Antifouling Biomimetic Liquid-Infused Stainless Steel: Application to Dairy Industrial Processing

Recent Developments in Slippery Liquid-Infused Porous Surface Coatings for Biomedical Applications

Slippery liquid-infused porous surface (SLIPS), inspired by the Nepenthes pitcher plant, exhibits excellent performances as it has a smooth surface and extremely low contact angle hysteresis. Biomimetic SLIPS attracts considerable attention from the researchers for different applications in self-cleaning, anti-icing, anticorrosion, antibacteria, antithrombotic, and other fields. Hence, SLIPS has shown promise for applications across both the biomedical and industrial fields. However, the manufacturing of SLIPS with strong bonding ability to different substrates and powerful liquid locking performance remains highly challenging. In this review, a comprehensive overview of research on SLIPS for medical applications is conducted, and the design parameters and common fabrication methods of such surfaces are summarized. The discussion extends to the mechanisms of interaction between microbes, cells, proteins, and the liquid layer, highlighting the typical antifouling applications of SLIPS. Furthermore, it identifies the potential of utilizing the controllable factors provided by SLIPS to develop innovative materials and devices aimed at enhancing human health.

Multielement simultaneous quantitative analysis of trace elements in stainless steel via full spectrum laser-induced breakdown spectroscopy

Laser-Induced Breakdown Spectroscopy (LIBS) instruments are increasingly recognized as valuable tools for detecting trace metal elements due to their simplicity, rapid detection, and ability to perform simultaneous multi-element analysis. Traditional LIBS modeling often relies on empirical or machine learning-based feature band selection to establish quantitative models. In this study, we introduce a novel approach-simultaneous multi-element quantitative analysis based on the entire spectrum, which enhances model establishment efficiency and leverages the advantages of LIBS. By logarithmically processing the spectra and quantifying the cognitive uncertainty of the model, we achieved remarkable predictive performance (R2) for trace elements Mn, Mo, Cr, and Cu (0.9876, 0.9879, 0.9891, and 0.9841, respectively) in stainless steel. Our multi-element model shares features and parameters during the learning process, effectively mitigating the impact of matrix effects and self-absorption. Additionally, we introduce a cognitive error term to quantify the cognitive uncertainty of the model. The results suggest that our approach has significant potential in the quantitative analysis of trace elements, providing a reliable data processing method for efficient and accurate multi-task analysis in LIBS. This methodology holds promising applications in the field of LIBS quantitative analysis.

Silicon-Based Superslippery/Superhydrophilic Striped Surface for Highly Efficient Fog Harvesting

Fog-harvesting performance is influenced by surface wettability, patterned structure and the heat transfer coefficient. In this work, we have prepared different surfaces with a stripe array of superhydrophilic, superslippery and superslippery/superhydrophilic surfaces for fog harvesting on silicon substrates using photolithography and silver-assisted chemical etching. The surface wettability and heat transfer coefficients of the above samples have been investigated. We analyzed the contact angle, sliding angle and transport state of droplets on these surfaces. The fog-harvesting rate of all samples under different voltages of the cooling pad (V = 0, 2.0, 2.5, 3.0, 3.5 V) was measured. Results showed that the superslippery/superhydrophilic striped surface could achieve rapid droplet nucleation, directional transport and efficient collection due to its superhydrophilic striated channels and the Laplace pressure difference between different wettability regions. At a condensation voltage of 3.5 V, the fog-harvesting rate efficiencies of the uniformly striped superhydrophilic and superslippery surface were 1351 mg·cm-2·h-1 and 1265 mg·cm-2·h-1, respectively, while the fog-harvesting rate of the superslippery/superhydrophilic striped surface was 1748 mg·cm-2·h-1. Compared with the original silicon surface, the maximum fog-harvesting rate of the superslippery/superhydrophilic striped surface was improved by 86.9%. This study offers significant insights into the impact of heat transfer and silicon surface wettability on the process of fog collection.

