Biomimetic self-cleaning surfaces: synthesis, mechanism and applications

Biomass-activated carbon-based superhydrophobic sponge with photothermal properties for adsorptive separation of waste oil

The increasing discharge of oily wastewater from life poses a serious threat to the ecological environment and human health. To develop green, efficient, and low-cost materials for oil-water separation, a superhydrophobic photothermal oil-absorbing sponge (CAC-PDA@MF) was prepared by using nanoscale coconut shell activated carbon (CAC) loaded on a melamine sponge in this study. The sponge had excellent superhydrophobicity (WCA of 159.53°) due to the reduction of surface energy by grafting long-chain silanes. The adsorption capacity of the sponge was 69.04 g/g-158.27 g/g for a wide range of oils and organic solvents, and the sponge had excellent mechanical properties for multiple adsorption and recovery of oil. After 50 cycles of oil-water separation, its separation efficiency was maintained at over 98 %. In addition, the material had high acid, alkali, and salt resistance as well as excellent photothermal conversion properties. Its surface temperature rose rapidly to 100 °C and above, at a light intensity of 1.0 kW/m2. The material was capable of adsorbing and recovering high-viscosity oils that were solid or semi-solid at room temperature. Its versatility and commercial value made it a promising candidate for a wide range of applications.

Energy Dissipation during Wenzel Wetting via Roughness Scale Interface Dynamics

A numerical method is proposed to simulate the roughness scale interface dynamics of a slow-moving fluid interface as it advances over a chemically homogeneous rough surface. Analysis of the governing augmented Navier-Stokes and Young's boundary condition equations shows how the local interface behavior can be represented via a series of incrementally advanced equilibrium interfacial morphologies. Combined with a roughness scale mechanical energy balance [Harvie, D. J. E. Contact-angle hysteresis on rough surfaces: mechanical energy balance framework. J. Fluid Mech. 2024, 986, A17], the simulations are used to calculate the energy dissipation associated with a surface decorated with a periodic array of round-edge square pillars. This dissipation is used to predict static contact angle hysteresis (CAH) from knowledge of just the surface roughness topography and equilibrium contact angle. We show that the energy dissipated varies approximately as ϕln ϕ (with ϕ being the area fraction), becoming zero as ϕ → 0. The CAH predicted by our method is in good agreement with the experimental results of Forsberg et al. [Forsberg, P. S.; Priest, C.; Brinkmann, M.; Sedev, R.; Ralston, J. Contact line pinning on microstructured surfaces for liquids in the Wenzel state. Langmuir 2010, 26, 860-865], thereby demonstrating that our numerical method of simulating interfacial dynamics adequately captures the real interface motion, as well as illustrating how far-field contact angle and energy dissipation approaches are consistent for this surface. We also compute CAH for an interface moving at 45° to the surface periodicity direction to show that the experimental measurements are bracketed by the 0° and 45° advance direction results. The proposed method opens up the field to quantitative analysis, surface functionalization, and design for different specific applications.

Energy dissipation during homogeneous wetting of surfaces with randomly and periodically distributed cylindrical pillars

HYPOTHESIS

Understanding contact angle hysteresis on rough surfaces is important as most industrially relevant and naturally occurring surfaces possess some form of random or structured roughness. We hypothesise that hysteresis can be described by the dilute defect model of Joanny & de Gennes [1] and that the energy dissipation occurring during the stick-slip motion of the contact line is key to developing a predictive equation for hysteresis.

EXPERIMENTS

We measured hysteresis on surfaces with randomly distributed and periodically arranged microscopic cylindrical pillars for a variety of different liquids in air. The inherent (flat surface) contact angles tested range from lyophilic (θe=33.8°) to lyophobic (θe=112.0°).

FINDINGS

A methodology for averaging the measured advancing and receding contact angles on random surfaces is presented. Based on these results correlations for roughness-induced energy dissipation are derived, and an equation for predicting the advancing and receding contact angles during homogeneous (Wenzel) wetting on random surfaces is presented. Equations that predict the onset of the alternate wetting conditions of hemiwicking, split-advancing, split-receding and heterogeneous (Cassie) wetting are also derived, thus defining the range of validity for the homogeneous wetting equation. A 'cluster' concept is proposed to explain the measurably higher hysteresis exhibited by structured surfaces compared to random surfaces.

Chitosan-Based Structural Color Films for Humidity Sensing with Antiviral Effect

This scientific investigation emphasizes the essential integration of nature's influence in crafting multifunctional surfaces with bio-inspired designs for enhanced functionality and environmental advantages. The study introduces an innovative approach, merging color decoration, humidity sensing, and antiviral properties into a unified surface using chitosan, an organo-biological polymer, to create cost-effective multilayered films through sol-gel deposition and UV photoinduced deposition of metal nanoparticles. The resulting chitosan films showcase diverse structural colors and demonstrate significant antiviral efficiency, with a 50% and 85% virus inhibition rate within a rapid 20 min reaction, validated through fluorescence cell expression and real-time qPCR (polymerase chain reaction) assays. Silver-deposited chitosan films further enhance antiviral activity, achieving remarkable 91% and 95% inhibition in independent assays. These films exhibit humidity-responsive color modifications across a 25-90% relative humidity range, enabling real-time monitoring validated through simulation studies. The proposed three-in-one functional surface can have versatile applications in surface decoration, medicine, air conditioning, and the food industry. It can serve as a real-time humidity sensor for indoor and outdoor surfaces, find use in biomedical devices for continuous humidity monitoring, and offer antiviral protection for frequently handled devices and tools. The customizable colors enhance visual appeal, making it a comprehensive solution for diverse applications.

Recyclable Superhydrophobic Surface Prepared via Electrospinning and Electrospraying Using Waste Polyethylene Terephthalate for Self-Cleaning Applications

Superhydrophobic surfaces, i.e., surfaces with a water contact angle (WCA) ≥ 150°, have gained much attention as they are multifunctional surfaces with features such as self-cleaning, which can be useful in various applications such as those requiring waterproof and/or protective films. In this study, we prepared a solution from recycled polyethylene terephthalate (PET) and fabricated a superhydrophobic surface using electrospinning and electrospraying processes. We observed that the fabricated geometry varies depending on the solution conditions, and based on this, we fabricated a hierarchical structure. From the results, the optimized structure exhibited a very high WCA (>156.6°). Additionally, our investigation into the self-cleaning functionality and solar panel efficiency of the fabricated surface revealed promising prospects for the production of superhydrophobic surfaces utilizing recycled PET, with potential applications as protective films for solar panels. Consequently, this research contributes significantly to the advancement of environmentally friendly processes and the progress of recycling technology.

