An overview of microneedle applications, materials, and fabrication methods.

Zahra Faraji Rad,Graham J Davies,Philip D Prewett

doi:10.3762/bjnano.12.77

Abstract

Microneedle-based microdevices promise to expand the scope for delivery of vaccines and therapeutic agents through the skin and withdrawing biofluids for point-of-care diagnostics – so-called theranostics. Unskilled and painless applications of microneedle patches for blood collection or drug delivery are two of the advantages of microneedle arrays over hypodermic needles. Developing the necessary microneedle fabrication processes has the potential to dramatically impact the health care delivery system by changing the landscape of fluid sampling and subcutaneous drug delivery. Microneedle designs which range from sub-micron to millimetre feature sizes are fabricated using the tools of the microelectronics industry from metals, silicon, and polymers. Various types of subtractive and additive manufacturing processes have been used to manufacture microneedles, but the development of microneedle-based systems using conventional subtractive methods has been constrained by the limitations and high cost of microfabrication technology. Additive manufacturing processes such as 3D printing and two-photon polymerization fabrication are promising transformative technologies developed in recent years. The present article provides an overview of microneedle systems applications, designs, material selection, and manufacturing methods.

Highlights

The concept of microneedle structures to penetrate painlessly the outermost layer of the skin, the stratum corneum (SC), was first introduced in 1976 [1]
Microneedles may be integrated into biosensors, micropumps, microfluidic chips, and microelectronic devices
The choice of manufacturing techniques for microneedles is dependent on material properties, fabrication cost, and desired height and shape of the microstructure

Summary

Introduction

The concept of microneedle structures to penetrate painlessly the outermost layer of the skin, the stratum corneum (SC), was first introduced in 1976 [1]. Unlike other microfabrication methods developed for microneedles, these rapid prototyping methods do not require expensive cleanroom facilities, and complex geometries can be realised in a shorter time and with less technical expertise This is a major advantage for fabrication of microneedle patch arrays requiring integration of microfluidic elements for point-of-care diagnostics or drug delivery. Fabricated sharp solid silicon microneedles, via wet etching with HNA, with approximately 160 μm height and a base diameter of about 111 μm for transdermal drug delivery [90]. It is increasingly clear that the favoured fabrication methods used to develop the generation of polymer microneedle point-ofcare tests and drug delivery patches will be photolithography, replica moulding, 3D printing, and micromachining. The penetration force linearly increases with array size and the use of controlled force mechanical inserters will almost certainly be required, building on simple spring-loaded commercial systems [108] to achieve the required forces without damaging the microneedles [109]

Conclusion

Findings

Fabrication methods