Surface-Initiated Polymerization with an Initiator Gradient: A Monte Carlo Simulation.

Due to the difficulty of accurately characterizing properties such as the molecular weight (Mn) and grafting density (σ) of gradient brushes (GBs), these properties are traditionally assumed to be uniform in space to simplify analysis. Applying a stochastic reaction model (SRM) developed for heterogeneous polymerizations, we explored surface-initiated polymerizations (SIPs) with initiator gradients in lattice Monte Carlo simulations to examine this assumption. An initial exploration of SIPs with 'homogeneously' distributed initiators revealed that increasing σ slows down the polymerization process, resulting in polymers with lower molecular weight and larger dispersity (D) for a given reaction time. In SIPs with an initiator gradient, we observed that the properties of the polymers are position-dependent, with lower Mn and larger D in regions of higher σ, indicating the non-uniform properties of polymers in GBs. The results reveal a significant deviation in the scaling behavior of brush height with σ compared to experimental data and theoretical predictions, and this deviation is attributed to the non-uniform Mn and D.

Growth of Double-Network Tough Hydrogel Coatings by Surface-Initiated Polymerization.

Hydrogel coatings exhibit versatile applications in biomedicine, flexible electronics, and environmental science. However, current coating methods encounter challenges in simultaneously achieving strong interfacial bonding, robust hydrogel coatings, and the ability to coat substrates with controlled thickness. This paper introduces a novel approach to grow a double-network (DN) tough hydrogel coating on various substrates. The process involves initial substrate modification using a silane coupling agent, followed by the deposition of an initiator layer on its surface. Subsequently, the substrate is immersed in a DN hydrogel precursor, where the coating grows under ultraviolet (UV) illumination. Precise control over the coating thickness is achieved by adjusting the UV illumination duration and the initiator quantity. The experimental measurement of adhesion reveals strong bonding between the DN hydrogel coating and diverse substrates, reaching up to 1012.9 J/m2 between the DN hydrogel coating and a glass substrate. The lubricity performance of the DN hydrogel coating is experimentally characterized, which is dependent on the coating thickness, applied pressure, and sliding velocity. The incorporation of 3D printing technology into the current coating method enables the creation of intricate hydrogel coating patterns on a flat substrate. Moreover, the hydrogel coating's versatility is demonstrated through its effective applications in oil-water separation and antifogging glasses, underscoring its wide-ranging potential. The robust DN hydrogel coating method presented here holds promise for advancing hydrogel applications across diverse fields.

Preparation of Protein A Membranes Using Propargyl Methacrylate-Based Copolymers and Copper-Catalyzed Alkyne-Azide Click Chemistry.

The development of convective technologies for antibody purification is of interest to the bioprocessing industries. This study developed a Protein A membrane using a combination of graft polymerization and copper(I)-catalyzed alkyne-azide click chemistry. Regenerated cellulose supports were functionalized via surface-initiated copolymerization of propargyl methacrylate (PgMA) and poly(ethylene glycol) methyl ether methacrylate (PEGMEMA300), followed by a reaction with azide-functionalized Protein A ligand. The polymer-modified membranes were characterized using attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR), gravimetric analysis, and permeability measurements. Copolymer composition was determined using the Mayo-Lewis equation. Membranes clicked with azide-conjugated Protein A were evaluated by measuring static and dynamic binding (DBC10) capacities for human immunoglobulin G (hIgG). Copolymer composition and degree of grafting were found to affect maximum static binding capacities, with values ranging from 5 to 16 mg/mL. DBC10 values did not vary with flow rate, as expected of membrane adsorbers.

Continuous Ultrathin Zwitterionic Covalent Organic Framework Membrane Via Surface-Initiated Polymerization Toward Superior Water Retention.

Efficient construction of proton transport channels in proton exchange membranes maintaining conductivity under varied humidity is critical for the development of fuel cells. Covalent organic frameworks (COFs) hold great potential in providing precise and fast ion transport channels. However, the preparation of continuous free-standing COF membranes retaining their inherent structural advantages to realize excellent proton conduction performance is a major challenge. Herein, a zwitterionic COF material bearing positive ammonium ions and negative sulphonic acid ions is developed. Free-standing COF membrane with adjustable thickness is constructed via surface-initiated polymerization of COF monomers. The porosity, continuity, and stability of the membranes are demonstrated via the transmission electron microscopy (TEM), atomic force microscopy (AFM), and scanning electron microscopy (SEM) characterization. The rigidity of the COF structure avoids swelling in aqueous solution, which improves the chemical stability of the proton exchange membranes and improves the performance stability. In the higher humidity range (50-90%), the prepared zwitterionic COF membrane exhibits superior capability in retaining the conductivity compared to COF membrane merely bearing sulphonic acid group. The established strategy shows the potential for the application of zwitterionic COF in the proton exchange membrane fuel cells.

