High‐Intensity Focused Ultrasound‐Induced Thermal Effect for Solid Polymer Materials

Abstract

In this study, high-intensity focused ultrasound (HIFU)-induced thermal effects for solid polymer materials are investigated systematically. Infrared camera imaging is used to monitor temperature changes. The effects of polymer structure, HIFU power, and sample thickness on the thermal effect are studied. The results show that the HIFU-induced heating effect is very quickly, and can be controlled spatially and temporally. More importantly, it is obviously different for different polymers. The main reason is attributed to the various inner friction behaviors of macromolecular chains. This fundamental study is helpful to understand the interaction mechanism between HIFU and polymer, when HIFU is used as a trigger for drug release, shape memory, etc.

A fully coupled thermo‐viscoelastic finite element model for self‐folding shape memory polymer sheets

“…The greatest increase in temperature corresponded to χ = 1. The rapid rise in temperature was consistent with experimental observations and computational results of temperature rise near or slightly above the T g in studies of polystyrene and other polymers acted upon by ultrasonic waves . In those studies, oscillating pressure waves interact with polymer chains which dissipate the mechanical energy through viscous shearing and relaxation .…”

“…As part of this study, we investigated viscous heating during the shrinking and folding of SMP sheets. Viscous heat generation arises from viscous sliding and shearing of polymer chains at the molecular level . This heating effect is significant in many polymer systems during the transition from glassy to rubbery behavior and is prevalent near the glass transition temperature, T g .…”

Focused ultrasound actuation of shape memory polymers; acoustic-thermoelastic modeling and testing

“…The heating of polymer is due to absorption of acoustic energy as a result of viscous shearing exerted by ultrasound focused waves and subsequent release of energy in the form of heat. 52 In the images, the highly concentrated spot in the center has the maximum temperature while the immediate surroundings outside of the focal spot has signicantly lower temperatures. This shows a sharp temperature gradient from center to the edges of the polymer demonstrating the highly localized heating effect of focused ultrasound.…”

“…[48][49][50][51] In their study, Kost et al 43 irradiated ultrasound on a polymer matrix for releasing drugs entrapped in the matrix. Liu et al 52 and Han et al…”

“…3,52,54,55 By turning off the ultrasound beam the shape recovery process can be paused at any time, which allows the polymer to have an intermediate but a stable shape.…”