Strong Surface Hydration Research Articles

Anti-fouling ternary zwitterionic coating membrane with strong surface hydration and salt resistant for efficient long-term emulsion separation in high salinity marine environment

Membrane separation has been acknowledged as an advanced technology to handle the oil spills. However, most of the superhydrophilic/underwater superhydrophobic membranes currently applied for oil/water separation would lose their superwettability when exposed to salty marine environments, leading to serious membrane plugging and separation performance deterioration. Herein, inspired by seawater fish and mussels, a simple, green, and versatile one-step co-deposition strategy is proposed for fabricating a ternary zwitterionic coating with strong surface hydration on diverse membranes, showing excellent anti-fouling properties in high salinity environments, even in the saturated NaCl solution. Moreover, the modified membrane performs well in the long term when separating surfactant-stabilized oil-in-seawater emulsion and with impressive recyclability. The ternary zwitterionic coating membrane exhibits great potential in treating oily wastewater in marine.

TiO2 Nanoparticles with Adjustable Phase Composition Prepared by an Inverse Microemulsion Method: Physicochemical Characterization and Photocatalytic Properties.

Titania nanoparticles (NPs) find wide application in photocatalysis, photovoltaics, gas sensing, lithium batteries, etc. One of the most important synthetic challenges is maintaining control over the polymorph composition of the prepared nanomaterial. In the present work, TiO2 NPs corresponding to anatase, rutile, or an anatase/rutile/brookite mixture were obtained at 80 °C by an inverse microemulsion method in a ternary system of water/cetyltrimethylammonium bromide/1-hexanol in a weight ratio of 17:28:55. The only synthesis variables were the preparation of the aqueous component and the nature of the Ti precursor (Ti(IV) ethoxide, isopropoxide, butoxide, or chloride). The materials were characterized with X-ray diffraction, scanning/transmission electron microscopy, N2 adsorption-desorption isotherms, FTIR and Raman vibrational spectroscopies, and diffuse reflectance spectroscopy. The synthesis products differed significantly not only in phase composition, but also in crystallinity, textural properties, and adsorption properties towards water. All TiO2 NPs were active in the photocatalytic decomposition of rhodamine B, a model dye pollutant of wastewater streams. The mixed-phase anatase/rutile/brookite nanopowders obtained from alkoxy precursors showed the best photocatalytic performance, comparable to or better than the P25 reference. The exceptionally high photoactivity was attributed to the advantageous electronic effects known to accompany multiphase titania composition, namely high specific surface area and strong surface hydration. Among the single-phase materials, anatase samples showed better photoactivity than rutile ones, and this effect was associated, primarily, with the much higher specific surface area of anatase photocatalysts.

Bioinspired Dopamine and N-Oxide-Based Zwitterionic Polymer Brushes for Fouling Resistance Surfaces.

Biofouling is a great challenge for engineering material in medical-, marine-, and pharmaceutical-related applications. In this study, a novel trimethylamine N-oxide (TMAO)-analog monomer, 3-(2-methylacrylamido)-N,N-dimethylpropylamine N-oxide (MADMPAO), was synthesized and applied for the grafting of poly(MADMPAO) (pMPAO) brushes on quartz crystal microbalance (QCM) chips by the combination of bio-inspired poly-dopamine (pDA) and surface-initiated atom transfer radical polymerization technology. The result of ion adsorption exhibited that a sequential pDA and pMPAO arrangement from the chip surface had different characteristics from a simple pDA layer. Ion adsorption on pMPAO-grafted chips was greatly inhibited at low salt concentrations of 1 and 10 mmol/L due to strong surface hydration in the presence of charged N+ and O- of zwitterionic pMPAO brushes on the outer layer on the chip surface, well known as the "anti-polyelectrolyte" effect. During BSA adsorption, pMPAO grafting also led to a marked decrease in frequency shift, indicating great inhibition of protein adsorption. It was attributed to weaker BSA-pMPAO interaction. In this study, the Au@pDA-4-pMPAO chip with the highest coating concentration of DA kept stable dissipation in BSA adsorption, signifying that the chip had a good antifouling property. The research provided a novel monomer for zwitterionic polymer and demonstrated the potential of pMPAO brushes in the development and modification of antifouling materials.