Spatiotemporal Control over Polynucleotide Brush Growth on DNA Origami Nanostructures.

DNA nanotechnology provides an approach to create precise, tunable, and biocompatible nanostructures for biomedical applications. However, the stability of these structures is severely compromised in biological milieu due to their fast degradation by nucleases. Recently, we showed how enzymatic polymerization could be harnessed to grow polynucleotide brushes of tunable length and location on the surface of DNA origami nanostructures, which greatly enhances their nuclease stability. Here, we report on strategies that allow for both spatial and temporal control over polymerization through activatable initiation, cleavage, and regeneration of polynucleotide brushes using restriction enzymes. The ability to site-specifically decorate DNA origami nanostructures with polynucleotide brushes in a spatiotemporally controlled way provides access to "smart" functionalized DNA architectures with potential applications in drug delivery and supramolecular assembly.

Synthesis of Poly (2-Acrylamido-2-methylpropanesulfnoinc Salt) Modified Carbon Spheres.

The paper reports a facile synthesis of novel anionic spherical polymer brushes which was based on grafting sodium 2-acrylamido-2-methylpropane-1-sulfonate from the surface of 4,4'-Azobis (4-cyanopentanoyl chloride)-modified carbon spheres. Various characterization methods involving a scanning electron microscope, energy dispersive X-ray spectroscopy, Fourier transform infrared spectrum, and thermo-gravimetric analysis were utilized to analyze the morphology, chemical composition, bonding structure, and thermal stability, respectively. The molecular weight (Mw) and polydispersity (Mw/Mn) of brushes were 616,000 g/mol and 1.72 determined by gel permeation chromatography experiments. Moreover, the dispersibility of ASPB in water and in the presence of aqueous NaCl solutions of different concentrations was investigated. Results show that the dispersibility of carbon spheres has been enhanced owing to grafted polyelectrolyte chains, while the zeta potential of the particle decreases and its brush layer shrinks upon exposure to sodium ions (Na+).

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.

Surface-Initiated Polymerizations Mediated by Novel Germanium-Based Photoinitiators.

Since surface-initiated photopolymerization techniques have gained increasing interest within the last decades, the coupling of photoinitiators to surfaces and particles has become an important research topic in material and surface sciences. In terms of surface modification and functionalization, covalently coupled photoinitiators and subsequent photopolymerizations are employed to provide a huge variety of surface properties, such as wettability, stimulus responsive features, antifouling behavior, protein binding, friction control, drug delivery, and many more. For this purpose, numerous type I and type II photoinitiators or other photosensitive moieties have been attached to different substrates so far. In our studies, a convenient and straightforward synthetic protocol to prepare a novel germanium-based photoinitiator (bromo-tris(2,4,6-trimethylbenzoyl)germane) in good yields was developed. The immobilization of this photoinitiator at the surface of silicon wafers and quartz plates was evidenced by X-ray photoelectron spectroscopy (XPS). Employing visible-light-triggered surface-initiated polymerization of different functional monomers, including acrylamide, perfluorodecyl acrylate, and fluorescein-o-acrylate, surfaces with various features such as hydrophilic/hydrophobic and fluorescent properties were prepared. This was also achieved in a spatially resolved manner. The polymer layers were characterized by contact angle measurements, UV-vis/fluorescence spectroscopy, spectroscopic ellipsometry, and XPS. The thicknesses of the surface grafted polymer layers ranged between 10 and 126 nm.

Use of a Photocleavable Initiator to Characterize Polymer Chains Grafted onto a Metal Plate with the Grafting-from Method.

