Design and Development of a Multiport Microfluidic Device for In Vitro Surface Stimulation of the Retina

Millions of people are affected by photoreceptor degeneration diseases, which cause permanent vision loss, and currently there is no cure available. Retinal prostheses using electrical current have emerged as a promising approach to treat and partially restore the vision lost to these diseases. However, electrical based prostheses have limitations in terms of providing high-resolution naturalistic vision. As an effective alternative approach, researchers are exploring stimulation of the retina with neurotransmitter chemicals. The feasibility of this approach was recently demonstrated by injecting glutamate chemical into the rat retinas using single port micropipettes. To advance this approach further, there is a need to inject nanoliters of chemicals at multiple points simultaneously over a 2D surface of the retina in order to study patterned stimulations through in-vitro experiments. Motivated by this need, this thesis was undertaken with the objective of developing a specialized multiport microfluidic device with individually addressable microports and tiny on-chip reservoirs. A multiport microfluidic device was designed to satisfy a number of functional requirements for in-vitro chemical stimulation experiments, allowing for injection of chemicals on the top side of the retina while recording the neural signals with a multielectrode array on the bottom side of the retina. The device was designed to feature a 3x3 array of 10 µm diameter outlet ports on the bottom side, with each port independently connected to a tiny on-chip reservoir storing the chemical on the top side via a microchannel, and a means for external pneumatic actuation for ejecting the stored chemicals through the outlet ports. The overall footprint area and thickness of the device were 1 sq. cm and 1.3 mm, respectively. A finite element model of the device was created and its output flow characteristics for various input pressures were analyzed. A prototype of the device was then built in two layers: a bottom silicon layer and a top glass layer. The bottom silicon layer containing the delivery ports and microchannels was microfabricated using conventional micromachining techniques, while the top glass layer containing the reservoirs was fabricated using ultrasonic machining process. Both layers were anodically bonded to create a complete prototype of the device. The eight reservoirs in the top layer were filled with glutamate chemical and each reservoir was independently coupled to an 8-channel pneumatic pressure injector via tubes and unions, and the device was experimentally characterized for volume injected at the outlet ports for various input pressures between 0.1-1 psi, and validated by the finite element simulation results. Following the characterization, the device was interfaced with explanted retinas, and by actuating the delivery ports selectively, the chemical was injected into retina through different combinations of ports and corresponding patterned 2D chemical stimulations of the retina were successfully demonstrated.