The hydrodynamic permeability and surface property of polyethersulfone ultrafiltration membranes with mussel-inspired polydopamine coatings

Polydopamine-based surface modification of hemoglobin particles for stability enhancement of oxygen carriers

Templated assembly techniques have been extensively used to develop various types of hemoglobin (Hb) loaded particles with improved performance. However, several instability issues must still be solved, including Hb exposure, enhanced Hb auto-oxidation, and the relatively weak binding of Hb to cross-linkers. Herein, to meet the stability requirements for novel hemoglobin-based oxygen carriers (HBOCs), hemoglobin-polydopamine particles (Hb-PDA) were fabricated using a mild process that combines the co-precipitation of Hb and an inorganic template with the spontaneous adhesion of PDA. The Hb-PDA showed uniform size distribution, chemical integrity of both Hb and PDA, high biocompatibility, and robust oxygen delivery. Our results demonstrated that the use of polydopamine as a biocompatible coating material reduced Hb leakage from the particles under both static and flow conditions, thus mitigating the toxicity associated with free Hb and strengthening the stability of Hb particles. In addition, Hb-PDA reduced HUVEC (Human Umbilical Vein Cells) oxidative injury and scavenged 85% of the available hydroxyl radicals, exhibiting its potential to act as an antioxidant for encapsulated Hb. Hb-PDA therefore shows significant promise as a cell-like structurally and functionally stable HBOCs.

Co-immobilization of ACH11 antithrombotic peptide and CAG cell-adhesive peptide onto vascular grafts for improved hemocompatibility and endothelialization

Surface modification by conjugating biomolecules has been widely proved to enhance biocompatibility of small-caliber artificial vascular grafts. In this study, we aimed at developing a multifunctional vascular graft that provides not only good hemocompatibility but also in situ rapid endothelialization. Herein, a vascular graft (inner diameter ∼2 mm) was fabricated by electrospinning with poly(lactic acid-co-caprolactone) and gelatin, and then biofunctionalized with antithrombotic peptide with sequence LTFPRIVFVLG (ACH₁₁) and cell adhesion peptide with sequence CAG through adhesive poly(dopamine) coating. We developed this graft with the synergistic properties of low thrombogenicity and rapid endothelialization. The successful grafting of both CAG and ACH₁₁ peptides was confirmed by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The surface micromorphology of the modified surfaces was observed by field emission scanning electron microscopy. Our results demonstrated that the multifunctional surface suppressed the denaturation of absorbed fibrinogen, hindered coagulation factor Xa activation, and inhibited platelet adhesion and aggregation. Importantly, this modified surface could selectively enhance endothelial cells adhesion, proliferation and release of nitric oxide. Upon in vivo implantation of 6 weeks, the multifunctional vascular graft showed improved patency and superior vascular endothelialization. Overall, the results effectively demonstrated that the co-immobilization of ACH₁₁ and CAG provided a promising method for the improvement of hemocompatibility and endothelialization of vascular grafts. STATEMENT OF SIGNIFICANCE: Electrospun small-caliber vascular grafts are increasingly used to treat cardiovascular diseases. Despite their success related to their good biodegradation and mechanical strength, they have some drawbacks, such as low hemocompatibility and endothelialization. The single-function ligands are insufficient to modify surface with both good hemocompatibility and rapid endothelialization simultaneously. Therefore, we functionalized electrospun vascular graft by novel antithrombotic peptide and cell-adhesive peptide to construct superior anticoagulation and ECs-selective adhesion surface in present study. The multifunctional vascular grafts benefit for high long-term patency and rapid endothelialization.

Bioinspired Modification of Layer-Stacked Molybdenum Disulfide (MoS2) Membranes for Enhanced Nanofiltration Performance

Inorganic nanofiltration membranes with high flux are urgently needed in water purification processes. Herein, polydopamine (PDA)-modified layer-stacked molybdenum disulfide (MoS2) nanofiltration membranes (NFMs) were fabricated via a pressure-assisted self-assembly process. The separation performance of the as-prepared membranes with various MoS2 loadings at different dopamine polymerization times was evaluated. The pure water permeance of PDA-modified MoS2 NFMs, with MoS2 loading of 0.1103 mg/cm2 at 4 h modification, could reach 135.3 LMH/bar. The rejection toward methylene blue could reach 100% with molecular weight cutoff approximately 671 Da and a high permeability of salts. Furthermore, the resultant membrane also exhibited a satisfactory long-term stability toward dye solution and antifouling property toward bovine serum albumin. This work may give inspiration to the development of inorganic membranes with high performance, especially high pure water permeance, for water-related processes.

