Tag: Animal surgery

Feeling Warm and Fuzzy

I have previously talked about developing a touch-free timer for use in surgery. The goal was to better enable a single researcher to maintain sterility during animal surgeries. I really think this is a genuine unmet need in the research world, and widespread adoption of touch-free surgery kit would be extremely beneficial, both to the researchers and to the animals.

Anyway, with the plan to expand my touch-free surgery range, I figured the next piece of kit should be a heat mat for keeping rodents warm in surgery. And again, I wanted something that can be controlled by touch-free sensors. Helpfully, Pi Hut sell a small, flexible heating pad:

Looking at the specs, it uses ~1 A of power, which is far more than we can safely run from an Arduino digital pin. In order to do this, we make use of a component called a MOSFET, which is a special kind of transistor used to amplify circuits. A MOSFET lets you use a digital signal (eg. an Arduino output pin) to fully switch a separate circuit (eg. a fully powered heat mat).

Therefore, using a MOSFET, I can control the power going to the heat mat by the digital output of the Arduino. I’ve mentioned pulse width modulation (PWM) before, and it is perfectly suited to this application. PWM will let me digitally control the amount of power going through the heat mat. And, best of all, because it’s digitally controlled, I can shift the PWM up/down with IR proximity sensors.

But, how to display the power going through the heat mat? For this, I again turned to Pi Hut, who sell a 10-segment LED bar:

Each LED in the bar is individually controlled, which means that I can set the Arduino to display an indication of the power going through the heat mat, on a scale of 1-10. Bringing it all together in a 3D printed housing, I have power up and power down proximity sensors, a power indicator bar, and a flexible heat mat that warms quickly to the extent determined by the user:

Touch-free heat mat for keeping rodents warm in surgery.

I have used this heat mat in surgery myself, and it worked really well. It heated up super quick and I could change the power of the heat mat to the temperature needed by the mouse. This piece of kit is indispensible for keeping rodents warm in surgery.

The one thing that I think it missing is an actual reading of the mouse’s temperature – I kept having to feel the surgery bed to check the temperature, which kind of defeats the purpose of being touch-free.

So, my next plan for this piece of kit is to add in a temperature sensor (whether a standalone one or one that runs through the Arduino, I have yet to figure out). Stay tuned for updates.

A Better Timer

This is a quick update to my previous blog post, where I explained making a touch-free surgery timer. Unfortunately, I found that it just wasn’t working well – as I explained previously, the low voltage used by that timer (1.5 V from a single AA battery) was not enough to make multiple IR sensors respond to the proximity of a finger.

After some brain-storming for how to fix this issue with sensing, I came to the conclusion that I really needed to start from scratch with a new (higher voltage) timer. I therefore scoured the internet for a timer with the following features:

  • Runs at 3-5 volts (ie. two or three 1.5 V batteries), but not from button batteries (they don’t have much capacity, so would drain too quickly)
  • Stopwatch and countdown timer functions
  • Controlled by limited number of pushbuttons (ideally Start/Stop and Reset for stopwatch, then “add minute” button to set up timer)
  • Has big light-up numbers for easy checking of timing

Finally, I found a timer that hit all my requirements, and only cost around £20 on Amazon (turns out the kind of timer I wanted with simple controls and big light-up numbers is targeted to children and the elderly):

So, I cracked the timer open, soldered in IR proximity sensors to the Start/Stop, Reset and Minute buttons, and found they worked great – I could control the timer by moving my finger to within 10 mm or so. Turns out there was some dead space inside the case, which meant that I could drill holes in the side and mount the sensors on the inside. I also added in a cutoff toggle switch to cut the power to the IR LED’s to prevent battery drain.

All in all, I’m really pleased with the new timer: I left it in the surgery room, and it’s going down brilliantly with the other lab members who’ve tried it.

No Touchy!

This came about when I was thinking about how to improve my surgery technique, in particular sterility. Not that I or people I’ve taught have ever had issues with infection, but maintaining good sterile technique can be difficult, and it certainly makes many routine tasks challenging. And, unlike “real” surgeons, who have a team of underlings to aid in their surgery, we researchers often undertake ours alone, or at most with a single technical helper.

So, what kind of routine tasks do we perform during surgery that could be done without touching anything? My first thought was a timer – we do a lot of virus injections with a nanoinjector, and we time how long we inject to ensure sufficient spread of the virus before retracting the needle. After much Googling and scouring of the internet, I was unable to find any “hands-free timer” that wasn’t a 30-second hand-washing timer. So I decided to develop my own.

First step to a hands-free timer is to find a switch of some kind that can be remotely activated, a proximity sensor of some kind. I wanted something cheap and crudely effective – ie. something that triggers upon proximity of an object (likely a human finger), with a detection distance of 5-10 mm. This lead me to two likely alternatives, a capacitive plate or an infrared sensor (Figure 1).

I bought some sensors to test, hooked them up to an Arduino and found that the IR sensor worked great, but the capacitive plate was very hit-or-miss. Right, so I knew which sensor I wanted to use, but now I needed to set them up on a timer. My first thought was to use my perennial favourite, the Arduino. And I did start setting that up, but then I found an old lab timer that I thought might make a quick and easy prototype (Figure 2A).

Opening the old timer up, I found that the buttons were simple conductive latches that connected the microcontroller pin to ground. All I had to do was correctly solder in the phototransistors of my IR sensors to perform the same latch, and I could activate the “buttons”. The one snag I found was that the timer ran off a single 1.5 V battery, which wasn’t really enough to produce a strong IR signal. This meant a couple of things:

  • I could only connect two IR sensors before the drain on the battery meant they ceased to function entirely; therefore, I hooked them up to START/STOP and RESET, to give me a functional stopwatch without the other functions.
  • The low power available from a single AA battery meant that even with only 2 IR sensors connected, they have low IR strength and therefore can only detect highly IR-reflective objects. It works for metal objects and gloved hands, so should work fine in surgery.

I connected up a couple of IR sensors to the existing circuit, as well as a toggle switch to turn off the power to the sensors to prevent battery drain when not in use. I then 3D-printed a box to house everything, giving me a prototype for my Touch-Free Timer (Figure 2B).

I had assumed that the timer, being so old, would not be in production any more. However, it looks like you can still buy it from lab suppliers, so I shouldn’t have any problems producing as many as are needed.