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Projects / Programmes source: ARIS

Study of intracellular forces by deformable photonic droplets

Research activity

Code Science Field Subfield
1.02.01  Natural sciences and mathematics  Physics  Physics of condesed matter 

Code Science Field
P250  Natural sciences and mathematics  Condensed matter: structure, thermal and mechanical properties, crystallography, phase equilibria 

Code Science Field
1.03  Natural Sciences  Physical sciences 
Keywords
lasers, microcavities, biophotonics, biomechanics, elasticity
Evaluation (rules)
source: COBISS
Researchers (10)
no. Code Name and surname Research area Role Period No. of publicationsNo. of publications
1.  39136  PhD Saša Harkai  Physics  Researcher  2022  26 
2.  29528  PhD Matjaž Humar  Physics  Head  2019 - 2022  186 
3.  52196  Matevž Marinčič  Physics  Researcher  2019 - 2022  13 
4.  36351  PhD Maruša Mur  Physics  Researcher  2019 - 2022  21 
5.  50669  PhD Urban Mur  Physics  Researcher  2020 - 2022  27 
6.  09089  PhD Igor Muševič  Physics  Researcher  2019 - 2022  752 
7.  52059  Gregor Pirnat  Physics  Junior researcher  2019 - 2022 
8.  38160  PhD Anja Pusovnik  Physics  Junior researcher  2019 - 2020  24 
9.  25670  PhD Miha Ravnik  Physics  Researcher  2019 - 2022  446 
10.  30871  PhD Maja Zorc  Physics  Researcher  2019 - 2022  57 
Organisations (2)
no. Code Research organisation City Registration number No. of publicationsNo. of publications
1.  0106  Jožef Stefan Institute  Ljubljana  5051606000  92,005 
2.  1554  University of Ljubljana, Faculty of Mathematics and Physics  Ljubljana  1627007  34,558 
Abstract
The forces acting in living organisms play crucial roles in various developmental, homeostatic and pathological processes. Intracellular forces drive processes such as mitosis whereas intercellular forces are known to influence a large array of cellular functions, including growth, differentiation, adhesion and migration. A number of techniques have been developed to measure the forces exerted by the cells to the environment. However, there are very few techniques for measuring the forces inside cells. The most widely employed are Forster resonance energy transfer (FRET)-based molecular tension sensors. Despite being a wonderful tool, the molecular tension sensors have many drawbacks such as sensitivity to environmental factors including pH, ion concentration and temperature, low photostability, low dynamic range and difficulty in calibration, which prevents straightforward conversion of the signal to absolute forces. Further, they provide only force magnitude measurement and not force direction. The role of forces in cell biology is still poorly understood, partially because of the limitations of these techniques. Therefore, better methods need to be developed. Notably, the PI of this project was the first to demonstrate a laser embedded inside a live cell with colleagues from Harvard University (PI is first author, Humar et al., Nature Photonics 2015), which is an unprecedented major advantage of this junior ARRS project leader and underlines the distinct cutting edge nature of this proposed research. Optical microcavities and lasers are perfect candidates for ultraprecise measurements, as required for exploring cell interior, since they are extremely sensitive to changes in the optical properties, size or shape of the cavities. Lasers are distinctly different -unique- compared to fluorescence based probes because of narrow emission linewidth, high coherence, large intensity and highly nonlinear output. Here, the main idea of this project is to develop an entirely new way of measuring forces in cells and ultimately living tissues by employing whispering-gallery mode (WGM) lasers made out of oil droplets embedded inside selected types of live cells, and then using this method to study cellular processes and cellular mechanics as revealed by force profiles. When the embedded droplet will be deformed –by the intra- or inter-cellular processes–, the laser emission from the droplet will change, enabling precise measurement of local forces or more generally, stresses. Comparing to current cellular force measurement methods, the proposed technique will have many advantages. It will provide high sensitivity, force direction measurement, large dynamic range (0.5 – 250 nN), direct force measurement and insensitivity to environmental factors. More specifically, first, we will develop and validate our method of force measurement on selected soft matter systems with similar mechanical properties as in cells and tissues. The developed method will then be applied to single live cells, exploring mechanical forces in a range of cellular phenomena, such as in growth, division and migration. The results will be interpreted by developing a mechanical model of the cells as isotropic and anisotropic viscoelastic objects, that will interact and with the embedded lasers. Finally, we will apply both experimental and numerical methods to realistic biological systems including cells under different biological conditions and 2D cell tissue models. This project aims to transform the cell lasers into a powerful tool for the study of biophysical and biochemical processes taking place on a single cell level by providing precise quantitative insight into mechanics of cells. More generally, better understanding of selected cellular processes will offer a novel pathway to developments and applications in biosciences and medicine, of clear benefit to the general society, in view of the performance of the human body as well as processes leading to diseases.
