These findings demonstrate that established RA is characterized by a persistent IgA ACPA response that exhibits ongoing affinity maturation. This observation suggests the presence of a persistent mucosal antigen that continually promotes the production of IgA plasmablasts and their affinity maturation and epitope spreading, thus leading to the generation of ACPAs that bind additional citrullinated antigens and more potently stimulate macrophage production of TNF.
While active fiber composites (AFC) based upon solid cross-section piezoelectric fibers are very useful for anisotropic activation of composites, they require high voltages and are constrained to non-conductive matrix materials. AFC's based upon hollow cross-section piezoelectric fibers have shown promise to lower operating voltages and broaden the choice of possible matrix materials. This paper presents an investigation of the key design parameters for hollow piezoelectric fibers (matrix/fiber Young's moduli, aspect ratio of the individual fibers, and the overall active composite volume fraction) and their effect on the performance, manufacturing and reliability of active fiber composites. Because the ultimate objective in utilizing active composites centers on their ability to deform, an analysis was conducted on existing fiber and lamina strain/electric field models to identify optimal parameter values and determine limitations via an embedment stress model. Fabrication of the fibers has a clear impact on these factors. To assess this, standard machinery inspection criteria was used to evaluate fibers, manufactured through microfabrication by coextrusion (MFCX), with respect to their geometric (cross-sectional ovality, eccentricity, straightness) and material (density, porosity, piezoelectric properties, Young's modulus) properties. These studies indicated that there are circumstances under which low aspect ratio (thin walled) fibers will be optimal, but clearly, reliability issues will arise. Unfortunately, little data exists on reliability of either hollow or solid piezoelectric fibers. To identify the primary failure mechanism, ultimate strength, strain-to-failure and interfacial shear strength were examined using three types of experimental tests: 1) tensile strain-to-failure, 2) single fiber fragmentation, and 3) single fiber indentation. From this work, it is clear there will always be design trade-offs present and it is important to consider performance, fabrication, and reliability
Active composites based on a hollow fiber topology have advantages over solid piezoelectric fiber composites in that they require lower voltages for activation and are not limited to electrically non-conductive matrix materials. One critical issue for hollow fiber composites is the fiber aspect ratio (ratio of wall thickness to fiber radius). In this paper analytical and finite element models, which include electric field variations, were developed to determine the "effective d 31 " of an individual piezoelectric hollow fiber. The effective fiber properties were used to derive a single-row lamina strain/electric field model from classical composite theory. The models were validated with a series of deflection/voltage experiments conducted with hollow piezoelectric fibers fabricated utilizing microfabrication by coextrusion (MFCX) techniques. To determine the feasibility of MFCX hollow fiber composites, the models and experimental results were employed to study the effect of the fiber aspect ratio on a variety of fiber/composite design issues: fiber/lamina performance, fiber strength, matrix material, and electric field effects (incomplete poling and field concentrations).
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