Document Type

Honors Thesis

Major

Biomedical Engineering

Advisor(s)

Bashir Khoda

Committee Members

Stephen Abbadessa, Julie DellaMattera, Michael Mason, Karissa Tilbury

Graduation Year

May 2022

Publication Date

Spring 5-2022

Abstract

Biofabrication is the process of creating complex biologic products, such as artificial tissues, from raw materials such as living cells, biomaterials, and molecules. This can be done using 3D printed bio-ink, which is a combination of biomaterials and cells. However, the bio-ink must be a shear thinning fluid to allow for high-resolution and continuous printing, but also demonstrate post-printing mechanical integrity to self- support the structure, which is challenging to achieve. The research conducted here investigates how to improve the mechanical functionality of bio-ink using additives available in Maine. Chitosan, sodium alginate, and TEMPO nano fibrillated cellulose were chosen as the candidate biomaterials due to their biocompatibility. The printability of the bio-ink can be determined by considering the rheological properties and printing parameters for numerous mixtures. This research focuses on how the mixture ratio affects the printability of the bio-ink, while also investigating the individual material contributions.

Rheological data of four ink compositions were compared, and a “design of experiments” approach was used to determine which hydrogel ink produced the smallest filament width, and therefore best quality, when printed. The four ink compositions used were 2:1:0.1 w/v%, 2:1:0.5 w/v%, 2:1.5:0.1 w/v%, and 2:1.5:0.5 w/v% of Alginate:TEMPO-NFC:Chitosan. A flow curve, amplitude sweep, and thixotropy test were conducted for each ink to gather viscosity and modulus values data, and all tests indicated that the tested inks would be successful in printing. Each ink was then 3D printed to analyze filament width, which revealed the ink of highest solid content resulted in the smallest width. Lastly, the design of experiments approach was applied to filament width and viscosities to reveal chitosan changes had the most effect on filament width, but T-NFC changes had the most effect on viscosity changes. Equations were also developed that can be used to predict the outcome variables of inks that could be tested in the future.

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