Electrospun fibrillary scaffold for electrochemical cell biomarkers detection.

A novel scaffold for in situ electrochemical detection of cell biomarkers was developed using electrospun nanofibers and commercial adhesive polymeric membranes. The electrochemical sensing of cell biomarkers requires the cultivation of the cells on/near the (bio)sensor surface in a manner to preserve an appropriate electroactive available surface and to avoid the surface passivation and sensor damage. This can be achieved by employing biocompatible nanofiber meshes that allow the cells to have a normal behavior and do not alter the electrochemical detection. For a better mechanical stability and ease of handling, nylon 6/6 nanofibers were collected on commercial polymeric membranes, at an optimal fiber density, obtaining a double-layered platform. To demonstrate the functionality of the fabricated scaffold, the screening of cellular stress has been achieved integrating melanoma B16-F10 cells and the (bio)sensor components on the transducer whereas the melanin exocytosis was successfully quantified using a commercial electrode. Either directly on the surface of the (bio)sensor or spatially detached from it, the integration of cell cultures in biosensing platforms based on electrospun nanofibers represents a powerful bioanalytical tool able to provide real-time information about the biomarker release, enzyme activity or inhibition, and monitoring of various cellular events.

Charge transport mechanisms in free-standing devices with electrospun electrodes.

Embedding electronic and optoelectronic devices in common, daily use objects is a fast developing field of research. New architectures are needed for migrating from the classic wafer- based substrates. Novel types of flexible PMMA/Au/Alq3/LiF/Al structures were obtained starting from electrospun polymer fibers. Thus, using an electrospinning process poly (methyl metacrylate) (PMMA) nanofibers were fabricated. A thin Au layer deposition rendered the fiber array conductive, this being further employed as the anode. The next steps consisted of the thermal evaporation of tris(8-hydroxyquinolinato) aluminum (Alq3) and aluminum deposition as the cathode. The Au covered PMMA nanofiber layer had a similar behavior with an indium tin oxide film i.e. low sheet resistance 10.6 Ω/sq and high transparency. The low electrode resistivities allow an electron drift mobility of about 10-6cm2V-1s-1at a low applied field, similar to the counterpart structures based on thin films. Concerning the relaxation processes in these structures, the Cole-Cole plots exhibit a slightly deformed semicircle, indicating a more complex equivalent circuit for the processes between metal electrodes and the active layer. This equivalent circuit includes reactance equivalent processes at the anode, cathode, in the active layer and most probably originates from the roughness of the metallic electrodes.

Bioinspired polypyrrole based fibrillary artificial muscle with actuation and intrinsic sensing capabilities.

A non-conventional, bioinspired device based on polypyrrole coated electrospun fibrous microstructures, which simultaneously works as artificial muscle and mechanical sensor is reported. Fibrous morphology is preferred due to its high active surface which can improve the actuation/sensing properties, its preparation still being challenging. Thus, a simple fabrication algorithm based on electrospinning, sputtering deposition and electrochemical polymerization produced electroactive aligned ribbon meshes with analogous characteristics as natural muscle fibers. These can simultaneously generate a movement (by applying an electric current/potential) and sense the effort of holding weights (by measuring the potential/current while holding objects up to 21.1 mg). Electroactivity was consisting in a fast bending/curling motion, depending on the fiber strip width. The amplitude of the movement decreases by increasing the load, a behavior similar with natural muscles. Moreover, when different weights were hung on the device, it senses the load modification, demonstrating a sensitivity of about 7 mV/mg for oxidation and - 4 mV/mg for reduction. These results are important since simultaneous actuation and sensitivity are essential for complex activity. Such devices with multiple functionalities can open new possibilities of applications as e.g. smart prosthesis or lifelike robots.

Direct and remote induced actuation in artificial muscles based on electrospun fiber networks.

The present work reports a new configuration of soft artificial muscle based on a web of metal covered nylon 6/6 micrometric fibers attached to a thin polydimethylsiloxane (PDMS) film. The preparation process is simple and implies the attachment of metalized fiber networks to a PDMS sheet substrate while heating and applying compression. The resulting composite is versatile and can be cut in different shapes as a function of the application sought. When an electric current passes through the metallic web, heat is produced, leading to local dilatation and to subsequent controlled deformation. Because of this, the artificial muscle displays a fast and ample movement (maximum displacement of 0.8 cm) when applying a relatively low voltage (2.2 V), a consequence of the contrast between the thermal expanse coefficients of the PDMS substrate and of the web-like electrode. It was shown that the electrical current producing this effect can originate from both direct electric contacts, and untethered configurations i.e. radio frequency induced. Usually, for thermal activated actuators the heating is produced by using metallic films or conductive carbon-based materials, while here a fast heating/cooling process is obtained by using microfiber-based heaters. This new approach for untethered devices is an interesting path to follow, opening a wide range of applications were autonomous actuation and remote transfer of energy are needed.

