Yawen Li

A BioMEMS review: MEMS technology for physiologically integrated devices

MEMS devices are manufactured using similar microfabrication techniques as those used to create integrated circuits. They often, however, have moving components that allow physical or analytical functions to be performed by the device. Although MEMS can be aseptically fabricated and hermetically sealed, biocompatibility of the component materials is a key issue for MEMS used in vivo. Interest in MEMS for biological applications (BioMEMS) is growing rapidly, with opportunities in areas such as biosensors, pacemakers, immunoisolation capsules, and drug delivery. The key to many of these applications lies in the leveraging of features unique to MEMS (for example, analyte sensitivity, electrical responsiveness, temporal control, and feature sizes similar to cells and organelles) for maximum impact. In this paper, we focus on how the biological integration of MEMS and other implantable devices can be improved through the application of microfabrication technology and concepts. Innovative approaches for improved physical and chemical integration of systems with the body are reviewed. An untapped potential for MEMS may lie in the area of nervous and endocrine system actuation, whereby the ability of MEMS to deliver potent drugs or hormones, combined with their precise temporal control, may provide new treatments for disorders of these systems.

BioMEMS for drug delivery

Recent research into methods of using microelectromechanical systems (MEMS) technology for medical and biological applications has developed several interesting devices. This paper reviews various approaches to the use of MEMS for drug therapy, including devices based on microporous silicon, microneedles, micropumps, and microreservoirs. Microdevices can improve drug therapy because they allow precise and complex dosing, induce less pain, or increase compliance. Microneedles have been tested on humans, and the other drug delivery MEMS have shown promise in vitro and in vivo. Investigations into the use of microelectromechanical systems (MEMS) technology to produce microdevices for drug delivery have expanded recently. We present several different approaches to the use of microdevices for drug therapy and the current state of the field.

A microfluidic bioreactor for increased active retrovirus output

Retroviruses are one of the most commonly used vectors in ongoing gene therapy clinical trials. To evaluate and advance virus production on the microscale platform, we have created a novel microfluidic bioreactor for continuous retrovirus production. We investigated the growth kinetics of a retroviral packaging cell line in microfluidic bioreactors for several compartment sizes, and packaging cells perfused in the microdevices showed similar growth kinetics to those cultured in conventional static conditions. To evaluate the efficiency of retrovirus production, virus titers from the microdevices were compared to those obtained from static tissue culture. When retrovirus production and collection were maintained at 37 degrees C, virus production levels were comparable for the microdevices and static tissue culture conditions. However, immediate cold storage downstream of the packaging cells in the microdevices resulted in 1.4- to 3.7-fold greater active virus production levels with the microdevices compared to the conventional static conditions over a 5 day period. Lastly, the use of microfluidics for virus production provides a continuous supply of virus supernatant for immediate infection of target cells or for preservation and storage. Such devices will be valuable for the optimization of production and evaluation of retroviruses and other viral vectors for gene therapy applications.

Mechanical testing of gold membranes on a MEMS device for drug delivery

A MEMS device for drug delivery has been developed to achieve controlled release of drugs on demand. It consists of a silicon substrate into which micro-reservoirs are etched that contain individual doses of drug. The release of drugs is achieved by the electrochemical dissolution of the gold membranes that seal individual reservoirs. It is desirable to non-destructively evaluate the mechanical properties of gold membranes on this drug delivery device and to understand the effect of various processing and loading factors on the membrane disintegration process. This study presents some initial bulge test results on gold membranes of this device. The bulge test was conducted by applying pressure to the reservoirs and measuring the deflection of the membrane using interferometry. The test also provides a reliable non-destructive method to evaluate the bottom nitride etching step in the microfabrication process, which is otherwise difficult to test using conventional methods. There is a decreasing trend in the burst pressure with longer corrosion time to the gold membrane. These results will guide us to optimize the design of gold membrane structure through microfabrication process to achieve more reliable device performance.

Effects of heat treatment on amorphous carbon nitride prepared by reactive magnetron sputtering

The amorphous CNx powders were prepared by reactive DC magnetron sputtering. Based on the DTA-TG analysis, a characteristic temperature (1440°C) was determined at which heat treatment was employed to crystallize the amorphous powders. Subsequent structural and compositional analysis were carried out on the heat-treated samples by using XRD, scanning Auger. The powder diffraction pattern revealed that α-C3N4 is the main crystalline thermodynamically stable phase in the predicted crystalline carbon nitrides. Nano crystallites were observed with compositions very close to that of the C3N4 crystal.