Brush Layer Research Articles

Mechanically Stable and Biocompatible Polymer Brush Coated Dental Materials with Lubricious and Antifouling Properties.

Surface modification plays a crucial role in enhancing the functionality of implanted interventional medical devices, offering added advantages to patients, particularly in terms of lubrication and prevention of undesired adsorption of biomolecules and microorganisms, such as proteins and bacteria, on the material surfaces. Utilizing polymer brushes for surface modification is currently a promising approach to maintaining the inherent properties of materials while introducing new functionalities to surfaces. Here, surface-initiated atom transfer radical polymerization (SI-ATRP) technology to effectively graft anionic, cationic, and neutral polymer brushes from a mixed silane initiating layer is employed. The presence of a polymer brush layer significantly enhances the lubrication performance of the substrates and ensures a consistently low coefficient of friction over thousands of friction cycles in aqueous environments. The antimicrobial efficacy of polymer brushes is evaluated against gram-positive Staphylococcus aureus (S. aureus) and gram-negative Escherichia coli (E. coli). It is observed that polym er brushes grafted to diverse substrate surfaces displays notable antibacterial properties, effectively inhibiting bacterial attachment. Furthermore, the polymer brush layer shows favorable biocompatibility and anti-inflammatory characteristics, which shows potential applications in dental materials, and other fields such as catheters and foodpackaging.

Growth phase-dependent changes in conformational and physicochemical properties of bacterial surface biopolymers lead to changes in bacterial adhesion strength at nanoscale and macroscale

This study presents a detailed investigation into conformational, physicochemical and adhesive characteristics of biopolymers on the surfaces of Escherichia coli and potential probiotic Bacillus subtilis harvested from middle-exponential phase (mid-EP), late-exponential phase (late-EP) and early-stationary phase (early-SP) of growth. The lengths to which bacterial surface biopolymers extend (biopolymer brush lengths), densities of grafted bacterial surface biopolymers indicating the amounts of molecules covering the bacterial surfaces (biopolymer grafting densities), adhesion forces of bacterial surface biopolymers to the model inert surfaces of silicon nitride (Si3N4), and the pull-off distances of biopolymers from Si3N4 were measured in water by atomic force microscopy (AFM). The Weibull analysis of AFM adhesion data showed that as the culture aged, the adhesive bonds between Si3N4 AFM tips and surface molecules of E. coli harvested from the culture were broken with a higher applied force. However, the highest applied force to break the bonds was required for B. subtilis in late-EP, followed by those required for cells in early-SP and mid-EP, respectively. The results of a steric model fitting to AFM approach force-distance (FD) curves and analysis of the pull-off distances in the AFM retraction FD curves showed higher biopolymer grafting density for E. coli in early-SP and longer biopolymer brush layer for B. subtilis in late-EP, which were associated with stronger adhesion to Si3N4 in water. The results of thermodynamic adhesion energy calculations based on the Wu model showed that polar interaction energy dominated the bacterial adhesion at the macroscale, the strength of which varied as a function of the growth phase for both E. coli and B. subtilis. The growth phase-dependent variation in polar components of thermodynamic adhesion energies between the bacteria and Si3N4 in water was consistent with the growth phase-dependent variation in the bond strengths between the bacteria and Si3N4 in water as revealed by the Weibull analysis of AFM adhesion data. Therefore, information obtained by Weibull analysis of nanoscale AFM bacterial adhesion data can be used to predict macroscale bacterial adhesion to the model inert Si3N4 surface in water.

PH-Responsive, Wide Color Gamut Dynamic Color Display Enabled by PDMAEMA Brush-Based Fabry-Perot Resonant Cavity.

