For the I2C interface, a good quality USB cable with appropriate connectors fitted should be good; decent ones have heavy power conductors plus a twisted pair for the data lines. (But a lot of cheap ones only have four very thin, equal, cores).
USB-C cables are available in long lengths and with power ratings - eg. 3A or 60W, but I've never had cause to chop up one of those yet to look at the cable makeup, though I'd expect power cores plus probably three pairs.
That may may be suitable for the link to the portable part, but would it eventually need to be something that can either be replaced or sterilised between procedures?
Or it could be fitted via a gland and a plug at the other end only.
For a chemical proof and ultra flexible type, you could use a polyurethane jacketed "chain cable", the type intended for robotics and machine tools to go around moving assemblies. The core strands are extremely fine, and the PU jacket near indestructable.
eg. This is a type we use, multiple twisted pairs - this two pair screend is 6mm diameter, the photo shows a rather larger 6 pair.
Or three pair
You probably don't need anything particularly fancy for prototyping, but again if the final thing needs to be washable, have a look at the Lemo FGG IP67 rated circular connectors. There are several size ranges and they are perfect for cables such as those above.