Study of Interfacial Rheology of Human Serum Albumin Microcapsules using Electrodeformation Technique

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.