Effect of surface compositional heterogeneities and microphase segregation of fluorinated amphiphilic copolymers on antifouling performance

High-speed cryo-microscopy reveals that ice-nucleating proteins of Pseudomonas syringae trigger freezing at hydrophobic interfaces

Ice-nucleating proteins (INpro) trigger the freezing of supercooled water droplets relevant to atmospheric, biological, and technological applications. The high ice nucleation activity of INpro isolated from the bacteria Pseudomonas syringae could be linked to the aggregation of proteins at the bacterial membrane or at the air-water interface (AWI) of droplets. Here, we imaged freezing onsets, providing direct evidence of these proposed mechanisms. High-speed cryo-microscopy identified the onset location of freezing in droplets between two protein-repellent glass slides. INpro from sterilized P. syringae (Snomax) statistically favored nucleation at the AWI of the droplets. Removing cellular fragments by filtration or adding surfactants increased the frequency of nucleation events at the AWI. On the other hand, cultivated intact bacteria cells or lipid-free droplets nucleated ice without an affinity to the AWI. Overall, we provide visual evidence that INpro from P. syringae trigger freezing at hydrophobic interfaces, such as the AWI or the bacterial membrane, with important mechanistic implications for applications of INpro.

Elastic and Self-Healing Copolymer Coatings with Antimicrobial Function

The revolutionary self-healing function for long-term and safe service processes has inspired researchers to implement them in various fields, including in the application of antimicrobial protective coatings. Despite the great advances that have been made in the field of fabricating self-healing and antimicrobial polymers, their poor transparency and the trade-off between the mechanical and self-healing properties limit the utility of the materials as transparent antimicrobial protective coatings for wearable optical and display devices. Considering the compatibility in the blending process, our group proposed a self-healing, self-cross-linkable poly{(n-butyl acrylate)-co-[N-(hydroxymethyl)acrylamide]} copolymer (AP)-based protective coating combined with two types of commercial cationic antimicrobial agents (i.e., dimethyl octadecyl (3-trimethoxysilylpropyl) ammonium chloride (DTSACL) and chlorhexidine gluconate (CHG)), leading to the fabrication of a multifunctional modified compound film of (AP/b%CHG)-grafted-a%DTSACL. The first highlight of this research is that the reactivity of the hydroxyl group in the N-(hydroxymethyl)acrylamide of the copolymer side chains under thermal conditions facilitates the "grafting to" process with the trimethoxysilane groups of DTSACL to form AP-grafted-DTSACL, yielding favorable thermal stability, improvement in hydrophobicity, and enhancement of mechanical strength. Second, we highlight that the addition of CHG can generate covalent and noncovalent interactions in a complex manner between the two biguanide groups of CHG with the AP and DTSACL via a thermal-triggered cross-linking reaction. The noncovalent interactions synergistically serve as diverse dynamic hydrogen bonds, leading to complete healing upon scratches and even showing over 80% self-healing efficiency on full-cut, while covalent bonding can effectively improve elasticity and mechanical strength. The soft nature of CHG also takes part in improving the self-healing of the copolymer. Moreover, it was discovered that the addition of CHG can enhance antimicrobial effectiveness, as demonstrated by the long-term superior antibacterial activity (100%) against Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacteria and the antifouling function on a glass substrate and/or a silica wafer coated by the modified polymer.

Protein adsorption on blood-contacting surfaces: A thermodynamic perspective to guide the design of antithrombogenic polymer coatings

Blood-contacting medical devices often succumb to thrombosis, limiting their durability and safety in clinical applications. Thrombosis is fundamentally initiated by the nonspecific adsorption of proteins to the material surface, which is strongly governed by thermodynamic factors established by the nature of the interaction between the material surface, surrounding water molecules, and the protein itself. Along these lines, different surface materials (such as polymeric, metallic, ceramic, or composite) induce different entropic and enthalpic changes at the surface-protein interface, with material wettability significantly impacting this behavior. Consequently, protein adsorption on medical devices can be modulated by altering their wettability and surface energy. A plethora of polymeric coating modifications have been utilized for this purpose; hydrophobic modifications may promote or inhibit protein adsorption determined by van der Waals forces, while hydrophilic materials achieve this by mainly relying on hydrogen bonding, or unbalanced/balanced electrostatic interactions. This review offers a cohesive understanding of the thermodynamics governing these phenomena, to specifically aid in the design and selection of hemocompatible polymeric coatings for biomedical applications. STATEMENT OF SIGNIFICANCE: Blood-contacting medical devices often succumb to thrombosis, limiting their durability and safety in clinical applications. A plethora of polymeric coating modifications have been utilized for addressing this issue. This review offers a cohesive understanding of the thermodynamics governing these phenomena, to specifically aid in the design and selection of hemocompatible polymeric coatings for biomedical applications.

