Stretchable and Conductive Composite Structural Color Hydrogel Films as Bionic Electronic Skins.

Electronic skins have received increasing attention in biomedical areas. Current efforts about electronic skins are focused on the development of multifunctional materials to improve their performance. Here, the authors propose a novel natural-synthetic polymers composite structural color hydrogel film with high stretchability, flexibility, conductivity, and superior self-reporting ability to construct ideal multiple-signal bionic electronic skins. The composite hydrogel film is prepared by using the mixture of polyacrylamide (PAM), silk fibroin (SF), poly(3,4-ethylenedioxythiophene):poly (4-styrene sulfonate) (PEDOT:PSS, PP), and graphene oxide (GO) to replicate colloidal crystal templates and construct inverse opal scaffolds, followed by subsequent acid treatment. Due to these specific structures and components, the resultant film is imparted with vivid structural color and high conductivity while retaining the composite hydrogel's original stretchability and flexibility. The authors demonstrate that the composite hydrogel film has obvious color variation and electromechanical properties during the stretching and bending process, which could thus be utilized as a multi-signal response electronic skin to realize real-time color sensing and electrical response during human motions. These features indicate that the proposed composite structural color hydrogel film can widen the practical value of bionic electronic skins.

Measuring the effective area and charge density of platinum electrodes for bionic devices.

OBJECTIVE: Neural stimulation is usually performed with fairly large platinum electrodes. Smaller electrodes increase the applied charge density, potentially damaging the electrode. Greater understanding of the charge injection mechanism is required for safe neural stimulation. APPROACH: The charge injection mechanism and charge injection capacity were measured by cyclic voltammetry. Electrodes were cleaned mechanically or by potential cycling in acidic solutions. The effective electrode area was measured by hydrogen adsorption or reduction of [Formula: see text]. MAIN RESULTS: The water window and safe potential window were affected by changes to electrolyte, electrode size, polishing method and oxygen concentration. Capacitance and Faradaic current contribute to the charge injection capacity. Varying voltammetric scan rate (measurement time), electrode size, polishing method, potential window, electrolyte and oxygen concentration affected the charge injection capacity and ratio of oxidation to reduction charge. Hydrogen adsorption in acidic solutions provided an inaccurate effective electrode area. Reduction of a solution phase redox species with a linear or radial diffusion profile could provide an effective electrode area. The charge density (charge injection capacity divided by electrode area) of a platinum electrode is dependent on the charge injection capacity and electrode area measurement technique. By varying cyclic voltammetric conditions, the charge density of platinum ranged from 0.15 to 5.57 mC cm-2. SIGNIFICANCE: The safe potential window, charge injection mechanism, charge injection capacity and charge density of platinum depends on electrolyte, size of the electrode, oxygen concentration and differences in electrode polishing method. The oxidation and reduction charge injection capacities are not equal. Careful control of a platinum electrodes surface may allow larger charge densities and safe use of smaller electrodes. New electrode materials and geometries should be tested in a consistent manner to allow comparison of potential suitability for neural stimulation.

Bionic baroreceptor corrects postural hypotension in rats with impaired baroreceptor.

BACKGROUND: Impairment of the arterial baroreflex causes orthostatic hypotension. Arterial baroreceptor sensitivity degrades with age. Thus, an impaired baroreceptor plays a pivotal role in orthostatic hypotension in most elderly patients. There is no effective treatment for orthostatic hypotension. The aims of this investigation were to develop a bionic baroreceptor (BBR) and to verify whether it corrects postural hypotension. METHODS AND RESULTS: The BBR consists of a pressure sensor, a regulator, and a neurostimulator. In 35 Sprague-Dawley rats, we vascularly and neurally isolated the baroreceptor regions and attached electrodes to the aortic depressor nerve for stimulation. To mimic impaired baroreceptors, we maintained intracarotid sinus pressure at 60 mm Hg during activation of the BBR. Native baroreflex was reproduced by matching intracarotid sinus pressure to the instantaneous pulsatile aortic pressure. The encoding rule for translating intracarotid sinus pressure into stimulation of the aortic depressor nerve was identified by a white noise technique and applied to the regulator. The open-loop arterial pressure response to intracarotid sinus pressure (n=7) and upright tilt-induced changes in arterial pressure (n=7) were compared between native baroreceptor and BBR conditions. The intracarotid sinus pressure-arterial pressure relationships were comparable. Compared with the absence of baroreflex, the BBR corrected tilt-induced hypotension as effectively as under native baroreceptor conditions (native, -39±5 mm Hg; BBR, -41±5 mm Hg; absence, -63±5 mm Hg; P<0.05). CONCLUSIONS: The BBR restores the pressure buffering function. Although this research demonstrated feasibility of the BBR, further research is needed to verify its long-term effect and safety in larger animal models and humans.