Date of Award

5-2014

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Mechanical Engineering

Advisor

Miller, Richard S

Committee Member

Huang, Yong

Committee Member

Qiao, Rui

Committee Member

Xuan, Xiangchun

Committee Member

Gao, Zhi

Abstract

Inkjet printing has found an increasing number of biofabrication applications, specifically organ printing, which has been emerging as a promising solution to the organ donor shortage. While some studies have been conducted to investigate various engineering problems associated with DOD inkjet printing of biological material-based fluids, the pinch-off, the cell-laden droplet formation, the effects of electric field on droplet formation, and challenges in 3D vascular-like construct fabrication haven't been systematically investigated. The objective of this study is to investigate the pinch-off, the cell-laden droplet formation, the effects of electric field on droplet formation, and manufacturing challenges during fabrication using DOD inkjet printing. The pinch-off process during DOD inkjet printing of viscoelastic alginate solutions is systematically investigated by studying the effects of sodium alginate (NaAlg) concentration and operating conditions on the pinch-off. It is found that there are four types of pinch-off during DOD inkjet printing of viscoelastic NaAlg solutions: front-pinching, exit-pinching, hybrid-pinching and middle-pinching. In particular, front-pinching is governed by a balance of inertial and capillary stresses, while exit-pinching is governed by a balance of elastic and capillary stresses. An operating diagram is constructed with respect to the Weber number and a proposed J number to classify regimes for different types of pinch-off. The cell-laden droplet formation is studied and compared with the droplet formation of polystyrene bead-based suspensions. It is found that the breakup time increases but the droplet size, droplet velocity, and number of satellites decrease as the cell concentration increases. Compared to the polystyrene bead-based suspension, the ejected fluid volume is less, the droplet velocity is smaller, and the breakup time is longer using the cell-laden bioink. The electric field-assisted droplet formation under piezoactuation-based DOD inkjet printing is investigated. It is found that droplet velocity increases and the droplet size decreases with the increase of the applied voltage. Pinch-off locations may vary depending on the applied voltage. The combination effect of the electric field and meniscus oscillation can be utilized to significantly reduce the droplet diameter. The electric field extends the capability of DOD inkjet printing to bioinks with high cell concentrations. The gained knowledge of DOD inkjet printing has been further applied to vertical and horizontal printing of 3D vascular-like constructs using cell-laden bioink. It is found that the maximum achievable height of overhang structure depends on the inclination angle during vertical printing. To overcome the deformation-induced construct defect during horizontal printing, a predictive compensation approach has been proposed to fabricate 3D tubular constructs horizontally. Alginate cellular tubes have also been successfully printed with a satisfactory post-printing cell viability of 87% immediately after printing and after 24 hours of incubation. Overall, this dissertation provides a better understanding of the pinch-off of viscoelastic alginate solutions, cell-laden droplet formation, effect of electric field on droplet formation under piezoactuation-based DOD inkjet printing, and fabrication process of 3D vascular-like constructs from bioink. This work would help better fabricate tissue-engineered blood vessels with a complex geometry using DOD inkjet printing.

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