A bio-inert and thermostable zwitterionic copolymer for the surface modification of PVDF membranes

PVDF/MOFs mixed matrix ultrafiltration membrane for efficient water treatment

Polyvinylidene fluoride (PVDF), with excellent mechanical strength, thermal stability and chemical corrosion resistance, has become an excellent material for separation membranes fabrication. However, the high hydrophobicity of PVDF membrane surface normally leads a decreased water permeability and serious membrane pollution, which ultimately result in low operational efficiency, short lifespan of membrane, high operation cost and other problems. Metal-organic frameworks (MOFs), have been widely applied for membrane modification due to its large specific surface area, large porosity and adjustable pore size. Currently, numerous MOFs have been synthesized and used to adjust the membrane separation properties. In this study, MIL-53(Al) were blended with PVDF casting solution to prepare ultrafiltration (UF) membrane through a phase separation technique. The optimal separation performance was achieved by varying the concentration of MIL-53(Al). The surface properties and microstructures of the as-prepared membranes with different MIL-53(Al) loading revealed that the incorporation of MIL-53(Al) enhanced the membrane hydrophilicity and increased the porosity and average pore size of the membrane. The optimal membrane decorated with 5 wt% MIL-53(Al) possessed a pure water permeability up to 43.60 L m-2 h-1 bar-1, while maintaining higher rejections towards BSA (82.09%). Meanwhile, the prepared MIL-53(Al)/LiCl@PVDF membranes exhibited an excellent antifouling performance.

PVDF/SiO2-g-CDs blended membrane for fluorescence detection and adsorption of metal ions

The preparation method of PVDF/SiO₂-g-CDs blended membrane was that the silanized modified carbon dots (CDs) were grafted onto the PVDF/SiO₂ blended membrane surface. The surface composition, morphology, hydrophilicity, fluorescence performance and metal ions adsorption performance of PVDF/SiO₂-g-CDs blended membrane were studied. The fluorescence quenching effect of the membrane with Hg²⁺ and Fe³⁺ was obvious. The quenching mechanism was the complexation of metal ions with the functional groups of CDs including -NH₂, -OH and -COOH. The optical detection limits of PVDF/SiO₂-g-CDs blended membrane for Hg²⁺ was 1.6 nM in the linear range of 0.0025-20 μM, and the optical detection limits for Fe³⁺ was 2.1 μM in the linear range of 0.5-5000 μM. The maximum adsorption capacity of PVDF/SiO₂-g-CDs blended membrane for Fe³⁺ was 47.04 mg·g^-1. The adsorption of the membrane conformed to the pseudo-second-order kinetics and Langumir model, and belonged to monolayer chemical adsorption on the membrane surface. Through adsorption thermodynamic analysis, adsorption was a spontaneous endothermic process. The recovery rate of fluorescence and adsorption capacity could still be maintained above 82% after five cycles. The PVDF/SiO₂-g-CDs blended membrane had the ability to regenerate. In summary, the PVDF/SiO₂-g-CDs blended membrane had the dual functions of detecting and adsorbing metal ions, and had broad application prospects in sewage treatment.

A Biofouling Resistant Zwitterionic Polysulfone Membrane Prepared by a Dual-Bath Procedure

This study introduces a zwitterionic material to modify polysulfone (PSf) membranes formed by a dual bath procedure, in view of reducing their fouling propensity. The zwitterionic copolymer, derived from a random polymer of styrene and 4-vinylpyrridine and referred to as zP(S-r-4VP), was incorporated to the PSf solution without any supplementary pore-forming additive to study the effect of the sole copolymer on membrane-structuring, chemical, and arising properties. XPS and mapping FT-IR provided evidence of the modification. Macrovoids appeared and then disappeared as the copolymer content increased in the range 1-4 wt%. The copolymer has hydrophilic units and its addition increases the casting solution viscosity. Both effects play an opposite role on transfers, and so on the growth of macrovoids. Biofouling tests demonstrated the efficiency of the copolymer to mitigate biofouling with a reduction in bacterial and blood cell attachment by more than 85%. Filtration tests revealed that the permeability increased by a twofold factor, the flux recovery ratio was augmented from 40% to 63% after water/BSA cycles, and irreversible fouling was reduced by 1/3. Although improvements are needed, these zwitterionic PSf membranes could be used in biomedical applications where resistance to biofouling by cells is a requirement.

