Synthesis and characterisation of phosphorylcholine-based polymers useful for coating blood filtration devices

Tethering zwitterionic polymer coatings to mediated glucose biosensor enzyme electrodes can decrease sensor foreign body response yet retain sensor sensitivity to glucose

Foreign body response (FBR) is a major challenge that affects implantable biosensors and medical devices, including glucose biosensors, leading to a deterioration in device response over time. Polymer shields are often used to mitigate this issue. Zwitterionic polymers (ZPs) are a promising class of materials that reduce biofouling of implanted devices. A series of ZPs each containing tetherable epoxide functional groups was synthesised for application as a polymer shield for eventual application as implantable glucose biosensors. The polymer shields were initially tested for the ability to resist fibrinogen adsorption and fibroblast adhesion. All synthesised ZPs showed comparable behaviour to a commercial Lipidure ZP in resisting fibrinogen adsorption. Nafion, a common anionic shield used against electrochemical interferents, showed higher protein adsorption and comparable cell adhesion resistance as uncoated control surfaces. However, a poly(2-methacryloyloxyethyl phosphorylcholine-co-glycidyl methacrylate) (MPC)-type ZP showed similar behaviour to Lipidure, with approximately 50% reduced fibrinogen adsorption and 80% decrease in fibroblast adhesion compared to uncoated controls. An MPC-coated amperometric glucose biosensor showed comparable current density and a 1.5-fold increase in sensitivity over an uncoated control biosensor, whereas all other polymer shields tested, including Lipidure, Nafion and a poly(ethyleneglycol) polymer, resulted in lower sensitivity and current density. Collectively, these characteristics make MPC-polymer shield coatings an appealing possibility for use in implantable glucose sensors and other implanted devices with the aim of reducing FBR while maintaining sensor performance.

Preparation of Biocompatible Poly(2-(methacryloyloxy)ethyl phosphorylcholine) Hollow Particles Using Silica Particles as a Template

Hydrophilic poly(2-(methacryloyloxy)ethyl phosphorylcholine) (PMPC) shows biocompatibility because the pendant phosphorylcholine group has the same chemical structure as the hydrophilic part of phospholipids that form cell membranes. Hollow particles can be used in various fields, such as a carrier in drug delivery systems because they can encapsulate hydrophilic drugs. In this study, vinyl group-decorated silica particles with a radius of 150 nm were covered with cross-linked PMPC based on the graft-through method. The radius of PMPC-coated silica particles increased compared to that of the original silica particles. The PMPC-coated silica particles were immersed in a hydrogen fluoride aqueous solution to remove template silica particles to prepare the hollow particles. The PMPC hollow particles were characterized by dynamic light scattering, infrared spectroscopy, thermogravimetric analysis, and transmission electron microscopy observations. The thickness of the hollow particle shell can be controlled by the polymerization solvent quality. When a poor solvent for PMPC was used for the polymerization, PMPC hollow particles with thick shells can be obtained. The PMPC hollow particles can encapsulate hydrophilic guest molecules by immersing the hollow particles in a high-concentration guest molecule solution. The biocompatible PMPC hollow particles can be used in a drug carrier.

Cononsolvency of Poly[2-(methacryloyloxy)ethyl phosphorylcholine] in Ethanol-Water Mixtures: A Neutron Reflectivity Study

