Biodegradability assessment of engineered model polymeric microparticles

Non-biodegradable polymeric microparticles (PMP) with a diameter < 5 mm are a serious threat to the environment and human health due to their increased prevalence. Biodegradable polymers such as polylactic acid (PLA), polybutylene succinate (PBS), and polycaprolactone (PCL) have been developed in the last decade as alternatives. These polymers have shown various degrees of biodegradation as films. Only a limited number of studies have examined whether they retain their degradation properties when converted into PMP, despite the upcoming changes in regulation for formulated products containing such PMP. The biodegradation of polymers consists of three important steps: (1) Biodeterioration, which is the modification of mechanical, chemical, and physical properties of the polymer due to the growth of microorganisms on or inside the surface of the polymers. (2) Biofragmentation, which is the conversion of polymers to oligomers and monomers and (3) Assimilation, where microorganisms are supplied by necessary carbon from the fragmentation of polymers and converted to CO2, water and biomass. This study aims to develop an in-vitro method for characterising the degradation of PMP using an enzyme, which can be applied to different systems to understand the ability of PMP to degrade in specific environments. PMPs, engineered using a solvent extraction method, were used as a model system and placed within an environment containing a microbial enzyme (lipase). PMPs have been engineered using three types of biodegradable polymers: polycaprolactone (PCL), poly (D, L-lactide-co-glycolide) – (PLGA), and poly[(R)-3-hydroxybutyric acid] – (PHB). An array of characterisation techniques (e.g. particle size distribution, transmitted light microscopy, and scanning electron microscopy imaging) is used to monitor the PMP’s physical and biological degradation characteristics as a function of time when placed within an environment containing a microbial enzyme. The PMPs were degraded using two methods by: 1) monitoring the release of fatty acid during degradation using a pH stat (related to stage 2 of the biodegradation process). The hypothesis is that at this stage, we can monitor the breakdown of hydrolysable bonds and expect to observe an increase in the amount of acid released as a function of time. Although the pH stat is widely used to for digestion studies (Mat et al., 2016), it is not used/seldom used in measuring biodegradability. 2) To study the production of carbon dioxide during degradation by measuring pressure, which is then used to calculate the amount of CO2 removed by the base in the instrument sleeve. This will allow to understand the secondary products of the biodegradation process, representing the final stage 3 of biodegradation i.e. the conversion of PMPs into CO2, water and biomass (Emadian et al., 2017). The hypothesis is that at this stage we expect to observe an increase of CO2 production as a function of time. By combining both acid release and CO2 production studies, a more complete understanding of the degradation behaviour of polymeric PMPs can be obtained.