| 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.

We demonstrate a novel, flexible and programmable method to pump liquid through microchannels in lab-on-a-chip systems without the use of an external pump. The pumping principle is based on the rotation of ferromagnetic Janus microspheres around permalloy disks, driven by an external rotating magnetic field. By placing the disks close to the edge of the microchannel, a pumping rate of at least 0.3 nL min(-1) was measured using tracking microspheres. Geometric programming of the pumping direction is possible by positioning the magnetic disk close to the side wall. A second degree of freedom in the pumping direction is offered by the rotational direction of the external magnetic field. This method is especially suited for flow-controlled recirculation of chemical and biological species in microchannels - for example, medium recirculation in culture chambers - opening the way towards novel, portable, on-chip applications without the need for external fluidic or electrical connections.