Solution Blown Nylon 6 Nanofibrous Membrane as Scaffold for Nanofiltration

In this work, a nylon 6 nanofibrous membrane was prepared via solution blowing technology and followed hot-press as scaffold for nanofiltration. The structure and properties of the hot-pressed nylon 6 nanofibrous membrane (HNM) were studied the effect of hot-pressing parameters and areal densities. Then an ultra-thin polyamide (PA) active layer was prepared by interfacial polymerization on HNM. The effects of nanofibrous scaffolds on the surface properties of ultra-thin nanofiltration membranes and their filtration performance were studied. Results showed that the nylon 6 nanofibers prepared at a concentration of 15 wt % had a good morphology and diameter distribution and the nanofibers were stacked more tightly and significantly reduced in diameter after hot pressing at 180 °C under the pressure of 15 MPa for 10 s. When the porous scaffold was prepared, HNM with an areal density of 9.4 and 14.1 g/m² has a better apparent structure, a smaller pore size, a higher porosity and a greater strength. At the same time, different areal densities of HNM have an important influence on the preparation and properties of nanofiltration membranes. With the increase of areal density, the uniformity of HNM increased while their surface roughness and pore size decreased, which is beneficial to the establishment of PA barrier layer. With areal density of 9.4 and 14.1 g/m², the as-prepared nanofiltration membrane has a smoother surface and more outstanding filtration performance. The pure water flux is 13.1 L m⁻² h⁻¹ and the filtration efficiencies for NaCl and Na₂SO₄ are 81.3% and 85.1%, respectively.

Antifouling Ultrafiltration Membranes with Retained Pore Size by Controlled Deposition of Zwitterionic Polymers and Poly(ethylene glycol)

We demonstrate antifouling ultrafiltration membranes with retained selectivity and pure water flux through the controlled deposition of zwitterionic polymers and poly(ethylene glycol) (PEG). Molecules for polymerization were immobilized on the membrane's surface yet prevented from attaching to the membrane's pores due to a backflow of nitrogen (N2) gas achieved using an in-house constructed apparatus that we named the polymer prevention apparatus, or "PolyPrev". First, the operating parameters of the PolyPrev were optimized by investigating the polymerization of dopamine, which was selected due to its versatility in enabling further chemical reactions, published metrics for comparison, and its oxidative self-polymerization. Membrane characterization revealed that the polydopamine-modified membranes exhibited enhanced hydrophilicity; moreover, their size selectivity and pure water flux were statistically the same as those of the unmodified membranes. Because it is well documented that polydopamine coatings do not provide a long-lasting antifouling activity, poly(2-methacryloyloxyethyl phosphorylcholine) (polyMPC, Mn = 30 kDa) and succinimidyl-carboxymethyl-ester-terminated PEG ( Mn = 40 kDa) were codeposited while dopamine was polymerizing to generate antifouling membranes. Statistically, the molecular-weight cutoff of the polyMPC- and PEG-functionalized membranes synthesized in the PolyPrev was equivalent to that of the unmodified membranes, and the pure water flux of the PEG membranes was equivalent to that of the unmodified membranes. Notably, membranes prepared in the PolyPrev with polyMPC and PEG decreased bovine serum albumin fouling and Escherichia coli attachment. This study demonstrates that by restricting antifouling chemistries from attaching within the pores of membranes, we can generate high-performance, antifouling membranes appropriate for a wide range of water treatment applications without compromising intrinsic transport properties.

Facile Preparation of Self-Assembled Polydopamine-Modified Electrospun Fibers for Highly Effective Removal of Organic Dyes

Polydopamine (PDA) nanoparticles can be used as an adsorbent with excellent adsorption capacity. However, nanosized adsorbents are prone to aggregation and thus are severely limited in the field of adsorption. In order to solve this problem, we utilized polydopamine in-situ oxidation self-polymerization on the surface of polycaprolactone (PCL)/polyethylene oxide (PEO) electrospun fiber after solvent vapor annealing (SVA) treatment, and successfully designed and prepared a PCL/PEO@PDA composite membrane. The SVA treatment regulated the microscopic morphology of smooth PCL/PEO electrospun fibers that exhibited a pleated microstructure, increasing the specific surface area, and providing abundant active sites for the anchoring of PDA nanoparticles. The PCL/PEO@PDA composite obtained by chemical modification of PDA demonstrated numerous active sites for the adsorption of methylene (MB) and methyl orange (MO). In addition, the PCL/PEO@PDA composites were reusable several times with good reutilization as adsorbents. Therefore, we have developed a highly efficient and non-agglomerated dye adsorbent that exhibits potential large-scale application in dye removal and wastewater purification.

