Supramolecular Polymer Brushes Grafted via Atom Transfer Radical Polymerization from Surfaces Presenting Non-covalent, Host-Guest Complex-Based Initiators

This paper describes the synthesis of supramolecular polymer brushes via surface-initiated polymerization from adamantane-functionalized initiators that are noncovalently bound to β-cyclodextrin- or cucurbit[7]uril-modified substrates. Surface-initiated atom transfer radical polymerization in aqueous media allowed the growth of various hydrophilic polymer brushes with film thicknesses of up to 40 nm from β-cyclodextrin functionalized surfaces. The adamantane moiety not only forms a host-guest complex with β-cyclodextrin, but also with cucurbit[7]uril, which provides opportunities to study the effect of the binding strength of these supramolecular motifs on the film thickness and grafting density of the resulting polymer brushes. Comparison of supramolecular polymer brushes grown from β-cyclodextrin and cucurbit[7]uril-based noncovalent initiators reveals differences in grafting density that are much smaller than expected based on the differences in the solution binding constant of the corresponding host-guest complexes. Both the β-cyclodextrin as well as the cucurbit[7]uril-anchored supramolecular brushes were remarkably robust toward detachment of the polymer grafts. These observations are attributed to the fact that the rates of formation and dissociation of the host-guest complexes are much faster as compared to diffusion of free, detached polymer chains through the polymer brush film. As a result, the surface-grafted polymer brush presents a steric barrier that prevents detachment of individual chains, and also allows surface-initiated polymerization from substrates to which initiators are bound via putatively weak β-cyclodextrin-based host-guest complexes.

CuBr-mediated surface-initiated controlled radical polymerization in air

Herein, we present a straightforward CuBr-mediated surface-initiated controlled radical polymerization (SI-CRP) method for fabricating polymer brushes using microliter volumes of reaction solution in air and at room temperature. The key advantage of this method is its ability to rapidly grow polymer brushes with oxygen tolerance, driven by the controlled disproportionation of CuI into CuII and Cu0 by CuBr and ligand. We demonstrate the successful preparation of homo-, block, patterned, and wafer-scale polymer brushes. Additionally, the catalyst in CuBr-mediated SI-CRP is reusable, long-lasting, and compatible with various monomers. This work broadens the potential of CuBr for polymer brush growth, making it accessible to both experts and non-experts.

Advances and Prospects in the Study of Spherical Polyelectrolyte Brushes as a Dopant for Conducting Polymers

Owing to their special structure and excellent physical and chemical properties, conducting polymers have attracted increasing attention in materials science. In recent years, tremendous efforts have been devoted to improving the comprehensive performance of conducting polymers by using the technique of "doping." Spherical polyelectrolyte brushes (SPBs) bearing polyelectrolyte chains grafted densely to the surface of core particles have the potential to be novel dopant of conducting polymers not only because of their spherical structure, high grafting density and high charge density, but also due to the possibility of their being applied in printed electronics. This review first presents a summary of the general dopants of conducting polymers. Meanwhile, conducting polymers doped with spherical polyelectrolyte brushes (SPBs) is highlighted, including the preparation, characterization, performance and doping mechanism. It is demonstrated that comprehensive performance of conducting polymers has improved with the addition of SPBs, which act as template and dopant in the synthesis of composites. Furthermore, the applications and future developments of conductive composites are also briefly reviewed and proposed, which would draw more attention to this field.

Supramolecular Polymer Brushes Grown by Surface-Initiated Atom Transfer Radical Polymerization from Cucurbit[7]uril-based Non-Covalent Initiators

Polymer brushes are densely grafted, chain end-tethered assemblies of polymers that can be produced via surface-initiated polymerization. Typically, this is accomplished using initiators or chain transfer agents that are covalently attached to the substrate. This manuscript reports an alternative route towards polymer brushes, which involves the use of non-covalent cucurbit[7]uril-adamantane host-guest interactions to surface-immobilize initiators for atom transfer radical polymerization. These non-covalent initiators can be used for the surface-initiated atom transfer radical polymerization of a variety of water-soluble methacrylate monomers to generate supramolecular polymer brushes with film thicknesses of more than 100 nm. The non-covalent nature of the initiator also allows facile access to patterned polymer brushes, which can be produced in straightforward fashion by drop-casting a solution of the initiator-modified guest molecules onto a substrate that presents the cucurbit[7]uril host.

