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

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 plus or minus 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-Mueller-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.