Only dermis is vascularized. Nutrients reach epidermis by diffusing through the tissue from the blood vessels. Underneath dermis is hypodermis (superficial fascia), also called subcutaneous tissue which is composed of loose connective tissue (mostly areolar and adipose).
A collagen dressing is a type of wound dressing that is made with a form of collagen to aid in the body's healing processes. Collagen is a category of structural proteins that are naturally present in almost every part of the human body and are especially common in connective tissue.
Collagen dressings are dressings that are derived from animal sources, such as bovine (cattle), equine (horse) or porcine (pig) sources. The collagen helps to promote the growth of new collagen at the wound site, prompting an often speedier recovery period.