Staff member publications
Development of smart functionalized materials for tissue engineering has attracted significant attention in recent years. In this work we have functionalized a free-standing film of isotactic polypropylene (i-PP), a synthetic polymer that is typically used for biomedical applications (e.g. fabrication of implants), for engineering a 3D all-polymer flexible interface that enhances cell proliferation by a factor of ca. three. A hierarchical construction process consisting of three steps was engineered as follows: (1) functionalization of i-PP by applying a plasma treatment, resulting in i-PPf; (2) i-PPf surface coating with a layer of polyhydroxymethy-3,4-ethylenedioxythiophene nanoparticles (PHMeEDOT NPs) by in situ chemical oxidative polymerization of HMeEDOT; and (3) deposition on the previously activated and PHMeEDOT NPs coated i-PP film (i-PPf/NP) of a graft conjugated copolymer, having a poly(3,4-ethylenedioxythiophene) (PEDOT) backbone, and randomly distributed short poly(ε-caprolactone) (PCL) side chains (PEDOT-g-PCL), as a coating layer of ∼9 μm in thickness. The properties of the resulting bioplatform, which can be defined as a robust macroscopic composite coated with a “molecular composite”, were investigated in detail, and both adhesion and proliferation of two human cell lines have been evaluated, as well. The results demonstrate that the incorporation of the PEDOT-g-PCL layer significantly improves cell attachment and cell growth not only when compared to i-PP but also with respect to the same platform coated with only PEDOT, constructed in a similar manner, as a control.
A fundamental feature of multicellular organisms is their ability to self-repair wounds through the movement of epithelial cells into the damaged area. This collective cellular movement is commonly attributed to a combination of cell crawling and 'purse-string' contraction of a supracellular actomyosin ring. Here we show by direct experimental measurement that these two mechanisms are insufficient to explain force patterns observed during wound closure. At early stages of the process, leading actin protrusions generate traction forces that point away from the wound, showing that wound closure is initially driven by cell crawling. At later stages, we observed unanticipated patterns of traction forces pointing towards the wound. Such patterns have strong force components that are both radial and tangential to the wound. We show that these force components arise from tensions transmitted by a heterogeneous actomyosin ring to the underlying substrate through focal adhesions. The structural and mechanical organization reported here provides cells with a mechanism to close the wound by cooperatively compressing the underlying substrate.
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-Muller-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.
We report on the development of micro/nanofabrication processes to create hierarchical surface topographies that expand from 50 nm to microns in size on different materials. Three different approaches (named FIB1, FIB2, and EBL) that combine a variety of techniques such as photolithography, reactive ion etching, focused ion beam lithography, electron beam lithography, and soft lithography were developed, each one providing different advantages and disadvantages. The EBL approach was employed to fabricate substrates comprising channels with features between 200 nm and 10 Î¼m in size on polymethylmethacrylate (PMMA), which were then used to investigate the independent or competitive effects of micro- and nanotopographies on cell adhesion and morphology. Rat mesenchymal stem cells (rMSCs) were cultured on four different substrates including 10 Î¼m wide and 500 nm deep channels separated by 10 Î¼m distances (MICRO), 200 nm wide and 100 nm deep nanochannels separated by 200 nm distances (NANO), their combination in parallel (PARAL), and in a perpendicular direction (PERP). Rat MSCs behaved differently on all tested substrates with a high degree of alignment (as measured by both number of aligned cells and average angle) on both NANO and MICRO. Furthermore, cells exhibited the highest level of alignment on PARAL, suggesting a synergetic effect of the two scales of topographies. On the other hand, cells on PERP exhibited the lowest alignment and a consistent change in morphology over time that seemed to be the result of interactions with both micro- and nanochannels positioned in the perpendicular direction, also suggesting a competitive effect of the topographies.
Shan, X., Díez-Pérez, I., Wang, L., Wiktor, P., Gu, Y., Zhang, L., Wang, W., Lu, J., Wang, S., Gong, Q., Li, J., Tao, N., (2012). Imaging the electrocatalytic activity of single nanoparticles Nature Nanotechnology , 7, (10), 668-672
The electrocatalytic properties of nanoparticles depend on their size, shape and composition. These properties are typically probed by measuring the total electrocatalytic reaction current of a large number of nanoparticles, but this approach is time-consuming and can only measure the average catalytic activity of the nanoparticles under study. However, the identification of new catalysts requires the ability to rapidly measure the properties of nanoparticles synthesized under various conditions and, ideally, to measure the electrocatalytic activity of individual nanoparticles. Here, we show that a plasmonic-based electrochemical current-imaging technique can simultaneously image and quantify the electrocatalytic reactions of an array of 1.6Â Ã—Â 10 5 platinum nanoparticles printed on an electrode surface, which could facilitate high-throughput screening of the catalytic activities of nanoparticles. We also show that the approach can be used to image the electrocatalytic reaction current and measure the cyclic voltammograms of single nanoparticles.