The thorough characterization of polymer chains grafted through a "grafting-from" process onto substrates based on the determination of number (Mn) and weight (Mw) average molar masses, as well as dispersity (Ɖ), is quite challenging. It requires the cleavage of grafted chains selectively at the polymer-substrate bond without polymer degradation to allow their analysis in solution with steric exclusion chromatography, in particular. The study herein describes a technique for the selective cleavage of PMMA grafted onto titanium substrate (Ti-PMMA) using an anchoring molecule that combines an atom transfer radical polymerization (ATRP) initiator and a UV-cleavable moiety. This technique allows the demonstration of the efficiency of the ATRP of PMMA on titanium substrates and verification that the chains were grown homogeneously.

Immobilization of poly-L-lysine brush via surface initiated polymerization for the development of long-term antibacterial coating for silicone catheter.

Bacterial colonization of indwelling catheter remains a major threat in healthcare units worldwide. Developing approaches to prevent catheter-associated infections (CAIs) is, therefore, in great demand. Herein, to endow silicone catheter with long-term antibacterial properties, antimicrobial poly-L-lysine (PLL) brush was developed on the surface of catheter via surface initiated ring open polymerization. Surface characterizations confirmed the successful immobilization of PLL. The PLL-tethered catheter showed potent antibacterial activities against catheter-associated urinary tract infections (CAUTIs) related pathogens. Moreover, after immersing in simulated body fluid for 28 days or incubating at 60 °C for 65 days, the bactericidal properties of PLL-tethered catheter were still retained. Furthermore, the PLL-tethered catheter exhibited good anti-infection activity and biocompatibility in vivo. The PLL-tethered surfaces hold great potential in the development of antibacterial silicone catheter to combat CAIs in clinical applications.

Functionalized N-Heterocyclic Carbene Monolayers on Gold for Surface-Initiated Polymerizations.

Although N-heterocyclic carbenes (NHCs) are superior to thiol adsorbates in that they form remarkably stable bonds with gold, the generation of NHC-based self-assembled monolayers (SAMs) typically requires a strong base and an inert atmosphere, which limits the utility of such films in many applications. Herein, we report the development and use of bench-stable NHC adsorbates, benzimidazolium methanesulfonates, for the direct formation of NHC films on gold surfaces under an ambient atmosphere at room temperature without the need for extraordinary precautions. The generated NHC SAMs were fully characterized using ellipsometry, X-ray photoelectron spectroscopy (XPS), polarization modulation infrared reflection-absorption spectroscopy (PM-IRRAS), and contact angle measurements, and they were compared to analogous SAMs generated from an NHC bicarbonate adsorbate. Based on these findings, a unique radical initiator α,ω-bidentate azo-terminated NHC adsorbate, NHC15AZO[OMs], was designed and synthesized for the preparation of SAMs on gold surfaces with both NHC headgroups bound to the surface. The adsorbate molecules in NHC15AZO SAMs can exist in a hairpin or a linear conformation depending on the concentration of the adsorbate solution used to prepare the SAM. These conformations were studied by a combination of ellipsometry, XPS, PM-IRRAS, and scanning electron microscopy using gold nanoparticles (AuNPs) as a tag material. Moreover, the potential utility of these unique radical-initiating NHC films as surface-initiated polymerization platforms was demonstrated by controlling the thickness of polystyrene brush films grown from azo-terminated NHC monolayer surfaces simply by adjusting the reaction time of the photoinitiated radical polymer growth process.

Crosslinked Polypeptide Films via RAFT-Mediated Continuous Assembly of Polymers.

Polypeptide coatings are a cornerstone in the field of surface modification due to their widespread biological potential. As their properties are dictated by their structural features, subsequent control thereof using unique fabrication strategies is important. Herein, we report a facile method of precisely creating densely crosslinked polypeptide films with unusually high random coil content through continuous assembly polymerization via reversible addition-fragmentation chain transfer (CAP-RAFT). CAP-RAFT was fundamentally investigated using methacrylated poly-l-lysine (PLLMA) and methacrylated poly-l-glutamic acid (PLGMA). Careful technique refinement resulted in films up to 36.1±1.1 nm thick which could be increased to 94.9±8.2 nm after using this strategy multiple times. PLLMA and PLGMA films were found to have 30-50 % random coil conformations. Degradation by enzymes present during wound healing reveals potential for applications in drug delivery and tissue engineering.

Advances in design and applications of polymer brush modified anisotropic particles.