Nature-Inspired High Temperature Scale-Resistant Slippery Lubricant-Induced Porous Surfaces (HTS-SLIPS)

Scale formation is a longstanding and unresolved problem in a number of fields, including power production, petroleum exploration, thermal desalination, and construction. Herein, a high-temperature scale-resistant slippery lubricant-induced surface (HTS-SLIPS) is developed by one-step electrodeposition and lubricant infusion. The fractal cauliflower-like morphology with lubricant oil is conducive to forming an ultralow contact angle hysteresis of ≈1°. The 10-d real-world boiling trial indicates that by replacing the uncoated surface with HTS-SLIPS, the reduction in scale mass is greater than 200% because of the low surface free energy (4.3 mJ m^-2 ) and outstanding smoothness (R_a  = 41 ± 8 nm) of HTS-SLIPS. Thanks to the scale retardation, the bubble departure frequency of HTS-SLIPS is eightfold higher than that of uncoated surfaces, signifying superior heat transfer efficiency. In these demonstrations, HTS-SLIPS coated spiral tube exhibits better flowability and lower pressure drop than the uncoated one. In addition, favorable compatibility between HTS-SLIPS and mechanical vibration is experimentally verified to strengthen the descaling of SLIPS synergistically. It is anticipated that the simple and scalable coating fabrication approach will be applicable in numerous industrial high-temperature processes where scale formation is encountered.

Design of Metal-Based Slippery Liquid-Infused Porous Surfaces (SLIPSs) with Effective Liquid Repellency Achieved with a Femtosecond Laser

Slippery liquid-infused porous surfaces (SLIPSs) have become an effective method to provide materials with sliding performance and, thus, achieve liquid repellency, through the process of infusing lubricants into the microstructure of the surface. However, the construction of microstructures on high-strength metals is still a significant challenge. Herein, we used a femtosecond laser with a temporally shaped Bessel beam to process NiTi alloy, and created uniform porous structures with a microhole diameter of around 4 µm, in order to store and lock lubricant. In addition, as the lubricant is an important factor that can influence the sliding properties, five different lubricants were selected to prepare the SLIPSs, and were further compared in terms of their sliding behavior. The temperature cycle test and the hydraulic pressure test were implemented to characterize the durability of the samples, and different liquids were used to investigate the possible failure under complex fluid conditions. In general, the prepared SLIPSs exhibited superior liquid repellency. We believe that, in combination with a femtosecond laser, slippery liquid-infused porous surfaces are promising for applications in a wide range of areas.

Reversible Control between Sliding and Pinning on Femtosecond Laser-Treated Nickel Foam Slippery Surfaces

Bioinspired slippery surfaces with excellent abilities, such as antifouling, anticorrosion, and drag reduction, have gained increasing attention due to their multifunction in chemistry, biology, and medicine. However, the present thermally responsive methods used for in situ paraffin-infused slippery surfaces (PISS) are usually based on a surface heat source or certain specific photothermal materials, which seriously hinders their practical applications. Herein, we present a kind of in situ PISS processed by femtosecond laser on nickel (Ni) foam with reversible droplet behavior between sliding and pinning controlled by a point heat source. By alternately loading and unloading the point heat source, switchable wettability for liquid droplets can be achieved. The reaction time of this smart surface to the temperature change is 4.47 ± 1.14 s. The relationship between droplet volumes and inclined angles on four different surfaces is quantitatively investigated. Furthermore, the as-prepared PISS display an impressive self-healing ability. In addition, by flexibly changing the action path of the point heat source, the droplet can realize the movement of different curves. This functional surface and in situ control method will be a promising candidate for manipulating droplet directional sliding behavior and smart temperature-responsive surfaces.

