Preparation of a thick polymer brush layer composed of poly(2-methacryloyloxyethyl phosphorylcholine) by surface-initiated atom transfer radical polymerization and analysis of protein adsorption resistance

Bioinspired zwitterionic triblock copolymers designed for colloidal drug delivery: 2 - Biological evaluation

In this work, poly(lactide) nanoparticles were equipped with a bioinspired coating layer based on poly[2-(methacryloyloxy)ethyl phosphorylcholine] and then evaluated when administered to the lungs and after intravenous injection. Compared to the plain counterparts, the chosen zwitterionic polymer shell prevented the coated colloidal formulation from aggregation and conditioned it for lower cytotoxicity, protein adsorption, complement activation and phagocytic cell uptake. Consequently, no interference with the biophysical function of the lung surfactant system could be detected accompanied by negligible protein and cell influx into the bronchoalveolar space after intratracheal administration. When injected into the central compartment, the coated formulation showed a prolonged circulation half-life and a delayed biodistribution to the liver. Taken together, colloidal drug delivery vehicles would clearly benefit from the investigated poly[2-(methacryloyloxy)ethyl phosphorylcholine]-based polymer coatings.

Microenvironment-regulated dual-hydrophilic coatings for glaucoma valve surface engineering

Glaucoma valves (GVs) play an essential role in treating glaucoma. However, fibrosis after implantation has limited their long-term success in clinical applications. In this study, we aimed to develop a comprehensive surface-engineering strategy to improve the biocompatibility of GVs by constructing a microenvironment-regulated and dual-hydrophilic antifouling coating on a GV material (silicone rubber, SR). The coating was based on a superhydrophilic polydopamine (SPD) coating with good short-range superhydrophilicity and antifouling abilities. In addition, SPD coatings contain many phenolic hydroxyl groups that can effectively resist oxidative stress and the inflammatory microenvironment. Furthermore, based on its in situ photocatalytic free-radical polymerization properties, the SPD coating polymerized poly 2-methylacryloxyethylphosphocholine, providing an additional long-range hydrophilic and antifouling effect. The in vitro test results showed that the microenvironment-regulated and dual-hydrophilic coatings had anti-protein contamination, anti-oxidation, anti-inflammation, and anti-fiber proliferation capabilities. The in vivo test results indicated that this coating substantially reduced the fiber encapsulation formation of the SR material by inhibiting inflammation and fibrosis. This design strategy for dual hydrophilic coatings with microenvironmental regulation can provide a valuable reference for the surface engineering design of novel medical implantable devices. STATEMENT OF SIGNIFICANCE: Superhydrophilic polydopamine (SPD) coatings were prepared on silicone rubber (SR) by a two-electron oxidation method. Introduction of pMPC to SPD surface using photocatalytic radical polymerization to obtain a dual-hydrophilic coating. The dual-hydrophilic coating effectively modulates the oxidative and inflammatory microenvironment. This coating significantly reduced protein contamination and adhesion of inflammatory cells and fibroblasts in vitro. The coating-modified SR inhibits inflammatory and fibrosis responses in vivo, promising to serve the glaucoma valves.

Bioinspired zwitterionic triblock copolymers designed for colloidal drug delivery: 1 - Synthesis and characterization

This study describes the synthesis and characterization of triblock copolymers composed of poly[2-(methacryloyloxy)ethyl phosphorylcholine]-block-poly(propylene glycol)-block-poly[2-(methacryloyloxy)ethyl phosphorylcholine] (PMPC-b-PPG-b-PMPC) intended for, but not limited to, applications in colloidal drug delivery. Atom transfer radical polymerization led to a library of well-defined PMPC-b-PPG-b-PMPC triblock copolymers with varying overall molecular weight (ranging from ∼5 to ∼25 kDa) and composition (weight fraction of the hydrophobic PPG block ranged from ∼10 to ∼50 wt%). The properties of the synthesized triblock copolymers were linked to the PPG to bioinspired PMPC block(s) ratio, where the more hydrophilic species showed adequate aqueous solubility, surface activity and biocompatibility (non-toxicity) in in vitro cell culture. Their amphiphilic nature makes them adsorb efficiently onto polymer nanoparticles, what improves colloidal stability under stress conditions and, furthermore, depletes proteins from unwanted adsorption to the underlying surface. The current findings strengthen our insights into structure-function relationships of PMPC-based coatings leading to protecting shells on relevant polymer nanoparticle formulations. PMPC-b-PPG-b-PMPC triblock copolymers composed of a hydrophobic PPG block of 2-4 kDa flanked by two hydrophilic PMPC blocks each of 5-10 kDa seem to be most promising to enhance colloidal drug delivery vehicles.