Altering the bio-inert properties of surfaces by fluorinated copolymers of mPEGMA

Hydrophilic materials display "bio-inert properties", meaning that they are less recognized as foreign substances by proteins and cells. Such materials are often water soluble; therefore, one general approach to enable the use of these materials in various applications deals with copolymerizing hydrophilic monomers with hydrophobic ones to facilitate such resulting copolymers water insoluble. However, reducing the hydrophilic monomer amount may reduce the bio-inert properties of the material. The decrease in bio-inert properties can be avoided when small amounts of fluorine are used in copolymers with hydrophilic monomers, as presented in this article. Even in small quantities (7.9 wt%), the fluorinated monomer, 1,1,1,3,3,3-hexafluoropropan-2-yl 2-fluoroacrylate (FAHFiP), contributed to the improved hydrophobicity of the polymers of the long side-chain poly(ethylene glycol) methyl ether methacrylate (mPEGMA) bearing nine ethylene glycol units turning them water insoluble. As evidenced by the AFM deformation image, a phase separation between the FAHFiP and mPEGMA domains was observed. The copolymer with the highest amount of the fluorinated monomer (66.2 wt%) displayed also high (82 %) FAHFiP amount at the polymer-water interface. In contrast, the hydrated sample with the lowest FAHFiP/highest mPEGMA amount was enriched of three times more hydrophilic domains at the polymer-water interface compared to that of the sample with the highest FAHFiP content. Thus, by adding a small FAHFiP amount to mPEGMA copolymers, water insoluble in the bulk too, could be turned highly hydrophilic at the water interface. The high content of intermediate water contributed to their excellent bio-inert properties. Platelet adhesion and fibrinogen adsorption on their surfaces were even more decreased as compared to those on poly(2-methoxyethyl acrylate), which is typically used in medical devices.

Probing the behavior and kinetic studies of amphiphilic acrylate copolymers with bovine serum albumin

This article presents that acrylate copolymers are the potential candidate against the adsorption of bovine serum albumin (BSA). A series of copolymers poly(methyl methacrylate) (pMMA), poly(3-sulfopropyl methacrylate-co-methyl methacrylate) p(SPMA-co-MMA), and poly(dimethylaminoethyl methacrylate-co-methyl methacrylate) p(DMAEMA-co-MMA) were synthesized via free radical polymerization. These amphiphilic copolymers are thermally stable with a glass transition temperature (Tg) 50-120 °C and observed the impact of surface charge on amphiphilic copolymers to control interactions with the bovine serum albumin (BSA). These copolymers pMD1 and pMS1 have surface charges, - 56.6 and - 72.6 mV at pH 7.4 in PBS buffer solution that controls the adsorption capacity of bovine serum albumin (BSA) on polymers surface. Atomic force microscopy (AFM) analysis showed minimum roughness of 0.324 nm and 0.474 nm for pMS1 and pMD1. Kinetic studies for BSA adsorption on these amphiphilic copolymers showed the best fitting of the pseudo-first-order model that showed physisorption and attained at 25 °C and pH 7.4 within 24 h.

Dual functionalized brush copolymers as versatile antifouling coatings

Polymer coatings containing both fouling-resistant and fouling-release components have been reported to show synergistic antifouling properties. However, it remains unclear how the polymer composition influences the antifouling performance, particularly regarding foulants of different sizes and biological natures. Herein, we prepare dual functionalized brush copolymers containing fouling-resistant poly(ethylene glycol) (PEG) and fouling-release polydimethylsiloxane (PDMS) and examine their antifouling performances against different biofoulants. We utilize poly(pentafluorophenyl acrylate) (PPFPA) as a reactive precursor polymer and graft amine-functionalized PEG and PDMS side chains to create PPFPA-g-PEG-g-PDMS brush copolymers of systematically varying compositions. The copolymer films spin-coated on silicon wafers exhibit surface heterogeneity that can be correlated well with the bulk composition of the copolymer. When the copolymer-coated surfaces are examined against protein (human serum albumin and bovine serum albumin) adsorption and cell (lung cancer cells and microalgae) adhesion, they are found to perform better than the homopolymers. The enhanced antifouling properties are attributed to the copolymers having a PEG-rich top layer and a PEG/PDMS mixed bottom layer that work synergistically to resist biofoulant attachment. Furthermore, the composition of the best-performing copolymer is different for different foulants, with PPFPA-g-PEG₃₉-g-PDMS₄₆ exhibiting the best antifouling properties against proteins and PPFPA-g-PEG₅₄-g-PDMS₃₀ exhibiting the best antifouling properties against cells. We explain this difference by considering the changes in the length scale of the surface heterogeneity in relation to the foulant sizes.

Hemocompatibility challenge of membrane oxygenator for artificial lung technology