Molecular mechanisms underlying the cononsolvency, a re-entrant coil-to-globule-to-coil conformational transition of polymer chains in mixtures of two good solvents, of poly[2-(methacryloyloxy)ethyl phosphorylcholine] (PMPC) in ethanol-water binary mixtures were complementarily investigated. This was accomplished by following a statistical mechanical model for competitive hydrogen bonding combined with the cooperative solvation concept as well as neutron reflectivity (NR) experiments employing contrast variation in the cononsolvents. The experimental re-entrant aggregation of the PMPC chains in ethanol-water mixed solvents, obtained on the basis of turbidity was accurately reproduced by theoretical calculations. The calculation proved the relatively strong cooperativity of ethanol and the preferential interaction of water, while the total coverage of solvents was the lowest at an ethanol volume fraction (f_ethanol) of 0.90. At this level, the cononsolvency was the most significant, and the collapsed PMPC chains were solvated with more water than the bulk mixed solvent. The ethanol-water cononsolvency for the PMPC brushes on a planar silicon wafer was investigated by NR experiments, and the solvent composition involved in the collapsed PMPC brush was addressed according to the contrast variation study with mixed solvents of water, deuterium oxide, ethanol-d₅, and ethanol-d₆. The collapsed PMPC brushes at f_ethanol = 0.90 contained more water than the bulk solvent. The preferential distribution of water in the collapsed PMPC brush was consistent with the simulation results. Therefore, the molecular mechanism for the cononsolvency of PMPC in ethanol-water mixed solvents based on competitive hydrogen bonding coupled with cooperative solvation was experimentally rationalized.

Solubilization of Paclitaxel by Self-Assembled Amphiphilic Phospholipid-Mimetic Polymers with Varied Hydrophobicity

2-Methacryloyloxyethyl phosphorylcholine (MPC) polymers have been used as a coating agent on medical devices and as a carrier in drug delivery systems (DDSs). Paclitaxel (PTX) is a water-insoluble anticancer drug whose solubilizer is necessary for administration. Block and random copolymers composed of hydrophilic MPC and butyl methacrylate, named PMB, show different properties, depending on the polymer sequence and MPC content. In the present study, we used amphiphilic MPC polymers comprising hydrophobic dodecyl methacrylate (DMA). The self-assembling properties and PTX solubilization of random and block poly(MPC-co-DMA)s (rPMDs and bPMDs) with different compositions were examined and compared. rPMDs with high DMA content formed large and relatively loose self-assembled structures, which solubilized PTX. However, bPMDs formed small and compact self-assembled structures with poor PTX solubilization. PTX solubilized by PMB with small and loose self-assembled structures showed efficient drug action, similar to free PTX; however, rPMDs fell short of demonstrating PTX efficiency. Our results suggest that the self-assembling properties and the hydrophobicity of amphiphilic MPC polymers largely affect PTX solubilization as well as drug action, which is required to be controlled by the polymer sequence, as well as the structure and composition of the hydrophobic monomer for efficient DDS.

Universal Intraductal Surface Antifouling Coating Based on an Amphiphilic Copolymer

Surface modification on the inner wall of medical or industrial polymeric catheters with a high length/diameter ratio is highly desired. Herein, a universal and facile method based on an amphiphilic copolymer was developed to immobilize an intraductal surface antifouling coating for a variety of polymeric catheters. A fouling-repelled thin layer was formed by swelling-driven adsorption via directly perfusing an amphiphilic copolymer [polyvinylpyrrolidone-polydimethylsiloxane-polyvinylpyrrolidone (PVP-PDMS-PVP)] solution into catheters. In this copolymer, hydrophobic PDMS was embedded into a shrinking cross-linked network of catheters; also, PVP segments migrated to the surface under driving water to form a hydrophilic antifouling coating. Moreover, because of the coordination between I₂ and pyrrolidone of PVP, the copolymer-modified intraductal surface was then infused with aqueous I₂ to form the PVP-I₂ complex, endowing this coating with bactericidal activity. Notably, diverse catheters with arbitrary shapes (circular, rectangular, triangular, and hexagonal) and different components (silicone, polyurethane, and polyethylene) were also verified to work using this interfacial interpenetration strategy. The findings in this work provide a new avenue toward facile and universal fabrication of intraductal surface antifouling catheters, creating a superior option for decreasing the consumable costs in industrial production and alleviating the pain of replacing catheters for patients.