Modular and Substrate-Independent Grafting-To Procedure for Functional Polymer Coatings

The ability to tailor polymer brush coatings to the last nanometer has arguably placed them among the most powerful surface modification techniques currently available. Generally, the synthesis procedures for polymer brushes are designed for a specific surface type and monomer functionality and cannot be easily employed otherwise. Herein, we describe a modular and straightforward two-step grafting-to approach that allows introduction of polymer brushes of a desired functionality onto a large range of chemically different substrates. To illustrate the modularity of the procedure, gold, silicon oxide (SiO₂), and polyester-coated glass substrates were modified with five different block copolymers. In short, the substrates were first modified with a universally applicable poly(dopamine) primer layer. Subsequently, a grafting-to reaction was performed on the poly(dopamine) films using five distinct block copolymers, all of which contained a short poly(glycidyl methacrylate) segment and longer segment of varying chemical functionality. Ellipsometry, X-ray photoelectron spectroscopy, and static water contact angle measurements confirmed successful grafting of all five block copolymers to the poly(dopamine)-modified gold, SiO₂, and polyester-coated glass substrates. In addition, our method was used to provide direct access to binary brush coatings, by simultaneous grafting of two different polymer materials. The ability to synthesize binary brush coatings further adds to the versatility of our approach and paves the way toward production of novel multifunctional and responsive polymer coatings.

Recent trends in MXene-based material for biomedical applications

MXene is a magical class of 2D nanomaterials and emerging in many applications in diverse fields. Due to the multiple advantageous characteristics of its fundamental components, such as structural, physicochemical, optical, and occasionally even biological characteristics. However, it is limited in the biomedical industry due to poor physiological stability, decomposition rate, and lack of controlled and sustained drug release. These limitations can be overcome when MXene forms composites with other 2D materials. The efficiency of pure MXene in biomedicine is inferior to that of MXene-based composites. The availability of functionality on the exterior part of MXene has a key role in the modification of their surface and their characteristics. This review provides an extensive discussion on the synthesizing of MXene and the role of the surface functionalities on the efficiency of MXene. In addition, a detailed discussion of the biomedical applications of MXene, including antibacterial activity, regenerative medicine, CT scan capability, drug delivery, diagnostics, MRI and biosensing capability. Furthermore, an outline of the future problems and challenges of MXene-based materials for biomedical applications was narrated. Thus, these salient features showcase the potential of MXene-based material and will be a breakthrough in biomedical applications in the near future.

Melanin-like nanoparticles: advances in surface modification and tumour photothermal therapy

Currently, tumor treatments are characterized by intelligence, diversity and personalization, but the therapeutic reagents used are often limited in clinical efficacy due to problems with water solubility, targeting, stability and multidrug resistance. To remedy these shortcomings, the application of multifunctional nanotechnology in the biomedical field has been widely studied. Synthetic melanin nanoparticles (MNPs) surfaces which contain highly reactive chemical groups such as carboxyl, hydroxyl and amine groups, can be used as a reaction platform on which to graft different functional components. In addition, MNPs easily adhere to substrate surface, and serve as a secondary reaction platform to modify it. The multifunctionality and intrinsic biocompatibility make melanin-like nanoparticles promising as a multifunctional and powerful nanoplatform for oncological applications. This paper first reviews the preparation methods, polymerization mechanisms and physicochemical properties of melanin including natural melanin and chemically synthesized melanin to guide scholars in MNP-based design. Then, recent advances in MNPs especially synthetic polydopamine (PDA) melanin for various medical oncological applications are systematically and thoroughly described, mainly focusing on bioimaging, photothermal therapy (PTT), and drug delivery for tumor therapy. Finally, based on the investigated literature, the current challenges and future directions for clinical translation are reasonably discussed, focusing on the innovative design of MNPs and further elucidation of pharmacokinetics. This paper is a timely and comprehensive and detailed study of the progress of MNPs in tumor therapy, especially PTT, and provides ideas for the design of personalized and customizable oncology nanomedicines to address the heterogeneity of the tumor microenvironment.