The artificial lung (AL) technology is one of the membrane-based artificial organs that partly augments lung functions, i.e. blood oxygenation and CO₂ removal. It is generally employed as an extracorporeal membrane oxygenation (ECMO) device to treat acute and chronic lung-failure patients, and the recent outbreak of the COVID-19 pandemic has re-emphasized the importance of this technology. The principal component in AL is the polymeric membrane oxygenator that facilitates the O₂/CO₂ exchange with the blood. Despite the considerable improvement in anti-thrombogenic biomaterials in other applications (e.g., stents), AL research has not advanced at the same rate. This is partly because AL research requires interdisciplinary knowledge in biomaterials and membrane technology. Some of the promising biomaterials with reasonable hemocompatibility - such as emerging fluoropolymers of extremely low surface energy - must first be fabricated into membranes to exhibit effective gas exchange performance. As AL membranes must also demonstrate high hemocompatibility in tandem, it is essential to test the membranes using in-vitro hemocompatibility experiments before in-vivo test. Hence, it is vital to have a reliable in-vitro experimental protocol that can be reasonably correlated with the in-vivo results. However, current in-vitro AL studies are unsystematic to allow a consistent comparison with in-vivo results. More specifically, current literature on AL biomaterial in-vitro hemocompatibility data are not quantitatively comparable due to the use of unstandardized and unreliable protocols. Such a wide gap has been the main bottleneck in the improvement of AL research, preventing promising biomaterials from reaching clinical trials. This review summarizes the current state-of-the-art and status of AL technology from membrane researcher perspectives. Particularly, most of the reported in-vitro experiments to assess AL membrane hemocompatibility are compiled and critically compared to suggest the most reliable method suitable for AL biomaterial research. Also, a brief review of current approaches to improve AL hemocompatibility is summarized. STATEMENT OF SIGNIFICANCE: The importance of Artificial Lung (AL) technology has been re-emphasized in the time of the COVID-19 pandemic. The utmost bottleneck in the current AL technology is the poor hemocompatibility of the polymer membrane used for O₂/CO₂ gas exchange, limiting its use in the long-term. Unfortunately, most of the in-vitro AL experiments are unsystematic, irreproducible, and unreliable. There are no standardized in-vitro hemocompatibility characterization protocols for quantitative comparison between AL biomaterials. In this review, we tackled this bottleneck by compiling the scattered in-vitro data and suggesting the most suitable experimental protocol to obtain reliable and comparable hemocompatibility results. To the best of our knowledge, this is the first review paper focusing on the hemocompatibility challenge of AL technology.

"Brush-like" Amphiphilic Polymer for Environmental Adaptive Coating

Multiple functional coating is urgently needed in complex service surroundings to meet various requirements. In this work, a brush-like amphiphilic copolymer of poly methacryloxyethyl dimethyl butyl ammonium bromide-polydimethylsiloxane (pMDBAB-PDMS) was synthesized to construct an environment-adaptive multifunctional coating based on the copolymer via the UV-curing method. The special molecule chains of the copolymer assembled predominately on the coating surface in different surroundings, which rendered the surface with various functions. In water-rich surroundings, the hydrophilic quaternary ammonium groups in the coating endow the coating surface with antifogging, oleophobicity underwater, self-cleaning, antibacteria, triboelectric resistance, and super lubrication properties. In dry air surroundings, the long, flexible, low surface energy molecular PDMS chains tend to distribute on the top of the coating surface, which gives a low friction coefficient and antioil properties. This work presents a strategy to construct environmental adaptive coating that has an important application prospect in the field of optical lens.

Nanoscale Biocompatible Structures Generated from Fluorinated Tripodal Phenylenes on Gold Nanoprisms

Modification of gold substrates with a stable, uniform and ultrathin layer of biocompatible materials is of tremendous interest for the development of bio-devices. We present the fabrication of hybrid systems consisting of triangular prism gold nanoparticles (Au@NTPs) covalently covered with tripod-shaped oligo(p-phenylenes) featuring trifluoromethyl groups. Their synthesis is accomplished using a biphenyl boronic ester as the key compound. Au@NTPs were prepared through a seedless procedure using 3-butenoic acid and benzyldimethyl ammonium chloride, and modified with aminothiol groups. Coverage of this amine-modified gold substrate with a self-assembled monolayer (SAM) of tripod-shaped molecules is carried out in ethanolic solution. The hybrid system avoids up to 70 % of protein corona formation, and allows unspecific attachment for bulky adsorbates, providing an optimal biosensing platform. Chemical composition and morphology are analyzed by transmission electron microscopy (TEM), UV-visible spectroscopy and field emission scanning electron microscopy (FESEM).

Rewritable Surface on a Plastic Substrate Using Fluorous Affinity

Fluorous chemistry has unique features and high potential applicability, which are distinct from those of nonfluorinated organic compounds. However, there are limited reports detailing the applications of fluorous-fluorous interactions (fluorophilicity or fluorous affinity), likely because these interactions are not found in nature. In the present study, we describe the rewritable surface functionalization of a plastic substrate based on fluorous affinity. Plastic substrates were dip-coated with a series of methacrylate-based fluoropolymers to generate fluorous surfaces. Fluorous-tagged small molecules [perfluoroalkyl (Rf) amines] were immobilized on the fluorous surfaces via fluorous-fluorous interactions, thereby introducing reactive functional groups (amino moieties) on the surface. The amino groups displayed on the surface (accessible by a reactant) were successfully quantified using a reactive fluorophore, which enabled quantitative analysis of the Rf-amines immobilized on the fluorous surface that were available for the subsequent reaction. The effects of the molecular structures of the fluoropolymers and Rf-amines on the surface immobilization of Rf-amines were also investigated quantitatively. The surface coated with a fluoropolymer containing -C₈F₁₇ most effectively immobilized an Rf-amine comprising two -C₆F₁₃ chains. The adhered Rf-amines were easily removed by washing the surface with methanol, and then, they could successfully be re-immobilized on the surface. Finally, the presented approach enabled the rewritable micropatterning of an Rf-tagged biomolecule on a plastic surface through microcontact printing.