Formation of Antifouling Brushes on Various Substrates Using a Melanin-Inspired Initiator Film

In this study, we developed a substrate-independent initiator film that can undergo surface-initiated polymerization to form an antifouling brush. Inspired by the melanogenesis found in nature, we synthesized a tyrosine-conjugated bromide initiator (Tyr-Br) that contains phenolic amine groups as the dormant coating precursor and α-bromoisobutyryl groups as the initiator. The resultant Tyr-Br was stable under ambient air conditions and underwent melanin-like oxidation only in the presence of tyrosinase to form an initiator film on various substrates. Subsequently, an antifouling polymer brush was formed using air-tolerant activators regenerated by electron transfer for atom transfer radical polymerization (ARGET ATRP) of zwitterionic carboxybetaine. The entire surface coating procedure, including the initiator layer formation and ARGET ATRP, occurred under aqueous conditions and did not require organic solvents or chemical oxidants. Therefore, antifouling polymer brushes can be feasibly formed not only on experimentally preferred substrates (e.g., Au, SiO₂, and TiO₂) but also on polymeric substrates such as poly(ethylene terephthalate) (PET), cyclic olefin copolymer (COC), and nylon.

Comparative Evaluation of Pseudomonas aeruginosa Adhesion to a Poly-(2-Methacryloyloxyethyl Phosphorylcholine)-Modified Silicone Hydrogel Contact Lens

Pseudomonas aeruginosa is the most common causative agent associated with microbial keratitis. During contact lens wear, pathogens may be introduced into the ocular environment, which might cause adverse events. Lehfilcon A is a recently developed contact lens with a water gradient surface composed of polymeric 2-methacryloyloxyethyl phosphorylcholine (MPC). MPC is re-ported to impart anti-biofouling properties onto modified substrates. Therefore, in this in vitro experimental study, we tested the capability of lehfilcon A to resist adhesion by P. aeruginosa. Quantitative bacterial adhesion assays using five strains of P. aeruginosa were conducted to compare the adherence properties of lehfilcon A to five currently marketed silicone hydrogel (SiHy) contact lenses (comfilcon A, fanfilcon A, senofilcon A, senofilcon C, and samfilcon A). Compared to lehfilcon A, we observed 26.7 ± 8.8 times (p = 0.0028) more P. aeruginosa binding to comfilcon A, 30.0 ± 10.8 times (p = 0.0038) more binding to fanfilcon A, 18.2 ± 6.2 times (p = 0.0034) more binding to senofilcon A, 13.6 ± 3.9 times (p = 0.0019) more binding to senofilcon C, and 29.5 ± 11.8 times (p = 0.0057) more binding to samfilcon A. These results demonstrate that, for various strains of P. aeruginosa, lehfilcon A reduces bacterial adhesion compared to other contact lens materials.

