Master thesis presentation Sofie Ekström, MPBIO

Abstract: The recent advancement within the field of 3D bioprinting has enabled its application in
areas such as the pharmaceutical industry, tissue engineering and many types of cell-based
research. The principle is to use 3D printing technology to print a variety of biomaterials
together with viable cells, to produce accurate tissue models by mimicking the environment
that the cells experience in vivo. The so-called bioinks used for 3D bioprin0ng are commonly
composed of hydrogels based on naturally derived polymers like gelatin, collagen, alginate or
nanofibrillated cellulose (NFC). Bioinks are viscoelastic materials which can be crosslinked
after being printed to keep their structure and shape. The crosslinking method and
conditions determine the stiffness of the resulting tissue construct, which can in turn also
affect the behaviour of incorporated cells. This study aims to investigate the influence of the
bioink's viscoelastic properties on both cell behaviour and printability of the bioink. The
studied bioinks include CELLINK Bioink, GelMA, GelMA C, GelXA and Photogel95, which are
crosslinked either ionically using a CaCl2 solution or using UV light, or a combination of the
two.
The bioinks' viscoelastic properties, as well as stiffness after crosslinking at two different
conditions for each bioink were initially investigated using rheological measurements, which
showed that different stiffnesses could be achieved. 3D bioprinting of the bioinks together
with mesenchymal stem cells (MSC) was used to produce samples which were crosslinked at
the same two conditions, cultured over 14 days and analyzed at several time points. The cell
viability was evaluated by fluorescent staining using Calcein-AM and propidium iodide (PI),
and the cell morphology by fluorescent staining using ActinGreen and DAPI, followed by
fluorescent microscopy imaging. The stiffness of the cell samples over time was also
evaluated by measurements at the same time points.
The stiffness measurements of the cell samples over time showed some unexpected results
and high variation between samples, which can to some extent be explained by the method
not being fully suitable or well-adapted for these samples. The cell viability was relatively
high at day 1 for all bioinks and crosslinking conditions, above 90 % for most samples but
around 80 % for a few. A decrease in cell viability was then observed for all samples at day 7
and day 14, for which several causes are discussed. The cell morphology analysis showed
cells stretching in all bioinks at day 7 and day 14, except for CELLINK Bioink. However, no
distinct correlations between the different crosslinking conditions and the cell behaviour
could be determined.

Examiner: Julie Gold

Supervisor: Elin, Cellink/Bico AB

Opponent: Oliver Forsell