Dynamic color-changing materials have attracted broad interest due to their widespread applications in visual sensing, dynamic color display, anticounterfeiting, and image encryption/decryption. In this work, we demonstrate a novel pH-responsive dynamic color-changing material based on a metal-insulator-metal (MIM) Fabry-Perot (FP) cavity with a pH-responsive poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA) brush layer as the responsive insulating layer. The pH-responsive PDMAEMA brush undergoes protonation at a low pH value (pH < 6), which induces different swelling degrees in response to pH and thus refractive index and thickness change of the insulator layer of the MIM FP cavity. This leads to significant optical property changes in transmission and a distinguishable color change spanning the whole visible region by adjusting the pH value of the external environment. Due to the reversible conformational change of the PDMAEMA and the formation of covalent bonds between the PDMAEMA molecular chain and the Ag substrate, the MIM FP cavity exhibits stable performance and good reproducibility. This pH-responsive MIM FP cavity establishes a new way to modulate transmission color in the full visible region and exhibits a broad prospect of applications in dynamic color display, real-time environment monitoring, and information encryption and decryption.

XPS Depth-Profiling Studies of Chlorophyll Binding to Poly(cysteine methacrylate) Scaffolds in Pigment-Polymer Antenna Complexes Using a Gas Cluster Ion Source.

X-ray photoelectron spectroscopy (XPS) depth-profiling with an argon gas cluster ion source (GCIS) was used to characterize the spatial distribution of chlorophyll a (Chl) within a poly(cysteine methacrylate) (PCysMA) brush grown by surface-initiated atom-transfer radical polymerization (ATRP) from a planar surface. The organization of Chl is controlled by adjusting the brush grafting density and polymerization time. For dense brushes, the C, N, S elemental composition remains constant throughout the 36 nm brush layer until the underlying gold substrate is approached. However, for either reduced density brushes (mean thickness ∼20 nm) or mushrooms grown with reduced grafting densities (mean thickness 6-9 nm), elemental intensities decrease continuously throughout the brush layer, because photoelectrons are less strongly attenuated for such systems. For all brushes, the fraction of positively charged nitrogen atoms (N+/N0) decreases with increasing depth. Chl binding causes a marked reduction in N+/N0 within the brushes and produces a new feature at 398.1 eV in the N1s core-line spectrum assigned to tetrapyrrole ring nitrogen atoms coordinated to Zn2+. For all grafting densities, the N/S atomic ratio remains approximately constant as a function of brush depth, which indicates a uniform distribution of Chl throughout the brush layer. However, a larger fraction of repeat units bound to Chl is observed at lower grafting densities, reflecting a progressive reduction in steric congestion that enables more uniform distribution of the bulky Chl units throughout the brush layer. In summary, XPS depth-profiling using a GCIS is a powerful tool for characterization of these complex materials.

Bottlebrush Polyethylene Glycol Nanocarriers Translocate across Human Airway Epithelium via Molecular Architecture-Enhanced Endocytosis.

Pulmonary drug delivery is critical for the treatment of respiratory diseases. However, the human airway surface presents multiple barriers to efficient drug delivery. Here, we report a bottlebrush poly(ethylene glycol) (PEG-BB) nanocarrier that can translocate across all barriers within the human airway surface. Guided by a molecular theory, we design a PEG-BB molecule consisting of a linear backbone densely grafted by many (∼1000) low molecular weight (∼1000 g/mol) polyethylene glycol (PEG) chains; this results in a highly anisotropic, wormlike nanocarrier featuring a contour length of ∼250 nm, a cross-section of ∼20 nm, and a hydrodynamic diameter of ∼40 nm. Using the classic air-liquid-interface culture system to recapitulate essential biological features of the human airway surface, we show that PEG-BB rapidly penetrates through endogenous airway mucus and periciliary brush layer (mesh size of 20-40 nm) to be internalized by cells across the whole epithelium. By quantifying the cellular uptake of polymeric carriers of various molecular architectures and manipulating cell proliferation and endocytosis pathways, we show that the translocation of PEG-BB across the epithelium is driven by bottlebrush architecture-enhanced endocytosis. Our results demonstrate that large, wormlike bottlebrush PEG polymers, if properly designed, can be used as a carrier for pulmonary and mucosal drug delivery.

