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Author ORCID Identifier

https://orcid.org/0000-0003-4001-7694

Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Chemical Engineering

Year Degree Awarded

2019

Month Degree Awarded

September

First Advisor

Shelly R. Peyton

Subject Categories

Chemical Engineering

Abstract

Bioengineers have aimed to design instructive extracellular matrix (ECM) models that can tailor the protein composition and biomechanics of the brain in vitro in order to study how astrocytes remodel the brain during trauma and inflammation. However, these parameters cannot be independently controlled in protein-based models, and although tunable in synthetic systems, current astrocyte cultures fail to retain their characteristic stellate morphology without becoming activated. To this date, there is no biomaterial model that can retain astrocyte quiescence in vitro. This dissertation sought to develop such an in vitro model that would enable the study of specific ECM factors that control astrocyte activation while retaining quiescent astrocytes in vitro. Here we introduce a synthetic hydrogel, that for the first time shows maintenance of astrocyte quiescence and control over activation on demand. We first characterized the human brain ECM via proteomics, and the brain biomechanics via needle-induced cavitation rheology and volume-controlled cavity expansion and incorporated the top ECM components responsible for integrin-mediated and MMP-mediated degradation alongside matched mechanical properties into a fully synthetic hydrogel. Using this hydrogel, composed of just PEG and peptides, we demonstrate control over astrocyte activation via tuning of the integrin-binding and MMP-degradable profile or via cytokine molecules, in contrast to other protein-based models like collagen where astrocytes remain in a reactive state. Finally, to aid with the implementation of biomaterials as in vitro platforms to predict in vivo physiology, the correlation between current 2D, 3D and in vivo studies of glioblastoma motility was explored, and how an effect size can help standardize comparison across labs and culture dimensions. An additional study highlighted the importance of adopting growth rate in drug metric responses and how these can be implemented in current biomaterial platforms. Overall, this work can help integrate biomaterials as models to predict in vivo physiology. This brain hydrogel system can be used as a new platform to model the physiological state of quiescent astrocytes and their reactivity upon injury, for the first time, in vitro.

Creative Commons License

Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License.

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