Search Results (300)

This study investigates the tribological performance and wear mechanisms of graphite and polydopamine/graphite (PDA/graphite) coatings on stainless steel under dry sliding conditions. While graphite is widely used as a solid lubricant, its poor adhesion to metal substrates limits long-term durability. Incorporating an adhesion-promoting PDA underlayer significantly improved coating lifetime and wear resistance. Tribological testing revealed that PDA/graphite coatings maintained a coefficient of friction (COF) below 0.15 for over seven times longer than graphite-only coatings. High-resolution scanning electron microscopy, SEM, and profilometry showed that PDA improved coating adhesion and suppressed lateral debris transport, confining wear to a narrow zone. Surface and counterface analyses confirmed enhanced graphite retention and formation of cohesive transfer films. Raman spectroscopy indicated only modest changes in the D and G bands. X-ray Photoelectron Spectroscopy, XPS analysis, confirmed that coating failure correlated with the detection of Fe and Cr peaks and oxide formation. Together, these results demonstrate that PDA enhances interfacial adhesion and structural stability without compromising lubrication performance, offering a strategy to extend the durability of carbon-based solid lubricant systems for high-contact-pressure applications. Full article

Melanin-related materials efficiently emulate the adhesion properties of natural mussel filaments and have been used advantageously for surface modification and for fabrication of electrochemical sensors for detection of environmentally relevant targets. The most applicable advantages of melanin-based coatings are their biocompatibility and versatility, and they can be easily prepared and modified according to simple and highly environmentally friendly procedures. For these reasons, melanin-related materials, in particular polydopamine, which can be obtained simply via oxidative polymerization of dopamine in an aqueous solution in the presence of atmospheric oxygen, have been applied in a large variety of scientific and technological fields. Here, we summarize and critically discuss the most recent and important applications of melanin-related materials in the development of electrochemical sensors for monitoring the environment and food. In particular, the examples used in this paper include toxic metal ions, drugs, and pesticides. In the final section of this paper, the actual limitations of the existing approach are discussed and possible future design improvements are suggested. Full article

Biocatalytic nanomembranes have emerged as promising platforms for micropollutant remediation, yet their practical application is hindered by limitations in removal efficiency and operational stability. This study presents an innovative approach for fabricating highly stable and efficient biocatalytic nanomembranes through the co-immobilization of horseradish peroxidase (HRP) and glucose oxidase (GOx) within a covalent organic framework (COF) nanocrystal. Capitalizing on the dynamic covalent chemistry of COFs during their self-healing and self-crystallization processes, we achieved simultaneous enzyme immobilization and framework formation. This unique confinement strategy preserved enzymatic activity while significantly enhancing stability. HRP/GOx@COF biocatalytic membrane was prepared through the loading of immobilized enzymes (HRP/GOx@COF) onto a macroporous polymeric substrate membrane pre-coated with a polydopamine (PDA) adhesive layer. At HRP and GOx dosages of 4 mg and 4.5 mg, respectively, and a glucose concentration of 5 mM, the removal rate of bisphenol A (BPA) reached 99% through the combined functions of catalysis, adsorption, and rejection. The BPA removal rate of the biocatalytic membrane remained high under both acidic and alkaline conditions. Additionally, the removal rate of dyes with different properties exceeded 88%. The removal efficiencies of doxycycline hydrochloride, 2,4-dichlorophenol, and 8-hydroxyquinoline surpassed 95%. In this study, the enzyme was confined in the ordered and stable COF, which endowed the biocatalytic membrane with good stability and reusability over multiple batch cycles. Full article

The enhanced mechanical durability of sprayed nanocellulose coatings at the macroscopic level is primarily required to promote their application in demanding industrial applications with frequently exposed surfaces. In this study, different coating configurations are designed by spraying aqueous cellulose nanofiber (CNF) suspensions in combination with boric acid (BA) as an internal crosslinker and polydopamine (PDA) as an adhesive interlayer onto glass substrates. Multilayer coatings (CNF/BA) or mixed-layer coatings (CNF + BA) with various concentrations of BA and numbers of sprayed layers are evaluated for maximized mechanical performance based on tape tests, rub tests, cross-cut tests, and scratching tests. Good adhesive strength was realized with an interlayer of PDA/BA (high-concentration BA = 10 mM). The highest cohesive strength was observed for a mixed CNF + BA coating (high-concentration BA = 10 mM) with a scratch resistance of 9 N, and a multilayer CNF/BA coating (gradient layers with ultra-high BA concentration = 100 mM) with a scratch resistance of 8 N. The coatings with the highest density did not uniquely introduce the best mechanical resistance when comparing CNF/BA and CNF + BA coatings, as the formation of BA crystals in multilayer coatings might negatively affect the mechanical properties through embrittlement. Alternatively, the mixed CNF + BA coatings with high BA concentrations provide high density and the best mechanical resistance. The favorable crosslinking corresponds to stabilized water contact angles and reduced spreading of the water as a function of time, while a decrease in coating density causes a reduction in transparency. The chemical interactions between CNF and BA are illustrated by infrared spectroscopy, confirming a reduction in free hydroxyl groups upon crosslinking. Full article

