Page 71 - IJB-10-4

International Journal of Bioprinting Unique characteristics of 3D-printed microneedles

2. Methods of manufacturing microneedles photoresist 16,17 are employed to create desired microneedle
patterns.
2.1. Traditional method of manufacturing
microneedles Microneedle fabrication using photolithography is
often combined with etching and uses materials such as
2.1.1. Indirect fabrication of microneedles silicon or metal. Etching is broadly categorized into dry
Micromolding methods can be further classified as direct etching and wet etching. Deep reactive ion etching (DRIE)
molding or reverse molding. Micromolding is extensively is a prevalent dry etching process for the manufacturing
used to manufacture polymer, ceramic, and hydrogel of microneedles, enabling microneedles with vertical
microneedles. Zhang et al. recently fabricated frozen side walls and high aspect ratios to be created 18,19 (Figure
polymer microneedles using the micromolding method 2B). On the other hand, wet etching primarily relies on
15
(Figure 2A). In addition, composite microneedles can be solution-based chemical reactions.
created in this way. This method is known for its simplicity,
cost-effectiveness, and high accuracy. However, it is not Laser machining, such as laser cutting and laser
suitable for microneedles with complex structures, and the ablation, is another versatile tool for manufacturing
microneedles are prone to damage. microneedles. Laser cutting is often employed to fabricate
metal and polymer microneedles. 20,21 Figure 2C shows
2.1.2. Direct fabrication of microneedles polydimethylsiloxane (PDMS) molds created by laser
Microfabrication techniques, such as photolithography cutting and polymer-based microneedles created from
and etching, can be used for the direct manufacturing of the molds. Laser cutting enables the mass production of
microneedles. Various light sources and the corresponding microneedles with relatively simple structures, although

Figure 2. Microneedles based on traditional manufacturing. (A) Process and physical image of direct molding method for producing ice microneedles.
15
Scale bar: 0.5 cm. (B) The process of manufacturing high aspect ratio microneedles based on deep reactive ion etching (DRIE). (C) Microneedle molds
19
manufactured made by laser cutting and images of polymer-based microneedles created using the molds. Reproduced with permission from ref.
20
(Copyright © 2019, Springer Nature).
Volume 10 Issue 4 (2024) 63 doi: 10.36922/ijb.1896