Shape-Adaptable Polymeric Particles for Controlled Delivery

Environmentally triggered shape reconfiguration is ubiquitous in biological systems and a key parameter in developing intelligent materials capable of various function oriented adaptations. While significant progress has been made in developing shape memory in bulk macroscale polymer materials, only a few examples of shape adaptability can be found in polymeric micro- and nanoparticles. In biotechnology and nanomedicine, though, morphological and shape adaptations of drug carriers offer unique opportunities in controlling shape-guided interactions with cells, vascular dynamics, transport across biobarriers, and recognition functions. Yet, unlike extensive studies on other physicochemical aspects of stimuli-responsive particle behavior, such as size, composition, surface morphology, permeability, swelling, and rigidity, the phenomenon of shape alteration in macro- and nanosized particulates has rarely been explored. This Perspective highlights recent developments in the, field of polymer particulates such as solid particles, micelles, hydrogels, and templated multilayer systems that undergo shape changes under various stimuli. The fundamental issues related to the design and shape-adaptable properties of both spherical and nonspherical particles are discussed as well as their prospective applications in controlled drug delivery.