Zwitterionic loose polyamide nanofiltration membrane with good antifouling properties for efficient removal of humic acid and dyes

Loose nanofiltration membrane exhibits significant advantages in removing organic pollutants due to its high selectivity at a lower operating pressure. Herein, a novel zwitterionic loose polyamide separation layer was designed and formed on the modified polyethersulfone substrate to obtain the zwitterionic loose nanofiltration (ZLNF) membrane with high water permeability and good antifouling properties. The BAPP-TMC polyamide layer was fabricated by the interfacial polymerization between 1,4-bis(3-aminopropyl)piperazine (BAPP) and trimesoyl chloride (TMC). Afterward, the BAPP-TMC polyamide layer was grafted with zwitterions by a facile surface modification. Owing to the fabrication of the relatively loose polyamide structure with zwitterions, the prepared ZLNF-0.2 membrane presented an ultra-high pure water permeability of 148.5 L m−2 h−1 bar−1 while maintaining relatively good removal capacities for organic pollutants. The removal rates for humic acid (HA, 100 ppm) and Congo Red (CR, 100 ppm) were 98.1 % and 97.6 %, respectively. Furthermore, the good hydrophilicity and strong surface hydration effect of zwitterions endowed the ZLNF membranes with excellent anti-organic fouling and antibacterial adhesion properties. The good antibacterial abilities of ZLNF membranes were also proved by the fluorescence staining results. Due to the effective separation performance and good antifouling properties, the fabricated ZLNF membranes present great application potential in removing natural organic matter and dyes.

In situ generation of zwitterionic-functionalized liquid metal-based polydimethylsiloxane antifouling coatings with self-healing ability

Predicated on the marine bio-adhesion strategy, we herein assembled tannic acid (TA) in-situ onto Gallium-based liquid metal (GLM) nanodroplets surface effectuating the formation of poly(TA/PEI) adhesive layer with polyethyleneimine (PEI) via Schiff-base reaction and/or Michael addition to derive poly(TA/PEI)-functionalized GLM nanodroplets (GLM-PEI). Subsequently, the zwitterionic precursor triisopropylsilyl methacrylate (TISM) was bonded with the amine group of poly(TA/PEI) through aza-Michael addition for extracting TISM-functionalized GLM nanodroplets (GLM-TISM). The on-site hydrolysis of the as-prepared GLM-TISM into a zwitterionic group could be achieved by placing the zwitterionic precursor triisopropylsilyl TISM in an aqueous environment. Therefore, the synergy created by the bactericidal activity of GLM nanodroplets along with the strong surface hydration of the zwitterionic group contributes towards the remarkable antifouling performance of the GLM-TISM, which exhibits good dispersibility in polydimethylsiloxane (PDMS) elastomer coating and as functional filler to fabricate nano-composite coatings (PDMS@GLM-TISM). The as-obtained PDMS@GLM-TISM demonstrate excellent antifouling effect with the inhibition of bacterial and algae adhesion (removal of more than 96 % of bacteria and 77 % of algae) under the synergistic effect of liquid metal and zwitterionic groups. Furthermore, GLM-TISM nanodroplets can furnish the PDMS coating with self-repair ability by crosslinking the unreacted vinyl monomer of PDMS with the exposure to GLM to initiate polymerization.

Hydration and antibiofouling of TMAO-derived zwitterionic polymers surfaces studied with atomistic molecular dynamics simulations

Zwitterionic polymers have emerged as a class of highly effective ultralow fouling materials for critical marine coating and biomedical applications. The recently developed trimethylamine N-oxide (TMAO)-derived zwitterionic polymers have demonstrated excellent antibiofouling capability in various chemical environments; however, it remains unclear how they interact with proteins at the microscopic level. To further investigate the antifouling mechanisms, we performed atomistic molecular dynamics (MD) simulations in combination with free-energy computations to provide an in-depth molecular understanding of the interactions of TMAO polymer brush (pTMAO) surfaces with proteins of opposite charges (positively charged lysozyme and negatively charged barnacle cement protein) in aqueous environments (pure water and saline solution). Our simulations revealed ordered structures of a condensed hydration water layer on the pTMAO surfaces in pure and saline water. The quantitative free energy analyses showed that the pTMAO surface has small protein desorption energy, but with a strong hydration energy barrier near the polymer surfaces to resist protein adsorption compared to other biofouling surfaces. The addition of salts only has a slight effect on the pTMAO surface’s exclusion of proteins due to the small interference of the structure of interfacial water. This study provides detailed knowledge of the strong surface hydration of zwitterionic polymers and its relation to salt impact, protein adsorption, and antibiofouling behavior of these important materials.

