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Richard Bibb, Nadine Nottrodt and Arnold Gillner

At the time of writing, the project has generated 26 growing in hydrogels developed within the ArtiVasc
conference presentations (2 pending), 15 journal pub- 3D Project. It is still challenging to find the right cul-
lications (with 5 in press or under review) and a PhD tivation media allowing not only adipocytes but also
thesis. Many more are currently in progress. pericytes and endothelia cells to grow under co-cul-
ture conditions. Biologists together with engineers
8. Discussion developed a bioreactor that can be perfused with me-

The results of ArtiVasc 3D are shaping the future. A dia to provide nutrition to all cultivated cells.
toolbox has been developed that can respond flexibly Since not only fatty tissue was the goal of the
to diverse materials, shapes and sizes. These results project but also three-layered skin, the biologists tried
can be viewed as a precursor to a fully automated to develop a dermal and epidermal tissue from exist-
process chain for the production of artificial blood ing protocols on top of the adipose tissue. In stainings,
vessels that can be integrated into existing lines. they were able to show the formation of all three lay-
Another highlight of the project is the successful ers. Analysis of the expression of typical tissue marker
breeding of adipose tissue in a novel bioreactor. The is still under investigation.
combination of the fatty tissue with an existing skin The final aim to build up a genuinely vascularized
model allowed the production of a full-thickness skin artificial skin remains a big challenge. Due to unfore-
model that has a thickness of up to 12 millimeters. seen challenges coming from the material and process
Throughout the four years of research, the re- development and a tight project plan, some steps tow-
searchers have faced many challenges that were not ards the vascularized tissue are still open. Up to now,
expected in the beginning. At the beginning, research- we have demonstrated the three-layered skin without
ers defined specifications that were to be met at the vessels. By using stereolithography as the build-up
end of the project. Those specifications ranged from strategy, branched porous vessels are available today.
material properties for processability, such as viscosity The integration and function of these available endo-
and material interaction, to the biological require- thelialized vessels has to be demonstrated. We expect
ments, such as biocompatibility and elasticity. The neo-angiogenesis from those porous blood vessels
material scientists met 9 out of 10 of those require- containing endothelial cells and pericytes, which
ments. Nevertheless, the development of two bio- would be a real benefit for the nutrition of the thick
compatible materials able to print next to each other fatty tissue because more natural and reliable proc-
and to dissolve one of these materials afterwards (i.e., esses are expected. However, this will most probably
a support material) was unfortunately not possible be a challenge for future research projects. The origi-
within the timeframe. This influences the build-up of nal plan in ArtiVasc 3D foresaw the generation of an
blood vessels within the combined automated process. elastic, branched blood vessel system, to provide a
Nevertheless, researchers found alternative routes to scaffold for endothelial cell and pericyte organization.
generate porous branched vessel structures by using Since we found that just a hollow channel in the mid-
stereolithography and produce linear porous vessels dle of a hydrogel could be used as a supply channel,
by using electrospinning or dip coating. Thus, new we could imagine different strategies for nutrition
technologies have been established to achieve the final supply and vessel organization without having a static
goal of porous vessels. scaffold wall. By just using functionalized hydrogels
While engineers worked on vessel generation, ano- that contain growth factors, those factors could be
ther group of chemists and biologists worked on the released by time dependent or by photo-induced de-
endothelialization of those vessels. It took a lot of ef- gradation of the hydrogel. This would add the fourth
fort, a huge number of materials and protocols to de- dimension (time or 4D) to the 3D printing technology
fine the best protocol for endothelialization. and could induce cell organization and blood vessel
In parallel, biologists and chemists broke new gro- formation with time [20] . Nevertheless, the generation
und in the field of fat tissue generation. The biggest, of a branched blood vessel scaffold is necessary for
and up until now unavailable, third layer of the three- other applications such as blood vessel replacement.
layered skin model. They developed protocols for iso- The other reason for such a scaffold is the connectivi-
lating cells and gained knowledge in handling of adi- ty to the natural tissue in case of implantation in the
pose tissue derived stem cells and mature adipocytes. future. This will not be possible with those self-org-
In the end, they could successfully demonstrate cells anized vessel systems.

International Journal of Bioprinting (2016)–Volume 2, Issue 1 99