Manufacturing USA: Study of Self-Supporting Nanoclay as Internal Scaffold Material for Printing of Skeletal Tissue Constructs

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This award supports research on three-dimensional (3D) extrusion bioprinting processes using a unique, biocompatible, nanoclay additive. Material extrusion bioprinting is a compression-based additive manufacturing process in which material is forced to flow through a nozzle to produce continuous filaments for layer-by-layer deposition. The addition of the nanoclay to hydrogels typically used in printing will increase the geometric complexity and mechanical integrity of the printed bioscaffold structures. Currently the extruded hydrogel should be rapidly gelled (solidified) to hold its shape immediately after printing, and to support the following printed layers. This limits the selection of printable biomaterials to those exhibiting suitable rapid gelation mechanisms, and limits the geometries feasible without the use of supporting materials that must be later removed. The nanoclay addition to the hydrogel functions as an internal scaffold material to hold the shape of the extruded material directly after printing. The printed construct is only gelled after the whole part is finished; this has the additional potential benefit of avoiding interlayer bonding issues and enhancing the structure's mechanical integrity. If successful, this research can advance U.S. bioprinting manufacturing capabilities and national welfare by enabling personalized, printed scaffolds for skeletal tissue engineering applications such as bone replacement and regeneration. The award will also facilitate training of the future workforce as students across all levels will gain exposure and experience in biomedical manufacturing. Additional educational outreach activities include engaging high school students in STEM immersion weeks organized by the Florida Center for Precollegiate Educational and Training.The research objective of this project is to understand the characteristics and fundamental processing limitations of thixotropic nanoclay only and nanoclay-hydrogel mixed colloids. Thixotropic, self-supporting gels, in particular silicate-based nanoclay colloids made from high-concentration Laponite nanoclay, transition from being viscous under static conditions to less viscous when stressed. This thixotropic, self-supporting property is also observed in various nanoclay-hydrogel mixed colloids, enabling Laponite nanoclay as a promising internal scaffold material for nanoclay-hydrogel composite 3D direct printing in air. To this end it is hypothesized that nanoclay colloids prepared at certain aging times and concentrations form an attractive gel state and result in a fractal network with thixotropic, self-supporting property. To test the hypothesis, the microstructure of high-concentration nanoclay colloids will be characterized using scattering and microscopic technologies to reveal their unique gel state. The fluid dynamics during nanoclay-enabled extrusion will be modeled using a volume of fluid-based simulation approach, and the filament formability will be represented using a set of non-dimensional numbers and further compared with experimental observations. Based on the shear and tensile yield stresses of high-concentration nanoclay colloids, the effect of material properties on the printable geometry will be determined using the Euler-Bernoulli beam theory and experimentally validated. Printed nanoclay-hydrogel scaffolds will be evaluated in terms of their degradation, biological, and biomineralization properties for skeletal tissue engineering applications.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.