Functionalized Ti3C2Tx-based nanocomposite coatings for anticorrosion and antifouling applications

Marine corrosion and biofouling are a major issue affecting the development of the marine industry. Traditional single-function coatings, such as those that provide either antifouling or anticorrosion, cannot meet the requirements in the current hostile conditions. In our study, block copolymer-functionalized Ti3C2Tx was successful prepared and employed to synthesize a nanocomposite coating with satisfactory antifouling and anticorrosion performances, in which the anticorrosion agent poly(2-mercaptobenzothiazole) (PMBTMA) was first grafted on the Ti3C2Tx surface, after which the antifouling agent poly(3-sulfopropyl methacrylate potassium (PSPMA) was grafted via surface-initiated atom transfer radical polymerization (SI-ATRP), to obtain the block copolymer (PMBTMA-co-PSPMA)-functionalized Ti3C2Tx (abbreviated as TMS). An appropriate corrosion protection and antifouling mechanism in the functionalized Ti3C2Tx-based epoxy nanohybrid coatings is proposed. It is noteworthy that the antibacterial activity of the proposed coating stems from the synergistic bactericidal effect of Ti3C2Tx and 2-mercaptobenzothiazole (MBT). The outstanding antibacterial properties of the TMS and the strong surface hydration of the anionic polymer brushes PSPMA, endow the as-prepared TMS-based nanocomposite coating (TMS/EP) with good antifouling performance (removal of more than 55% of bacteria and removal rate of microalgae up to 71%). More importantly, the TMS/EP has excellent corrosion resistance ability, which is due to the good synergistic anticorrosion barrier effect of Ti3C2Tx nanosheets and the on-demand release of corrosion inhibitor MBT during the corrosion process.

PDMS and POSS-dangling zwitterionic polyurethane coatings with enhanced anti-icing performance

Poly(sulfobetaine methacrylate) (PSBMA)-based zwitterionic polyurethane (ZPU), polydimethylsiloxane (PDMS)-dangling ZPU (PDMS-D + ZPU) and polyhedral oligomeric silsesquioxane (POSS)-dangling ZPU (POSS-D + ZPU) were prepared via atom transfer radical polymerization, quaternization reaction and crosslinking reaction to establish a superior anti-icing formulation. Obtained ZPU, PDMS-D + ZPU and POSS-D + ZPU coatings in contact with water all could support a self-lubricating water layer by the strong surface hydration and enrichment of zwitterionic PSBMA segments. In contrast, the PDMS-D + ZPU coating held the lowest amount of bound water due to the surface coverage of low-surface-tension PDMS chains, resulting in the lowest ice propagation rate. The POSS-D + ZPU coating held the highest amount of bound water because the aggregation of hard POSS particles on the surface induced more hydrophilic channels to enhance hydration of PSBMA. The hard POSS particles also served as a crystal nucleus to accelerate ice formation on the surface of POSS-D + ZPU coating. However, hydrophobic POSS allowed the POSS-D + ZPU coating to exhibit a lower ice propagation rate than ZPU coating. Additionally, both PDMS-D + ZPU and POSS-D + ZPU coatings were found to maintain low ice adhesion strength after multiple icing/de-icing cycles due to the synergism among the crosslinked structure, self-lubricating water layer and hydrophobic units.

Surface Hydration and Antifouling Activity of Zwitterionic Polymers.