Anchorable phosphorylcholine copolymer synthesis and cell membrane mimetic antifouling coating fabrication for blood compatible applications

Protein adsorption and platelet activation on biomedical devices contacting blood may lead to the formation of thrombus. The thrombogenicity of biomaterials could be minimized or prevented by anchoring a cell membrane mimetic antifouling coating (CMMAC). Here, we report the construction of a CMMAC by a newly designed 2-methacryloyloxyethyl phosphorylcholine (MPC) copolymer (PMPCC) containing 5-20 carboxylic long arm side chains. The long arm provides its end carboxylic group with more freedom and a larger reaction space for an easier and more efficient surface anchoring. With the assistance of mussel-inspired universal adhesive polydopamine (PDA), different material surfaces precoated with PDA can immobilize the PMPCC via multipoint anchoring of the randomly distributed carboxylic side chains. The multipoint anchoring results in a stabilized and condensed PDA-PMPCC coating. The phosphorylcholine zwitterions of the densely immobilized PMPCC polymers form a cell outer membrane mimetic interface in an aqueous environment, endowing excellent properties of resisting protein adsorption, platelet activation and blood cell adhesion. More importantly, the PDA-PMPCC-coated glass surface can suppress thrombus formation for more than 24 h, while the bare glass surface forms obvious thrombus in 6 h tested in the same blood. Furthermore, the fabrication of the PDA-PMPCC coating is simple and material-independent. Therefore, the simple synthesis, facile surface coating and excellent hemocompatibility of the PMPCC make it a promising material for biomimetic surface modification.

Characterization of smoke generated during the use of surgical knife in laparotomy surgeries

The staff in hospitals is the high-risk group affected by indoor air pollution for operational reasons. However, there is a lack of relevant information and research on surgical smoke in Taiwan. This study analyses the substance of the smoke and develops relative strategies to prevent harm from the working place. This study aims to evaluate the surgical smoke generated during laparotomy and laparoscopic operation. The relationship between smoke and the risk of health-care workers was also discussed in order to set suitable solutions for smoke collection and emission. The study measured surgical smoke of 30 cases in operating rooms in three different hospitals, smoke was collected at different timings and different areas during the operation using a low-flow sampler. The concentration and accumulation number of size 0.3 μm suspended particles were the highest among all size of particles in different detection areas and timing. The concentration number of 0.3 μm and 0.5 μm particles reached the maximum after 10 min of electrosurgical treatment; however, the concentration number of 5 μm particles began to decrease after 5-15 min of the treatment. Besides, the cumulative particle numbers of 0.3 μm and 0.5 μm in laparoscopic operation were higher than those of laparotomy after 10 min of the treatment. This study suggests that surgical smoke prevention should use smoke evacuator; health-care workers should also wear a highly efficient tight seal-fit mask in the operating room to avoid damage to their health and cause chronic diseases.Implications: Indoor air pollution in medical institutions is a topic of less concern, and the health of healthcare workers is threatened by surgical smoke that generated during operations. This study measured and analyzed the harmful substances in the surgical smoke in the operating rooms of hospitals, and put forward the corresponding suggestions. In April 2018, legislators in Taiwan also convened a seminar on "Respiratory protection for operating room personnel in medical institutions". The seminar applied the findings of this study and adopted the recommendations to improve related equipment and strategies in future plans.

Phosphorylcholine- and cation-bearing copolymer coating with superior antibiofilm and antithrombotic properties for blood-contacting devices

The phosphorylcholine- and cation-bering copolymer coating endowed the blood-contacting devices with superior antibiofilm and antithrombotic ability.

Formation of Hydrophobic Domains on the poly(MPC-co-Dodecyl Methacrylate)-Coated Surface Recognized by Macrophage-like Cells

Copolymers comprising 2-methacryloyloxyethyl phosphorylcholine (MPC) and hydrophobic methacrylic esters were used as biomembrane-mimetic polymers to provide blood compatibility. In the present study, we compared the surfaces coated with two MPC polymers with different alkyl groups, namely, poly(MPC-co-butyl methacrylate) (PMB) and poly(MPC-co-dodecyl methacrylate) (PMD), to clarify the effect of their hydrophobic units. Various substrates, such as poly(ethylene terephthalate), polycarbonate, polypropylene, acrylonitrile-butadiene-styrene copolymer, and stainless steel, were coated with ethanol solutions containing various concentrations of PMD or PMB. The solubility of PMD in ethanol changed depending on the water content. Scanning probe microscopy and rhodamine 6G staining revealed heterogeneous microstructures on the PMD-coated surface but not on the PMB-coated surface. Adhesion of various cells was efficiently suppressed by the PMD coating at lower concentration than the PMB coating, except regarding the adhesion of macrophage-like RAW264.7 cells. Our results suggest that the dodecyl groups in PMD increased its affinity for the substrates and simultaneously induced the formation of hydrophobic domains recognized by RAW264.7 cells.

