Molecular Dynamics Study on Properties of Hydration Layers above Polymer Antifouling Membranes.

Zwitterionic polymers as crucial antifouling materials exhibit excellent antifouling performance due to their strong hydration ability. The structure−property relationship at the molecular level still remains to be elucidated. In this work, the surface hydration ability of three antifouling polymer membranes grafting on polysiloxane membranes Poly(sulfobetaine methacrylate) (T4-SB), poly(3-(methacryloyloxy)propane-1-sulfonate) (T4-SP), and poly(2-(dimethylamino)ethyl methacrylate) (T4-DM) was investigated. An orderly packed, and tightly bound surface hydration layer above T4-SP and T4-SB antifouling membranes was found by means of analyzing the dipole orientation distribution, diffusion coefficient, and average residence time. To further understand the surface hydration ability of three antifouling membranes, the surface structure, density profile, roughness, and area percentage of hydrophilic surface combining electrostatic potential, RDFs, SDFs, and noncovalent interactions of three polymers' monomers were studied. It was concluded that the broadest distribution of electrostatic potential on the surface and the nature of anionic SO3- groups led to the following antifouling order of T4-SB > T4-SP > T4-DM. We hope that this work will gain some insight for the rational design and optimization of ecofriendly antifouling materials.

Slippery-Liquid-Infused Electrostatic Flocking Surfaces for Marine Antifouling Application.

Most marine antifouling coatings rely on the release of toxic biocides to prevent fouling organisms from attaching, causing environmental pollution. This work proposes a biocide-free environmentally friendly marine antifouling strategy. Slippery-liquid-infused electrostatic flocking surfaces (S-EFSs) were prepared by combining electrostatic flocking and slippery liquid infusion. They exhibited complete mussel resistance after comparing adhesion to the surface of different materials in the laboratory. In addition, the unique surface morphology including lubricant was found to be crucial to their antifouling performance. Real-time polymerase chain reaction showed that different surfaces significantly affected the gene-expression levels of the mussels' foot proteins, where higher levels on S-EFSs meant that the mussels tried to secrete more proteins but they failed to adhere. Moreover, a 148-day field test showed that S-EFSs can resist not only mussels but also tubeworms, tunicates, and barnacles, and the total fouling area decreased by more than 50% compared to control samples. Notably, the maturity of electrostatic flocking technology and the simplicity of the modification steps used endow this strategy with the potential to significantly reduce the economic loss caused by marine biofouling in practical applications.

Facile Access to Multisensitive and Self-Healing Hydrogels with Reversible and Dynamic Boronic Ester and Disulfide Linkages.

Multifunctional and multiresponsive hydrogels have presented a promising platform to design and fabricate smart devices for application in a wide variety of fields. However, their preparations often involve multistep preparation of multiresponsive polymer precursors, tedious reactions to introduce functional groups or sophisticated molecular designs. In this work, a multifunctional boronic acid-based cross-linker bis(phenylboronic acid carbamoyl) cystamine (BPBAC) was readily prepared from inexpensive commercially available 3-carboxylphenylboronic acid (CPBA) and cystamine dihydrochloride, which has the ability to cross-link the cis-diols and catechol-containing hydrophilic polymers to form hydrogels. Due to the presence of the reversible and dynamic boronate ester and disulfide bonds, the obtained hydrogels were demonstrated to not only possess pH, glucose, and redox triresponsive features, but also have autonomic self-healing properties under ambient conditions. Moreover, we can modulate the rheological and mechanical properties by simply adjusting the BPBAC amount. The features, such as commercially available starting materials, easy-to-implement approach, and versatility in controlling cross-linking network and mechanical properties, make the strategy described here a promising platform for fabricating multifunctional and smart hydrogels.

Design and synthesis of a new bioactive compound for marine antifouling inspired by natural products.