It is believed that the strong surface hydration of zwitterionic polymers leads to excellent antifouling properties. This Perspective presents the recent developments in studies on such surface hydration in situ using sum frequency generation (SFG) vibrational spectroscopy. SFG research provides direct molecular level evidence that zwitterionic polymers have strong surface hydration, which prevents protein adsorption and marine animal attachment. The salt effect and protein interaction on surface hydration of zwitterionic polymers have also been examined using SFG. Possible future research directions on surface hydration of new zwitterionic polymers including zwitterionic hydrogels, copolymers, and mixed charged polymers are discussed. It is also important to combine experimental SFG studies with computer simulations to further elucidate the surface hydration to understand antifouling mechanisms.

Strong Surface Hydration and Salt Resistant Mechanism of a New Nonfouling Zwitterionic Polymer Based on Protein Stabilizer TMAO.

Zwitterionic polymers exhibit excellent nonfouling performance due to their strong surface hydrations. However, salt molecules may severely reduce the surface hydrations of typical zwitterionic polymers, making the application of these polymers in real biological and marine environments challenging. Recently, a new zwitterionic polymer brush based on the protein stabilizer trimethylamine N-oxide (TMAO) was developed as an outstanding nonfouling material. Using surface-sensitive sum frequency generation (SFG) vibrational spectroscopy, we investigated the surface hydration of TMAO polymer brushes (pTMAO) and the effects of salts and proteins on such surface hydration. It was discovered that exposure to highly concentrated salt solutions such as seawater only moderately reduced surface hydration. This superior resistance to salt effects compared to other zwitterionic polymers is due to the shorter distance between the positively and negatively charged groups, thus a smaller dipole in pTMAO and strong hydration around TMAO zwitterion. This results in strong bonding interactions between the O- in pTMAO and water, and weaker interaction between O- and metal cations due to the strong repulsion from the N+ and hydration water. Computer simulations at quantum and atomistic scales were performed to support SFG analyses. In addition to the salt effect, it was discovered that exposure to proteins in seawater exerted minimal influence on the pTMAO surface hydration, indicating complete exclusion of protein attachment. The excellent nonfouling performance of pTMAO originates from its extremely strong surface hydration that exhibits effective resistance to disruptions induced by salts and proteins.

Cationic Alternating Polypeptide Fixed on Polyurethane at Multiple Sites for Excellent Antibacterial and Antifouling Properties.

Bacterial infection and blockage are severe problems for polyurethane (PU) catheters and there is an urgent demand for surface-functionalized polyurethane. Herein, a cationic alternating copolymer comprising allyl-substituted ornithine and glycine (allyl-substituted poly(Orn-alter-Gly)) with abundant carbon-carbon double bond functional groups (C═C) is designed. Polyurethane is prepared with a large quantity of C═C groups (PU-D), and different amounts of allyl-substituted poly(Orn-alter-Gly) are grafted onto the PU-D surface (PU-D-2%AMPs and PU-D-20%AMPs) via the C═C functional groups. The chemical structures of the allyl-substituted poly(Orn-alter-Gly) and polyurethane samples (PU, PU-D, PU-D-2%AMPs, and PU-D-20%AMPs) are characterized and the results reveal that allyl-substituted poly(Orn-alter-Gly) is decorated on the polyurethane. PU-D-20%AMPs shows excellent antibacterial activity against Escherichia coli, Enterococcus faecalis, and Staphylococcus aureus because of the high surface potential caused by cationic allyl-substituted poly(Orn-alter-Gly), and it also exhibits excellent long-term antibacterial activity and antibiofilm properties. PU-D-20%AMPs also has excellent antifouling properties because the cationic copolymer is fixed at multiple reactive sites, thus avoiding the formation of movable long chain brush. A strong surface hydration barrier is also formed to prevent adsorption of proteins and ions, and in vivo experiments reveal excellent biocompatibility. This flexible strategy to prepare dual-functional polyurethane surfaces with antibacterial and antifouling properties has large potential in biomedical implants.