Cellulose acetate ultrafiltration membranes customized with bio-inspired polydopamine coating and in situ immobilization of silver nanoparticles

Schematic representation of the surface modification of cellulose acetate membranes with self-polymerized dopamine and in situ immobilization of AgNPs.

Bioinspired Surface Functionalization for Improving Osteogenesis of Electrospun Polycaprolactone Nanofibers

Electrospun nanofibers, with a typical interconnected porous structure mimicking the extracellular matrix, are commonly used in bone tissue engineering. However, to the best of our knowledge, few studies have been reported to investigate the enhancement of osteogenesis capability of electrospun polycaprolactone (PCL) nanofibers based on bioinspired surface functionalization. In this study, a universal and versatile approach was proposed to spontaneously modify the electrospun PCL nanofibers with bioactive nano-hydroxyapatite (nHA), using dopamine as an effective bioadhesive agent. The evaluation of scanning electron microscopy, energy-dispersive spectroscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis, and surface wettability indicated that nHA was successfully coated onto electrospun nanofibers (PCL-PDHA). Furthermore, in vitro cell experiment including adhesion, proliferation, and osteogenic capability and in vitro biomineralization test in simulated body fluid revealed that the PCL-PDHA nanofibers were biocompatible to MC3T3-E1 cells, and the osteogenesis and biomineralization capabilities were greatly improved in comparison with that of PCL nanofibers. In summary, the facile bioinspired surface functionalization method introduced in the present study, due to its universality and versatility, not only can be used to improve osteogenesis of electrospun nanofibers but also can be regarded as an avenue to achieve other predesigned purposes in biomedical engineering.

Elucidation of Titanium Dioxide Nucleation and Growth on a Polydopamine-Modified Nanoporous Polyvinylidene Fluoride Substrate via Low-Temperature Atomic Layer Deposition

Interfaces combining polydopamine (PDA) and nanoparticles have been widely utilized for fabricating hybrid colloidal particles, thin films, and membranes for applications spanning biosensing, drug delivery, heavy metal detection, antifouling membranes, and lithium ion batteries. However, fundamental understanding of the interaction between PDA and nanoparticles is still limited, especially the impact of PDA on nanoparticle nucleation and growth. In this work, PDA is used to generate functional bonding sites for depositing titanium dioxide (TiO₂) via atomic layer deposition (ALD) onto a nanoporous polymer substrate for a range of ALD cycles (<100). The resulting hybrid membranes are systematically characterized using water contact angle, scanning electron microscopy, atomic force microscopy, nitrogen adsorption and desorption, and X-ray photoelectron spectroscopy (XPS). An intriguing nonlinear relationship was observed between the number of ALD cycles and changes in surface properties (water contact angle and surface roughness). Together with XPS study, those changes in surface properties were exploited to probe the nanoparticle nucleation and growth process on complex PDA-coated porous polymer substrates. Molecular level understanding of inorganic and polymer material interfaces will shed light on fine-tuning nanoparticle-modified polymeric membrane materials.

Antifouling amphiphilic silicone coatings for dairy fouling mitigation on stainless steel

Pasteurization of dairy products is plagued by fouling, which induces significant economic, environmental and microbiological safety concerns. Herein, an amphiphilic silicone coating was evaluated for its efficacy against fouling by a model dairy fluid in a pilot pasteurizer and against foodborne bacterial adhesion. The coating was formed by modifying an RTV silicone with a PEO-silane amphiphile comprised of a PEO segment and flexible siloxane tether ([(EtO)₃Si-(CH₂)₂-oligodimethylsiloxane_m-block-(OCH₂CH₂)_n-OCH₃]). Contact angle analysis of the coating revealed that the PEO segments were able to migrate to the aqueous interface. The PEO-modified silicone coating applied to pretreated stainless steel was exceptionally resistant to fouling. After five cycles of pasteurization, these coated substrata were subjected to a standard clean-in-place process and exhibited a minor reduction in fouling resistance in subsequent tests. However, the lack of fouling prior to cleaning indicates that harsh cleaning is not necessary. PEO-modified silicone coatings also showed exceptional resistance to adhesion by foodborne pathogenic bacteria.