Composite Fibers Based on Polycaprolactone and Calcium Magnesium Silicate Powders for Tissue Engineering Applications.

The present work reports the synthesis and characterization of polycaprolactone fibers loaded with particulate calcium magnesium silicates, to form composite materials with bioresorbable and bioactive properties. The inorganic powders were achieved through a sol-gel method, starting from the compositions of diopside, akermanite, and merwinite, three mineral phases with suitable features for the field of hard tissue engineering. The fibrous composites were fabricated by electrospinning polymeric solutions with a content of 16% polycaprolactone and 5 or 10% inorganic powder. The physico-chemical evaluation from compositional and morphological points of view was followed by the biological assessment of powder bioactivity and scaffold biocompatibility. SEM investigation highlighted a significant reduction in fiber diameter, from around 3 µm to less than 100 nm after the loading stage, while EDX and FTIR spectra confirmed the existence of embedded mineral entities. The silicate phases were found be highly bioactive after 4 weeks of immersion in SBF, enriching the potential of the polymeric host that provides only biocompatibility and bioresorbability. Moreover, the cellular tests indicated a slight decrease in cell viability over the short-term, a compromise that can be accepted if the overall benefits of such multifunctional composites are considered.

Synthesis of Core-Double Shell Nylon-ZnO/Polypyrrole Electrospun Nanofibers.

Core-double shell nylon-ZnO/polypyrrole electrospun nanofibers were fabricated by combining three straightforward methods (electrospinning, sol-gel synthesis and electrodeposition). The hybrid fibrous organic-inorganic nanocomposite was obtained starting from freestanding nylon 6/6 nanofibers obtained through electrospinning. Nylon meshes were functionalized with a very thin, continuous ZnO film by a sol-gel process and thermally treated in order to increase its crystallinity. Further, the ZnO coated networks were used as a working electrode for the electrochemical deposition of a very thin, homogenous polypyrrole layer. X-ray diffraction measurements were employed for characterizing the ZnO structures while spectroscopic techniques such as FTIR and Raman were employed for describing the polypyrrole layer. An elemental analysis was performed through X-ray microanalysis, confirming the expected double shell structure. A detailed micromorphological characterization through FESEM and TEM assays evidenced the deposition of both organic and inorganic layers. Highly transparent, flexible due to the presence of the polymer core and embedding a semiconducting heterojunction, such materials can be easily tailored and integrated in functional platforms with a wide range of applications.

Functionalization of eggshell membranes with CuO-ZnO based p-n junctions for visible light induced antibacterial activity against Escherichia coli.

Biopolymers provide versatile platforms for designing naturally-derived wound care dressings through eco-friendly pathways. Eggshell membrane (ESM), a widely available, biocompatible biopolymer based structure features a unique 3D porous interwoven fibrous protein network. The ESM was functionalized with inorganic compounds (Ag, ZnO, CuO used either separately or combined) using a straightforward deposition technique namely radio frequency magnetron sputtering. The functionalized ESMs were characterized from morphological, structural, compositional, surface chemistry, optical, cytotoxicity and antibacterial point of view. It was emphasized that functionalization with a combination of metal oxides and exposure to visible light results in a highly efficient antibacterial activity against Escherichia coli when compared to the activity of individual metal oxide components. It is assumed that this is possible due to the fact that an axial p-n junction is created by joining the two metal oxides. This structure separates into components the charge carrier pairs promoted by visible light irradiation that further can influence the generation of reactive oxygen species which ultimately are responsible for the bactericide effect. This study proves that, by employing inexpensive and environmentally friendly materials (ESM and metal oxides) and fabrication techniques (radio frequency magnetron sputtering), affordable antibacterial materials can be developed for potential applications in chronic wound healing device area.

Palladium/palladium oxide coated electrospun fibers for wearable sweat pH-sensors.

The work describes the development of a flexible, hydrogel embedded pH-sensor that can be integrated in inexpensive wearable and non-invasive devices at epidermal level for electrochemical quantification of H+ ions in sweat. Such a device can be useful for swift, real time diagnosis and for monitoring specific conditions. The sensors' working electrodes are flexible poly(methyl methacrylate) electrospun fibers coated with a thin gold layer and electrochemically functionalized with nanostructured palladium/palladium oxide. The response to H+ ions is investigated by cyclic voltammetry and electrochemical impedance spectroscopy while open circuit potential measurements show a sensitivity of aprox. -59 mV per pH unit. The modification of the sensing interface upon basic and acid treatment is characterized by scanning and transmission electron microscopy and the chemical composition by X-ray photoelectron spectroscopy. In order to demonstrate the functionality of the pH-sensor at epidermal level, as a wearable device, the palladium/palladium oxide working electrode and silver/silver chloride reference electrode are embedded within a pad of polyacrylamide hydrogel and measurements in artificial sweat over a broad pH range were performed. Sensitivity up to -28 mV/pH unit, response time below 30 s, temperature dependence of approx. 1 mV/°C as well as the minimum volume to which the sensor responses of 250 nanoliters were obtained for this device. The proposed configuration represents a viable alternative making use of low-cost and fast fabrication processes and materials.

