Magnetically Controlled Microscale Probing and Manipulation of Fibrous Hydrogel Matrices for Mechanobiological In Vitro Studies
Embargoed until 2024-06-01
Author
Date
2023Type
- Doctoral Thesis
ETH Bibliography
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Abstract
Throughout the human body, mechanical forces critically influence cell fate and function. The investigation of mechanical regulation in health and disease is of growing interest in biomedical research to complement biochemical insights and to identify novel treatment strategies. Efforts to develop physiologically relevant in vitro models of tissues are progressively leading to approaches that go beyond two-dimensional cell layers. In particular, the consideration of the three-dimensional (3D) architecture of living tissues has driven the implementation of 3D culture matrices incorporating extracellular components that can be tuned with regards to composition, structure, and rigidity.
Cancer is a prominent example where mechanical alterations of cells and tissues are highly relevant for the diagnosis and the progression of the disease, particularly during the process of metastasis. Metastatic cancer cells disseminate from a primary tumor, travel through tissues and the circulatory system and eventually lead to the establishment of distant secondary tumors. To study these processes and the involved mechanical factors, 3D matrices are highly valuable to model tumor tissue in vitro.
The characterization of mechanical properties within physiologically relevant 3D tissue models, however, is restricted by the volumetric character of intact tissue systems. Further, the aspect of scale for mechanical measurement must be considered if values relevant to tissueresiding cells shall be obtained. Moreover, while 3D tissue culture models are increasingly implementing aspects of matrix composition and stiffness, the role of dynamic forces exerted by tissue residing cells are still mostly neglected.
To address these limitations, this thesis presents the fabrication, characterization, and application of magnetically controlled, rod-shaped microparticles (μRods) to probe and manipulate modelled 3D tissue environments on a scale relevant to individual cells. Collagen I (Col I) hydrogel networks are frequently employed for the reconstitution of 3D models of the cellsurrounding tissue matrix and are the system of choice throughout the presented work.
The fabrication and characterization of two types of magnetic μRods are described in a first part of the thesis, along with the presentation of two magnetic control systems to generate rotating magnetic fields. Next, spatiotemporal probing and manipulation of heterogenous extracellular matrix networks at a scale relevant to individual cells using μRods fabricated from cobalt and nickel is presented. Image analysis and physical modeling were used to examine the mechanical stimuli applied to Col I hydrogel networks. Shear moduli were determined to be in the range of Pascal to tens of kPascal and effects including local fiber densification and proximity to rigid boundaries were found to influence stiffness values. Further, the range and dynamics of fiber network deformation in response to magnetic torques were analyzed. Torques on the order of 10 pNm were found to result in network deformations reaching tens of micrometers away from the actuated μRod. Volumetric imaging during 3D actuation of network-embedded μRods further demonstrated the ability to analyze μRod deflection in 3D samples, illustrating the ability to go beyond two-dimensional approaches.
Long-term micromechanical actuation of 3D tumor models was performed using μRods produced from iron. A custom-built magnetic field generator was constructed to actuate several samples over longer periods of time under standard cell culture conditions. Again, the extent of Col I hydrogel deformation by the magnetically actuated μRods was analyzed. Over several days, invasive tumor spheroids were cultured in Col I hydrogel matrices containing μRods that were actuated at a frequency of 1 Hz. Image-based analysis indicated increased invasive behavior of cancer cells when subjected to cyclic mechanical deformation of the surrounding matrix. Additionally, local application of μRods in the vicinity of tumor spheroids was shown to result in cancer cell migration in the direction of the transiently applied mechanical strain of the Col I matrix.
In summary, this thesis presents magnetic μRods as microscale actuators that operate within 3D in vitro tissue models. Controlled by uniform rotating magnetic fields, these microagents are employed to mechanically characterize and actuate reconstituted tissue environments from the perspective of individual, tissue-residing cells. Implementing mechanical probing and actuation of 3D tissue models using these approaches could complement standardized test procedures which are so far mainly focused on biochemical markers, eventually allowing for a more holistic view on the investigated models.
The ability to probe mechanical properties within intact 3D in vitro systems in a noninvasive, spatiotemporally resolved manner can be used to interrogate the optically inaccessible micromechanical profile of the microenvironment surrounding a cell. Insights into the prevailing mechanics that co-regulate cell fate and function could be an asset for characterizing and identifying mechanical drivers of disease states. Further, the controlled application of cyclic mechanical deformation within 3D cell culture matrices over longer periods of time enables studies that incorporate dynamic deformation to otherwise static cell culture systems. Show more
Permanent link
https://doi.org/10.3929/ethz-b-000614567Publication status
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Contributors
Examiner: Schürle-Finke, Simone
Examiner: Zenobi-Wong, Marcy
Examiner: Özkale-Edelmann, Berna
Publisher
ETH ZurichOrganisational unit
09619 - Schürle-Finke, Simone / Schürle-Finke, Simone
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