Research Progress of Superhydrophobic Materials in the Field of Anti-/De-Icing and Their Preparation: A Review

Accumulated ice has brought much damage to engineering and people's lives. The accumulation of ice can affect the flight safety of aircraft and lead to the failure of cables and power generation blades; it can even cause damage to human life. Traditional anti-icing and de-icing strategies have many disadvantages such as high energy consumption, low efficiency, or pollution of the environment. Therefore, inspired by animal communities, researchers have developed new passive anti-icing materials such as superhydrophobic material. In this paper, the solid surface wetting phenomenon and superhydrophobic anti-icing and de-icing mechanism were introduced. The methods of fabrication of superhydrophobic surfaces were summarized. The research progress of wear-resistant superhydrophobic coatings, self-healing/self-repairing superhydrophobic coatings, photothermal superhydrophobic coatings, and electrothermal superhydrophobic coatings in the field of anti-icing and de-icing was reviewed. The current problems and challenges were analyzed, and the development trend of superhydrophobic materials was also prospected in the field of anti-icing and de-icing. The practicality of current superhydrophobic materials should continue to be explored in depth.

Design and Biomimicry: A Review of Interconnections and Creative Potentials

The study and application of biological knowledge favor the creation of innovative projects in several areas, so it is necessary to better understand the use of these resources specifically in the field of design. Thus, a systematic review was undertaken to identify, describe, and analyze the contributions of biomimicry to design. For this purpose, the integrative systematic review model, called the Theory of Consolidated Meta-Analytical Approach, was used, carrying out a search on the Web of Science with the descriptors "design" and "biomimicry". For the period from 1991 to 2021, 196 publications were retrieved. The results were organized according to areas of knowledge, countries, journals, institutions, authors, and years. Citation, co-citation, and bibliographic coupling analyses were also performed. The investigation highlighted the following research emphases: the conception of products, buildings, and environments; the exploration of natural structures and systems to create materials and technologies; the use of biomimetic creative tools in product design; and projects focused on saving resources and implementing sustainability. It was noted that there was a tendency for authors to adopt a problem-based approach. It was concluded that the study of biomimicry can stimulate the development of multiple skills in design, improving creativity, and enhancing the potential integration of sustainability into production cycles.

Enhanced self-cleaning performance of bio-inspired micropillar-arrayed surface by shear

Inspired by the sliding behavior of gecko feet during climbing, the contribution of the shear effect to the self-cleaning performance of a bio-inspired micropillar-arrayed surface is studied through a load-shear-pull contact process. It is found that self-cleaning efficiency can be enhanced significantly by shear. The efficiency also depends on microparticle size. For the case of relatively large and small microparticles, self-cleaning efficiency increases first and then almost keeps a constant with the increase of shear distance at different preloads. For medium microparticles, shear can effectively improve self-cleaning efficiency only when the preload is small. The mechanical mechanism under such enhancement is mainly due to the varying contact states between microparticles and micropillars with the shear distance. When the shear distance is large enough, the final self-cleaning efficiency is not sensitive to shear distance anymore because the contact state reaches dynamic equilibrium. Based on such a self-cleaning mechanism of large microparticles, a simple and effective manipulator that can efficiently transfer solid particles is further proposed.

Particulate-Droplet Coalescence and Self-Transport on Superhydrophobic Surfaces

Particulate transport from surfaces governs a variety of phenomena including fungal spore dispersal, bioaerosol transmission, and self-cleaning. Here, we report a previously unidentified mechanism governing passive particulate removal from superhydrophobic surfaces, where a particle coalescing with a water droplet (∼10 to ∼100 μm) spontaneously launches. Compared to previously discovered coalescence-induced binary droplet jumping, the reported mechanism represents a more general capillary-inertial dominated transport mode coupled with particle/droplet properties and is typically mediated by rotation in addition to translation. Through wetting and momentum analyses, we show that transport physics depends on particle/droplet density, size, and wettability. The observed mechanism presents a simple and passive pathway to achieve self-cleaning on both artificial as well as biological materials as confirmed here with experiments conducted on butterfly wings, cicada wings, and clover leaves. Our findings provide insights into particle-droplet interaction and spontaneous particulate transport, which may facilitate the development of functional surfaces for medical, optical, thermal, and energy applications.

Advances in the development of superhydrophobic and icephobic surfaces

Superhydrophobicity and icephobicity are governed by surface chemistry and surface structure. These two features signify a potential advance in surface engineering and have recently garnered significant attention from the research community. This review aims to simulate further research in the development of superhydrophobic and icephobic surfaces in order to achieve their wide-spread adoption in practical applications. The review begins by establishing the fundamentals of the wetting phenomenon and wettability parameters. This is followed by the recent advances in modeling and simulations of the response of superhydrophobic surfaces to static and dynamic droplets contact and impingement, respectively. In view of their versatility and multifunctionality, a special attention is given to the development of these surfaces using nanocomposites. Furthermore, the review considers advances in icephobicity, its comprehensive characterization and its relation to superhydrophobicity. The review also includes the importance of the use of superhydrophobic surface to combat viral and bacterial contamination that exist in fomites.

Fundamentals and utilization of solid/ liquid phase boundary interactions on functional surfaces

The affinity of macroscopic solid surfaces or dispersed nano- and bioparticles towards liquids plays a key role in many areas from fluid transport to interactions of the cells with phase boundaries. Forces between solid interfaces in water become especially important when the surface texture or particles are in the colloidal size range. Although, solid-liquid interactions are still prioritized subjects of materials science and therefore are extensively studied, the related literature still lacks in conclusive approaches, which involve as much information on fundamental aspects as on recent experimental findings related to influencing the wetting and other wetting-related properties and applications of different surfaces. The aim of this review is to fill this gap by shedding light on the mechanism-of-action and design principles of different, state-of-the-art functional macroscopic surfaces, ranging from self-cleaning, photoreactive or antimicrobial coatings to emulsion separation membranes, as these surfaces are gaining distinguished attention during the ongoing global environmental and epidemic crises. As there are increasing numbers of examples for stimulus-responsive surfaces and their interactions with liquids in the literature, as well, this overview also covers different external stimulus-responsive systems, regarding their mechanistic principles and application possibilities.

