Bioactive nanomembranes of semiconductor polythiophene and thermoplastic polyurethane: thermal, nanostructural and nanomechanical properties

Abstract

Free-standing and supported nanomembranes have been prepared by spin-coating mixtures of a semiconducting polythiophene (P3TMA) derivative and thermoplastic polyurethane (TPU). Thermal studies of TPU:P3TMA blends with 60 : 40, 50 : 50, 40 : 60 and 20 : 80 weight ratios indicate a partial miscibility of the two components. Analysis of the glass transition temperatures allowed us to identify the highest miscibility for the blend with a 40 : 60 weight ratio, this composition being used to prepare both self-standing and supported nanomembranes. The thickness of ultra-thin films made with the 40 : 60 blend ranged from 11 to 93 nm, while the average roughness was 16.3 ± 0.8 nm. In these films the P3TMA-rich phase forms granules, which are dispersed throughout the rest of the film. Quantitative nanomechanical mapping has been used to determine the Young's modulus value by applying the Derjanguin–Müller–Toporov (DMT) contact mechanics model and the adhesion force of ultra-thin films. The modulus depends on the thickness of the films, values determined for the thicker (80–140 nm)/thinner (10–40 nm) regions of TPU, P3TMA and blend samples being 25/35 MPa, 3.5/12 GPa and 0.9/1.7 GPa, respectively. In contrast the adhesion force is homogeneous through the whole surface of the TPU and P3TMA films (average values: 7.2 and 5.0 nN, respectively), whereas for the blend it depends on the phase distribution. Thus, the adhesion force is higher for the TPU-rich domains than for the P3TMA-rich domains. Finally, the utility of the nanomembranes for tissue engineering applications has been proved by cellular proliferation assays. Results show that the blend is more active as a cellular matrix than each of the two individual polymers.