Transgender people who take HRT (hormone replacement therapy) often use intramuscular injections to provide their bodies the exogenous hormones they need. Depending on if someone is trans-feminine or trans-masculine, their medicine comes in the form of either testosterone cypionate or estradiol valerate, respectively. Both use a 1-inch needle and a 1mL syringe, with a dosage of less than half a mL.
With such a long needle as 1-inch, self administration can be pretty nerve-wracking--so it's common to develop some needle-phobia that poses an obstacle for treatment. I, for one, tend to procrastinate because of my own heebie jeebies, and I've been doing it for years.
There are issues that come with improper technique in inserting and injecting that can cause pain and bleeding. The problems I've run into myself are: 1) pricking myself prematurely with the needle, which dulls the point and makes the subsequent, intentional insertion painful; 2) breaking through the dermis too slowly; 3) inserting the needle into the muscle too quickly; 4) inserting non-perpendicularly; 5) dispensing the dose too quickly which can cause a lingering, dull ache, and 6) withdrawing the needle too slowly or non-perpendicularly, causing painful scratching on the way out.
The idea behind this auto-injector is that it uses servo motors instead of springs that most auto-injectors have, so that the speeds of insertion and injection can be precisely set so it's a a comfortable injection every time. It is very uncommon to find an auto-injector that even works with intra-muscular because of these reasons. With servo control, the initial 1mm of puncture can be made relatively quickly at 25-50mm/sec, and the rest of the travel through the muscle can be set to a comfortable 5mm/sec. (I tested these speeds myself with a syringe and a stopwatch, someone's gotta do it). After the needle reaches the end of the stroke, the plunger can start descending at its own slower rate (about 1-2mm/sec) until the full dose is dispensed. At that point, the whole syringe body can retract at a quick rate for a comfortable withdrawal.
The way this device works specifically is both the servos have pinions, which move along a rack. First they move down at the same rate, the upper one connected to the plunger and the lower one connected to the syringe body, so that the syringe as a whole moves down, without dispensing. Then the lower servo stops and upper servo moves down by itself, moving the plunger relative to the syringe body to dispense the dose. Then finally, both servos move up at the same rate to withdraw the needle out of the body. (Note: add diagrams here)
I haven't prototyped this project yet, because I left my resin printers in storage. I did buy the parts and plan to build this when the tools are available. I think that this thing could be made for less than $50 using Alibaba parts instead of Amazon (I hope tariffs don't shred that idea), and I think it would be reasonable to sell it for $75-$100. I haven't done that much serious market research other than talking to my trans friends about it, and the trans-specific endocrinologist at UCSB who was a fervent proponent of the idea.
So as of now the status of this project is:
Coming soon...