Efficient Bubble Transport on Bioinspired Topological Ultraslippery Surfaces

Slippery liquid-infused porous surfaces (SLIPS) with micro-/nanostructures inspired by the Nepenthes pitcher plant exhibit excellent characteristics in terms of liquid repellency, self-healing, pressure tolerance, and so forth. In particular, stable bubble transport on SLIPS can be achieved when the surface is submerged in water. However, more precise and sophisticated bubble manipulations on SLIPS still remain challenging. In this research, a three-dimensional topological SLIPS combined with a submillimeter rice leaf-like groove array is fabricated to guide the underwater bubble motion precisely. The dynamic behavior and wetting state of bubbles on SLIPS were investigated experimentally. Furthermore, topological SLIPS with different geometric textures were designed and created for sophisticated bubble manipulations, such as fast bubble directional transport and collection. The results indicated that a lubricant with low surface tension and low viscosity could improve the adhesion force to bubbles and the transport velocity of bubbles, simultaneously. The current findings are helpful to deepen the cognition of interaction between bubbles and SLIPS and to promote their wide applications in the field of smart bubble manipulation and catalytic chemistry.

Recent Progress of Bioinspired Scalephobic Surfaces with Specific Barrier Layers

Bioinspired superwettable surfaces have been widely harnessed in diverse applications such as self-cleaning, oil/water separation, and liquid transport. So far, only a little work is focused on scalephobic capability of those superwettable surfaces. However, the troublesome scale deposition will inevitably be observed in our daily production and life, greatly reducing heat transfer efficiency and inhibiting the liquid transport. To address this annoying problem, as the emerging strategy, specific barrier layers are introduced onto superwettable surfaces to reduce or even avoid the direct contact between scale and the surfaces. In this feature article, we first provide the basic concept of bioinspired scalephobic surfaces with specific barrier layers. Then, we briefly introduce the typical fabrication methods of scalephobic surfaces. Later, we summarize recent progress of bioinspired scalephobic surfaces with specific barrier layers. Furthermore, we point out the guiding theory and criteria for the stability of barrier layers. Finally, we put forward the forecast on the existing problems and future direction in bioinspired scalephobic surfaces.

Innovative fouling-resistant materials for industrial heat exchangers: a review

Fouling of heat exchangers (HEs) has become a major concern across the industrial sector. Fouling is an omnipresent phenomenon but is particularly prevalent in the dairy, oil, and energy industries. Reduced energy performance that results from fouling represents significant operating loss in terms of both maintenance and impact on product quality and safety. In most industries, cleaning or replacing HEs are currently the only viable solutions for controlling fouling. This review examines the latest advances in the development of innovative materials and coatings for HEs that could mitigate the need for costly and frequent cleaning and potentially extend their operational life. To better understand the correlation between surface properties and fouling occurrence, we begin by providing an overview of the main mechanisms underlying fouling. We then present selected key strategies, which can differ considerably, for developing antifouling surfaces and conclude by discussing the current trends in the search for ideal materials for a range of applications. In our presentation of all these aspects, emphasis is given wherever possible to the potential transfer of these innovative surfaces from the laboratory to the three industries most concerned by HE fouling problems: food, petrochemicals, and energy production.

A critical review on surface modifications mitigating dairy fouling

Thermal treatments performed in food processing industries generate fouling. This fouling deposit impairs heat transfer mechanism by creating a thermal resistance, thus leading to regular shutdown of the processes. Therefore, periodic and harsh cleaning-in-place (CIP) procedures are implemented. This CIP involves the use of chemicals and high amounts of water, thus increasing environmental burden. It has been estimated that 80% of production costs are owed to dairy fouling deposit. Since the 1970s, different types of surface modifications have been performed either to prevent fouling deposition (anti-fouling) or to facilitate removal (fouling-release). This review points out the impacts of surface modification on type A dairy fouling and on cleaning behaviors under batch and continuous flow conditions. Both types of anti-fouling and fouling-release coatings are reported as well as the different techniques used to modify stainless steel surface. Finally, methods for testing and characterising the effectiveness of coatings in mitigating dairy fouling are discussed.