Copper contamination in the environment poses significant risks to both soil and human health, making the need for reliable monitoring methods crucial. In this study, we report the use of the EmStat Pico module as potentiostat to develop a portable electrochemical biosensor for copper detection, utilizing yeast Saccharomyces cerevisiae cells immobilized on a polydopamine (PDA)-coated screen-printed electrode (SPE). By optimizing the sensor design with a horizontal assembly and the volume reduction in the electrolyte solution, we achieved a 10-fold increase in current density with higher range of copper concentrations (0–300 µM CuSO₄) compared to traditional (or previous) vertical dipping setups. Additionally, the use of genetically engineered copper-responsive yeast cells further improved sensor performance, with the recombinant strain showing a 1.7-fold increase in current density over the wild-type strain. The biosensor demonstrated excellent reproducibility (R² > 0.95) and linearity over a broad range of copper concentrations, making it suitable for precise quantitative analysis. To further enhance portability and usability, a Bluetooth-enabled electrochemical platform was integrated with a web application for real-time data analysis, enabling on-site monitoring and providing a reliable, cost-effective tool for copper detection in real world settings. This system offers a promising solution for addressing the growing need for efficient environmental monitoring, especially in agriculture. Full article

We present a straightforward emulsion-induced interfacial anisotropic assembly method for in- situ synthesis of bowl-shaped, self-encapsulated mesoporous polydopamine (BMPDA) nanocontainers (M-M@P) loaded with 2-mercaptobenzimidazole (2-MBI). Results showed that the loading capacity of the bowl-shaped mesoporous polydopamine reaches 24 wt.%. The M-M@P exhibits a cumulative MBI release of 91.61% after immersion in a 3.5 wt.% NaCl solution at pH = 2 for 24 h, accompanied by a corrosion inhibition efficiency of 95.54%. Additionally, the acid-responsive M-M@P not only enables controlled release of MBI but also synergistically promotes the formation of a protective film on the carbon steel substrate via the chelation of PDA-Fe³⁺, thereby enhancing the self-healing performance of waterborne epoxy coatings. Full article

Pancreatic calculi, a common complication of chronic pancreatitis, significantly contribute to ductal obstruction, increased intraductal pressure, and debilitating abdominal pain. Although endoscopic pancreatic duct stenting alleviates ductal stenosis, conventional stents lack litholytic functionality, limiting their therapeutic efficacy. To address this challenge, we developed a drug-eluting pancreatic duct stent coated with a carboxymethyl chitosan methacrylate (CMCSMA)-based hydrogel utilizing 50% w/v citric acid (CA) as a litholytic agent. Polydopamine (PDA) interlayer was employed to enhance interfacial adhesion between the hydrogel and the stent surface. The CMCSMA hydrogel exhibited favorable physicochemical properties, including rapid gelation, excellent compressive strength (229.2 ± 14.8 kPa), hemocompatibility, and cytocompatibility. In vitro release studies revealed sustained CA release, achieving 66.3% cumulative release within 72 h. The hydrogel-coated stent demonstrated superior litholytic activity, dissolving over 90% of pancreatic calculi within 24 h. These results underscore the potential of CMCSMA-CA hydrogel-coated stents as a biocompatible and effective local drug delivery platform for targeted pancreatic duct litholysis. Full article

This study provides a comparison between magnetic-to-thermal energy conversion efficiency in liquid and gel phases under high-frequency magnetic fields. Magnetite cores (11 ± 2 nm) were tested as water-based ferrofluids and as 5 wt% agar ferrogels, both with and without a biocompatible polydopamine (PDA) shell. A custom two-phase coil switched between rotating (RMF) and alternating (AMF) modes, enabling phase- and coating-dependent effects to be measured at identical field strengths and frequencies (100–300 kHz, 1–4 kA/m). Across all conditions, RMF generated 1.7–2.1 times more specific loss power (SLP) than AMF, and moving from the liquid to the gel phase reduced SLP by 5–8%, indicating that heating is controlled by Néel relaxation with negligible Brownian contribution. SLP rose with magnetic-field amplitude according to a power law, while hysteretic losses remained minimal. PDA improved colloidal stability and biocompatibility without harming the heating performance, lowering SLP by <17%. Within Brezovich limits, the system still exceeded therapeutic hyperthermia thresholds. Thus, in this iron-oxide/PDA system, neither medium viscosity nor the PDA shell’s non-magnetic mass significantly affects thermal energy output, an important finding for translating laboratory calorimetry data into reliable, application-oriented modelling for magnetic hyperthermia. Full article

