Mark C. Peterman

Ion Channels and Lipid Bilayer Membranes Under High Potentials Using Microfabricated Apertures

Membrane-bound proteins are important from both a scientific and a technological point of view. However, their study and application require a stable lipid bilayer to maintain protein function. Here we provide a method for producing lipid bilayers across apertures on a silicon substrate using a Langmuir–Blodgett technique commonly used with Teflon films. These bilayers display the same properties as those across apertures in Teflon in terms of capacitance, conductance, noise, and protein insertion and function. In addition, the bilayers remain stable at higher transmembrane potentials than those in Teflon, typically remaining unbroken over ±400 mV. These properties are demonstrated by the insertion of the staphylococcal protein pore α-hemolysin into pre-formed bilayers, and subsequent current recording at high potentials (±400 mV).

Building thick photoresist structures from the bottom up

Micromachining has pushed the limits of photolithography in the vertical direction. We demonstrate a new technique for producing structures in thick photoresists, with excellent contact alignment and high aspect ratios using a standard UV source. In this technique, we exposed the resist from the bottom by defining the mask as part of the substrate. By doing so, we successfully created high aspect ratio and multiple-layer structures. Additionally, the structures have a slight inward taper, a very useful feature for molding. This technique is a new way of thinking about photolithography, allowing novel structures and simplified processing.

Towards a Neurotransmitter-Based Retinal Prosthesis Using an Inkjet Print-head

Electronic chips that provide a patterned stimulus to cells in the retina may provide a viable treatment for age-related macular degeneration. A surrogate MEMS device, in the form of a print-head from a desktop printer, has been used to eject a pattern of neurotransmitters (bradykinin) onto living rat pheochromocytoma (PC12) cells. Fluorescent calcium imaging was used to measure the patterned stimulation of individual cells. The chemical stimulation of cells by directed microfluidic delivery may have applications in retinal prosthetic devices, and in other prosthetic implants in the nervous system.

Novel Interface to Biological Systems for Retinal Prosthetics

The development of retinal prostheses requires a method for interconnecting an imaging system to the retina. Such a system must be able to individually address and stimulate retinal neurons, a significant advance from current technology. As a step toward this goal, we present a novel electronic-to-biologic interface using microfabricated apertures in a silicon substrate. Apertures are created in a thin silicon nitride membrane, after which the surface is appropriately modified to support cell growth. Excitable cells are seeded on the device and imaged using Ca 2+ -sensitive fluorescent dyes in either an inverted or confocal microscope. Using rat pheochromocytoma (PC12) cells, we show the ability to stimulate locally through the apertures. The device allows for the stimulation of cells at precise locations, a necessary requirement for future high-resolution retinal prostheses.