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 interstial 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.
Bibliographical noteFunding Information:
This work was supported by National Science Foundation Grant BES-9424063 and the Coating Process Fundamentals Program of the Center for Interfacial Engineering at the University of Minnesota. The authors thank Dr. Michael Bench for help with the microscopy.
- Scanning electron microscopy