| Toward the development of neuroprosthesis, we propose a 3-D regenerative neural interface design for connecting with the peripheral nervous system. This approach relies on bifurcating microstructures to achieve defasciculated ingrowth patterns and, consequently, high selectivity. In vitro studies were performed to validate this design by showing that fasciculation during nerve regeneration can be influenced by providing a scaffold to guide growth appropriately. With this approach, neurites can be separated from one another and guided toward specific electrode sites to create a highly selective interface. The neurite separation characteristics were examined for smaller microchannel structures (2.5 and 5 m wide) and larger microchannels (10 and 20 m wide), with smaller microchannels shown to be statistically more effective at initiating separation. Electrodes incorporated at different locations within the microchannels allowed for the recording and tracking of action potential propagation. Microchannel size was also found to play an important role in this regard, with smaller microchannels amplifying the recordable extracellular signal; a twofold increase in the signal to noise ratio was found for 5 m wide microchannels.

Many neural interfacing strategies, such as the sieve electrode and the cultured probe, rely on neurite growth to establish neural contact. But this growth is subject to natural fasciculation, compromising the effectiveness of these interfacing strategies by reducing potential selectivity. This in vitro study shows that the fasciculation mechanism can be manipulated by providing an appropriate microchannel scaffold to guide and influence growth, thereby achieving a high degree of selectivity. The microchannels employed have a bifurcation from a primary channel into two secondary channels. This bifurcating microstructure was able to support and promote fasciculated growth over 70% of the time for microchannels widths of 2.5, 5, 10 and 20 microm. Fasciculation is shown to be a strong force during ingrowth, with the initiation of neurite separation related to random spatial exploration. Narrower microchannels initiate separated growth better. Once separated growth starts fasciculation results in an even distribution of neurite growth across the bifurcation. The reduction from 20 microm to 10 microm wide channels also resulted in a 3-fold decrease in ingrowing neurites performing 180 degrees turns to exit the microchannel via the entrance. No neurite turning was observed for both the 5 and 2.5 microm wide channels.

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In this study neural (N)-cadherin, neural cell adhesion molecule (N-CAM) and L1 proteins and their antibody equivalents were covalently immobilized on a polyethylene-imine (PEI)-coated glass surface to form neuron-adhesive coatings. Impedance sensing and (supplementary) image analysis were used to monitor the effects of these CAMs. Immobilization of high concentrations of both N-cadherin protein and antibody led to good adhesion of neurons to the modified surface, better than surfaces treated with 30.0 and 100.0 µg ml(-1) N-CAM protein and antibody. L1 antibody and protein coating revealed no significant effect on neuronal cell-substrate adhesion. In a second series of combinatorial experiments, we used the same antibodies and proteins as medium-additives to inhibit cell-cell adhesion between neurons. Adhesion of neurons cultured on N-cadherin protein or antibody-modified surfaces was lowered by the addition of a soluble N-cadherin protein and antibody to the culturing medium, accelerating neuronal aggregation. The presence of a soluble N-CAM antibody or protein had no effect on the adhesion of neuronal cells on a N-cadherin protein-modified surface. On a N-cadherin antibody-coated surface, the addition of a soluble N-CAM protein led to cell death of neurons after 48 h, while a N-CAM antibody had no effect. In the presence of a soluble N-cadherin protein and antibody the aggregation of neurons was inhibited, both on N-CAM protein and N-CAM antibody-modified surfaces. Neurons cultured on immobilized antibodies were less affected by the addition of soluble CAM blockers than neurons cultured on immobilized proteins, indicating that antibody-protein bonds are more stable compared to protein-protein bonds.

Abstract-We propose and validated a design for a highly selective "endcap" regenerative neural interface towards a neuroprosthesis. In vitro studies using rat cortical neurons determine if a branching microchannel structure can counter fasciculated growth and cause neurites to separate from one another, allowing for greater selective contact. Initial studies find that narrower branching microchannels achieve improved neurite separation. Electrical stimulation of neurites within microchannels is possible, as is recording of neurite action potentials with the microchannels acting as electrical signal amplifiers.Index Terms-Neural interface, tissue engineering, regenerative electrode, bidirectional communication interface.