Blood-Compatible Surfaces with Phosphorylcholine-Based Polymers for Cardiovascular Medical Devices

For the acquisition of blood-compatible materials, various hydrophilic polymers for surface modification have been examined. Among them, polymers with a representative phospholipid polar group, the phosphorylcholine (PC) group, are a successful example. These polymers were designed from inspiration of the cell membrane surface and provide protein adsorption resistance even following contact with plasma. This important property is based on the unique hydration state of water molecules surrounding hydrated polymer; in other words, water molecules weakly interact with the polymers and maintain their favorable cluster structure through hydrogen bonding. These polymers are not only hydrophilic, but also electrically neutral, important characteristics which make hydrogen bonding with water molecules less likely to occur and avoid hydrophobic interactions. Phosphorylcholine groups and other zwitterionic structures are significant as hydrophilic functional groups meeting these important requirements. In this review, blood compatibility of a polymer having a PC group is introduced in relation to its hydration structure, followed by a description of the applications of this polymer to cardiovascular medical devices.

Real-Time Study of the Adsorption and Grafting Process of Biomolecules by Means of Bloch Surface Wave Biosensors

A combined label-free and fluorescence surface optical technique was used to quantify the mass deposited in binary biomolecular coatings. These coatings were constituted by fibronectin (FN), to stimulate endothelialization, and phosphorylcholine (PRC), for its hemocompatibility, which are two properties of relevance for cardiovascular applications. One-dimensional photonic crystals sustaining a Bloch surface wave were used to characterize different FN/PRC coatings deposited by a combination of adsorption and grafting processes. In particular, the label-free results permitted to quantitatively assess the mass deposited in FN adsorbed (185 ng/cm²) and grafted (160 ng/cm²). PRC binding to grafted FN coatings was also quantified, showing a coverage as low as 10 and 12 ng/cm² for adsorbed and grafted PRC, respectively. Moreover, desorption of FN deposited by adsorption was detected and quantified upon the addition of PRC. The data obtained by the surface optical technique were complemented by water contact angle and X-ray photoelectron spectroscopy (XPS) analyses. The results were in accordance with those obtained previously by qualitative and semiquantitative techniques (XPS, time-of-flight secondary ion mass spectrometry) on several substrates (PTFE and stainless steel), confirming that grafted FN coatings show higher stability than those obtained by FN adsorption.

New Aliphatic Glycerophosphoryl-Containing Polyurethanes: Synthesis, Platelet Adhesion and Elution Cytotoxicity Studies

In this study new poly(ether)urethanes (PEUs) based on aliphatic diisocyanates were synthesized with phospholipid-like residues as chain extenders. The primary objective was to prepare new polyurethanes from diisocyanates that are less toxic than the aromatic ones widely used in medical-grade polyurethanes, in order to investigate the effect of the different aromatic or aliphatic hard segment content on the final properties of the materials. Some glycerophospho residues were simultaneously introduced to enhance the hemocompatibility of these materials. Polymers were prepared by a conventional two-step solution polymerization procedure using hexamethylene diisocyanate (HDI) and dodecametilendiisocyanate (DDI) and poly(1,4-butanediol) with molecular weight 1000 to form prepolymers, which were subsequently polymerized with 1-glycerophosphorylcholine (1-GPC) or glycerophosphorylserine (GPS) to act as chain extenders. The reference polymers bearing 1,4-butandiol (BD) were also synthesized. The polymers obtained were characterized by Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance (1H NMR), and differential scanning calorimetry (DSC). The hemocompatibility of synthesized segmented polyurethanes was preliminarily investigated by platelet-rich plasma contact studies and related scanning electron microscopy (SEM) photographs as well as by cell viability assay after cell exposure to material elutions to assess the effect of any toxic leachables coming out from the samples. Two of the polymers gave interesting results, suggesting the desirability of further investigation into their possible use in biomedical devices.

