Electronic Thesis and Dissertation Repository

Thesis Format

Monograph

Degree

Master of Engineering Science

Program

Biomedical Engineering

Collaborative Specialization

Musculoskeletal Health Research

Supervisor

Flynn, Lauren E.

Abstract

Pre-conditioning of adipose-derived stromal cells (ASCs) by tuning the cellular microenvironment during expansion has the potential to modulate their pro-regenerative functionality. The current study investigated the effects of microcarrier composition (decellularized adipose tissue versus collagen), oxygen tension (2% versus ~20% O2) and stirring rate (static, 20, 40 rpm) on human ASCs cultured within spinner flask bioreactors. Dynamic culturing under 20% O2 resulted in more consistent cell growth on both microcarrier substrates, leading to increases in microcarrier contraction and stiffness. Culturing on the microcarriers modulated the hASC immunophenotype, with varying CD90 and CD26 expression levels observed under the different culture conditions. Interestingly, the gene expression levels of a range of pro-angiogenic and immunomodulatory factors were enhanced in the hASCs cultured on the collagen microcarriers at 20 rpm and 2% O2, supporting that the conditions within stirred bioreactors can be tuned to pre-condition hASCs for applications in vascular regeneration.

Summary for Lay Audience

Recent years have shown an increase in both researchers’ and the public’s interest in cell therapies for regenerative medicine applications. However, the most appropriate cell populations and methods for generating these cells for use in humans remain unclear, with billions of cells required for a single treatment. Found in human fat, adipose-derived stromal cells (ASCs) offer a possible solution. ASCs are abundant and easily accessible in the human body, in contrast to bone marrow-derived stromal cells (BMSCs), which are associated with a painful extraction process and low abundance. ASCs are known to secrete pro-regenerative proteins that can shift the immune response towards healing and encourage blood vessel growth, termed paracrine factors. Unfortunately, while more abundant than BMSCs, extracted ASCs do not meet the required cell numbers for clinical treatment without cell expansion, commonly done on tissue culture polystyrene (TCPS). With long-term expansion on TCPS, the capacity of ASCs to grow and secrete beneficial paracrine factors is reduced, thus diminishing their pro-regenerative properties. Evidently, a new expansion strategy is needed to maintain and ideally enhance the regenerative capacity of ASCs. Recognizing this need, this project focused on investigating the use of stirred bioreactor systems for expanding human ASCs. Within the bioreactors, culturing the ASCs on small scaffolds, termed microcarriers, designed to mimic the environment in which the cells reside within their native tissues was investigated as a promising approach to help maintain the desired cellular characteristics during expansion. Further, culturing ASCs under low oxygen levels and under varying stirring rates were explored as additional methods of tuning the cell culture environment to increase cell growth and augment paracrine factor expression levels. Overall, this study highlights strategies to augment the pro-regenerative capacity of ASCs during expansion, offering a potential alternative to cell growth on TCPS, with the aim of establishing improved culture methods to generate well-characterized therapeutic cell populations that could be applied in the future in clinical treatments.

Creative Commons License

Creative Commons Attribution 4.0 License
This work is licensed under a Creative Commons Attribution 4.0 License.

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