Shape-transformation of polymersomes from glassy and crosslinkable ABA triblock copolymers

Stretched or wrinkled? Looking into the polymer conformation within polymersome membranes

Self-assembly of amphiphilic block-copolymers into polymersomes is a well-established concept. In this membrane, the hydrophilic part is considered to be loosely assembled towards the solvent, and the hydrophobic part on the inside of the membrane is considered to be more densely packed. Within the membrane, this hydrophobic part could now have a stretched conformation or be a random coil, depending on the available space and also on the chemical nature of the polymer. We now analysed the literature for works on polymersomes that determined the membrane thickness via cryo-TEM and analysed the hydrophobic part of their polymers for their conformation. Over all available block-copolymers, a variety of trends became obvious: the longer a hydrophobic block, the more coiled the conformation and the bulkier the side chains, the more stretched the polymer became. Polymers with less conformational freedom like semi-crystalline ones were present in a more stretched conformation. Both trends could be exemplified on various occasions in this cross-literature meta-study. This overview hence provides additional insight into the physical chemistry of block-copolymer membranes.

Shape Transformation of Polymer Vesicles

Life activities, such as respiration, are accomplished through the continuous shape modulation of cells, tissues, and organs. Developing smart materials with shape-morphing capability is a pivotal step toward life-like systems and emerging technologies of wearable electronics, soft robotics, and biomimetic actuators. Drawing inspiration from cells, smart vesicular systems have been assembled to mimic the biological shape modulation. This would enable the understanding of cellular shape adaptation and guide the design of smart materials with shape-morphing capability. Polymer vesicles assembled by amphiphilic molecules are an example of remarkable vesicular systems. The chemical versatility, physical stability, and surface functionality promise their application in nanomedicine, nanoreactor, and biomimetic systems. However, it is difficult to drive polymer vesicles away from equilibrium to induce shape transformation due to the unfavorable energy landscapes caused by the low mobility of polymer chains and low permeability of the vesicular membrane. Extensive studies in the past decades have developed various methods including dialysis, chemical addition, temperature variation, polymerization, gas exchange, etc., to drive shape transformation. Polymer vesicles can now be engineered into a variety of nonspherical shapes. Despite the brilliant progress, most of the current studies regarding the shape transformation of polymer vesicles still lie in the trial-and-error stage. It is a grand challenge to predict and program the shape transformations of polymer vesicles. An in-depth understanding of the deformation pathway of polymer vesicles would facilitate the transition from the trial-and-error stage to the computing stage. In this Account, we introduce recent progress in the shape transformation of polymer vesicles. To provide an insightful analysis, the shape transformation of polymer vesicles is divided into basic and coupled deformation. First, we discuss the basic deformation of polymer vesicles with a focus on two deformation pathways: the oblate pathway and the prolate pathway. Strategies used to trigger different deformation pathways are introduced. Second, we discuss the origin of the selectivity of two deformation pathways and the strategies used to control the selectivity. Third, we discuss the coupled deformation of polymer vesicles with a focus on the switch and coupling of two basic deformation pathways. Last, we analyze the challenges and opportunities in the shape transformation of polymer vesicles. We envision that a systematic understanding of the deformation pathway would push the shape transformation of polymer vesicles from the trial-and-error stage to the computing stage. This would enable the prediction of deformation behaviors of nanoparticles in complex environments, like blood and interstitial tissue, and access to advanced architecture desirable for man-made applications.

Reshaping Membrane Polymorphism of Polymer Vesicles through Dynamic Gas Exchange

The quest for a universal method to shape the vesicular morphology in dynamic and diversified manners is a challenging topic of cell mimicry. Here we present a simple gas exchange strategy that can direct the deformation movements of polymer vesicles. Such vesicles are assembled by a class of gas-based dynamic polymers, where CO₂ connects between the frustrated Lewis pair via dynamic gas-bridged bonds. Use of other competitive gases (N₂O, SO₂, or C₂H₄) to in situ exchange the CO₂ linkages can change the polymer structure and drive the membrane to proceed with three fundamental movements, including membrane stretching, membrane incurvation, and membrane protrusion, thus remolding the shapes of polymersomes. The choices of gas types, concentrations, and combinations are crucial to adjusting the vesicle evolution, local change of membrane curvature, and anisotropic geometrical transformation. This will become a generalized strategy to control the vesicular polymorphism and deformable behavior.

Combining Nanoparticle Shape Modulation and Polymersome Technology in Drug Delivery

This paper highlights the potential benefits of using self-assembled polymeric nanoparticles of various shapes to enhance drug uptake. First, we highlight the growth and development of the polymersome, using a liposome as a blueprint for amphiphilic codelivery. Then, we focus on the advantages of nanoparticle elongation, drawing from the field of solid nanoparticles, as opposed to self-assembled vesicles which have not yet been extensively explored in shape-modulated drug delivery applications. Notably, regardless of the material used in the solid nanoparticle systems, more elongated shapes lead to greater cellular uptake, decreased interaction with the reticuloendothelial system macrophages, and increased circulation times. Finally, we highlight the methods currently being developed to modulate polymersome shape, thus providing a drug delivery system with the benefits derived from amphiphilicity and elongated structures. Current methods employed to modulate polymersome shape involve osmotic pressure gradients, solvent switching, and the use of cross-linking agents. Although these methods are successful in modulating polymersome shapes and the benefits of elongated nanoparticles in therapeutic targeting are clear, these methods have not yet been explored for applications in drug delivery.