Gold Nanorods Stabilized by Biocompatible and Multifunctional Zwitterionic Copolymer for Synergistic Cancer Therapy

A zwitterionic copolymer between methacryloyloxyethyl phosphorylcholine (MPC) and methacrylic acid (MA), PMAMPC is introduced as a potential versatile polymeric stabilizer for gold nanorods (AuNRs). The MA units in the copolymer serve as built-in feature for multiple functionalization, namely introducing additional thiol groups as active sites for binding with the AuNRs and conjugating with doxorubicin (DOX), an anticancer drug via acid-labile hydrazone linkage. The MPC units, on the other hand, provide biocompatibility and antifouling characteristics. The chemically modified PMAMPC can act as an effective stabilizer for AuNRs yielding PMAMPC-DOX-AuNRs with a fairly uniform size and shape with good colloidal stability. In vitro cytotoxicity suggested that PMAMPC can not only improve the AuNRs biocompatibility, but also decrease DOX toxicity to a certain extent. The PMAMPC-DOX-AuNRs were efficiently internalized inside cancer cells and localized in lysosomes, where DOX was presumably acid-triggered released as monitored by confocal laser scanning microscopic analysis and flow cytometry. Furthermore, the combined photothermal-chemo treatment of cancer cells using PMAMPC-DOX-AuNRs exhibited a higher therapeutic efficacy than either single treatment alone. These results suggested that the PMAMPC-DOX-AuNRs could potentially be applied in pH-triggered drug delivery for synergistic cancer therapy.

Micrometre and nanometre scale patterning of binary polymer brushes, supported lipid bilayers and proteins

Binary polymer brush patterns were fabricated via photodeprotection of an aminosilane with a photo-cleavable nitrophenyl protecting group. UV exposure of the silane film through a mask yields micrometre-scale amine-terminated regions that can be derivatised to incorporate a bromine initiator to facilitate polymer brush growth via atom transfer radical polymerisation (ATRP). Atomic force microscopy (AFM) and imaging secondary ion mass spectrometry (SIMS) confirm that relatively thick brushes can be grown with high spatial confinement. Nanometre-scale patterns were formed by using a Lloyd's mirror interferometer to expose the nitrophenyl-protected aminosilane film. In exposed regions, protein-resistant poly(oligo(ethylene glycol)methyl ether methacrylate) (POEGMEMA) brushes were grown by ATRP and used to define channels as narrow as 141 nm into which proteins could be adsorbed. The contrast in the pattern can be inverted by (i) a simple blocking reaction after UV exposure, (ii) a second deprotection step to expose previously intact protecting groups, and (iii) subsequent brush growth via surface ATRP. Alternatively, two-component brush patterns can be formed. Exposure of a nitrophenyl-protected aminosilane layer either through a mask or to an interferogram, enables growth of an initial POEGMEMA brush. Subsequent UV exposure of the previously intact regions allows attachment of ATRP initiator sites and growth of a second poly(cysteine methacrylate) (PCysMA) brush within photolithographically-defined micrometre or nanometre scale regions. POEGMEMA brushes resist deposition of liposomes, but fluorescence recovery after photobleaching (FRAP) studies confirm that liposomes readily rupture on PCysMA "corrals" defined within POEGMEMA "walls". This leads to the formation of highly mobile supported lipid bilayers that exhibit similar diffusion coefficients to lipid bilayers formed on surfaces such as glass.

