Silvia Taccola

Toward a New Generation of Electrically Controllable Hygromorphic Soft Actuators

An innovative processing strategy for fabricating soft structures that possess electric- and humidity-driven active/passive actuation capabilities along with touch- and humidity-sensing properties is reported. The intrinsically multifunctional material comprises an active thin layer of poly(3,4-ethylenedioxythiophene):poly-(styrene sulfonate) in a double-layered structure with a silicone elastomer and provides an opportunity toward developing a new class of smart structures for soft robotics.

Microwrinkled Conducting Polymer Interface for Anisotropic Multicellular Alignment

Surfaces with controlled micro and nanoscale topographical cues are useful as smart scaffolds and biointerfaces for cell culture. Recently, use of thin-film and surface wrinkling is emerging as a rapid unconventional method for preparing topographically patterned surfaces, especially suited for the production of smart patterns over large area surfaces. On the other hand, there is an increasing interest in employing conducting polymers as soft, biocompatible, conductive biointerfaces or as parts of bioelectronic devices. A novel convenient and versatile method is presented for producing anisotropic topographical cues at the micro- and nanoscale on conducting polymer surfaces. Micro and nanowrinkles were formed during the heat-shrinking process of a thermo-retractable polystyrene substrate. Surface wrinkling was due to the mismatch between the mechanical properties of a conducting polymer ultrathin film and the substrate. Various geometries of wrinkled structures were prepared, demonstrating the tunability of topography depending on the thickness of the conductive film. A method for patterning the conductive properties of the wrinkled substrates was also presented. Such surfaces acted as smart scaffolds for the functional alignment of cells, envisioning their electrical stimulation. Cell adhesion and proliferation were evaluated, comparing different topographies, and a preferential anisotropic alignment of C2C12 murine skeletal muscle cells along wrinkles was demonstrated. The observed trends were also confirmed concerning the formation of aligned myotubes in C2C12 differentiation stage. Furthermore, improved results in terms of aligned and mature myotube formation were obtained by co-culturing C2C12 cells with a fibroblasts feeder layer. The combination of living cells and tunable conductive nanowrinkles will represent a unique tool for the development of innovative biomedical devices.

Characterization of Free-Standing PEDOT:PSS/Iron Oxide Nanoparticle Composite Thin Films and Application As Conformable Humidity Sensors

In this study, a new simple, fast, and inexpensive technique for the preparation of free-standing nanocomposite ultrathin films based on the conductive polymer poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) and embedding iron oxide nanoparticles (NPs) is presented. These nanofilms were fabricated by a single step of spin-coated assisted deposition in conjunction with a release technique (supporting layer technique) to detach them from the substrate. Free-standing nanofilms can be easily transferred onto several substrates due to their high conformability, preserving their functionalities. The effect of the addition of iron oxide nanoparticles on the structural and functional properties of the PEDOT:PSS nanofilms is investigated through topography, thickness, magnetic, magneto-optical activity, and conductivity characterizations. PEDOT:PSS and PEDOT:PSS/iron oxide NP nanofilms were tested as resistive humidity sensors. Their sensitivity to humidity was found to increase with increasing nanoparticle concentration. On the basis of these results, it is expected that these composites may furnish inexpensive and reliable means for relative humidity detection.

Thin film free-standing PEDOT:PSS/SU8 bilayer microactuators

Several smart active materials have been proposed and tested for the development of microactuators. Among these, conjugated polymers are of great interest because miniaturization improves their electrochemical properties, such as increasing the speed and stress output of microactuators, with respect to large-scale actuators. Recently we developed a novel fabrication process to obtain robust free-standing conductive ultra-thin films made of the conjugated polymer poly(3, 4-ethylenedioxythiophene) doped with the polyanion poly(styrenesulfonate) (PEDOT:PSS). These conductive free-standing nanofilms, with thicknesses ranging between a few tens to several hundreds of nm, allow the realisation of new all polymer microactuators using facile microfabrication methods. Here, we report a novel processing method for manufacturing all polymer electrochemical microactuators. We fabricated and patterned free-standing PEDOT:PSS/SU8 bilayer microactuators in the form of microfingers of a variety of lengths using adapted microfabrication procedures. By imposing electrochemical oxidation/reduction cycles on the PEDOT:PSS we were able to demonstrate reversible actuation of the microactuators resulting in bending of the microfingers. A number of possible applications can be envisaged for these small, soft actuators, such as microrobotics and cell manipulation.

