Development of poly (lactic-co-glycolic acid) (PLGA) based implants using hot melt extrusion (HME) for sustained release of drugs: The impacts of PLGA's material characteristics.

Hot melt extrusion (HME) processed Poly (lactic-co-glycolic acid) (PLGA) implant is one of the commercialized drug delivery products, which has solid, well-designed shape and rigid structures that afford efficient locoregional drug delivery on the spot of interest for months. In general, there are a variety of material, processing, and physiological factors that impact the degradation rates of PLGA-based implants and concurrent drug release kinetics. The objective of this study was to investigate the impacts of PLGA's material characteristics on PLGA degradation and subsequent drug release behavior from the implants. Three model drugs (Dexamethasone, Carbamazepine, and Metformin hydrochloride) with different water solubility and property were formulated with different grades of PLGAs possessing distinct co-polymer ratios, molecular weights, end groups, and levels of residual monomer (high/Viatel and low/ Viatel Ultrapure). Physicochemical characterizations revealed that the plasticity of PLGA was inversely proportional to its molecular weight; moreover, the residual monomer could impose a plasticizing effect on PLGA, which increased its thermal plasticity and enhanced its thermal processability. Although the morphology and microstructure of the implants were affected by many factors, such as processing parameters, polymer and drug particle size and distribution, polymer properties and polymer-drug interactions, implants prepared with Viatel PLGA showed a smoother surface and a stronger PLGA-drug intimacy than the implants with Viatel Ultrapure PLGA, due to the higher plasticity of the Viatel PLGA. Subsequently, the implants with Viatel PLGA exhibited less burst release than implants with Viatel Ultrapure PLGA, however, their onset and progress of the lag and substantial release phases were shorter and faster than the Viatel Ultrapure PLGA-based implants, owing to the residual monomer accelerated the water diffusion and autocatalyzed PLGA hydrolysis. Even though the drug release profiles were also influenced by other factors, such as composition, drug properties and polymer-drug interaction, all three cases revealed that the residual monomer accelerated the swelling and degradation of PLGA and impaired the implant's integrity, which could negatively affect the subsequent drug release behavior and performance of the implants. These results provided insights to formulators on rational PLGA implant design and polymer selection.