Page 290 - IJB-9-2

International Journal of Bioprinting Methodology of hydrogel printability

Table 1. Mechanical and regeneration properties required of a characteristics for the printing conditions to be used in a
hydrogel suitable for bioprinting studies very specific way. The disadvantages of using measuring
instruments, such as rheometers or viscometers, include:
Cell regeneration properties [10] Mechanical
properties [12] (i) associated high cost, which has deterred many research
Non-cytotoxic and non-immunogenic Density teams from owning the instruments for determining the
printability of hydrogels, and (ii) the need to spend large
Mimic the extracellular matrix to achieve Porosity quantities of hydrogel, which is also expensive, for the study.
cell adhesion, propagation and osteogenic
differentiation at the implantation site Both commercial ready-to-use hydrogels and
Degradable or hydrolyzable by endogenous Stability reconstitution kits, produced under sterile and high-
enzymes quality conditions, are very costly that not all research
Structurally stable and mechanically strong Adhesion groups can afford to expend them just for testing purposes.
Adequate porosity (for the purpose of cellular pH and In addition, cell viability tests are often expensive as
interaction, control of bioactive factor release, temperature well, so it is important to have cheaper methods that can
nutritional and oxygen exchange) easily determine whether a hydrogel has the necessary
– Biodegradability wettability to allow cell survival. Due to the high costs of
both measuring instruments (rheometer or viscometer)
live/dead tests offered by commercial companies, and the and bioprinting materials to be studied (hydrogels), a
use of image processing software such as ImageJ . methodology is proposed that allows printability studies to
[8]
be carried out without the use of expensive equipment or
Hydrogels are hydrophilic and cross-linked polymers, large expenditure of material.
which can absorb and swell in water and biofluids, and
transform into insoluble 3D networks that give them To carry out the aforementioned studies, and after
[9]
elastic properties when subjected to different stresses carrying out the sessile drop method to determine the
during bioprinting. Furthermore, they can be composed possible cell viability in the bioprinted structure, Bio
of either natural, synthetic, or hybrid materials . When X bioprinter was used, allowing the ideal pressure and
[6]
choosing a hydrogel for bioprinting that guarantees both temperature parameters to be adjusted for each hydrogel
cell viability and structural integrity, it is important to within the parameters of cell viability, thanks to its
ensure that the hydrogel embodies a number of properties integrated drop test. This test makes it possible, with a low
that make them suitable for cell regeneration . Also, the material cost, to determine whether the hydrogel in question
[10]
mechanical properties of the hydrogel must be taken into could achieve good printability. Thus, at ideal pressure and
account, which must be within certain ranges (Table 1). temperature conditions for each hydrogel, comparisons
[11]
Other properties such as concentration and viscosity could be made between the different hydrogels, thanks
have to be taken into account because some of the above- to the combination of different tests that provide data on
mentioned properties depend on them . the printability of the same, to identify hydrogels that do
[12]
not meet the required needs, with the aim of selecting the
Certain tests can be carried out to determine the stability hydrogels with higher chance of printability.
of hydrogels used in bioprinting, so as to provide an estimate
of the mechanical stability and an approximation of the cell In this paper, we propose a methodology combining
viability. Another important parameter to take into account different tests that characterize printability of different
when using hydrogels in bioprinting is their printability. hydrogels, which help determine the hydrogels with
Without good printability, hydrogels do not have the the best mechanical properties and the best biological
capacity to reproduce biomimetic structures. Often, the properties to allow cell survival with the least possible
measurement of printability can be carried out by different waste of material. Since there is currently no ISO standard
rheometry and viscosity studies that require highly specific for characterizing printability in terms of cell viability,
equipment, which is very expensive and consumes a large the methodology described herein may be of great use to
amount of the material to be studied. Rheometers are very researchers in this field.
precise measuring instruments that can determine and 2. Objectives
analyze the behavior of different materials in deformation
and flow processes. Thus, they can provide useful data for The aim of this study is to develop a new methodology
the characterization of hydrogels used in bioprinting, such to configure and characterize hydrogels from different
as viscosity, creep, shear strain, deformation, and shear existing tests to achieve an optimal compromise between
rate. With the knowledge of these data, it would be possible printability and cell viability in a process optimized to
to determine which hydrogel has the best printability minimize material utilization.

Volume 9 Issue 2 (2023) 282 https://doi.org/10.18063/ijb.v9i2.667