Exploring the relevance between load-bearing capacity and surface friction behavior based on a layered hydrogel cartilage prototype

Cartilage is well lubricated over a lifetime and this phenomenon is attributed to both of the surface hydration lubrication and the matrix load-bearing capacity. Lubricious hydrogels with a layered structure are designed to mimic cartilage as potential replacements. While many studies have concentrated on improving surface hydration to reduce friction, few have experimentally detected the relationship between load-bearing capacity of hydrogels and their interface friction behavior. In this work, a bilayer hydrogel, serving as a cartilage prototype consisted of a top thick hydrated polymer brush layer and a bottom hydrogel matrix with tunable modulus was designed to investigate this relationship. The coefficient of friction (COF, μ) is defined as the sum of interfacial component (μInt) and deformation/hysteresis component (μHyst). The presence of the top hydration layer effectively dissipates contact stress and reduces the interface interaction (μInt), leading to a stable and low COF. The contribution of mechanical deformation (μHyst) during the sliding shearing process to COF can be significantly reduced by increasing the local mechanical modulus, thereby enhancing the load-bearing capacity. These results show that the strategy of coupling surface hydration layer with a high load-bearing matrix can indeed enhance the lubrication performance of hydrogel cartilage prototypes, and implies a promising routine for designing robust soft matter lubrication system and friction-control devices.

Lubricated PDMS-bearing ladderlike polysilsesquioxane coating: Fabrication and factors governing its long-term ice-shedding performance

Reacting an epoxy-bearing ladder-like polysilsesquioxane (LASQ) with mono-carboxy-terminated poly(dimethyl siloxane) (PDMS-COOH) yields LASQ-PDMS, a blend of LASQ and a graft (g) copolymer LASQ-g-PDMS. Photolyzing a cast film of LASQ-PDMS containing a cationic ring-opening polymerization initiator produces a robust and wear-resistant coating. Such a coating presents a liquid-like surface PDMS brush layer that imparts anti-smudge and ice-shedding properties. These properties are significantly enhanced via the application of a silicone oil (SO) as a lubricant. Investigated in this study are the effects of changing the molecular weight and mass fraction of PDMS as well as the molecular weight of a SO or composition of a SO mixture on properties of the lubricated LASQ-PDMS coating. These properties include the coating’s hardness, water repellence, wear resistance, SO retainability, initial ice adhesion strength (τ), variation of τ with the number of abrasions made by steel wool on a coating, and variation of τ with the number of icing/de-icing cycles. This systematic study establishes the exceptional wear resistance of the LASQ-PDMS coatings and reveals SO retainability as the primary factor governing the long-term ice-shedding performance of the coatings.

Hydrogen Bonding Inside Anionic Polymeric Brush Layer: Machine Learning-Driven Exploration of the Relative Roles of the Polymer Steric Effect, Charging, and Type of Screening Counterions

Hydrogen Bonding Inside Anionic Polymeric Brush Layer: Machine Learning-Driven Exploration of the Relative Roles of the Polymer Steric Effect, Charging, and Type of Screening Counterions

Thermo-responsive poly(di(ethylene glycol) methyl ether methacrylate) brushes as substrate-independent release coatings for cell culture and selective cell separation and purification

Abstract A systematic study on the surface-initiated polymerization of di(ethylene glycol) methyl ether methacrylate (DEGMA) by atom transfer radical polymerization (ATRP) from glass, silicon, titanium as well as tissue culture polystyrene (TCPS) is reported in an attempt to expand the known thermoresponsive poly(di(ethylene glycol) methyl ether methacrylate) (PDEGMA) cell release layers on gold to other substrates. The use of these substrate materials requires an altered immobilization chemistry to couple a bromide containing ATRP initiator to the surfaces. Using aminosilanes or polydopamine as coupling layers for the attachment of α-bromoisobutyryl bromide (BiBB) and the direct functionalization of surface hydroxyl groups with trichlorosilane-functionalized ATRP initiators all surfaces studied were shown to facilitate the growth of PDEGMA brushes using the same conditions that were reported previously for polymerization on gold. The brush layers obtained were characterized systematically using wetting, ellipsometry, X-ray photoelectron spectroscopy (XPS) as well as atomic force microscopy (AFM) analyses. Selective cell release and separation of PaTu 8988t and NIH 3T3 cells, which are known to exhibit different behavior after temperature drop-induced brush swelling, was observed for all substrates, albeit for different brush thicknesses, implying variations in initiator and also PDEGMA grafting density. The successful modification of biomedically relevant materials (Ti and TCPS) implies that the previously reported stem cell purification and selective cell release of various cell types, which is facilitated by PDEGMA brushes, can be realized and consequently scaled up in the future.

