Polymersomes, hollow spherical nano-to-microscale polymer assemblies, have increasingly become important constructs in the development of biomimetic materials that expand the library of functional and robust analogs to lipid-based vesicles. As compared to liposomes, polymersomes possess superior physical properties and the nearly unlimited potential for synthetic fine-tuning. Herein we improve on the physical properties of these polymer vesicles by introducing platinum-based metal−ligand cross-links into the hydrophobic core, which gave the vesicles demonstrated resistance to destabilization by surfactants over un-cross-linked polymersomes. The formation of cross-links was capable of being selectively reversed by the addition of phosphines. In addition, the Pt(0) cross-links retained their catalytic activity for the hydrosilylation of alkenes.
■ INTRODUCTIONLiving organisms' ability to adapt to changing environments has inspired a range of biomimetic materials that change physical properties in response to different stimuli. Stimuli-responsive polymers have been designed that use a variety of inputs, such as redox potential, 1 light, 2 and mechanical loading, 3 to affect such physical changes as permeability, 4 solubility, 5 and even luminescence. 6 Incorporating stimuli-responsiveness into vesicle structures that mimic cell membranes has been an important goal in developing nanodelivery systems capable of directed content release for therapeutic applications. Such systems would also be attractive platforms for the development of membrane-based nanoreactors to understand and exploit features of transport and chemical transformation in confined geometries. Generally, these vesicular analogues of biological cells are made up of phospholipid bilayers, a convenient choice because they are the major components of cellular membranes in nature. However, lipid-based systems are often limited in terms of chemical diversity and mechanical stability.Recently, amphiphilic block copolymers have been purposed to replace lipids as a vesicle forming molecule. 7 These polymersomes offer the distinct advantage of increased robustness, 8,9 improved barrier properties, 10,11 and a nearly infinite library of suitable amphiphilic copolymers. Indeed, the vast number of monomers that can be polymerized in a controlled manner to produce vesicle-forming polymers means that there are almost as many different chemical moieties available for modification, pre-or postpolymerization. 12−15 Because of this versatility, polymer vesicles have been designed for a myriad of potential uses, such as drug and gene delivery systems 16,17 and cascade nanoreactors. 18 One example of the chemical versatility of vesicle forming polymers is the number of ways devised to cross-link these structures. Covalent systems are well-known and include disulfide bonds, 19 free radical cross-linking of polymer sidechain groups by redox couples, 20,21 and polymers with reactive side-chain groups. 22−24 These cross-linking systems can be used to increase vesicle robus...
