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Development of ultra-thin microfluidic chips with wettability for immobilization of Caenorhabditis elegans during irradiation-PDMS microfluidic chips without need for anesthesia that enables us to  observe for a long time while immobilizing motion of living organisms

Abstract

The National Institutes for Quantum and Radiological Science and Technology (QST; President: Dr. Toshio Hirano), and Biocosm Inc. (CEO: Dr. Hajime Hiratsuka) jointly developed a PDMS microfluidic chip (Fig. 1) with wettability for enclosing various biological samples such as animals and plants cells and various micro-organisms.

Background: Radiation such as X-rays, gamma rays, and heavy ion beam is widely used for biological applications such as cancer diagnosis and treatment, and ion beam breeding. Furthermore, a lot of studies and technical developments to investigate the radiation effects are also proceeding. Microbeam irradiation is a powerful means to identify a site with radiation sensitivity in the living organisms. Takasaki Advanced Radiation Research Institute of QST has been developing a technology to irradiate individual cells under microscopic observation by heavy-ion microbeam. With the heavy-ion microbeam, we also have been establishing a method for targeted microbeam irradiation of several model animals such as microorganisms, nematodes, silkworms, and medaka. 

Objective: Targeted microbeam irradiation of the nematode Caenorhabditis elegans allows the effective knockdown of specific regions, thus helping to identify their roles in processes such as locomotion. We previously employed on-chip immobilization of individuals without anesthesia; however, this method was limited by the thickness of the polydimethylsiloxane (PDMS) microfluidic chip, which prevented the detection of ions passing through the animal, and by dehydration of the animals after prolonged immobilization. In the present study, we aimed to develop an ion-penetrable ultra-thin PDMS microfluidic chip and explore suitable conditions for preventing the dehydration of the animals.

Results: We developed 300-µm-ultra-thin, wettable, ion-penetrable, PDMS chips for immobilizing C. elegans, referred to as Worm Sheets (Fig. 2). Using a collimating microbeam system, we demonstrated that carbon ions (having ~1 mm range in water) could pass through the chip, thus allowing the ions to be detected and the applied radiation dose to therefore by measured accurately. We also examined the locomotion of C. elegans following on-chip immobilization. Locomotion was decreased on unwettable chips as a result of dehydration due to evaporation, but not on wettable chips. This improved, wettable chip will become a powerful tool for prolonged immobilizing C. elegans, and is widely applicable not only to microbeam irradiation but also to neurobiological assays.

 Fig. 1  Worm Sheet (Biocosm Inc.).

 The thickness of this wettable PDMS microfluidic chip for C. elegans is 300 μm, and 25 straight microfluidic channels are formed on the surface (depth, 70 μm; width, 60 μm).

Fig. 2  Immobilization of C. elegans individuals using Worm Sheet.

[Upper] Procedure of the on-chip immobilization using Worm Sheet (Sectional view).

[Bottom] C. elegans individuals enclosed in a microfluidic channels on Worm Sheet (Overhead view).

Reference 

Title: Development of ultra-thin chips for immobilization of Caenorhabditis elegans in microfluidic channels during irradiation and selection of buffer solution to prevent dehydration 

Authors: Michiyo Suzuki*, Tetsuya Sakashita, Yuya Hattori, Yuichiro Yokota, Yasuhiko Kobayashi, Tomoo Funayama        *Corresponding Author

 Affiliation: Department of Radiation-Applied Biology Research, Takasaki Advanced Radiation Research Institute, National Institutes for Quantum and Radiological Science and Technology (QST), 1233 Watanuki, Takasaki, Gunma 370-1292, Japan. 

Journal: Journal of Neuroscience Methods (Elsevier), Vol. 306 (1 August, 2018), pp. 32-37.

 URL (Online publication): https://doi.org/10.1016/j.jneumeth.2018.05.025