Core-shell nanowire arrays based on ZnO and CuxO for water stable photocatalysts.

Staggered gap radial heterojunctions based on ZnO-CuxO core-shell nanowires are used as water stable photocatalysts to harvest solar energy for pollutants removal. ZnO nanowires with a wurtzite crystalline structure and a band gap of approximately 3.3 eV are obtained by thermal oxidation in air. These are covered with an amorphous CuxO layer having a band gap of 1.74 eV and subsequently form core-shell heterojunctions. The electrical characterization of the ZnO pristine and ZnO-CuxO core-shell nanowires emphasizes the charge transfer phenomena at the junction and at the interface between the nanowires and water based solutions. The methylene blue degradation mechanism is discussed taking into consideration the dissolution of ZnO in water based solutions for ZnO nanowires and ZnO-CuxO core-shell nanowires with different shell thicknesses. An optimum thickness of the CuxO layer is used to obtain water stable photocatalysts, where the ZnO-CuxO radial heterojunction enhances the separation and transport of the photogenerated charge carriers when irradiating with UV-light, leading to swift pollutant degradation.

Flexible Delivery Patch Systems based on Thermoresponsive Hydrogels and Submicronic Fiber Heaters.

This paper proposes a novel, flexible, low cost administration patch which could be used as a non-invasive, controlled transdermal drug delivery system. The fabricated device consists in a flexible microfiber architecture heater covered with a thermoresponsive hydrogel, namely poly(N-isopropylacrylamide), as a matrix for the incorporation of active molecules. The manufacturing process consists of two main steps. First, the electrospun poly(methyl methacrylate) fiber networks are sputter coated with a thin gold layer and attached to flexible poly(ethylene terephthalate) substrates to obtain the heating platforms. Second, the heaters are encapsulated in poly(ethylene terephthalate) foils and covered with poly(N-isopropylacrylamide) hydrogel sheets. In order to illustrate the functionality of the fabricated patch, the hydrogel layer is loaded with methylene blue aqueous solution and is afterwards heated via Joule effect, by applying a voltage on the metalized fibers. The methylene blue releasing profiles of the heated patch are compared with those of the unheated one and the influence of parameters such as hydrogel composition and morphology, as well as the applied voltage values for microheating are investigated. The results indicate that the fabricated patch can be used as a drug administration instrument, while its performance can be tuned depending on the targeted application.

Polypyrrole Actuator Based on Electrospun Microribbons.

The development of soft actuators by using inexpensive raw materials and straightforward fabrication techniques, aiming at creating and developing muscle like micromanipulators, represents an important challenge nowadays. Providing such devices with biomimetic qualities, for example, sensing different external stimuli, adds even more complexity to the task. We developed electroactive polymer-coated microribbons that undergo conformational changes in response to external physical and chemical parameters. These were prepared following three simple steps. During the first step nylon-6/6 microribbons were fabricated by electrospinning. In a second step the microribbons were one side coated with a metallic layer. Finally, a conducting layer of polypyrrole was added by means of electrochemical deposition. Strips of polypyrrole-coated aligned microribbon meshes were tested as actuators responding to current, pH, and temperature. The electrochemical activity of the microstructured actuators was investigated by recording cyclic voltammograms. Chronopontentiograms for specific current, pH, and temperature values were obtained in electrolytes with different compositions. It was shown that, upon variation of the external stimulus, the actuator undergoes conformational changes due to the reduction processes of the polypyrrole layer. The ability of the actuator to hold and release thin wires, and to collect polystyrene microspheres from the bottom of the electrochemical cell, was also investigated.

Electrochromic properties of polyaniline-coated fiber webs for tissue engineering applications.

By combining the electrospinning method advantages (high surface-to-volume ratio, controlled morphology, varied composition and flexibility for the resulting structures) with the electrical activity of polyaniline, a new core-shell-type material with potential applications in the field of artificial muscles was synthesized. Thus, a poly(methylmethacrylate) solution was electrospun in optimized conditions to obtain randomly oriented polymer fiber webs. Further, a gold layer was sputtered on their surface in order to make them conductive and improve the mechanical properties. The metalized fiber webs were then covered with a PANI layer by in situ electrochemical polymerization starting from aniline and using sulphuric acid as oxidizing agent. By applying a small voltage on PANI-coated fiber webs in the presence of an electrolyte, the oxidation state of PANI changes, which is followed by the device color modification. The morphological, electrical and biological properties of the resulting multilayered material were also investigated.