Current advancements in the creation of anisotropy in particles and their surface modification with polymer brushes have established a new class of hybrid materials termed polymer brush modified anisotropic particles (PBMAP). PBMAPs display unique property combinations, e.g., multi-functionality in multiple directions along with smart behavior, which is not easily achievable in traditional hybrid materials. Typically, anisotropic particles can be categorized based on three different factors, such as shape anisotropy (geometry driven), compositional anisotropy (functionality driven), and surface anisotropy (spatio-selective surface modification driven). In this review, we have particularly focused on the synthetic strategies to construct the various type of PBMAPs based on inorganic or organic core which may or may not be isotropic in nature, and their applications in various fields ranging from drug delivery to catalysis. In addition, superior performances and fascinating properties of PBMAPs over their isotropic analogues are also highlighted. A brief overview of their future developments and associated challenges have been discussed at the end.

An initiator- and catalyst-free hydrogel coating process for 3D printed medical-grade poly(ε-caprolactone).

Additive manufacturing or 3D printing as an umbrella term for various materials processing methods has distinct advantages over many other processing methods, including the ability to generate highly complex shapes and designs. However, the performance of any produced part not only depends on the material used and its shape, but is also critically dependent on its surface properties. Important features, such as wetting or fouling, critically depend mainly on the immediate surface energy. To gain control over the surface chemistry post-processing modifications are generally necessary, since it's not a feature of additive manufacturing. Here, we report on the use of initiator and catalyst-free photografting and photopolymerization for the hydrophilic modification of microfiber scaffolds obtained from hydrophobic medical-grade poly(ε-caprolactone) via melt-electrowriting. Contact angle measurements and Raman spectroscopy confirms the formation of a more hydrophilic coating of poly(2-hydroxyethyl methacrylate). Apart from surface modification, we also observe bulk polymerization, which is expected for this method, and currently limits the controllability of this procedure.

In situ conversion from crew-cut to hairy micelles by surface-initiated polymerization.

Whether spherical micelles of block copolymers have short or long coronas is intrinsically determined by the molecular weight of the corona-forming block with respect to that of the core block before the micelles are assembled. Because of the inherent conditions of packing copolymer chains into a micelle, the core diameter is altered when we assemble a micelle from a block copolymer having a long corona block, compared to that having a short corona block with the same length of the core block. However, micelles with the same core diameter but having various corona lengths can be guaranteed when the corona is extended upon surface-initiated polymerization on the micelles. Herein, we demonstrated in situ conversion from crew-cut to hairy micelles by selectively extending a corona block while maintaining the spherical shape of block copolymer micelles. We first synthesized block copolymers having a chain transfer agent (CTA) positioned at the end of the corona block and then assembled them into a crew-cut micelle. Employing this micelle as an assembly of macro-CTAs, we conducted surface-initiated polymerization on the micelle by photo-induced energy/electron transfer reversible addition-fragmentation chain transfer (PET-RAFT) polymerization. Since PET-RAFT enables the polymerization at room temperature, the corona block was selectively extended with preservation of the core diameter, thereby converting a crew-cut micelle to a hairy one. In addition, by applying the same polymerization protocol to a worm-like micelle, we could selectively extend the coronas, leading to the formation of a worm-like micelle with a long corona. If such copolymer chains were assembled into a micelle, we would obtain a spherical micelle instead of a worm-like micelle having a hairy corona, which is difficult to assess because of the inherent packing problem.

Programmable Site-Specific Functionalization of DNA Origami with Polynucleotide Brushes.

Combining surface-initiated, TdT (terminal deoxynucleotidyl transferase) catalyzed enzymatic polymerization (SI-TcEP) with precisely engineered DNA origami nanostructures (DONs) presents an innovative pathway for the generation of stable, polynucleotide brush-functionalized DNA nanostructures. We demonstrate that SI-TcEP can site-specifically pattern DONs with brushes containing both natural and non-natural nucleotides. The brush functionalization can be precisely controlled in terms of the location of initiation sites on the origami core and the brush height and composition. Coarse-grained simulations predict the conformation of the brush-functionalized DONs that agree well with the experimentally observed morphologies. We find that polynucleotide brush-functionalization increases the nuclease resistance of DONs significantly, and that this stability can be spatially programmed through the site-specific growth of polynucleotide brushes. The ability to site-specifically decorate DONs with brushes of natural and non-natural nucleotides provides access to a large range of functionalized DON architectures that would allow for further supramolecular assembly, and for potential applications in smart nanoscale delivery systems.

