Advancing techniques for engineered tissue models of the bone marrow

Hematopoietic stem cells give rise to the blood and immune systems in organisms. These rare cells reside within the bone marrow and are the functional units of hematopoietic stem cell transplants, also known as bone marrow transplants. Methods to model the bone marrow and expand hematopoietic stem cells ex vivo are constantly evolving; however, models that capture the hypoxic nature and heterogeneity of natural tissues such as the bone marrow are difficult to develop. Oxygen tension is known to play a role in several physiological processes, such as wound healing and angiogenesis. Though the bone marrow is a hypoxic tissue, relatively few hematopoietic studies incorporate hypoxia as a biological variable. Here, we applied hypoxia to a gelatin methacrylamide hydrogel model of the perivascular bone marrow niche and demonstrated the importance of oxygen tension in the hematopoietic stem cell isolation process for engineered models of the bone marrow. We then turn to a new class of biomaterial – granular hydrogels – which have the potential to recapitulate natural tissue heterogeneity due to their composition by discrete microgel subunits that are packed together. We tuned the synthesis conditions for gelatin maleimide, enabling microfluidic emulsion of monodisperse, cell-laden microgels. Building on that foundation, we developed a first-generation microgel-based approach toward hematopoietic stem cell-mesenchymal stromal cell co-culture. Through this work, we showed the importance of hydrogel configuration: mesenchymal stromal cells encapsulated in microgels had a more potent transcriptional profile relative to macrogel-encapsulated mesenchymal stromal cells. This granular platform also showed the potential to preserve long-term repopulating hematopoietic stem cells with the addition of mesenchymal stromal cells. Finally, to better understand granular hydrogels, we embarked on a collaborative effort to describe the rheology of granular hydrogels. This work sets a foundation for the measurement and understanding of remodeling in granular constructs and develops an understanding of the connection between tunable granular hydrogel parameters and flow behavior for 3D printing applications. We applied the Kamani-Donley-Rogers yield stress fluid model to describe granular hydrogel mechanics and the transition (yielding, unyielding) between predominantly elastic and predominantly viscous deformation regimes. We systematically varied parameters including the granular composition between gelatin and poly(ethylene glycol) particles, and we reported the impact of microgel and granular hydrogel parameters such as particle size and polydispersity upon rheological properties. Taken together, these efforts demonstrate the importance of hypoxia in biomaterial models, bring forth a new class of material to the field of hematopoietic stem cell biology, and establish guiding principles to measure, understand, and design granular materials for tissue engineering applications.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Chemical Engineering

Grantor

University of Illinois Urbana-Champaign

Year dc:date

2025

Author dc:creator

• Thompson, Gunnar B.

Contributors dc:contributor

• Harley, Brendan A.C.
• García, Andrés J.
• Kraft, Mary L
• Rogers, Simon A

• Hematopoietic stem cell
• hydrogel
• microgel
• granular hydrogel
• hypoxia
• bone marrow
• gelatin
• microfluidic
• rheology
• yield stress fluid

Statement dc:rights

• Copyright 2025 Gunnar Thompson

Language dc:language

en

Handle dc:identifier

https://hdl.handle.net/2142/132774

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/132774