Fluorine-containing bio-inert polymers: Roles of intermediate water

Fluorine-containing polymers are used not only in industrial processes but also in medical applications, because they exhibit excellent heat, weather, and chemical resistance. As these polymers are not easily degraded in our body, it is difficult to use them in applications that require antithrombotic properties, such as artificial blood vessels. The material used for medical applications should not only be stable in vivo, but it should also be inert to biomolecules such as proteins or cells. In this review, this property is defined as "bio-inert," and previous studies in this field are summarized. Bio-inert materials are less recognized as foreign substances by proteins or cells in the living body, and they must be covered at interfaces designed with the concept of intermediate water (IW). On the basis of this concept, we present here the current understanding of bio-inertness and unusual blood compatibility found in fluoropolymers used in biomedical applications. IW is the water that interacts with materials with moderate strength and has been quantified by a variety of analytical methods and simulations. For example, by using differential scanning calorimetry (DSC) measurements, IW was defined as water frozen at around -40°C. To consider the role of the IW, quantification methods of the hydration state of polymers are also summarized. These investigations have been conducted independently because of the conflict between hydrophobic fluorine and bio-inert properties that require hydrophilicity. In recent years, not many materials have been developed that incorporate the good points of both aspects, and their properties have seldom been linked to the hydration state. This has been critically performed now. Furthermore, fluorine-containing polymers in medical use are reviewed. Finally, this review also describes the molecular design of the recently reported fluorine-containing bio-inert polymers for controlling their hydration state. STATEMENT OF SIGNIFICANCE: A material covered with a hydration layer known as intermediate water that interacts moderately with other objects is difficult to be recognized as a foreign substance and exhibits bio-inert properties. Fluoropolymers show high durability, but conflict with bio-inert characteristics requiring hydrophilicity as these research studies have been conducted independently. On the other hand, materials that combine the advantages of both hydrophobic and hydrophilic features have been developed recently. Here, we summarize the molecular architecture and analysis methods that control intermediate water and provide a guideline for designing novel fluorine-containing bio-inert materials.

Matching the Cellulose/Silica Films Surface Properties for Design of Biomaterials That Modulate Extracellular Matrix

The surface properties of composite films are important to know for many applications from the industrial domain to the medical domain. The physical and chemical characteristics of film/membrane surfaces are totally different from those of the bulk due to the surface segregation of the low surface energy components. Thus, the surfaces of cellulose acetate/silica composite films are analyzed in order to obtain information on the morphology, topography and wettability through atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and contact angle investigations. The studied composite films present different surface properties depending on the tetraethyl orthosilicate (TEOS) content from the casting solutions. Up to a content of 1.5 wt.% TEOS, the surface roughness and hydrophobicity increase, after which there is a decrease in these parameters. This behavior suggests that up to a critical amount of TEOS, the results are influenced by the morphology and topographical features, after which a major role seems to be played by surface chemistry-increasing the oxygenation surfaces. The morphological and chemical details and also the hydrophobicity/hydrophilicity characteristics are discussed in the attempt to design biological surfaces with optimal wettability properties and possibility of application in tissue engineering.

Facile photochemical synthesis of main-chain-type semifluorinated alternating copolymers catalyzed by conventional amines or halide salts

In this work, we report a much simpler and low-cost method to prepare main-chain-type semifluorinated alternating copolymers by the formation of a halogen bond (XB) complex between α,ω-diiodoperfluoroalkanes and amines/halide salts. It is interesting that the terminal iodine functional group of the polymer chains is easily lost in the amine-promoted system, while the loss can be significantly reduced by adding a small amount of water. Importantly, the system promoted by halide salts can ensure complete retention of the iodine functional group. Overall, the establishment of this method provides a new strategy for designing smart fluoropolymer materials in a green and environmentally friendly facile manner under irradiation with visible light at room temperature.

Transparent and Flexible Amphiphobic Coatings with Excellent Fold Resistance via Solvent-Free Coating and Photocuring of Fluorinated Liquid Nitrile-Butadiene Rubber

Amphiphobic surfaces have been developed for various applications. However, the harsh construction conditions and multistep processes limit their practical application. Especially for those with a particular surface roughness and morphology, the amphiphobic property might provide a slight deformation. Here, a facile large-area construction of transparent and flexible amphiphobic coatings with excellent fold resistance has been established by simple casting of the fluorinated liquid nitrile-butadiene rubber (F-LNBR) followed by solvent-free photocuring. It was found that the fluorocarbon groups could concentrate onto the coating surface during the UV-induced photocuring. With a certain coating amount, a stable oleophobic coating was achieved with static contact angles of about 95° and 111° for nonpolar oil (n-hexadecane) and polar oil (diiodomethane). Most importantly, the static contact angles of water and diiodomethane of the amphiphobic coatings on the iron sheet increased after bending and remained around 131° and 120° after being completely folded in half for 100 cycles because the inner fluorocarbon groups could be squeezed out from the flexible cross-linked rubber matrix as a reservoir. Such features indicated the promising self-cleaning and surface protection of the proposed transparent and flexible amphiphobic coatings for deformable substrates.