Lotus-Leaf-Inspired Biomimetic Coatings: Different Types, Key Properties, and Applications in Infrastructures

A universal infrastructural issue is wetting of surfaces; millions of dollars are invested annually for rehabilitation and maintenance of infrastructures including roadways and buildings to fix the damages caused by moisture and frost. The biomimicry of the lotus leaf can provide superhydrophobic surfaces that can repel water droplets, thus reducing the penetration of moisture, which is linked with many deterioration mechanisms in infrastructures, such as steel corrosion, sulfate attack, alkali-aggregate reactions, and freezing and thawing. In cold-region countries, the extent of frost damage due to freezing of moisture in many components of infrastructures will be decreased significantly if water penetration can be minimized. Consequently, it will greatly reduce the maintenance and rehabilitation costs of infrastructures. The present study was conducted to explore any attempted biomimicry of the lotus leaf to produce biomimetic coatings. It focuses on anti-wetting characteristics (e.g., superhydrophobicity, sliding angle, contact angle), self-cleaning capability, durability, and some special properties (e.g., light absorbance and transmission, anti-icing capacity, anti-fouling ability) of lotus-leaf-inspired biomimetic coatings. This study also highlights the potential applications of such coatings, particularly in infrastructures. The most abundant research across coating materials showed superhydrophobicity as being well-tested while self-cleaning capacity and durability remain among the properties that require further research with existing promise. In addition, the special properties of many coating materials should be validated before practical applications.

A critical review on microbial carbonate precipitation via denitrification process in building materials

The naturally occurring biomineralization or microbially induced calcium carbonate (MICP) precipitation is gaining huge attention due to its widespread application in various fields of engineering. Microbial denitrification is one of the feasible metabolic pathways, in which the denitrifying microbes lead to precipitation of carbonate biomineral by their basic enzymatic and metabolic activities. This review article explains all the metabolic pathways and their mechanism involved in the MICP process in detail along with the benefits of using denitrification over other pathways during MICP implementation. The potential application of denitrification in building materials pertaining to soil reinforcement, bioconcrete, restoration of heritage structures and mitigating the soil pollution has been reviewed by addressing the finding and limitation of MICP treatment. This manuscript further sheds light on the challenges faced during upscaling, real field implementation and the need for future research in this path. The review concludes that although MICP via denitrification is an promising technique to employ it in building materials, a vast interdisciplinary research is still needed for the successful commercialization of this technique.

Bio-inspired strategies for next-generation perovskite solar mobile power sources

Smart electronic devices are becoming ubiquitous due to many appealing attributes including portability, long operational time, rechargeability and compatibility with the user-desired form factor. Integration of mobile power sources (MPS) based on photovoltaic technologies with smart electronics will continue to drive improved sustainability and independence. With high efficiency, low cost, flexibility and lightweight features, halide perovskite photovoltaics have become promising candidates for MPS. Realization of these photovoltaic MPS (PV-MPS) with unconventionally extraordinary attributes requires new 'out-of-box' designs. Natural materials have provided promising designing solutions to engineer properties under a broad range of boundary conditions, ranging from molecules, proteins, cells, tissues, apparatus to systems in animals, plants, and humans optimized through billions of years of evolution. Applying bio-inspired strategies in PV-MPS could be biomolecular modification on crystallization at the atomic/meso-scale, bio-structural duplication at the device/system level and bio-mimicking at the functional level to render efficient charge delivery, energy transport/utilization, as well as stronger resistance against environmental stimuli (e.g., self-healing and self-cleaning). In this review, we discuss the bio-inspired/-mimetic structures, experimental models, and working principles, with the goal of revealing physics and bio-microstructures relevant for PV-MPS. Here the emphasis is on identifying the strategies and material designs towards improvement of the performance of emerging halide perovskite PVs and strategizing their bridge to future MPS.

Nitrogen doped titanium dioxide as an aesthetic antimicrobial filler in dental polymers

OBJECTIVE

To develop an aesthetic resin composite using a nitrogen-doped titanium dioxide (NTiO₂) filler that possesses antimicrobial properties against cariogenic bacteria.

METHODS

N-TiO₂ powder was manufactured by calcining commercial TiO₂ with urea. Free radical release from the N-TiO₂ powder under visible light irradiation was analysed using UV-Vis spectrophotometry. The N-TiO₂ powder was incorporated into a dental resin and the photocatalytic activity assessed using a dye under both visible light and dark conditions. Using XTT assay to measure the cellular metabolic activity, the antibacterial properties of the N-TiO₂ /resin composite discs were tested using Streptococcus mutans.

RESULTS

Doping nitrogen of TiO₂ resulted in a band gap shift towards the visible light spectrum, which enabled the powder to release reactive oxygen species when exposed to visible light. When incorporated into a dental resin, the N-TiO₂/resin composite still demonstrated sustained release of reactive oxygen species, maintaining its photocatalytic activity and showing an antibacterial effect towards Streptococcus mutans under visible light conditions.

SIGNIFICANCE

N-TiO₂ filled resin composite shows great promise as a potential aesthetic resin based adhesive for orthodontic bonding.

Carbon Nanomaterials Modified Biomimetic Dental Implants for Diabetic Patients

Dental implants are used broadly in dental clinics as the most natural-looking restoration option for replacing missing or highly diseased teeth. However, dental implant failure is a crucial issue for diabetic patients in need of dentition restoration, particularly when a lack of osseointegration and immunoregulatory incompetency occur during the healing phase, resulting in infection and fibrous encapsulation. Bio-inspired or biomimetic materials, which can mimic the characteristics of natural elements, are being investigated for use in the implant industry. This review discusses different biomimetic dental implants in terms of structural changes that enable antibacterial properties, drug delivery, immunomodulation, and osseointegration. We subsequently summarize the modification of dental implants for diabetes patients utilizing carbon nanomaterials, which have been recently found to improve the characteristics of biomimetic dental implants, including through antibacterial and anti-inflammatory capabilities, and by offering drug delivery properties that are essential for the success of dental implants.

