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Srbova L, Arasalo O, Lehtonen AJ, Pokki J. Measuring mechanical cues for modeling the stromal matrix in 3D cell cultures. SOFT MATTER 2024; 20:3483-3498. [PMID: 38587658 DOI: 10.1039/d3sm01425h] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/09/2024]
Abstract
A breast-cancer tumor develops within a stroma, a tissue where a complex extracellular matrix surrounds cells, mediating the cancer progression through biomechanical and -chemical cues. Current materials partially mimic the stromal matrix in 3D cell cultures but methods for measuring the mechanical properties of the matrix at cell-relevant-length scales and stromal-stiffness levels are lacking. Here, to address this gap, we developed a characterization approach that employs probe-based microrheometry and Bayesian modeling to quantify length-scale-dependent mechanics and mechanical heterogeneity as in the stromal matrix. We examined the interpenetrating network (IPN) composed of alginate scaffolds (for adjusting mechanics) and type-1 collagen (a stromal-matrix constituent). We analyzed viscoelasticity: absolute-shear moduli (stiffness/elasticity) and phase angles (viscous and elastic characteristics). We determined the relationship between microrheometry and rheometry information. Microrheometry reveals lower stiffness at cell-relevant scales, compared to macroscale rheometry, with dependency on the length scale (10 to 100 μm). These data show increasing IPN stiffness with crosslinking until saturation (≃15 mM of Ca2+). Furthermore, we report that IPN stiffness can be adjusted by modulating collagen concentration and interconnectivity (by polymerization temperature). The IPNs are heterogeneous structurally (in SEM) and mechanically. Interestingly, increased alginate crosslinking changes IPN heterogeneity in stiffness but not in phase angle, until the saturation. In contrast, such changes are undetectable in alginate scaffolds. Our nonlinear viscoelasticity analysis at tumor-cell-exerted strains shows that only the softer IPNs stiffen with strain, like the stromal-collagen constituent. In summary, our approach can quantify the stromal-matrix-related viscoelasticity and is likely applicable to other materials in 3D culture.
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Affiliation(s)
- Linda Srbova
- Department of Electrical Engineering and Automation, Aalto University, Espoo, FI-02150, Finland.
| | - Ossi Arasalo
- Department of Electrical Engineering and Automation, Aalto University, Espoo, FI-02150, Finland.
| | - Arttu J Lehtonen
- Department of Electrical Engineering and Automation, Aalto University, Espoo, FI-02150, Finland.
| | - Juho Pokki
- Department of Electrical Engineering and Automation, Aalto University, Espoo, FI-02150, Finland.
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Lehtonen AJ, Arasalo O, Srbova L, Heilala M, Pokki J. Magnetic microrheometry of tumor-relevant stiffness levels and probabilistic quantification of viscoelasticity differences inside 3D cell culture matrices. PLoS One 2023; 18:e0282511. [PMID: 36947558 PMCID: PMC10032533 DOI: 10.1371/journal.pone.0282511] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2022] [Accepted: 02/16/2023] [Indexed: 03/23/2023] Open
Abstract
The progression of breast cancer involves cancer-cell invasions of extracellular matrices. To investigate the progression, 3D cell cultures are widely used along with different types of matrices. Currently, the matrices are often characterized using parallel-plate rheometry for matrix viscoelasticity, or liquid-like viscous and stiffness-related elastic characteristics. The characterization reveals averaged information and sample-to-sample variation, yet, it neglects internal heterogeneity within matrices, experienced by cancer cells in 3D culture. Techniques using optical tweezers and magnetic microrheometry have measured heterogeneity in viscoelasticity in 3D culture. However, there is a lack of probabilistic heterogeneity quantification and cell-size-relevant, microscale-viscoelasticity measurements at breast-tumor tissue stiffness up to ≃10 kPa in Young's modulus. Here, we have advanced methods, for the purpose, which use a magnetic microrheometer that applies forces on magnetic spheres within matrices, and detects the spheres displacements. We present probabilistic heterogeneity quantification using microscale-viscoelasticity measurements in 3D culture matrices at breast-tumor-relevant stiffness levels. Bayesian multilevel modeling was employed to distinguish heterogeneity in viscoelasticity from the effects of experimental design and measurement errors. We report about the heterogeneity of breast-tumor-relevant agarose, GrowDex, GrowDex-collagen and fibrin matrices. The degree of heterogeneity differs for stiffness, and phase angle (i.e. ratio between viscous and elastic characteristics). Concerning stiffness, agarose and GrowDex show the lowest and highest heterogeneity, respectively. Concerning phase angle, fibrin and GrowDex-collagen present the lowest and the highest heterogeneity, respectively. While this heterogeneity information involves softer matrices, probed by ≃30 μm magnetic spheres, we employ larger ≃100 μm spheres to increase magnetic forces and acquire a sufficient displacement signal-to-noise ratio in stiffer matrices. Thus, we show pointwise microscale viscoelasticity measurements within agarose matrices up to Young's moduli of 10 kPa. These results establish methods that combine magnetic microrheometry and Bayesian multilevel modeling for enhanced heterogeneity analysis within 3D culture matrices.
