Insertion Behavior of Microneedles for Drug Delivery

Abstract

Drug dosage delivered by drug-coated microneedle is dependent on needle insertion behavior. The insertion length and gripping force at varied insertion speeds are determined quantitatively using a precision test frame. The ratio of inserted depth to pressed depth was found to rise asymptotically to a plateau, but decreased rapidly to zero insertion when the needles are pressed less than 1000 microns deep for both silicone rubber and porcine skin. No insertion was observed when the needles are pressed less than 200 microns. The gripping force exerted onto the inserted needle by the skin decreased by 0.1N per mm of needle diameter and insertion depth. The short insertion depth and low force suggest that drug delivery using short 300 micron microneedles would be tenuous. High insertion speeds can help to improve drug delivery, but the improvement is limited to large needles since the results from this study showed that insertions become speedindependent when the needle diameter is less than 130 microns.