A novel electrochemical biosensing method with double-layered polymer brush modified electrode

We developed a novel electrochemical biosensor electrode that has a potential to reduce background noise for which we constructed an original conductive substrate modified with a double-layered polymer brush structure that is water impermeable and can control biomolecules adsorption/desorption. In this study, a hydrophobic poly(tert-butyl methacrylate) brush layer was prepared on a gold electrode, and then, the tert-butyl group near the outermost surface was dissociated by the acid treatment to obtain a hydrophilic carboxy group, thereby fabricating a conductive substrate with the double-layered polymer brush structure. Formation of the double-layered polymer brush structure was indicated by surface wettability and optical analyses. The potential difference and hydrogen ion concentration, which is a typical parameter of the surrounding environment, were linearly correlated with the gold electrode having a double-layered polymer brush structure with carboxyl groups. However, there was no correlation on gold electrodes with self-assembled monolayers presenting carboxy groups. It is considered that the pH responsiveness of the carboxy groups on the outermost surface could be exhibited remarkably because the charge state in the vicinity of the surface became constant due to the hydrophobic polymer brush layer having a certain thickness. The target DNA could be captured more efficiently at the probe DNA-immobilized electrode with the double-layered polymer brush structure than when using COOH-SAM. This is the first report of the application of the double-layered polymer brush structure for the electrochemical biosensing, and it will be an excellent surface modification method to reduce background noise.

In Situ Electrical Monitoring of Methylated DNA Based on Its Conformational Change to G-Quadruplex Using a Solution-Gated Field-Effect Transistor

Methylated DNA is not only a diagnostic but also a prognostic biomarker for early-stage cancer. However, sodium bisulfite sequencing as a "gold standard" method for detection of methylation markers has some drawbacks such as its time-consuming and labor-intensive procedures. Therefore, simple and reliable methods are required to analyze DNA sequences with or without methylated residues. Herein, we propose a simple and direct method for detecting DNA methylation through its conformation transition to G-quadruplex using a solution-gated field-effect transistor (SG-FET) without using labeled materials. The BCL-2 gene, which is involved in the development of various human tumors, contains G-rich segments and undergoes a conformational change to G-quadruplex depending on the K⁺ concentration. Stacked G-quadruplex strands move close to the SG-FET sensor surface, resulting in large electrical signals based on intrinsic molecular charges. In addition, a dense hydrophilic polymer brush is grafted using surface-initiated atom transfer radical polymerization onto the SG-FET sensor surface to reduce electrical noise based on nonspecific adsorption of interfering species. In particular, control of the polymer brush thickness induces electrical signals based on DNA molecular charges in the diffusion layer, according to the Debye length limit. A platform based on the SG-FET sensor with a well-defined polymer brush is suitable for in situ monitoring of methylated DNA and realizes a point-of-care device with a high signal-to-noise ratio and without the requirement for additional processes such as bisulfite conversion and polymerase chain reaction.

Predicting the In Vivo Performance of Cardiovascular Biomaterials: Current Approaches In Vitro Evaluation of Blood-Biomaterial Interactions

The therapeutic efficacy of a cardiovascular device after implantation is highly dependent on the host-initiated complement and coagulation cascade. Both can eventually trigger thrombosis and inflammation. Therefore, understanding these initial responses of the body is of great importance for newly developed biomaterials. Subtle modulation of the associated biological processes could optimize clinical outcomes. However, our failure to produce truly blood compatible materials may reflect our inability to properly understand the mechanisms of thrombosis and inflammation associated with biomaterials. In vitro models mimicking these processes provide valuable insights into the mechanisms of biomaterial-induced complement activation and coagulation. Here, we review (i) the influence of biomaterials on complement and coagulation cascades, (ii) the significance of complement-coagulation interactions for the clinical success of cardiovascular implants, (iii) the modulation of complement activation by surface modifications, and (iv) in vitro testing strategies.

Biodegradable phosphorylcholine copolymer for cardiovascular stent coating

Phosphorylcholine (PC) based polymer coatings with excellent biocompatibility have shown successful commercialization in drug-eluting stents. However, poor degradability represents a challenge in the application of biodegradable stents. Herein, a biodegradable phosphorylcholine copolymer is developed based on one-step radical ring-opening polymerization (RROP). This copolymer was synthesized by copolymerization of a PC unit, degradable ester (2-methylene-1,3-dioxepane, MDO) unit and non-degradable butyl methacrylate (BMA) unit, which showed ratio controllability by changing the monomer ratio during polymerization. We demonstrated that the copolymer with the ratio of 34% MDO, 19% MPC and 47% BMA could form a stable coating by ultrasonic spray, and showed good blood compatibility, anti-adhesion properties, biodegradability, and rapamycin eluting capacity. In vivo study revealed its promising application as a biodegradable stent coating. This work provides a facile path to add biodegradability into PC based polymers for further bio-applications.