Underwater Superoleophobic Matrix-Formatted Liquid-Infused Porous Biomembranes for Extremely Efficient Deconstitution of Nanoemulsions

Wettability is one of the most critical interfacial properties of any surface. Surfaces with special wettability such as superwetting or superantiwetting are being intensively explored for their wide-ranging applicability by a biomimetic exploration of unusual wetting phenomena in nature. This study provides a green water-infused superoleophobic composite membrane by boosting bacteria nanocellulose growth on a reinforcement fibrous substrate. It was shown that this versatile antifouling membrane is capable of removing water from surfactant-stabilized oil-in-water micro/nanoemulsions and helps to isolate the oil fraction with very high filtration efficiency. The renewable membrane based on bacteria nanocellulose matrices can vastly improve current technologies by cultivating a naturally occurring soft materials approach with lubricious conformal interfaces to effectively and simply cover suitable surfaces.

Lubricant-infused directly engraved nano-microstructures for mechanically durable endoscope lens with anti-biofouling and anti-fogging properties

While a clear operating field during endoscopy is essential for accurate diagnosis and effective surgery, fogging or biofouling of the lens can cause loss of visibility during these procedures. Conventional cleaning methods such as the use of an irrigation unit, anti-fogging surfactant, or particle-based porous coatings infused with lubricants have been used but proven insufficient to prevent loss of visibility. Herein, a mechanically robust anti-fogging and anti-biofouling endoscope lens was developed by forming a lubricant-infused directly engraved nano-/micro-structured surface (LIDENS) on the lens. This structure was directly engraved onto the lens via line-by-line ablation with a femtosecond laser. This directly engraved nano/microstructure provides LIDENS lenses with superior mechanical robustness compared to lenses with conventional particle-based coatings, enabling the maintenance of clear visibility throughout typical procedures. The LIDENS lens was chemically modified with a fluorinated self-assembled monolayer (F-SAM) followed by infusion of medical-grade perfluorocarbon lubricants. This provides the lens with high transparency (> 70%) along with superior and long-lasting repellency towards various liquids. This excellent liquid repellency was also shown to be maintained during blood dipping, spraying, and droplet condensation experiments. We believe that endoscopic lenses with the LIDENS offer excellent benefits to endoscopic surgery by securing clear visibility for stable operation.

Design novel three-dimensional network nanostructure for lubricant infused on titanium alloys towards long-term anti-fouling

Titanium alloys, recognized as a marine material with great potential, are currently facing serious biofouling problems, which greatly limits its application range. To improve the antifouling performance of titanium alloys, three unique surface of three-dimensional network, grass-like and linear nanostructures were obtained on titanium alloys via hydrothermal treatment in this work. Further, slippery liquid-infused porous surfaces (SLIPSs) were fabricated on titanium alloys via infusing PFPE lubricant into these nanostructures. Water contact angles and sliding angles of SLIPSs were measured to evaluate the effect of nanostructures on the stability of PFPE lubricant layer. Anti-fouling capability of SLIPSs were investigated by quantifying the cells of chlorella and phaeodactylum tricornutum (P. tricornutum)adhered to titanium alloys. The results shows that all the SLIPSs exhibited remarkable inhibition capacity for the settlement of chlorella and P. tricornutum. Among them, the SLIPS with three-dimensional network nanostructure displayed the longest-term anti-fouling performance, and its reduction rate of P. tricornutum and chlorella reaching 77.2 % and 84.5 % after being cultivated for 21 days, respectively, indicating that there existed a positive correlation between the stability of lubricant layer in the artificial seawater and the antifouling effect.

Single and multi-functional coating strategies for enhancing the biocompatibility and tissue integration of blood-contacting medical implants

Device-associated clot formation and poor tissue integration are ongoing problems with permanent and temporary implantable medical devices. These complications lead to increased rates of mortality and morbidity and impose a burden on healthcare systems. In this review, we outline the current approaches for developing single and multi-functional surface coating techniques that aim to circumvent the limitations associated with existing blood-contacting medical devices. We focus on surface coatings that possess dual hemocompatibility and biofunctionality features and discuss their advantages and shortcomings to providing a biocompatible and biodynamic interface between the medical implant and blood. Lastly, we outline the newly developed surface modification techniques that use lubricant-infused coatings and discuss their unique potential and limitations in mitigating medical device-associated complications.

