PLA-based functionally graded laminates for tunable controlled release of carvacrol obtained by combining electrospinning with solvent casting

A novel approach was designed to fabricate high-added value manufacts, starting from cost-effective materials and combining well-known processing techniques. Bi- and three-layered, functionally graded laminates were achieved by direct electrospinning onto dense substrates. The architecture of each multilayer comprises a dense layer formed by solvent casting, which is constituted by polylactic acid (PLA) and carvacrol, and one or two electrospun fibrous skin layers, consisting of PLA only. Processing-structure-properties relationships of such materials were investigated. As regards mechanical behavior, the amount of fibrous PLA layers determined an increase of stiffness from 20 to 35 MPa, adequately predicted by isostrain model, whereas the breaking properties proved to be governed by the dense layer, with values of tensile strength (6 MPa) and elongation at break (200%) almost ten-folded with respect to those of electrospun fibrous PLA. As concerns carvacrol release behavior, the presence of fibrous skin, especially in three-layered structures, proved to progressively reduce the burst delivery at early stage of immersion, while enhancing the depletion time, i.e. the release activity, of such devices from 288 to 795 h. Furthermore, a correlation was found between the thickness of fibrous layers and release kinetics, thus suggesting that adjusting simple variables, such as electrospinning time, allows to control the ultimate properties of these devices. Moreover, this approach enables gathering the mechanical robustness of a dense film with the extremely large specific area of fibrous materials, thus showing promising potential for a broad range of application fields.