A substrate-independent ultrathin hydrogel film as an antifouling and antibacterial layer for a microfiltration membrane anchored via a layer-by-layer thiol-ene click reaction

Herein, a substrate-independent ultrathin hydrogel film was constructed on a microfiltration membrane through layer-by-layer (LbL) thiol-ene click chemistry to improve the antifouling and antibacterial properties. In our strategy, ene-functionalized dopamine was synthesized and coated onto a model substrate (polyethersulfone membrane) to introduce double bonds as anchoring sites for the hydrogel film; thiol-functionalized poly[oligo(ethylene glycol)mercaptosuccinate] (POEGMS) and ene-functionalized P(SBMA-co-AA) were synthesized as hydrogel precursors. The membrane was alternately immersed in the precursor solutions to form the ultrathin hydrogel film. Finally, Ag nanoparticles (AgNPs) were loaded into the hydrogel layer by adsorption and reduction procedures. By coating the hydrogel films, the loaded AgNPs could kill almost all the contacting bacteria and the bacteria in the surroundings, and the enhanced hydrophilicity of the modified membrane could effectively prevent the attachment of the bacteria. The membrane flux showed no significant decrease, the rejection ratio of BSA increased from 51% to 89%, and the F_RR increased from 36% to 90%. Moreover, the improvement of the hemocompatibility was confirmed by the decline in the plasma protein adsorption, prolonged clotting times, low hemolysis ratio, and prevention of platelet adhesion. Compared with that of other techniques for attaching hydrogel films, the main advantage of the current technique is that the hydrogel film thickness could be well controlled within the nanometer range; thus, it could significantly improve the antifouling and antibacterial properties of the membrane, but without compromising its permeability. Another advantage is that it is versatile for various substrates such as PVDF, PAN, and CA. This study opens up a facile and versatile route for anchoring ultrathin hydrogel film onto polymeric membranes to achieve excellent antifouling, antibacterial and hemocompatible properties.

Fabrication of lithium ion imprinted hybrid membranes with antifouling performance for selective recovery of lithium

The LIHMs showed a distinctive adsorption capacity (27.10 mg g⁻¹) and permselectivity (β_K/Li = 5.3780, β_Ca/Li = 21.9402, β_Mg/Li = 15.5620) for Li⁺, which resulted from the effect of the special imprinted sites.

Bioinspired Synthesis of Mesoporous Gold-silica Hybrid Microspheres as Recyclable Colloidal SERS Substrates

Noble metal nanostructures have been intensively investigated as active substrates for surface-enhanced Raman spectroscopy (SERS) from visible to near-IR wavelengths. However, metal nanoparticle-based SERS analysis in solutions is very challenging due to uncontrollable and irreproducible colloid aggregation. Here we report the templated synthesis of porous gold-silica hybrid microspheres and their application as reusable colloidal SERS substrates. Mesoporous polymer microspheres are synthesized and used as templates for the synthesis of non-aggregated gold nanoparticles, followed by polydopamine-mediated silicification to fabricate mesoporous gold-silica hybrid microspheres. The mesoporous hybrid particles detect crystal violet in the order of 10^-8 M and provide the structural durability of the immobilized gold nanoparticles, allowing them to be recycled for repeated SERS analyses for analytes in a solution with the similar sensitivity. This work suggests that the mesoporous gold-silica hybrid microspheres are attractive SERS substrates in terms of reusability, sensitivity, and stability.

Modified polyether-sulfone membrane: a mini review

Polyethersulfone has been widely used as a promising material in medical applications and waste-treatment membranes since it provides excellent mechanical and thermal properties. Hydrophobicity of polyethersulfone is considered one main disadvantage of using this material because hydrophobic surface causes biofouling effects to the membrane which is always thought to be a serious limitation to the use of polyethersulfone in membrane technology. Chemical modification to the material is a promising solution to this problem. More specifically surface modification is an excellent technique to introduce hydrophilic properties and functional groups to the polyethersulfone membrane surface. This review covers chemical modifications of the polyethersulfone and covers different methods used to enhance the hydrophilicity of polyethersulfone membrane. In particular, the addition of amino functional groups to polyethersulfone is used as a fundamental method either to introduce hydrophilic properties or introduce nanomaterials to the surface of polyethersulfone membrane. This work reviews also previous research reports explored the use of amino functionalized polyethersulfone with different nanomaterials to induce biological activity and reduce fouling effects of the fabricated membrane.