From Material Properties to Clinical Potential: Natural vs.Synthetic Polymers as API Carriers

Polymeric carriers are pivotal in modern drug delivery, enabling controlled release, enhanced stability and targeted transport of active pharmaceutical ingredients (APIs). This narrative review compares natural, semi-synthetic and synthetic polymers as API carriers based on their physicochemical and biological properties in order to assess their potential for preclinical and clinical development.Natural polymers (e.g., chitosan (CS), alginate, hyaluronic acid, poly(3-hydroxybutyrate)) offer exceptional biocompatibility, biodegradability and inherent bioactivity. However, their clinical translation is frequently hindered by batch-to-batch variability, potential immunogenicity and limited mechanical strength. On the other hand, synthetic polymers (e.g., poly(lactic-co-glycolic acid) (PLGA), polyethylene glycol (PEG), polylactic acid (PLA)) provide a tunable degradation kinetics, a precise molecular architecture and ahigh reproducibility. In this narrative review we try to evaluate how crucial physicochemical parameters, including molecular weight, biological properties, pharmacokinetics, degradation mechanisms and stability directly influence API release. While natural polymers offer un-matched bioactivity and biocompatibility, synthetic polymers excel in structural precision and reproducibility. Most evidence discussed comes from in vitro and animal studies and the conclusions therefore concern the potential of the carriers for further clinical development. The review does not assess clinical efficacy. It seems that harnessing the synergy between those two distinct classes holds the key to modern medical approaches focused on improving the pharmacological properties of drugs and ensuring their prolonged release through the use of polymeric carriers.