Page 84 - MSAM-3-1

Materials Science in Additive Manufacturing Bioactive hydrogels for 3D bioprinting

set to 70 mm and 0.5 mm, respectively. After calibration each printed filament was measured at 20 random points at
and temperature setting of the lower fixture, samples three replications. The filament uniformity is defined using
were carefully placed and enclosed by a hood. Dynamic the following equations:
viscosity of hydrogel-BBG inks was taken as the average of
ϒ
ϒ
the data for shear rate (  ) in the range of 1 <  < 10 s , Cofficient of variation (CV) = SD (W ) (I)
-1
i i 1,n=
at temperatures including 25, 30, 35, and 40°C. The shear n i ∑ W
thinning behavior of the dressings was measured through a n i
shear rate ramp from 0.1 to 1000 s over a 10-min duration
-1
at 25, 30, 35, and 40°C. Filament uniformity (FU)=1−Coefficient of variation (CV) (II)
2.4.4. Mechanical properties where W and SD (W) are the filament width measured
i
i
at each random point and the standard deviation of
The mechanical properties of the 3D-printed scaffolds
were measured utilizing an Instron 5969 Universal Testing filament widths at the random points, respectively. A lower
System (USA). A dual-column apparatus designed for coefficient of variation (CV) means a higher filament
tensile tests was used in accordance with ASTM F2150-8 uniformity.
standard. Specimens were stretched at the rate of 5 mm/ 2.5.3. Shape fidelity
min until ruptured at 20°C. Young’s modulus for the 51 52
specimens was determined from the stress-strain curve. Following the work of Ouyang et al. and Kyle et al.,
The BlueHill Universal testing software was employed for we define shape fidelity (SF) as a measure of how closely
test control and data analysis. A total of five repetitions (n scaffold pores, intended to be square-shaped, resemble
= 5) were conducted for each set of parameters. perfect squares. This is characterized using the following
equation:
2.5. Printability measurement
P 2
In this study, the printability measurement involved Shape fidelity (SF) = (III)
the assessment of various printing outcomes in terms of 16A
extrudability, filament uniformity, and scaffold shape
fidelity, as described below. We studied the effects of ink where A is the pore area, and P is the pore perimeter. As
composition (with varying BBG content) and printing illustrated in Figure 2, in a porous scaffold designed with
parameters, including nozzle (ink) temperature and square-shaped pores, the actual pore shape may appear
extrusion pressure, on printing outcomes. in a different shape (such as an oval shape), deviating
from the intended square shape. We measured the area
2.5.1. Extrudability and perimeter for each pore using ImageJ software,
Ouyang et al. categorized hydrogel extrudability based and then obtained the shape fidelity as the average of
on gelation conditions of the extruded filament: over- shape fidelity values calculated, using Equation III, for
gelation, ideal gelation, and under-gelation. Achieving 10 randomly selected pores in each scaffold, with three
51
ideal gelation is crucial for extrudability, which is replications, for each ink composition at corresponding
characterized by a consistent flow with a smooth desired temperature and extrusion pressure. Note that
filament. Over-gelation is characterized by inconsistent SF is equal to 1 for a perfect square, and a pore with a
lumpy flow, resulting in irregular filament shape and lower SF value has a larger deviation from the square
poor layer attachment. Under-gelation is characterized shape.
by a state akin to that of a liquid, or in some instances,
the formation of droplets. Under-gelation may result 2.6. Statistical analysis
in the merging of adjacent layers and the formation of All experiments in this study were conducted with a
pores with a predominantly circular rather than square minimum of three replications for each sample per test.
morphology. 52 All data are expressed as mean ± standard deviation (SD).
One-way analysis of variance (ANOVA) was employed to
2.5.2. Filament uniformity determine statistical differences among different groups.
A series of single-layer straight lines were printed to assess This statistical test enables the evaluation of overall
the uniformity of the printed filaments, similar to what was group differences and determines if there are significant
previously described in literature. Filaments were printed differences between the means of these groups. Significance
8
at 25, 30, 35, and 40°C, with three replications for each was set at the P < 0.05. Statistical analyses were performed
ink composition and printing parameter set. The width of using Microsoft Excel.

Volume 3 Issue 1 (2024) 5 https://doi.org/10.36922/msam.2845