I'm studying a new TPU (thermoplastic polyurethane) anti-shock device for dogs, a sort of accordion-shaped piece to place between the collar and the leash, and I was wondering if it could suffer some sort of microbial attack. The product must be optimized as failure occurs too often (it breaks near the ends, never in the center) and although I think it is a notch related fatigue problem, I'm curious about other possible causes. I observed some yellowing which can be related to microbial attack as well as to UV exposure. Can someone help me or give me ideas how to investigate on this?