Drawing inspiration from nature to develop anti-fouling coatings: the development of biomimetic polymer surfaces and their effect on bacterial fouling

The development of self-cleaning biomimetic surfaces has the potential to be of great benefit to human health, in addition to reducing the economic burden on industries worldwide. Consequently, this study developed a biomimetic wax surface using a moulding technique which emulated the topography of the self-cleaning Gladiolus hybridus (Gladioli) leaf. A comparison of topographies was performed for unmodified wax surfaces (control), biomimetic wax surfaces, and Gladioli leaves using optical profilometry and scanning electron microscopy. The results demonstrated that the biomimetic wax surface and Gladioli leaf had extremely similar surface roughness parameters, but the water contact angle of the Gladioli leaf was significantly higher than the replicated biomimetic surface. The self-cleaning properties of the biomimetic and control surfaces were compared by measuring their propensity to repel Escherichia coli and Listeria monocytogenes attachment, adhesion, and retention in mono- and co-culture conditions. When the bacterial assays were carried out in monoculture, the biomimetic surfaces retained fewer bacteria than the control surfaces. However, when using co-cultures of the bacterial species, only following the retention assays were the bacterial numbers reduced on the biomimetic surfaces. The results demonstrate that such surfaces may be effective in reducing biofouling if used in the appropriate medical, marine, and industrial scenarios. This study provides valuable insight into the anti-fouling physical and chemical control mechanisms found in plants, which are particularly appealing for engineering purposes.

Wetting-regulated gas-involving (photo)electrocatalysis: biomimetics in energy conversion

(Photo)electrolysis of water or gases with water to species serving as industrial feedstocks and energy carriers, such as hydrogen, ammonia, ethylene, propanol, etc., has drawn tremendous attention. Moreover, these processes can often be driven by renewable energy under ambient conditions as a sustainable alternative to traditional high-temperature and high-pressure synthesis methods. In addition to the extensive studies on catalyst development, increasing attention has been paid to the regulation of gas transport/diffusion behaviors during gas-involving (photo)electrocatalytic reactions towards the goal of creating industrially viable catalytic systems with high reaction rates, excellent long-term stabilities and near-unity selectivities. Biomimetic surfaces and systems with special wetting capabilities and structural advantages can shed light on the future design of (photo)electrodes and address long-standing challenges. This article is dedicated to bridging the fields of wetting and catalysis by reviewing the cutting-edge design methodologies of both gas-evolving and gas-consuming (photo)electrocatalytic systems. We first introduce the fundamentals of various in-air/underwater wetting states and their corresponding bioinspired structural properties. The relationship amongst the bubble transport behavior, wettability, and porosity/tortuosity is also discussed. Next, the latest implementations of wetting-related design principles for gas-evolving reactions (i.e. the hydrogen evolution reaction and oxygen evolution reaction) and gas-consuming reactions (i.e. the oxygen reduction reaction and CO2 reduction reaction) are summarized. For photoelectrode designs, additional factors are taken into account, such as light absorption and the separation, transport and recombination of photoinduced electrons and holes. The influences of wettability and 3D structuring of (photo)electrodes on the catalytic activity, stability and selectivity are analyzed to reveal the underlying mechanisms. Finally, remaining questions and related future perspectives are outlined.

Nanotextured Mold Surface with DLC Coating for Reduction in Residual Ceramic Particles

In the ceramic industry, ceramic particles remain on a mold surface due to which the mold requires frequent cleaning during press molding, reducing productivity. Surface texturing and tetrahedral amorphous carbon (ta-C) coatings are well-known surface-energy controllable treatments developed for low adhesion, low friction, and high wear resistance. In the present paper, we demonstrate the effect of reducing ceramic residues using nanotexturing, ta-C coatings, and their combination. We compare two surface morphologies (i.e., 770 nm pitch nanotexturing and flat) and five materials (i.e., nonhardened steel, hardened steel, ta-C, and two types of nitrogen-doped ta-C (ta-CNx). Molding test results show that the ta-C coating on flat surfaces with the highest hardness of 30 GPa shows the lowest residual amount of 5.9 μg for Al₂O₃ ceramic particles. The amount is 82% less than that of the nonhardened steel. The ta-CNx₂₀, made with a nitrogen flow rate of 20 sccm, shows the lowest residual amount of 234 μg for SiO₂ ceramic particles, which is 81% less than that of the nontextured ta-CNx₂₀. In conclusion, we provide design guidelines for nanotextured mold surfaces including the texturing pitch should be small enough for ceramic particles; the mold surface should be sufficiently hard; the lower the surface energy per unit area, the less residues of ceramic particles.

Sliding Water Droplet on Oil Impregnated Surface and Dust Particle Mitigation

Self-cleaning of surfaces becomes challenging for energy harvesting devices because of the requirements of high optical transmittance of device surfaces. Surface texturing towards hydrophobizing can improve the self-cleaning ability of surfaces, yet lowers the optical transmittance. Introducing optical matching fluid, such as silicon oil, over the hydrophobized surface improves the optical transmittance. However, self-cleaning ability, such as dust mitigation, of the oil-impregnated hydrophobic surfaces needs to be investigated. Hence, solution crystallization of the polycarbonate surface towards creating hydrophobic texture is considered and silicon oil impregnation of the crystallized surface is explored for improved optical transmittance and self-cleaning ability. The condition for silicon oil spreading over the solution treated surface is assessed and silicon oil and water infusions on the dust particles are evaluated. The movement of the water droplet over the silicon oil-impregnated sample is examined utilizing the high-speed facility and the tracker program. The effect of oil film thickness and the tilting angle of the surface on the sliding droplet velocity is estimated for two droplet volumes. The mechanism for the dust particle mitigation from the oil film surface by the sliding water droplet is analyzed. The findings reveal that silicon oil impregnation of the crystallized sample surface improves the optical transmittance significantly. The sliding velocity of the water droplet over the thick film (~700 µm) remains higher than that of the small thickness oil film (~50 µm), which is attributed to the large interfacial resistance created between the moving droplet and the oil on the crystallized surface. The environmental dust particles can be mitigated from the oil film surface by the sliding water droplet. The droplet fluid infusion over the dust particle enables to reorient the particle inside the droplet fluid. As the dust particle settles at the trailing edge of the droplet, the sliding velocity decays on the oil-impregnated sample.

