Application of external forces on 3D hydrogels

External forces are an important factor in tissue formation, development, and maintenance. We have developed a method to stretch soft hydrogels, such as fibrin and collagen gels, from their circumference, using an elastic silicone strip.
Advantages of this method include the ability to strain extremely soft hydrogels in 3D while executing in situ live microscopy, and the freedom to manipulate the geometry and size of the sample.
By considering the design of various geometries, we use our method to program strain gradients along different chosen axes, providing a framework for engineering tissues with complex gradient structure, such that occur in interfacial tissues such as tendon-bone or cartilage-bone.

Relevant papers:

  • Avishy Roitblat Riba, Sari Natan, Avraham Kolel, Hila Rushkin, Oren Tchaicheeyan, Ayelet Lesman. Straining 3D Hydrogels with Uniform Z-Axis Strains While Enabling Live Microscopy Imaging. Annals of Biomedical Engineering, 48, 868–880. December 2019. doi: 10.1007/s10439-019-02426-7
  • A. Kolel, A. Roitblat Riba, S. Natan, O. Tchaicheeyan, E. Saias, A. Lesman. Controlled Strain of 3D Hydrogels under Live Microscopy Imaging. Journal of Visual Experiments, J. Vis. Exp. (166), e61671, doi:10.3791/61671, Sep. 2020.
Top: Schematic of the stretching approach with the silicone strip (orange), circular gel (cut-out in the middle), and fabric extenders (green) that connect the silicone to the stretching device.
Bottom: Gel fiber alignment in response to external stretch. Images taken at the center of a fluorescently-labeled gel before and after stretch.

Mechanical interaction with the environment

Mechanical communication between cells

The unique nonlinear mechanics of the fibrous extracellular matrix (ECM) facilitates propagation of forces, supporting a mechanism of long-range cell-cell mechanical communication that would be impossible for linear elastic substrates. When seeded in fibrous gels, pairs of cells or cell aggregates can induce bands of deformed gel extending between them, indicating their mechanical coupling. We use computational finite element simulations and biological experiments to reveal how mechanical forces, exerted by contractile cells, are transmitted in fibrous nonlinear environments, and how these forces can reach out neighboring cells and regulate their biological activity.

Related papers:

  • David Gomez, Eial Teomy, Ayelet Lesman, Yair Shokef. Target finding in fibrous biological environments. New J. Phys. New J. Phys. 22 103008 Oct 2020.
  • Assaf Nahum, Yoni Koren, Sari Natan, Shahar Goren, Ayelet Lesman, Assaf Zaritsky. Quantifying the dynamics of long-range cell-cell mechanical communication. July 2020, bioRxiv preprint. doi:
  • Sari Natan, Yoni Koren, Ortal Shelah, Shahar Goren, Ayelet Lesman. Long-range mechanical coupling of cells in 3D fibrin gels. Molecular Biology of the Cell, Volume 31, No. 14, July 2020. * This article appears on the cover
  • Shahar Goren, Yoni Koren, Xinpeng Xu, Ayelet Lesman. Elastic Anisotropy Governs the Range of Cell-Induced Displacements. Biophysical Journal. March 2020 .Volume 118, Issue 5, 10 March 2020, Pages 1152-1164.
  • David Gomez, Sari Natan, Yair Shokef, Ayelet Lesman. Mechanical Interaction between Cells Facilitates Molecular Transport. Advanced Biosystems, Volume 3, Issue 12, November 2019.
  • Amots Mann, Ran S Sopher, Shahar Goren, Ortal Shelah, Oren Tchaicheeyan, Ayelet Lesman. Force chains in cell-cell mechanical communication. Journal of the Royal Society Interface. 16 (159), Oct 2019.
  • Ran S Sopher, Hanan Tokash, Sari Natan, Mirit Sharabi, Ortal Shelah, Oren Tchaicheeyan, Ayelet Lesman. Nonlinear elasticity of the ECM fibers facilitates efficient inter-cellular communication. Biophysical J. 2;115(7):1357-1370, 2018. *This article appears on the cover

Force transmission in anisotropic fibrous environments

The mechanical and structural properties of fibrous materials dynamically evolve and develop as they are strained. Together with Dr. Raya Sorkin (Chemistry, TAU), we use laser tweezers to study how forces propagate in fibrous gels that are put under tension and become elastically anisotropic. This line of research provides insight into the mechanisms how mechanical cues are transmitted between biological cells, and provide inspiration for the design of new biomaterials.

Forces exerted by growing roots

Plant roots are considered one of the most efficient soil explorers. As opposed to the penetration strategy of other organisms, that is based on pushing through soil, roots penetrate by growing, adding new cells at the tip and elongating over a well-defined growth zone. In collaboration with Dr. Yasmin Meroz (Plant Sciences, TAU), we study the forces applied by plant roots in agar gel by traction force microscopy, and use finite element modeling to reveal the advantages of the growth mechanism.

Top: Covers of Molecular Biology of the Cell (left) and Biophysical Journal (right), presenting pairs of green fluorescently-labeled fibroblasts, embedded within 3D fibrin gels, as were captured in our lab using confocal microscopy. Dense and aligned fibers between the cells are highly visible, indicating mechanical couplings between the cells.
Bottom: 2D Finite-elements simulation of two contracting cells in a fibrous network, resembling fibrin gel.
0.75 micron polystyrene beads (blue) embedded in fibrin gel (green). Optical tweezers are used to apply localized forces and observe the material response.
Green fluorescently-labeled root of Arabidopsis plant growing within 3D agar gel. Measuring the forces applied by the root is enabled by analyzing the displacements of a micron size fluorescent beads (in white).

Novel biomaterials for Tissue Engineering

Scaffold based on coral-derived collagen fibers

In collaboration with Prof. Rami Haj-Ali (TAU, Mechanical Engineering), we extract centimeter-long collagen fibers from Sarcophyton soft corals, and wrap them around frames to create aligned fiber arrays. We study their biocompatibility and ability to support formation of various oriented tissues, such as skeletal muscle tissue.

Related papers:

  • Ortal Shelah, Shir Wertheimer, Rami Haj-Ali, Ayelet Lesman. Coral-derived Collagen Fibers for Engineering Aligned Tissues. Tissue Engineering Part A. July 2020, 27, 3-4. Feb 15, 2021.
  • Shir Wertheimer, Mirit Sharabi, Ortal Shelah, Ayelet Lesman, Rami Haj-Ali. Bio-composites reinforced with unique coral collagen fibers: Towards biomimetic-based small diameter vascular grafts. Journal of the Mechanical Behavior of Biomedical Materials, April 2020, In Press.

Seaweed cellulose scaffolds from green macroalgae

In collaboration with Prof. Alexander Golberg (Porter environment, TAU), we apply decellularization-recellularization approach of Marine macroalgae species Ulva sp. and Cladophora sp. to produce cellulose scaffolds for in-vitro mammalian cell growth. We test their biocompatibility and ability to support tissue engineering.

Related papers:

Nurit Bar-Shai, Orna Sharabani-Yosef, Meiron Zollmann, Ayelet Lesman, Alexander Golberg. Seaweed cellulose scaffolds derived from green macroalgae for tissue engineering. Scientific Reports. 2021 Jun 4;11(1):11843. doi: 10.1038/s41598-021-90903-2. PMID: 34088909.

Manual extraction of collagen fibers from the coral. After extraction, the collagen fibers were wrapped around a frame in a unidirectional orientation.
The production of cellulose scaffolds out of two types of green macro-algae (left): Ulva sp. (top) and Cladophora sp. (bottom). Fabrication samples (right).