Chain Length and Grafting Density Dependent Enhancement in the Hydrolysis of Ester-Linked Polymer Brushes

Colloidal Rod-Like Particles with Temperature-Driven Tunable Interactions

Temperature-sensitive rod-like colloidal particles were synthesized by grafting a temperature-responsive polymer, poly(2-(dimethylamino)ethyl methacrylate) (PDMA), on the surface of high aspect ratio silica rods by surface-initiated atom transfer radical polymerization. The stability of the grafted polymer on the surface of the particles in aqueous solutions was found to deteriorate with time, leading to a gradual decrease of the polymer content of the hybrid colloids, which was attributed to the mechanically activated hydrolysis of the labile bonds at the polymer-silica interface. The polymer degrafting was significantly suppressed by first growing a hydrophobic poly(methyl methacrylate) block onto the particle surface to act as a barrier layer for the penetration of water molecules at the polymer-particle interface, followed by chain-extension with the hydrophilic PDMA chains. Dynamic light scattering, microscopy, and rheological measurements revealed that the PDMA block conferred a temperature-responsive behavior to the rod-like particles, which formed aggregates at temperatures above the lower critical solution temperature (LCST) of the polymer. However, in contrast to their spherical counterparts, the polymer-grafted rod-like particles did not exhibit complete thermo-reversibility upon lowering the solution temperature below the LCST of PDMA, which was reflected by different values of the diffusion coefficient for the heating and cooling cycles, indicating an irreversible rod particle aggregation upon increasing the temperature.

Entropy-Enhanced Mechanochemical Activation for Thermal Degrafting of Surface-Tethered Dry Polystyrene Brushes

Dry polymer brushes have attracted great attention because of their potential utility in regulating interface properties. However, it is still unknown whether dry polymer brushes will exhibit degrafting behavior as a result of thermal annealing. Herein, a study of the conformational entropy effect on thermal degrafting of dry polystyrene (PS) brushes is presented. For PS brushes with an initial grafting density (σ_pⁱⁿⁱ) of 0.61 nm^-2, degrafting behavior was observed at 393 K, and the equilibrium σ_p was approximately 0.14 nm^-2 at 413 K. However, for brushes with σ_pⁱⁿⁱ ≤ 0.14 nm^-2, thermal degrafting was not observed even if the temperature was increased to 453 K. Furthermore, we found that the degrafting rate was faster for PS brushes with higher σ_pⁱⁿⁱ and higher molecular weights when σ_pⁱⁿⁱ > 0.14 nm^-2. Our findings confirmed that degrafting is a mechanochemical activation process driven by tension imposed on bonds that anchor the chains to the surface, and the process is amplified by conformational entropy.

Synthetic strategies to enhance the long-term stability of polymer brush coatings

High-density, end-anchored macromolecules that form so-called polymer brushes are popular components of bio-inspired surface coatings. In a bio-memetic approach, they have been utilized to reduce friction, repel contamination and control...

Molecular bottlebrush with pH-responsive cleavable bonds as a unimolecular vehicle for anticancer drug delivery

Drug delivery systems with targeted and smart properties have emerged as an efficient strategy to overcome the challenges of cancer chemotherapy such as toxic side effects and the development of multidrug resistance. In this study, a biocompatible bottlebrush polymer poly((3-(2-bromo-2-methylpropionate)propyldimethylsilyloxy)ethyl methacrylate)-graft-poly(2-methacryloyloxyethyl phosphorylcholine) P(BIBS-EMA)-g-PMPC with pH-responsive silanol cleavable bond was designed and developed for delivery of doxorubicin. A549 cell line of human lung carcinoma was tested. The synthesized bottlebrush polymer was analyzed and characterized via Fourier transform infrared spectroscopy, FTIR, nuclear magnetic resonance spectroscopy, ¹H NMR, gel permeation chromatography, GPC, dynamic laser light scattering, DLS, and static laser light scattering, SLS, techniques. The cleavage process was also precisely studied to confirm the pH-responsiveness of such bottlebrush polymers. In vitro loading and release studies of doxorubicin as a model drug were examined and the results showed a pH-dependent release manner with a twice higher release rate under cancerous tissue conditions compared to standard physiological conditions. MTT cytotoxicity assay was also performed to prove the biocompatibility of the designed polymeric platform on healthy human cells. Due to the presence of bio-inspired poly(2-methacryloyloxyethyl phosphorylcholine) side chains in the prepared bottlebrush polymer, the formed polymer-drug complex could also exhibit effective internalization into tumor cells. These facts further support the potential use of this carrier in drug delivery applications and for further in vivo studies.