Surface-Mediated Construction of an Ultrathin Free-Standing Covalent Organic Framework Membrane for Efficient Proton Conduction.

As a new class of crystalline porous organic materials, covalent organic frameworks (COFs) have attracted considerable attention for proton conduction owing to their regular channels and tailored functionality. However, most COFs are insoluble and unprocessable, which makes membrane preparation for practical use a challenge. In this study, we used surface-initiated condensation polymerization of a trialdehyde and a phenylenediamine for the synthesis of sulfonic COF (SCOF) coatings. The COF layer thickness could be finely tuned from 10 to 100 nm by controlling the polymerization time. Moreover, free-standing COF membranes were obtained by sacrificing the bridging layer without any decomposition of the COF structure. Benefiting from the abundant sulfonic acid groups in the COF channels, the proton conductivity of the SCOF membrane reached 0.54 S cm-1 at 80 °C in pure water. To our knowledge, this is one of the highest values for a pristine COF membrane in the absence of additional additives.

Mixed Polymer Brushes for "Smart" Surfaces.

Mixed polymer brushes (MPBs) are composed of two or more disparate polymers covalently tethered to a substrate. The resulting phase segregated morphologies have been extensively studied as responsive "smart" materials, as they can be reversible tuned and switched by external stimuli. Both computational and experimental work has attempted to establish an understanding of the resulting nanostructures that vary as a function of many factors. This contribution highlights state-of-the-art MPBs studies, covering synthetic approaches, phase behavior, responsiveness to external stimuli as well as novel applications of MPBs. Current limitations are recognized and possible directions for future studies are identified.

Surface Initiated Polymer Thin Films for the Area Selective Deposition and Etching of Metal Oxides.

The area selective growth of polymers and their use as inhibiting layers for inorganic film depositions may provide a valuable self-aligned process for fabrication. Polynorbornene (PNB) thin films were grown from surface-bound initiators and show inhibitory properties against the atomic layer deposition (ALD) of ZnO and TiO2. Area selective control of the polymerization was achieved through the synthesis of initiators that incorporate surface-binding ligands, enabling their selective attachment to metal oxide features versus silicon dielectrics, which were then used to initiate surface polymerizations. The subsequent use of these films in an ALD process enabled the area selective deposition (ASD) of up to 39 nm of ZnO. In addition, polymer thickness was found to play a key role, where films that underwent longer polymerization times were more effective at inhibiting higher numbers of ALD cycles. Finally, while the ASD of a TiO2 film was not achieved despite blanket studies showing inhibition, the ALD deposition on polymer regions of a patterned film produced a different quality metal oxide and therefore altered its etch resistance. This property was exploited in the area selective etch of a metal feature. This demonstration of an area selective surface-grown polymer to enable ASD and selective etch has implications for the fabrication of both micro- and nanoscale features and surfaces.

Dual atom transfer radical polymerization for ultrasensitive electrochemical DNA detection.

Atom transfer radical polymerization as a form of controlled/living radical polymerization is particularly attractive. In this work, dual atom transfer radical polymerization (ATRP) is reported for ultrasensitive DNA detection. Firstly, a peptide nucleic acid (PNA) modified with a thiol group was self-assembled on an electrode surface to capture target DNA (TDNA). The initiator of the first ATRP (ATRP-1), α-bromoisobutyric acid (BIBA), was linked to forming PNA/DNA heteroduplexes via coordination of Zr4+. The polymer chain formed by the monomer of ATRP-1 (2-(2-bromoisobutyryloxy) ethyl methacrylate, BIEM) was also one of initiators of the second ATRP (eATRP-2). The other initiator of eATRP-2 was additional BIBA. ATRP-1 involves activator regeneration by electron transfer (ARGET) ATRP, regulated via excess reducing agent. eATRP-2 is electrochemically mediated ATRP which can control the polymerization via an appropriate applied potential. Compared with one ATRP, more monomers of eATRP-2 modified with ferrocene are attached to electrode surface. Under optimal conditions, this dual ATRP strategy provides a low limit of detection (25 aM, ~150 molecules) with satisfactory selectivity and stability. Importantly, this strategy presents a useful prospect for the field of biomolecule detection.