Development of skin interfacing cannula.

The skin interfacing potential of various velours, felts, foams and rough cast surfaces of some polymers was investigated by bonding these substances to solid core silastic rods using Dow-Corning Medical Adhesive Type A. These dummy cannulae were implanted as skin penetrating rods onto the dorsum of canines, goats, and swine. Vitreous carbon buttons were also investigated as to their potential. Over 200 individual implants were made and some retained in place for 2 yrs. Only the nylon and dacron velours held much promise as a long-term interfacing material. A "growth phenomenon" was observed using the velour material and this, we feel, is related to a permanent marriage between basal cells and adjacent monofilament fibers. Subsequent maturation of these cells carries the monofilament fibers to the surface causing the entire cannula to "grow". Since the maturation rate is apparently slower in humans, it does not detract from their potential application. The maturation rate is also much more rapid on the dorsum than on the ventral surfaces.