Effect of Salt on Phosphorylcholine-based Zwitterionic Polymer Brushes

A quantitative investigation of the responses of surface-grown biocompatible brushes of poly(2-(methacryloyloxy)ethyl phosphorylcholine) (PMPC) to different types of salt has been carried out using ellipsometry, quartz crystal microbalance (QCM) measurements, and friction force microscopy. Both cations and anions of varying valency over a wide range of concentrations were examined. Ellipsometry shows that the height of the brushes is largely independent of the ionic strength, confirming that the degree of swelling of the polymer is independent of the ionic character of the medium. In contrast, QCM measurements reveal significant changes in mass and dissipation to the PMPC brush layer, suggesting that ions bind to phosphorylcholine (PC) groups in PMPC molecules, which results in changes in the stiffness of the brush layer, and the binding affinity varies with salt type. Nanotribological measurements made using friction force microscopy show that the coefficient of friction decreases with increasing ionic strength for a variety of salts, supporting the conclusion drawn from QCM measurements. It is proposed that the binding of ions to the PMPC molecules does not change their hydration state, and hence the height of the surface-grown polymeric brushes. However, the balance of the intra- and intermolecular interactions is strongly dependent upon the ionic character of the medium between the hydrated chains, modulating the interactions between the zwitterionic PC pendant groups and, consequently, the stiffness of the PMPC molecules in the brush layer.

Nanoprecipitation of polymeric nanoparticle micelles based on 2-methacryloyloxyethyl phosphorylcholine (MPC) with 2-(diisopropylamino)ethyl methacrylate (DPA), for intracellular delivery applications

Biodistribution of nanoparticle-based intracellular delivery systems is mediated primarily by particle size and physicochemical properties. As such, overcoming the rapid removal of these by the reticuloendothelial system remains a significant challenge. To date, a number of copolymer nanoparticle systems based on 2-methacryloyloxyethyl phosphorylcholine (MPC) with 2-(diisopropylamino)ethyl methacrylate (DPA), displaying biomimetic and pH responsive properties, have been published, however these have been predominately polymersome based, whilst micelle systems have remained relatively unexplored. This study utilised nanoprecipitation to investigate the effects of solvent and buffer choice upon micelle size and polydispersity, and found using methanol produced monodisperse micelles of circa 70 nm diameter, whilst ethanol produced polydisperse systems with nanoparticles of circa 128 nm diameter. The choice of aqueous buffer, dialysis of the systems, extended storage, and exposure to a wide temperature range (5-70 °C) had no significant effect on micelle size, and the systems were highly resistant to dilution, indicating excellent colloidal stability. Optimisation of the nanoprecipitation process, post precipitation, was investigated, and model drugs successfully loaded whilst maintaining system stability. Subsequent in vitro studies suggested that the micelles were of negligible cellular toxicity, and an apparent cellular uptake was observed via confocal laser scanning microscopy. This paper presents the first report of an optimised nanoprecipitation methodology for the formation of MPC-DPA nanoparticle micelles, and in doing so achieved monodisperse systems with the size and physicochemical characteristics seen as desirable for long circulating therapeutic delivery vehicles.

Non-covalent phosphorylcholine coating reduces protein adsorption and phagocytic uptake of microparticles

Phosphorylcholine co-polymer was assembled on model polystyrene microparticles through a simple, widely-applicable ethanol coating process. The coating rendered particles resistant to protein adsorption and phagocytosis by macrophages, making it useful for a range of biological applications.

Substrate independent coating formation and anti-biofouling performance improvement of mussel inspired polydopamine

Anti-biofouling performance of mussel inspired polydopamine coating can be improved significantly by simple coordination, oxidation, heating or grafting treatment.

Bioactive technologies for hemocompatibility

The contact of any biomaterial with blood gives rise to multiple pathophysiologic defensive mechanisms such as activation of the coagulation cascade, platelet adhesion and activation of the complement system and leukocytes. The reduction of these events is of crucial importance for the successful clinical performance of a cardiovascular device. This can be achieved by improving the hemocompatibility of the device materials or by pharmacologic inhibition of the key enzymes responsible for the activation of the cascade reactions, or a combination of both. Different strategies have been developed during the last 20 years, and this article attempts to review the most significant, by dividing them into three main categories: bioinert or biopassive, biomimetic and bioactive strategies. With regard to bioactive strategies, particular attention is given to heparin immobilization and recent related technologies. References from both scientific literature and commercial sites are provided. Future development and studies are suggested.

