Vein vs. Symthetic. Typically natural bypass grafts are your own vein or artery. It is also possible to use cryopreserved vein or artery from a cadaver (less common but an option). Synthetic grafts are made either or gore-tex /ptfe or woven polyester (dacron). The natural grafts are less likely to clot when there is poor circulation and they are less prone to infection.
Sure. Natural grafts for a bypass would be to use something like a leg vein to bypass an artery. A synthetic graft is using a man-made graft. Both have advantages and disadvantages. Your surgeon should explain the differences and benefits of both types of grafts.