Drug administration via the transdermal route is an evolving field that provides an alternative to oral and parenteral routes of therapy. Several microneedle (MN) based approaches have been developed. Among these, coated MNs (typically where drug is deposited on MN tips) are a minimally invasive method to deliver drugs and vaccines through the skin. In this review, we describe several processes to coat MNs. These include dip coating, gas jet drying, spray coating, electrohydrodynamic atomisation (EHDA) based processes and piezoelectric inkjet printing. Examples of process mechanisms, conditions and tested formulations are provided. As these processes are independent techniques, modifications to facilitate MN coatings are elucidated. In summary, the outcomes and potential value for each technique provides opportunities to overcome formulation or dosage form limitations. While there are significant developments in solid degradable MNs, coated MNs (through the various techniques described) have potential to be utilized in personalized drug delivery via controlled deposition onto MN templates.

Complex micro- and nano-structures enable crucial developments in the healthcare remit (e.g., pharmaceutical and biomaterial sciences). In recent times, several technologies have been developed and explored to address key healthcare challenges (e.g., advanced chemotherapy, biomedical diagnostics and tissue regeneration). Electrohydrodynamic atomization (EHDA) technologies are rapidly emerging as promising candidates to address these issues. The fundamental principle driving EHDA engineering relates to the action of an electric force (field) on flowing conducting medium (formulation) giving rise to a stable Taylor cone. Through careful optimization of process parameters, material properties and selection, nozzle and needle design, and collection substrate method, complex active micro- and nano-structures are engineered. This short review focuses on key selected recent and established advances in the field of pharmaceutical and biomaterial applications.