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Competing Interests: None.

Objective: Retinal prostheses must be able to activate cells in a selective way in order to restore high-fidelity vision. However, inadvertent activation of far-away retinal ganglion cells (RGCs) through electrical stimulation of axon bundles can produce irregular and poorly controlled percepts, limiting artificial vision. In this work, we aim to provide an algorithmic solution to the problem of detecting axon bundle activation with a bi-directional epiretinal prostheses., Methods: The algorithm utilizes electrical recordings to determine the stimulation current amplitudes above which axon bundle activation occurs. Bundle activation is defined as the axonal stimulation of RGCs with unknown soma and receptive field locations, typically beyond the electrode array. The method exploits spatiotemporal characteristics of electrically-evoked spikes to overcome the challenge of detecting small axonal spikes., Results: The algorithm was validated using large-scale, single-electrode and short pulse, ex vivo stimulation and recording experiments in macaque retina, by comparing algorithmically and manually identified bundle activation thresholds. For 88% of the electrodes analyzed, the threshold identified by the algorithm was within ±10% of the manually identified threshold, with a correlation coefficient of 0.95., Conclusion: This works presents a simple, accurate and efficient algorithm to detect axon bundle activation in epiretinal prostheses., Significance: The algorithm could be used in a closed-loop manner by a future epiretinal prosthesis to reduce poorly controlled visual percepts associated with bundle activation. Activation of distant cells via axonal stimulation will likely occur in other types of retinal implants and cortical implants, and the method may therefore be broadly applicable.

Purpose: Corneal opacity is a leading cause of reversible blindness worldwide. An electronic corneal prosthesis, or intraocular projector, could potentially restore high-quality vision without need for corneal clarity., Materials and Methods: Four intraocular projection systems were constructed from commercially available electronic components and encased in biocompatible plastic housing. They were tested for optical properties, biocompatibility, heat dissipation, waterproofing, and accelerated wear. A surgical implantation technique was developed., Results: Intraocular projectors were produced of a size that can fit within the eye. Their optics produce better than 20/200 equivalent visual acuity. MTT assay demonstrated no cytotoxicity of devices in vitro . Temperature testing demonstrated less than 2°C increase in temperature after 1 h. Three devices lasted over 12 weeks under accelerated wear conditions. Implantation surgery was demonstrated via corneal trephination insertion in a cadaver eye., Conclusion: This is the first study to demonstrate and characterize fully functional intraocular projection systems. This technology has the potential to be an important new tool in the treatment of intractable corneal blindness.

Objective: Epiretinal prostheses are designed to restore vision in people blinded by photoreceptor degenerative diseases, by directly activating retinal ganglion cells (RGCs) using an electrode array implanted on the retina. In present-day clinical devices, current spread from the stimulating electrode to a distant return electrode often results in the activation of many cells, potentially limiting the quality of artificial vision. In the laboratory, epiretinal activation of RGCs with cellular resolution has been demonstrated with small electrodes, but distant returns may still cause undesirable current spread. Here, the ability of local return stimulation to improve the selective activation of RGCs at cellular resolution was evaluated., Approach: A custom multi-electrode array (512 electrodes, 10 μm diameter, 60 μm pitch) was used to simultaneously stimulate and record from RGCs in isolated primate retina. Stimulation near the RGC soma with a single electrode and a distant return was compared to stimulation in which the return was provided by six neighboring electrodes., Main Results: Local return stimulation enhanced the capability to activate cells near the central electrode (<30 μm) while avoiding cells farther away (>30 μm). This resulted in an improved ability to selectively activate ON and OFF cells, including cells encoding immediately adjacent regions in the visual field., Significance: These results suggest that a device that restricts the electric field through local returns could optimize activation of neurons at cellular resolution, improving the quality of artificial vision.

MSC can act as a pluripotent source of reparative cells during injury and therefore have great potential in regenerative medicine and tissue engineering. However, the response of MSC to many growth factors and cytokines is unknown. Many envisioned applications of MSC, such as treating large defects in bone, involve in vivo implantation of MSC attached to a scaffold, a process that creates an acute inflammatory environment that may be hostile to MSC survival. Here, we investigated cellular responses of MSC on a biomaterial surface covalently modified with epidermal growth factor (EGF). We found that surface-tethered EGF promotes both cell spreading and survival more strongly than saturating concentrations of soluble EGF. By sustaining mitogen-activated protein kinase kinase-extracellular-regulated kinase signaling, tethered EGF increases the contact of MSC with an otherwise moderately adhesive synthetic polymer and confers resistance to cell death induced by the proinflammatory cytokine, Fas ligand. We concluded that tethered EGF may offer a protective advantage to MSC in vivo during acute inflammatory reactions to tissue engineering scaffolds. The tethered EGF-modified polymers described here could be used together with structural materials to construct MSC scaffolds for the treatment of hard-tissue lesions, such as large bony defects. Disclosure of potential conflicts of interest is found at the end of this article.

Bone marrow mesenchymal stem cells (BMMSCs) are pluripotent cells capable of differentiating into several cell types and are thus an attractive cell source for connective tissue engineering. A challenge in such a use is expansion and directed seeding in vitro, requiring proliferation and survival, and directed migration, respectively, prior to functional differentiation. The epidermal growth factor (EGF) receptor (EGFR) is the prototypal growth factor receptor and elicits these responses from a wide variety of stromal, epithelial, and endothelial cells. Ligands for this receptor are appealing for use in tissue engineering because they are relatively resistant to biological extremes and amenable to high-volume production. Therefore, we determined whether an EGFR ligand, EGF, could be used for ex vivo expansion of BMMSCs. EGF stimulated motility in rat and immortalized human BMMSCs. EGF-induced proliferation was observed in immortalized human BMMSCs but was not apparent in rat BMMSCs under our experimental conditions. EGF did not, however, rescue either type of BMMSC from apoptosis due to lack of serum. During our examination of key signaling intermediaries, EGF caused robust phosphorylation of extracellular signal-regulated protein kinase (ERK) and protein kinase B/akt (AKT) but only minimal phosphorylation of EGFR and phospholipase C-gamma in rat BMMSCs, whereas in the human BMMSCs these intermediaries were all strongly activated. EGF also induced robust ERK activation in primary porcine mesenchymal stem cells. EGF pretreatment or cotreatment did not interfere with secondarily induced differentiation of either type of BMMSC into adipogenic or osteogenic lineages. Platelet-derived growth factor (PDGF) effects were similar to but not additive with those elicited by EGF, with some quantitative differences; however, PDGF did interfere with the differentiation of these BMMSCs. These findings suggest that EGFR ligands could be used for ex vivo expansion and direction of BMMSCs.