Cell membrane-inspired phospholipid polymers for developing medical devices with excellent biointerfaces

This review article describes fundamental aspects of cell membrane-inspired phospholipid polymers and their usefulness in the development of medical devices. Since the early 1990s, polymers composed of 2-methacryloyloxyethyl phosphorylcholine (MPC) units have been considered in the preparation of biomaterials. MPC polymers can provide an artificial cell membrane structure at the surface and serve as excellent biointerfaces between artificial and biological systems. They have also been applied in the surface modification of some medical devices including long-term implantable artificial organs. An MPC polymer biointerface can suppress unfavorable biological reactions such as protein adsorption and cell adhesion - in other words, specific biomolecules immobilized on an MPC polymer surface retain their original functions. MPC polymers are also being increasingly used for creating biointerfaces with artificial cell membrane structures.

Ultrathin antifouling coatings with stable surface zwitterionic functionality by initiated chemical vapor deposition (iCVD)

Antifouling thin films of poly[N,N-dimethyl-N-methacryloxyethyl-N-(3-sulfopropyl)-co-2-(dimethylamino)ethyl methacrylate-co-ethylene glycol dimethacrylate] (PDDE) were synthesized via a substrate-independent and all-dry-initiated chemical vapor deposition (iCVD) technique followed by a diffusion-limited vapor-phase reaction with 1,3-propane sultone. Coated surfaces exhibited very low absorption of various foulants including bovine serum albumin (BSA), humic acid (HA), and sodium alginate (SA), as measured with the quartz crystal microbalance with dissipation monitoring (QCM-D). The fouling by humic acid was dependent on the presence of divalent cations such as Ca(2+). Both depth profiling and angle-resolved X-ray photoelectron spectroscopy (XPS) measurements indicated that the zwitterionic groups were highly concentrated in the top ~3 nm of the film. The contact angle measurements revealed a limited degree of surface chain reorganization upon contacting water. The dynamic contact angles remained unchanged after 100 days of storage in air, indicating the stability of the interface. The coating was substrate-independent, and the film was conformal on surface nanostructures including trenches, reverse osmosis membranes, and electrospun nanofiber mats.

Optimized molecular structure of photoreactive biocompatible block copolymers for surface modification of metal substrates

Poly(2-methacryloyloxyethyl phosphorylcholine)-b-poly(2-methacryloyloxyethyl phosphate-co-2-cinnamoyloxyethyl methacrylate) (PMPC-b-P(MPA/CMA)) was prepared by reversible addition-fragmentation chain transfer (RAFT)-controlled radical polymerization. The block copolymers were coated on stainless steel (SUS316L) and other metal substrates, and then the surface was subsequently irradiated with UV light. The wettability of a specimen surface treated with a block copolymer was improved in comparison with that of an untreated SUS316L plate. From X-ray photoelectron spectroscopy (XPS) data, it was clear that the P(MPA/CMA) block worked as a binding site on the SUS316L surface. The surface density of the block copolymer-immobilized SUS316L surface was influenced by the molecular weight of the PMPC block. The stability of the immobilized layer was improved by UV irradiation, which induced intermolecular dimerization of the CMA. In addition to the SUS316L surface, various other metal surfaces could be modified by surface immobilization of block copolymers. Serum protein adsorption and fibroblast adhesion were effectively reduced by surface immobilization of block copolymers with optimal molecular weight of PMPC block. The nonfouling property was preserved after 1 week of cell cultivation.

