Chemical gradients development

During diffusion, a c i gradient develops in the chemically homogeneous material. 

While new chemical product development has historically been the domain of chemists, the use of chemical products by consmners invariably involves some transformation of the product due to applied stresses, temperature gradients, physicochemical hydrodynamics, mass transfer, etc., making product use a process in the chemical engineering sense. [2,4] Thus the analysis of product behavior ultimately requires the same fundamentals as the analysis of process behavior, and is well suited to study by chemical engineers. 

Electrokinetic processing of soils, by application of a direct current through a wet soil mass, results in the development of electrical, hydraulic, and chemical gradients. The formation of an acidic front at the anode from water electrolysis and the induced electroosmotic flux of the pore fluid enable the removal of those contaminants that can be solubilized, desorbed from the soil, or simply carried by the pore fluid. The fundamental basis of each of these two main processes is described below. 

Models of the lateral interspace have been developed that include diffusion within the channel as well as bounding membranes of finite permeability [55,56]. The model of Weinstein and Stephenson [57] extended these efforts by incorporating the three ionic species Na, and Cl into a model of the whole epitheUum. Within both cell and channel the ions move in response to both chemical gradients and electric fields according to the Nemst-Planck equation... 

While homogeneous stimulus-response assays are more straightforward, a particularly useful kind of assay relies on heterogenous stimuh in the form of chemical gradients. A device for creating controlled linear, parabolic, and periodic concentration gradients was developed by... 

A perfusion microbioreactor has been developed based on mass transport simulation to find out reasonable culture scales with relatively low chemical gradients [10]. Here a PDMS surface is treated with surfactant solution to reduce nonspecific serum protein adsorption, which keeps the culture conditions steady. As described above, to achieve physiologically meaningful functions in vitro, a culture with a larger number of cells and higher density must be obtained. 

Microfluidics is an emerging field that is finding a lot of applications in cell biology. The ability to precisely control the various mechanical cues like shear stress and to produce and maintain precise chemical gradients, good optical resolution, and biocompatibility makes microfluidic platform a useful tool to develop three-dimensional migration assays. This chapter will cover and discuss the potential use of some three-dimensional migration assays developed in a microfluidic system. 

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