Cylindrical Zwitterionic Particles via Interpolyelectrolyte Complexation on Molecular Polymer Brushes

Effect of Polyelectrolyte Charge Density on the Linear Viscoelastic Behavior and Processing of Complex Coacervate Adhesives

It is well-known that the phase behavior and physicochemical and adhesive properties of complex coacervates are readily tuneable with the salt concentration of the medium. For toxicity reasons, however, the maximum applicable salt concentration in biomedical applications is typically low. Consequently, other strategies must be implemented in order to optimize the properties of the resulting complex coacervates. In this work, the effect of the charge density of a strong polyanion on the properties of complex coacervates was studied. To control this charge density, statistical anionic/charge-neutral hydrophilic copolymers were synthesized by means of an elegant protection/deprotection strategy and subsequently complexed with a strong polycation. The resulting complexes were observed to have an increasing water content as well as faster relaxation dynamics, with either increasing salt concentration or decreasing charge density. Time-salt and time-salt-charge density superpositions could be performed and showed that the relaxation mechanism of the complex coacervates remained unchanged. When the charge density was decreased, lower salt concentration complexes became suitable for viscoelastic adhesion with improved injectability. Such complex coacervates are promising candidates for injectable biomedical adhesives.

Precision nanoengineering for functional self-assemblies across length scales

As nanotechnology continues to push the boundaries across disciplines, there is an increasing need for engineering nanomaterials with atomic-level precision for self-assembly across length scales, i.e., from the nanoscale to the macroscale. Although molecular self-assembly allows atomic precision, extending it beyond certain length scales presents a challenge. Therefore, the attention has turned to size and shape-controlled metal nanoparticles as building blocks for multifunctional colloidal self-assemblies. However, traditionally, metal nanoparticles suffer from polydispersity, uncontrolled aggregation, and inhomogeneous ligand distribution, resulting in heterogeneous end products. In this feature article, I will discuss how virus capsids provide clues for designing subunit-based, precise, efficient, and error-free self-assembly of colloidal molecules. The atomically precise nanoscale proteinic subunits of capsids display rigidity (conformational and structural) and patchy distribution of interacting sites. Recent experimental evidence suggests that atomically precise noble metal nanoclusters display an anisotropic distribution of ligands and patchy ligand bundles. This enables symmetry breaking, consequently offering a facile route for two-dimensional colloidal crystals, bilayers, and elastic monolayer membranes. Furthermore, inter-nanocluster interactions mediated via the ligand functional groups are versatile, offering routes for discrete supracolloidal capsids, composite cages, toroids, and macroscopic hierarchically porous frameworks. Therefore, engineered nanoparticles with atomically precise structures have the potential to overcome the limitations of molecular self-assembly and large colloidal particles. Self-assembly allows the emergence of new optical properties, mechanical strength, photothermal stability, catalytic efficiency, quantum yield, and biological properties. The self-assembled structures allow reproducible optoelectronic properties, mechanical performance, and accurate sensing. More importantly, the intrinsic properties of individual nanoclusters are retained across length scales. The atomically precise nanoparticles offer enormous potential for next-generation functional materials, optoelectronics, precision sensors, and photonic devices.

Toward Effective and Adsorption-Based Antifouling Zipper Brushes: Effect of pH, Salt, and Polymer Design

The undesired spontaneous deposition and accumulation of matter on surfaces, better known as fouling, is a problematic and often inevitable process plaguing a variety of industries. This detrimental process can be reduced or even prevented by coating surfaces with a dense layer of end-grafted polymer: a polymer brush. Producing such polymer brushes via adsorption presents a very attractive technique, as large surfaces can be coated in a quick and simple manner. Recently, we introduced a simple and scalable two-step adsorption strategy to fabricate block copolymer-based antifouling coatings on hydrophobic surfaces. This two-step approach involved the initial adsorption of hydrophobic-charged diblock copolymer micelles acting as a primer, followed by the complexation of oppositely charged-antifouling diblock copolymers to form the antifouling brush coating. Here, we significantly improve this adsorption-based zipper brush via systematic tuning of various parameters, including pH, salt concentration, and polymer design. This study reveals several key outcomes. First of all, increasing the hydrophobic/hydrophilic block ratio of the anchoring polymeric micelles (i.e., decreasing the hydrophilic corona) promotes adsorption to the surface, resulting in the most densely packed, uniform, and hydrophilic primer layers. Second, around a neutral pH and at a low salt concentration (1 mM), complexation of the weak polyelectrolyte (PE) blocks results in brushes with the best antifouling efficacy. Moreover, by tuning the ratio between these PE blocks, the brush density can be increased, which is also directly correlated to the antifouling performance. Finally, switching to different antifouling blocks can increase the internal density or strengthen the bound hydration layer of the brush, leading to an additional enhancement of the antifouling properties (>99% lysozyme, 87% bovine serum albumin).