Understanding the Effect of Hydration on the Bio-inert Properties of 2-Hydroxyethyl Methacrylate Copolymers with Small Amounts of Amino- or/and Fluorine-Containing Monomers

Materials exhibiting "bio-inert properties" are essential for developing medical devices because they are less recognized as foreign substances by proteins and cells in the living body. We have reported that the presence of intermediate water (IW) with the water molecules loosely bound to a polymer is a useful index of the bio-inertness of materials. Here, we analyzed the hydration state and the responses to biomolecules of poly(2-hydroxyethyl methacrylate) (PHEMA) copolymers including small amounts of 2-(dimethylamino)ethyl methacrylate (DMAEMA) (N-series) or/and 2,2,2-trifluoroethyl methacrylate (TFEMA) (F-series). The hydration structure was analyzed by differential scanning calorimetry (DSC), the molecular mobility of the produced copolymers by temperature derivative of DSC (DDSC), and the water mobility by solid ¹H pulse nuclear magnetic resonance (NMR). Although the homopolymers did not show bio-inert properties, the binary and ternary PHEMA copolymers with low comonomer contents showed higher bio-inert properties than those of PHEMA homopolymers. The hydration state of PHEMA was changed by introducing a small amount of comonomers. The mobility of both water molecules and hydrated polymers was changed in the N-series nonfreezing water (NFW) with the water molecules tightly bound to a polymer and was shifted to high-mobility IW and free water (FW) with the water molecules scarcely bound to a polymer. On the other hand, in the F-series, FW turned to IW and NFW. Additionally, a synergetic effect was postulated when both comonomers coexist in the copolymers of HEMA, which was expressed by widening the temperature range of cold crystallization, contributing to further improvement of the bio-inert properties.

Recent Developments in the Design of Non-Biofouling Coatings for Nanoparticles and Surfaces

Biofouling is a major issue in the field of nanomedicine and consists of the spontaneous and unwanted adsorption of biomolecules on engineered surfaces. In a biological context and referring to nanoparticles (NPs) acting as nanomedicines, the adsorption of biomolecules found in blood (mostly proteins) is known as protein corona. On the one hand, the protein corona, as it covers the NPs' surface, can be considered the biological identity of engineered NPs, because the corona is what cells will "see" instead of the underlying NPs. As such, the protein corona will influence the fate, integrity, and performance of NPs in vivo. On the other hand, the physicochemical properties of the engineered NPs, such as their size, shape, charge, or hydrophobicity, will influence the identity of the proteins attracted to their surface. In this context, the design of coatings for NPs and surfaces that avoid biofouling is an active field of research. The gold standard in the field is the use of polyethylene glycol (PEG) molecules, although zwitterions have also proved to be efficient in preventing protein adhesion and fluorinated molecules are emerging as coatings with interesting properties. Hence, in this review, we will focus on recent examples of anti-biofouling coatings in three main areas, that is, PEGylated, zwitterionic, and fluorinated coatings.

Understanding the Role of Shape and Composition of Star-Shaped Polymers and their Ability to Both Bind and Prevent Bacteria Attachment on Oral Relevant Surfaces

In this study, we have prepared a series of 4- and 6-arm star-shaped polymers with varying molecular weight and hydrophobicity in order to provide insight into the role and relationship that shape and composition have on the binding and protecting of oral relevant surfaces (hydroxyapatite, HAP) from bacteria colonization. Star-shaped acrylic acid polymers were prepared by free-radical polymerization in the presence of chain transfer agents with thiol groups, and their binding to the HAP surfaces and subsequent bacteria repulsion was measured. We observed that binding was dependent on both polymer shape and hydrophobicity (star vs. linear), but their relative efficacy to reduce oral bacteria attachment from surfaces was dependent on their hydrophobicity only. We further measured the macroscopic effects of these materials to modify the mucin-coated HAP surfaces through contact angle experiments; the degree of angle change was dependent on the relative hydrophobicity of the materials suggesting future in vivo efficacy. The results from this study highlight that star-shaped polymers represent a new material platform for the development of dental applications to control bacterial adhesion which can lead to tooth decay, with various compositional and structural aspects of materials being vital to effectively design oral care products.

The blood compatibility challenge. Part 2: Protein adsorption phenomena governing blood reactivity

The adsorption of proteins is the initiating event in the processes occurring when blood contacts a "foreign" surface in a medical device, leading inevitably to thrombus formation. Knowledge of protein adsorption in this context has accumulated over many years but remains fragmentary and incomplete. Moreover, the significance and relevance of the information for blood compatibility are not entirely agreed upon in the biomaterials research community. In this review, protein adsorption from blood is discussed under the headings "agreed upon" and "not agreed upon or not known" with respect to: protein layer composition, effects on coagulation and complement activation, effects on platelet adhesion and activation, protein conformational change and denaturation, prevention of nonspecific protein adsorption, and controlling/tailoring the protein layer composition. STATEMENT OF SIGNIFICANCE: This paper is part 2 of a series of 4 reviews discussing the problem of biomaterial associated thrombogenicity. The objective was to highlight features of broad agreement and provide commentary on those aspects of the problem that were subject to dispute. We hope that future investigators will update these reviews as new scholarship resolves the uncertainties of today.