A marine antifouling compound, N-octyl-2-hydroxybenzamide (OHBA), inspired by ceramide and paeonol molecules, was created. First, methyl salicylate was synthesized with salicylic acid and methanol, followed by n-octylamine through an ester-amine condensation reaction. Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy, and mass spectrometry confirmed the characteristic structure of the OHBA compound. Bioassays showed that OHBA inhibits the growth of typical marine fouling organisms, such as Vibrio azureus, Navicula subminuscula, Ulva pertusa, Mytilus edulis, and Amphibalanus amphitrite, indicating its broad-spectrum antifouling ability. A one-year marine real-sea test further demonstrated the excellent antifouling properties of OHBA. OHBA is also extremely biodegradable, with a half-life of 6.3 days, making it a less environmentally harmful replacement for widely-used heavy metal-containing antifoulants.

Recent Progress in Functionalized Coatings for Corrosion Protection of Magnesium Alloys-A Review.

Magnesium (Mg) and its alloys, which have good mechanical properties and damping capacities, are considered as potential candidate materials in the industrial field. Nevertheless, fast corrosion is the main obstacle that seriously hinders its wide applications. Surface modification is an available method to avoid the contact between corrosive media and Mg substrates, thus extending the service life of Mg-based materials. Generally, manufacturing a dense and stable coating as physical barriers can effectively inhibit the corrosion of Mg substrates; however, in some complex service environments, physical barrier coating only may not satisfy the long-term service of Mg alloys. In this case, it is very important to endow the coating with suitable functional characteristics, such as superhydrophobic and self-healing properties. In this review, the various surface treatments reported are presented first, followed by the methods employed for developing superhydrophobic surfaces with micro/nanostructuring, and an overview of the various advanced self-healing coatings, devolved on Mg alloys in the past decade, is further summarized. The corresponding preparation strategies and protection mechanisms of functional coatings are further discussed. A potential research direction is also briefly proposed to help guide functional strategies and inspire further innovations. It is hoped that the summary of this paper will be helpful to the surface modification of Mg alloys and promote the further development of this emerging research field.

Crawling and adhesion behavior of Halamphora sp. based on different parts of Folium Sennae-like film: Evaluation of analytical methods for anti-diatom experimental results.

Anti-diatom testing is a basic method to evaluate the anti-fouling performance of coatings. Many existing results of anti-diatom performances are evaluated based on their attachment number or coverage area, ignoring the influence of the crawling and adhesion behavior of diatoms on the analysis results. Here, a Folium Sennae-like film with multiple structural units was prepared by considering the influence of diatom attachment behaviors on the analysis results. The anti-diatom performances of different parts (divided and called four parts: edge, surface, cross striation, and vertical pattern) on the Folium Sennae-like film were evaluated using the counting and area methods. Obviously, the anti-diatom performance of the Folium Sennae-like film was superior to that of epoxy resin without structure. Under equal areas, the average numbers of diatoms on the cross striation and the vertical pattern were similar to the surface. It was found that the attachment behavior of Halamphora sp. is affected by microstructure units, rather than the combined structure of which the scale is much larger than that of diatoms. Meanwhile, the average attachment area for the unit number of diatoms was calculated. The diatom attachment area without microstructure, surface, cross striation, or vertical pattern was 81.751, 106.950, 73.904, and 84.376 µm2, respectively. Moreover, the static and dynamic motion behaviors of Halamphora sp. were studied, and the theory for Halamphora sp. attachment was modeled in three dimensions. The variable morphology of Halamphora sp. lead to inaccurate results for diatom analyses based on the counting and area methods, which is summarized here. This study discusses the evaluation method of coatings by anti-diatom performance, further promoting the research of diatoms in the field of antifouling.

The mussel-inspired micro-nano structure for antifouling:A flowering tree.

