Electrostriction is the basis of electromechanical coupling in all insulators. The quadratic electrostrictive strain x ij associated with induced polarization components Pk and P l is given by x ij = Q ijkl P k P l . Two converse electrostrictive effects may also be defined. In this paper, some trends in structure−property relationships that govern electrostriction are identified, along with the problems that limit our understanding of this fundamental electromechanical property. Electrostrictive coefficients range from the ∼10-3 m4/C2 in relaxor ferroelectrics to ∼103 m4/C2 in some polymers. High-sensitivity techniques, such as interferometry or compressometry, are necessary to accurately measure electrostrictive effects in most insulators. But even in low-K dielectrics, electrostrictive stresses may initiate breakdown in high-field environments such as microelectronic components with small dimensions, high-voltage insulators, or in high-power lasers. In polymeric materials, charge injection mechanisms may produce local electric field concentrations that can cause large electrostrictive strains. The electromechanical properties in polymers have also been observed to vary with the thickness of the specimen. A brief description of the anharmonic nature of electrostriction and its frequency dependence is included.

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Alternating tangential flow filtration (ATF) has become one of the primary methods for cell retention and clarification in perfusion bioreactors. However, membrane fouling can cause product sieving losses that limit the performance of these systems. This study used scanning electron microscopy and energy dispersive X‐ray spectroscopy to identify the nature and location of foulants on 0.2 μm polyethersulfone hollow fiber membranes after use in industrial Chinese hamster ovary cell perfusion bioreactors for monoclonal antibody production. Membrane fouling was dominated by proteinaceous material, primarily host cell proteins along with some monoclonal antibody. Fouling occurred primarily on the lumen surface with much less protein trapped within the depth of the fiber. Protein deposition was also most pronounced near the inlet/exit of the hollow fibers, which are the regions with the greatest flux (and transmembrane pressure) during the cyclical operation of the ATF. These results provide important insights into the underlying phenomena governing the fouling behavior of ATF systems for continuous bioprocessing.

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