One-Pot Synthesis of Strong Anionic/Charge-Neutral Amphiphilic Block Copolymers

Despite the ever more versatile polymerization techniques that are becoming available, the synthesis of macromolecules with tailored functionalities can remain a lengthy endeavor. This becomes more conspicuous when the implementation of incompatible chemistries (i.e., strong polyelectrolytes) within sequence-controlled polymers is desired, often requiring (i) polymerization, (ii) chain extension, and (iii) postpolymerization modification. Herein, we explore the production of strong anionic/charge-neutral block copolymers (BCPs) in a one-pot fashion. This straightforward three-step process includes the synthesis of a macroinitiator and chain extension via rapid and efficient photomediated atom transfer radical polymerization, followed by in situ deprotection to expose the polyanionic domains. The resulting BCPs, which are strong amphiphiles by nature, are capable of self-assembly in aqueous media, as evidenced by dynamic light scattering, small-angle X-ray scattering, ζ-potential measurements, and transmission electron microscopy. We further demonstrate the versatility of our methodology by producing several BCPs through sampling of a single reaction mixture, enabling the straightforward production of strong polymer amphiphiles.

Scalable Fabrication of Reversible Antifouling Block Copolymer Coatings via Adsorption Strategies

Fouling remains a widespread challenge as its nonspecific and uncontrollable character limits the performance of materials and devices in numerous applications. Although many promising antifouling coatings have been developed to reduce or even prevent this undesirable adhesion process, most of them suffer from serious limitations, specifically in scalability. Whereas scalability can be particularly problematic for covalently bound antifouling polymer coatings, replacement by physisorbed systems remains complicated as it often results in less effective, low-density films. In this work, we introduce a two-step adsorption strategy to fabricate high-density block copolymer-based antifouling coatings on hydrophobic surfaces, which exhibit superior properties compared to one-step adsorbed coatings. The obtained hybrid coating manages to effectively suppress the attachment of both lysozyme and bovine serum albumin, which can be explained by its dense and homogeneous surface structure as well as the desired polymer conformation. In addition, the intrinsic reversibility of the adhered complex coacervate core micelles allows for the successful triggered release and regeneration of the hybrid coating, resulting in full recovery of its antifouling properties. The simplicity and reversibility make this a unique and promising antifouling strategy for large-scale underwater applications.

Polyelectrolyte Complexes from Oppositely Charged Filamentous Viruses

Here, we present an explorative study on a new type of polyelectrolyte complex made from chemically modified filamentous fd viruses. The fd virus is a semiflexible rod-shaped bacteriophage with a length of 880 nm and a diameter of 6.6 nm, which has been widely used as a well-defined model system of colloidal rods to investigate phase, flow, and other behavior. Here, chemically modified viruses have been prepared to obtain two types with opposite electrical charges in addition to a steric stabilization layer by poly(ethylene glycol) (PEG) grafting. The complex formation of stoichiometric mixtures of these oppositely charged viruses is studied as a function of virus and salt concentration. Furthermore, static light scattering measurements show a varying, strong increase in scattering intensity in some samples without visual macroscopic complex formation. Finally, the results of the complex formation are rationalized by comparing to model calculations on the pair interaction potential between oppositely charged viruses.

Strong Anionic/Charge-Neutral Block Copolymers from Cu(0)-Mediated Reversible Deactivation Radical Polymerization

Despite recent developments in controlled polymerization techniques, the straightforward synthesis of block copolymers that feature both strong anionic and charge-neutral segments remains a difficult endeavor. In particular, solubility issues may arise during the direct synthesis of strong amphiphiles and typical postpolymerization deprotection often requires harsh conditions. To overcome these challenges, we employed Cu(0)-mediated reversible deactivation radical polymerization (Cu(0)-RDRP) on a hydrophobic isobutoxy-protected 3-sulfopropyl acrylate. Cu(0)-RDRP enables the rapid synthesis of the polymer, reaching high conversions and low dispersities while using a single solvent system and low amounts of copper species. These macromolecules are straightforward to characterize and can subsequently be deprotected in a mild yet highly efficient fashion to expose their strongly charged nature. Furthermore, a protected sulfonate segment could be grown from a variety of charge-neutral macroinitiators to produce, after the use of the same deprotection chemistry, a library of amphiphilic, double-hydrophilic as well as thermoresponsive block copolymers (BCPs). The ability of these various BCPs to self-assemble in aqueous media was further studied by dynamic light scattering, ζ-potential measurements as well as atomic force and electron microscopy.

Molecular polymer bottlebrushes in nanomedicine: therapeutic and diagnostic applications

Molecular polymer bottlebrushes are densely grafted, individual macromolecules with nanoscale proportions. The last decade has seen an increased focus on this material class, especially in nanomedicine and for biomedical applications. This Feature Article provides an overview of major developments in this area to highlight the many opportunities that these polymer architectures bring to nano-bio research. The article covers aspects of bottlebrush synthesis and summarises their use in drug and gene delivery, imaging, as theranostics and as prototype materials to correlate nanoparticle structure and composition to biological function and behaviour. Areas for future research in this area are discussed.