Name: immobilization of live caenorhabditis elegans individuals using an ultra-thin polydimethylsiloxane microfluidic chip with water retention
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Description: Watch this Scientific Journal Video about Immobilization of Live Caenorhabditis elegans Individuals Using an Ultra-thin Polydimethylsiloxane Microfluidic Chip with Water Retention at JoVE.com

The authors thank Dr. Atsushi Higashitani for kind advice regarding treatment of C. elegans and Drs. Yuya Hattori, Yuichiro Yokota, and Yasuhiko Kobayashi for valuable discussions. The authors thank the Caenorhabditis Genetic Center for providing strains of C. elegans and E. coli. We thank the crew of the cyclotron of TIARA at QST-Takasaki for their kind assistance with the irradiation experiments. We thank Dr. Susan Furness for editing a draft of this manuscript. This study was supported in part by KAKENHI (Grant Numbers JP15K11921 and JP18K18839) from JSPS to M.S.

1. Strains and maintenance
<ol>
	<li>Select a suitable strain of C. elegans and Escherichia coli (food) depending on the purpose of the experiment. 
	NOTE: In the present paper, wild-type N210C. elegans (Figure 2A) is generally used, and HBR4:goeIs3[pmyo-3::GCamP3.35::unc-54 - 3&#39;utr, unc-119(+)]V11 is only employed for imaging assay. E. coli OP50 was used as food for C...

<ol>
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A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Imaging+the+activity+of+neurons+and+muscles.">Imaging the activity of neurons and muscles.</a> WormBook. 2, 1-13 (2006).</li><li>Aubry, G., Lu, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+perspective+on+optical+developments+in+microfluidic+platforms+for+Caenorhabditis+elegans+research.">A perspective on optical developments in microfluidic platforms for Caenorhabditis elegans research.</a> Biomicrofluidics. 8, 011301 (2014).</li><li>Lumirror Catalog. 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On-chip immobilization of C. elegans under live conditions using a wettable PDMS microfluidic chip enables the efficient targeted microbeam irradiation of multiple animals. The ease of handling and features to prevent drying make this system suitable for applications not only in microbeam irradiation, but also in several behavioral assays. These worm sheets have already been commercialized and can be easily obtained. Conventional microfluidic chips, such as olfactory chips, are associated with problems including...

Radiation, including X-rays, gamma rays, and heavy-ion beam, is widely used for biological applications such as in cancer diagnosis and treatment, and for ion-beam breeding. Numerous studies and technical developments are currently focusing on the effects of radiation1,2,3. Microbeam irradiation is a powerful means of identifying radiosensitive sites in living organisms4. The Takasaki Advanced Radiation Research Institute of National Institutes for Quantum and Radiological Science and Technology (QST-Takasaki) has been developing a technology to irradiate individual cells under microscopic observation using heavy-ion microbeams5, and has established methods to enable targeted microbeam irradiation of several model animals, such as the nematode Caenorhabditis elegans4,6, silkworms7, and Oryzias latipes (Japanese medaka)8. Targeted microbeam irradiation of the nematode C. elegans allows the effective knockdown of specific regions, such as the nerve ring in the head region, thus helping to identify the roles of these systems in processes such as locomotion.
A method for on-chip immobilization of C. elegans individuals without the need for anesthesia has been developed to allow for microbeam irradiation4. In addition, to improve microfluidic chips used in the previous study4, we have recently developed wettable, ion-penetrable, polydimethylsiloxane (PDMS) microfluidic chips, referred to as worm sheets (see Table of Materials), for immobilizing C. elegans individuals9. These comprise of ultra-thin soft sheets (thickness = 300 &#181;m; width = 15 mm; length = 15 mm) with multiple (20 or 25) straight microfluidic channels (depth = 70 &#181;m; width = 60 &#181;m or 50 &#181;m; length = 8 mm) at the surface (Figure 1A-D). The microfluidic channels are open and allow multiple animals to be enclosed in them simultaneously (Figure 1E). The sheets are resilient to allow the microfluidic channels to be expanded (by ~10%, Figure 1F), and the elasticity allows animals to be enveloped gently. Also, owing to the self-adsorption capacity of the PDMS, animals can be sealed in the channels by covering the surface of the worm sheet with a thin cover film, in which animals are not pushed into the channels for enclosure. By turning the cover film over, we can easily collect the animals.
The channels do not hurt the worms when they are being enclosed or when they are collected. Furthermore, the sheets are made from PDMS, which is essentially hydrophobic, but water retention can be achieved by imparting hydrophilicity to the material. The water retention and thickness are favorable characteristics of the worm sheets. The water-retention capacity prevents dehydration of the animals after prolonged immobilization and enables long-term observations to be carried out.
In addition, as described previously9, the sheets are only 300 &#181;m thick, allowing heavy ions such as carbon ions (with a range of about 1 mm in water) to pass through the sheet enclosing the animals. This allows the ion particles to be detected and the applied radiation dose to be measured accurately. Moreover, the worm sheets can be reused and are thus economical. With the conventional injection method, the animals enclosed are sometimes dead and they cannot be taken out of the channel; their eggs can also clog the channels. This makes the chip unusable. Chips are, therefore, basically disposable and the cost-benefit ratio is poor.
In the present paper, we describe in detail a series of methods for on-chip immobilization of live C. elegans individuals using worm sheets. Through locomotion assays of animals 3 h after on-chip immobilization, we evaluated the suitable cover film. In addition, we showed the examples of on-chip immobilization for both imaging observations and microbeam irradiation.

