Tuning physical and chemical attributes of the synthetic implant poly(L-lactic acid) and its effects on biological stimulation

Abstract: Poly(lactic acid) (PLA) is a polymer chain consisting of repeating units of lactic acid (LA) used in various biomedical applications because of its biocompatible features. It is commonly used as a subdermal filler and constitutes as the main ingredient in SculptraR, which is a collagen regenerating filler used to treat lipoatrophy of the cheeks or to rejuvenate the skin. The presence of macrophages triggers a foreign body reaction in response to PLA, which in turn prompts fibroblasts to gradually increase collagen fibers in the dermis. This literature study investigates how physical properties such as Mw, morphology, stereochemistry as well as chemical properties, influence the biological response and degradation of PLA. Additionally, a comparison of other bio stimulants, substituents and copolymers were performed. The aim of this study was constructed in collaboration with Galderma. All aspects that were taken into consideration affected the biological response and degradation to some extent. The degradation of the PLLA microspheres has a noticeable correlation to the biological immune response. An increase in the Mw and degree of crystallinity results in a decrease in degradation rate. Morphology greatly influences the immune response and particle size is vital for the degradation as well as biostimulation. The most suitable stereoisomer of PLA is the (L)-form based on both biological response and degradation. Decomposition of PLLA varies depending on the Mw which is affected by the pH of the surrounding environment. Compared to other substances used in biodegradable products, PLLA is regarded as the most auspicious for a durable result. PDLLA has desirable biological responses but is degraded too fast. PDLA is not suitable as a dermal filler due to its inflammatory response and bad collagen regeneration.