Mussels are typical marine fouling organisms that attach to surfaces though secretions, which is generally the focus of research on mussel-related fouling. This study reveals "a flowering tree" structure on mussel shells with antifouling performance. Based on the antifouling mechanism of surface microstructure, we prepared mussel-like shells (P) using the biomimetic replication method. Mussel adhesion experiments were conducted to examine the anti-mussel performances of the mussel shells and P. The anti-diatom performances of the mussel-like shells were also evaluated using three types of diatoms. The mussels responded differently to different locations on the shells, and the flowering tree microstructure exhibited excellent antifouling performance. In addition, VP (P immersed in vinyl silicon oil) and HP (P immersed in hydroxyl silicone oil) were prepared. The anti-diatom performance of VP was better than those of P and HP, indicating that hydrophobicity has a greater influence on anti-diatom performance than electronegativity. The newly discovered antifouling micro-nano structure was parameterized, revealing that a branch of the flowering tree has an inclination of 13.3° to the surface with a height of 210.1 nm. The results of this study provide insights for further investigations of bionic micro-nano structures in the field of antifouling.

Secretion mechanism and adhesive mechanism of diatoms: Direct evidence from the quantitative analysis.

Diatoms are one of the biofouling species attached to the substrate that can cause substrate corrosion, fuel consumption and destruction of the ecological balance. Therefore, the study of single-cellfouling organisms, particularly, the quantitative analysis of extracellular polymeric substances (EPS) is essential for antifouling. Atomic Force Microscope (AFM) was used to quantify three types of diatoms: Nitzschia closterium (N. closterium), Phaeodactylum tricornutum (P. tricornutum) and Halamphora sp. The situation of N. closterium was analyzed multiple times and the results showed that the adhesion value range of N. closterium with nacked chromatophores was three times larger than the mature one. The discovery of the EPS secretion from chromatophore is discussed in this paper, and the proposed mechanism has special implications to study the adhesive protein. Adhesion capabilities of different diatom genera and species were revealed as well. The average adhesion values of N. closterium, P. tricornutum and Halamphora sp. were about 1.7 nN, 3.3 nN and 2.5 nN, respectively, which suggest P. tricornutum could be a better candidate for testing diatom resistance on epoxy materials in the lab. Experimental data and discussions in this paper provide insights for further study of diatoms in the field of antifouling.

Zwitterionic modified electrostatic flocking surfaces for diatoms and mussels resistance.

Environmentally friendly antifouling coatings without biocide release need to be developed. Herein, a vertical array of nylon fibers coated with poly(sulfobetaine methacrylate) (PSBMA) was prepared by the electrostatic flocking technique and free radical polymerization catalyzed by Fe2+, which are called zwitterionic electrostatic flocking surfaces (ZEFS). The ZEFS showed resistance to diatoms because the fiber diameter was smaller than the diatom size. At the same time, the ZEFS prevented mussels adhesion. The number of plaques on the ZEFS was reduced by more than 98% and 96% compared with the glass surface and polydimethylsiloxane (PDMS) after a 4-day assay. The special surface morphology of the vertical arrangement of fibers makes it difficult for the mussels to empty seawater. Zwitterionic surface modification further enhanced the resistance to mussel adhesion. The ZEFS showed strong hydrophilicity with an underwater oil contact angle of up to 152 ± 2.4°, which reduces the adhesion work of mussel protein adhesion to the fibers and the wettability of the protein on the fiber surface. In addition, the zwitterionic layer exhibited good stability in artificial seawater, and it retained more than 96% stability after 30 days immersion in artificial seawater.

Three-dimensional flower-like shaped Bi5O7I particles incorporation zwitterionic fluorinated polymers with synergistic hydration-photocatalytic for enhanced marine antifouling performance.

