ELECTRICAL AND COMPUTER ENGINEERING PROFESSOR KAREN CHEUNG DESIGNS BIOMEDICAL MICRODEVICES FOR NEUROPROSTHETIC APPLICATIONS AND CELL CULTURE AND CHARACTERIZATION.
ADVANCES IN MICROELECTROMECHANICAL SYSTEMS (MEMS) have enabled low-cost, high-functionality devices such as inertial sensors, microscale vacuum pumps, automotive airbag accelerometers, and many others. This breakthrough technology has also made it possible to bring together the previously unrelated disciplines of biology and microelectronics, in a field known as BioMEMS. Biomedical engineer Karen Cheung is exploring significant potential applications of this promising field.
IMPROVING THE BIOCOMPATIBILITY OF NEURAL IMPLANTS
Neural interfaces provide a connection between the electrical activity of neural tissue and technology. They are used in applications such as deep-brain stimulation of Parkinson's disease patients, and recording neuronal electrical activity to control prosthetic devices. For the latter application, current technology uses scalp-based electrodes to record electroencephalograph signals, which are then used to control the prosthesis. Although non-invasive, this approach suffers from distortion through the skull and dura, which causes reduced spatial resolution. Silicon-based neural implants have the necessary spatial resolution to record individual neurons, but their stiffness causes inflammation and scarring that interfere with the signal and eventually make them ineffective.Karen Cheung has used her microfabrication expertise to design a flexible, polymer-based microelectrode array with a better mechanical match to brain tissue than silicon-based probes. Her probe has been shown to work as well as silicon-based arrays in short-term (acute) applications in rodents, and to function well for several months in chronic applications.
In collaboration with Dr. Jay Kizhakkedathu of the Centre for Blood Research at UBC, Cheung is now investigating novel surface coatings to minimize the central nervous system's response to polymer-based implants, including protein adsorption. She also hopes to incorporate anti-inflammatory drugs in the coatings.
"Our group is focusing on biocompatibility," she says, "changing the surface properties of the implants to improve the tissue reaction." If successful, Cheung's work will go a long way toward making long-term neural interfaces feasible. An Ontario biomedical device manufacturer has already expressed interest.
MIMICKING THE IN VIVO ENVIRONMENT
In another strand of research, Cheung is fabricating a microfluidic device to culture and characterize breast cancer cells for screening of anti-cancer agents. By capturing traditional lab processes such as incubation and assaying on a lab-on-a-chip device, a much smaller number of cells, as obtained in needle biopsies, can be examined. They can be more easily tracked and characterized, making diagnosis and drug screening faster and cheaper.Cancer cells are introduced into Cheung's device suspended in a hydrogel. In this three-dimensional environment, signalling between cells, and their mechanical support on the hydrogel "scaffolding," more closely approximate the in vivo situation than in the 2D environment of a flat Petri dish. Oxygen concentrations, crucial to the effectiveness of anti-cancer drugs, can be modelled more accurately. The flow rate of the drug can be governed via a channel on the bottom of the device to mimic varying concentrations in the body. "I wanted to create a model where we can better control parameters," Cheung says, "decide how big our gel structure is, and the distance of the cells from the oxygen or drug flow. We're combining some of the hydrogel approach with microtechnology to do assays on a small scale."
Cheung plans to collaborate with Dr. Calvin Roskelley at UBC and Dr. Marcel Bally of the BC Cancer Agency to test different concentrations and administration sequences of existing anti-cancer drugs using her new assay technique. Pharmaceutical companies, among others, may soon be knocking on her door.
By going small, Cheung is tackling some big issues in neuroprosthetics and breast cancer research.
Karen Cheung can be reached at 604-827-4114 or kcheung@ece.ubc.ca