Thermally Stable Bioinert Zwitterionic Sulfobetaine Interfaces Tolerated in the Medical Sterilization Process

This work introduces a thermally stable zwitterionic structure able to withstand steam sterilization as a general antifouling medical device interface. The sulfobetaine methacrylate (SBMA) monomer and its polymer form are among the most widely used zwitterionic materials. They are easy to synthesize and have good antifouling properties. However, they partially lose their properties after steam sterilization, a common procedure used to sterilize biomedical interfaces. In this study, ultrahigh-performance liquid chromatography/mass spectrometry (UHPLC-MS) was used to analyze and discuss the molecular structure of SBMA before and after a steam sterilization procedure, and a strategy to address the thermal stability issue proposed, using sulfobetaine methacrylamide (SBAA) instead of SBMA. Interestingly, it was found that the chemical structure of SBAA material can withstand the medical sterilization process at 121 °C while maintaining good antifouling properties, tested with proteins (fibrinogen), bacteria (Escherichia coli), and whole blood. On the other hand, SBMA gels failed at maintaining their excellent antifouling properties after sterilization. This study suggests that the SBAA structure can be used to replace SBMA in the bioinert interface of sterilizable medical devices, such as rayon fiber membranes used for disease control.

Which Are the Main Surface Disinfection Approaches at the Time of SARS-CoV-2?

Among many guidelines issued by the World Health Organization to prevent contagion from novel coronavirus (SARS-CoV-2), disinfection of animate and inanimate surfaces has emerged as a key issue. One effective approach to prevent its propagation can be achieved by disinfecting air, skin, or surfaces. A thorough and rational application of an Environmental Protection Agent for disinfection of surfaces, as well as a good personal hygiene, including cleaning hands with appropriate products (e.g., 60–90% alcohol-based product) should minimize transmission of viral respiratory pathogens such as SARS-CoV-2. Critical issues, associated with the potential health hazard of chemical disinfectants and the ineffective duration of most of the treatments, have fostered the introduction of innovative and alternative disinfection approaches. The present review aims to provide an outline of methods currently used for inanimate surface disinfection with a look to the future and a focus on the development of innovative and effective disinfection approaches (e.g., metal nanoparticles, photocatalysis, self-cleaning, and self-disinfection) with particular focus on SARS-CoV-2. The research reviews are, usually, focused on a specific category of disinfection methods, and therefore they are limited. On the contrary, a panoramic review with a wider focus, as the one here proposed, can be an added value for operators in the sector and generally for the scientific community.

Comb-like structural modification stabilizes polyvinylidene fluoride membranes to realize thermal-regulated sustainable transportation efficiency

Hydrophobic micro-porous membrane such as polyvinylidene fluoride (PVDF) with excellent thermal-/chemical-stability and low surface energy has received extensive attention in industrial water treatment and sustainable energy conversion. However, undesirable contaminants caused by inevitable proteins or microorganisms adhesion may lead to a rapid loss of separation efficiency, which significantly deteriorate their porous structures and eventually limit their practical performance. Herein, we present a scalable approach for fabricating comb-like copolymer modified PVDF membranes (PVDF-PN@AgNPs) that prevent bacteria from proliferating on the surface and temperature-controlled release of adhered contaminants. Comb-like structured copolymers were imparted to a polydopamine (PDA)-treated PVDF membrane by Michael addition reaction, which enabled a covalent binding of comb-like structured copolymers to the membrane. Such unique structural design of grafted copolymer, containing hydrophilic side chain and temperature-responsive chain backbone, stably prevents bacteria adhesion and provides reversible surface wettability. Therefore, the resultant membranes were evaluated to prevent bacterial adhesion, high touch-killing efficiency and temperature-controlled contaminants release (~99% of protein and ~75% of bacteria). Moreover, with the collapse and stretch of grafted copolymer chain backbone, the synthetic membrane further reversibly adjusted inner micro-porous structure and surface wettability, which eventually helped to achieve variable water fluid transport efficiency. This study not only provides a feasible structural design for stably coping with the challenging of antifouling and subsequent contamination adhesion of PVDF membrane, but also potentially answers the significant gap between lab research advances and practical application, particularly in the industrial membrane field.

Preparation of medical hydrophilic and antibacterial silicone rubber via surface modification

Bacterial adhesion of medical indwelling devices shortens their service life and brings about infections in patients. The combination of hydrophilic and antibacterial modifications can not only kill the bacteria in contact with the surface, but also avoid the adhesion of dead bacteria. From this view, with a self-made quaternary ammonium salt and a zwitterion as the modifiers, a modified silicone rubber, SR-g-(DMAPS-co-QA), was prepared via random co-grafting. The static water angle test and antibacterial assays proved the enhancement of both the hydrophilicity and antibacterial activity. In addition, compared with the unmodified silicone rubber, after 7 days of co-cultivation in E. coli suspension, SR-g-(DMAPS-co-QA) demonstrated good resistance to biofilm formation. Furthermore, to simulate the real situation, its antibacterial effect in dynamic flow condition was measured, confirming that SR-g-(DMAPS-co-QA) still maintained good antibacterial performance after a 48 hour cyclic flow of E. coli bacterial suspension.

Surface modification of silicone rubber to enhance hydrophilicity and antibacterial effect.