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Fayyazbakhsh, et al.

Figure 2. Fabrication of 3D-printed wound dressings with alginate, gelatin, and human dermal fibroblasts for partial-thickness burn wounds
followed by 10 min crosslinking with calcium chloride solution.

a Rheometer (HAAKE™ MARS™, Thermo Scientific, the crystal. A fresh reference spectrum was recorded after
MA, USA) using a parallel plate (diameter = 35 mm) every five scans and deducted from the obtained spectra.
setup with a frequency of 1 Hz and a gap of 1 mm at All the recorded spectra were analyzed with OMNIC
22°C for 300 s. All measurements were performed within 9.2.41 software (Thermo Scientific, MA, USA), and
the linear viscoelastic region. To relate the rheological data showed as Transmittance (%) against wavenumber
−1
behavior and bioink composition, the storage modulus (cm ). The IR Spectrum data from Sigma Aldrich were
and loss modulus (G’ and G”, respectively) were analyzed used to identify characteristic chemical bonds in gelatin,
for the various gelatin: alginate ratios. alginate, and water.
The viscosity and shear thinning behavior of the
non-printed hydrogels with different ratios of gelatin 2.5. Swelling capacity and biodegradation rate
and alginate were measured by a rotational rheometer measurement
(Kinexus, Ultra+, Malvern Instruments Ltd., UK) using a To determine the further interactions between the wound
parallel plate setup for shear rate ramp test with a 0.5 mm and dressing, the swelling capacity and the degradation
gap at 22°C. The tests were conducted using a solvent rate of the 3D-printed dressings were recorded after
trap to avoid drying during the test. To relate the shear soaking in phosphate-buffered saline (PBS). Samples
thinning behavior and bioink composition, the shear were dried at room temperature, and the dry weight of the
stress, shear strain, and shear rate were measured for the samples was recorded as W (n = 3). Then, the samples
D
various gelatin: alginate ratios. were immersed in 3 mL PBS at 32°C to reach equilibrium
swelling and subsequent degradation. The weight changes
2.4.2. Mechanical testing in determined time intervals were recorded for up to
A uniaxial tensile test was performed on the dog-bone- 7 days as the dressings will stay on the wound for up to
shaped scaffolds of dimensions 25 × 50 × 1 mm in 7 days. The dressing’s swelling capacity and degradation
3
accordance with the ASTM F2150-8 standard. Young’s rate were calculated using the following equations:
moduli of the 3D-printed scaffolds were measured using W − W
the Universal Instron 5969 Dual Column Testing System Swellingcapacity % () = max D ×100 (1)
W
(Instron, MA, USA) and the BlueHill Universal Software D
system (n = 3). The scaffolds were assessed using a W − W Week1
D
mechanical load frame at a speed of 5 mm/min typical for Degradationratemgmin( / ) = 72460 (2)
×
×
polymer specimens to measure the modulus of elasticity,
yield strength, and yield strain of the scaffolds. where W is the initial dry weight, W max is the
D
maximum weight of the scaffolds after immersion, and
2.4.3. Fourier-transform infrared spectroscopy (FTIR) W week1 is the weight after 1 week of immersion in PBS.
A Nicolet iS50 FTIR spectrophotometer (Thermo 2.6. Hydration activity test
Scientific, MA, USA) equipped with a diamond crystal
cell of attenuated total reflection accessory in the mid-IR To measure the effect of gelatin: alginate ratio on
region (4000 – 400 cm ). All the spectra were recorded hydration activity, firstly, the total amount of water
−1
at a resolution of 4 cm with 32 scans with a data spacing in each 3D-printed scaffold was measured using
−1
of 0.482 cm . 500 μL of each hydrogel sample were thermogravimetric analysis on 250°C for 10 min (SDT
−1
loaded on the beam splitter area to make a thin film on Q600 V20.9 Build 20, Universal V4.5A TA Instruments,
International Journal of Bioprinting (2022)–Volume 8, Issue 4 277