<table border="0" cellpadding="0" cellspacing="0" style="width:1151px;" width="1152">
	<tbody>
		<tr height="40">
			<td height="40" style="height:40px;width:223px;">C. elegans wild-type strain</td>
			<td style="width:125px;">Caenorhabditis Genetics Center (CGC) , Minnesota, USA</td>
			<td style="width:353px;">N2</td>
			<td style="width:449px;">Wild-type C. elegans strain generally used in this study</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:223px;">C. elegans unc-119(e2498) III mutant strain</td>
			<td style="width:125px;">Caenorhabditis Genetics Center (CGC) , Minnesota, USA</td>
			<td style="width:353px;">CB4845</td>
			<td style="width:449px;">C. elegans strain only employed as an example of mutants with abnormal body shape&#160;</td>
		</tr>
		<tr height="64">
			<td height="64" style="height:64px;width:223px;">C. elegans transgenic strain HBR4</td>
			<td style="width:125px;">Caenorhabditis Genetics Center (CGC) , Minnesota, USA</td>
			<td style="width:353px;">HBR4</td>
			<td style="width:449px;">The genotype of this transgenic C. elegans strain is HBR4:goeIs3[pmyo-3::GCamP3.35:: unc-54&#8211;3&#8217;utr, unc-119(+)]V. This strain was only employed for imaging observation.</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:223px;">E. coli strain</td>
			<td style="width:125px;">Caenorhabditis Genetics Center (CGC) , Minnesota, USA</td>
			<td style="width:353px;">OP50</td>
			<td style="width:449px;">E. coli strain used as food for C. elegans</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Worm Sheet IR (50/60)</td>
			<td style="width:125px;">Biocosm, Inc., Hyogo, Japan</td>
			<td>BCM17-0001</td>
			<td style="width:449px;">Microfluidic chip with 25 straight 50/60-&#181;m width channels used in all experiments and observation in this paper&#160;</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Worm Sheet 60</td>
			<td style="width:125px;">Biocosm, Inc., Hyogo, Japan</td>
			<td>BCM18-0001</td>
			<td style="width:449px;">Microfluidic chip with 20 straight 60 &#181;m-width channels. This is sitable for adults 3-5 days after hatching at 20&#176;C.&#160;</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Worm Sheet 50</td>
			<td style="width:125px;">Biocosm, Inc., Hyogo, Japan</td>
			<td>BCM18-0002</td>
			<td style="width:449px;">Microfluidic chip with 20 straight 50 &#181;m-width channels. This is sitable for youg adults ~3 days after hatching at 20&#176;C.&#160;</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">MICRO COVER GLASS</td>
			<td style="width:125px;">MATSUNAMI GLASS IND. LTD.</td>
			<td>C030401</td>
			<td style="width:449px;">Cover glass (thickness: 130-170 &#181;m) used in locomotion assays in Protocol 3</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Polystyrene Film</td>
			<td style="width:125px;">Biocosm, Inc., Hyogo, Japan</td>
			<td>BCM18-0001/ BCM18-0002</td>
			<td style="width:449px;">Bundled items of Worm Sheets. PS filim (thickness: ~130 &#181;m) used in locomotion assays in Protocol 3.</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Polyester Film Lumirror</td>
			<td style="width:125px;">TORAY INDUSTRIES, INC., Tokyo, Japan</td>
			<td>Lumirror T60 (t 125 &#181;m)</td>
			<td style="width:449px;">PET filim (thickness: 125 &#181;m) used in locomotion assays in Protocol 3</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">IWAKI 60 mm/non-treated dish</td>
			<td style="width:125px;">AGC Techno Glass Co., Ltd., Shizuoka, Japan).</td>
			<td>1010-060</td>
			<td style="width:449px;">Non-treated dish used in incuvation of C. elegans in Protocol 1</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">IWAKI 35 mm/non-treated dish</td>
			<td style="width:125px;">AGC Techno Glass Co., Ltd., Shizuoka, Japan).</td>
			<td>1010-035</td>
			<td style="width:449px;">Non-treated dish used in locomotion assays in Protocol 3</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Milli-Q</td>
			<td style="width:125px;">Merck, France</td>
			<td></td>
			<td style="width:449px;">Ultrapure water</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Kimwipe S-200</td>
			<td style="width:125px;">Nippon Paper Crecia Co., Ltd., Tokyo, Japan</td>
			<td>62020</td>
			<td style="width:449px;">120 mm x 215 mm; 200 sheets/ box</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">WormStuff Worm Pick</td>
			<td style="width:125px;">Genesee Scientific Corporation, CA, USA)</td>
			<td>59-AWP</td>
			<td style="width:449px;">Platina picker specilized for picking up C. elegans</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:223px;">Research Stereo Microscope System</td>
			<td style="width:125px;">OLYMPUS CORPORATION, Tokyo, Japan</td>
			<td>SZX16</td>
			<td style="width:449px;">Micriscope used in all experiments and observation in this paper</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:223px;">Motorized Focus Stand for SZX16</td>
			<td style="width:125px;">OLYMPUS CORPORATION, Tokyo, Japan</td>
			<td style="width:353px;">SZX2-ILLB</td>
			<td style="width:449px;">This was used for bright field observation in Protocol 3-8.</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Objective Lens (&#215;1)</td>
			<td style="width:125px;">OLYMPUS CORPORATION, Tokyo, Japan</td>
			<td>SDFPLAPO1&#215;PF</td>
			<td style="width:449px;">NA: 0.15; W.D.: 60 mm. This lends was used for bright field observation in Protocol 3-8.</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Objective Lens (&#215;2)</td>
			<td style="width:125px;">OLYMPUS CORPORATION, Tokyo, Japan</td>
			<td>SDFPLAPO2XPFC</td>
			<td style="width:449px;">NA: 0.3; W.D.: 20 mm. This&#160; lends was used for imaging observations.</td>
		</tr>
	</tbody>
</table>