Patterned Free-Standing Conductive Nanofilms for Ultraconformable Circuits and Smart Interfaces

A process is presented for the fabrication of patterned ultrathin free-standing conductive nanofilms based on an all-polymer bilayer structure composed of poly(3,4-ethylenedioxythiophene)/poly(styrene sulfonate) and poly(lactic acid) (PEDOT:PSS/PLA). Based on the strategy recently introduced by our group for producing large area free-standing nanofilms of conductive polymers with ultrahigh conformability, here an inkjet subtractive patterning technique was used, with localized overoxidation of PEDOT:PSS that caused the local irreversible loss of electrical conductivity. Different pattern geometries (e.g., interdigitated electrodes with various spacing, etc.) were tested for validating the proposed process. The fabrication of individually addressable microelectrodes and simple circuits on nanofilm having thickness ∼250 nm has been demonstrated. Using this strategy, mechanically robust, conformable ultrathin polymer films could be produced that can be released in water as free-standing nanofilms and/or collected on surfaces with arbitrary shapes, topography and compliance, including human skin. The patterned bilayer nanofilms were characterized as regards their morphology, thickness, topography, conductivity, and electrochemical behavior. In addition, the electrochemical switching of surface properties has been evaluated by means of contact angle measurements. These novel conductive materials can find use as ultrathin, conformable electronic devices and in many bioelectrical applications. Moreover, by exploiting the electrochemical properties of conducting polymers, they can act as responsive smart biointerfaces and in the field of conformable bioelectronics, for example, as electrodes on tissues or smart conductive substrates for cell culturing and stimulation.

Low-voltage dielectric elastomer actuators with stretchable electrodes fabricated by supersonic cluster beam implantation

Supersonic cluster beam implantation of Ag nanoparticles is proposed for the fabrication of stretchable and compliant electrodes for dielectric elastomer actuators (DEAs) with reduced thickness. Thanks to the low-energy and finely tunable implantation process, a nanocomposite Ag/polydimethylsiloxane electrode layer is produced with a moderate stiffening effect for the DEA in contrast with a common deposition strategy for electrodes. Thin DEAs with an overall thickness of 17u2009μm were fabricated and tested under different preloading conditions, demonstrating a max uniaxial actuation strain of 2.5% at an actuation voltage of 765u2009V, lower than the typical voltage values of DEAs. The electrodes remained conductive up to 40% strain, and they fully recovered the original resistance after 70% stretching. Our results represent a significant step towards the development of DEAs operating at reduced actuation voltages, by stacking of micrometer-thick elastomer films, paving the way to novel applications in soft robotics.Supersonic cluster beam implantation of Ag nanoparticles is proposed for the fabrication of stretchable and compliant electrodes for dielectric elastomer actuators (DEAs) with reduced thickness. Thanks to the low-energy and finely tunable implantation process, a nanocomposite Ag/polydimethylsiloxane electrode layer is produced with a moderate stiffening effect for the DEA in contrast with a common deposition strategy for electrodes. Thin DEAs with an overall thickness of 17u2009μm were fabricated and tested under different preloading conditions, demonstrating a max uniaxial actuation strain of 2.5% at an actuation voltage of 765u2009V, lower than the typical voltage values of DEAs. The electrodes remained conductive up to 40% strain, and they fully recovered the original resistance after 70% stretching. Our results represent a significant step towards the development of DEAs operating at reduced actuation voltages, by stacking of micrometer-thick elastomer films, paving the way to novel applications in soft robotics.

On the injectability of free-standing magnetic nanofilms

AbstractFree-standing films with sub-micrometric thickness, composed of soft polymers and functional nanostructures are promising candidates for many potential applications in the biomedical field, such as reduced port abdominal surgery. In this work, freely suspended poly(L-lactic acid) nanofilms with controlled morphology embedding superparamagnetic iron oxide nanoparticles were fabricated by spin-coating deposition. The mechanical properties of magnetic nanofilms were investigated by Strain-Induced Elastic Buckling Instability for Mechanical Measurements (SIEBIMM) test. Our results show that these freely suspended nanocomposite nanofilms are highly flexible and deformable, with Young’s moduli of few GPa. Since they can be handled in liquid with syringes, a quantitative description of the nanofilms behavior during the manipulation with clinically applicable needles has been also provided. These magnetic nanofilms, remotely controllable by external electromagnetic fields, have potential applications in minimally invasive surgery as injectable nanopatches on inner organs wall.n Graphical abstractᅟ