WO3-Based Slippery Liquid-Infused Porous Surfaces with Long-Term Stability

Slippery liquid-infused porous surfaces (SLIPS) inspired by Nepenthes pitcher plants exhibit excellent hydrophobicity, antifouling and anti-icing properties, and long-term durability under pressure and temperature. SLIPS have potential applications including in biomedical devices, self-cleaning structures, and water-resistant coatings. A big challenge posed by SLIPS is the durability of the lubricant in the porous layer. Herein, uniform tungsten oxide nanofiber networks were synthesized on the surface of stainless steel through a simple one-step hydrothermal method. WO₃ nanofiber networks on stainless steels were chemically modified, filled with a lubricant, and prepared as SLIPS with excellent liquid repellency and good anti-biofouling properties. The relationship of the nanostructures and the slippery properties of the obtained WO₃-based SLIPS have been investigated in detail in this work. The liquid retention and long-term stability of the SLIPS were characterized using high shear force and water flow impact. We found that the long-term durability of the SLIPS is strongly related to the diameters and the Brunauer-Emmett-Teller surface areas of the WO₃ nanostructures. The durability of the SLIPS is better when the diameter of the WO₃ nanostructures is smaller. The WO₃-based SLIPS prepared in this work exhibit outstanding slippery property, anti-biofouling, and long-term stability under extreme conditions such as high shear rate and water washing and thus may have potential application for surface modification of medical devices in the future.

Life and death of liquid-infused surfaces: a review on the choice, analysis and fate of the infused liquid layer

We review the rational choice, the analysis, the depletion and the properties imparted by the liquid layer in liquid-infused surfaces – a new class of low-adhesion surface.

Liquid-Infused Surfaces: A Review of Theory, Design, and Applications

Due to inspiration from the Nepenthes pitcher plant, a frontier of devices has emerged with unmatched capabilities. Liquid-infused surfaces (LISs), particularly known for their liquid-repelling behavior under low tilting angles (<5°), have demonstrated a plethora of applications in medical, marine, energy, industrial, and environmental materials. This review presents recent developments of LIS technology and its prospective to define the future direction of this technology in solving tomorrow's real-life challenges. First, an introduction to the different models explaining the physical phenomena of these surfaces, their wettability, and viscous-dependent frictional forces is discussed. Then, an outline of different emerging strategies required to fabricate a stable liquid-infused interface is presented, including different substrates, lubricants, surface chemistries, and design parameters which can be tuned depending on the application. Furthermore, applications of LIS coatings in the areas of anticorrosion, antifouling, anti-icing, self-healing, droplet manipulation, and biomedical devices will be presented followed by the limitations and future direction of this technology.

Nature-Inspired Liquid Infused Systems for Superwettable Surface Energies

The development of an innovative interfacial wetting strategy known as liquid infused systems offers great promise for the advanced design of superwetting and superantiwetting substrates to overcome the drawbacks of textured surfaces classified under the heading of Cassie/Wenzel states. The potential value of nature-inspired surfaces has significant potential to address scientific and technological challenges within the field of interfacial chemistry. The objective of the current review is to provide insights into a fruitful and young field of research, highlight its historical developments, examine its nature-inspired design principles, gauge recent progress in emerging applications, and offer a fresh perspective for future research.

Antibacterial durability and biocompatibility of antibacterial-passivated 316L stainless steel in simulated physiological environment

