The first thing I want to do is point you to some great information on general theory and the regulatory status of particulates for medical devices. There is an excellent article by Susan Reynolds and Ryan Lunceford on thebasics of particulate testing. It talks about the prevalent use of USP 788, as I have done in my previous article on medical device particulates here, including some specifics on the differences between laser counting versus microscopic counting of particles.
The article is a few years old, and at that time, the AAMI was not yet finished writing its report on setting medical device particulate limits. However, now that report is out, and you can find it here. Personally, I found it a little vague. It does not give any sort of concrete limits to follow, and is not any sort of draft guidance. It is good for figuring out how to think about this when going about your own particulate tests, however.
One item touched on by both the AAMI report and the article is composition. Specifically for hydrophilic coatings and/or lubricious coatings, these particles have characteristic identities. Like anything else, a major consituent of particulate could be clean room dust, which originates from human skin or clothing, or other particles tracked in from the outside. However, after abrasion, it can also be due to coating wear particulate. In fact, one method of testing durability for a hydrophilic coating is to run it through a tortuous path test and then measure the amount of particulate in the path after multiple cycles. For increasing number of cycles, you can track the increase in particle count.
Again, this is just an idea and not a standard. There are no suggested limits for a test like this right now. Everything in this field is at this point "unregulated", and we are all concerned about what the FDA will eventually do to throw a wrench in the innovation in the name of hypersensitivity.