How can i make it?

a sponge is a great idea! a very diff alternative! what if u hot glue thread or cords for boundaries or to outline certain parts and use ons and other common place things like that. You could even paint coins with a paint pen. cotton could also be used - you can make them smaller by cutting them smaller and rolling them into smaller . Oh - and with coins, you can place a smaller one within a big one (like a dime inside a penny) to have one be the outer wall - like in the nucleus (I think - its been a while since I took bio) :) Good luck to you! :) Be creative!