All-atom molecular dynamics simulations showing the dynamics of small organic molecules in water-solvated polyelectrolyte brush layers.

Polyelectrolyte brushes can introduce functionality to surfaces and because of this, these brushes have been studied extensively. In many applications, these brushes are used in solutions that contain a variety of molecules. While the interaction between polyelectrolyte brushes and molecules has been studied via coarse-grained simulations and experiments, such interaction has not been studied in molecular detail. An understanding of interactions in such molecular detail may prove crucial in the design of future brush coatings that can enable desired adsorption of different organic and biological molecules. Therefore, we present a first all-atom molecular dynamics simulations study of poly(sodium acrylate) brushes in contact with a small organic molecule, γ-butyrolactone. Within this molecular framework, we study the interaction of this lactone molecule with the brush layer and study the ensuing absorption and dynamics of the lactone inside the brush layer. The lactone is found to prefer to remain in the bulk solution; however, when absorbed, lactone molecules are found to have significantly reduced mobilities as compared to that in the bulk solution and are able to massively influence the properties of the brush-entrapped water molecules. These findings provide unprecedented details about the absorption-driven changes to molecular structure and dynamics of the lactone molecules and the water molecules inside the brush layer and can only be uncovered by our all-atom MD simulations. Such explicit and atomistically-resolved information, taking into account the specific chemical nature of the interacting systems, is rare in the context of designing polymer and PE brush-based coatings. Thus, we anticipate that our findings will be crucial in the design of future brush coatings aimed at providing adsorption platforms for different organic and biomolecules.

Direct measurements & simplified models of colloidal interactions & diffusion with adsorbed macromolecules.

We report total internal reflection microscopy measurements of 3D trajectories of ensembles of micron sized colloidal particles near interfaces with and without adsorbed macromolecules. Evanescent wave scattering reveals nanometer scale motion normal to planar surfaces and sub-diffraction limit lateral motion is resolved via image analysis. Equilibrium and non-equilibrium analyses of particle trajectories reveal self-consistent position dependent energies (energy landscapes) and position dependent diffusivities (diffusivity landscapes) both perpendicular and parallel to interfaces. For bare colloids and surfaces, electrostatic and hydrodynamic interactions are accurately quantified with established analytical theories. For colloids and surfaces with adsorbed macromolecules, conservative forces are accurately quantified with models for interactions between brush layers, whereas directly measured position dependent diffusivities require novel models of spatially varying permeability within adsorbed layers. Agreement between spatially resolved interactions and diffusivities and rigorous simplified models provide a basis to consistently interpret, predict, and design colloidal transport in the presence of adsorbed macromolecules for diverse applications.

Shear thickening in suspensions of particles with dynamic brush layers.

Control of frictional interactions among liquid-suspended particles has led to tunable, strikingly non-Newtonian rheology via the formation of strong flow constraints as particles come into close proximity under shear. Typically, these frictional interactions have been in the form of physical contact, controllable via particle shape and surface roughness. We investigate a different route, where molecular bridging between nearby particle surfaces generates a controllable constraint to relative particle movement. This is achieved with surface-functionalized colloidal particles capable of forming dynamic covalent bonds with telechelic polymers that comprise the suspending fluid. At low shear stress this results in particles coated with a uniform polymer brush layer. Beyond an onset stress σ* the telechelic polymers become capable of bridging and generate shear thickening. Over the size range investigated, we find that the dynamic brush layer leads to dependence of σ* on particle diameter that closely follows a power law with exponent -1.76. In the shear thickening regime, we observe an enhanced dilation in measurements of the first normal stress difference N1 and reduction in the extrapolated volume fraction required for jamming, both consistent with an effective particle friction that increases with decreasing particle diameter. These results are discussed in light of predictions for suspensions of hard spheres and of polymer-grafted particles.