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Affiliation(s)
- Arttu J Lehtonen
- Department of Electrical Engineering and Automation, Aalto University, Espoo, Finland
| | - Ossi Arasalo
- Department of Electrical Engineering and Automation, Aalto University, Espoo, Finland
| | - Linda Srbova
- Department of Electrical Engineering and Automation, Aalto University, Espoo, Finland
| | - Maria Heilala
- Department of Applied Physics, Aalto University, Espoo, Finland
| | - Juho Pokki
- Department of Electrical Engineering and Automation, Aalto University, Espoo, Finland
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Magnetically Propelled Chained Nanocomposites for On-Demand Biologically Relevant Media Exploration. J Colloid Interface Sci 2022; 629:287-296. [DOI: 10.1016/j.jcis.2022.08.154] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2022] [Revised: 08/10/2022] [Accepted: 08/24/2022] [Indexed: 11/21/2022]
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Pokki J, Zisi I, Schulman E, Indana D, Chaudhuri O. Magnetic probe-based microrheology reveals local softening and stiffening of 3D collagen matrices by fibroblasts. Biomed Microdevices 2021; 23:27. [PMID: 33900463 PMCID: PMC8076128 DOI: 10.1007/s10544-021-00547-2] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Changes in extracellular matrix stiffness impact a variety of biological processes including cancer progression. However, cells also actively remodel the matrices they interact with, dynamically altering the matrix mechanics they respond to. Further, cells not only react to matrix stiffness, but also have a distinct reaction to matrix viscoelasticity. The impact of cell-driven matrix remodeling on matrix stiffness and viscoelasticity at the microscale remains unclear, as existing methods to measure mechanics are largely at the bulk scale or probe only the surface of matrices, and focus on stiffness. Yet, establishing the impact of the matrix remodeling at the microscale is crucial to obtaining an understanding of mechanotransduction in biological matrices, and biological matrices are not just elastic, but are viscoelastic. Here, we advanced magnetic probe-based microrheology to overcome its previous limitations in measuring viscoelasticity at the cell-size-scale spatial resolution within 3D cell cultures that have tissue-relevant stiffness levels up to a Young's modulus of 0.5 kPa. Our magnetic microrheometers exert controlled magnetic forces on magnetic microprobes within reconstituted extracellular matrices and detect microprobe displacement responses to measure matrix viscoelasticity and determine the frequency-dependent shear modulus (stiffness), the loss tangent, and spatial heterogeneity. We applied these tools to investigate how microscale viscoelasticity of collagen matrices is altered by fibroblast cells as they contract collagen gels, a process studied extensively at the macroscale. Interestingly, we found that fibroblasts first soften the matrix locally over the first 32 hours of culture, and then progressively stiffen the matrix thereafter. Fibroblast activity also progressively increased the matrix loss tangent. We confirmed that the softening is caused by matrix-metalloproteinase-mediated collagen degradation, whereas stiffening is associated with local alignment and densification of collagen fibers around the fibroblasts. This work paves the way for the use of measurement systems that quantify microscale viscoelasticity within 3D cell cultures for studies of cell-matrix interactions in cancer progression and other areas.
