Page 134 - IJB-8-2

3D Printing of Hollow Microneedle Patches
(405 nm) was modulated into the customized pattern of successively soaked in 75% ethanol for 24 h and ×1
the HMN by DMD on the basis of the aforementioned phosphate-buffered saline (PBS) for 24 h to improve the
printing picture. Thirdly, digital light projected from biocompatibility of HMNPs. The resultant HMNPs were
DMD was adjusted by a high magnification microlens to dried at room temperature before used.
improve the printing resolution. Finally, the resin in the
reservoir was solidified according to the special spatial 2.5. In vitro biocompatibility of HMNPs
distribution of digital light in the monomer solutions and In accordance with EN ISO 10993-12:2012 guidelines,
a 3D structure was formed. In addition, various structures the in vitro biocompatibility of HMNPs was conducted
of HMNs were prepared by adjusting printing pictures. using six 1 cm cubes with the same printing materials
3
HMNPs were fabricated to prepare HMN syringes. and post-processing as HMNPs. The cubes were soaked
The printing picture of the HMN array and substrate in 6 ml of PBS for 24 h to obtain the extract of printing
were drawn respectively. Multiple annular pictures materials [25’26] . Skin cells of human adult low calcium high
were arranged to form a printing picture of the HMN temperature (HaCaT, human-immortalized keratinocytes)
array. The printing picture of the substrate was set as a and human dermal fibroblast (HDF) were used to assess
rectangular picture with large white circles of HMNs the toxicity of the printed HMNPs. Cells were cultured in
turned to nonexposed area. The glass slide was placed each well of 96-well microtiter plates, treated with 180 μl
on a photosensitive resin bath before printing. The of fresh culture medium plus 20 μl of the extract for each
HMNP was printed consecutively in two steps. First, the well. The negative control was incubated with 180 μl
photosensitive resin underwent polymerization under the of fresh culture medium and 20 μl of sterile PBS. After
first projected light pattern originating from the printing incubated for 24 h (day 1) and 72 h (day 3), CCK-8 assay
picture of HMN array and HMNs formed. Then, the
second projected light pattern from the printing picture of was used to analyze cell viability with an absorbance
the substrate was exposed in turn, and the substrate of the wavelength of 450 nm.
HMNP was printed and the HMMP was obtained. 2.6. Mechanical strength testing of HMNs
The morphology of 3D-printed HMNs and HMNPs
were observed by the camera and scanning electron Compression test of a single HMN was performed to
microscope (SEM) (JSM-7500F) at 15 kV. investigate the mechanical property of HMNs by a dynamic
mechanical analysis (DMA) (Q800 TA Instruments).
2.3. Simulation of the HMN formation process In brief, a single HMN was placed on the test stage

To visualize the diffractive lithography by microlens effect positioned vertically and a metal probe was moved to the
and the complicated diffracted intensity distribution within point where it touched the tip of HMN. The metal probe
the photosensitive resin in our fabrication, numerical was then moved vertically downward at a compressive
simulation was implemented using an electromagnetic force of 2.5 N/min. The deformation process of the HMN
wave beam envelope module in COMSOL Multiphysics during compression tests was captured by a camera. The
software. The ultraviolet (UV) light electric field when relationship between compression displacement and
z = 0 (the surface of liquid resin), namely, E (r’, 0) was static force was recorded by TA Instruments Universal
introduced as uniform distribution propagating along Analysis 2000 (software of DMA). The fracture (failure)
the positive z-direction. The original intensity at z =0 force was the turning point of static force on the curve.
was set as I = 30 mW.cm , according to the UV power 2.7. Puncture experiment and skin healing
–2
0
measurement and the attenuation coefficients along
needle growing direction were set as C =0.9627, C =0, experiment
0
1
and C =0.002878, respectively [23,24] . Puncture experiment was applied on the skin of mice to
2
2.4. Post-treatment of HMNPs evaluate the skin insertion ability of HMNPs. The hair on
the back of mouse was shaved and depilated immediately
The printed HMNPs were separated from the glass after death by over anesthesia of the mouse and then
slide with a sharp blade. Since there were residual wiped clean with saline. HMNPs were inserted into the
uncured materials on the printed products, HMNPs were dorsal skin of mice for 3 min to check their puncture
soaked in anhydrous ethanol 3 times (each with 2 min) ability. Then, the treated skin was fixed with formalin for
to completely remove the residual resin on the surface 48 h and rinsed with running water for 2 h. Samples were
and in the cavity of microneedles. HMNPs were then then dehydrated before they were embedded in paraffin.
dried. To enhance the mechanical properties of printed Five-micrometer-thick cross-sections were cut from the
objects, HMNPs were exposed to UV-visible radiation samples followed by hematoxylin-eosin (H&E) staining.
at 450 nm under a light-emitting diode, LED lamp for In addition, we applied HMNPs to the mouse skin for
3 min to polymerize remaining uncured resin. They were 3 min, and then removed them to verify whether the skin

126 International Journal of Bioprinting (2022)–Volume 8, Issue 2