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Optimized vascular network by stereolithography for tissue engineered skin

Figure 5. WSS as a function of the bifurcation geometry.
using according to equation (5); algorithm will minimise the recirculation area and
Step 5: Get a new l and l (dashed lines in Figure 6), thus minimise the trapped nutrient and oxygen. This
0
1
then go to step 1; algorithm was applied to employ rounded junctions
Step 6: End of the algorithm. instead of sharp joints. the STL file of the vascular
By applying this algorithm, an update vascular system system will also be generated automatically [18,19] using
is shown in Figure 7(B). this algorithm.
From Figure 7(A), it is shown that sharp junctions
are used in all bifurcation points. These sharp apices 2.3 The design summary and the porous vessel
at junctions of bifurcated vessels need to be avoided wall generation
because they are considered as risk factors for local To optimise a vascular network embedded in the skin
mechanical weakness [23] . Rounding the apex at each patch to supply tissues and cells nutrient and oxygen,
junction can be one of the solutions. The authors exchange waste and to support angiogenesis, we
developed an algorithm of computational geometry for considered the design criteria in both macro-scale and
the construction of vascular branches using a rounded micro-scale. It can be described as four criteria, which
apex [18,19] . CFD simulations were also carried out to test are:
the design and they concluded that rounded junctions (a)To maximise the nutrient supply and waste
in the bifurcation branch result in a more uniform WSS exchange
distribution compared to sharp junctions. They also (b)To minimise the resistance to blood flow
concluded that the construction generated using their (c)To ensure the shear stress on the vessel wall is in
the healthy range
(d)To avoid the blood recirculation.
Using the methodology discussed in sections 2.1 and
2.2; these four criteria can be achieved. Additionally,
the final construction of the vascular system is easy
to transfer to the STL file format. Actual blood vessel
walls are of a semi-permeable material, and thus enable
diffusion of nutrients, oxygen, waste products and CO ,
2
from and to the blood flow. This function is however
difficult to reproduce with materials compatible with AM
techniques. Instead, our proposed solution aims to enable
the diffusion through engineered pores in the vascular
walls. Because of the limited spatial resolution and
relatively slow build-up time offered by AM equipment,
direct manufacturing of capillaries with smaller
diameters (< 10 µm) is infeasible. The pores were also
designed to enable angiogenesis – the natural generation
and growth of new vessels out of the vessel pores. This
Figure 6. The correction algorithm approach allows the smaller capillaries to extend where

6 International Journal of Bioprinting (2018)–Volume 4, Issue 2