Controlling the Hydration Structure with a Small Amount of Fluorine To Produce Blood Compatible Fluorinated Poly(2-methoxyethyl acrylate)

Poly(2-methoxyethyl acrylate) (PMEA) shows excellent blood compatibility because of the existence of intermediate water. Various modifications of PMEA by changing its main or side chain's chemical structure allowed tuning of the water content and the blood compatibility of numerous novel polymers. Here, we exploit a possibility of manipulating the surface hydration structure of PMEA by incorporation of small amounts of hydrophobic fluorine groups in MEA polymers using atom-transfer radical polymerization and the (macro) initiator concept. Two kinds of fluorinated MEA polymers with similar molecular weights and the same 5.5 mol % of fluorine content were synthesized using the bromoester of 2,2,3,3,4,4,5,5,6,6,7,7,8,8-pentadecafluoro-1-octanol (F15) and poly(2,2,2-trifluoroethyl methacrylate) (PTFEMA) as (macro) initiators, appearing liquid and solid at room temperature, respectively. The fibrinogen adsorption of the two varieties of fluorinated MEA polymers was different, which could not be explained only by the bulk hydration structure. Both polymers show a nanostructured morphology in the hydrated state with different sizes of the features. The measured elastic modulus of the domains appearing in atomic force microscopy and the intermediate water content shed light on the distinct mechanism of blood compatibility. Contact angle measurements reveal the surface hydration dynamics-while in the hydrated state, F15- b-PMEA reorients easily to the surface exposing its PMEA part to the water, the small solid PTFEMA block with high glass-transition temperature suppresses the movement of PTFEMA- b-PMEA and its reconstruction on the surface. These findings illustrate that in order to make a better blood compatible polymer, the chains containing sufficient intermediate water need to be mobile and efficiently oriented to the water surface.

Cu nanoparticles constrain segmental dynamics of cross-linked polyethers: a trade-off between non-fouling and antibacterial properties

Copper has a strong bactericidal effect against multi-drug resistant pathogens and polyethers are known for their resistance to biofilm formation. Herein, we combined Cu nanoparticles (NPs) and a polyether plasma polymer in the form of nanocomposite thin films and studied whether both effects can be coupled. Cu NPs were produced by magnetron sputtering via the aggregation in a cool buffer gas whereas polyether layers were synthesized by Plasma-Assisted Vapor Phase Deposition with poly(ethylene oxide) (PEO) used as a precursor. In situ specific heat spectroscopy and XPS analysis revealed the formation of a modified polymer layer around the NPs which propagates on the scale of a few nanometers from the Cu NP/polymer interface and then transforms into a bulk polymer phase. The chemical composition of the modified layer is found to be ether-deficient due to the catalytic influence of copper whereas the bulk polymer phase exhibits the chemical composition close to the original PEO. Two cooperative glass transition phenomena are revealed that belong to the modified polymer layer and the bulk phase. The former is characterized by constrained mobility of polymer segments which manifests itself via a 30 K increase of dynamic glass transition temperature. Furthermore, the modified layer is characterized by the heterogeneous structure which results in higher fragility of this layer as compared to the bulk phase. The Cu NPs/polyether thin films exhibit reduced protein adsorption; however, the constrained segmental dynamics leads to the deterioration of the non-fouling properties for ultra-thin polyether coatings. The films are found to have a bactericidal effect against multi-drug resistant Gram-positive Methicillin-Resistant Staphylococcus aureus and Gram-negative Pseudomonas aeruginosa.

Bead-type polystyrene/nano-CaCO3 (PS/nCaCO3) composite: a high-performance adsorbent for the removal of interleukin-6

A novel nano-CaCO₃ (nCaCO₃) particle composite-derived polystyrene (PS) resin was successfully synthesized by a suspension polymerization method. The nCaCO₃ reinforced PS material (PS/nCaCO₃) possessed a structure with abundant mesopores of high porosity, high specific surface area (828.3 m² g^-1) and large pore volume (1.83 cm³ g^-1). It was revealed that the incorporation of nCaCO₃ into the PS matrix enhanced both the mechanical strength which can prevent the fragmentation and its adsorption capacity for interleukin-6 (IL-6, M_W = 24.0 kDa) from human plasma. The adsorption isotherm could be described by the Langmuir model and classified as S-3 type, showing an IL-6 uptake of up to 25.6 ng g^-1 at an equilibrium concentration of about 500 ng L^-1. The adsorption capacity for IL-6 of PS/nCaCO₃ is not only significantly higher than that of PS (without nCaCO₃), but also superior to those of currently available adsorbents that are under clinical studies (e.g., CytoSorb™ towards cytokines). In addition, the PS/nCaCO₃ adsorbent also had good hemocompatibility and showed no leakage of nCaCO₃ in the plasma in a flowing model system. Therefore, the synthesized PS/nCaCO₃ nano-composite has a great potential to be used as an efficient adsorbent for the removal of interleukin-6 (IL-6) from blood of inflammatory and auto-immune disease patients through hemoperfusion.

Povidone-iodine-functionalized fluorinated copolymers with dual-functional antibacterial and antifouling activities

Povidone-iodine-functionalized fluorinated polymer coatings with dual-functional antibacterial and antifouling activities should be very promising in practical biomedical applications.

