Humidity-Controlled Micro-Additive Manufacturing with Polymeric Bioinks

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Bio-inks are biocompatible hydrogels and water-soluble polymers that are used to additively manufacture next-generation medical and pharmaceutical products. These materials are synthesized to carry substantial amounts of water along with living cells, their nutrients or drugs, while supporting their activity or controllably releasing them in the human body. Through additive manufacturing, bio-inks precisely loaded with bio-materials can be extruded and assembled layer-by-layer to fabricate personalized artificial tissues and drug delivery vehicles. Success of such groundbreaking technologies relies heavily on how precisely they mimic the native tissues they are working with. This requirement poses a significant manufacturing challenge since human tissues are highly complex with critical feature sizes in the order of tens of microns. Current bio-printing technologies, having a print resolution of greater than 100 microns, are incapable of printing sufficiently fine features. Challenges arise because of a lack of a complete understanding of the bio-ink behavior when printing smaller features, and other practical issues such as rapid drying of the smaller printed geometries leading to print non-uniformity. This project will address these scientific challenges and substantially increase the resolution of bio-printed components. If successful, this novel approach will advance U.S. bioprinting manufacturing capabilities and National Welfare by enabling the realization of effective personalized medicine. Immediate impacts in this regard will include increased success rate in artificial tissue implants for treatment of degenerative diseases, and higher effectiveness of drug delivery through the skin in the treatment of chronic skin diseases, which affect more than 30% of the population. The research activities of this project will be closely integrated with educational and outreach activities. Educational components will prepare the next generation of engineers to work in biomedical related additive manufacturing technologies, while the planned outreach will increase the public's awareness and understanding of these exciting technologies. This research seeks to achieve controllable micro-additive manufacturing of bio-inks via localized humidity and temperature control at the printhead nozzle. It is believed that local control of these parameters will prevent the higher bio-ink drying rates, associated with smaller printed geometries, that currently hinder high-resolution print uniformity and adhesion between subsequent build layers. The fundamental aspects of the humidity-controlled printing process will be studied through a combined experimental and computational modelling approach. Tasks include; 1) characterization of the humidity and temperature dependent visco-elasto-capillary behavior of various hydrogels and water-soluble polymers, 2) generation a multi-physics-based computational model, incorporating visco-elasto-capillary action, to capture ink deposition and layer-to-layer fusion mechanisms under specified humidity and temperature conditions, and 3) experimental validation of the model by examining the mechanical integrity and properties of high resolution, bio-printed structures. The findings of this work will advance the science of hydrogels and water-soluble polymers, while also informing product and bio-printing process design.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.