Accuracy and feasibility of piezoelectric inkjet coating technology for applications in microneedle-based transdermal delivery

Coated microneedles have shown immense promise for use in transdermal delivery and diagnostics, due to their ability to painlessly breach the skin's outermost stratum corneum layer and interact with the epidermal layers immediately beneath. In this work, we use an off-the-shelf piezoelectric dispensing system to demonstrate the feasibility of depositing material directly on to steeply-sloping microneedle sidewalls, without the need for specific needle array positioning or material pretreatment. In the first instance, an analysis of deposition accuracy shows that over 95% of dispensed droplets land within 20 μm of the target. Through the use of sequential dispense and drying steps, 3.2 nL of a model drug formulation has been deposited onto both silicon and polymeric microneedles with highly sloped (71°) sidewalls; these are the steepest surfaces that have been coated to date. Finally, preliminary ex-vivo skin studies have been performed to show that the material may be successfully transferred from the needle to skin. Despite the smooth surfaces, ultrasharp tips and steep sidewalls of these structures, piezoelectric dispense techniques are clearly feasible for microneedle coating and may offer a promising alternative to conventional coating processes.