Surface-Segregation-Induced Nanopapillae on FDTS-Blended PDMS Film and Implications in Wettability, Adhesion, and Friction Behaviors

Polymer composites have been extensively used to tune the surface property (e.g., wettability, friction, and adhesion) for its advantages of cost-effectiveness, high efficiency, and ease of fabrication. In this work, different amount of trichloro(1H,1H,2H,2H-perfluorooctyl)silane (FDTS) was added into poly(dimethylsiloxane) elastomer to prepare polymer composite films and were selected as a model to illustrate the effects of surface segregation on surface topology, wettability, friction, and adhesion. The results show that the added FDTS forms aggregations and increasing the content of FDTS leads to the difficulty of air bubble elimination, increase in viscosity, and drop in transparency. Driven by the differences of chemical potential, FDTS aggregations migrate to the air-polymer interface, resulting in surface enrichment and formation of nanopapillae (1-200 nm). This phenomenon becomes more significant with the increment in FDTS. The change in surface composition and structure generates profound effects on wettability, friction, and adhesion. The addition of FDTS makes the surface relatively oleophobic and further increasing the content of FDTS does not helpful in improving the oleophobicity due to the notable aggregation. Friction forces first grow with the increasing content of FDTS and then decline after the maximum point at 1.0 wt % of FDTS, which is attributed to the generated regular larger nanopappillae at high concentration. However, these larger nanopapillae lead to the increase in adhesion because more interactions are formed. The findings demonstrate the behaviors of FDTS in polymer composites and provide important guidance for controlling the formation of nanostructures via aggregation and phase segregation and exploring their implications on surface properties.

Betulin-Constituted Multiblock Amphiphiles for Broad-Spectrum Protein Resistance

Multiblock-like amphiphilic polyurethanes constituted by poly(ethylene oxide) and biosourced betulin are designed for antifouling and synthesized by a convenient organocatalytic route comprising tandem chain-growth and step-growth polymerizations. The doping density of betulin (D_B) in the polymer chain structure is readily varied by a mixed-initiator strategy. The spin-coated polymer films exhibit unique nanophase separation and protein resistance behaviors. Higher D_B leads to enhanced surface hydrophobicity and, unexpectedly, improved protein resistance. It is found that the surface holds molecular-level heterogeneity when D_B is substantially high due to restricted phase separation; therefore, broad-spectrum protein resistance is achieved despite considerable surface hydrophobicity. As D_B decreases, the distance between adjacent betulin units increases so that hydrophobic nanodomains are formed, which provide enough landing areas for relatively small-sized proteins to adsorb on the surface.

Antifouling membranes for sustainable water purification: strategies and mechanisms

One of the greatest challenges to the sustainability of modern society is an inadequate supply of clean water. Due to its energy-saving and cost-effective features, membrane technology has become an indispensable platform technology for water purification, including seawater and brackish water desalination as well as municipal or industrial wastewater treatment. However, membrane fouling, which arises from the nonspecific interaction between membrane surface and foulants, significantly impedes the efficient application of membrane technology. Preparing antifouling membranes is a fundamental strategy to deal with pervasive fouling problems from a variety of foulants. In recent years, major advancements have been made in membrane preparation techniques and in elucidating the antifouling mechanisms of membrane processes, including ultrafiltration, nanofiltration, reverse osmosis and forward osmosis. This review will first introduce the major foulants and the principal mechanisms of membrane fouling, and then highlight the development, current status and future prospects of antifouling membranes, including antifouling strategies, preparation techniques and practical applications. In particular, the strategies and mechanisms for antifouling membranes, including passive fouling resistance and fouling release, active off-surface and on-surface strategies, will be proposed and discussed extensively.

Preparation and characterization of an amphiphilic polyamide nanofiltration membrane with improved antifouling properties by two-step surface modification method

Membrane fouling is an urgent problem needing to be solved for practical application of nanofiltration membranes. In this study, an amphiphilic nanofiltration membrane with hydrophilic domains as well as low surface energy domains was developed, to integrate a fouling-resistant defense mechanism and a fouling-release defense mechanism. A simple and effective two-step surface modification of a polyamide NF membrane was applied. Firstly, triethanolamine (TEOA) with abundant hydrophilic functional groups was grafted to the membrane surface via reacting with the residual acyl chloride group of the nanofiltration membrane, making the nanofiltration membranes more hydrophilic; secondly, the 1H,1H,2H,2H-perfluorodecyltrichlorosilane (PFTS), well-known as a low surface energy material, was covalently grafted on the hydroxyl functional groups through hydrogen bonding. Filtration experiments with model foulants (bovine serum albumin (BSA) protein solution, humic acid solution (HA) and sodium alginate solution (SA)) were performed to estimate the antifouling properties of the newly developed nanofiltration membranes. As a result of surface modification proposed in this study the antifouling properties of an amphiphilic modified F-PA/PSF membrane were enhanced more than 10% compared to the PA/PSF specimen in terms of flux recovery ratio.

Schematic diagram of amphiphilic NF membrane by a two-step modification.

(PtBA-co-PPEGMEMA-co-PDOMA)-g-PPFA polymer brushes synthesized by sequential RAFT polymerization and ATRP

This article reports the synthesis of semi-fluorinated (PtBA-co-PPEGMEMA-co-PDOMA)-g-PPFA polymer brushes for self-cleaning anti-fouling surfaces.

