Page 244 - IJB-10-5

International Journal of Bioprinting 3D printed hydrogels for tumor therapy

Table 1. Concentrations of HAp, MgHAp, GelMA, and PDA in different printing inks.
GelMAL GelMAH HAp MgHAp PDA Photoinitiator
(% w/v) (% w/v) (% w/v) (% w/v) (% w/v) (% w/v)
GelMA 10 10 0 0 0 0.2
HAp/GelMA 10 10 2 0 0 0.2
MgHAp/GelMA 10 10 0 2 0 0.2
MgHAp/GelMA-PDA 10 10 0 2 0.5 0.2
Abbreviations: GelMA, gelatin methacryloyl; GelMAH, GelMA with a high degree of methacrylation; GelMAL, GelMA with a low degree of
methacrylation; HAp, hydroxyapatite; MgHAp, magnesium-substituted hydroxyapatite; PDA, polydopamine.

The storage moduli (G´) and loss moduli (G˝) of the inks The structural fidelity of printed GelMA, HAp/GelMA,
subjected to a maximum strain (γ) of 1.0% were measured MgHAp/GelMA, and MgHAp/GelMA-PDA hydrogels was
at a frequency range of 0.1–100 rad/s at 25°C. The G´ and determined using the ImageJ software by calculating the
G˝ of the inks crosslinked by UV exposure for 5 min were expansion percentage of printed strut. It was calculated
also measured. Moreover, the thixotropic behavior of the according to the following formula:
inks was studied by repetitive application of shear rates of ( D − )
D
0.1 s for 120 s and 100 s for 60 s at 25°C. Strut diameter expansion percentage % () = 1 0 ×100 (II)
−1
−1
D 0
2.4. 3D printing of MgHAp/GelMA-PDA hydrogels
3D printing of GelMA, HAp/GelMA, MgHAp/GelMA, where D is the diameter of printed strut of hydrogels,
1
and MgHAp/GelMA-PDA hydrogels was performed using and D is the diameter of designed strut of hydrogels.
0
a 3D bioprinter (3D Discovery™ Evolution, regenHU Ltd.,
Switzerland). The printing inks were transferred into a 2.5.2. Morphology and microstructure
syringe and installed on the 3D bioprinter. The printing The morphology and microstructure of printed GelMA,
temperature was set to 25°C, and the printing platform was HAp/GelMA, MgHAp/GelMA, and MgHAp/GelMA-PDA
kept at room temperature. The inner diameter of printing hydrogels were determined using an SEM. Dry GelMA,
nozzle was 0.26 mm. The printing speed was set to 8 mm/s HAp/GelMA, MgHAp/GelMA, and MgHAp/GelMA-PDA
to match the ink extrusion rate. After 3D printing, the hydrogel samples were sputter-coated with a thin layer of gold.
hydrogels were exposed to 5-min UV light irradiation Then, the morphology and microstructure of the gold-coated
for covalently crosslinking GelMA polymer chains. samples were observed under SEM in a high vacuum mode
Subsequently, the 3D-printed GelMA, HAp/GelMA, at 10 kV. Additionally, to visualize the presence of MgHAp
MgHAp/GelMA, and MgHAp/GelMA-PDA hydrogels nanocomposites in hydrogel samples, the energy dispersive
were freeze-dried and stored at 4°C for further use. X-ray spectrometer (EDS) mapping was performed.

2.5. Characterization of 3D-printed 2.5.3. Mechanical properties
MgHAp/GelMA-PDA hydrogels The mechanical properties of 3D-printed GelMA, HAp/
GelMA, MgHAp/GelMA, and MgHAp/GelMA-PDA
2.5.1. Printability of inks and structural fidelity of hydrogels crosslinked by UV light were determined
printed hydrogels through compression tests. Dry and wet hydrogel samples
The printability (Pr) values of GelMA, HAp/GelMA, (10 mm in diameter and 5 mm in height) were compressed
MgHAp/GelMA, and MgHAp/GelMA-PDA inks were at a testing speed of 0.5 mm/min using a universal
calculated using the ImageJ software to measure the mechanical testing machine (Model 5848, Instron Ltd.,
area and perimeter of interconnected pores of hydrogels USA), respectively. The ultimate compression strength of
immediately after 3D printing. Pr values were calculated printed hydrogels was the highest load at the break divided
using the following formula: 38 by the original cross-sectional area of the hydrogel samples.
Young’s modulus of printed hydrogels was calculated using
the slope of the initial linear section of stress–strain curves.
2
Pr = L (I)
16A 2.5.4. Swelling behavior and in vitro degradation
To investigate the dynamic swelling behavior, dry hydrogel
where Pr is the printability value of printing inks, L is samples were weighed and measured as W . Then, hydrogel
0
the perimeter of the printed pore, and A is the area of the samples were immersed in PBS at 37°C water baths. At
pore in the printed hydrogels. each predetermined time point, hydrogel samples were

Volume 10 Issue 5 (2024) 236 doi: 10.36922/ijb.3526