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

Table 3. (Continued...)
DLP Hollow Shape: Conical Fracture force: >300 N 79
Height: 1000 μm (5 × 5)
Base diameter: 1000 μm
Bore diameters: 0.25 × 0.25 mm
Hydrogel Shape: Conical Fracture force: 22 N 50
Height: 700 µm (2 × 3)
TPP Hollow Shape: Conical Fracture force: As the external diameter 80
Heights: 200–400 μm increases, it can reach 2.5 N when the
Diameters: 80–120 μm outer diameter is 180 μm
Tip wall thickness: 5 μm
Solid Shape: Open-channel Fracture force: 10 N (4 × 4) 73
Height: 700 μm
Diameter: 150 μm
Solid Shape: Cone Fracture force: 1.26 N 81
Height: 1000 μm
Base diameter: 245 μm
Tip diameter: 1.6 μm
LCD Hollow Shape: Triangular-pyramid Fracture force: 42 N 56
Height: 1000 μm
Tip diameter: 85 μm
Spacing: 3000 μm
CLIP Coated Shape: Square pyramidal Penetrate the skin of mice 59
Height: 1000 μm
Base wide: 333 μm
Spacing: 1000 μm
SOPL Solid Shapes: Round, triangle, cross, and star- Fracture force: 8 N 60
shapes
Height: 1000–3000 μm
Hollow Shape: Beveled tip Fracture force: 4 N 61
Height: 1000 μm
SLS/SLM Hollow Shape: Cylindrical - 82
Height: 1200 μm
Wall thickness: 100 μm
Outer diameter: 200 μm
Inner diameter: 120 μm

source. VP-based 3D printing has quickly emerged as of the microneedles. DLP printing can perform the 3D
a popular method capable of producing various types of construction of molecules in aqueous solution at relatively
structurally intricate microneedles. low concentrations through photocrosslinking. 69,70 For
instance, researchers have successfully used riboflavin as
Stereolithography (SLA) can produce intricate and fine
microneedle structures, such as the common hollow type, a photoinitiator to fabricate silk fibroin (SF) microneedle
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arrays on a flexible PET film (Figure 4D).
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pyramids, cones, and cross-shaped structures (Figure
4A–C). Notably, a simple, low-cost, and customizable Two-photon polymerization (TPP) uses near-infrared
manufacturing method for microneedle molds has been femtosecond lasers to create intricate 3D structures at the
reported. This approach devises a two-step “printing nanoscale. Thanks to its exceptional high resolution, TPP
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and filling” method to fabricate molds for microneedles, has allowed the design of a super sharp microneedle with a
improving the efficiency of mass production. side channel reservoir (Figure 4E) and enabled apertures
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Digital light processing (DLP) relies on a micromirror of any shape to be made (Figure 4F). 52,73 Although TPP has
array to cure photosensitive polymers layer by layer, unparalleled high printing resolution, it is more expensive
resulting in higher printing speeds. However, the and slower compared to other 3D printing technologies.
printed product may exhibit a staircase structure at the Continuous liquid interface production (CLIP) is a
microscale, which may negatively impact the structure cutting-edge 3D printing technology that optimizes both

Volume 10 Issue 4 (2024) 66 doi: 10.36922/ijb.1896