Tuning structural relaxations, mechanical properties, and degradation timescale of PLLA during hydrolytic degradation by blending with PLCL-PEG

TL;DR

This study explores how blending PLLA with PLCL-PEG can effectively modify its mechanical properties and degradation rate, enabling tailored bioresorbable materials for medical applications with improved performance and controlled degradation times.

Contribution

It introduces a novel blending strategy with PLCL-PEG to tune PLLA's properties, providing insights into degradation mechanisms and optimizing material performance.

Findings

Degradation rate of PLLA accelerated by PLCL-PEG addition.

Low PLCL-PEG blends show enthalpy relaxation and embrittlement.

Moderate PLCL-PEG blends maintain ductility and strength.

Abstract

Poly-L-lactide (PLLA) is a popular choice for medical devices due to its bioresorbability and superior mechanical properties compared with other polymers. However, although PLLA has been investigated for use in bioresorbable cardiovascular stents, it presents application-specific limitations which hamper device therapies. These include low toughness and strength compared with metals used for this purpose, and slow degradation. Blending PLLA with novel polyethylene glycol functionalised poly(L-lactide-co-$\varepsilon$-caprolactone) (PLCL-PEG) materials has been investigated here to tailor the mechanical properties and degradation behaviour of PLLA. This exciting approach provides a foundation for a next generation of bioresorbable materials whose properties can be rapidly tuned. The degradation of PLLA was significantly accelerated by addition of PLCL-PEG. After 30 days of degradation, several structural changes were observed in the polymer blends, which were dependent on the level of PLCL-PEG addition. Blends with low PLCL-PEG content displayed enthalpy relaxation, resulting in embrittlement, while blends with high PLCL-PEG content displayed crystallisation, due to enhanced chain mobility brought on by chain scission, also causing embrittlement. Moderate PLCL-PEG additions (10% PLCL(70:30)-PEG and 20 - 30% PLCL(80:20)-PEG) stabilised the structure, reducing the extent of enthalpy relaxation and crystallisation and thus retaining ductility. Compositional optimisation identified a sweet spot for this blend strategy, whereby the ductility was enhanced while maintaining strength. Our results indicate that blending PLLA with PLCL-PEG provides an effective method of tuning the degradation timescale and mechanical properties of PLLA, and provides important new insight into the mechanisms of structural relaxations that occur during degradation, and strategies for regulating these.