Phospholipid-based multifunctional coating via layer-by-layer self-assembly for biomedical applications

As an important class of biomaterials，bionics inspired materials has been widely used in creating extracorporeal and implantable medical devices. However, specific service environment is often faced with multiple requirements rather than single function. Herein, we designed a phospholipid-based multifunctional coating with phospholipids-based polymers, type I collagen (Col-I) and Arg-Glu-Asp-Val (REDV) peptide, via layer-by-layer assembly. The successful synthesis of the polymers and the coating is proved by a series of characterization methods including Fourier transforming infrared spectra (FTIR), proton nuclear magnetic resonance (¹H NMR), ultraviolet-visible spectra (UV) and X-ray photoelectron spectroscopy (XPS), while the assembly process and quality change of the coating were monitored via quartz crystal microbalance (QCM). Besides, hydrophilicity and roughness of this coating was analyzed via water contact angle (WCA) and atomic force microscope (AFM), respectively. Finally, results from platelet adhesion, activation assay, smooth muscle cells (SMCs) and endothelial cells (ECs) cultures indicated that the multifunctional coating could strongly inhibit platelet adhesion and SMCs proliferation, hence provide practical application of the coating with good biocompatibility, especially the anticoagulant property and cell compatibility. It is expected that this coating may be used in blood-contacting fields such as cardiovascular stent or other devices in the future.

Radical polymerization as a versatile tool for surface grafting of thin hydrogel films

The surface of solid substrates is the main part that interacts with the environment.

Surface Modification by Polyzwitterions of the Sulfabetaine-Type, and Their Resistance to Biofouling

Films of zwitterionic polymers are increasingly explored for conferring fouling resistance to materials. Yet, the structural diversity of polyzwitterions is rather limited so far, and clear structure-property relationships are missing. Therefore, we synthesized a series of new polyzwitterions combining ammonium and sulfate groups in their betaine moieties, so-called poly(sulfabetaine)s. Their chemical structures were varied systematically, the monomers carrying methacrylate, methacrylamide, or styrene moieties as polymerizable groups. High molar mass homopolymers were obtained by free radical polymerization. Although their solubilities in most solvents were very low, brine and lower fluorinated alcohols were effective solvents in most cases. A set of sulfabetaine copolymers containing about 1 mol % (based on the repeat units) of reactive benzophenone methacrylate was prepared, spin-coated onto solid substrates, and photo-cured. The resistance of these films against the nonspecific adsorption by two model proteins (bovine serum albumin-BSA, fibrinogen) was explored, and directly compared with a set of references. The various polyzwitterions reduced protein adsorption strongly compared to films of poly(nbutyl methacrylate) that were used as a negative control. The poly(sulfabetaine)s showed generally even somewhat higher anti-fouling activity than their poly(sulfobetaine) analogues, though detailed efficacies depended on the individual polymer-protein pairs. Best samples approach the excellent performance of a poly(oligo(ethylene oxide) methacrylate) reference.

Enzyme Immobilization in Polyelectrolyte Brushes: High Loading and Enhanced Activity Compared to Monolayers