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Affiliation(s)
- Juho Pokki
- Department of Mechanical Engineering, Stanford University, Stanford, CA, USA. .,Department of Electrical Engineering and Automation, Aalto University, Espoo, Finland.
| | - Iliana Zisi
- Department of Mechanical Engineering, Stanford University, Stanford, CA, USA
| | - Ester Schulman
- Department of Mechanical Engineering, Stanford University, Stanford, CA, USA
| | - Dhiraj Indana
- Department of Mechanical Engineering, Stanford University, Stanford, CA, USA
| | - Ovijit Chaudhuri
- Department of Mechanical Engineering, Stanford University, Stanford, CA, USA
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Vilela D, Cossío U, Parmar J, Martínez-Villacorta AM, Gómez-Vallejo V, Llop J, Sánchez S. Medical Imaging for the Tracking of Micromotors. ACS NANO 2018; 12:1220-1227. [PMID: 29361216 DOI: 10.1021/acsnano.7b07220] [Citation(s) in RCA: 91] [Impact Index Per Article: 15.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/05/2023]
Abstract
Micro/nanomotors are useful tools for several biomedical applications, including targeted drug delivery and minimally invasive microsurgeries. However, major challenges such as in vivo imaging need to be addressed before they can be safely applied on a living body. Here, we show that positron emission tomography (PET), a molecular imaging technique widely used in medical imaging, can also be used to track a large population of tubular Au/PEDOT/Pt micromotors. Chemisorption of an iodine isotope onto the micromotor's Au surface rendered them detectable by PET, and we could track their movements in a tubular phantom over time frames of up to 15 min. In a second set of experiments, micromotors and the bubbles released during self-propulsion were optically tracked by video imaging and bright-field microscopy. The results from direct optical tracking agreed with those from PET tracking, demonstrating that PET is a suitable technique for the imaging of large populations of active micromotors in opaque environments, thus opening opportunities for the use of this mature imaging technology for the in vivo localization of artificial swimmers.
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Affiliation(s)
- Diana Vilela
- Institute for Bioengineering of Catalonia (IBEC), The Barcelona Institute of Science and Technology , Baldiri Reixac 10-12, 08028 Barcelona, Spain
- Max Planck Institute for Intelligent Systems Institution , Heisenbergstraße 3, 70569 Stuttgart, Germany
| | - Unai Cossío
- Radiochemistry and Nuclear Imaging Group, CIC biomaGUNE , Paseo Miramón 182, 20014 San Sebastián, Spain
| | - Jemish Parmar
- Institute for Bioengineering of Catalonia (IBEC), The Barcelona Institute of Science and Technology , Baldiri Reixac 10-12, 08028 Barcelona, Spain
- Max Planck Institute for Intelligent Systems Institution , Heisenbergstraße 3, 70569 Stuttgart, Germany
| | | | - Vanessa Gómez-Vallejo
- Radiochemistry and Nuclear Imaging Group, CIC biomaGUNE , Paseo Miramón 182, 20014 San Sebastián, Spain
| | - Jordi Llop
- Radiochemistry and Nuclear Imaging Group, CIC biomaGUNE , Paseo Miramón 182, 20014 San Sebastián, Spain
| | - Samuel Sánchez
- Institute for Bioengineering of Catalonia (IBEC), The Barcelona Institute of Science and Technology , Baldiri Reixac 10-12, 08028 Barcelona, Spain
- Max Planck Institute for Intelligent Systems Institution , Heisenbergstraße 3, 70569 Stuttgart, Germany
- Institució Catalana de Recerca i Estudis Avancats (ICREA) , Pg. Lluís Companys 23, 08010 Barcelona, Spain
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Ceylan H, Giltinan J, Kozielski K, Sitti M. Mobile microrobots for bioengineering applications. LAB ON A CHIP 2017; 17:1705-1724. [PMID: 28480466 DOI: 10.1039/c7lc00064b] [Citation(s) in RCA: 150] [Impact Index Per Article: 21.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
Untethered micron-scale mobile robots can navigate and non-invasively perform specific tasks inside unprecedented and hard-to-reach inner human body sites and inside enclosed organ-on-a-chip microfluidic devices with live cells. They are aimed to operate robustly and safely in complex physiological environments where they will have a transforming impact in bioengineering and healthcare. Research along this line has already demonstrated significant progress, increasing attention, and high promise over the past several years. The first-generation microrobots, which could deliver therapeutics and other cargo to targeted specific body sites, have just been started to be tested inside small animals toward clinical use. Here, we review frontline advances in design, fabrication, and testing of untethered mobile microrobots for bioengineering applications. We convey the most impactful and recent strategies in actuation, mobility, sensing, and other functional capabilities of mobile microrobots, and discuss their potential advantages and drawbacks to operate inside complex, enclosed and physiologically relevant environments. We lastly draw an outlook to provide directions in the veins of more sophisticated designs and applications, considering biodegradability, immunogenicity, mobility, sensing, and possible medical interventions in complex microenvironments.
