The majority of conventional controlled release technologies tend to be based around encapsulant systems in which a polymeric binder or gel typically responds to changes in the local environment in which the delivery device has been placed. The contents are often released when the particle, capsule, film or droplet is exposed to the appropriate physico-chemical trigger (typically a change in pH) with the time-release-dose delivery characteristics controlled through manipulation of the encapsulant formulation. In this communication, the adaptation of this core strategy for use in the next generation of transdermal microdevices or smart patch is explored. The core rationale of this work relates to the development of microneedle patches through which a drug could be transported across the skin barrier upon activation by an appropriate electrochemical trigger.

The microneedle in this case serves as the entry point through the strateum corneum whilst acting as a physical barrier to the transport of the drug from a reservoir within the patch.  Upon activation, the microneedle dissolves thereby allowing the release of the therapeutic agent as indicated in Figure 1A,B.

The methodology proposed herein focuses on the ability to control the dissolution of the conductive composite microneedle through an application of a specified potential trigger. Central to this approach is the design and fabrication of a novel nanostructured conductive film based on a composite of carbon nanoparticles and cellulose acetate phthalate (CAP). This is created through the solvent cast method onto a silicone microneedle template shown in Figure 1C.  Under normal conditions, the conductive coating remains intact but, upon imposing a reducing potential on the carbon composite layer, the local pH is increased which results in the solubilisation of the pH sensitive CAP binder components. The latter is the structural glue that holds the microneedle together and thus the subsequent swelling effectively leads to the dissolution of the microneedle architecture and the release of the drug. The presentation covers three aspects: the design and characterisation of the carbon composite microneedles, the ability to electrochemically manipulate the structural integrity of the needles and the ability to effect the controlled release of model drugs such as codeine, methotrexate and fentanyl.