Preparation of a Novel CO2-Responsive Polymer/Multiwall Carbon Nanotube Composite

A CO2-responsive composite of multiwall carbon nanotube (MWCNT) coated with polydopamine (PDA) and polydimethylamino-ethyl methacrylate (PDMAEMA) was prepared. The PDA was first self-polymerized on the surface of carbon nanotube. 2-bromoisobutyryl bromide (BiBB) was then immobilized by PDA and then initiated the ATRP of DMAEMA on the carbon nanotube surface. The resulting composite was characterized by Fourier-transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM). The CO2-responsive test was performed by bubbling CO2 into the mixture of MWCNT-PDA-PDMAEMA composite in water. A well-dispersed solution was obtained and the UV-Vis transmittance decreased dramatically. This is attributed to the reaction between PDMAEMA and CO2. The formation of ammonium bicarbonates on the surface of carbon nanotubes leads to the separation of nanotube bundles. This process can be reversed as the removal of CO2 by bubbling N2.

Zwitterionic PMCP-functionalized titanium surface resists protein adsorption, promotes cell adhesion, and enhances osteogenic activity

Titanium (Ti) has excellent biocompatibility and corrosion resistance and is widely used as a biomedical material for orthopedic implants. However, the bare Ti surface limits cell adhesion without biological activity and promotes unnecessary protein adsorption, which can activate the coagulation pathway with blood-contacting devices. To improve the antifouling and biological activity of Ti, zwitterionic poly[2-(methacryloyloxy)ethyl choline phosphate] (PMCP) was used to modify the Ti surface via surface-initiated atom transfer radical polymerization. The Ti-PMCP surface reduced bovine serum albumin and fibrinogen adsorption owing to the zwitterionic antifouling property. Ti-PMCP is involved in the unique interaction between PMCP on the Ti surface and phosphate choline on cell membranes, and therefore, the Ti-PMCP surface can promote the adhesion and proliferation of MC3T3-e1 cells and bone marrow mesenchymal cells (BMSCs). In addition, the Ti-PMCP surface was effective in promoting the osteogenic differentiation of MC3T3-e1 cells and BMSCs because the phosphate group in MCP can stimulate osteogenic signaling pathways. Therefore, the PMCP-modified Ti surface can resist protein adsorption and promote the adhesion, proliferation, and differentiation of osteoblast-related cells and has great potential in bone tissue engineering.

Drug Release from Thermo-Responsive Polymer Brush Coatings to Control Bacterial Colonization and Biofilm Growth on Titanium Implants

Despite decades of biomedical advances, the colonization of implant devices with bacterial biofilms is still a leading cause of implant failure. Clearly, new strategies and materials that suppress both initial and later stage bacterial colonization are required in this context. Ideal would be the implementation of a bactericidal functionality in the implants that is temporally and spatially triggered in an autonomous fashion at the infection site. Herein, the fabrication and validation of functional titanium-based implants with triggered antibiotic release function afforded via an intelligent polymer coating is reported. In particular, thermo-responsive poly(di(ethylene glycol) methyl ether methacrylate) (PDEGMA) brushes on titanium implants synthesized via a surface-initiated atom transfer radical polymerization with activators regenerated through the electron transfer technique (ARGET ATRP) allows for a controlled and thermally triggered release of the antibiotic levofloxacin at the wound site. Antibiotic loaded brushes are investigated as a function of thickness, loading capacity for antibiotics, and temperature. At temperatures of the infection site >37 °C the lower critical solution temperature behavior of the brushes afforded the triggered release. Hence, in addition to the known antifouling effects, the PDEGMA coating ensured enhanced bactericidal effects, as demonstrated in initial in vivo tests with rodents infected with Staphylococcus aureus.

