Biodegradable synthetic polymers for biomedical and tissue engineering applications: tailoring degradation kinetics...

The adoption of biodegradable synthetic polymers in biomedical and tissue engineering becomes a focal point, offering alternative solutions to organ transplantation and conventional permanent restoration. The key principle in developing scaffold-based for physiological implantation is the synchronisation of polymer's degradation kinetics with the regeneration timeline of host tissues. Different implantation lesions exhibit vastly different healing durations, ranging from a few weeks to several months or years. A mismatch timeline can be detrimental where premature degradation will remove the physical framework needed for cell integration, whereas overly slow degradation will restrict spaces for new tissue growth. This review study provides a comprehensive discussion on the degradation mechanisms of biodegradable synthetic polymers in physiological environments. Four widely studied polymers-polylactic acid (PLA), polyvinyl alcohol (PVA), polycaprolactone (PCL), and polyurethane (PU)-were reviewed in depth on the degradation mechanisms and influencing factors. Scientific experimental data from the previous studies were summarised, including degradation percentage, experimental conditions, degradation timeline, and estimated complete degradation period. Specifically, four degradation mechanisms are associated with the degradation of synthetic polymers in physiological environments including chemical hydrolysis, enzymatic-mediated metabolism, oxidative degradation, and pH-dependent degradation. Each of the mechanisms may act independently or synergistically under different biological conditions. The degradation of polymers is accordingly influenced by the chemical structures, fabrication routes, degradation pathways, and physicochemical factors. These data are correlated with their optimal use in biomedical and TE applications for fast regenerating tissues to slow-healing or load-bearing structures. Comprehensively, PVA is aligned well with short-to-intermediate healing tissues such as the skin and the cornea due to its high degradation capability, while PLA, PCL, and PU that degrade from weeks to years are suitable for mediate-healing soft tissues to long-term implantations such as load-bearing bone, cartilage, ligament, neural, and vascular implantations. By aligning polymer degradation profiles with the biological timelines of tissue regeneration, this review provides a translational framework for synthetic polymer selection to enable optimum scaffold's functionalities and clinical outcomes.