Narrow Results

In order to improve the anti-corrosion performance of thin stainless steel bipolar plates of proton exchange membrane fuel cell (PEMFC), the carbon film (of about 0.82-$\mu$m thickness) was fabricated on the thin stainless steel by laser direct writing technology irradiating the formed dense polydopamine (PDA) film. The results indicated that the PDA film has partially transformed into nanocrystalline graphite. Laser power and scanning speed had great effect on the anti-corrosion performance of the final obtained film in simulated PEMFC environment. When the laser power is 3.5 W and the scanning speed is 10 mm/s, the film obtained on the thin stainless steel has the best electrochemical performance in simulated PEMFC environment. Its corrosion current densities were $8.64\mu$A $\cdot$ cm${}^{-2}$@ −0.1 V (versus SCE) and $1.33\mu$A $\cdot$ cm ${}^{-2}$@ 0.6 V (versus SCE) in simulated anode and cathode environments, respectively. Compared with the bare thin stainless steel, the corresponding corrosion current densities decreased by 45% and 62%. The results obtained in this text provide a novel strategy for modifyingPEMFC thin metal bipolar plates.

Ti6Al4V alloy of titanium is a significant biomaterial due to its biocompatible nature, but it lacks required bioactivity to make it mimic properties to a human bone. Thus, hydroxyl-apatite (HAp), an inorganic compound found in human bones, is generally coated onto Ti6Al4V substrates to improve their bio-characteristics. But, HAp itself lacks certain bio-functionalities, such as allowing tissue bone regeneration and poor binding to the Ti6Al4V substrate, which results in osteoporosis and reduced bioactivity of the bio-implant, respectively. The proposed way out for this is the further doping of HAp with Strontium (Sr) for enabling tissue bone regeneration as well as addition of Polydopamine (PDA) for improved adhesion of HAp-based coatings with the substrate. Moreover, PDA results in increased drug delivery area and thus can be used as a material for enhancing resistance to bacterial growth. The present study demonstrates an experimental work on deposition of HAp, HAp with PDA and HAp with PDA and Sr coatings deposited onto Ti6Al4V alloy by means of biomimetic coating technique. Initially the pure HAp coatings were deposited using 10 SBF (simulated body fluid) solution and optimized in terms of time duration for desired coating uniformity. Then, for the optimized coating duration, the PDA pretreated Ti6Al4V substrates were coated, utilizing HAp, and Sr (at two different compositions) combinations were deposited through modified 10 SBF solutions. The characterization involving microstructural analysis and phase detection was performed for all these coatings using Scanned Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS) and X-Ray Diffraction (XRD) of the coated substrates and adhesion strength was calculated using a standard pull out adhesion test ISO 13779–4. The study showed an effective and comparatively cheap method of depositing organic coatings using biomimetic technique to obtain improved bio-functionalities in metallic implants at low temperatures.

A biomimetic and facile approach for integrating Fe₃O₄ and Au with polydopamine (PDA) was proposed to construct gold-coated Fe₃O₄ nanoparticles (Fe₃O₄@Au–PDA) with a core–shell structure by coupling in situ reduction with a seed-mediated method in aqueous solution at room temperature. The morphology, structure and composition of the core–shell structured Fe₃O₄@Au–PDA nanoparticles were characterized by transmission electron microscopy (TEM), X-ray powder diffraction (XRD) and X-ray photoelectron spectrometry (XPS). The formation process of Au shell was assessed using a UV-Vis spectrophotometer. More importantly, according to investigating changes in PDA molecules by Fourier transform infrared spectroscopy (FTIR) and in preparation process of the zeta-potential data of nanoparticles, the mechanism of core–shell structure formation was proposed. Firstly, PDA-coated Fe₃O₄ are obtained using dopamine (DA) self-polymerization to form thin and surface-adherent PDA films onto the surface of a Fe₃O₄ "core". Then, Au seeds are attached on the surface of PDA-coated Fe₃O₄ via electrostatic interaction in order to serve as nucleation centers catalyzing the reduction of Au³⁺ to Au⁰ by the catechol groups in PDA. Accompanied by the deposition of Au, PDA films transfer from the surface of Fe₃O₄ to that of Au as stabilizing agent. In order to confirm the reasonableness of this mechanism, two verification experiments were conducted. The presence of PDA on the surface of Fe₃O₄@Au–PDA nanoparticles was confirmed by the finding that glycine or ethylenediamine could be grafted onto Fe₃O₄@Au–PDA nanoparticles through Schiff base reaction. In addition, Fe₃O₄@Au–DA nanoparticles, in which DA was substituted for PDA, were prepared using the same method as that for Fe₃O₄@Au–PDA nanoparticles and characterized by UV-Vis, TEM and FTIR. The results validated that DA possesses multiple functions of attaching Au seeds as well as acting as both reductant and stabilizing agent, the same functions as those of PDA.

