[
International Worm Meeting,
2021]
In nature, C. elegans live in a rich 3-dimensional environment. However, their behavior has been assessed almost exclusively on the open, flat surface of NGM (Nematode Growth Medium) plates, the golden standard for C. elegans culture in the lab. We present a method to build 3-dimensional behavioral arenas for C. elegans by directly 3D-printing NGM hydrogel. This is achieved by using a highly customized fused deposition modeling (FDM) 3D-printer, extensively modified to employ NGM hydrogel as ink, i.e., the Parnon Printer. The result is the advancement of 3-dimensional complexity of behavioral assays. To demonstrate the potential of our method, we use the 3D-printed arenas to assess C. elegans physical barrier crossing ability, in the context of aging (young, middle-aged adults), feeding history (fully fed, starved animals) and prior experience (have been or not in the presence of a similar 3D structure before). We also explore the usage of 3D-printed structures to spatially confine C. elegans egg laying behavior. C. elegans behavior in 3-dimensional environments is by definition not possible to explore on standard flat NGM plates. Therefore, the findings reported here would likely not have been brought to light if the Parnon Printer had not been developed. We consider these work a decisive step toward characterizing C. elegans 3-dimensional behavior, an area long overlooked due to technical constrains. We envision our method of 3D-printing NGM arenas as a powerful tool in behavioral neurogenetics and neuroethology.
[
International Worm Meeting,
2021]
The platinum worm pick, a fixture in C. elegans laboratories for decades, has two drawbacks: (1) the high cost of platinum, a significant problem in many educational settings, and (2) the reliance on an open flame for sterilization, which presents safety hazards. To address the first drawback, we evaluated whether platinum could be replaced with an alternative metal. An ideal worm pick cools quickly after heating, withstands high temperature without degradation, can be flattened and shaped easily, and is inexpensive. With these criteria in mind, we compared 90% platinum, 10% iridium wire (PT9010) with 5 alternatives: stainless steel (SS), Nickel 200, two nickel chromium (Nichrome) alloys, and iron-chromium-aluminum (FeCrAl). To measure cooling rate we built a circuit to resistively heat wires (all 255 microm in diameter) to 800 C and measured the time it took them to cool to 25 C. We found that PT9010 and FeCrAl cooled more rapidly (6-7 s) than the other metals tested (8-9 s). To assay heat resistance we conducted a bending test after 3000 heating cycles of duration 4 s at 800 C. All materials except SS showed good heat resistance, withstanding >50 bends after 3000 heating cycles. SS exhibited poor heat resistance, breaking spontaneously after ~300 cycles. All materials could be easily flattened using standard tools. With regard to cost, all alternative materials were < 0.20 USD/m, as compared to 140 USD/m for PT9010. These results show that all metal alloys tested except for SS represent reasonable, economical alternatives for worm picks. The most promising is FeCrAl which cools as rapidly as platinum, exhibits good heat resistance, and is available at a fraction of the cost. Next, to explore an alternative to flame sterilization, we designed an electric worm pick consisting of a loop of PT9010 or FeCrAl wire attached to a handle containing a rechargeable battery and circuit board. Depressing a button causes current to flow through the loop, heating it to about 800 C within 2 s. A battery charge lasts for ~500 sterilizations. Worm researchers who tested the device reported that the wire loop could be used similar to a worm pick and that electric sterilization promoted faster work since no movements to a flame were necessary. Our device represents a convenient and safer alternative to flame-sterilized worm picks. We are using a similar loop-based worm picking technique in our automated worm picking system (see abstract by Zihao Li et al).