Catalysis by enzymes on surfaces has many applications. However, strategies for efficient enzyme immobilization with preserved activity are still in need of further development. In this work, we investigate polyelectrolyte brushes prepared by both grafting-to and grafting-from with the aim to achieve high catalytic activity. For comparison, self-assembled monolayers that bind enzymes with the same chemical interactions are included. We use the model enzyme glucose oxidase and two kinds of polymers: anionic poly(acrylic acid) and cationic poly(diethylamino)methyl methacrylate. Surface plasmon resonance and spectroscopic ellipsometry are used for accurate quantification of surface coverage. Besides binding more enzymes, the "3D-like" brush environment enhances the specific activity compared to immobilization on self-assembled monolayers. For grafting-from brushes, multilayers of enzymes were spontaneously and irreversibly immobilized without conjugation chemistry. When the pH was between the pI of the enzyme and the p K_a of the polymer, binding was considerable (thousands of ng/cm² or up to 50% of the polymer mass), even at physiological ionic strength. However, binding was observed also when the brushes were neutrally charged. For acidic brushes (both grafting-to and grafting-from), the activity was higher for covalent immobilization compared to noncovalent. For grafting-from brushes, a fully preserved specific activity compared to enzymes in the liquid bulk was achieved, both with covalent (acidic brush) and noncovalent (basic brush) immobilization. Catalytic activity of hundreds of pmol cm^-2 s^-1 was easily obtained for polybasic brushes only tens of nanometers in dry thickness. This study provides new insights for designing functional interfaces based on enzymatic catalysis.

Design of a star-like hyperbranched polymer having hydrophilic arms for anti-biofouling coating

A star-like hyperbranched polymer having hydrophilic poly(ethyleneoxide acrylate) arms (HB-PEO9A) was prepared by a core-first method based on atom transfer radical polymerization. The PEO9A layer coated on a solid substrate was dissolved by water, and effectively inhibited protein adsorption and cell adhesion.

Ion-Specific Hydration States of Zwitterionic Poly(sulfobetaine methacrylate) Brushes in Aqueous Solutions

The ion-specific hydration states of zwitterionic poly(3-( N-2-methacryloyloxyethyl- N, N-dimethyl)ammonatopropanesulfonate) (PMAPS) brushes in various aqueous solutions were investigated by neutron reflectivity (NR) and atomic force microscopy (AFM). The asymmetric hydration state of the PMAPS brushes was verified from the NR scattering-length density profiles, while the variation in their swollen thickness was complementary as determined from AFM topographic images. PMAPS brushes got thicker in any salt solutions, while the extent of swelling and the dimensions of swollen chain structure were dependent on the ion species and salt concentration in the solutions. Anion specificity was clearly observed, whereas cations exhibited weaker modulation in ion-specific hydration states. The anion specificity could be ascribed to ion-specific interactions between the quaternary ammonium cation in sulfobetaine and the anions. The weak cation specificity was attributed to the intrinsically weak cohesive interactions between the weakly hydrated sulfonate anion in sulfobetaine and the strongly hydrated cations. The ion-specific hydration of PMAPS brushes was largely consistent with the ion-specific aggregation state of the PMAPS chains in aqueous solutions.

Label-Free Specific Detection and Collection of C-Reactive Protein Using Zwitterionic Phosphorylcholine-Polymer-Protected Magnetic Nanoparticles

In this study, poly[2-methacryloyloxyethyl phosphorylcholine (MPC)]-protected Fe₃O₄ nanoparticles were prepared and used for the label-free specific detection and collection of an acute inflammation marker, C-reactive protein (CRP), in a simulated body fluid. The Fe₃O₄ nanoparticle surface was modified using poly(MPC) by surface-initiated atom-transfer radical polymerization. The density of poly(MPC) was 0.16 chains/nm², and the colloidal stability of the nanoparticles in aqueous media and human plasma was effectively improved by surface modification. The size of the as-prepared poly(MPC)-protected Fe₃O₄ nanoparticles was ∼200 nm. After coming into contact with CRP, the nanoparticles aggregated as CRP comprises five subunits, and each subunit can bind to a phosphorylcholine group with two free Ca²⁺ ions. The change in the nanoparticle size exhibited a good correlation with the CRP concentration in the range of 0-600 nM. A low limit of detection of 10 nM for CRP was observed. The particles effectively reduced the adsorption of nonspecific proteins, and the change in the nanoparticle size with CRP was not affected by the coexistence of bovine serum albumin at a concentration 1000 times greater than that of CRP. Nanoparticle aggregates formed using CRP were dissociated using ethylenediamine- N, N, N', N'-tetraacetic acid, disodium salt, thereby regenerating poly(MPC)-protected Fe₃O₄ nanoparticles. In addition, CRP was collected from aqueous media using an acidic buffer solution and human plasma. CRP-containing aqueous solutions were treated with poly(MPC)-protected Fe₃O₄. After poly(MPC)-protected Fe₃O₄ nanoparticles were separated using a neodymium magnet and centrifugation, the concentration of CRP in the media dramatically decreased. In stark contrast, the concentration of albumin present in the test solution did not change even after treatment with the nanoparticles. Therefore, nanoparticles specifically recognize CRP from complex biological fluids. Although inhibition tests in the presence of 1,2-dioleoyl- sn-glycero-3-phosphocholine liposomes or free poly(MPC) were also carried out, the binding of poly(MPC)-protected Fe₃O₄ to CRP was not affected by these inhibitors. In conclusion, poly(MPC)-brush-bearing magnetic nanoparticles can serve not only as reliable materials for detecting and controlling the levels of CRP in simulated body fluids but also as diagnostic and therapeutic materials.