Polydopamine (PDA) capsule and core–shell structures with tailored structures and properties are of particular interests due to their multifunctions and potential applications as new colloidal structures in diverse fields. Among the available fabrication methods, PDA film onto colloidal particles followed by selective template removal has attracted extensive attention due to its advantages of precise control over the size, wall thickness and functions of the obtained capsules. The past several years has witnessed a rapid increase of research concerning the new fabrication strategies, functionalization and applications of this kind of capsules and core–shell structures, particularly in many fields such as drug delivery, catalysis, antibacterial, etc. In this review, the very recent progress of the capsule and core–shell structures based on PDA are summarized. There are basically two sections, including the fabrication process of PDA capsules, core–shell structures, and the various applications based on PDA.

Polydopamine-coated Fe₃O₄ (Fe₃O₄@PDA) nanoparticles (NPs) were prepared as synergistic redox mediators for the catalytic reduction, by NaBH₄, of azo dyes such as methyl orange (MO) and methyl red (MR). Transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) were applied to determine their surface morphology, surface chemistry and detailed chemical composition, respectively. The latter technique confirmed the presence of quinone moieties. Moreover, a vibrating sample magnetometer (VSM) was used to confirm the superparamagnetic properties of these NPs. The characteristic optical absorption maximum of MO at 462nm was used to monitor the decolorization process. This was employed to determine the catalytic activity in the reaction. An enhancement of the catalytic activity of the magnetic-separable Fe₃O₄@PDA nanocatalyst over that of PDA microspheres (MPs) was observed. Moreover, their reusability and stability were also investigated. A synergistic electron transfer mechanism involving both Fe₃O₄ and PDA moieties was proposed as follows: the quinone moieties and Fe (III) species in Fe₃O₄@PDA NPs served as systematic redox mediators, with quinone receiving an electron from NaBH₄. The reduced quinone next transfers an electron to the Fe (III) moiety, generating an Fe (II) species that in turn transfers an electron to the azo dye. We determined that this process resulted in enhanced reductive degradation of azo dyes when compared with PDA MPs. Moreover, Fe₃O₄@PDA NPs could be magnetically separated and recycled. We therefore concluded that these NPs show great potential in the immobilization of homogeneous catalysts in the chemical reduction processes of azo dyes.

Halloysite nanotubes@polydopamine (HNTs@PDA) nanocomposites were successfully synthesized, and Au nanoparticles (Au NPs) were loaded on HNTs@PDA by electrostatic adsorption. The electrochemical sensor based on HNTs@PDA–Au nanocomposites was constructed. The effect of the composition, structure and property of HNTs@PDA–Au on the response performance of the sensor was explored. The morphology and composition of the nanocomposites were characterized by field emission scanning electron microscopy, transmission electron microscopic, X-ray diffraction, energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. Electrochemical results revealed HNTs@PDA–Au as the sensing interface with good effect on electrocatalytic oxidation of N₂H₄. This sensor detected N₂H₄ in the range from 0.75$\mu$mol$\cdot$L${}^{-1}$ to 2.8mmol$\cdot$L${}^{-1}$, with a sensitivity of 171.7$\mu$A (mmol$\cdot$L${}^{-1}{)}^{-1}$cm${}^{-2}$ and a detection limit of 0.25$\mu$mol$\cdot$L${}^{-1}$ (S/N $=$ 3).

Nanofiber mats produced by electrospinning, with the advantages of specific surface area, porosity and chemical tenability, are an ideal support material for deposition of metal$-$organic framework (MOF) crystals. In this study, four types of MOFs (MIL-53(Al), ZIF-8, UiO-66-NH₂ and NH₂-MIL-125(Ti)) were deposited on polydopamine (PDA)-modified electrospun polyvinyl alcohol (PVA)/SiO₂ organic$-$inorganic hybrid nanofiber mats by bulky synthesis. Because of the formation of Si–O–C–O–Si bridges between PVA chains and silica network, electrospun PVA/SiO₂ organic$-$inorganic hybrid nanofiber mats are quite stable in water or organic solvents and at high temperature are suitable as supports for MOFs deposition. The PDA layer, which exhibits a powerful adhesive ability to attach foreign objects, can effectively improve growth of MOFs on the surface of PVA/SiO₂ nanofiber mats. The obtained MOF composites combining the unique properties of electrospun nanofibers mats and MOFs particles become flexible and tailorable, greatly expanding the application range of MOFs materials. The synthesized MOF composites were used to adsorb chloramphenicol (CAP) in water. It was found that the four MOF composites could remove CAP from water effectively and MIL-53(Al) composite had the highest adsorption capacity due to the higher specific surface area.