Layer-by-layer construction of CS-CNCs multilayer modified mesh with robust anti-crude-oil-fouling performance for efficient oil/water separation

Filtration membranes, with excellent anti-fouling capability, are ideal for actual oily sewage treatment, but the absence of a pre-hydration procedure is still a challenge. In this study, we demonstrated an environmentally friendly, and economical route to solve this problem by depositing chitosan (CS)-cellulose nanocrystals (CNCs) multilayer on stainless steel mesh (SSM) via simple layer-by-layer (LBL) self-assembly method. Due to the chemical structure, the CNCs have a large number of hydrophilic groups that are tightly bound to the surface, so the CS-CNCs multilayer modified mesh can maintain their strong surface hydration ability in air or oil, and will not be contaminated by crude oil even in a dry state. Besides, the CS-CNCs multilayer modified mesh exhibits superamphiphilic, underwater superoleophobic, and under-oil superhydrophilic functions. Moreover, the modified mesh also shows high rejection rate for crude oil/water mixture (99.92%) and diverse oil-in-water emulsions (>99.58%). What's more, the mesh has excellent reusability and chemical stability. The outstanding advantages in low-cost, environmental protection, biodegradability, anti-crude-oil-fouling performance, and efficient oil/water separation, endow our CS-CNCs multilayer modified mesh with great potential in complicated oily sewage purification.

Self-healing polydimethylsiloxane antifouling coatings based on zwitterionic polyethylenimine-functionalized gallium nanodroplets

There is an urgent need to develop effective and eco-friendly nanostructured coatings for marine antifouling to replace traditional coatings, while ensuring they do not lead to environmental hazards. Gallium-based liquid metal (GLM), which has unique antibacterial and non-toxic properties, has potential for applications in antifouling. In this study, GLM nanodroplets modified with zwitterionic polymer (polyethylenimine-quaternized derivative, PEIS) based antifouling agent were prepared successfully via sonication and Michael-addition, which could potentially be incorporated into the polydimethylsiloxane coating (PDMS) as a functional filler. A series of characterization methods, such as infrared spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy, have proved the successful modification of GLM nanodroplets with PEIS. The PEIS functionalized GLM nanodroplets exhibit good anti-bacterial properties due to synergistic bactericidal activity of Ga3+ stemming from GLM nanodroplets and the quaternary ammonium group from zwitterionic polymer PEIS. The synergistic anti-bacterial properties of PEIS-GLM nanodroplets and strong surface hydration of zwitterionic polymer PEIS result in remarkable antifouling performance of the filler. Subsequently, through the observation of the cross section, the as-prepared PEIS modified GLM nanodroplets exhibit good dispersibility in the PDMS coating, which also ensures that the PEIS-GLM@PDMS coating has satisfactory antifouling effect (removal of above 90% bacteria and 70% microalgae). Furthermore, the PEIS modified GLM nanodroplets endow the PDMS coating with self-healing properties by reason of the crosslinking of unreacted vinyl in PDMS by exposed GLM initiating polymerization under external mechanical force.

Computational Investigation of Antifouling Property of Polyacrylamide Brushes.

Antifouling materials and coatings have broad fundamental and practical applications. Strong hydration at polymer surfaces has been proven to be responsible for their antifouling property, but molecular details of interfacial water behaviors and their functional roles in protein resistance remain elusive. Here, we computationally studied the packing structure, surface hydration, and protein resistance of four poly(N-hydroxyalkyl acrylamide) (PAMs) brushes with different carbon spacer lengths (CSLs) using a combination of molecular mechanics (MM), Monte Carlo (MC), and molecular dynamics (MD) simulations. The packing structure of different PAM brushes were first determined and served as a structural basis for further exploring the CSL-dependent dynamics and structure of water molecules on PAM brushes and their surface resistance ability to lysozyme protein. Upon determining an optimal packing structure of PAMs by MM and optimal protein orientation on PAMs by MC, MD simulations further revealed that poly(N-hydroxymethyl acrylamide) (pHMAA), poly(N-(2-hydroxyethyl)acrylamide) (pHEAA), and poly(N-(3-hydroxypropyl)acrylamide) (pHPAA) brushes with shorter CSLs = 1-3 possessed a much stronger binding ability to more water molecules than a poly(N-(5-hydroxypentyl)acrylamide) (pHPenAA) brush with CSL = 5. Consequently, CSL-induced strong surface hydration on pHMAA, pHEAA, and pHPAA brushes led to high surface resistance to lysozyme adsorption, in sharp contrast to lysozyme adsorption on the pHPenAA brush. Computational studies confirmed the experimental results of surface wettability and protein adsorption from surface plasmon resonance, contact angle, and sum frequency generation vibrational spectroscopy, highlighting that small structural variation of CSLs can greatly impact surface hydration and antifouling characteristics of antifouling surfaces, which may provide structural-based design guidelines for new and effective antifouling materials and surfaces.