Significance for science
This project is a direct contribution to the cutting edge of modern biosciences, with clear impact on the interdisciplinary interplay between biophysics, photonics, and sensors. The injected oil droplets will enable unprecedented sensitivity in measurement of intracellular forces on a non-molecular level which is of fundamental importance for understanding cell mechanics. As sensors, our proposed method will yield cutting edge measurement range (0.5 – 250 nN), beyond the typical measurement range of 1 – 50 pN of molecular force sensors. The broad measurement range will be complemented by multiple other highly relevant advantages, including much larger dynamic range, insensitivity to chemical factors and photobleaching, not requiring calibration or reference image and finally, the direct ability to jointly measure force magnitude as well as force direction. Furthermore, the developed measurements over larger surface area within the cell will also give information about the forces at the scale of the cytoskeleton as a whole, relevant for the development and understanding of the formidable challenge of the cell model. Ultimately, our proposed method could also be used in vivo, since the lasing can be detected through scattering tissue. The ability to measure droplet size, shape and surface tension could be applied to almost any system involving droplets. Indeed, beyond this project, embedding droplets in cells may enable an array of different other applications such as generation of artificial adipocytes in the cells. The intracellular droplets developed here could also enable better understanding of several other biological processes not only force. Namely, the detection of chemical species, temperature, electric potential and other physical parameters. As non-scientific impact, the project will involve students of various levels to get involved into a top-level scientific works, contributing to the quality of their education. Also partially, this work is a transfer of knowledge started at Harvard University to two top-level Slovenian scientific institutions, allowing for opening of a highly novel and interesting research direction –in future possibly, a field– in Slovenia.
Significance for the country
This project is a direct contribution to the cutting edge of modern biosciences, with clear impact on the interdisciplinary interplay between biophysics, photonics, and sensors. The injected oil droplets will enable unprecedented sensitivity in measurement of intracellular forces on a non-molecular level which is of fundamental importance for understanding cell mechanics. As sensors, our proposed method will yield cutting edge measurement range (0.5 – 250 nN), beyond the typical measurement range of 1 – 50 pN of molecular force sensors. The broad measurement range will be complemented by multiple other highly relevant advantages, including much larger dynamic range, insensitivity to chemical factors and photobleaching, not requiring calibration or reference image and finally, the direct ability to jointly measure force magnitude as well as force direction. Furthermore, the developed measurements over larger surface area within the cell will also give information about the forces at the scale of the cytoskeleton as a whole, relevant for the development and understanding of the formidable challenge of the cell model. Ultimately, our proposed method could also be used in vivo, since the lasing can be detected through scattering tissue. The ability to measure droplet size, shape and surface tension could be applied to almost any system involving droplets. Indeed, beyond this project, embedding droplets in cells may enable an array of different other applications such as generation of artificial adipocytes in the cells. The intracellular droplets developed here could also enable better understanding of several other biological processes not only force. Namely, the detection of chemical species, temperature, electric potential and other physical parameters. As non-scientific impact, the project will involve students of various levels to get involved into a top-level scientific works, contributing to the quality of their education. Also partially, this work is a transfer of knowledge started at Harvard University to two top-level Slovenian scientific institutions, allowing for opening of a highly novel and interesting research direction –in future possibly, a field– in Slovenia.
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