High-Frequency Ultrasound as a Novel Stimulus for Poly(N-isopropylacrylamide) Microgels

• Applicant: Dr. Seyedamin Rahimzadeh
• Subject Area: Experimental and Theoretical Physics of Polymers
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 546899245

Poly(N-isopropylacrylamide) (PNIPAM) microgels, as stimuli-responsive polymer networks, find versatile applications in smart coatings, foams, emulsions, and biomedical systems, owing to their unique properties both in bulk and/or at interfaces. Although their benign behavior in the human body has not been approved, they can still be studied as a model system for drug delivery applications (e.g., they can be loaded with drug particles and, upon an external stimulus, release them at the intended site). PNIPAM microgels, in addition to responding to temperature changes, can be modified to be sensitive to other external stimuli such as light and magnetic fields, offering the advantage of faster response times compared to temperature changes. In this project, we establish NON-DESTRUCTIVE high-frequency ultrasound (in the MHz range) as a novel stimulus, benefiting from its fast triggering capability, high penetration depth, and the advantage of not requiring additional modifications compared to microgels designed for light or magnetic stimuli. The volume phase transition (VPT) of the microgels under ultrasound will be investigated using a recently modified dynamic light scattering method. The primary objective is to understand the correlation between ultrasound-induced microgel oscillation and the viscous dissipation of ultrasound energy, ultimately leading to their dehydration. In this context, we track the hydrodynamic diameter of microgels for the duration of ultrasonic actuation, concurrently investigating the influence of ultrasound properties (frequency and amplitude), microgel characteristics (size, stiffness), and surrounding parameters (such as temperature and (co)solvents) on their VPT. This comprehensive study aims to contribute to the understanding of how PNIPAM microgels behave under the influence of high-frequency ultrasound, paving the way for potential advancements in drug delivery and other applications. The insights gained from this research could open new avenues for the development of responsive materials with enhanced properties and functionalities.

• DFG Programme: Research Grants