Hydrophilic and Apolar Hydration in Densely Grafted Cationic Brushes and Counterions with Large Mobilities.

We employ an all-atom molecular dynamics (MD) simulation framework to unravel water microstructure and ion properties for cationic [poly(2-(methacryloyloxy)ethyl) trimethylammonium chloride] (PMETAC) brushes with chloride ions as counterions. First, we identify locally separate water domains (or first hydration shells) each around {N(CH3)3}+ and the C═O functional groups of the PMETAC chain and one around the Cl- ion. These first hydration shells around the respective moieties overlap, and the extent of the overlap depends on the nature of the species triggering it. Second, despite the overlap, the water molecules in these domains demonstrate disparate properties dictated by the properties of the atoms and groups around which they are located. For example, the presence of the methyl groups makes the {N(CH3)3}+ group trigger apolar hydration as evidenced by the corresponding orientation of the dipole of the water molecules around the {N(CH3)3}+ moiety. These water molecules around the {N(CH3)3}+ group also have enhanced tetrahedrality compared to the water molecules constituting the hydration layer around the C═O group and the Cl- counterion. Our simulations also identify that there is an intervening water layer between the Cl- ion and {N(CH3)3}+ group: this layer prevents the Cl- ion from coming very close to the {N(CH3)3}+ group. As a consequence, there is a significantly large mobility of the Cl- ions inside the PMETAC brush layer. Furthermore, the C═O group of the polyelectrolyte (PE) chain, due to the partial negative charge on the oxygen atom and the specific structure of the PMETAC brush system, demonstrates strongly hydrophilic behavior and enforces a specific dipole response of water molecules analogous to that experienced by water around anionic species of high charge density. In summary, our findings confirm that PMETAC brushes undergo hydrophilic hydration at one site and apolar hydration at another site and ensure large mobility of the supported Cl- counterions.

Ice‐Shedding Endurance Enhancement of Lubricated Polyurethane NP‐GLIDE Coating Through Dual Cross‐Linking with Covalent and Hydrogen Bonds

AbstractAn NP‐GLIDE coating, featuring a liquid‐like polymer brush layer on its surface and nanopools of a grafted liquid ingredient for dewetting enablement within its matrix, is normally covalently cross‐linked (CX). This paper introduces a dually cross‐linked (DX) NP‐GLIDE coating, employing urethane bonds and H─bonds for crosslinking. Both the DX and CX coatings, utilizing poly(dimethyl siloxane) (PDMS) as the dewetting enabler, exhibit low ice adhesion strengths (τ). Post‐lubrication with silicone oil (SO), ice is readily shed under gravity from the coatings. The DX coating maintains low τ over numerous icing/de‐icing cycles, outlasting the CX coating. This durability is likely due to the lubricant‐loss‐responsive nature of the DX matrix. The matrix increases its H─bond cross‐links responding to lubricant loss and the cross‐linking density increase triggers additional lubricant release into the PDMS brush layer. This cyclic process persists over time. Under optimal conditions after 31 icing/de‐icing cycles, the lubricated DX coating demonstrates an impressively low τ of 1.8 ± 0.5 kPa. In contrast, the lubricated CX counterpart has a τ of 32 ± 11 kPa, while plain glass records a τ of 325 ± 14 kPa. This study underscores the significant potential of dual cross‐linking for enhancing ice‐shedding endurance of coatings.

Surface Forces Characterization of Concentrated PMMA Brush Layers under Applied Load and Shear.