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Affiliation(s)
- Hakan Ceylan
- Physical Intelligence Department, Max Planck Institute for Intelligent Systems, 70569 Stuttgart, Germany.
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Buttinoni I, Steinacher M, Spanke HT, Pokki J, Bahmann S, Nelson B, Foffi G, Isa L. Colloidal polycrystalline monolayers under oscillatory shear. Phys Rev E 2017; 95:012610. [PMID: 28208468 DOI: 10.1103/physreve.95.012610] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2016] [Indexed: 11/07/2022]
Abstract
In this paper we probe the structural response to oscillatory shear deformations of polycrystalline monolayers of soft repulsive colloids with varying area fraction over a broad range of frequencies and amplitudes. The particles are confined at a fluid interface, sheared using a magnetic microdisk, and imaged through optical microscopy. The structural and mechanical response of soft materials is highly dependent on their microstructure. If crystals are well understood and deform through the creation and mobilization of specific defects, the situation is much more complex for disordered jammed materials, where identifying structural motifs defining plastically rearranging regions remains an elusive task. Our materials fall between these two classes and allow the identification of clear pathways for structural evolution. In particular, we demonstrate that large enough strains are able to fluidize the system, identifying critical strains that fulfill a local Lindemann criterion. Conversely, smaller strains lead to localized and erratic irreversible particle rearrangements due to the motion of structural defects. In this regime, oscillatory shear promotes defect annealing and leads to the growth of large crystalline domains. Numerical simulations help identify the population of rearranging particles with those exhibiting the largest deviatoric stresses and indicate that structural evolution proceeds towards the minimization of the stress stored in the system. The particles showing high deviatoric stresses are localized around grain boundaries and defects, providing a simple criterion to spot regions likely to rearrange plastically under oscillatory shear.
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Affiliation(s)
- Ivo Buttinoni
- Laboratory for Interfaces, Soft Matter and Assembly, Department of Materials, ETH Zurich, CH-8093, Zurich, Switzerland
| | - Mathias Steinacher
- Laboratory for Interfaces, Soft Matter and Assembly, Department of Materials, ETH Zurich, CH-8093, Zurich, Switzerland
| | - Hendrik Th Spanke
- Laboratory for Interfaces, Soft Matter and Assembly, Department of Materials, ETH Zurich, CH-8093, Zurich, Switzerland
| | - Juho Pokki
- Institute of Robotics and Intelligent Systems, ETH Zurich, CH-8092, Zurich, Switzerland
| | - Severin Bahmann
- Institute of Robotics and Intelligent Systems, ETH Zurich, CH-8092, Zurich, Switzerland
| | - Bradley Nelson
- Institute of Robotics and Intelligent Systems, ETH Zurich, CH-8092, Zurich, Switzerland
| | - Giuseppe Foffi
- Laboratoire de Physique des Solides, CNRS, Université Paris-Sud, Université Paris-Saclay, Orsay 91405, France
| | - Lucio Isa
- Laboratory for Interfaces, Soft Matter and Assembly, Department of Materials, ETH Zurich, CH-8093, Zurich, Switzerland
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Singh AV, Sitti M. Patterned and Specific Attachment of Bacteria on Biohybrid Bacteria-Driven Microswimmers. Adv Healthc Mater 2016; 5:2325-31. [PMID: 27240122 DOI: 10.1002/adhm.201600155] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2016] [Revised: 04/14/2016] [Indexed: 11/06/2022]
Abstract
A surface patterning technique and a specific and strong biotin-streptavidin bonding of bacteria on patterned surfaces are proposed to fabricate Janus particles that are propelled by the attached bacteria. Bacteria-driven Janus microswimmers with diameters larger than 3 μm show enhanced mean propulsion speed. Such microswimmers could be used for future applications such as targeted drug delivery and environmental remediation.
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Affiliation(s)
- Ajay Vikram Singh
- Physical Intelligence Department; Max Planck Institute for Intelligent Systems; Heisenbergstr. 3 70569 Stuttgart Germany
| | - Metin Sitti
- Physical Intelligence Department; Max Planck Institute for Intelligent Systems; Heisenbergstr. 3 70569 Stuttgart Germany
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