Surface Wettability and Electrical Resistance Analysis of Droplets on Indium-Tin-Oxide Glass Fabricated Using an Ultraviolet Laser System

Indium tin oxide (ITO) is widely used as a substrate for fabricating chips because of its optical transparency, favorable chemical stability, and high electrical conductivity. However, the wettability of ITO surface is neutral (the contact angle was approximately 90°) or hydrophilic. For reagent transporting and manipulation in biochip application, the surface wettability of ITO-based chips was modified to the hydrophobic or nearly hydrophobic surface to enable their use with droplets. Due to the above demand, this study used a 355-nm ultraviolet laser to fabricate a comb microstructure on ITO glass to modify the surface wettability characteristics. All of the fabrication patterns with various line width and pitch, depth, and surface roughness were employed. Subsequently, the contact angle (CA) of droplets on the ITO glass was analyzed to examine wettability and electrical performance by using the different voltages applied to the electrode. The proposed approach can succeed in the fabrication of a biochip with suitable comb-microstructure by using the optimal operating voltage and time functions for the catch droplets on ITO glass for precision medicine application. The experiment results indicated that the CA of droplets under a volume of 20 μL on flat ITO substrate was approximately 92° ± 2°; furthermore, due to its lowest surface roughness, the pattern line width and pitch of 110 μm exhibited a smaller CA variation and more favorable spherical droplet morphology, with a side and front view CA of 83° ± 1° and 78.5° ± 2.5°, respectively, while a laser scanning speed of 750 mm/s was employed. Other line width and pitch, as well as scanning speed parameters, increased the surface roughness and resulted in the surface becoming hydrophilic. In addition, to prevent droplet morphology collapse, the droplet’s electric operation voltage and driving time did not exceed 5 V and 20 s, respectively. With this method, the surface modification process can be employed to control the droplet’s CA by adjusting the line width and pitch and the laser scanning speed, especially in the neutral or nearly hydrophobic surface for droplet transporting. This enables the production of a microfluidic chip with a surface that is both light transmittance and has favorable electrical conductivity. In addition, the shape of the microfluidic chip can be directly designed and fabricated using a laser direct writing system on ITO glass, obviating the use of a mask and complicated production processes in biosensing and biomanipulation applications.

Co-inspired hydroxyapatite-based scaffolds for vascularized bone regeneration

Hydroxyapatite (HA) is the main inorganic component of human bone. Inspired by nacre and cortical bone, hydroxyapatite-based coil scaffolds were successfully prepared. The scaffolds presented "brick and mortar" multi-layered structure of nacre and multi-layered concentric circular structure of cortical bone. Because of bioactive components and hierarchical structure, the scaffolds possessed good compressive strength (≈95 MPa), flexural strength (≈161 MPa) and toughness (≈1.1 MJ/m³). In addition, they showed improved angiogenesis and osteogenesis in rat and rabbit critical sized bone defect models. By mimicking co-biological systems, this work provided a feasible strategy to optimize the properties of traditional tissue engineering biological materials for vascularized bone regeneration.

Recent Developments in Biomimetic Antifouling Materials: A Review

The term 'biomimetic' might be applied to any material or process that in some way reproduces, mimics, or is otherwise inspired by nature. Also variously termed bionic, bioinspired, biological design, or even green design, the idea of adapting or taking inspiration from a natural solution to solve a modern engineering problem has been of scientific interest since it was first proposed in the 1960s. Since then, the concept that natural materials and nature can provide inspiration for incredible breakthroughs and developments in terms of new technologies and entirely new approaches to solving technological problems has become widely accepted. This is very much evident in the fields of materials science, surface science, and coatings. In this review, we survey recent developments (primarily those within the last decade) in biomimetic approaches to antifouling, self-cleaning, or anti-biofilm technologies. We find that this field continues to mature, and emerging novel, biomimetic technologies are present at multiple stages in the development pipeline, with some becoming commercially available. However, we also note that the rate of commercialization of these technologies appears slow compared to the significant research output within the field.

Recent Progress in the Abatement of Hazardous Pollutants Using Photocatalytic TiO2-Based Building Materials

Titanium dioxide (TiO2) has been extensively investigated in interdisciplinary research (such as catalysis, energy, environment, health, etc.) owing to its attractive physico-chemical properties, abundant nature, chemical/environmental stability, low-cost manufacturing, low toxicity, etc. Over time, TiO2-incorporated building/construction materials have been utilized for mitigating potential problems related to the environment and human health issues. However, there are challenges with regards to photocatalytic efficiency improvements, lab to industrial scaling up, and commercial product production. Several innovative approaches/strategies have been evolved towards TiO2 modification with the focus of improving its photocatalytic efficiency. Taking these aspects into consideration, research has focused on the utilization of many of these advanced TiO2 materials towards the development of construction materials such as concrete, mortar, pavements, paints, etc. This topical review focuses explicitly on capturing and highlighting research advancements in the last five years (mainly) (2014-2019) on the utilization of various modified TiO2 materials for the development of practical photocatalytic building materials (PBM). We briefly summarize the prospective applications of TiO2-based building materials (cement, mortar, concretes, paints, coating, etc.) with relevance to the removal of outdoor/indoor NOx and volatile organic compounds, self-cleaning of the surfaces, etc. As a concluding remark, we outline the challenges and make recommendations for the future outlook of further investigations and developments in this prosperous area.

Wetting Properties of Transparent Anatase/Rutile Mixed Phase Glancing Angle Magnetron Sputtered Nano-TiO2 Films

Transparent polycrystalline TiO2 thin films have been deposited on unheated glass substrates using RF reactive magnetron sputtering. Depositions were carried out at different glancing angles and with different total gas mixture pressures. The variation of these parameters affected the crystal phase composition and the surface morphology. Depending on the glancing angle and the pressure, rutile, mixed anatase/ rutile and pure anatase were deposited at low substrate temperature. Both hydrophilic and hydrophobic TiO2 were obtained, exhibiting fast photoconversion to superhydrophilic upon UV irradiation. The effect of the materials physicochemical properties on the wettability and rate of the UV induced superhydrophilicity is evaluated.

Functionalization of Plastic Parts by Replication of Variable Pitch Laser-Induced Periodic Surface Structures

Surface functionalization of plastic parts has been studied and developed for several applications. However, demand for the development of reliable and profitable manufacturing strategies is still high. Here we develop and characterize a new process chain for the versatile and cost-effective production of sub-micron textured plastic parts using laser ablation. The study includes the generation of different sub-micron structures on the surface of a mold using femtosecond laser ablation and vario-thermal micro-injection molding. The manufactured parts and their surfaces are characterized in consideration of polymer replication and wetting behavior. The results of the static contact angle measurements show that replicated Laser-Induced Periodic Surface Structures (LIPSSs) always increase the hydrophobicity of plastic parts. A maximum contact angle increase of 20% was found by optimizing the manufacturing thermal boundary conditions. The wetting behavior is linked to the transition from a Wenzel to Cassie–Baxter state, and is crucial in optimizing the injection molding cycle time.

