Dissolving Microneedles for Transdermal Drug Delivery

Abstract

Microfabrication technology has been adapted to produce micron- scale needles as a safer and painless alternative to hypodermic needle injection, especially for protein biotherapeutics and vaccines. This study presents a novel design that encapsulates sensitive biomolecules within microneedles that dissolve within the skin for bolus or sustained delivery and leave behind no biohazardous sharp medical waste. A novel fabrication process was developed based on casting a viscous aqueous solution during centrifugation to fill a micro-fabricated mold with biocompatible carboxymethylcellulose or amylopectin formulations. This process encapsulated sulforhodamine B, bovine serum albumin, and lysozyme as model drugs; lysozyme was shown to retain full enzymatic activity after encapsulation and to remain 96% active after storage for two months at room temperature. Microneedles were also shown to be strong enough to insert into human cadaver skin and then to dissolve within minutes. Bolus delivery was achieved by encapsulating model drug just within microneedle shafts. For the first time, sustained delivery over hours to days was achieved by encapsulating drug within the microneedle backing, which served as a controlled release drug reservoir that delivered drug by a combination of swelling the backing with interstitial fluid drawn out of the skin and drug diffusion into the skin via channels formed by dissolved microneedles. We conclude that dissolving microneedles can be designed to encapsulate sensitive biomolecules, insert into skin, and enable bolus or sustained release drug delivery.