< SNIP >
Mother of God...
Please don't do this!
I get freaked out about infection using sterile medical catheters. The risk of infection is absolutely real, and if it reaches your kidneys can be extremely serious or even fatal.
You have no idea what mold release chemicals, plasticizers, curing agents, etc., went into the manufacture of that USB cable, or any other non-medical device for that matter. Many of them are made in parts of the world where quality control isn't exactly first priority.
I've ordered medical grade, sterile, catheters and insertion trays from three different suppliers now. Not one of them has asked for a prescription. One of them is a fetish site, for Pete's sake. The other two look to be legit medical suppliers, but if you read the product reviews on their pages it's clear that not all of their users are medically in need... You can buy the "right" thing for less than $3.00/ea.
If you decide that making your own medical devices for internal use is easier/more cost effective, make sure you're in close proximity to medical care and may God have mercy on your soul.