Lipid-Hydrogel-Nanostructure Hybrids as Robust Biofilm-Resistant Polymeric Materials

Despite extensive efforts toward developing antibiofilm materials, efficient prevention of biofilm formation remains challenging. Approaches based on a single strategy using either bactericidal material, antifouling coatings, or nanopatterning have shown limited performance in the prevention of biofilm formation. This study presents a hybrid strategy based on a lipid-hydrogel-nanotopography hybrid for the development of a highly efficient and durable biofilm-resistant material. The hybrid material consists of nanostructured antifouling, biocompatible polyethylene glycol-based polymer grafted with an antifouling zwitterionic polymer of 2-methacryloyloxyethyl phosphorylcholine. Based on the unique composite nanostructures, the lipid-hydrogel-nanostructure hybrid exhibits superior dual functionalities of antifouling and bactericidal activities against Gram-negative and Gram-positive bacteria, compared with those of surfaces with simple nanostructures or antifouling coatings. Additionally, it preserves the robust antibiofilm activity even when the material is damaged under external mechanical stimuli thanks to the polymeric composite nanostructure.

Surface functionalization of polytetrafluoroethylene substrate with hybrid processes comprising plasma treatment and chemical reactions

Polytetrafluoroethylene (PTFE) exhibits excellent mechanical properties and chemical stability and has been widely used in medical fields for the preparation of implantable medical devices. However, the implantation of PTFE in living systems results in inflammation reactions and infections at the surface thus limits its long-term applications. For PTFE surface modification, we examined the effects of mussel-inspired polydopamine (PDA) coating and the further introduction of functional groups. During PDA coating, the plasma pretreatment on PTFE enhanced the stability of the PDA coating layer. Furthermore, the introduction of functional groups on the PDA layer was carried out using reactive functional groups for the photoinduced graft polymerization of methacrylate. For instance, 2-methacryloyloxyethyl phosphorylcholine (MPC) could be polymerized from the surface of the substrate. These chemical modifications were confirmed step by step using spectroscopes to obtain the hydrophilic surface of the poly(MPC)-modified PTFE. The protein adsorption behaviors on PTFE and poly(MPC)-modified PTFE were compared to understand biocompatibility characteristics of these substrates. The surface of PTFE was immediately covered with albumin and the contact between the substrate and the serum resulted in an increase in the fibrinogen composition with time. On the other hand, fewer proteins were adsorbed on the poly(MPC)-modified PTFE substrate. Thus, this modification procedure would serve as a strategy for safer alterations in PTFE surfaces to expand the life span of the PTFE-carrying medical devices in living systems.

