  In the present work, we conducted mechanical characterization of the membrane
of human serum albumin (HSA) microcapsules using the electrodeformation
technique which shows that HSA capsules are strain-softening in nature. The
viscoelasto-electrohydrodynamic model was utilized to understand the creep
mechanism in the HSA capsules. The effect of different reaction parameters such
as protein concentration and pH on the morphology of the capsule membrane was
investigated, and an attempt has been made to correlate microstructure with the
mechanical properties. The pH has a remarkable effect on the morphology of HSA
microcapsules which is also reflected in their mechanical characteristics. The
capsule synthesized with carbonate buffer shows very distinct morphology with
pores on the membrane surface, making the membrane less elastic with
significant nonrecoverable creep. The capsules synthesized with different
protein concentrations at the same pH condition show different morphology and
thus different rheological properties. Capsules with a low concentration of HSA
show smooth membrane structure with higher Young's modulus than the capsules
synthesized at a very high concentration which show a rough folded wavy
structure with low membrane elastic modulus. The effect of frequency on the
interfacial rheological properties of human serum albumin capsules was studied
using a frequency sweep test using the electrodeformation technique. The
rheological properties were computed incorporating the
viscoelasto-electrohydrodynamic model for the oscillatory response of capsules.
The results show that the elastic response dominates in the high-frequency
regime. Thus the electrodeformation technique allows studying the effect of
very high-frequency 1 Hz to 1 kHz, which is otherwise not possible with the
conventional rheometers.
