Microneedle Coating Methods: A Review with a Perspective

Abstract

A coated microneedle array comprises sharp micrometer-sized needle shafts attached to a base substrate and coated with a drug on their surfaces. Coated microneedles are under investigation for drug delivery into the skin and other tissues, and a broad assortment of active materials, including small molecules, peptides, proteins, deoxyribonucleic acids, and viruses, have been coated onto microneedles. To coat the microneedles, different methods have been developed. Some coating methods achieve selective coating of just the microneedle shafts, whereas other methods coat not only microneedle shafts but also the array base substrate. Selective coating of just the microneedle shafts is more desirable since it provides control over drug dosage, prevents drug waste, and offers high delivery efficiency. Different excipients are added to the coating liquid to modulate its viscosity and surface tension in order to achieve uniform coatings on microneedles. Coated microneedles have been used in a broad range of biomedical applications. To highlight these different applications, a table summarizing the different active materials and the amounts coated on microneedles is provided. We also discuss factors that should be considered when deciding suitability of coated microneedles for new-drug delivery applications. In recent years, many coated microneedles have been investigated in human clinical trials, and there is now a strong effort to bring the first coated microneedle-based product to market.

Bio-inspired microneedle design for efficient drug/vaccine coating

“…While this early engineering proof-of-concept work has not considered specific drugs or vaccines, we expect that coating of a wide range of formulations should be possible once the contact angle constraints are met. A good review of the active materials that have been coated onto microneedles to date is available in (Ingrole and Gill 2019).…”

“…It is preferable that drug loading is concentrated around the lateral surfaces of the microneedle, and around the upper portions in particular (see Fig. 2 of (Ingrole and Gill 2019)), as a number of works have shown that microneedles do not penetrate to their full height due to skin elasticity and compression, and that penetration depth is generally limited to between half and two-thirds of needle height (Enfield et al 2010; Ripolin et al 2017). Because of this, it is desirable that drug cargo is not located around the lower regions of the needle, as it does not enter the skin and is therefore wasted.…”

Microneedle Arrays Combined with Nanomedicine Approaches for Transdermal Delivery of Therapeutics

“…As presented in Table 1 , various formulations have been coated on MNs to facilitate the skin permeation of therapeutic agents, including vaccines, proteins, and hormones. More detailed information about coated MNs can be found in other publications [ 34 , 35 ].…”

Engineering Targeting Materials for Therapeutic Cancer Vaccines

“…They are minimally painful for the patient and can be self-administered. The needle tips can be coated with protein, viruses, drugs or immunotherapy and will release the payload in a controlled slow manner (Ingrole and Gill, 2019). In the context of melanoma, for instance, transdermal delivery of immunotherapies with microneedles has demonstrated promising efficacy (Ye et al, 2017).…”