Page 497 - IJB-10-5

International Journal of Bioprinting 3D bioprinting of full-thickness skin with a rete ridge structure

may not always match that of the precursor cartridge due to a controlled temperature of 4°C, consistent with the
the complex flow path created by the precursor cartridge, bioprinting temperature. Subsequently, the obtained shear
syringe, and nozzle, as well as the non-Newtonian viscosity data of SdECM were fitted to the power-law fluid
properties of the hydrogel. Therefore, achieving the desired model (Equation I):
cross-sectional shape required a trial-and-error process,
which was time-consuming and unaffordable. m −1
µ ⋅ γ = K · (I)
In this study, we fabricated FTSEs with a rete ridge
structure using a preset extrusion bioprinting technique. To
achieve this without an ineffective trial-and-error process, where K is the flow consistency index, γ˙ is the shear rate
we used a computational fluid dynamics (CFD) method and m is the flow behavior index. The shear viscosity data
to design a precursor cartridge to print deep and narrow of the alginate solution were fitted to the Carreau model
fissure structures. The dermal layer was bioprinted within (Equation II):
the 3D-printed polycaprolactone (PCL) frame, which
provides structural support until the bioink used in the n −1
·
dermal layer is fully gelled. This was followed by furrowing µ µ = 0 ⋅ +1[ ( λγ )] 2 (II)
2
steps to establish a substrate for the stable anchoring of
strands produced by the preset extrusion bioprinting
process for creating a fissured structure. The epidermis where μ is the viscosity value at zero shear rate, λ is the
0
was formed by differentiating keratinocytes on the surface characteristic time, and n is the power index.
of the dermis with fissure structures. We conducted 2.2. Computational simulation for the design of a
histological and immunostaining analyses, followed by UV precursor cartridge
treatment, which confirmed differences between the rete To design a precursor cartridge for generating narrow
ridge and conventional FTSEs using dermal-epidermal fissures within extruded strands, CFD simulation was
junction (DEJ), epidermal, and proliferation markers. conducted. 3D computer-aided design (CAD) models
These differences yield test results akin to those in vivo, of bioinks in the bioprinting process were created with
suggesting that preset extrusion 3D bioprinting techniques dimensions matching those of the precursor cartridge,
can serve as a useful tool for fabricating structures that syringe, and nozzle using SolidWorks 2022 (Dassault
mimic in vivo environments. System, France). The 3D CAD model was then imported
to COMSOL Multiphysics 5.6 (COMSOL Inc., Sweden).
2. Materials and methods
Initially, the physics module for the laminar flow of
2.1. Preparation and characterization of hydrogels single-phase fluids was used to simulate the flow of bioinks
Porcine skin-derived decellularized ECM (SdECM) was during the bioprinting process. The viscosity of bioinks was
prepared as described in a previous study. Briefly, dermal based on rheological data. The inlet pressure was applied
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tissue was cut and immersed in phosphate-buffered at the top of the precursor cartridge, corresponding to the
saline (PBS; Welgene, Korea), containing 0.5% trypsin actual bioprinting pressure, while the pressure at the end
(Welgene, Korea) and 0.2% ethylene diamine tetra acetic of the nozzle was set to zero relative pressure as an outlet.
acid (EDTA; Welgene, Korea), for 24 h. Subsequently, The other boundaries were considered as walls with a no-
the treated dermal tissues were washed, followed by the slip condition. Subsequently, the model was discretized to
addition of PBS containing 1% Triton X-100 (Samchun the tetrahedral solid mesh by an automatic mesh generator
Pure Chemical Co., Ltd., Korea) for 24 h. Decellularized and then solved with the Navier-Stokes equation using a
tissues were washed several times with distilled water and stationary solver.
lyophilized. SdECM was solubilized through digestion with
0.5 M acetic acid (Sigma-Aldrich, United States of America To visualize the cross-sectional pattern at the outlet
[USA]) containing pepsin (1 mg/10 mg lyophilized of the printing nozzle, particle tracing for the fluid flow
SdECM). The SdECM was dissolved in 0.5 M acetic acid interface was used in the solved result for the velocity field
and neutralized to a concentration of 3.25% (w/v) for use of laminar flow simulation. The massless solid particles
25
in 3D bioprinting. Alginate (A2033; Sigma-Aldrich, USA) were released on the domain of alginate hydrogel, and
was dissolved in PBS at a concentration of 2.75% (w/v). all boundaries were set to the wall and conditioned as
As the hydrogels used in this study were non-Newtonian “Freeze.” Subsequently, the simulation was performed
fluids, their shear viscosity profiles were obtained using a with a time-dependent solver. Finally, the cross-section of
rheometer (Kinexus pro+; NETZSCH GmbH, Germany) the end of the nozzle was visualized by implementing the
with cone-plate geometry and a 1 mm gap, maintaining Poincaré map.

Volume 10 Issue 5 (2024) 489 doi: 10.36922/ijb.3961