Biological membranes play an essential role in living organisms by providing stable and functional compartments, preserving cell architecture, whilst supporting signalling and selective transport that are mediated by a variety of proteins embedded in the membrane. However, mimicking cell membranes – to be applied in artificial systems – is very challenging because of the vast complexity of biological structures. In this respect a highly promising strategy to designing multifunctional hybrid materials/systems is to combine biological molecules with polymer membranes or to design membranes with intrinsic stimuli-responsive properties. Here we present supramolecular polymer assemblies resulting from self-assembly of mostly amphiphilic copolymers either as 3D compartments (polymersomes, PICsomes, peptosomes), or as planar membranes (free-standing films, solid-supported membranes, membrane-mimetic brushes). In a bioinspired strategy, such synthetic assemblies decorated with biomolecules by insertion/encapsulation/attachment, serve for development of multifunctional systems. In addition, when the assemblies are stimuli-responsive, their architecture and properties change in the presence of stimuli, and release a cargo or allow “on demand” a specific in situ reaction. Relevant examples are included for an overview of bioinspired polymer compartments with nanometre sizes and membranes as candidates in applications ranging from drug delivery systems, up to artificial organelles, or active surfaces. Both the advantages of using polymer supramolecular assemblies and their present limitations are included to serve as a basis for future improvements.

/pdf/bioinspired-polymer-vesicles-and-membranes-for-biological-3d546sxrk4.pdf

Bioinspired polymer vesicles and membranes for biological and medical applications

Catalysis by small molecules (≤1000 Da, 10−9 m) that are capable of binding and activating substrates through attractive, noncovalent interactions has emerged as an important approach in organic and organometallic chemistry. While the canonical noncovalent interactions, including hydrogen bonding, ion pairing, and π stacking, have become mainstays of catalyst design, the cation–π interaction has been comparatively underutilized in this context since its discovery in the 1980s. However, like a hydrogen bond, the cation–π interaction exhibits a typical binding affinity of several kcal mol−1 with substantial directionality. These properties render it attractive as a design element for the development of small-molecule catalysts, and in recent years, the catalysis community has begun to take advantage of these features, drawing inspiration from pioneering research in molecular recognition and structural biology. This Review surveys the burgeoning application of the cation–π interaction in catalysis.

The Cation–π Interaction in Small-Molecule Catalysis

Very stable and bright emitting amine-terminated Si nanoparticles (NPs) with different alkyl chain lengths between the Si core and amine end-group are synthesized. The obtained NPs have a spherical shape and homogeneous size distribution (1.57 ± 0.24 nm). Their emission can be tuned from the UV to the blue spectral region, in a controllable fashion, by only changing the alkyl spacer length. The emission quantum yields are ∼12% for all synthesized Si NPs. Excited state lifetimes are in the ns range and point to a direct band gap excitation. NH2-terminated Si NPs exhibit an exceptional stability over a wide pH range (1–13) and high temperatures (120 °C). The diffusion coefficient of prepared Si NPs is determined by fluorescence correlation spectroscopy (FCS) to be 3.3 × 10−10 m2 s−1. The derived size of Si NPs from mobility corresponds to 1.4 nm which is in a good agreement with the size obtained by transmission electron microscopy (TEM). Prepared Si NPs are shown to be highly suitable for bioimaging studies as they are readily taken up by BV2 cells. Si NPs are located in the cells cytosol. Proliferation of stained BV2 cells is observed and showed that newly formed cells are also stained with Si NPs, indicating their minimal toxicity. By using Si NPs it is possible to stain multiple cell generations by only staining the mother cells.

Amine-terminated silicon nanoparticles: synthesis, optical properties and their use in bioimaging

Polymersomes as synthetic analogues of liposomes appear frequently in relevant literature as promising candidates for a wide range of different applications including drug delivery, theranostic multitools, and nanoreactors. In particular, as nanotransporters for nanomedical applications in vivo, requirements concerning the reproducible manufacturing and reliable size control are extremely high. This Perspective highlights the importance of size control especially in the context of nanomedicine and gives an overview of the theoretical background of amphiphilic self-assembly leading to different preparation methods, where their feasibility of controlling polymersomes’ size is discussed.

