Retinal prostheses are being developed to restore vision for those with retinal diseases such as retinitis pigmentosa or age-related macular degeneration. Since neural prostheses depend upon electrical stimulation to control neural activity, optimal stimulation parameters for successful encoding of visual information are one of the most important requirements to enable visual perception. In this paper, we focused on retinal ganglion cell (RGC) responses to different stimulation parameters and compared threshold charge densities in wild-type and rd1 mice. For this purpose, we used in vitro retinal preparations of wild-type and rd1 mice. When the neural network was stimulated with voltage- and current-controlled pulses, RGCs from both wild-type and rd1 mice responded; however the temporal pattern of RGC response is very different. In wild-type RGCs, a single peak within 100 ms appears, while multiple peaks (approximately four peaks) with ∼ 10 Hz rhythm within 400 ms appear in RGCs in the degenerated retina of rd1 mice. We find that an anodic phase-first biphasic voltage-controlled pulse is more efficient for stimulation than a biphasic current-controlled pulse based on lower threshold charge density. The threshold charge densities for activation of RGCs both with voltage- and current-controlled pulses are overall more elevated for the rd1 mouse than the wild-type mouse. Here, we propose the stimulus range for wild-type and rd1 retinas when the optimal modulation of a RGC response is possible.

The electrode-specific formation of polydopamine films is achieved by applying positive voltage to the target electrodes at pH 6.0. The functionalization of the films is simultaneously carried out by co-depositing dopamine with molecules of interest onto the electrode.

An array of chemically functionalized electrodes is a versatile platform for investigation/manipulation of the electroactive cellular functions that are realized in the network fashion, as well as for multiplexed detection of analytes. For example, multielectrodes have been used intensively for both perturbation of many cellular systems with electrical stimulations and measurements of electrical signals from them at the spatiotemporal resolution in the applications, such as chipbased sensors [1] and prosthetic devices, [2] along with fundamental studies of electrophysiology. [3] In particular, nerve cells are a representative example for electrically excitable cells, the functions of which are achieved by the tightly polarized electrical communications between neurons, and multielectrodes have been the core part of neuron-material interfaces. [2,4] In vitro neuron-multielectrode interfaces have generally been formed by coating all of the electrode surfaces with one kind of neuron-adhesive molecules, such as poly(amino acid)s or peptides. [5] Although this coating approach has been successful in collective studies of neuronal connectivity and activities, [6] it would be desirable for sophisticated control and manipulation of neurons to develop methods for coating and functionalizing each electrode independently. The electrode addressability would allow us to locate or manipulate neurons or synapses with directionality control, because the electrodes are asymmetrically functionalized, not to mention being beneficial in multiplexed detection of targets. The differently functionalized electrodes on a substrate also could be utilized to investigate the responses of neurons at the single-cell level at a time.Electrochemically driven reactions on self-assembled monolayers have been used for electrode-selective functionalizations, [7] but this approach requires a specific electrode material, depending on the self-assembling molecules, and cumbersome synthetic procedures. As an alternative, conducting polymers have been adopted for coating of neural electrodes. [8] Although they can be electrochemically deposited onto the electrodes with relative ease, while retaining electrical properties of the electrodes for neural interfaces in the reliable manner, direct functionalization is not possible owing to the lack of functionalizable groups in their structures. [9] In this work, we report the electrochemically driven formation of polydopamine (pDA) films that are substrateindependent, simple to functionalize, and site-addressable.We have previously reported that the substrate-independent, bulk-coated pDA film did not impede the functions of the electrodes, suggesting one of the optimal materials for neural interfaces. [10] The facile functionalization of pDA films by codeposition was also demonstrated in the bulk coating. [11] Because the polymerization of dopamine is thought to occur through oxidative coupling of 1,2-dihydroxybenzene (catechol), we reasoned that the electrochemical method [12] could be utilized to deposi...

The transforming growth factor beta/bone morphogenetic protein-activated Smad signaling pathway plays a complicated role in the maintenance of human embryonic stem cell (hESC) pluripotency and in the cell fate decision of hESCs. Here, we report that sustained inhibition of the transforming growth factor beta type I receptor (also termed activin receptor-like kinase or ALK) using a chemical inhibitor selective for ALK4/5/7 (ALKi) leads to the cardiac differentiation of hESCs under feeder-free and serum-free conditions. Treatment with ALKi reduced Smad2/3 phosphorylation and increased Smad1/5/8 phosphorylation in hESCs, suggesting a requirement for active Smad1/5/8 signaling for cardiac induction in these cells when ALK/Smad2/3 is inhibited. Importantly, active basic fibroblast growth factor (bFGF) signaling was also required for ALKi-mediated cardiac differentiation of monolayer-cultured hESCs. The FGF receptor inhibitor SU5402 blocked ALKi-mediated cardiac induction in hESCs, whereas bone morphogenetic protein-4 enhanced the ALKi-induced increase in phospho-Smad1/5/8 levels but failed to induce the cardiac differentiation of hESCs and instead promoted trophoblastic differentiation. We also confirmed that ALKi potentially enhanced the cardiac differentiation of human embryoid bodies, as determined by expression of cardiac-specific markers, increased beating areas, and action potential recorded from beating areas. These results demonstrate that an ALKi could be used as a potential cardiac-inducing agent and that the development of culture conditions that provide an appropriate balance between ALK/Smad and bFGF signaling is necessary to direct the fate of hESCs into the cardiac lineage.