Poly(ε-caprolactone) and poly(lactic acid) in implantable applications: From biodegradable polymers to emerging vitrimer nanocomposites.

Poly(ε-caprolactone) (PCL) and poly(lactic acid) (PLA) are widely used biodegradable polyesters for orthopaedic fixation, craniofacial reconstruction, soft-tissue scaffolds, and drug delivery because of their biocompatibility, processability, and tuneable degradation. However, their chemically static structures lack dynamic bond exchange, limiting adaptation after implantation, damage recovery, and integration of structural performance with degradation and biological functionality. Dynamic covalent networks, especially vitrimers, can introduce such adaptability through exchange reactions that enable stress relaxation, reprocessability, welding, self-healing, and reshaping while maintaining dimensional stability. This review critically examines the progression of PCL- and PLA-based implant materials from conventional biodegradable polyesters to emerging vitrimer nanocomposites, with emphasis on degradation behaviour, mechanical design, and biomedical applications. It further analyses recent developments in dynamic covalent networks and vitrimer chemistries, linking exchange mechanisms to thermomechanical performance and functional behaviour. Unlike existing reviews, this work establishes a systematic framework integrating dynamic covalent network chemistry, nanoparticle-mediated interfacial effects, and implant performance, thereby providing design considerations for next-generation biodegradable vitrimer nanocomposites. The emerging role of nanoparticles (NPs) as vitrimer nanofillers is considered, particularly their ability to provide reinforcement, influence relaxation kinetics and interfacial interactions, and enable stimuli-responsive behaviour. Because PCL- and PLA-based vitrimer nanocomposites remain insufficiently explored, this review goes beyond summarizing existing studies by identifying transferable design principles from epoxy-, polyurethane-, and other dynamic nanocomposite systems to guide their future development. Finally, key challenges related to NP effects, degradability, biocompatibility, and long-term stability under physiologically relevant conditions, as well as barriers to clinical translation, are highlighted.