Page 291 - IJB-9-2

International Journal of Bioprinting Methodology of hydrogel printability

This methodology enables the classification of new
materials according to different characterization tests, such
as sessile drop method, filament collapse test, quantitative
evaluation of the state of gelation, and printing grid test.
To this end, we developed the techniques mentioned and
created a platform adapted to the Bio X bioprinter for
filament collapse test. In the process, we assigned numerical
values to help determine hydrogels with the most suitable
characteristics for bioprinting.

3. Methodology
This methodology is designed to characterize hydrogels
that are going to be used to bioprint cells inside them, i.e.,
those that can be printed at temperatures close to 37°C.
First of all, the pressure and temperature parameters were
adjusted by means of the droplet test of the extrusion-
based bioprinter so that they were always within the
ranges that allow cell viability. Therefore, as a reference, the
temperature should not exceed 37°C, while the pressure Figure 2. Chamber generated to carry out the sessile drop method using
should not exceed 30 kPa, according to some authors . a non-absorbent bed and appropriate illumination.
[13]
The bioprinter must be kept in a temperature- and
humidity-controlled environment. In this study, the loaded with cells for bioprinting. The paper also presents
bioprinter was placed in a temperature- and humidity- some examples with real data for better understanding.
controlled chamber manufactured by the team, using a PID 3.1. Sessile drop method
temperature and humidity controller, a thermal resistor, The sessile droplet method is based on the contact angle
and a humidifier. BIO X bioprinter from CELLINK was of a hydrogel droplet on a surface, and provides data on
used to perform this methodology.
its wettability and on its ability to wet the surface of a
[15]
A battery of tests was carried out to test and process the solid. Contact angles between 0° and 90° have been found
hydrogels so that we were able to make precise comparisons to indicate a wettable, hydrophilic surface, while an angle
between the different hydrogels we analyzed. In order to between 90° and 180° indicates a non-wettable, hydrophobic
carry out the test on different hydrogels and to know which surface [16,17] . Hydrophilicity or wettability of biomaterials
one is the most suitable for the bioprinting of biomimetic is considered a very important parameter for certain
structures, it is necessary to study the printability together applications, such as cell adhesion in tissue engineering .
[18]
with other characteristics , such as resistance to traction In order to measure the contact angle, a chamber
[14]
or compression, and even the deformation that can be was made, in which a glass plate was placed at its base,
produced. In addition, the amount of material used was which does not absorb the material to be studied. At the
optimized in the methodology to reduce the relevant costs, same time, a light source was placed at the upper part of
while ensuring that quantitative and visual results showing the chamber to generate a vertical illumination on the
which hydrogel presents the best structural characteristics hydrogel drop without forming shadows that could hinder
could be obtained.
the image capture process (Figure 2).
In addition, the proposed methodology can also
After adding the drop to be studied in the chamber,
provide data on cell viability of hydrogels, which helps images were captured in a perpendicular angle from the
decide whether to load hydrogels with cells. Sessile drop glass plate using a USB 40× to 100× digital microscope,
method allows discarding hydrogels with poor cell viability and software (AMCap) was used to digitize the image on
results, thereby obviating the need in such a case to perform the computer. In this way, precise images could be taken of
biological assays. Cell viability can be further checked with all the hydrogel droplets from the same angle. These images
tests such as the LIVE/DEAD® assay, or by assessing cell must be processed by an image processing program, such as
metabolic activity with MTT assay, among others.
ImageJ or Fiji, to measure the contact angle. They can also
This work aims to provide a unified methodology for be measured by computer-aided design (CAD) software,
characterizing the printability of hydrogels that will be which can also measure the contact angle.

Volume 9 Issue 2 (2023) 283 https://doi.org/10.18063/ijb.v9i2.667