heyas; cool hair, is that yours? somebody was making some hospital/medical/accessibility things.... once upon a time. not sure how that ended up. as for painting the sling.... make the lines from the shoulders to the arm straight, so it looks as if the sling is holding weight. (unless he's supposed to be lifting his arm inside the sling, in which case, you need deeper shadows and wrinkles.) the shadow/wrinkling deal looks like it has a good start, but you need to put more in. and strengthen the contrast.