Dr. Kroeppler wants to record a recommendation on an injection involving an integumentary system protein. If he needs to identify the protein that provides firmness and strength to the skin, he would describe

Collagen is the main structural protein that gives skin firmness and strength. Keratin strengthens the outer skin and hair, elastin allows skin to stretch and recoil, and melanin provides pigment. Therefore, the correct choice is collagen.

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