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.
Cortisone injection, in my practice, is used for hypertrophic or keloid scarring and reduction in inflammation. These type of scars are indicative of over-stimulation of collagen. Cortisone is injected to slow collenogenesis and decrease inflammation. A decline in reddness is also noted if discoloraton has occurred. The area injected may be swollen for a few minutes. Following the initial edema and absorption of the fluid, the tissue should not be more swollen than pre-injection.