Concentrated polymer brushes (CPBs) are known to exhibit excellent lubrication properties. However, the frictional behaviors of CPBs vary, depending on their preparation and operating conditions. In order to understand such complicated properties, it is necessary to determine their structures and correlate them with their properties, during shear motion. In this study, we employed surface forces and resonance shear measurement (RSM) as well as refractive index measurement using fringes of equal chromatic order (FECO) for studying the structure of the CPBs of poly(methyl methacrylate) (PMMA) in toluene. The obtained elastic (ks) and viscous (bs) parameters based on the RSM for the PMMA-PMMA were higher than those obtained for PMMA-silica over the entire distance range. With the increasing shear amplitude on the PMMA-PMMA under an applied load, the bs value first increased and then decreased while the ks value monotonically decreased. These behaviors were consistent with those of the thicker CPBs reported in a previous paper (Soft Matter, 2019). Thus, the dynamics of the CPBs under the applied load and shear were not dependent on the thickness of the polymer brushes in this case. The density distribution of the swollen PMMA brushes along the distance in the thickness direction of the brush layer was estimated by using the measured refractive index values, showing that the fraction of the PMMA brushes in the outer region from the surface (20% in the thickness) was ca. 10%. This lower density region near the surface of the swollen CPBs enabled them to interpenetrate with each other. Changes in the refractive index value under shear were observed, indicating that the interpenetrated PMMA chains were pulled out with increasing shear amplitude. These results demonstrated that broader applications of CPBs are possible by regulating the friction between them under different operating conditions, even for usually lubricious CPBs.

Low-Fouling and Antibacterial Polymer Brushes via Surface-Initiated Polymerization of a Mixed Zwitterionic and Cationic Monomer.

The use of surface-grafted polymer brushes with combined low-fouling and antibacterial functionality is an attractive strategy to fight biofilm formation. This report describes a new styrene derivative combining a quaternary ammonium group with a sulfobetaine group in one monomer. Surface-initiated polymerization of this monomer on titanium and a polyethylene (PE) base material gave bifunctional polymer brush layers. Grafting was achieved via surface-initiated atom transfer radical polymerization from titanium or heat-induced free-radical polymerization from plasma-activated PE. Both techniques gave charged polymer layers with a thickness of over 750 nm, as confirmed by ToF-SIMS-SPM measurements. The chemical composition of the brush polymers was confirmed by XPS and FT-IR analysis. The surface charge, characterized by the ζ potential, was positive at different pH values, and the number of solvent-accessible excess ammonium groups was found to be ∼1016 N+/cm2. This led to strong antibacterial activity against Gram-positive and Gram-negative bacteria that was superior to a structurally related contact-active polymeric quaternary ammonium brush. In addition to this antibacterial activity, good low-fouling properties of the dual-function polymer brushes against Gram-positive and Gram-negative bacteria were found. This dual functionality is most likely due to the combination of antibacterial quaternary ammonium groups with antifouling sulfobetaines. The combination of both groups in one monomer allows the preparation of bifunctional brush polymers with operationally simple polymerization techniques.

Composition-Orientation Induced Mechanical Synergy in Nanoparticle Brushes with Grafted Gradient Copolymers.

Gradient poly(methyl methacrylate/n-butyl acrylate) copolymers, P(MMA/BA), with various compositional ratios, were grafted from surface-modified silica nanoparticles (SiO2-g-PMMA-grad-PBA) via complete conversion surface-initiated activator regenerated by electron transfer (SI-ARGET) atom transfer radical polymerization (ATRP). Miniemulsion as the reaction medium effectively confined the interparticle brush coupling within micellar compartments, preventing macroscopic gelation and enabling complete conversion. Isolation of dispersed and gelled fractions revealed dispersed particle brushes to feature a higher Young's modulus, toughness, and ultimate strain compared with those of the "gel" counterparts. Upon purification, brush nanoparticles from the dispersed phase formed uniform microstructures. Uniaxial tension testing revealed a "mechanical synergy" for copolymers with MMA/BA = 3:2 molar ratio to concurrently exhibit higher toughness and stiffness. When compared with linear analogues of similar composition, the brush nanoparticles with gradient copolymers had better mechanical properties, attributed to the synergistic effects of the combination of composition and propagation orientation, highlighting the significance of architectural design for tethered brush layers of such hybrid materials.