immobilization of live caenorhabditis elegans individuals using an ultra-thin polydimethylsiloxane microfluidic chip with water retention

Radiation is widely used for biological applications and for ion-beam breeding, and among these methods, microbeam irradiation represents a powerful means of identifying radiosensitive sites in living organisms. This paper describes a series of on-chip immobilization methods developed for the targeted microbeam irradiation of live individuals of Caenorhabditis elegans. Notably, the treatment of the polydimethylsiloxane (PDMS) microfluidic chips that we previously developed to immobilize C. elegans individuals without the need for anesthesia is explained in detail. This chip, referred to as a worm sheet, is resilient to allow the microfluidic channels to be expanded, and the elasticity allows animals to be enveloped gently. Also, owing to the self-adsorption capacity of the PDMS, animals can be sealed in the channels by covering the surface of the worm sheet with a thin cover film, in which animals are not pushed into the channels for enclosure. By turning the cover film over, we can easily collect the animals. Furthermore, the worm sheet shows water retention and allows C. elegans individuals to be subjected to microscopic observation for long periods under live conditions. In addition, the sheet is only 300 &#181;m thick, allowing heavy ions such as carbon ions to pass through the sheet enclosing the animals, thus allowing the ion particles to be detected and the applied radiation dose to be measured accurately. Because selection of the cover films used for enclosing the animals is very important for successful long-term immobilization, we conducted the selection of the suitable cover films and showed a recommended one among some films. As an application example of the chip, we introduced imaging observation of muscular activities of animals enclosing the microfluidic channel of the worm sheet, as well as the microbeam irradiation. These examples indicate that the worm sheets have greatly expanded the possibilities for biological experiments.

