Biomedical subjects

MC Flickinger

Publications and source records attributed to MC Flickinger.

5 recordsLinked to original sources

PubMed1999

Microstructure Evolution in Polymer Latex Coatings for Whole-Cell Biocatalyst Application.

The microstructure evolution of two poly(vinyl acetate-co-acrylic acid) latex coatings was elucidated by cryogenic scanning electron microscopy (cryo-SEM) and atomic force microscopy. The stages documented are particle suspension, consolidation, deformation, partial coalescence into a coherent film, and rehydration of the latter. Of particular interest is formation of a porous polymeric matrix of desired porosity and permeability of remnant interstices between deformed and partially coalesced particles; the application is to biocatalytic coatings in which viable bacteria are imprisoned in porous latex coatings. Effects of drying condition and time, rehydration behavior of latex, and the presence of glycerol on the microstructure of latex coatings were revealed by time-sectioning and cryofracture techniques of cryo-SEM. Results showed that porosity and permeability can be controlled by choice of drying and rehydration protocols. Evidence showed that glycerol retarded particle deformation, compaction, and coalescence and that substantial amounts of glycerol were expelled to the surface of the coating as drying proceeded. Implications for design of bacteria-laden and bacteria-free coating layers are discussed. Copyright 1999 Academic Press.

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PubMed1999

Microstructure of a Biocatalytic Latex Coating Containing Viable Escherichia coli Cells.

Cryogenic scanning electron microscopy (cryo-SEM) was employed to visualize the microstructure of latex coatings in which viable Escherichia coli cells were entrapped for use as biocatalysts. Cryo-SEM examination of surfaces and fracture cross sections of dry and hydrated coatings cast with or without glycerol revealed two different porosities in the films: a macroporosity in which the bacterial cells reside and a microporosity made up of the interstitial voids between partially coalesced latex polymer particles. Polymer particle consolidation and coalescence in the cell-laden coatings were at an earlier stage than in cell-free latex coatings detailed in a companion paper. Coatings cast with glycerol showed a lesser degree of latex particle consolidation and coalescence than those cast without glycerol. However, the effect of glycerol was not as pronounced as in cell-free coatings. We conclude that part of the added glycerol is sequestered inside the bacterial cells and the portion remaining outside the cells retards the latex film formation process and enhances microporosity. Two commercial acrylic acid/vinyl acetate copolymer latexes were examined. Coatings made with the polydisperse latex showed less microporosity and a greater degree of particle welding than those made with the nearly monodisperse latex. Copyright 1999 Academic Press.

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PubMed1999

Construction of a thread coater and use of azocasein release To characterize the sealant coat porosity of fibers coated with latex biocatalytic coatings

A single-stage annular fiber coating method with co-current dry-air drying at 30 degrees C has been developed for multilayer coating of 128 &mgr;m diameter polyester thread (yarn) with latex films as a model for enzyme immobilization and development of a filament biocatalytic filter. Acrylic vinyl acetate polymer coatings were sequentially metered onto the fibers by the combination of a flexible squeegee and a red rubber annulus. The thread coater can operate over a range of 0.07-1.37 m/min thread velocities while delivering a nearly constant and reproducible polymer loading of 30. 8 +/- 1.3 mg/m. A 100% polyester, 278.9 denier thread was precoated with latex to generate an approximately 369 denier sealed filament. The filament was then coated with a latex + sulfanilamide-azocasein mixture and sealed with a polymer top coat. The permeability of the polymer sealant top coat was characterized using entrapped azocasein as a tracer molecule and monitoring the azocasein release upon rehydration of the coated threads. Azocasein release rate decreased with curing time at 30 degrees C until 2 days and was invariant after 2-3 days of curing. A 282 mOsm rehydrating solution was sufficient to suppress increased azocasein release due to top coat blistering. No enhancement in the permeability of the top coat was observed when high molecular weight water soluble polymers (WSPs) were used as fillers. This probably results from the low WSP to latex ratio used (0.05-0.1) and the slow rate of WSP leaching compared to the release of azocasein. A method using 60-120 mesh silica was also developed to study the effect of mechanical abrasion of the coated threads as measured by azocasein release kinetics.

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PubMed1998

Method for construction of a simple laboratory-scale nonwoven filament biocatalytic filter

A method is described for constructing a simple laboratory-scale nonwoven filament biocatalytic filter (FBF) from multilayer acrylic vinyl acetate copolymer coated thread (yarn) potentially useful for investigation of biotransformations using entrapped enzymes or viable microorganisms. The porous structure of a commercial 128 &mgr;m, 279 denier, 100% polyester thread was sealed with a latex coat (precoat), then coated with a latex + sulfanilamide-azocasein mixture, and finally coated with a latex top coat to generate the multilayer coated thread. The FBF was constructed by drawing the thread across a 4 cm diameter rubber O-ring in the form of multiple layers and sealing the layers with silicone sealer. The FBF is combatible with a commercially available filter housing containing a flow distrtibutor. A method for characterizing the permeability of the sealant (top) coat of the FBF using azocasein release was also developed.

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PubMed1996

An Approach to Hierarchically Structured Porous Zirconia Aggregates

Presented here is a simple, inexpensive approach to aggregating colloids into hierarchically structured spherical particles. Successive aggregation steps are used to assemble a particle that is self-similar on two size scales and is permeated by an ordered pore network with a bidisperse size distribution. The structure of the micro- and macropore networks as well as the mechanical integrity of the structure can be controlled by varying sintering conditions.

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