Figure 3 – Characterization of the eSF microfluidic hydrogel. A)
Oscillatory rheological measurements (frequency 1 Hz) for eSF hydrogels
at different concentrations (6%, 12%, and 14 %). B) ATR-FTIR spectra
for the 3D eSF hydrogel (with 14% eSF) retaining the amorphous protein
structure for at least 7 days. C) Tensile tests on 14% eSF microfluidic
platform and photograph showcasing the high degree of deformation of the
eSF hydrogel.
Next, we evaluate the capability of the eSF chip to recover to other
types of mechanical actuation, namely manual tension, torsion, and
bending (Figure 4 A). We found that the eSF chip displayed a remarkable
flexibility. The chip was stretched, bent, and twisted without breaking
or damaging the inner channel for at least 3 days when kept in medium or
PBS to avoid dehydration (Figure 4 A) (see supplementary info ).
This deformation ability could be optimal in a myriad of tissue models,
such as lung, heart and colon, which present dynamic stretching
movements (30,
31). Moreover, this opens the way to
deepen mechanobiology studies in the field of cancer.
Some concerns were raised due to the hydrophilicity of the material and
if it could perfuse water-based solutions efficiently through the
channel. Figure 4 B) shows the injection of a blue ink flowing along the
whole serpentine channel, demonstrating the ability of the eSF platform
to flow fluids. Additionally, the eSF microfluidic chips showed its
capacity to generate molecular gradients (see supplementary
info ). The slope of such gradients could be accurately tuned by
adjusting the concentration of silk: higher concentrations lead to
slower gradient formation due to smaller pore size and lower
concentration lead to faster gradient formation due to large pore sizes.
Indeed, one of the main properties of eSF is the ease of tuning
mechanical stiffness (from 1 kPa to 1 MPa) and long-term stability in
various environments. Finally, Figure 4 C) shows the flow of micro-sized
structures along the curved microchannel, highlighting the laminar flow
of the fluid being transported.