Pin selections

Choosing pins for your preparations is important. Especially for physiological experiments run on a Sylgard-coated dish. Here are some choices:

1) Tungsten needles

   This is standard and classic. I used to make them a lot when I was using isopod heart preps (very small). There are a lot to talk about how to make them.  However, I don't use them any more just because it takes a tedious time in electropolishing. I just don't have time for that. Plus, it needs extra care for a highly corrosive chemical solution.

2) Stainless steel pins

   We mainly use 10 µm diameter ones purchased from FST. These are great pins, but you need to cut them to proper length; 1 cm is too long for our preparations. Don't use a pinching wire cutter, because it crushes the cut end.  Just use regular dissection scissors. I use the fine scissors with serrated edge.

3) Cactus spines

10 µm diameter is too large for smaller brains such as those from Melibe and Flabellina. Some people use the tips of glass microelectrodes, but they are too fragile to handle with forceps. They also mess up the Sylgard floor, because the broken tips will remain there.
   We use cactus spines. Just one cactus stick can provide us enough pins. We harvest pins every time we do experiments. It keeps us running fine as long as we don't forget watering them once a month.
   I don't know their species names. The diameters about the size of my thumb. The white produces finer spines than the yellow.

4) Coffee filter

Do you have an old coffee filter? Check it out. Some coffee filters are made of fine stainless steel mesh. The diameter of the steel fiber is about the same as the FST pins (10 µm). This Zig-zag shape will prevent it from being pushed out from Sylgard resin. Indeed, short FST pins sometimes get repelled and pushed out of a freshly-made Sylgard resin.

May be not just for pins. Such a fine stainless fiber may be useful for some other purposes, too. Any ideas?

Left two, Cactus spines; middle two, coffee filter fibers; right two, FST pins (10 µm diameter).
 

   The FST pins are most commonly used in our lab. This is the hardest among the three, but difficult to handle with once bent.

   Cactus spines are the finest, but not very sturdy enough for reuse. Often crushed by forceps.

   The coffee filter fiber has the same thickness as the FST pins, but much softer. Their zig-zag shape can be useful for secure fix.