Degrafting of Polymer Brushes by Exposure to Humid Air

It is well-known that polymer brushes can degraft in aqueous liquids. Here we show that brushes can deteriorate in humid air too. We observe that the detachment rate of the brushes increases with increasing relative humidity and hydrophilicity of the brushes. We relate this to the increase in water absorption as these parameters are increased. Our results imply that protective measures that are at present being developed for applications of brushes in liquids will also be key in enabling the long-term storage and utilization of hydrophilic brushes in air.

Pegylated Metal-Phenolic Networks for Antimicrobial and Antifouling Properties

Metal-phenolic networks (MPNs) have recently attracted great interest in material chemistry and biomaterials because of their biocompatible, versatile, and multifunctional properties. In this paper, we describe a facile method for preparation of a designable antifouling, antimicrobial, and substrate-independent coating assembled from the coordination of metal ions and catecholic groups. Hydrophilic and catecholic polymers were synthesized by copolymerization of dopamine methacrylamide (DMA) and poly(ethylene glycol)methyl methacrylate (PEGMA) to afford p(PEGMA- co-DMA). To investigate the assembly and formation of MPN films, two different metal ions, that is, ferrous (Fe^II) and ferric (Fe^III) ions, to react with p(PEGMA- co-DMA) were compared. The binding constants between iron ions and p(PEGMA- co-DMA) have been investigated by ultraviolet-visible spectroscopy (UV-vis). Measurements with atomic force microscopy, contact angle goniometer, and X-ray photoelectron spectroscopy (XPS) were carried out to quantitatively analyze the surface morphology, wettability, and interfacial elemental compositions of coatings, respectively. Moreover, ellipsometric measurements were performed to obtain the film thickness and grafting density. In addition, the pH-responsive property of the MPN films was investigated at different pH values, showing fast disassembly of the networks at low pH. The antifouling properties of the obtained coatings were analyzed by exposing them to bacteria of Escherichia coli and Staphylococcus epidermidis and NIH-3T3 fibroblasts under observation of fluorescence microscopy and cell imaging analysis. The findings suggest that the MPN from complexation of p(PEGMA- co-DMA) and metal ions provides excellent antifouling, pH-responsive, and biocompatible properties on a wide range of substrates. Furthermore, the released iron ions can effectively suppress the growth of bacteria. Accordingly, the new coating architecture offers a universal feature to control surface properties and functionalization for various applications.

Ultrahighly Charged Amphiphilic Polymer Brushes with Super-Antibacterial and Self-Cleaning Capabilities

Bacterial infection on biomaterial devices and the subsequent medical risks pose a serious problem in both human healthcare and industrial applications, resulting in a prevalence of various antimicrobial materials. Cationic amphiphilic polymer has been proposed to be a new generation of efficient antibacterial material, but the surface modified by such types of polymers still shows incomplete bactericidal ability and easily contaminated performance. With this in mind, a novel kind of geminized cationic amphiphilic polymer brush surface has been developed in this study, presenting a complete antibacterial activity, because of the synergistic biocidal effect of electrostatic and hydrophobic interactions, as well as the minimized contact area between bacteria and polymer surface. A structure self-adjustment process of polymer brush construction has been proposed, in which the mutual interference among cationic head groups can be avoided and the electrostatic repulsion and hydrophobic attraction can be balanced, in the formation of a smooth and tight surface. A self-cleaning capability of polymer surface has been performed via hydrolysis and degradation, maintaining a high antibacterial activity. Therefore, we provide a facile and possible manipulation strategy to fabricate super-antibacterial and self-cleaning surfaces in a wide range of biomedical and industrial applications.

