Microvascular networks are not simple straight microchannels but rather complex geometries composed by successive
asymmetric divergent and convergent bifurcations. Despite the extensive research work in this field, still lack of
knowledge about the blood flow behavior in microvascular networks. The current study applies the most current
advanced visualization and microfabrication techniques to provide further insights into to the blood flow in network
geometries. Hence, by using a high-speed video microscopy system, blood flow measurements and visualizations of the
cell-free layer (CFL) were performed along a microchannel network composed by several divergent and convergent
bifurcations. The inlet flow rate was kept constant whereas the hematocrit (Hct) and the depth of the geometry was
changed in order to evaluate their effects into the CFL thickness. The results, show clearly that the Hct has a significant
impact on the CFL thickness whereas the effect of reducing the depth did not contribute to a noticeable change on the
CFL. In addition, the in vitro blood flow results reported here provide for the first time that in microfluidic devices
having several asymmetric confluences it is likely to have the formation of several CFLs not only around the walls but
also in middle of the main channels just downstream of the last confluence apex. Although, to best of our knowledge
there is no evidence that this kind of flow phenomenon also happens in vivo, we believe that for microvascular networks
with similar geometries and under similar flow conditions tested in this work, this kind of phenomenon may also
happen in vivo. Furthermore, the results from this study could be extremely helpful to validate current numerical
microvascular network models and to develop more realistic multiphase numerical models of blood flow in microcirculation.
This work was supported by Fundação para a Ciência e a Tecnologia
(FCT), Portugal, under the strategic grants UID/EMS/04077/2019,
UID/EEA/04436/2019 and UID/EMS/00532/2019. The authors are
also grateful for the partial funding of FCT through the projects POCI-
01-0145-FEDER-016861, POCI-01-0145-FEDER-028159, NORTE-01-
0145-FEDER-029394, NORTE-01-0145-FEDER-030171, funded by
COMPETE2020, NORTE2020, PORTUGAL2020, and FEDER, and the
PhD grant SFRH/BD/91192/2012.
