Date of Graduation

12-2022

Document Type

Thesis

Degree Name

Master of Science in Biological Engineering (MS)

Degree Level

Graduate

Department

Biological and Agricultural Engineering

Advisor/Mentor

Jin-Woo Kim

Committee Member

Steven Tung

Second Committee Member

Jun Zhu

Third Committee Member

Joshua Sakon

Keywords

3D Bioprinting, Biopolymers, Cellulose Nanocrystals, Nanocellulose, Scaffold Engineering

Abstract

3D bioprinting of biological scaffolds requires control of the physicochemical properties of each unique structures. A promising material for control of properties is hydrogels, which can help create biomimetic scaffolds with controlled spatial arrangement of materials by integrating biological materials directly into layers during the bioprinting process. Nanocellulose offers a unique combination of properties including mechanical, biomimetic, and biocompatibility. These properties offer flexibility over the types, shapes, and applications of their printed hydrogel scaffolds, (i.e., tissue, drug, encapsulation). However, 3D bioprinting of nanocellulose-based hydrogels requires high loading percentages (i.e., >10 wt%) or chemical crosslinkers (i.e., bis(acyl)phosphane oxides (BAPO)). High solid content of nanocellulose results in high printing pressures and stress (i.e., >400kPa, >3kPa respectively) on extruded materials, leading to deviation in desired structures as well as undue stress on active biological materials in inks. Current chemical crosslinking methods require harsh chemicals (i.e., acids or bases) exposure and/or high-intensity light exposure (e.g., photo-crosslinkers), leading to potential for damage to biological components. In this study, solutions were explored to overcome the challenge to 3D bioprinting of nanocelluloses, i.e., the needs of high solid content and/or chemical crosslinking. Specifically, lower solid content inks with biocompatible crosslinking agents were investigated to reduce printing pressure and stress on biological components during bioprinting. Four biocompatible crosslinking agents were selected: methyl cellulose, glycerol, epoxidized soybean oil, and poly-epichlorohydrin. Printability of cellulose nanocrystal (CNC) scaffolds with each crosslinking agent was evaluated by assessing pre-print properties of inks, printing parameters, and printed structure characteristics. Rheological evaluation of crosslinked inks showed potential for 3D printing based on tan(δ) and viscous properties. Consistent printing was observed withing an acceptable range (i.e., <110kPa, <1.1KPa) for pressure and stress respectively across differing nozzle sizes. Differences in structural properties (i.e., alignment, strength, aqueous stability) was observed showing promise for tunability of structural characteristics based on crosslinker and/or printing parameters. Overall, nanocellulose, CNC specifically, shows great potential for 3D bioprinting and tissue engineering.

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