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

Figure 3. Microneedles fabricated by 3D printing based on extrusion. (A) Schematic of PLA microneedles fabricated by FDM combined with chemical
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etching. Reproduced with permission from ref. (Copyright © 2021, Spring Nature). (B) Post-stretching for preparing the needle tips. Reproduced with
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permission from ref. (Copyright © 2020, Elsevier).
printing speed and accuracy by enabling continuous, microneedle manufacturing. However, the subsequent
rather than layer-by-layer, additive manufacturing. CLIP polishing process still requires complex manual operations.
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was specifically designed for manufacturing microneedles,
allowing for the rapid generation of microneedles with 3. Application of 3D-printed microneedles
various parameters. Static optical projection lithography 3.1. Drug delivery
(SOPL) is another promising new technology that enables Transdermal drug delivery is one of the most prominent
the rapid manufacturing of various microneedle shapes applications of microneedles. Hollow microneedles and
with different tip angle (Figure 4G).
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inkjet-printed drugs on microneedles are common drug
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2.2.3. Powder bed fusion delivery methods. 53,78 Plamadeala et al. took advantage of
Power bed fusion (PBF) creates 3D structures by the high precision of TPP 3D printing to adorn pyramid-
sintering or melting powders at designated regions on a shaped microneedles with bioinspired microstructures
powder bed. Selective laser sintering (SLS) and selective (Figure 5A). Each microstructure is only 23 microns in
laser melting (SLM) are the most two common PBF 3D length, and an array of microstructures can be attached
printing processes. SLS utilizes a laser source to selectively to the microneedles. This pioneering design facilitates
irradiate and sinter powders, allowing for the layer-by- rapid drug coating, reflecting the good reproducibility of
layer production of complex 3D structures. SLM works 3D printing and its ability to process refined structures.
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in a similar manner to SLS, with the main difference being Huang et al. designed a microrobot containing
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that SLM uses fully melted metal powders. Fiedler et al. microneedles that achieve fast self-oriented and target
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developed a micro SLM system to 3D-print a hollow drug delivery in the mucosa. In addition, microneedles
microneedle with a diameter of 50 μm, but its surface was have also enabled breakthroughs in vaccine delivery. 85-87
not smooth and the hollow part was blocked. Compared Caudill et al. designed a polymer microneedle system
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to SLS, superior mechanical properties can be achieved for vaccine formulation and delivery. The researchers
with SLM-printed parts, showing its great potential for successfully demonstrated that the vaccine delivered
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Volume 10 Issue 4 (2024) 67 doi: 10.36922/ijb.1896