Herein, several novel composite films consisting of three-dimensional (3D) Bi5O7I flower-like shaped microsphere and zwitterionic fluorinated polymer (ZFP) were successfully fabricated with the aim of achieving high anti-fouling performance. The prepared Bi5O7I flower-like shaped microsphere particles with diameters in the range of 2∼3 µm were uniformly distributed on the surface and in the internal of ZFP. Benefiting from the hydration layer formed by the ZFP and the efficient photocatalytic performance of Bi5O7I flower-like microsphere, the resultant optimized Bi5O7I/ZFP composite film exhibited an excellent diatom anti-settling performance and a high antibacterial rate of 99.09% and 99.66% towards Escherichia coli and Staphylococcus aureus. In addition, the composite films possessed the strengthened visible light absorption, the effectively separation and transfer of the photo-induced electrons and holes, the large number of hydroxyl (OH) radicals and superoxide radicals (O2-) all in Bi5O7I/ZFP systems, all of which were beneficial for the photocatalytic antifouling activity. More importantly, the synergistic hydration-photocatalytic effect of the Bi5O7I/ZFP composite films are answerable for the improvement of the antifouling property compared to the control. Thus, the synergistic hydration-photocatalytic contribution of Bi5O7I/ZFP composite film will shows promise for potential application in marine antifouling.

Fully Repairable Slippery Organogel Surfaces with Reconfigurable Paraffin-Based Framework for Universal Antiadhesion.

Constructing a slippery lubricant-infused surface (SLIS) whose internal microstructure and surface properties can be fully repaired helps to improve its property stability and extend technological implications but has presented a huge challenge. A class of fully repairable slippery organogel surfaces (SOSs), which uses microstructured paraffin as reconfigurable supporting structure and silicone oil as lubricant dispersion medium, is reported here. Attributed to nearly 90 wt % of silicone oil stored in the slippery organogel system and good compatibility with the paraffin-based framework, SOSs combine continuous lubricity and reliable lubricant storage stability. Furthermore, the thermally sensitive paraffin-based framework can quickly switch between solid supporting structure and liquid solution according to the ambient temperature, thereby achieving rapid regeneration of microstructure. This unique system consisting of reconfigurable framework and flowable lubricant derives two types of repairs aimed at varying degrees of damage. Significantly, the easy-to-prepare SOS, on the other hand, allows the adoption of various substrate surfaces for different purposes to form an antiadhesion coating and exhibits excellent antistain, antialgae, and anti-icing performance, thus greatly improving the flexibility of such materials in practical applications.

Fatigue-Resistant, Notch-Insensitive Zwitterionic Polymer Hydrogels with High Self-Healing Ability.

Introducing self-healing properties into hydrogels can prolong their application lifetime. However, achieving mechanical strength without sacrificing self-healing properties is still a major challenge. We prepared a series of zwitterionic polymer hydrogels by random copolymerization of zwitterionic ionic monomer (SBMA), cationic monomer (DAC) and hydrophilic monomer (HEMA). The ionic bonds and hydrogen bonds formed in the hydrogels can efficiently dissipate energy and rebuild the network. The resulting hydrogels show high mechanical strength (289-396 KPa of fracture stress, 433-864 % of fracture stress) and have great fatigue resistance. The hydrogel with a 1 : 1 molar ratio of SBMA:DAC possesses the best self-healing properties (self-healing efficiency up to 96.5 % at room temperature for 10 h). The self-healing process is completely spontaneous and does not require external factors to assist. In addition, the hydrogel also possesses notch insensitivity with a fracture energy of 12000 J m-2 . After combining the conductivity of RGO aerogel, the hydrogel/RGO composites show good strain sensitivity with high reliability and self-healing ability, which has certain significance in broadening the application of these zwitterionic hydrogels.

Improved Simultaneous Decolorization and Power Generation in a Microbial Fuel Cell with the Sponge Anode Modified by Polyaniline and Chitosan.

