In vitro models of biological barriers (e.g., lung epithelium, intestinal epithelium) provide an important benchmark for studying the physiopathological processes (e.g., nutrient and metabolite exchange, interactions with external virus or bacteria) involved in the development of several diseases (e.g., respiratory tract infections, carcinomas). These models represent a reliable platform for a more rapid identification of the most customizable pharmaceutical therapies for their treatment.
Producing sustainable in vitro models obtained from solvents and biopolymers derived from industrial by-products add an important value to this underestimated source of valuable (bio)materials. This works aims at demonstrating the suitability of processing together solvents derived from levulinic acid (LA) (extracted from biomasses) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) (synthesized by bacteria strains and whose production is facilitated by LA) to produce electrospun membranes as proof-of-concept of sustainable, engineered biological barrier fully derived from LA as starting feedstock.
Preliminary experiments were performed to identify the most suitable LA-derived solvents (ɤ-valerolactone, 2-methyltetrahydrofuran, methyl ethyl ketone, methyl and ethyl levulinate) and PHBV concentration for obtaining homogenous solutions processable by electrospinning. To enhance the solubility of PHBV in the LA-derivative solvents, formic acid (FA) (co-product of LA industrial synthesis) was added at various volume ratios obtaining binary solvents. Among the tested solutions, PHBV (200 mg mL-1) in MEK/FA (volume ratio 50:50) was the most suitable for the goal of this work.
The electrospinning process was further improved by identifying the optimal process parameters (e.g., applied voltage, spinneret-collector distance, flow rate), and a customized heating system to maintain the PHBV solution in MEK/FA in liquid phase (at 60 °C) was designed and developed on purpose. Self-supporting and microporous mats with micropore size comprises between 1-7 µm were successfully electrospun. These mats show irregular and flat fibers that are partially fused due to not complete evaporation of MEK/FA solvent. Moreover, these mats show an average elastic modulus of 75 MPa and an hydrophobic contact angle of 115° comparable to other electrospun PHBV mats reported in literature [1,2]. Cell experiments demonstrated that the developed fibrous PHBV mats do not negatively alter cell viability of A549 adenocarcinomic human alveolar basal epithelial cells which adhere and proliferate on the surface of the PHBV mats forming a confluent monolayer of epithelial cells after 48 h.
Globally, these results show for the first time the great potential of converting sustainable solvents and biopolymers, both derived from LA as starting feedstock, into added-value microporous membranes which can potentially be used as sustainable in vitro models of biological barriers.
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 A Bianco et al. Mater. Sci. Eng. C 33, 1067–1077 (2013).