Recent advances in porous microneedles: materials, fabrication, and transdermal applications

Leilei Bao,Beomjoon Kim,Jongho Park,Gwenaël Bonfante

doi:10.1007/s13346-021-01045-x

Abstract

In the past two decades, microneedles (MNs), as a painless and simple drug delivery system, have received increasing attention for various biomedical applications such as transdermal drug delivery, interstitial fluid (ISF) extraction, and biosensing. Among the various types of MNs, porous MNs have been recently researched owing to their distinctive and unique characteristics, where porous structures inside MNs with continuous nano- or micro-sized pores can transport drugs or biofluids by capillary action. In addition, a wide range of materials, including non-polymers and polymers, were researched and used to form the porous structures of porous MNs. Adjustable porosity by different fabrication methods enables the achievement of sufficient mechanical strength by optimising fluid flows inside MNs. Moreover, biocompatible porous MNs integrated with biosensors can offer portable detection and rapid measurement of biomarkers in a minimally invasive manner. This review focuses on several aspects of current porous MN technology, including material selection, fabrication processes, biomedical applications, primarily covering transdermal drug delivery, ISF extraction, and biosensing, along with future prospects as well as challenges.Graphical abstract

Highlights

Microneedles (MNs), having microscopic needle structures, were initially developed to facilitate transdermal drug delivery by piercing human skin and providing transport conduits across the stratum corneum with a thickness of 10–15 μm [1, 2]
In the evaluation of penetration using the PGMA porous MNs applied with a vertical force of 0.5 N/needle, more than 80% of the penetration efficiency was achieved with a porosity below 50%
The results indicated that insulin-loaded gradient PLGA-based porous MNs slowly and effectively lowered the blood glucose level of rabbits in comparison with the hypodermic injection of insulin at the same dose, which showed the feasibility of insulin delivery with minimal invasiveness using porous MNs

Summary

Introduction

Microneedles (MNs), having microscopic needle structures, were initially developed to facilitate transdermal drug delivery by piercing human skin and providing transport conduits across the stratum corneum with a thickness of 10–15 μm [1, 2]. Among several types of metals, titanium has been extensively applied for biomedical devices such as dental and orthopaedic implants owing to its biocompatibility and excellent mechanical strength [72] By capitalising on these properties, solid [73], coated [74], hollow [75, 76], and the recently developed porous titanium MNs were researched for various biomedical transdermal applications such as macro-molecular drug (e.g. insulin) loading and delivery [30, 77]. It has been extensively employed in the field of MNs for biomedical and clinical applications (e.g. drug-encapsulated nano- and micro-particle delivery) because of its biocompatibility and biodegradability [87,88,89] Several approaches, such as emulsion followed by coating, hot embossing, and porogen leaching were developed to fabricate PLGA porous structures [32, 38, 58].

Fabrication methods

Findings

Conclusion