All hydrophilic coatings have some sort of bioerosion, degradation, and/or resorption rates in vivo. For most coatings of this nature, those rates are high, which means they are not always suitable for implantation.
Honestly, that's a rather broad and general statement about the utility of implantable hydrophilic coatings. In reality it goes back to a question I like to ask a lot on this blog:
What is your application?
Let me break that out into some more specific thought questions:
What kind of device do you want to coat?
WHY do you want to coat it?
Do you want it to be slippery?
Closely associated with water to prevent fogging or misting?
Given your answer to the question above, exactly WHEN do you want the coating to possess those properties during the life of the device?
Pre-implantation? During implantation? During explantation? The whole time?
Given that last answer, how long is that time period? Minutes? Hours? Days? Weeks? Forever?
In many cases, for example in the case of an implantable cardiac pacemaker, surgeons may be complaining that it is difficult to squish the leads into place during the procedure. A lubricious coating might help with that. However, once the device is implanted, who cares about what happens to the coating as long as it is biocompatible? Or maybe I should ask: do you care what happens?
If you do care, then you need to ask yourself why. Is there some other function a slippery, non-thrombogenic, water-loving coating will serve a purpose after implanting that pacemaker?
Most of the time, when clients come to me asking for permanent hydrophilic coatings, it actually turns out that they do not need them to be permanent. They just need them to fulfill a temporary role, which the coating can do easily, and then when it goes away it is of no consequence.