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.

Therapeutic systems to induce reactive oxygen species (ROS) have received tremendous success in the research of tumor theranostics, but suffered daunting challenges in limited efficacy originating from low presence of reactants and reaction kinetics within cancer cells. Here, ferrous sulfide‐embedded bovine serum albumin (FeS@BSA) nanoclusters, in an amorphous nature, are designed and synthesized via a self‐assembly approach. In acidic conditions, the nanoclusters degrade and simultaneously release H₂S gas and Fe²⁺ ions. The in vitro study using Huh7 cancer cells reveals that Fe²⁺ released from FeS@BSA nanoclusters induces the toxic hydroxyl radical (·OH) effectively via the Fenton reaction. More interestingly, H₂S gas released intracellularly presents the specific suppression effect to catalase activity of cancer cells, resulting in the promoted presence of H₂O₂ that facilitates the Fenton reaction of Fe²⁺ and consequently promotes ROS induction within the cells remarkably. After intravenous administration, the nanoclusters accumulate in the tumors of mice via the enhanced permeability and retention effect and present strong magnetic resonance imaging (MRI) signals. The findings confirm this therapeutic system can enable superior anti‐tumor performance with MRI guidance and negligible side effects. This study, therefore, offers an alternative gas‐amplified ROS‐based therapeutic platform for synergetic tumor treatment.

Glucose‐oxidase (GOx)‐mediated starvation by consuming intracellular glucose has aroused extensive exploration as an advanced approach for tumor treatment. However, this reaction of catalytic oxidation by GOx is highly dependent on the on‐site oxygen content, and thus starvation therapy often suffers unexpected anticancer outcomes due to the intrinsic tumorous hypoxia. Herein, porous platinum nanospheres (pPts), incorporated with GOx molecules (PtGs), are synthesized to enable synergistic cancer therapy. In this system, GOx can effectively catalyze the oxidation of glucose to generate H₂O₂, while pPt triggers the decomposition of both endogenous and exogenous H₂O₂ to produce considerable content of O₂ to facilitate the glucose consumption by GOx. Meanwhile, pPt induces remarkable content of intracellular reactive oxygen species (ROS) under an alternating electric field, leading to cellular oxidative stress injury and promotes apoptosis following the mechanism of electrodynamic therapy (EDT). In consequence, the PtG nanocomposite exhibits significant anticancer effect both in vitro and in vivo. This study has therefore demonstrated a fascinating therapeutic platform enabling oxygen‐inductive starvation/EDT synergistic strategy for effective tumor treatment.