Question: How does alginate act as an invisibility cloak in the body? Is there a set mechanism of action or is it unknown?

Katrina Wesencraft answered on 24 Mar 2020:

The thing we like about alginate is that it’s a ‘bioinvisible’ polymer – so the material can be implanted without bothering your immune system. The immune system is really complicated so I don’t think we understand the exact mechanism but there a couple of things to think about. The circulating white blood cells either can’t detect alginate, or they decide to ignore it for some reason. Some materials trigger something called the ‘foreign body response’ when you implant them but alginate doesn’t do this. We create a tiny jelly bubble (200 micrometres diameter – about the width of a human hair) and trap the cells inside. Alginate is selectively permeable, so nutrients can get in to feed the cells, while compounds that the cells produce can get out (I work with cells that produce insulin). The pores in the material allow these substances to flow in and out, but they’re too small for large immune cells and antibodies to get in. This should stop the cells inside from being attacked by the immune system.