7 wt% chitosan. Using the solvent-cast particulate leaching (SCPL) method, highly porous structures were fabricated with an average pore size of about 240 μm. This pore size is considered optimal for promoting cell infiltration and bone tissue ingrowth.
Results
Despite a reduction in PCL crystallinity, the hybrid scaffolds retained excellent shape memory properties. They could be deformed upon heating, fitted into model defects, and reliably recovered their original shape upon cooling.
Mechanical properties
With a compressive modulus of about 6 MPa and a compressive strength of approximately 31 MPa, the values were within the range of trabecular bone. The materials also exhibited high toughness and did not fracture in a brittle manner under load.
Surface properties
Even small amounts of chitosan markedly improved hydrophilicity. While pure PCL scaffolds remained hydrophobic, hybrid scaffolds with ≥2.5% chitosan showed significantly reduced water contact angles. This increase in wettability was accompanied by higher water uptake, which in turn accelerated degradation. Scaffolds with higher chitosan content degraded significantly faster than pure PCL controls - an advantage for osseointegration.
Antimicrobial effects
At chitosan contents as low as 0.8%, a significant reduction in Candida albicans biofilm formation was observed. With higher concentrations, this effect increased further. Moreover, the leachates released from the scaffolds also strongly inhibited biofilm formation in the surrounding medium, demonstrating that both the scaffold surface and released chitosan contributed to antimicrobial activity.
Discussion
These results highlight that hybridizing PCL with chitosan creates a powerful platform for bone regeneration. The combination of shape memory behavior, mechanical stability, improved hydrophilicity, controlled degradation, and antimicrobial activity is unique.
The scaffolds can be provided as pre-fabricated implants, which are heated during surgery, molded to fit the defect, and then harden at body temperature, maintaining their shape while simultaneously supporting healing through their biological functionality.
However, further preclinical studies are necessary to assess biocompatibility and long-term behavior in animal models. Nonetheless, the current findings already demonstrate that these hybrid scaffolds hold the potential to transform regenerative surgery and improve the treatment of patients with complex bone defects.
Conclusion
The work of Dixon et al. represents a major step forward in the development of multifunctional biomaterials. By combining PCL and chitosan, the researchers successfully created shape-memory scaffolds that are mechanically robust, bioactive, and antimicrobial. This innovation opens new perspectives for “off-the-shelf” implants that can be applied flexibly and actively support the healing process.
Reference
Dixon, D. T.; Shields, A. G.; Stafslien, S. J.; Vander Wal, L.; Grunlan, M. A. Hybrid Chitosan/PCL Shape Memory Scaffolds with Potential for Bone Regeneration and Infection Resistance. ACS Biomater. Sci. Eng. 2025. https://doi.org/10.1021/acsbiomaterials.5c01160
First published on 28th of August 2025
Revised on 28th of August 2025