Microneedle Patches for Transdermal Drug Delivery: Types, Fabrication Methods, Characterization, and Biomedical Applications

Abstract

Background: Microneedles (MNs) represent a minimally invasive transdermal drug delivery technology that bypasses the primary barrier to dermal penetration — the stratum corneum — by creating transient micron-scale channels in the skin without stimulating pain receptors in the dermis. Over the past two decades, microneedle research has advanced from early proof-of-concept laboratory studies to promising clinical applications encompassing vaccine delivery, insulin administration, long-acting therapeutics, hormone therapy, and cosmetic interventions. The capacity of microneedles to deliver molecules of widely varying molecular weight and physicochemical properties — including large biologics and nucleic acids that are otherwise completely impermeable to the skin — positions them as a uniquely versatile transdermal delivery platform.

Objective: This review provides a comprehensive critical analysis of microneedle types, fabrication materials and methods, characterization approaches, mechanisms of drug delivery, therapeutic applications, and comparative performance relative to conventional transdermal and systemic delivery routes, with emphasis on research published up to 2022.

Results and Discussion: Five principal microneedle types — solid, coated, dissolving, hollow, and hydrogel-forming — each offer distinct advantages in terms of drug loading, release kinetics, skin penetration efficiency, and patient safety. Advances in fabrication technology including micromolding, drawing lithography, inkjet printing, and additive manufacturing have expanded material options from silicon and metal to an array of biodegradable polymers and natural biopolymers. Microneedle patches have demonstrated clinical feasibility for vaccination, insulin delivery, and long-acting contraceptive therapy, with multiple products in active clinical development as of 2022.

Conclusion: Microneedle-based transdermal delivery systems combine the patient convenience and safety of transdermal patches with the ability to deliver a broad range of pharmacological agents, including biologics that were previously restricted to injection. Continued advances in fabrication precision, drug loading capacity, and regulatory pathway clarity will determine the pace of clinical translation for this promising technology.