Polymer Entrapment

FIGURE 8.18 (a) Phase contrast micrograph of cardiac myocytes patterned in the acrylic channel. Time courses of fluorescence of cytosolic Ca2+ measured at points 1 and 2 denoted in the micrograph (b) when all myocytes were placed in laminar flows of the buffer, (c) 2 min after localized delivery of 100-pM octanol only to the upper part of the image (point 1) [198]. Reprinted with permission from the Royal Society of Chemistry. 

Escherichia coli cells (BL21) were entrapped in hydrogel micropatches. The cells were found to remain viable in the patches. Furthermore, diffusion of small molecules through the polymer (with 1-10 nm pores) to the cells allows cell reactions to be studied. For example, the fluorescent dye BCECF-AM diffused to the cells and the dye was converted to BCECF by intracellular enzymes present only in live cells [1053]. 

A layer-by-layer microfluidics technology was used to construct a 3D microscale hierarchical tissue-like structure. For instance, three layers of tissues, fibroblasts (human lung), myocytes (smooth muscle cells), and endothelial cells (human umbilical vein) were cultured on top of each other using consecutive microchannel cell matrix delivery. Cell viability was confirmed by fluorescent staining [862]. 

Microwells defined in agarose were used to culture nerve cells. The dendrite growth of the nerve cells was studied in narrow tunnel-shaped channels in agarose. The tunnels were fabricated by photo-thermal etching the agarose [863]. 

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Entrapment of biochemically reactive molecules into conductive polymer substrates is being used to develop electrochemical biosensors (212). This has proven especially useful for the incorporation of enzymes that retain their specific chemical reactivity. Electropolymerization of pyrrole in an aqueous solution containing glucose oxidase (GO) leads to a polypyrrole in which the GO enzyme is co-deposited with the polymer. These polymer-entrapped GO electrodes have been used as glucose sensors. A direct relationship is seen between the electrode response and the glucose concentration in the solution which was analyzed with a typical measurement taking between 20 to 40 s. 

To assess the utility of this resin, we chose to employ it in the evaluation of the heterogeneity of a commercial polymer-entrapped Pd(OAc)2 precatalyst, Pd-EnCat, also sold by Reaxa. This precatalyst was designed with the goal of providing a heterogeneous catalyst that would allow simple removal of palladium from reactions (24-26). PVPy and QTU were first used as poisons in the Heck reaction of iodobenzene and n-butyl acrylate in DMF using PdfC as the palladium... 

Richardson JM, Jones CW (2006) Poly(4-vinylpyridine) and quadrapure TU as selective poisons for soluble catalytic species in palladium-catalyzed couphng reachons - apphcation to leaching from polymer-entrapped palladium. Adv Synth Catal 348 1207... 

Bettmann H., Rehm H.J. 1984. Degradation of phenol by polymer entrapped microorganisms, Appl. Microbiol. BiotechnoL, 20, 285-290. 

Cosnier and coworkers coupled the polymer entrapment strategy with the use of CNTs as porous conductive support [28]. Methyl viologen as a redox mediator covalently bound to the polymer ensured a high indirect electron transfer from D. jructosovorans hydrogenase to the CNTs. Again, a 10-fold increase in... 

A colored printing ink for contact lenses has been detailed (91,92). A method for making a hydrophilic contact lens is comprised of the steps of providing a polymeric contact lens and coating a portion of a surface of the lens with a coat. This coat contains a colorant, and a crosslmked binder polymer. The binder polymer entraps the colorant and adheres to the lens. A binder polymer for a colored base ink is summarized in Table 7.12. 

Stopping polymer flow results in a significantly increased permeability to polymer solution. This phenomenon cannot be explained by the polymer entrapment in small channels. In the no-flow period, the entrapped polymer molecules would have to leave these pores very easily, which could occur only by diffusion. But the motion of polymer molecules is highly restricted in these pores therefore, a concentration equalization by diffusion is very unlikely. 

Using a certain flow velocity at which the injected polymer concentration exceeds the critical polymer concentrations, the porous material will strip out all the excess polymer concentration above the critical concentration value. The accumulations of this excess polymer concentration take place not only at the inlet surface, but also in depth. If the injected concentration is equal to or less than the critical polymer concentration, no continuous polymer buildup will occur anywhere in the porous medium. The number of entrapped polymer molecules should be proportional to the polymer concentration above the critical polymer concentration. Since the excess polymer concentration is greatest at the injection face, the rate of polymer entrapment is also highest at this location. 

In the low permeability sand the absolute retention versus applied concentration curves show a leveling oif section. This fact is related to the mechanism of polymer entrapment in small pores. In very small pores (173 md sand), less polymer concentration is needed to effectively restrict a continuous polymer buildup in these pores. 

Kottke PA, Kranz C, Kwon YK, Masson JF, Mizaikoflf B, Fedorov AG (2008) Theory of polymer entrapped enzyme ultramicroelectrodes flindamentals. J Electroaneil Chem 612 208-218... 

Another approach is based on the application of redox polders, e.g. osmium complex-modified poly(vinyl pyridine) (9-11) or ferrocene-modified poly(siloxanes) (12,13X crosslinked together with an enzyme on the top of the electrode. The electron transfer fi-om the active site of the polymer-entrapped enzyme to the electrode surfece occurs to a first polymer-bound mediator which has suflSdently approached the prosthetic group to attain a fast rate constant for the electron-tranrfer reaction. From this first mediator the redox equivalents are transported along the polymer chains by means of electron hopping between adjacent polymer-linked mediator molecules (Fig. 2). Extremely fast amperometric enzyme electrodes have been obtained with si ificantly decreased dependence fi-om the oxygen partial pressure. However, die redox polymer/enzyme/crosslinker mbcture has to applied either manually or by dipcoating procedures onto the electrode surface. 

K. Mosbach and P. O. Larsson (1970), Preparation and application of polymer-entrapped enzymes and microorganisms in microbial transformation processes with special reference to steroid ll-j5-hydroxylation and d -dehydrogenation. Biotechnol. Bioeng. 13, 19-27. 

Piezoelectric microdispensing and ink-jet printing systems have been used to form spots of polymer-entrapped enzymes and the resulting structures have been analyzed using SECM [107-109]. Particular attention has been devoted to create dual enzyme structures from GOx and catalaze [108]. 

Figure 1. Reaction of blood to different surfaces a) natural blood vessel wall consisting of endothelium (E) and subendo-thelial connective tissue (CT) shows no thrombogenic reaction to flowing blood, b) rough surfaced porous polymers entrap and clot blood as it flows past. Fibrinogen in blood precipitates as fibrin entrapping the blood cells, c) smooth surfaced polymers form small platelet aggregates at the interface with the blood, which embolize into the blood stream.

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