Stainless steel (SS) has been widely applied as one of the most efficient implant metal materials, although corrosion and infection in body environment are still challenging. Herein, an antibacterial passivation method was employed to enhance the antibacterial performance and corrosion resistance of the medical 316L SS. The result proved that the antibacterial-passivated 316L SS exhibited stable antibacterial activity and effectively inhibited the formation of bacterial biofilm. Electrochemical measurements combined with X-ray photoelectron spectroscopy technique were used to study the corrosion resistance and semiconductor behavior of passivated 316L SS immersed in simulated physiological environment. The results indicated that the 316L SS after antibacterial passivation treatment for 1 h, soaking in the medium for 10 days, showed satisfactory corrosion resistance attributing to proper Cu deposition in the passive film. The anodic stripping voltammetry measurement further confirmed that the Cu-bearing passive film could continuously release Cu ions into medium. The zebrafish test demonstrated an excellent in vivo biocompatibility for the 316L SS with antibacterial passivation for 0.5 and 1 h, respectively. In addition, changes of surface roughness, contact angle and chemical composition after antibacterial passivation played an important role in explaining the antibacterial mechanism, which could be clearly divided into contact killing and ionic release killing. Hence, the antibacterial passivation treatment was preliminarily proved as a potential way for enhancing the persistent antibacterial activity and corrosion resistance of 316L SS.

Designing Liquid-Infused Surfaces for Medical Applications: A Review

The development of new technologies is key to the continued improvement of medicine, relying on comprehensive materials design strategies that can integrate advanced therapeutic and diagnostic functions with a variety of surface properties such as selective adhesion, dynamic responsiveness, and optical/mechanical tunability. Liquid-infused surfaces have recently come to the forefront as a unique approach to surface coatings that can resist adhesion of a wide range of contaminants on medical devices. Furthermore, these surfaces are proving highly versatile in enabling the integration of established medical surface treatments alongside the antifouling capabilities, such as drug release or biomolecule organization. Here, the range of research being conducted on liquid-infused surfaces for medical applications is presented, from an understanding of the basics behind the interactions of physiological fluids, microbes, and mammalian cells with liquid layers to current applications of these materials in point-of-care diagnostics, medical tubing, instruments, implants, and tissue engineering. Throughout this exploration, the design parameters of liquid-infused surfaces and how they can be adapted and tuned to particular applications are discussed, while identifying how the range of controllable factors offered by liquid-infused surfaces can be used to enable completely new and dynamic approaches to materials and devices for human health.

Biomimetic Liquid-Repellent Surfaces by Ultrafast Laser Processing

This review is focused on the realization of liquid-repellent surfaces, inspired by two biological models: “dry” superhydrophobic leaves and “slippery” liquid-repellent carnivorous plants using ultrafast laser processing. After a short introduction to a biomimetic development process, an overview of the laser-fabricated structures, which were intensively used for the realization of biomimetic “dry” and “slippery” liquid-repellent surfaces, is given. The influence of process parameters on the structure morphology is discussed. A summary of superhydrophobic and liquid-repellent modifications of different materials (metals, semiconductors, and polymers), including wettability characteristics and processing details, is provided. The technological applications of laser-structured liquid-repellent surfaces are discussed.

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.

Food-Safe Modification of Stainless Steel Food-Processing Surfaces to Reduce Bacterial Biofilms

Biofilm formation on stainless steel (SS) surfaces of food-processing plants, leading to food-borne illness outbreaks, is enabled by the attachment and confinement of pathogens within microscale cavities of surface roughness (grooves, scratches). We report foodsafe oil-based slippery coatings (FOSCs) for food-processing surfaces that suppress bacterial adherence and biofilm formation by trapping residual oil lubricant within these surface cavities to block microbial growth. SS surfaces were chemically functionalized with alkylphosphonic acid to preferentially wet a layer of food-grade oil. FOSCs reduced the effective surface roughness, the adhesion of organic food residue, and bacteria. FOSCs significantly reduced Pseudomonas aeruginosa biofilm formation on standard roughness SS-316 by 5 log CFU cm^-2, and by 3 log CFU cm^-2 for mirror-finished SS. FOSCs also enhanced surface cleanability, which we measured by bacterial counts after conventional detergent cleaning. Importantly, both SS grades maintained their antibiofilm activity after the erosion of the oil layer by surface wear with glass beads, which suggests that there is a residual volume of oil that remains to block surface cavity defects. These results indicate the potential of such low-cost, scalable approaches to enhance the cleanability of SS food-processing surfaces and improve food safety by reducing biofilm growth.