Biomedical MicroElectroMechanical Systems

Wen Li |


Research in the MicroTechnology Laboratory at Michigan State University includes inorganic and organic micro/nano-electro-mechanical (MEMS/NEMS) systems, implantable neuroprosthetic devices, microfluidics, sensors and actuators, polymer MEMS processing techniques, and microelectronics integration and packaging methods.

Implantable Neuroprosthetic Devices

The goal of this research aims at developing highly miniaturized, implantable neural interface systems, which can be widely used by neuroscientists and clinical researchers in animal studies to advance our knowledge on abnormal neuronal connectivity and behavioral readout underlying different brain disorders and injuries. In particular, we have developed a variety of multi-channel hybrid Opto-Electro neural interfacing devices, including a flexible, multichannel ECoG-µLED array, a LED-coupled waveguide array, a wirelessly powered optrode array, and a polycrystalline diamond (PCD) probe. These devices are mechanically flexible, biocompatible, miniaturized, and lightweight, suitable for chronic implantation in small freely behaving animals.

Polymer MEMS Manufacturing Methods

Our group is also interested in developing novel polymer processing techniques for making microscale optical devices. In particular, we invented a droplet backside exposure (DBE) method, which uses conventional ultraviolet photolithography technique to monolithically construct varying-length, hollow/solid microneedles on a dome-shaped SU-8 droplet. The SU-8 droplet is confined within the wetting barrier at an air/liquid/hydrophilic-/hydrophobic- polymer interface. The contact angle of the droplet is tuned precisely from ~5° to 80°, using specific plasma treatments. In addition, we developed a room-temperature, vapor-induced dewetting (VID) method for making µ-lens arrays on heterogeneous polymeric surfaces that are selectively pre-treated with low-energy SF6 or O2 plasma.

Graphene Nanosensor and Nanoelectronics

Graphene, a single free-standing atomic layer of carbon, has extraordinary electrical, optical, and thermal properties. For applications in nanoelectronics, stable doping of intrinsic graphene into semiconducting materials is one of the most challenging aspects. To overcome this challenge, we developed novel nanomanufacturing and chemical doping methods to achieve p-type or n-type graphene with excellent air stability and high mobility. Specifically, introducing nanoscale patterns (ribbons or holes) onto intrinsic graphene films can result in p-type semiconducting properties. Chemically stable, reversible n-type doping is achieved using SU-8 as the electron doping and encapsulating material. By selectively patterning p- and n-type regions within a single graphene sheet, recently we realized monolithically integrated graphene nanocircuits on both rigid and flexible substrates.