Visualization of Mechanochemically-Assisted Degrafting of Surface-Tethered Poly(Acrylic Acid) Brushes

We report visualization of mechanochemically assisted degrafting of surface-tethered poly(acrylic acid) (PAA) brushes in a basic aqueous buffer at nanometer to micrometer length scale by monitoring changes in local etching of silicon substrates. PAA brushes were prepared by surface-initiated atom transfer radical polymerization and incubated in 0.1 M ethanolamine buffer (pH 9.0) with 0.5 M NaCl. Morphological changes of the underlying substrates were monitored by scanning electron microscopy and atomic force microscopy. The appearance of regular-shaped pits indicated etching of the substrate, and both their number and size grew with increasing incubation time. We compared the etching behaviors for PAA, poly(methyl methacrylate) (PMMA), and poly(poly(ethylene glycol) methacrylate) (PPEGMA) brushes grafted on silicon substrates. After incubation for 7 days, the substrate of PMMA brush remained intact. In PAA brush systems, we detected the formation of a few large pits whose size grew in time. Many pits showed up on the substrate of PPEGMA brush but with substantially smaller size compared to PAA. Our findings suggest that hydrophobicity and stability of the grafted polymers play an important role in the morphological changes of the underlying silicon substrates under given incubation conditions.

Optimisation of grafting of low fouling polymers from three-dimensional scaffolds via surface-initiated Cu(0) mediated polymerisation

Well-controlled low fouling polymers brushes were grafted from the surface of biodegradable electrospun fibres for advanced tissue engineering applications.

Reduced Lateral Confinement and Its Effect on Stability in Patterned Strong Polyelectrolyte Brushes

The stability of strong polyelectrolyte brushes (PEBs) was studied in bulk and in patterned structures. Thick PEBs of poly([(2-methacryloyloxy)ethyl]trimethylammonium chloride) with thicknesses >100 nm were synthesized using single electron transfer living radical polymerization. Brush patterning was identified using deep-ultraviolet photolithography by means of either a top-down (TD) or bottom-up (BU) method, with features as small as 200 nm. The brushes were soaked in water under a range of pH or temperature conditions, and the hydrolysis was monitored through dry-state ellipsometry and atomic force microscopy measurements. BU patterns showed reduced degrafting for smaller patterns, which was attributed to increased stress relaxation at such dimensions. In contrast to the already relaxed BU-patterned brush, a TD-patterned brush possesses perpendicular structures that result from the use of orthogonal lithography. It was found that the TD process induces cross-linking on the sidewall, which subsequently fortifies the sidewall materials. This modification of the polymer brushes hindered the stress relaxation of the patterns, and the degrafting trends became irrelevant to the pattern sizes. With proper tuning, the cross-linking on the sidewall was minimized and the degrafting trends were again relaxation-dependent.

Highly Selective Capture Surfaces on Medical Wires for Fishing Tumor Cells in Whole Blood

The detection of circulating tumor cells (CTCs) in the blood of cancer patients is a challenging task. CTCs are, especially at the early stages of cancer development, extremely rare cells hidden in a vast background of regular blood cells. We describe a new strategy for the isolation of CTCs from whole blood. The key component is a medical wire coated with a multilayer assembly that allows highly specific capture of EpCAM (epithelial cell adhesion molecule) positive CTCs from blood. The assembly is generated in a layer-by-layer fashion through photochemically induced C,H insertion reactions and consists of a protective layer, which shields the contacting solution from the metal, a protein resistant layer, which prevents nonspecific interactions with proteins and a layer containing the EpCAM antibodies. In vitro experiments show that these surfaces can capture tumor cells from whole blood with enrichment factors (specifically vs nonspecifically bound cells) of up to about 3000 compared to the number of leucocytes in the blood. The purity of the isolated cells is greater than 90%. After "fishing" them from the blood, the cells, still bound to the wire, can be genetically analyzed. This demonstrates that this strategy might prove useful for next generation sequencing.