Page 292 - IJB-9-2

International Journal of Bioprinting Methodology of hydrogel printability

Table 2. Example of hydrogel characterization using the sessile
drop method
Material Temperature (⁰C) Contact angle
Matrigel 9 45
15 48
ColMA (Cs = 5) 9 32
15 31
Figure 3. Contact angle at the solid–air interface.
3.2. Filament collapse test
After taking four measurements of each hydrogel Filament collapse test allows the deflection of the hydrogel
droplet, the following results were obtained : filaments to be determined as they pass through pillars
[19]
(i) A contact angle of less than 35° indicates that spaced at different distances. These distances span from
the surfaces are too hydrophilic, which prevents shorter to longer range, with deflection being more likely
interactions with cells. to occur at longer distances.
(ii) A contact angle of greater than 80° indicates that To obtain the collapse rate, the hydrogel must be
the surfaces are too hydrophobic, which can lead to deposited on top of the platform pillars (Figure 4), so that
protein denaturation. it passes through the least spaced pillars first and ends at
the most spaced pillars.
(iii) A contact angle between 35° and 80° is ideal for
a hydrogel for moderate wettability property From the differences between the theoretical area and
(Figure 3). the real area, the collapse rate is obtained (C ) using the
f
equation below :
[21]
The study can be carried out at different temperatures c c
for each hydrogel, which makes it possible to analyze the C = A − A a •100 (I)
t
%
behavior of the hydrogels as a function of the bioprinting f A t c
temperature. This study is designed for the subsequent where A t is the total area, and A a is the area generated after
c
c
introduction of cells into a hydrogel under human body depositing the filament (real area).
temperature conditions, so temperatures at around 37°C In this way, if the real area and the theoretical area
have been chosen, which is the optimum temperature for coincide while the filament does not collapse, the collapse
maximum cell viability.
coefficient is 0%. Using an image processing program such
An example of hydrogel characterization using the as ImageJ, or a vector drawing program such as AutoCAD
sessile drop method is given in Table 2. In this example, that allows the measurement of angles by scaling images,
Matrigel and ColMA (Cs = 10) were used. Matrigel is a the total area (A t ) of the square formed by the adjacent
c
material that requires low temperature for its maintenance columns and the area generated after depositing the
as it polymerizes at room temperature. Therefore, its filament (A a ) are calculated (Figure 4).
c
temperature must be low both when performing the sessile
drop method and when using it as a bioink in the bioprinter. The collapse of each separation of the pillars is calculated
Although due to its low bioprinting temperature, this individually, starting with the end of the platform with the
hydrogel is not suitable for cell-loaded bioprinting, the smallest separation between the pillars and maintaining
good results obtained in the sessile drop method indicate the consecutive order in which the measurements are
that it is suitable for subsequent loading of cells into the taken (C , C , C ...). With the data obtained, a table is
f1
f2
f3
bioprinter-generated structure because the contact angles made in which after calculating the C for each separation,
f
are between 35° and 80°. It can also be seen in Table 2 that the exact point at which the hydrogel collapses completely
the ColMA material (Cs = 10), with a contact angle of 32° or partially can be observed.
and 31° at 9°C and 15°C, respectively, did not perform well With the data obtained from this test, a table is
in the sessile drop method. As a consequence, the cells obtained that allows the comparison of different hydrogels,
started to die 3 days after printing. thus providing a quantitative method for determining the
mechanical stability of hydrogels, which allows them to be
This method does not determine the actual cell viability
of a hydrogel, but rather provides information on the compared with greater precision.
wettability of the hydrogel, related to cell adhesion and An example of a hydrogel exposed to the filament
propagation . collapse test can be seen in Table 3. The hydrogel used
[20]

Volume 9 Issue 2 (2023) 284 https://doi.org/10.18063/ijb.v9i2.667