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International Journal of Bioprinting 3D bioprinting of collagen hydrogels

Figure 2. Characterization of the collagen biomaterial ink (CML-Ink). (A) Printability zone of the CML-Ink. (B) Gum-forming properties of the collagen
solution (Col) and CML-Ink. (C) Extrudability of the CML-Ink. (D) Stability and uniformity of the CML-Ink. (E) A multi-step rheological test of Col
and the CML-Ink. (F) Extrudable performance of Col and the CML-Ink. (G) Viscosity of Col and the CML-Ink at different shear rates. (H) Dynamic step
strain amplitude test of Col and the CML-Ink. Abbreviations: MA: Methacrylic anhydride; LAP: Lithium phenyl-2,4,6-trimethylbenzoylphosphinate; Gʹ:
Storage modulus; G˝: Loss modulus.

increased significantly, with Gʹ rising by 14 times compared as the shear rate increased. The CML-Ink exhibited a
to its pre-illumination level. In contrast, Col maintained linear decrease, suggesting stable shear thinning behavior
constant values of Gʹ and G˝ before and after illumination. across the tested range and suitability for extruded
These findings indicate that the mechanical strength of the 3D printing.
CML-Ink substantially improved following illumination at
405 nm. A dynamic step strain amplitude test (γ = 1.0 or 300%)
was carried out at 25 °C to replicate the extrusion process of
The Col and CML-Ink were loaded into the syringe Col and the CML-Ink in a syringe through continuous step
used for 3D printing, with consistent extrusion speed changes of oscillating strain (Figure 2H). Upon application
and needle size, adhering to the printing conditions. The of high strain (300%), the internal structure of both Col
extrusion pressure experiment was carried out at room and the CML-Ink was immediately disrupted, leading to a
temperature to determine the extrudable performance decrease in Gʹ to approximately 9 and 21 Pa, respectively,
of the prepared ink (Figure 2F). Col exhibited noticeable with Gʹ becoming lesser than G˝ and exhibiting a sol-like
fluctuations in the pushing force required during the appearance. However, upon reduction to low strain (1%),
extrusion process. In contrast, the CML-Ink could be the Gʹ and G˝ of both materials almost fully recovered
consistently extruded as a uniform fine filament with a within a few seconds, with Gʹ surpassing G˝ and displaying
pushing force of approximately 15 N, indicating its stable a gel-like appearance. Both Col and CML-Ink demonstrated
extrudable performance and suitability for 3D printing. rapid sol-gel conversion ability during the three rupture
The dynamic viscosities of Col and the CML-Ink were and reforming cycles, indicating their ability to swiftly
measured at 25 °C across shear rates of 0.1–100 s (Figure transition to a sol state during syringe extrusion and return
−1
2G). The viscosity of both Col and the CML-Ink decreased to the pre-extrusion gel state immediately afterward.

Volume 10 Issue 5 (2024) 549 doi: 10.36922/ijb.4069