Initial Cell Adhesion onto a Phospholipid Polymer Brush Surface Modified with a Terminal Cell Adhesion Peptide

Dynamic changes in the properties of adsorbed protein layers at material surfaces make it difficult to analyze a cell adhesion behavior. Adhesion is affected by the ligand molecules in the adsorbed protein layers on the material's surface. This study aimed to quantitatively analyze the initial cell adhesion onto a polymeric surface modified with immobilized cell adhesion molecules with a well-defined structure. Peptides containing an arginine-glycine-aspartic acid (RGD) sequence were introduced at almost all the termini of the grafted poly(2-methacryloyloxyethyl phosphorylcholine) [poly(MPC)] chains using a click reaction at a highly protein-resistant poly(MPC) brush layer. Thus, the surface could bind to the cell membrane proteins only through the immobilized RGD. Furthermore, the degree of polymerization of the grafted poly(MPC) chains could control the hydrated poly(MPC) brush layer softness, as determined by measuring the dissipation energy loss using a quartz crystal microbalance. At the initial stage of cell adhesion, the density of cells adhering to the RGD-immobilized poly(MPC) brush layers did not depend on the poly(MPC) brush layer softness. However, spreading of the adherent cells was inhibited on the RGD-immobilized poly(MPC) brush layers with a higher softness. Hence, the results suggested that the layer softness did not affect the binding number between the RGD and cell membrane protein during initial cell adhesion; however, the intracellular signaling triggered by the RGD-receptor interaction was inhibited. The poly(MPC) brush surface carrying immobilized cell adhesion molecules has the potential to analyze precisely the effect of the properties of cell adhesion molecules on initial cell adhesion.

Improved antifouling properties of photobioreactors by surface grafted sulfobetaine polymers

To improve the antifouling (AF) properties of photobioreactors (PBR) for microalgal cultivation, using trihydroxymethyl aminomethane (tris) as the linking agent, a series of polyethylene (PE) films grafted with sulfobetaine (PE-SBMA) with grafting density ranging from 23.11 to 112 μg cm^-2 were prepared through surface-initiated atom transfer radical polymerization (SI-ATRP). It was found that the contact angle of PE-SBMA films decreased with the increase in the grafting density. When the grafting density was 101.33 μg cm^-2, it reached 67.27°. Compared with the PE film, the adsorption of protein on the PE-SBMA film decreased by 79.84% and the total weight of solid and absorbed microalgae decreased by 54.58 and 81.69%, respectively. Moreover, the transmittance of PE-SBMA film recovered to 86.03% of the initial value after cleaning, while that of the PE film recovered to only 47.27%. The results demonstrate that the AF properties of PE films were greatly improved on polySBMA-grafted surfaces.

Surface-Initiated Controlled Radical Polymerization: State-of-the-Art, Opportunities, and Challenges in Surface and Interface Engineering with Polymer Brushes

The generation of polymer brushes by surface-initiated controlled radical polymerization (SI-CRP) techniques has become a powerful approach to tailor the chemical and physical properties of interfaces and has given rise to great advances in surface and interface engineering. Polymer brushes are defined as thin polymer films in which the individual polymer chains are tethered by one chain end to a solid interface. Significant advances have been made over the past years in the field of polymer brushes. This includes novel developments in SI-CRP, as well as the emergence of novel applications such as catalysis, electronics, nanomaterial synthesis and biosensing. Additionally, polymer brushes prepared via SI-CRP have been utilized to modify the surface of novel substrates such as natural fibers, polymer nanofibers, mesoporous materials, graphene, viruses and protein nanoparticles. The last years have also seen exciting advances in the chemical and physical characterization of polymer brushes, as well as an ever increasing set of computational and simulation tools that allow understanding and predictions of these surface-grafted polymer architectures. The aim of this contribution is to provide a comprehensive review that critically assesses recent advances in the field and highlights the opportunities and challenges for future work.