Active C. elegans individuals could be immobilized successfully using an ultra-thin, wettable PDMS, microfluidic chip (worm sheet). We investigated the suitability of different cover films for sealing the worm sheet, as described in protocol section 3. To evaluate the sealing effects of the cover films, we determined the motility of animals 3 h after on-chip immobilization using cover glass (thickness: 130-170 &#181;m), PET film (thickness: 125 &#181;m), and PS film (thickness: ~...

Watch this Scientific Journal Video about Immobilization of Live Caenorhabditis elegans Individuals Using an Ultra-thin Polydimethylsiloxane Microfluidic Chip with Water Retention at JoVE.com

Immobilization of Live Caenorhabditis elegans Individuals Using an Ultra-thin Polydimethylsiloxane Microfluidic Chip with Water Retention

A series of immobilization methods has been established to allow the targeted irradiation of live Caenorhabditis elegans individuals using a recently developed ultra-thin polydimethylsiloxane microfluidic chip with water retention. This novel on-chip immobilization is also adequate for imaging observations. The detailed treatment and application examples of the chip are explained.

Immobilization of Live Caenorhabditis elegans Individuals Using an Ultra-thin Polydimethylsiloxane Microfluidic Chip with Water Retention

Radiation is widely used for biological applications and for ion-beam breeding, and among these methods, microbeam irradiation represents a powerful means ...

One advantage of this protocol is that the worm sheet is easy to handle. The sheet has features that prevent drying, enabling us to conduct microbeam irradiation to living animals, perform several behavioral assays, and long-term observation. The microfluidic channels in this worm sheet are open, making it easier to collect animals.These worm sheets can also be used repeatedly, making them more economical. When we were developing this technique, we wanted to irradiate only a part of the animals with a microbeam under a microscope. So we needed clear, very thin chips capable of holding the animals.To begin, place a thin, transparent sheet onto the stage for use as a bottom cover film. Gently position a worm sheet on the bottom cover film with flat tweezers. Place at least three droplets of buffer solution on the surface of a 6 centimeter, non-treated Petri dish.Then, pick several adult C.elegans with a platina picker from a culture plate. Transfer the animals to a droplet with the platina picker and allow the animals to swim in buffer to remove any bacteria. Wash the animals in two separate droplets and rinse the animals in another droplet.Next, place a droplet of buffer solution onto the surface of the worm sheet. Remove the washed animals from the buffer droplet, and transfer them to a droplet on the worm sheet. Use flat tweezers to place a PS cover film over the worm sheet, and press gently over the channels from one end of the sheet to the other.Or simply drop animals into droplet and gently seal with the cover film so droplet spreads between the cover and the worm sheets with the animals within the channel. Confirm the animals are alive by checking for movement with a microscope at 1-2x magnification. Record the animals'positions and specifically note the number of the channel in which each animal's enclosed, and the position of each animal in the channel.For collecting immobilizing animals, use flat tweezers to remove the cover film from the worm sheet, then drop 10-15 microliters of buffer solution onto one of the microfluidic channels enclosing the animals. Under the stereomicroscope, observe the animals as they start to spin. Then use the platina picker to pick up the swimming animals and transfer them to an assay plate.After enclosing the animals as previously demonstrated, observe fluorescent spots on the animals with a flourescence microscope. Then image calcium ion wave propagation using video acquisition to observe dynamic activities. Place the used worm sheet onto a six centimeter petri-dish and place about 100 microliters of sterilized ultra-pure water onto the sheet.Use gloved fingers to spread water on the surface of the sheet and wash off any contaminants. Next, use disposable wipes to remove the moisture from the worm sheet. Dispense five milliliters of 70%ethanol into the Petri-dish and use gloved fingers to spread the ethanol over the worm sheet.Finally, after the sheet is dry, place the sheet on a sterile Petri-dish and cover. Using this protocol, the suitability of different cover films was investigated. There was no significant difference in motility between control animals and animals enclosed in microfluidic channels with PS film.In contrast, motility was significantly reduced in animals enclosed under a cover glass. The motility of animals enclosed with a pet film was also significantly decreased. It is important to select cover films for the sealing of microfluidic channels carefully.Using this protocol, we evaluated the suitability of different cover films through locomotion assays of the animals three hours after on-chip immobilization. Using this technique, we intended to develop an ultra-thin wettable chip only for microbeam irradiation. However, these worm sheets have already been used for imaging and behavioral assays beyond their original applications.

Research

JoVE Journal

Bioengineering

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