Shape memory polymers (SMPs) are used in a wide range of applications in the fields of medicine, electronics, space technology and textiles among others. Consequently, an emphasis on finding an efficient means of actuating these polymers, especially for sensitive and remote applications becomes important. Focused Ultrasound (FU) induced thermal actuation of SMPs has proven to be a safe, remote and flexible technique of achieving spatially and temporally controllable shape recovery. Increasing research is being done to model the shape memory behavior since it forms the basic necessity for SMP use in any application. However, it has mostly been numerical in nature. In this study, we develop a comprehensive analytical model to understand the dynamics of the FU induced shape recovery of SMPs with a focus on acoustic, medium, material and geometric nonlinearities. We estimate the acoustically induced thermal energy inside the SMP and incorporate that energy in an analytical model to understand the change in temperature dependent mechanical properties of SMP as a result of FU exposure. Using these properties, governing equations of motion for an Euler- Bernoulli SMP cantilever beam are formulated through Generalized Hamilton’s Principle. An analytical solution to trace the recovery of the beam is obtained using method of multiple scales for weak geometric nonlinearities. The model is experimentally validated and is able to successfully give a closed form expression for the amount of shape recovery achieved as a function of acoustic parameters, thus eliminating the need of analyzing any intermediary acoustic, thermal and elastic behavior.
Advancements in controlled drug delivery (CDD) technology still face major challenges in practice, including chemical issues with synthesizing biocompatible drug containers, releasing the pharmaceutical compounds at the targeted location in a controlled time rate and using an effective and safe trigger for initiating the drug release. This work aims to overcome these challenges with employing biodegradable shape memory polymer (SMP) based drug-delivery containers. Besides biological safety, biodegradability ensures that no further surgery will be needed for the removal of the containers. Focused ultrasound (FU) is used as a trigger for noninvasively stimulating SMP-based drug capsules. FU has a superior capability to localize the heating effect, thus initiating a controlled shape recovery process only in selected parts of the polymer, which affects the amount of drug released. The current research uses a mathematical multiphysics model which performs an acoustic-thermoelastic analysis, to optimize the design of SMP containers. The proposed designs exploit various parameters such as nonlinearity, absorption and diffraction effects, as well as input power and frequency of the propagating acoustic wave to attain the desired shape recovery, as required by the application or location of drug release. The acoustic-thermoelastic effects on the SMP containers are studied with the help of finiteelement methods. Multilayer simulations are performed at millimeter scale to mimic the in vivo conditions of a drug delivery container travelling inside an artery. By manipulating the design and the shape recovery rate of the SMP containers, velocity of the drug particles is controlled and directed towards a specific location.