Annexin V-Conjugated Mixed Micelles as a Potential Drug Delivery System for Targeted Thrombolysis

To alleviate the hemorrhagic side effect of thrombolysis therapy, a thrombus targeted drug delivery system based on the specific affinity of Annexin V to phosphatidylserine exposed on the membrane surface of activated platelet was developed. The amphiphilic and biodegradable biomaterial, polycaprolactone-block-poly(2-(dimethylamino)ethyl methacrylate)-block-poly(2-hydroxyethyl methacrylate) (PCL-b-PDMAEMA-b-PHEMA (PCDH)) triblock polymer, was synthesized via ring opening polymerization (ROP) and atom transfer radical polymerization (ATRP) to use as the nanocarriers of thrombolytic drug. In order to conjugate Annexin V to the polymer, PCDH was modified by succinic anhydride via ring-opening reaction to introduce the carboxyl group (PCDH-COOH). After preparation of PCDH/PCDH-COOH (9/1, m/m) mixed micelles, Annexin V was coupled with the micelles using carbodiimide chemistry. The blood clot lysis assay in vitro confirmed that lumbrokinase-loaded targeted micelles (LKTM) had stronger thrombolysis potency than free lumbrokinase (LK) and LK-loaded nontargeted micelles (LKM, P < 0.05). In vivo thrombolytic assay, multispectral, optoacoustic tomography (MSOT) was used to assess the target ability of LKTM. The results of MSOT images indicated the fluorescence intensity of the LKTM group located in the blood clot position were significantly stronger than the LKM group. A 5 mm of carotid artery containing blood clot was cut out 24 h later after administration to assess the degree of thrombolysis. The results of thrombolytic assay in vivo were consistent with the assay in vitro, which the differences between LK, LKM, and LKTM groups were both statistically significant. All the results of thrombolysis assays above proved that the capacity of thrombolysis in the LKTM group was optimal. It suggested that Annexin V-conjugated micelles will be a potential drug delivery system for targeted thrombolysis.

Heterogeneous surfaces to repel proteins

The nonspecific adsorption of proteins is usually undesirable on solid surfaces as it induces adverse responses, such as platelet adhesion on medical devices, negative signals of biosensors and contamination blockage of filtration membranes. Thus, an important scheme in material science is to design and fabricate protein-repulsive surfaces. Early approaches in this field focused on homogeneous surfaces comprised of single type functionality. Yet, recent researches have demonstrated that surfaces with heterogeneities (chemistry and topography) show promising performance against protein adsorption. In this review, we will summarize the recent achievements and discuss the new perspectives in the research of developing and characterizing heterogeneous surfaces to repel proteins. The protein repulsion mechanisms of different heterogeneous surfaces will also be discussed in details, followed by the perspective and challenge of this emerging field.

Enhanced oil-fouling resistance of poly(ether sulfone) membranes by incorporation of novel amphiphilic zwitterionic copolymers

A heterogeneous PES membrane modified with novel amphiphilic zwitterionic copolymers that displayed dramatically enhanced oil-fouling resistance.

Transparent superhydrophobic coatings from amphiphilic-fluorinated block copolymers synthesized by aqueous polymerization-induced self-assembly

Preparation of transparent and superhydrophobic coatings by co-deposition of an aqueous solution of an amphiphilic fluorinated block copolymer with silica was developed.

Microphase Structure, Crystallization Behavior, and Wettability Properties of Novel Fluorinated Copolymers Poly(perfluoroalkyl acrylate-co-stearyl acrylate) Containing Short Perfluorohexyl Chains

Novel fluorinated copolymers of stearyl acrylate (SA) and (perfluorohexyl)ethyl acrylate (C6A), (perfluorohexyl)ethyl methacrylate (C6MA), 2-[[[[2-(perfluorohexyl)]-sulfonyl]methyl] amino]ethyl acrylate (C6SA), and methacrylate (C6SMA) were synthesized via miniemulsion copolymerization. The extremely hydrophobic monomers perfluoroalkyl acrylate (FA) and SA acted as the reactive costabilizer in the miniemulsion system. The microstructure and surface wetting properties of the copolymers were characterized by (1)H NMR, FT-IR, and dynamic contact angle test. The crystallization behaviors and fine surface structures of the copolymer films were determined by differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) analysis. The self-assembled aggregation and roughness of the copolymer films were investigated by atomic force microscopy (AFM). The results showed that the fluorinated side chains interrupted and impeded the crystallizable side chains of SA from forming complete crystals. And the Tm and ΔHf of the copolymers were decreased as a consequence of this effect. The fluorinated side chains in P(C6A/SA) and P(C6MA/SA) arranged between the crystallizable hydrocarbon side chains of SA, while the crystallization structure of fluorinated and nonfluorinated pendant groups existed all at once in copolymers P(C6SA/SA) and P(C6SMA/SA). The four copolymers exhibited very low surface free energy and excellent dynamic water repellency attributed to the restriction of perfluoroalkyl groups combined with crystallization of stearyl pendant groups.

Protein-resistance performance of amphiphilic copolymer brushes consisting of fluorinated polymers and polyacrylamide grafted from silicon surfaces

A series of random copolymer brushes of acrylamide (AM) and 2-(perfluorinated hexyl)ethyl methacrylate (FMA) were grafted from initiator-functionalized silicon wafers by surface-initiated atom transfer radical polymerization.