Making microporous nanometre-scale fibrous PLA aerogels with clean and reliable supercritical CO2 based approaches

Abstract

Polylactic acid (PLA) aerogels, with a multiscale structure consisting of nanometre-scale fibres and interconnected micropores, were here fabricated by a novel thermal induced phase separation (TIPS) approach. The developed process is based on a biocompatible route combining ethyl lactate (EL) as a non-toxic solvent for PLA and supercritical CO2 (scCO2) as a clean drying agent. First, PLA was dissolved in EL to prepare homogeneous solutions with a polymer concentration ranging from 3 to 5.5wt%. Subsequently, TIPS was generated by the controlled decrease of the temperature down to a temperature lower than the solution gelation point. Finally, solvent exchange, alcogel formation and scCO2 drying allowed the manufacture of the desired nanometre-scale fibrous PLA aerogels. In particular, PLA aerogels with homogeneous morphology and constituted by an overall porosity in the range of 90–95% and a specific surface area in the range of 70–95m2/g were manufactured by modulating polymer concentration in the starting EL solution, gelation temperature and EL extraction conditions. The obtained aerogels possessed a bimodal structure of fibres with a mean length of 100–200nm coupled with nanopores of a mean diameter down to 2nm. Finally, the combination of TIPS with gas foaming and porogen leaching techniques was explored as a suitable strategy to obtain multifunctional micro- and nano-sized fibrous PLA materials, suitable of providing biomimetic three-dimensional platforms for tissue engineering scaffolds.