Molecular simulations and understanding of antifouling zwitterionic polymer brushes.

Zwitterionic materials are an important class of antifouling biomaterials for various applications. Despite such desirable antifouling properties, molecular-level understanding of the structure-property relationship associated with surface chemistry/topology/hydration and antifouling performance still remains to be elucidated. In this work, we computationally studied the packing structure, surface hydration, and antifouling property of three zwitterionic polymer brushes of poly(carboxybetaine methacrylate) (pCBMA), poly(sulfobetaine methacrylate) (pSBMA), and poly((2-(methacryloyloxy)ethyl)phosporylcoline) (pMPC) brushes and a hydrophilic PEG brush using a combination of molecular mechanics (MM), Monte Carlo (MC), molecular dynamics (MD), and steered MD (SMD) simulations. We for the first time determined the optimal packing structures of all polymer brushes from a wide variety of unit cells and chain orientations in a complex energy landscape. Under the optimal packing structures, MD simulations were further conducted to study the structure, dynamics, and orientation of water molecules and protein adsorption on the four polymer brushes, while SMD simulations to study the surface resistance of the polymer brushes to a protein. The collective results consistently revealed that the three zwitterionic brushes exhibited stronger interactions with water molecules and higher surface resistance to a protein than the PEG brush. It was concluded that both the carbon space length between zwitterionic groups and the nature of the anionic groups have a distinct effect on the antifouling performance, leading to the following antifouling ranking of pCBMA > pMPC > pSBMA. This work hopefully provides some structural insights into the design of new antifouling materials beyond traditional PEG-based antifouling materials.

Effect of Surface Hydration on Antifouling Properties of Mixed Charged Polymers.

Interfacial water structure on a polymer surface in water (or surface hydration) is related to the antifouling activity of the polymer. Zwitterionic polymer materials exhibit excellent antifouling activity due to their strong surface hydration. It was proposed to replace zwitterionic polymers using mixed charged polymers because it is much easier to prepare mixed charged polymer samples with much lower costs. In this study, using sum frequency generation (SFG) vibrational spectroscopy, we investigated interfacial water structures on mixed charged polymer surfaces in water and how such structures change while being exposed to salt solutions and protein solutions. The 1:1 mixed charged polymer exhibits excellent antifouling property whereas other mixed charged polymers with different ratios of the positive/negative charges do not. It was found that on the 1:1 mixed charged polymer surface, SFG water signal is dominated by the contribution of the strongly hydrogen bonded water molecules, indicating strong hydration of the polymer surface. The responses of the 1:1 mixed charged polymer surface to salt solutions are similar to those of zwitterionic polymers. Interestingly, exposure to high concentrations of salt solutions leads to stronger hydration of the 1:1 mixed charged polymer surface after replacing the salt solution with water. Protein molecules do not substantially perturb the interfacial water structure on the 1:1 mixed charged polymer surface and do not adsorb to the surface, showing that this mixed charged polymer is an excellent antifouling material.

Ultralow fouling membranes by surface modification with functional polydopamine

We report a facile, versatile, and novel approach for the design of ultralow fouling membranes via mussel-inspired molecular functionalization and zwitterionization. Using mussel-inspired polydopamine (PDA) coatings on polysulfone microporous membranes, active molecules with tertiary amine functionality (N,N-dimethylethylenediamine (DMDA)) were grafted via Michael addition through primary amine groups. The DMDA-functionalized membrane was further reacted with 1,3-propane sultone to obtain zwitterionic membrane. The variation of surface chemistry and surface wettability upon molecular functionalization was monitored with X-ray photoelectron spectroscopy (XPS) and water contact angle measurements. Following molecular functionalization, the membranes became more hydrophilic due to strong surface hydration with PDA, and zwitterionic functional groups. The functionalized membranes showed ultralow bovine serum albumin (BSA) protein adsorption and high flux recovery after protein filtration. The versatile nature of PDA modification along with its molecular functionalization allows for the design of ultralow fouling surfaces, making this a promising membrane modification technique for water filtration and separation, but also for other antifouling applications.