Non-sticky and Free-forward Performances of Grubs against Soil

The intriguing non-sticky and free-forward performances of grubs against soil deeply attract our interests. In this study, the life cycle and body morphology of a kind of grubs, larvae of Japanese rhinoceros beetles, are introduced. The uniformly oriented hierarchical micro structures pattern on the back epidermis is firstly reported. The rotating and forwarding motion configuration of grubs in soil is unraveled. The friction and adhesion properties of grubs are evaluated and compared with typical materials. The biological electroosmosis induced adhesion reduction effect and the hierarchical structures pattern induced anisotropic friction feature are highlighted.

A comparison between electrospinning and rotary-jet spinning to produce PCL fibers with low bacteria colonization

One of the important components in tissue engineering is material structure, providing a model for fixing and the development of cells and tissues, which allows for the transport of nutrients and regulatory molecules to and from cells. The community claims the need for new materials with better properties for use in the clinic. Poly (ε-caprolactone) (PCL) is a biodegradable polymer, semi crystalline, with superior mechanical properties and has attracted an increasing interest due to its usefulness in various biomedical applications. Herein, two different methods (electrospinning versus rotary jet spinning) with different concentrations of PCL produced ultra thin-fibers each with particular characteristics, verified and analyzed by morphology, wettability, thermal and cytotoxicity features and for bacteria colonization. Different PCL scaffold morphologies were found to be dependent on the fabrication method used. All PCL scaffolds showed greater mammalian cell interactions. Most impressively, rotary-jet spun fibers showed that a special rough surface decreased bacteria colonization, emphasizing that no nanoparticle or antibiotic was used; maybe this effect is related with physical (scaffold) and/or biological mechanisms. Thus, this study showed that rotary jet spun fibers possess a special topography compared to electrospun fibers to reduce bacteria colonization and present no cytotoxicity when in contact with mammalian cells.

Self-Cleaning Mechanism: Why Nanotexture and Hydrophobicity Matter

Dust particles can adhere to surfaces, thereby decreasing the efficiency of diverse processes, such as light absorption by solar panels. It is well known that superhydrophobicity reduces the friction between water droplets and the surface, thus allowing water drops to slide/roll and detach (clean) particles from surfaces. However, the forces that attach and detach particles from surfaces during the self-cleaning mechanism and the effect of nanotextures on these forces are not fully understood. To shed light on these forces and the effect of nanotexture on them, we prepared four Si-based samples (relevant to solar panels): (1) smooth or (2) nanotextured hydrophilic surfaces and (3) smooth or (4) nanotextured hydrophobic surfaces. In agreement with previous publications, it is shown that the efficiency of particle removal increases with hydrophobicity. Furthermore, nanotexture enhances the hydrophobicity, whereby particle removal is further increased. Specifically, hydrophilic particle removal increased from ∼41%, from hydrophilic smooth Si wafers to 98% from superhydrophobic Si-based nanotextured surfaces. However, the reason for the increased particle removal is not low friction between the droplets and the superhydrophobic surfaces; it is the reduction of the adhesion force between the particle and the surface and the altered geometry of the water-particle-air line tension acting on the particles on superhydrophobic surfaces, which increases the force that can detach particles from the surfaces. The experimental methods we used and the criterion for particle removal we derived can be implemented to engineer self-cleaning surfaces using other surfaces and dust particles, exhibiting different chemistries and/or textures.

Multifunctional Silica-Silicone Nanocomposite with Regenerative Superhydrophobic Capabilities

Superhydrophobic surfaces have been garnering increased interest because of their adaptive characteristics. However, concerns regarding their durability and complex fabrication techniques have limited their widespread adoption. In our study, we have developed an effective, durable, and versatile silica-silicone nanocomposite that can be applied through spray coating or bulk synthesized as superhydrophobic monoliths through a facile, economic, and scalable fabrication technique. For spray-coated samples, superhydrophobicity was achieved for concentrations above 9%. However, poor adhesion was observed for concentrations above 20%. Through extensive surface morphology studies, it was determined that a delicate balance between the polymer and dispersed superhydrophobic silica nanoparticles exists at a concentration of 14%. This concentration is necessary for developing the desired hierarchical structure and providing sufficient adhesion with the substrate. The monoliths were fabricated into complex geometries, with superhydrophobicity being observed in the 5 and 9% specimens. The hierarchical structure was formed through controlled surface abrasion, which created the microscale roughness and concurrently exposed the embedded silica nanoparticles. It was found that a monolith with a concentration of 9% provides excellent water repellency as well as a suitable emulsion viscosity to facilitate the molding process. Though compressive loading (up to 10 MPa) damages the monolith, the superhydrophobic performance can be quickly restored through abrasive layer removal. Both spray-coated and monolith specimens retained their superhydrophobicity after being subjected to high temperatures (up to 350 °C) and corrosive environments (pH 1-13) for 2 h.

From one species to another: A review on the interaction between chemistry and microbiology in relation to cleaning in the built environment

Since the advent of soap, personal hygiene practices have revolved around removal, sterilization, and disinfection-both of visible soil and microscopic organisms-for a myriad of cultural, aesthetic, or health-related reasons. Cleaning methods and products vary widely in their recommended use, effectiveness, risk to users or building occupants, environmental sustainability, and ecological impact. Advancements in science and technology have facilitated in-depth analyses of the indoor microbiome, and studies in this field suggest that the traditional "scorched-earth cleaning" mentality-that surfaces must be completely sterilized and prevent microbial establishment-may contribute to long-term human health consequences. Moreover, the materials, products, activities, and microbial communities indoors all contribute to, or remove, chemical species to the indoor environment. This review examines the effects of cleaning with respect to the interaction of chemistry, indoor microbiology, and human health.

Hierarchical Structures for Superhydrophobic and Superoleophobic Surfaces

Many surfaces possessing robust super liquid repellency are hierarchically structured on the nano- and micrometer scales. Several examples are found in nature, such as the self-cleaning leaves of lotus plants and anisotropic, water-guiding rice leaves. Each surface design has unique properties optimized for specific wetting conditions. In this invited feature article, we review both natural and artificial hierarchical surface structures and their function in repelling liquids. We discuss different types of structures needed in various wetting situations and draw some general conclusions as a guideline for designing robust superhydrophobic and superoleophobic surfaces.

