Leaf-Inspired Authentically Complex Microvascular Networks for Deciphering Biological Transport Process

The vascular transport
of molecules, cells, and nanoconstructs
is a fundamental biophysical process impacting tissue regeneration,
delivery of nutrients and therapeutic agents, and the response of
the immune system to external pathogens. This process is often studied
in single-channel microfluidic devices lacking the complex tridimensional
organization of vascular networks. Here, soft lithography is employed
to replicate the vein system of a Hedera elix leaf
on a polydimethilsiloxane (PDMS) template. The replica is then sealed
and connected to an external pumping system to realize an authentically
complex microvascular network. This satisfies energy minimization
criteria by Murray’s law and comprises a network of channels
ranging in size from capillaries (∼50 μm) to large arterioles
and venules (∼400 μm). Micro-PIV (micro–particle
image velocimetry) analysis is employed to characterize flow conditions
in terms of streamlines, fluid velocity, and flow rates. To demonstrate
the ability to reproduce physiologically relevant transport processes,
two different applications are demonstrated: vascular deposition of
tumor cells and lysis of blood clots. To this end, conditions are
identified to culture cells within the microvasculature and realize
a confluent endothelial monolayer. Then, the vascular deposition of
circulating breast (MDA-MB 231) cancer cells is documented throughout
the network under physiologically relevant flow conditions. Firm cell
adhesion mostly occurs in channels with low mean blood velocity. As
a second application, blood clots are formed within the chip by mixing
whole blood with a thrombin solution. After demonstrating the blood
clot stability, tissue plasminogen activator (tPA) and tPA-carrying
nanoconstructs (tPA-DPNs) are employed as thrombolytics. In agreement
with previous data, clot dissolution is equally induced by tPA and
tPA-DPNs. The proposed leaf-inspired chip can be efficiently used
to study a variety of vascular transport processes in complex microvascular
networks, where geometry and flow conditions can be modulated and
monitored throughout the experimental campaign.