Molecular Understanding and Structural-Based Design of Polyacrylamides and Polyacrylates as Antifouling Materials

Design and synthesis of highly bioinert and biocompatible antifouling materials are crucial for a broad range of biomedical and engineering applications. Among antifouling materials, polyacrylamides and polyacrylates have proved so promising because of cheap raw materials, ease of synthesis and applicability, and abundant functional groups. The strong surface hydration and the high surface packing density of polyacrylamides and polyacrylates are considered to be the key contributors to their antifouling property. In this article, we review our studies on the design and synthesis of a series of polyacrylamides and polyacrylates with different molecular structures. These polymers can be fabricated into different architectural forms (brushes, nanoparticles, nanogels, and hydrogels), all of which are highly resistant to the attachment of proteins, cells, and bacteria. We find that small structural changes in the polymers can lead to large enhancement in surface hydration and antifouling performance, both showing a positive correlation. This reveals a general design rule for effective antifouling materials. Furthermore, polyacrylamides and polyacrylates are readily functionalized with other bioactive compounds to achieve different new multifunctionalities.

Superior Antifouling Performance of a Zwitterionic Peptide Compared to an Amphiphilic, Non-Ionic Peptide.

The aim of this study was to explore the influence of amphiphilic and zwitterionic structures on the resistance of protein adsorption to peptide self-assembled monolayers (SAMs) and gain insight into the associated antifouling mechanism. Two kinds of cysteine-terminated heptapeptides were studied. One peptide had alternating hydrophobic and hydrophilic residues with an amphiphilic sequence of CYSYSYS. The other peptide (CRERERE) was zwitterionic. Both peptides were covalently attached onto gold substrates via gold-thiol bond formation. Surface plasmon resonance analysis results showed that both peptide SAMs had ultralow or low protein adsorption amounts of 1.97-11.78 ng/cm2 in the presence of single proteins. The zwitterionic peptide showed relatively higher antifouling ability with single proteins and natural complex protein media. We performed molecular dynamics simulations to understand their respective antifouling behaviors. The results indicated that strong surface hydration of peptide SAMs contributes to fouling resistance by impeding interactions with proteins. Compared to the CYSYSYS peptide, more water molecules were predicted to form hydrogen-bonding interactions with the zwitterionic CRERERE peptide, which is in agreement with the antifouling test results. These findings reveal a clear relation between peptide structures and resistance to protein adsorption, facilitating the development of novel peptide-containing antifouling materials.

Probing the Surface Hydration of Nonfouling Zwitterionic and PEG Materials in Contact with Proteins.

Zwitterionic polymers and poly(ethylene glycol) (PEG) have been reported as promising nonfouling materials, and strong surface hydration has been proposed as a significant contributor to the nonfouling mechanism. Better understanding of the similarity and difference between these two types of materials in terms of hydration and protein interaction will benefit the design of new and effective nonfouling materials. In this study, sum frequency generation (SFG) vibrational spectroscopy was applied for in situ and real-time assessment of the surface hydration of the sulfobetaine methacrylate (SBMA) and oligo(ethylene glycol) methacrylate (OEGMA) polymer brushes, denoted as pSBMA and pOEGMA, in contact with proteins. Whereas a majority of strongly hydrogen-bonded water was observed at both pSBMA and pOEGMA surfaces, upon contact with proteins, the surface hydration of pSBMA remained unaffected, but the water ordering at the pOEGMA surface was disturbed. The effects of free sulfobetaine, free PEG chains with two different molecular weights, and PEG coated gold nanoparticles on the surface hydration of proteins were investigated. The results indicated that free sulfobetaine could strengthen the protein hydration layer, but free PEG chains greatly disrupt the protein hydration layer and likely directly interact with the protein molecules. In contrast to free PEG, the PEG chains anchored on the nanoparticles behave similarly to the pOEGMA surface and could induce strong hydrogen bonding of the water molecules at the protein surfaces.