Self-disinfecting surfaces and infection control

According to World Health Organization, every year in the European Union, 4 million patients acquire a healthcare associated infection. Even though some microorganisms represent no threat to healthy people, hospitals harbor different levels of immunocompetent individuals, namely patients receiving immunosuppressors, with previous infections, or those with extremes of age (young children and elderly), requiring the implementation of effective control measures. Public spaces have also been found an important source of infectious disease outbreaks due to poor or none infection control measures applied. In both places, surfaces play a major role on microorganisms' propagation, yet they are very often neglected, with very few guidelines about efficient cleaning measures and microbiological assessment available. To overcome surface contamination problems, new strategies are being designed to limit the microorganisms' ability to survive over surfaces and materials. Surface modification and/or functionalization to prevent contamination is a hot-topic of research and several different approaches have been developed lately. Surfaces with anti-adhesive properties, with incorporated antimicrobial substances or modified with biological active metals are some of the strategies recently proposed. This review intends to summarize the problems associated with contaminated surfaces and their importance on infection spreading, and to present some of the strategies developed to prevent this public health problem, namely some already being commercialized.

Bioinspired Photodetachable Dry Self-Cleaning Surface

Geckos have adapted to the complicated natural environment with its excellent climbing ability. Current artificial gecko-inspired synthetic adhesives (GSAs) mimic gecko's attach-detach mechanism by creating anisotropic and hierarchical structures. Easy detachment and high self-cleaning capability are still the unsolved problems in GSAs. This study presents an unprecedented photodetachable mechanism of making bioinspired smart surfaces utilizing carbon dot (CD)-doped polydimethylsiloxane (PDMS) composites. Under ultraviolet (UV) irradiation, it could be triggered up to 80.46% reduction of adhesion force between PDMS-CDs bioinspired surfaces and contaminating particles. A load-drag-pull (i.e., LDP) test mimicking gecko's locomotion was adopted to test the dry self-cleaning capabilities of these bioinspired surfaces, where the falling rate of the model contaminates (PS micropellets; average size in diameter ∼8 μm) can reach up to 54.83% after seven repeated steps under UV irradiation. The significantly improved dry self-cleaning capability is attributed to the photothermal effect of CDs inside the PDMS matrix. The mechanism proposed in this work will find its applications in the realms of climbing robots, space adhesive devices, and self-cleaning, advanced gripping technologies for pick and place or assembly.

Enantioselective Dynamic Self-Assembly of Histidine Droplets on Pillar[5]arene-Modified Interfaces

The self-assembly of macroscopic droplets on interfaces has attracted much attention and shown promising potential in the field of materials as a sensing or delivery system. Herein, we reported a new strategy to construct a d-tartaric acid-functionalized pillar[5]arene (d-TP5) interface for macroscopic differentiation of histidine enantiomers. At the molecular level, it has been proved that d-TP5 has the ability to distinguish between l-Histidine and d-Histidine ( K_L/ K_D = 4.6). Furthermore, a functional d-TP5 surface was constructed by a click reaction and characterized by contact angle measurements and attenuated total reflection-Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy analyses. The d-TP5 surface exhibited the selective dynamic adhesion of l-His droplets on the tilted interface. It means that a d-TP5 surface can distinguish histidine enantiomers at a macrolevel. The amount of d/l-His absorbed by a d-TP5 surface and the morphology of His particles formed by removing the solvent have been investigated to prove that the self-assembly of His occurs on the d-TP5 surface. The possible mechanism has been discussed from host-guest interaction and chiral recognition. The proposed chiral material displays rapidly remarkable selectivity and is convenient to be utilized, which should be suitable for comprehending chiral recognition processing and applied to chiral recognition detection of histidine in a living body.

Self-Lubricanting Slippery Surface with Wettability Gradients for Anti-Sticking of Electrosurgical Scalpel

Soft tissue sticking on electrosurgical scalpels in minimally invasive surgery can increase the difficulty of operation and easily lead to medical malpractice. It is significant to develop new methods for anti-sticking of soft tissue on electrosurgical scalpels. Based on the characteristics of biomimetic ultra-slippery surface, a self-lubricating slippery surface with wettability gradients on electrosurgical scalpel was designed and fabricated. Non-uniformly distributed cylindrical micro pillars, which constitute the wettability gradients, were prepared by an electrolytic etching process and the theoretic of the spontaneous liquid spreading process was analyzed. The silicophilic property of wettability gradients surface was modified by octadecyltrichlorosilane (OTS) self-assembling coat with biocompatible liquid lubricant dimethyl silicone oil. The contact angle of gradient’s surface at different temperatures was measured. The transportation behaviors of both water and dimethyl silicone oil on the wettability gradient’s surface were investigated; the results illustrate that the wettability gradient’s slippery surface can successfully self-lubricate from regions with low pillar density to regions with high pillar density, ascribed to the unbalanced Young’s force. The anti-sticking capability of the electrosurgical scalpel with self-lubricating slippery surface was tested. Both the adhesion force and adhesion mass under different cycles were calculated. The results suggest that the as-prepared slippery surface has excellent anti-sticking ability associated with better durability.

Tough Reversible Adhesion Properties of a Dry Self-Cleaning Biomimetic Surface

Geckos have one of the world's most efficient reversible adhesion systems. Even walking in dusty conditions, geckos can dislodge up to 80% of contaminants and recover their adhesion capability after walking as few as four steps. Thus far, artificial dry self-cleaning materials inspired by the geckos' hierarchical fibrillar structure have been only able to remove 55% of collected large particle contaminants with 30 steps. Challenges, including low mechanical strength, low stiffness, and short fatigue time keep these materials from being used in practical applications. This study involves the novel fabrication of dry self-cleaning surfaces with a high mechanical performance and an outstanding dry self-cleaning property. Imposing a load-drag-pull process similar to a gecko's foot adhesion process, our biomimetic surfaces could dislodge up to 59% of microparticles (∼8 μm) with as few as five steps. Furthermore, the surface had an excellent screening ability at low temperatures regardless of the surface roughness similarity. The surfaces were also proven to be scratch resistant. The biomimetic surfaces exhibit enhanced dry self-cleaning and mechanical properties and could be promising in applications such as reusable adhesives, biochips, aerospace satellite waste collection, and screening equipment.

