Multiscale modelling for the heterogeneous strength of biodegradable polyesters

Durability of Biodegradable Polymer Nanocomposites

Biodegradable polymers (BP) are often regarded as the materials of the future, which address the rising environmental concerns. The advancement of biorefineries and sustainable technologies has yielded various BP with excellent properties comparable to commodity plastics. Water resistance, high dimensional stability, processability and excellent physicochemical properties limit the reviewed materials to biodegradable polyesters and modified compositions of starch and cellulose, both known for their abundance and relatively low price. The addition of different nanofillers and preparation of polymer nanocomposites can effectively improve BP with controlled functional properties and change the rate of degradation. The lack of data on the durability of biodegradable polymer nanocomposites (BPN) has been the motivation for the current review that summarizes recent literature data on environmental ageing of BPN and the role of nanofillers, their basic engineering properties and potential applications. Various durability tests discussed thermal ageing, photo-oxidative ageing, water absorption, hygrothermal ageing and creep testing. It was discussed that incorporating nanofillers into BP could attenuate the loss of mechanical properties and improve durability. Although, in the case of poor dispersion, the addition of the nanofillers can lead to even faster degradation, depending on the structural integrity and the state of interfacial adhesion. Selected models that describe the durability performance of BPN were considered in the review. These can be applied as a practical tool to design BPN with tailored property degradationand durability.

Mechanical and hydrolytic properties of thin polylactic acid films by fused filament fabrication

Thin polymeric films are widely used as medical applications such as cell culture, stent, drug delivery and mechanical fixation. One of the most commonly used materials is polylactic acid (PLA) - a material, which is non-toxic, biodegradable and biocompatible. Fused filament fabrication (FFF) is a preferable additive manufacturing technique to manufacture polymers, where PLA is one of the most common materials. FFF is a promising technique for customised biomedical applications due to its relatively low cost and geometrical flexibility where biomedical applications are patient tailored. This study is the first to consider FFF monolayered thin films of PLA in terms of mechanical and hydrolytic properties at 37 °C in vitro degradation. Throughout degradation, the reduction in mechanical properties was examined by analysing molecular weight and thermal properties. FFF monolayered PLA underwent autocatalytic bulk degradation with no proof of significant mass loss. Young's modulus, ultimate tensile strength and molecular weight reduced by approximately 60%, 86%, and 80% after 280 days, respectively, while the degree of crystallinity increased by 143% in comparison to benchmark thin films at day 0. It was found that the decrease in mechanical properties was more sensitive to the increase in crystallinity in the early stage of the degradation, while the molecular weight was more dominant in the late stage of the degradation. This study provides practical information in terms of mechanical properties to support medical device designers in a range of potential end-use biomedical applications to achieve safe functional products over the required degradation lifetime.