Page 553 - IJB-10-5

International Journal of Bioprinting 3D bioprinting of collagen hydrogels

To further verify the stability and uniformity of CML- a 405 nm light source upon the start of extrusion printing.
Ink, Orange G (Aladdin Biochemical Technology Co., Ltd., After printing the first layer, observations were made
China) was added and mixed with CML-Ink to extract the through photographs. Subsequently, a two-layer structure
shape of a “butterfly” and “sun,” accompanied by 405 nm was printed to examine the impact of accumulated printed
blue light irradiation. layers on the printing size.
To evaluate the extrudability of Col and CML-Ink, Pentagonal and heart-shaped models were 3D printed
they were loaded into a 5 mL syringe with a needle inner using CML-Ink, followed by photographic observation.
diameter of 0.25 mm. A needle tester (BosinTech, China) Finally, a 3D model of a rabbit’s head and ears, featuring
was employed to measure the time-dependent extrusion a complex structure, was designed and introduced for
force required for Col and CML-Ink over 30 s. The materials, 3D printing.
Col and CML-Ink, were loaded into sterile syringes, which
were then connected to the needle device. The extrusion 2.5. Characterization of 3D-printed
was performed at a constant speed of 10 mm/min, and the collagen-based scaffold
thrust magnitude was measured continuously over 30 s at 2.5.1. Scanning electron microscopyv
room temperature. The CML-Ink was extrusion-based 3D printed into porous

2.3.4. Rheological test scaffolds, named CML-scaffold, with a pore size of 1.00
Rheological tests were performed utilizing a modular mm under the aforementioned 3D printing conditions.
compact rheometer (MCR 302; Anton Paar, Germany) The CML-scaffold was then subjected to freeze-drying.
equipped with a 25 mm stainless steel parallel plate Scanning electron microscopy (SEM) was employed
geometry. A multi-step rheological test was carried out to analyze the microscopic dimensions of the lyophilized
to assess the dynamic mechanical properties of both Col CML-scaffold. The scaffold underwent gold spraying
and CML-Ink before and after illumination. The changes treatment for 5 mins inside an ion sputtering machine
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in the storage modulus (Gʹ) and loss modulus (G˝) of (Hitachi, Japan). A field emission scanning electron
Col and CML-Inks were evaluated before, after 30 s, and microscope (Hitachi S-4800; Hitachi, Japan) was used to
following 405 nm illumination. These measurements were observe the size and microstructural features of the scaffold
performed at 25 °C under an angular frequency of 1 rad/s at a voltage of 5.0 kV.
and a strain of 1%.
2.5.2. Mechanical characteristics
To explore the shear-thinning properties of Col and Rotational rheological measurements were performed
CML-Ink, viscosity as a function of shear rate (at ω = 1 rad/s on Col and CML-scaffold with an angular frequency of 1
and γ = 1%) was measured over a range of 0.01–100 s-¹. rad/s, covering a strain range of 1–100%. Additionally, a
The dynamic step strain amplitude test, conducted at both constant shear strain of 1% was maintained, and frequency
low strain (γ = 1.0%) and high strain (γ = 300%) conditions scanning was carried out on the Col and CML-scaffold in
for three cycles, aimed to investigate the sol–gel transition the range of 0.1–100 Hz.
properties of Col and CML-Ink.
Compression tests were employed to assess the
2.4. Extrusion 3D bioprinting of CML-Ink alterations in mechanical strength of both Col and CML-
3D models were designed and generated in SolidWorks scaffold at 25 °C using a universal testing machine (AGX-V
CAD software, and subsequently saved in STL file format. 500 N; Shimadzu, Japan). Cylindrical CML-scaffold
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3D bioprinting was conducted using a 3D bioprinter structures, with a height of 2 mm and a diameter of 15
(BIOMAKER2i; Shangpu Boyuan Biotechnology Co., mm, were fabricated using 3D printing. Similarly, Col was
LTD., China) equipped with a modular electric sprinkler placed in a mold of the same size to create the cylinder.
head compatible with a disposable standard 5 mL BD The cylindrical hydrogels were positioned on the lower
syringe. The CML-Ink was loaded into a 5 mL syringe for pressure plate, and the upper pressure plate was set to
3D printing, utilizing a 25 G needle with an inner diameter move at 10 mm/min until rupture. Force and displacement
of 0.25 mm. were recorded in each case.
A computer-aided design (CAD) model featuring a The mechanical properties of the CML-scaffold were
grid pattern (8.00 × 8.00 × 2.00 mm) was selected, with further verified through tensile measurements. A universal
a line distance set at 500 μm. The model was sectioned, mechanical tester (AGX-V 500 N; Shimadzu, Japan) was
and the printing parameters were configured as follows: a employed to assess the tensile properties of the CML-
printing speed of 3 mm/s, extrusion speed of 0.3 mm³/s, scaffold. Rectangular CML-scaffold samples (25 × 5 ×1.5
and immediate irradiation of the extruded contours with mm) were fabricated via 3D printing. The tensile test was

Volume 10 Issue 5 (2024) 545 doi: 10.36922/ijb.4069