ABSTRACT
During the past two decades the development of drug delivery systems (DDSs) has been a revolutionary cue for the advancement of conventional approaches of drug administration in medicine and thus has opened new frontiers such as micromedicine and nanomedicine. These frontiers encompass therapeutic, diagnostic, as well as theranostic approaches and have witnessed seminal growth in the recent past [1]. Micro-/nanotechnology that enables the fabrication of fine and ultrafine structures (e.g., particles, fibers, wires, etc., on
the nanom eter scale) using diverse materials has played a pivotal role in the development of these frontier areas. The success of micro-/nanomedicine is governed to a great extent by the availability of polymeric m aterial which can be used for human applications. Till date, multiple polymeric m aterials have been approved by the United States Food and Drug Administration (US FDA) [2] for their application as DDSs, which largely include polyesters, polyacrylates, polyanhydrides, polyamides, and polycarbonates. Among these, polyesters represent a major class where multiple polyester-based DDSs have been approved by the US FDA for application in humans [3, 4], including polylactic acid (PLA), polyglycolic acid (PGA), polylacticco-glycolic acid (PLGA), polydioxanone, polycaprolactone (PCL), and poly(trimethyl carbonate) [3, 5, 67]. Further, the potential of polyester-based polymers as versatile DDSs has been demonstrated by their ability to encapsulate diverse therapeutic molecules/cargo (e.g., synthetic drugs, proteins, or deoxyribonucleic acid [DNA]) inside the polymer matrix [8, 9]. In contrast to the administration of a free drug, encapsulation of a drug inside polyester-based particulate DDSs not only ensures its protection in hostile environments and desirable release kinetics, but can also improve its bioavailability and thus facilitate high payload delivery [2]. Currently there are more than 10 polyester-based DDSs available commercially in the m arket [9]. For example, two of the PLGA-based DDSs are Zoladex® (PLGA/goserelin acetate), which is used for the treatm ent of prostate cancer, and Lupron Depot® (PLGA/leuprolide acetate), which is used for the treatm ent o f prostate cancer and endometriosis [10]. Due to their desirable properties, polyester-based m aterials show high potential for the development of future DDSs employing DNA, small interfering ribonucleic acid (siRNA), messenger ribonucleic acid (mRNA), aptamer, and other novel synthetic/peptide-based therapeutic molecules. While existing polyester-based DDSs have shown good success, innovations in polymer chemistry combined with the discovery of novel therapeutic molecules are continuously fueling the development of newer biodegradable, biocompatible, tissue-specific, stimuli-responsive (pH, temperature, pressure, light, ionic concentration, and catalytic based) polyester-based DDSs [11].