Biomimetic affinity membrane roll column for rapid purification of C-reactive protein

To in-depth explore the action mechanism of C-reactive protein (CRP) and precisely study its signaling pathways, it is essential to acquire high-purity CRP while preserving its intact structure and functionality. In this study, we propose and fabricate a high-density 2-methacryloyloxyethyl phosphorylcholine (MPC)-modified membrane roll column (MPC-MRC) using a surface-initiated atom transfer radical polymerization (SI-ATRP) approach, which can overcome these limitations (long incubation time and low adsorption capacity) of conventional enrichment materials. The MPC-MRC incorporates a high-density 2-hydroxyethyl methacrylate polymer brush to prevent non-specific protein adsorption and multiple MPC polymer brush layers for high-performance enrichment of CRP in the company of calcium ions. Furthermore, the MPC-MRC exhibits high permeability, hydrophilicity, and mechanical strength. Compared to previous technologies, this novel material demonstrates significantly higher CRP binding capacity (310.3 mg/g), shorter processing time (only 15 min), and lower cost (only 12 USD/column). Notably, the MPC-MRC enables fast and effective purification of CRP from both human and rat serum, exhibiting good selectivity, recovery (> 91.3 %), and purity (> 95.2 %). Thus, this proposed purification approach based on MPC-MRC holds great potential for target protein enrichment from complex samples, as well as facilitating in-depth studies of its biological functions.

Grafting of Multifunctional Polymer Brushes from a Glass Surface: Surface‐Initiated Atom Transfer Radical Polymerization as a Versatile Tool for Biomedical Materials Engineering

AbstractThe unique features of poly[2‐(dimethylamino)ethyl methacrylate] (PDMAEMA), such as its sensitivity to external stimuli like pH and the presence of tertiary amine groups that can be easily quaternized to introduce antibacterial properties, make it a promising platform for biomedical applications. In this contribution, a facile, cost‐effective, and ecological procedure for controlled grafting of PDMAEMA brushes from a glass surface, both in mL and µL scale, is developed. This concept involves utilizing an aqueous solution of sunflower honey as a source of reducing sugars to accelerate surface‐initiated activators regenerated by electron transfer atom transfer radical polymerization. The PDMAEMA chains covalently grafted to the glass surface are then quaternized to form an antibacterial film. The thickness of the polymeric brush layer is determined by atomic force microscopy, while the chemical composition is analyzed by time of flight secondary ion mass spectrometry. Water contact angle measurements demonstrate the pH‐sensitivity of PDMAEMA pointing out the potential application of the prepared material as smart surfaces. Furthermore, the antibacterial tests against Gram‐positive and Gram‐negative bacteria strains are performed. The protein adsorption is used to evaluate the biocompatibility of the prepared surfaces. The resulting glass materials can serve as multifunctional surfaces for various purposes.

Synthesis and Characterization of Stimuli-Responsive Polymer Brushes in Nanofluidic Channels.

Nanochannels with controllable gating behavior are attractive features in a wide range of nanofluidic applications including viral detection, particle sorting, and flow regulation. Here, we use selective sidewall functionalization of nanochannels with a polyelectrolyte brush to investigate the channel gating response to variations in solution pH and ionic strength. The conformational and structural changes of the interfacial brush layer within the channels are interrogated by specular and off-specular neutron reflectometry. Simultaneous fits of the specular and off-specular signals, using a dynamical theory model and a fitting optimization protocol, enable detailed characterization of the brush conformations and corresponding channel geometry under different solution conditions. Our results indicate a collapsed brush state under basic pH, equivalent to an open gate, and an expanded brush state representing a partially closed gate upon decreasing the pH and salt concentration. These findings open new possibilities in noninvasive in situ characterization of tunable nanofluidics and lab-on-chip devices with advanced designs and improved functionality.