Of Mice and the Internet of Things

Ever since the long lost time of my PhD (about a decade ago), I have been excited by telemetry. More specifically, the use of telemetry and wireless technology to obtain high quality physiological data from mice.

During my PhD, I used telemetry to record ECG in transgenic mice, using DSI’s transmitters (www.datasci.com). ECG was actually my second choice for investigating cardiovascular control in our knockout strain, but the blood pressure transmitters were too challenging for me to be confident in spending that much of our limited grant funding on.

The reason we wanted blood pressure recordings is that it is a much more reliable readout for the stimulation of the cardiovascular system, as there are many reflex control on heart rate that make it tricky to understand exactly what is going on (for example, if you stimulate cardiac output, you might well increase heart rate along with blood pressure, but then your baroreflex kicks in and the heart rate drops). As it turns out, I was able to delve into heart rate variability analyses using the ECG transmitters, which formed a large part of my thesis, so all turned out fine.

Anyway, I have more recently been using DSI telemetry to investigate body temperature and locomotor activity in mice, but have found myself getting annoyed. Between the surgery and singly housing animals, crappy battery life and expensive refurbs, short range recording and signal dropouts, it’s been getting on my nerves. And it’s 2021, why are we still using transmitters and recording technology that was developed 20 years ago?

After some time niggling away at the back of my mind that there must be a better way, I had a conversation with my dad about something he’s been working on (he’s technically retired, but is working with an old friend from the oil drilling business) about uses of the Internet of Things. This is one of those terms I’d heard, but thought it was a bit of a gimmick, like amphibious cars, or smartphones.

In fact, it turns out technology has reached the point where everything can be connected. For example, from the industrial sector that he was talking about, they can monitor the temperature of a certain piece of machinery, the pressure inside the system, performance indicators, pollution levels etc. Really, anything that might possibly want monitoring can have a sensor placed inside, which will be quiescent until certain parameters are met, and then it pings out a signal. This means that the battery drain is negligible, and the sensors can remain in place for years. Hearing this, I was excited to check out the state of the technology for my experiments; as researchers we are prone to just use the same as we always have. Here’s what I envisaged:

  • A transmitter that is small enough to implant through a (fat) needle, negating the need for pesky surgery
  • The signal is long-range enough, and includes identifying information, that you can have a single receiver for a number of group-housed mice
  • Implants are single-use – cheap(er) than DSI and disposable, so no faffing with refurbs and sterilisation

It’s possible that my desired were too restrictive, particularly with regards to the maximum size, because after much internet scouring, the best I was able to find was implantable ID chips like this from Unified Information Devices (UID – www.uidevices.com):

These are injectable RFID chips that are primarily used for mouse identification. Apparently, such things are fairly common in industry, where you would subcutaneously implant every mouse with an RFID chip, allowing you to essentially scan a mouse like a barcode and it brings up all the relevant information about that animal.

The UID implants take the identification a step further, also providing a temperature readout along with the animal ID. Unfortunately, this normally requires you to “beep” the mouse with your reader at very close (likely skin contact) range. However, UID also produce a “mouse matrix”, that can read the info (including body temp and track movements) from outside the cage. They are quite pricey though.

The reason this is needed is that the RFID chips don’t have a battery, instead the tiny microchip is temporarily powered by the electromagnetic waves from the reader itself (same as the chips in most modern cash/credit cards).

So, I’ve been thinking, couldn’t you put a tiny battery inside, and low-powered, infrequent data transmission? You would only have to transmit every 5 or 10 minutes, so surely even a tiny battery could manage that? There is a product called Anipill, which takes a similar approach (www.animals-monitoring.com). Their 1.7g implant sends out data at various timeframes from 1 min to 1 hour, and you can record data from a number of animals (up to 8) simultaneously from a single receiver, which improves the animal welfare by allowing group housing. This seems to be exactly what I had been thinking of, but with a capsule size of around 18 x 9 mm, it is far bigger than I had wanted.

Sadly then, if this company can’t make transmitters anywhere near small enough for injecting, then it’s probably not possible, at least with current technology. But, this is an area that is only improving from the advance of technology, so I will not lose my interest so easily.

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