Browsing by Author "Bhargava, Aarushi"
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- Dynamics of smart materials in high intensity focused ultrasound fieldBhargava, Aarushi (Virginia Tech, 2020-05-06)Smart materials are intelligent materials that change their structural, chemical, mechanical, or thermal properties in response to an external stimulus such as heat, light, and magnetic and electric fields. With the increase in usage of smart materials in many sensitive applications, the need for a remote, wireless, efficient, and biologically safe stimulus has become crucial. This dissertation addresses this requirement by using high intensity focused ultrasound (HIFU) as the external trigger. HIFU has a unique capability of maintaining both spatial and temporal control and propagating over long distances with reduced losses, to achieve the desired response of the smart material. Two categories of smart materials are investigated in this research; shape memory polymers (SMPs) and piezoelectric materials. SMPs have the ability to store a temporary shape and returning to their permanent or original shape when subjected to an external trigger. On the other hand, piezoelectric materials have the ability to convert mechanical energy to electrical energy and vice versa. Due to these extraordinary properties, these materials are being used in several industries including biomedical, robotic, noise-control, and aerospace. This work introduces two novel concepts: First, HIFU actuation of SMP-based drug delivery capsules as an alternative way of achieving controlled drug delivery. This concept exploits the pre-determined shape changing capabilities of SMPs under localized HIFU exposure to achieve the desired drug delivery rate. Second, solving the existing challenge of low efficiency by focusing the acoustic energy on piezoelectric receivers to transfer power wirelessly. The fundamental physics underlying these two concepts is explored by developing comprehensive mathematical models that provide an in-depth analysis of individual parameters affecting the HIFU-smart material systems, for the first time in literature. Many physical factors such as acoustic, material and dynamical nonlinearities, acoustic standing waves, and mechanical behavior of materials are explored to increase the developed models' accuracy. These mathematical frameworks are designed with the aim of serving as a basic groundwork for building more complex smart material-based systems under HIFU exposure.
- Focused ultrasound actuation of shape memory polymers; acoustic-thermoelastic modeling and testingBhargava, Aarushi; Peng, Kaiyuan; Stieg, Jerry; Mirzaeifar, Reza; Shahab, Shima (The Royal Society of Chemistry, 2017-09-18)Controlled drug delivery (CDD) technologies have received extensive attention recently. Despite recent efforts, drug releasing systems still face major challenges in practice, including low efficiency in releasing the pharmaceutical compounds at the targeted location with a controlled time rate. We present an experimentally-validated acoustic-thermoelastic mathematical framework for modeling the focused ultrasound (FU)-induced thermal actuation of shape memory polymers (SMPs). This paper also investigates the feasibility of using SMPs stimulated by FU for designing CDD systems. SMPs represent a new class of materials that have gained increased attention for designing biocompatible devices. These polymers have the ability of storing a temporary shape and returning to their permanent or original shape when subjected to external stimuli such as heat. In this work, FU is used as a trigger for noninvasively stimulating SMP-based systems. FU has a superior capability to localize the heating effect, thus initiating the shape recovery process only in selected parts of the polymer. The multiphysics model optimizes the design of a SMP-based CDD system through analysis of a filament as a constituting basestructure and quantifies its activation under FU. Experimental validations are performed using a SMP filament submerged in water coupled with the acoustic waves generated by a FU transducer. The modeling results are used to examine and optimize parameters such as medium properties, input power and frequency, location, geometry and chemical composition of the SMP to achieve favorable shape recovery of a potential drug delivery system.