Reduced Blood Cell Adhesion on Polypropylene Substrates through a Simple Surface Zwitterionization

To overcome the thrombogenic reactions of hydrocarbon-based biomaterials in clinical blood treatment, we introduce a model study of surface zwitterionization of a polypropylene (PP) substrate using a set of well-defined copolymers for controlling the adhesion of blood cells in vitro. Random and block copolymers containing zwitterionic units of 2-methacryloyloxyethyl phosphorylcholine (MPC), [3-(methacryloylamino)propyl]dimethyl(3-sulfopropyl)ammonium hydroxide inner salt (SBAA), or nonionic units of 2-hydroxyethyl methacrylate (HEMA) with a controlled hydrophobic segment of 70% n-butyl methacrylate (BMA) units in these polymers were synthesized through reversible addition-fragmentation chain transfer polymerization. A systematic study of how zwitterionic and nonionic copolymer architectures associated with controlled chain orientation via hydration processes affect blood compatibility is reported. The surface wettability of PP substrates coated with the block copolymer with poly(MPC) (PMPC) segments was higher than that of the random copolymer poly(MPC-random-BMA). However, only the random copolymers with SBAA units demonstrate a higher surface wettability. The PP substrate coated with nonionic copolymers containing HEMA units showed relatively lower hydration capability associated with higher protein adsorption, platelet adhesion, and leukocyte attachment than those with zwitterionic copolymers. The random copolymer poly(SBAA-random-BMA) coated on the PP substrates exhibited resistance to cell adhesion in human whole blood at a level comparable to that of MPC copolymers. An ideal zwitterionic PP substrate could be obtained by coating it with a block copolymer composed of PMPC and poly(BMA) (PBMA) segments, PMPC-block-PBMA. The water contact angle decreased dramatically from approximately 100° on the original PP substrate to 11° within 30 s. The number of blood cells attached on PMPC-block-PBMA decreased significantly to less than 2.5% of that on original PP. These results prove that the rational design of zwitterionic polymers incorporated with a hydrophobic anchoring portion provides a promising approach to reduce blood cell adhesion and protein adsorption of hydrocarbon-based biomaterials applied in direct contact with human whole blood.

Photoreactive Initiator for Surface-Initiated ATRP on Versatile Polymeric Substrates

We synthesized 4-azidophenylcarbonyloxyethyl-2-bromoisobutyrate (AzEBI) for construction of a polymer brush layer on a desired area on various polymeric substrates. After 3.0 min of exposure to UV irradiation, the phenylazide groups of AzEBI decomposed and formed covalent bonds with the polymeric substrate surfaces to introduce an initiator of atom transfer radical polymerization (ATRP). The reaction area of AzEBI was regulated using a photomask during photoreaction and surface initiated ATRP of 2-methacryloyloxyethyl phosphorylcholine (MPC) occurred on the desired part of the surface. In the area with poly(MPC), the surface was superhydrophilic and the adhesion of HeLa cell was effectively suppressed. The AzEBI allows the construction of polymer brush layer in anywhere and would expand the potential application of ATRP to prepare polymer brush layer on polymeric substrates.

Diffusion-Induced Hydrophilic Conversion of Polydimethylsiloxane/Block-Type Phospholipid Polymer Hybrid Substrate for Temporal Cell-Adhesive Surface

In this study, diffusion-induced hydrophobic-hydrophilic conversion of the surface of the cross-linked polydimethylsiloxane (PDMS) substrate was realized by employing a simple swelling-deswelling process of PDMS substrate in a block-type polymer solution with the aim of development of a temporal cell-adhesive substrate. The ABA block-type polymer composed of poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) segment and PDMS segment with over 70% of dimethylsiloxane unit composition could be successfully incorporated in the PDMS substrate during the swelling-deswelling process to prepare the PDMS/phospholipid block copolymer hybrid substrates. During the aging process of the PDMS substrate for 4 days in aqueous medium, its surface property changed gradually from hydrophobic to hydrophilic. X-ray photoelectron spectroscopy and atomic force microscopy data provided strong evidence that the time-dependent hydrophilic conversion of the PDMS/block-type phospholipid polymer hybrid substrate was induced by the diffusion of the hydrophilic PMPC segment in the block-type polymer to be tethered on the substrate. During the hydrophilic conversion process, surface-adsorbed fibronectin was gradually desorbed from the substrate surface, and this resulted in successful detachment of two-dimensional connected cell crowds.