Page 99 - IJB-2-1

Richard Bibb, Nadine Nottrodt and Arnold Gillner

ning, as well as enabling biofunctionalization. The curable was successfully used to build branched por-
[2]
most important challenge of the material development ous blood vessels by stereolithography . However,
research was not related to a singular parameter, but developing an entirely compatible support material
rather the combination of all of the desired properties proved challenging and was not achieved during the
within an appropriate combination of materials. With- project. Consequently, as inkjet printing necessitates a
in this WP, the materials were also evaluated regard- removable support material, it was not possible to in-
ing their chemical, physical, thermal and mechanical kjet print vessel structures as envisaged. Additional
properties as well as fundamental tests of cytotoxicity. research was done on gelatin development for additive
manufacturing of vessel substitutes [3,4] .
4.1 Objectives of WP2 To allow endothelialization of those vessels, an inn-

The overall goal of WP2 was to provide a new tailored er-surface functionalization was necessary. The Uni-
material that fulfilled the requirements for soft tissue versity of Stuttgart developed a procedure for coating
engineering whilst also being compatible with the these vessels with heparin, which allows homogen-
[5]
combined AM processes and biofunctionalization. eous cell cultivation . For local functionalization of
• To design and synthesize 40 chemical struc- vessel scaffolds and cell guidance of the surrounding
tures for blood vessel materials and supporting scaffold, localized laser functionalization was inves-
[6]
scaffold materials for 3D AM processes and fi- tigated . Another aspect was the scaffold material for
ber materials for electrospinning, the surrounding fat. For that reason, two kinds of ma-
• To characterize materials in terms of their che- terials are considered. One kind of materials are elec-
mical structure, thermal and mechanical prop- trospun fibres as scaffolds while the other kind are
erties, viscosity, photo-curing behavior, surface hydrogels filling the pores between the fibres and pro-
functionality and cytotoxicity, viding growth factors and allow nutrition of embedded
[7]
• To adapt polymers for AM and for the needs of cells . Furthermore, a huge number of electro-
blood vessel systems in regard to demands for spinnable materials were tested for their biocompa-
permeability, mechanical properties and bio- tibility and showed very promising results (INNO).
compatibility, Electrospun meshes have been successfully charac-
• To modify surfaces of polymers to enable bio- terized for their use in adipose tissue generation [8–10] .
functionalization,
• To analyze long-term (1–6 months) behavior of 5. Process Development (WPs 3, 4, 7 and 8)
basic materials for the vascular system. The overall goal of this section was to develop and
4.2 Objectives of WP5 demonstrate a combined AM process that integrated
the three technologies inkjet printing, stereolithogra-
The overall objective was the biofunctionalization of phy/MPP and electrospinning to build up the vascula-
the artificial vascular structures and of the surrounding rized scaffold utilizing the newly developed materials.
fiber matrix obtained from WPs 2 and 4. The biofunc- The design of the vascular structures is essential to
tionalization was specifically aimed for the following: enable them to replicate human tissue performance.
• To minimize cytotoxicity of the biofunctiona- The design and modelling tasks involved physiologi-
lized material, cal simulation and testing to define the optimum vessel
• To control cell adhesion and migration on ma- dimensions and configuration. This was done through
terial surfaces and to stimulate proliferation by theoretical calculations, physical experimentation and
binding functional groups to the surface, Computational Fluid Dynamics (CFD). To enable AM
• To stimulate neo-angiogenesis, the design phase needed to incorporate the optimized
• To design a process that can be integrated into parameters and produce three-dimensional models that
the proposed combined AM process. would define the structures. The design tasks involved
the creation of a bespoke Computer-Aided Design
4.3 Highlights
(CAD) application that could take in physiological
Materials compatible with inkjet printing, stereolitho- parameters, number of branches, skin patch size, ves-
graphy/MPP for blood vessel generation were devel- sel diameters, etc. and automatically generate the ves-
oped to fulfil the main requirements. An elastic, pho- sel structure as a solid three-dimensional computer
tocurable polymer that is inkjet printable and UV- model in a format suitable for AM (e.g., STL file). In

International Journal of Bioprinting (2016)–Volume 2, Issue 1 95