An experimental-theoretical analysis of protein adsorption on peptidomimetic polymer brushes

Surface-grafted water-soluble polymer brushes are being intensely investigated for preventing protein adsorption to improve biomedical device function, prevent marine fouling, and enable applications in biosensing and tissue engineering. In this contribution, we present an experimental-theoretical analysis of a peptidomimetic polymer brush system with regard to the critical brush density required for preventing protein adsorption at varying chain lengths. A mussel adhesive-inspired DOPA-Lys (DOPA = 3,4-dihydroxy-phenylalanine; Lys = lysine) pentapeptide surface grafting motif enabled aqueous deposition of our peptidomimetic polypeptoid brushes over a wide range of chain densities. Critical densities of 0.88 nm(-2) for a relatively short polypeptoid 10-mer to 0.42 nm(-2) for a 50-mer were identified from measurements of protein adsorption. The experiments were also compared with the protein adsorption isotherms predicted by a molecular theory. Excellent agreements in terms of both the polymer brush structure and the critical chain density were obtained. Furthermore, atomic force microscopy (AFM) imaging is shown to be useful in verifying the critical brush density for preventing protein adsorption. The present coanalysis of experimental and theoretical results demonstrates the significance of characterizing the critical brush density in evaluating the performance of an antifouling polymer brush system. The high fidelity of the agreement between the experiments and molecular theory also indicate that the theoretical approach presented can aid in the practical design of antifouling polymer brush systems.

Effect of brush thickness and solvent composition on the friction force response of poly(2-(methacryloyloxy)ethylphosphorylcholine) brushes

The frictional properties of poly(2-(methacryloyloxy)ethylphosphorylcholine) (PMPC) brushes grown from planar silicon surfaces by atom transfer radical polymerization (ATRP) have been characterized using in situ friction force microscopy (FFM). The dry thicknesses of the PMPC brushes ranged from 20 to 421 nm. For brush layers with dry thicknesses greater than ca. 100 nm, the coefficient of friction decreased with increasing film thickness. For shorter brushes, the coefficient of friction varied little with brush thickness. We hypothesize that the amount of bound solvent increases as the brush length increases, causing the osmotic pressure to increase and yielding a reduced tendency for the brush layer to deform under applied load. A comparison of the force-displacement plots acquired for various PMPC brushes under water supports this hypothesis, since a greater repulsive force is measured for thicker brushes. FFM was also used to investigate the well-known co-nonsolvency behavior exhibited by PMPC chains. For a PMPC brush layer of 307 nm dry thickness, the friction force was determined as a function of the volume fraction of alcohol in alcohol/water mixtures. Unlike a previous macroscopic study, a significant increase in the coefficient of friction was observed for ethanol/water mixtures at a volume fraction of 90%. This is attributed to brush collapse due to co-nonsolvency, leading to loss of hydration of the brush chains and hence substantially reduced lubrication. Force measurements normal to the surface indicate much greater hysteresis between approaching and retraction curves under co-nonsolvency conditions. However, no such effect was observed for 2-propanol/water and methanol/water mixtures over a wide range of volume fractions, in agreement with recent ellipsometric studies of PMPC brushes.

Lipid-like Diblock Copolymer as an Additive for Improving the Blood Compatibility of Poly(lactide-co-glycolide)

To optimize the blood biocompatibility of poly(lactide-coglycolide) (PLGA), lipid-like diblock copolymer poly(DL-lactide)-block-poly(2-methacryloyloxyethyl phosphorylcholine) (PLA-b-PMPC) was employed as a surface-modifying additive. The blends of PLGA and PLA-b-PMPC coated poly(ethylene terephthalate) membranes were prepared by dip-coating. ATR-FTIR spectroscopy showed the incorporation of phosphorylcoline groups in the blends and contact angle results indicated that the hydrophilicity of the blends improved with increasing PLA-b-PMPC content. The plasma recalcification time of polymer coating was prolonged and the amount of adherent platelets on coating surface was decreased by introducing PLA-b-PMPC. The adhesion of polymer coating on the gold electrode of quartz crystal microbalance was monitored and PLGA containing PLA-b-PMPC additives showed excellent polymer—metal adhesion. These results show that the blends of PLGA and lipid-like PLA-b-PMPC could be used as high performance biodegradable polymer coatings for blood contact medical devices.