TiO2 nanowire-templated hierarchical nanowire network as water-repelling coating

Extraordinary water-repelling properties of superhydrophobic surfaces make them novel candidates for a great variety of potential applications. A general approach to achieve superhydrophobicity requires low-energy coating on the surface and roughness on nano- and micrometre scale. However, typical construction of superhydrophobic surfaces with micro-nano structure through top-down fabrication is restricted by sophisticated fabrication techniques and limited choices of substrate materials. Micro-nanoscale topographies templated by conventional microparticles through surface coating may produce large variations in roughness and uncontrollable defects, resulting in poorly controlled surface morphology and wettability. In this work, micro-nanoscale hierarchical nanowire network was fabricated to construct self-cleaning coating using one-dimensional TiO2 nanowires as microscale templates. Hierarchical structure with homogeneous morphology was achieved by branching ZnO nanowires on the TiO2 nanowire backbones through hydrothermal reaction. The hierarchical nanowire network displayed homogeneous micro/nano-topography, in contrast to hierarchical structure templated by traditional microparticles. This hierarchical nanowire network film exhibited high repellency to both water and cell culture medium after functionalization with fluorinated organic molecules. The hierarchical structure templated by TiO2 nanowire coating significantly increased the surface superhydrophobicity compared to vertical ZnO nanowires with nanotopography alone. Our results demonstrated a promising strategy of using nanowires as microscale templates for the rational design of hierarchical coatings with desired superhydrophobicity that can also be applied to various substrate materials.

3D Printing of Lotus Root-Like Biomimetic Materials for Cell Delivery and Tissue Regeneration

Biomimetic materials have drawn more and more attention in recent years. Regeneration of large bone defects is still a major clinical challenge. In addition, vascularization plays an important role in the process of large bone regeneration and microchannel structure can induce endothelial cells to form rudimentary vasculature. In recent years, 3D printing scaffolds are major materials for large bone defect repair. However, these traditional 3D scaffolds have low porosity and nonchannel structure, which impede angiogenesis and osteogenesis. In this study, inspired by the microstructure of natural plant lotus root, biomimetic materials with lotus root-like structures are successfully prepared via a modified 3D printing strategy. Compared with traditional 3D materials, these biomimetic materials can significantly improve in vitro cell attachment and proliferation as well as promote in vivo osteogenesis, indicating potential application for cell delivery and bone regeneration.

Preparation of Robust Superhydrophobic Halloysite Clay Nanotubes via Mussel-Inspired Surface Modification

In this study, a novel and convenient bio-inspired modification strategy was used to create stable superhydrophobic structures on halloysite clay nanotubes (HNTs) surfaces. The polydopamine (PDA) nanoparticles can firmly adhere on HNTs surfaces in a mail environment of pH 8.5 via the oxidative self-polymerization of dopamine and synthesize a rough nano-layer assisted with vitamin M, which provides a catechol functional platform for the secondary reaction to graft hydrophobic long-chain alkylamine for preparation of hierarchical micro/nano structures with superhydrophobic properties. The micromorphology, crystal structure, and surface chemical composition of the resultant superhydrophobic HNTs were characterized by field emission scanning electron (FE-SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). The as-formed surfaces exhibited outstanding superhydrophobicity with a water contact angle (CA) of 156.3 ± 2.3°, while having little effect on the crystal structures of HNTs. Meanwhile, the resultant HNTs also showed robust stability that can conquer various harsh conditions including strong acidic/alkaline solutions, organic solvents, water boiling, ultrasonic cleaning, and outdoor solar radiation. In addition, the novel HNTs exhibited excellent packaged capabilities of phase change materials (PCMs) for practical application in thermal energy storage, which improved the mass fractions by 22.94% for stearic acid and showed good recyclability. These HNTs also exhibited good oil/water separation ability. Consequently, due to the superior merits of high efficiency, easy operation, and non-toxicity, this bionic surface modification approach may make HNTs have great potentials for extensive applications.

Influence of Nanotechnology and the Role of Nanostructures in Biomimetic Studies and Their Potential Applications

With the advent of nanotechnology, by looking further deep down into the molecular level, today, we are able to understand basic and applied sciences even better than ever before. Not only has nanoscience and nanotechnology allowed us to study the composing structures of materials in detail, it has also allowed us to fabricate and synthesize such nanostructures using top-down and bottom-up approaches. One such field, which has been significantly influenced by the dawn of nanotechnology is biomimetics. With powerful spectroscopic and microscopic tools presenting us with images like double nanostructured pillars on the lotus surface for superhydrophobicity, the conical protuberances of moth eye demonstrating anti-reflection properties and nanostructured spatulae of gecko feet for high adhesivity, we are now able to fabricate these structures in the lab with properties showing close resemblance to their natural counterparts. Here, we present a review of various nanostructures that exist in nature, their fabrication techniques and some of their promising future applications. We hope this review will provide the reader with a basic understanding of what biomimetics is and how nanotechnology has significantly influenced this field.

Biomimetic Principles to Develop Blood Compatible Surfaces

Functionalized biomaterial surface patterns capable of resisting nonspecific adsorption while retaining their bioactivity are crucial in the advancement of biomedical technologies, but currently available biomaterials intended for use in whole blood frequently suffer from nonspecific adsorption of proteins and cells, leading to a loss of activity over time. In this review, we address two concepts for the design and modification of blood compatible biomaterial surfaces, zwitterionic modification and surface functionalization with glycans – both of which are inspired by the membrane structure of mammalian cells – and discuss their potential for biomedical applications.

Antimicrobial peptide coatings for hydroxyapatite: electrostatic and covalent attachment of antimicrobial peptides to surfaces

The interface between implanted devices and their host tissue is complex and is often optimized for maximal integration and cell adhesion. However, this also gives a surface suitable for bacterial colonization. We have developed a novel method of modifying the surface at the material-tissue interface with an antimicrobial peptide (AMP) coating to allow cell attachment while inhibiting bacterial colonization. The technology reported here is a dual AMP coating. The dual coating consists of AMPs covalently bonded to the hydroxyapatite surface, followed by deposition of electrostatically bound AMPs. The dual approach gives an efficacious coating which is stable for over 12 months and can prevent colonization of the surface by both Gram-positive and Gram-negative bacteria.