You got it. It's because it's hard. The closest thing we have to this is dialysis, and we need to replace the business end (dialyzer) of the device every trea

You got it. It's because it's hard. The closest thing we have to this is dialysis, and we need to replace the business end (dialyzer) of the device every treatment. It's biofouling. The body naturally wants to attack and foul up anything that's not natural. It's a classic problem in implants.