Begell House Inc.
Critical Reviews™ in Biomedical Engineering
CRB
0278-940X
37
3
2009
Miniaturized Microfluidic Formats for Cell-Based High-Throughput Screening
193-257
10.1615/CritRevBiomedEng.v37.i3.10
Sarvesh
Upadhyaya
Department of Mechanical Engineering, McMaster University, Canada
Ponnambalam R.
Selvaganapathy
Mechanical Engineering, McMaster University, Hamilton, Ontario, Canada
microfluidics
cell based assay
high throughput screening
electrokinetic pumps
nanoporous membrane
Cell-based high-throughput screening (HTS) has become an important method used in pharmaceutical drug discovery, and is presently carried out using robots and micro-well plates. A microfluidic-based device for cell-based HTS using a traditional cell-culture protocol would be a key enabler in miniaturization and in increasing throughput without consequent detrimental effects on the physiological significance of the screen. In this paper, we illustrate the advances in miniaturization of cell-based HTS, especially using microfabrication and microfluidics. We also detail a novel microfluidic HTS device targeted for cell-based assays using traditional non-compartmentalized agar gel as a cell-culture medium and electric control over drug dose. The basic design of this device consists of a gel layer supported by a nanoporous membrane that is bonded to microchannels underneath it. The pores of the membrane are blocked everywhere except in selected regions that serve as fluidic interfaces between the microchannel below and the gel above. Upon application of an electric field, nanopores start to act as electrokinetic pumps. By selectively switching an array of such micropumps, a number of spots containing drug molecules are created simultaneously in the gel layer. By diffusion, drugs reach the top surface of the gel where cells are to be grown. Based on this principle, a number of different devices can be fabricated using microfabrication technology. The fabricated devices include a single drug spot-forming device, a multiple drug spot-forming device, and a microarray drug spot-forming device. By controlling the pumping potential and duration, spots sizes ranging from 200 μ;m to 6 mm in diameter and having inter-spot distances of 0.4 to 10 mm have been created. The absence of diffusional transport through the nanoporous interfaces without an electric field is demonstrated. A number of representative molecules, including surrogate drug molecules (trypan blue and methylene blue) and biomolecules (DNA and protein) were selected for demonstration purposes. A dosing range of 50 to 3000 μ;g and a spot density of 156 spots/cm2 were achieved. The drug spot density was found to be limited by molecular diffusion in gel, so a numerical study was carried to determine ways to increase density. Based on this simulation, a diffusion barrier was proposed, which uses a specially dimensioned (having shallow grooves) gel sheet to reduce diffusion.
Biomaterials, Fibrosis, and the Use of Drug Delivery Systems in Future Antifibrotic Strategies
259-281
10.1615/CritRevBiomedEng.v37.i3.20
Ryan J.
Love
School of Biomedical Engineering, McMaster University, Canada
Kim S.
Jones
School of Biomedical Engineering and Department of Chemical Engineering, McMaster University, Canada
foreign body giant cells
myofibroblasts
inflammation
biocompatibility
tissue engineering
All biomaterials, when implanted into the body, elicit an inflammatory response that evolves into fibrovascular tissue formation on and around the material. As a result, material scientists and tissue engineers should be concerned about host response to tissue-engineered constructs that have a biomaterial component, because the host response to this component will interfere with device function and reduce the lifespan of tissue engineering devices in vivo. The fibrotic response to biomaterials is not unlike pathological fibrosis of the liver, lung, kidney, and peritoneum in many ways: i) the presence of mononuclear leukocytes are common in the local environment of both pathological fibrosis and biomaterial-induced fibrosis even though cells of mesenchymal origin are responsible for laying the majority of the extracellular matrix; ii) paracrinesignaling molecules, such as transforming growth factor β1, are essential mediators of fibrosis, whether it is pathological or biomaterial induced; and iii) injury and/or the presence of foreign materials (including bacterial components, toxins, or man-made objects) are essential initiators for the development of the fibrotic response. This review discusses mechanisms and research methodology related to pathological fibrosis that is of interest to researchers focused on biomaterials. Potential research models for the study of fibrosis from the fields of biomaterials and drug delivery are also discussed, which may be of interest to scientists working on the pathology of fibrotic disease.