are then selected and must meet the general 'biocompatibility' require-
ments. Prototypes are built and tested to include biocompatibility
evalua- tions based on ASTM standard procedures. The device is validated
for sterility and freedom from pyrogens before it can be tested on
animals or humans. Medical devices are classified as class I, II or III
depending on their invasiveness. Class I devices can be marketed by
submitting notification to the FDA. Class II and III devices require
either that they show equivalence to a device marketed prior to 1976 or
that they receive pre-marketing approval. The time from device
conception to FDA approval can range from months (class I device) to in
excess of ten years (class III device). Therefore, much planning is
necessary to pick the best regulatory approach. 2. Wound Dressings and
Skin Replacement 2.1 Introduction Wounds to the skin are encountered
every day. Minor skin wounds cause some pain, but these wounds will heal
by themselves in time. Even though many minor wounds heal effectively
without scarring in the absence of treatment, they heal more rapidly if
they are kept clean and moist. Devices such as Band-Aids are used to
assist in wound healing. For deeper wounds, a variety of wound dressings
have been developed including cell cultured artificial skin. These
materials are intended to promote healing of skin damaged or removed as
a result of skin grafting, ulceration, burns, cancer excision or
mechanical trauma.