Electroless nickel deposition (ELD) is an autocatalytic technique extensively used to impart conductive, protective, and mechanical functionalities to inherently non-conductive synthetic substrates. This review systematically explores the fundamental mechanisms of electroless nickel deposition, emphasising recent advancements in surface activation methods, solvent systems, and microstructural control. Critical analysis reveals that bio-inspired activation methods, such as polydopamine (PDA) and tannic acid (TA), significantly enhance coating adhesion and durability compared to traditional chemical etching and plasma treatments. Additionally, solvent engineering, particularly using polar aprotic solvents like dimethyl sulfoxide (DMSO) and ethanol-based systems, emerges as a key strategy for achieving uniform, dense, and flexible coatings, overcoming limitations associated with traditional aqueous baths. The review also highlights that microstructural tailoring, specifically the development of amorphous-nanocrystalline hybrid nickel coatings, effectively balances mechanical robustness (hardness exceeding 800 HV), flexibility, and corrosion resistance, making these coatings particularly suitable for wearable electronic textiles and smart materials. Furthermore, commercial examples demonstrate the real-world applicability and market readiness of nickel-coated synthetic fibres. Despite significant progress, persistent challenges remain, including reliable long-term adhesion, internal stress management, and environmental sustainability. Future research should prioritise environmentally benign plating baths, standardised surface activation protocols, and scalable deposition processes to fully realise the industrial potential of electroless nickel coatings. Full article

This study presents the development and comprehensive evaluation of magnesium-based implants with surface modifications using selected polymers and bioactive compounds. The implants were fabricated via plasma electrolytic oxidation (PEO), followed by the application of chitosan, polydopamine (PDA), and gold nanoparticles as bioactive surface coatings. In vitro experiments, including FT-IR spectroscopy, scanning electron microscopy (SEM), wettability tests, biodegradation assays in simulated body fluid (SBF), electrochemical corrosion analysis, and cytotoxicity tests using MG-63 osteoblast-like cells, were employed to assess the physicochemical and biological properties of the materials. The PEO + PDA-modified samples demonstrated the highest corrosion resistance (−1.15 V corrosion potential), enhanced cell viability (~95%), and favorable surface wettability (contact angle ~12.5°), outperforming other tested configurations. These findings suggest that PEO combined with PDA offers a synergistic effect, leading to superior biocompatibility and degradation control compared to unmodified magnesium or single-coating strategies. The developed implants hold promise for orthopedic applications requiring biodegradable, bioactive, and cytocompatible materials. Full article

Magnesium alloy stents exhibit significant potential in the treatment of cardiovascular and cerebrovascular diseases due to their remarkable mechanical support and biodegradability. However, bare magnesium alloy stents often degrade too quickly and exhibit inadequate biocompatibility, which severely restricts their clinical applicability. Herein, a composite coating consisting of an MgF₂ conversion layer, a polydopamine (PDA) layer, fucoidan, and hyaluronic acid was prepared to enhance the corrosion resistance and biocompatibility of ZE21B alloy for a vascular stent application. The modified ZE21B alloy exhibited relatively high surface roughness, moderate wettability, and better corrosion resistance. Moreover, the modified ZE21B alloy with a low hemolysis rate and fibrinogen adsorption level confirmed improved hemocompatibility for medical requirements. Furthermore, the ZE21B alloy modified with fucoidan and hyaluronic acid enhanced the adhesion, proliferation, and NO release of endothelial cells (ECs). Simultaneously, it inhibits the adhesion and proliferation of smooth muscle cells (SMCs), promoting a competitive advantage for ECs over SMCs due to the synergistic effects of fucoidan and hyaluronic acid. The incorporation of fucoidan and hyaluronic acid markedly improved the corrosion resistance and biocompatibility of the ZE21B magnesium alloy. This development presents a straightforward and effective strategy for the advancement of biodegradable vascular stents. Full article

Utilizing renewable energy for green hydrogen production via electrolyzed seawater is a promising technology for the future. However, undesired chlorine evolution and the corrosive nature of seawater are crucial challenges for direct seawater splitting technology. In this work, heterojunctions of CoS₂/FeS₂ encapsulated in N-doped carbon nanocubes (denoted as CoS₂/FeS₂@NC) were designed by proposing the synchronous pyrolysis and vulcanization of polydopamine-coated coordination polymers. Such a synthetic strategy was demonstrated to be effective in increasing the favorable exposure of active sites, moderately regulating electronic structure, and remarkably facilitating charge transfer due to the controllable generation of unique core–shell structures with suitable carbon shells, leading to the excellent bifunctional electrocatalytic performance and enhanced stability of electrocatalysts. As a result, CoS₂/FeS₂@NC can be revealed as a superior water splitting catalyst, possessing a small voltage of 1.75 V and requiring 100.0 mA cm⁻² in 1 M KOH alkaline solution and 1.80 V for alkaline seawater media, with satisfactory long-term stability. This work presents fresh strategies for designing core–shell heterostructures and developing green technology for hydrogen production. Full article