In recent years, microbial fuel cell (MFC) has been regarded as a promising technology for dye wastewater treatment. Compared with traditional anaerobic reactors, MFC has better decolorization effect while producing electricity simultaneously. In this paper, a double-chamber MFC with the sponge anode modified by polyaniline and chitosan-NCNTs was employed for simultaneous azo dye decolorization and bioelectricity generation. The influence of dye concentration, co-substrate concentration, and operating temperature on the performance of MFC with the modified anodes were studied. The results showed that a high decolorization efficiency (98.41%) and maximum power density (2816.67 mW m-3) of MFC equipped with modified bioanodes were achieved due to the biocompatibility and bioelectrocatalysis of modified material. And the biomass on the modified anode's surface was increased by 1.47 times. Additionally, microbial community analysis revealed that the modification of polyaniline and chitosan-NCNTs improved the selective enrichment of specific communities and the main microorganism was the electroactive and decolorizing bacteria Enterobacter (62.84%). Therefore, the composite anode is capable of fully utilizing the synergistic role of various materials, leading to superior performance of dye decolorization in MFCs. This work provided a strategy for the research on the recovery of biomass energy and decolorization in wastewater treatment. Graphical Abstract.

Biodegradation behavior of micro-arc oxidation coating on magnesium alloy-from a protein perspective.

Protein exerts a critical influence on the degradation behavior of absorbable magnesium (Mg)-based implants. However, the interaction mechanism between protein and a micro-arc oxidation (MAO) coating on Mg alloys remains unclear. Hereby, a MAO coating was fabricated on AZ31 Mg alloy. And its degradation behavior in phosphate buffer saline (PBS) containing bovine serum albumin (BSA) was investigated and compared with that of the uncoated alloy. Surface morphologies and chemical compositions were studied using Field-emission scanning electron microscope (FE-SEM), Fourier transform infrared spectrophotometer (FT-IR) and X-ray diffraction (XRD). The degradation behavior of the bare Mg alloy and its MAO coating was studied through electrochemical and hydrogen evolution tests. Cytotoxicity assay was applied to evaluate the biocompatibility of Mg alloy substrate and MAO coating. Results indicated that the presence of BSA decreased the degradation rate of Mg alloy substrate because BSA (RCH(NH2)COO‾) molecules combined with Mg2+ ions to form (RCH(NH2)COO)2Mg and thus inhibited the dissolution of Mg(OH)2 by impeding the attack of Cl‾ ions. In the case of MAO coated Mg alloy, the adsorption of BSA on MAO coating and the formation of (RCH(NH2)COO)2Mg exhibited a synergistic effect and enhanced the corrosion resistance of the coated alloy significantly. Furthermore, cell bioactive assay suggested that the MAO coating had good viability for MG63 cells due to its high surface area.

A Modular Coassembly Approach to All-In-One Multifunctional Nanoplatform for Synergistic Codelivery of Doxorubicin and Curcumin.

Synergistic combination therapy by integrating chemotherapeutics and chemosensitizers into nanoparticles has demonstrated great potential to reduce side effects, overcome multidrug resistance (MDR), and thus improve therapeutic efficacy. However, with regard to the nanocarriers for multidrug codelivery, it remains a strong challenge to maintain design simplicity, while incorporating the desirable multifunctionalities, such as coloaded high payloads, targeted delivery, hemodynamic stability, and also to ensure low drug leakage before reaching the tumor site, but simultaneously the corelease of drugs in the same cancer cell. Herein, we developed a facile modular coassembly approach to construct an all-in-one multifunctional multidrug delivery system for the synergistic codelivery of doxorubicin (DOX, chemotherapeutic agent) and curcumin (CUR, MDR modulator). The acid-cleavable PEGylated polymeric prodrug (DOX-h-PCEC), tumor cell-specific targeting peptide (CRGDK-PEG-PCL), and natural chemosensitizer (CUR) were ratiometrically assembled into in one single nanocarrier (CUR/DOX-h-PCEC@CRGDK NPs). The resulting CUR/DOX-h-PCEC@CRGDK NPs exhibited several desirable characteristics, such as efficient and ratiometric drug loading, high hemodynamic stability and low drug leakage, tumor intracellular acid-triggered cleavage, and subsequent intracellular simultaneous drug corelease, which are expected to maximize a synergistic effect of chemotherapy and chemosensitization. Collectively, the multifunctional nanocarrier is feasible for the creation of a robust nanoplatform for targeted multidrug codelivery and efficient MDR modulation.