Spin-coated poly (vinylidene fluoride) (PVDF) membrane and electrospun PVDF nanofibers were fabricated and surface modified with in-situ self-polymerization of dopamine or surface deposition of polydopamine. The morphology, composition and phase, hydrophilicity and dye degradation effects of these composite were quantitatively investigated. The results indicated that surface modified PVDF membrane and nanofibers exhibited excellent dye degradation capacity. Specifically, in-situ self-polymerization of dopamine could induce homogeneous distribution of polydopamine on the piezo-catalysis materials, providing favorable spatial conditions for the adsorption of dye molecules and enhancing dye degradation.

Titanium (Ti) and its alloys have been widely used as clinical implant biomaterials. However, protein adhesion and bacterial infection can negatively impact the efficacy of these implants. To combat this, a promising strategy is to develop a versatile coating on Ti materials that endows them with antifouling and antibacterial capabilities. This work focused on the development of a polydopamine (PDA) and poly(sulfobetaine methacrylate) (PSBMA) co-deposition coating on Ti substrates. The coating contained copper ions, iron ions, and catechol groups, which coordinated to assemble bimetal-phenolic networks (bMPNs). Digital imaging, SEM, AFM, XPS, water contact angle, and film thickness tests confirmed the success of the modification. The antibacterial properties of the coating were evaluated using Gram-positive Staphylococcus aureus, while the cytotoxicity of the coating on human umbilical vein endothelial cells was also examined. The results demonstrated an excellent improvement in hydrophilicity, antibacterial properties, and benign biocompatibility of the coated Ti substrate, making it suitable for bioimplants and medical devices.

In this study, antibacterial activity and long-lasting release of silver for clinical applications were achieved by utilizing silver nanoparticles on the Titania nanotubes (TNTs) through in situ polymerization of polydopamine (PDA). TNTs were synthesized with the hydrothermal process from Titania nanoparticles. Then the surface modification of TNTs was accomplished by in situ polymerization of PDA and silver ions were reduced on the PDA surface. The feature of obtained samples was characterized using transmission electron microscope (TEM), field emission scanning electron microscope (FESEM), X-ray diffraction spectroscopy (XRD), Fourier-transform infrared spectroscopy (FTIR) and atomic absorption spectrophotometry (AAS). The results showed that PDA layer formed on the synthesized anatase TNTs surface. This used as reduction agent for silver ions as well as an adhesive layer to tethering the silver nanoparticles on TNTs surface. AAS results indicated that silver ions reduction to silver nanoparticles on the TNTs surface increased from 3.1 wt.% to 9.6 wt.% in presence of PDA. Also, the results of silver release revealed that PDA worked as an adhesive layer by chelating silver nanoparticles on TNTs and slowing silver ions release rate which implying the possible long-term antibacterial activity of PDA coated TNTs. Besides that, TNTs showed 33% antibacterial activity which is half than silver loaded TNTs-PDA samples. This confirms that PDA have extraordinary effect on the antibacterial activity. This work offers a facile process for the preparation of long-lasting silver based antibacterial activity and facilitates their clinical application in the modern biomedical fields.

In this study, we investigated the self-polymerization of dopamine in alkaline solution to form the composite of polydopamine (PDA)/Ag and Ag nanoparticles (NPs) array. We use the reduction properties of PDA to change silver ions into silver NPs. We also use the adhesion properties of PDA to provide a new method to attach Ag NPs or put Ag NPs array on substrates. These NPs and array are a powerful platform for further functionalization, such as the electro-optic application field.

Ti6Al4V alloy of titanium is a significant biomaterial due to its biocompatible nature, but it lacks required bioactivity to make it mimic properties to a human bone. Thus, hydroxyl-apatite (HAp), an inorganic compound found in human bones, is generally coated onto Ti6Al4V substrates to improve their bio-characteristics. But, HAp itself lacks certain bio-functionalities, such as allowing tissue bone regeneration and poor binding to the Ti6Al4V substrate, which results in osteoporosis and reduced bioactivity of the bio-implant, respectively. The proposed way out for this is the further doping of HAp with Strontium (Sr) for enabling tissue bone regeneration as well as addition of Polydopamine (PDA) for improved adhesion of HAp-based coatings with the substrate. Moreover, PDA results in increased drug delivery area and thus can be used as a material for enhancing resistance to bacterial growth. The present study demonstrates an experimental work on deposition of HAp, HAp with PDA and HAp with PDA and Sr coatings deposited onto Ti6Al4V alloy by means of biomimetic coating technique. Initially the pure HAp coatings were deposited using 10 SBF (simulated body fluid) solution and optimized in terms of time duration for desired coating uniformity. Then, for the optimized coating duration, the PDA pretreated Ti6Al4V substrates were coated, utilizing HAp, and Sr (at two different compositions) combinations were deposited through modified 10 SBF solutions. The characterization involving microstructural analysis and phase detection was performed for all these coatings using Scanned Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS) and X-Ray Diffraction (XRD) of the coated substrates and adhesion strength was calculated using a standard pull out adhesion test ISO 10779–4. The study showed an effective and comparatively cheap method of depositing organic coatings using biomimetic technique to obtain improved bio-functionalities in metallic implants at low temperatures.