Page 57 - IJB-8-2

Chand, et al.
A B

C

Figure 3. Contour of wall shear stress for (A) tapered conical, (B) conical, and (C) cylindrical nozzle with outlet diameter 0.3 mm at inlet
pressure 0.20 MPa with regions of MWSS emphasized.

attained for other combination of outlet diameter and
pressure. The region of maximum shear stress is longer
in cylindrical nozzle because it has a uniform radius and
requires a constant pressure throughout for extrusion in
contrast to conical needles where high pressure is only
needed at the tip of the nozzle . Billiet et al. also
[15]
[25]
compared conical and cylindrical nozzle of internal
diameter 200 mm at 1 bar inlet pressure and noted that
the conical nozzle experienced greater shear stress for
approximately 1 mm near the outlet, but the cylindrical
nozzle experienced lower shear stress for >16 mm from
the nozzle. This meant that cell death was higher in the
cylindrical nozzle due to the higher passage time in the
high shear stress region. This observation is indicative of
the reduced cell viability in tubular (cylindrical) nozzles Figure 4. Graph of inlet mass flow rate with respect to pressure for
compared to conical nozzles, as shown by experimental different nozzles.
observations [26,27] . [17]
The cylindrical nozzles that have a smaller required, which consequently increases shear stress .
volumetric footprint compared to the conical nozzle In our simulations, an inlet mass flow rate >0.003 kg/s
are ideal for printing in confined spaces and can reduce was obtained in a cylindrical nozzle with an outlet
wastage of bioink, which is an added benefit while using diameter of 0.50 mm only at 0.25 MPa inlet pressure
expensive biomaterials or cells . Although the MWSS with a corresponding MWSS of 1490 Pa. In contrast,
[7]
in the cylindrical nozzle is much lower, the mass flow an inlet mass flow rate >0.003 kg/s was obtained in a
rate is comparatively lower than the tapered conical and tapered conical and conical nozzle with outlet diameter
conical nozzle for the same nozzle diameter and pressure, 0.50 mm at 0.15 MPa inlet pressure with a corresponding
as shown in Figure 4. Since the flow rate is proportional MWSS of 1142 Pa and 1360 Pa, respectively. The
to the applied pressure, increased pressure translates to difference in mass flow rate was more drastic at lower
an increased flow rate [28] . This means that to achieve the inlet pressure values; for instance, the mass flow rates
same flow rate in the cylindrical nozzle as in the conical were 0.0017 kg/s and 0.0015 kg/s for tapered conical
and tapered conical nozzle, a greater pressure would be and conical nozzles, respectively, but the mass flow

International Journal of Bioprinting (2022)–Volume 8, Issue 2 49