You could probably just give it a hard jet of water from a hose head or something or use Dawn dish soap and then give it a real good rinse. Sun drying the branches in the sun after a wash will get it dry from the inside out, so mold will be less likely to grow in the cage and on the branches. Urates are usually sort of chalky when they dry so if you still can't get them off with soap and strong water, then maybe soak the branches and then apply some scrubbing force. I don't see why they would be so difficult to remove though, because I don't usually face any trouble when cleaning teh branches and the bottom of the cage where the droppings are.