International Symposium on LifeChips 2006

Toward Implantable Micro Drug Delivery System
Delivery of small volumetric-sensitive materials using a micro pumping system has become a pressing issue in the fields of chemistry, biology, and medicine. In this paper, we present two microvalves which are targeting the implantable drug delivery systems; 1) the micropumping system employing two check valves whose operation mimics that of venous valves, 2) the pH responsive microvalve embedding hydrogel microsphere fabricated via ‘on the fly’ photopolymerization. 1) Micropumping system: Our check valve has a mono leaflet and is constructed via the in-situ fabrication method inside the PDMS platform. We used 4-hydroxybutyl acrylate (4-HBA) as an elastic and photopolymerizable leaflet material. We mixed the triton X-100 with the 4-HBA pre-polymer solution to circumvent the leaflet’s stiction problem. We constructed the micro pumping system by combining two venous-like check valves with an oscillating polymeric diaphragm driven by pneumatic force. We evaluated the performance of the pumping system according to the various conditions. We also investigated the feasibility of delivering sensitive materials by using mouse embryo fibroblast cells. 2) pH responsive microvalve: Here, we suggest a new method that allows the mass production of a stimuli-responsive microvalve through the use of a pre-made microsphere as an actuating element and this fabrication process resembles the assembly of commercial products in a factory. We have massively fabricated pH-responsive microspheres through the use of PDMS-based microfluidic apparatus and an ‘on the fly’ photopolymerization method. By incorporation of this microsphere into the microvalve during the fabrication process, we have produced a pH-responsive microfluidic valve in a simple way. The operation and the function of the fabricated microvalve were evaluated through diverse experiments. We expect this will be utilized as drug delivery system operating to the human body’s condition.

Biography
Sanghoon Lee (Prof. at Korea University) received the B.S. degree in electrical engineering and the M.S. and Ph.D. degrees in biomedical engineering from the Seoul National University in Korea, in 1983, 1987, and 1992, respectively. From 1992 to 2005, he was an Instructor, Assistant Professor and Professor in the Department of Biomedical Engineering at the Dankook University(Korea). Now, he is a professor in Department of Biomedical Engineering at the Korea University(Korea). From 1985 to 1992, he was a researcher in the Department of Biomedical Engineering at the Seoul National University Hospital. He was visiting scientist in the Department of Biomedical Engineering at the University of Wisconsin-Madison, in 2002. He had broad interests in biomedical instrumentation, and the development and use of microdevices for applications in medicine and biotechnology. His current interests are as follows; 1) ‘on the fly’ fabrication of curved microstructures such as micro-sized fiber, tube and sphere(we call ‘factory on a chip’), 2) micro encapsulation of liquid samples and cells using the microfluidic chip, 3) development of polymeric microvalve (including stimuli responsive valve) and micropumping system, 4) fabrication of flexible electrode (PDMS substrate) for the artificial vision or the recovery of sensory function, and 5) fabrication of Lab-Chip for the biochemical analysis or cell culture. His researches were introduced at ‘Nature (review paper)’, ‘New Scientists’, and ‘Chemical Technology’ etc.