Techniques To Control Polymersome Size

The field of biomimicry is embracing the construction of complex assemblies that imitate both biological structure and function Advancements in the design of these mimetics have generated a growing vision for creating an artificial cell or protocell Polymersomes are vesicles that can be made from synthetic, biological, or hybrid polymers and can be used as a model template to build cell-like structures In this perspective, we discuss various areas where polymersomes have been used to mimic cell functions as well as areas in which the synthetic flexibility of polymersomes would make them ideal candidates for a biomembrane mimetic Designing a polymersome that comprehensively displays the behaviors discussed herein has the potential to lead to the development of an autonomous, responsive particle that resembles the intelligence of a biological cell

/pdf/engineering-polymersome-protocells-w65631okal.pdf

Engineering Polymersome Protocells.

Vesicles from Pluronic L121 (PEO5-PPO68-PEO5) triblock copolymers were first stabilized by a permanent interpenetrating polymer network and then gently immobilized onto a glass or mica surface. Fluorescence-labeled micrometer-sized vesicles were visualized with confocal laser scanning microscopy, and smaller sized capsules, around 100 nm, were probed by liquid atomic force microscopy. The immobilized vesicles were weakly attached to a negatively charged surface via negatively charged polyelectrolytes in combination with Mg2+ ions and can be reversibly detached from the surface by slightly elevated temperatures. To illustrate that the immobilized vesicles remain responsive to external stimuli, we show that it is possible to transform their shape from spherical to cylindrical by introducing a second Pluronic, namely, P123 (PEO20-PPO70-PEO20). The detailed transition process has been recorded in real time by confocal laser scanning microscopy. Electron microscopy studies confirmed that a similar morphology change also occurs in the bulk.

Gentle immobilization of nonionic polymersomes on solid substrates.

Vesicles from Pluronic L121 (PEO5−PPO68−PEO5) triblock copolymers were stabilized by an interpenetrating polymer network from pentaerythritol tetraacrylate by UV or thermal initiator induced radical polymerization. Fluorescence labeling, atomic force microscopy, and electron microscopy studies were used to study the morphology of the particles and showed that stable vesicles are formed. The block copolymers are noncovalently trapped in the interpenetrating polyacrylate network. The stabilized vesicles retain their size for more than 1 month at room temperature. Upon cooling, the vesicles reversibly lose block copolymer.

Stabilization of Polymersome Vesicles by an Interpenetrating Polymer Network

Vesicles from Pluronic L121 (PEO5-PPO68-PEO5) triblock copolymers were stabilized against aggregation by Pluronic P85 (PEO26-PPO40-PEO26) micelles. Both the vesicles and the micelles were reinforced by an interpenetrating polymer network from pentaerythritol tetraacrylate (PETA). AFM, electron microscopy and fluorescence labeling studies are used to investigate the morphology of the capsules. The P85 micelles are integrated into the L121 polymersome walls, while both types of Pluronic block copolymer are also non-covalently trapped in their respective interpenetrating acrylate networks. The micelle-containing vesicles retain their size upon heating until at least 33 °C. Upon cooling below room temperature the vesicles reversibly lose block copolymers. It was shown that the double-stabilized vesicles are readily internalized in HeLa and Caco-2 cells.

Pluronic polymersomes stabilized by core cross-linked polymer micelles

Small unilamellar vesicles are formed spontaneously by simple mixing of lamellae-forming diblock copolymer PB10PE10 (PB is a butylene oxide block, and PE an ethylene oxide block) with micelle-forming diblock copolymer PB10PE18. Small angle neutron scattering (SANS) measurements show that the average vesicle radius may be as small as 30 nm with a polydispersity index of 0.15. From the SANS measurements it can also be deduced that the vesicles have a 3.4 nm thick hydrophobic membrane core and a 1.2 nm hydrophilic corona. Furthermore, it is seen that the vesicles coexist with spherical micelles. The influence of the mixing ratio as well as the concentration of the polymeric components is studied. Results of the micelle size, the vesicle size and the shell structure are confirmed by cryo-TEM measurements.

Small monodisperse unilamellar vesicles from binary copolymer mixtures

Two vinyl-terminated bent core-shaped liquid crystalline molecules that exhibit thermotropic antiferroelectric SmCPA phases have been covalently attached onto a hydrogen-terminated silicon(111) sur...

Antonius T. M. Marcelis

Papers

Gentle immobilization of nonionic polymersomes on solid substrates.

Stabilization of Polymersome Vesicles by an Interpenetrating Polymer Network

Pluronic polymersomes stabilized by core cross-linked polymer micelles

Small monodisperse unilamellar vesicles from binary copolymer mixtures

Covalent attachment of bent-core mesogens to silicon surfaces.