Advances, Challenges, and Opportunities of Poly(γ-butyrolactone)-Based Recyclable Polymers

The discovery and prosperous growth of synthetic polymers have presented both significant advantages and daunting challenges in the last century. To address the issues of environmental pollution and fossil consumption, recyclable, degradable, and/or biobased polymers have been given much attention in the polymer science community. This viewpoint focuses on the emerging fully chemical recyclable poly(γ-butyrolactone)-based polymers. The breakthrough from nonpolymerizable to efficient polymerization is highlighted by the benefits of the development of a series of catalysis for ring-opening polymerization of γ-butyrolactone. Subsequently, the design of γ-butyrolactone derivatives and synthesis of more recyclable polymers are summarized together with the discussions about the structure and property relationship. Finally, the remaining challenges and promising opportunities are suggested in order to provide insights into the further direction for sustainable polymers.

Polymer brush growth by oxygen-initiated RAFT polymerization on various substrates

We developed a user-friendly method for growing polymer brushes on various substrates in the presence of air by O2-SI-RAFT polymerization and mussel-inspired surface chemistry. In particular, PHEMA brushes grew to 856 nm on the titanium substrate.

Correlation between Tribological Properties and the Quantified Structural Changes of Lysozyme on Poly (2-hydroxyethyl methacrylate) Contact Lens

The ocular discomfort is the leading cause of contact lens wear discontinuation. Although the tear proteins as a lubricant might improve contact lens adaptation, some in vitro studies suggested that the amount of adsorbed proteins could not simply explain the lubricating performance of adsorbed proteins. The purpose of this study was to quantify the structural changes and corresponding ocular lubricating properties of adsorbed protein on a conventional contact lens material, poly (2-hydroxyethyl methacrylate) (pHEMA). The adsorption behaviors of lysozyme on pHEMA were determined by the combined effects of protein–surface and protein–protein interactions. Lysozyme, the most abundant protein in tear, was first adsorbed onto the pHEMA surface under widely varying protein solution concentrations to saturate the surface, with the areal density of the adsorbed protein presenting different protein–protein effects within the layer. These values were correlated with the measured secondary structures, and corresponding friction coefficient of the adsorbed and protein covered lens surface, respectively. The decreased friction coefficient value was an indicator of the lubricated surfaces with improved adaptation. Our results indicate that the protein–protein effects help stabilize the structure of adsorbed lysozyme on pHEMA with the raised friction coefficient measured critical for the innovation of contact lens material designs with improved adaptation.

Fabrication of 2D Block Copolymer Brushes via a Polymer-Single-Crystal-Assisted-Grafting-to Method

Block copolymer brushes are of great interest due to their rich phase behavior and value-added properties compared to homopolymer brushes. Traditional synthesis involves grafting-to and grafting-from methods. In this work, a recently developed "polymer-single-crystal-assisted-grafting-to" method is applied for the preparation of block copolymer brushes on flat glass surfaces. Triblock copolymer poly(ethylene oxide)-b-poly(l-lactide)-b-poly(3-(triethoxysilyl)propyl methacrylate) (PEO-b-PLLA-b-PTESPMA) is synthesized with PLLA as the brush morphology-directing component and PTESPMA as the anchoring block. PEO-b-PLLA block copolymer brushes are obtained by chemical grafting of the triblock copolymer single crystals onto a glass surface. The tethering point and overall brush pattern are determined by the single crystal morphology. The grafting density is calculated to be ≈0.36 nm^-2 from the atomic force microscopy results and is consistent with the theoretic calculation based on the PLLA crystalline lattice. This work provides a new strategy to synthesize well-defined block copolymer brushes.

Boosting or moderating surface-initiated Cu(0)-mediated controlled radical polymerization with external additives

External additives regulate the copper disproportionation/comproportionation equilibrium to control polymer brush growth in surface-initiated Cu(0)-mediated controlled radical polymerization.