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A study of the final deposition of inkjet-printed complex bioink drops
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A study of the final deposition of inkjet-printed complex bioink drops

Paul Raju Kaneelil
Master of Science (M.S.), Drexel University
Jun 2018
DOI:
https://doi.org/10.17918/t7s9-qp74
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Abstract

Evaporation (Meteorology) Fluid Mechanics Mechanical Engineering Tissue Engineering
Regenerative medicine has been gaining a great deal of popularity in the recent years due to the advent of technology that allows for the fabrication of lost tissues and organs in the human body. A process that enables this fabrication is called bioprinting, which uses additive manufacturing methods such as inkjet printing to create 3D cellular scaffolds out of polymer-based bioinks. In recent years, 4D bioprinting was introduced where the inkjet-printed 3D structure evolves over time and self-folds into a desired shape upon the application of a stimulus. One of the parameters that influences the folding is the deposition morphology of the 3D structure. However, the underlying physics of the deposition morphology of bioinks still remains elusive. In this study, the effect of substrate temperature and drop size on the final deposition morphology of an inkjet-printed bioink droplet were investigated. Substrate temperature was varied between 22°C and 80°C, and drop size was varied from 200pL to 65nL. Increasing substrate temperature resulted in the formation of a coffee-ring deposition and increasing drop size led to the formation of a volcano-like deposition. The thermal and surfactant Marangoni numbers for each case were calculated and were found to be independent of the substrate temperature. Furthermore, the surfactant Marangoni was found to be the dominant flow among the various Marangoni flows in all the cases studied here. Thus, with increasing substrate temperature, the strength of the Marangoni flows stays constant while the evaporation-driven flow to the contact line intensifies, resulting in a coffee-ring deposition. With increasing drop size, the Marangoni flows are strengthened (i.e. the Marangoni number increases), which should theoretically result in a uniform deposition rather than the volcano-like deposition observed. This unexpected result may be caused by polymer gelation during evaporation, as also recently indicated by others. Nevertheless, more work needs to be done to understand the details behind how the various components of the bioink govern the deposition dynamics and morphology.

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