This review delves into environmentally conscious sustainable packaging materials, focusing on biodegradable polymers and innovative surface modification methodologies. Synthetic plastics have revolutionized various industries due to their physical attributes and affordability, particularly in packaging applications. Nonetheless, the substantial volume of plastic waste, especially from non-biodegradable sources, has provoked heightened environmental apprehensions. Notably, polymers derived from natural sources, such as cellulose, are classified as biopolymers and esteemed for their ecological benevolence. Among these, cellulose and its derivatives stand out as renewable and abundant substances, holding promise for sustainable packaging solutions. Nano-sized cellulose fibers’ incorporation into biodegradable films garners interest due to their remarkable surface area, robust mechanical strength, and other commendable properties. Surface modification techniques, such as a polydopamine (PDA) coating, have been explored to improve the dispersion, interfacial compatibility, and mechanical performance of cellulose nanocrystals (CNC) when incorporated into biodegradable polymer films. In this sense, PDA, derived from mussel proteins’ dopamine component, displays exceptional adhesion to diverse surfaces and has been extensively scrutinized for its distinctive attributes. Therefore, the core focus of this review was to approach ecologically friendly packaging materials, specifically investigating the synergy between CNC and PDA. The unparalleled adhesive characteristics of PDA serve as a catalyst for enhancing CNC, thereby elevating the performance of biodegradable polymers with potential implications across various domains. Full article

A critical barrier to the clinical translation of biodegradable magnesium (Mg)-based materials lies in their rapid degradation rate in physiological environment, which leads to premature structural failure and compromised cytocompatibility. Micro-arc oxidation (MAO) coatings offer preliminary corrosion mitigation for Mg alloys, while their inherent structural porosity compromises long-term durability in physiological environment. To address this limitation, we developed a hierarchical coating system consisting of a dense Mg(OH)₂ interlayer (MAO/HT) superimposed on the MAO-treated substrate, followed by a functional polydopamine (PDA) topcoat to create a MAO/HT/PDA composite architecture. The surface characteristics and crystalline structures of these coatings were systematically characterized using field-emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD). The corrosion resistance and interfacsial stability in physiological environment were quantitatively assessed through electrochemical analyses and long-term immersion tests in simulated body fluid (SBF). The cytocompatibility of the coatings was assessed by directly culturing osteoblast on the coated samples. The results reveal that the Mg(OH)₂ film possesses a bulk-like structure and effectively seals the micro-pores of the MAO coating. The current density of MAO/HT/PDA sample decreases by two orders of magnitude compared to that of MAO sample, indicating excellent corrosion resistance. The PDA layer not only acts as a strong barrier to improve the corrosion performance of the coating but also helps maintain the stability of the coating, thus delaying coating destruction in SBF. Moreover, the osteoblast culture results suggest that the MAO/HT/PDA coating promotes cell spread and proliferation noticeably compared to both the MAO and MAO/HT coatings. This study provides compelling evidence that the Mg(OH)₂/PDA composite coating is biodegradable and offers outstanding protection for micro-arc oxidized magnesium. As a result, it holds great promise for significant applications in the field of orthopedic medicine. Full article

Global growth in antimicrobial resistance (AMR) has accelerated the need for novel therapy beyond the scope of conventional antibiotics. In the last decade, polydopamine (PDA), a mussel-inspired polymer with redox capability, remarkable adhesion, and biocompatibility, has emerged as a universal antimicrobial coating with widespread uses. At the same time, extracellular vesicles (EVs) and particularly exosomes have gained prominence for their intrinsic cargo delivery and immune-modulating properties. Here, we summarize the synergistic value of PDA and exosome integration into multifunctional antimicrobial nanoplatforms. We discuss the inherent antimicrobial activity of PDA and exosomes; the advantages of PDA coating, including increased exosome stability, ROS generation, and surface functionalization; and current methodologies towards designing PDA-exosome hybrids. This review also mentions other antimicrobial polymers and nanocomposites that may be employed for exosome modification, such as quaternized chitosan, zwitterionic polymers, and polymer–metal composites. Most significant challenges, such as the maintenance of exosome integrity, coating uniformity, biocompatibility, scalability, and immunogenicity, are addressed. Finally, future research directions are highlighted, with emphasis on intelligent, stimulus-responsive coatings, AMP incorporation, and clinical translation. Collectively, this review underscores the promise of PDA-coated exosomes as potential antimicrobial therapeutics against AMR with potential applications in wound healing, implant protection, and targeted infection control. Full article