Peter Hosking - Living Cell Technologies
To start the encapsulation process, we mix the islets with the alginate solution and we pump them through a needle. Now, if this is the needle, essentially what we’re doing is pumping the solution containing alginate and islets through this needle. At the tip of this needle, we have a jet of air, and as the alginate and islets flow out of the needle, they’re cut off into very, very small drops, and these drops are around about 600 microns in size. They’ll fall from the needle into a container, which has a solution of very concentrated calcium chloride that will immediately form spheres of alginate and encapsulate the islet. That happens because the alginate has negative charges. The calcium and the calcium chloride, of course, have positive charges, and the calcium forms bonds in between the negatively charged alginate, which causes the solidification of the alginate.
So now we have an islet inside a sphere of alginate, the next thing we really have to do is make sure that that capsule has both strength, integrity and porosity so that it can function properly. And what we use for that is a compound called poly-L-ornithine. So we first of all put a coating of poly-L-ornithine onto the alginate, wash it, put a second more dilute coating on, wash it again and then we put a final coat of alginate on. And the final coat of alginate binds to the outer layer of the poly-L-ornithine and forms a protective coat for the capsule.