Date of Award

Spring 1-1-2017

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

First Advisor

Robert R. McLeod

Second Advisor

Stephanie J. Bryant

Third Advisor

Virginia L. Ferguson

Fourth Advisor

Sean E. Shaheen

Fifth Advisor

Juliet T. Gopinath

Abstract

The goal of this thesis was to locally photopattern cytocompatible hydrogels to exhibit a wide range of mechanical properties and to probe the fundamental parameters governing these materials printed via stereolithography (SLA). Fabricating cell-laden structures with locally defined mechanical properties is non-trivial because the use of multiple precursor materials is wasteful, slow, and can lead to cell-death. To investigate the range of mechanical properties a single precursor solution can produce, I initially formed a single-network hydrogel and cyclically in- swelled fresh precursor solution followed by photo-exposure of the swollen gel (“swelling + exposure” or SE cycle). Because transport (i.e., diffusion and swelling) can occur on the same time scale as photopolymerization reaction kinetics, I first characterized the variable modulus hydrogels in bulk to isolate the reaction kinetics. In these experiments, I demonstrated the ability modify the mechanical and chemical (i.e., compressive modulus, toughness, crosslink density, swelling ratio) properties by up to 10-fold using only 2-4 SE cycles.

I then used the understanding gained via these bulk experiments to locally photopattern the elastic modulus of a cytocompatible hydrogel with pixel-limited resolution (~10s μm) employing a custom SLA system. Here I demonstrated the ability to fabricate hydrogels with a 500% elastic moduli increase with respect to the unpatterned hydrogel using atomic force microscopy. I monitored monomer attachment to the existing matrix as a function of SE cycle using confocal fluorescence microscopy to characterize the shape and size of printed features. I validated that the dependence of these features on material and processing conditions could be explained by a first-order reaction/diffusion model. With this understanding, I fabricated SLA 3D printed, soft, cytocompatible hydrogels (~10s kPa) with ~250 µm channels in addition to fabricating 3D printed stiff, cytocompatible hydrogels (39 MPa) both with ~10 µm resolution.

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