Polymer-nanotube-enzyme composites as active antifouling films

Antimicrobial Polymer Surfaces Containing Quaternary Ammonium Centers (QACs): Synthesis and Mechanism of Action

Synthetic polymer surfaces provide an excellent opportunity for developing materials with inherent antimicrobial and/or biocidal activity, therefore representing an answer to the increasing demand for antimicrobial active medical devices. So far, biologists and material scientists have identified a few features of bacterial cells that can be strategically exploited to make polymers inherently antimicrobial. One of these is represented by the introduction of cationic charges that act by killing or deactivating bacteria by interaction with the negatively charged parts of their cell envelope (lipopolysaccharides, peptidoglycan, and membrane lipids). Among the possible cationic functionalities, the antimicrobial activity of polymers with quaternary ammonium centers (QACs) has been widely used for both soluble macromolecules and non-soluble materials. Unfortunately, most information is still unknown on the biological mechanism of action of QACs, a fundamental requirement for designing polymers with higher antimicrobial efficiency and possibly very low toxicity. This mini-review focuses on surfaces based on synthetic polymers with inherently antimicrobial activity due to QACs. It will discuss their synthesis, their antimicrobial activity, and studies carried out so far on their mechanism of action.

High-Performance Polyurea Improved by Reactive Nanocluster for Antibiofouling

Polyurea has found applications in protective coatings. Yet, the too fast polymerization and lack of functions limit its application. Herein, we report a high-performance polyurea via the stepwise polymerization of an isocyanate (NCO)-terminated prepolymer consisting of poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol) (PPG-b-PEG-b-PPG) with a nanocluster synthesized via the hydrolysis of N-phenylaminomethyltriethoxysilane. Such a nanocluster contains low-reactivity secondary amines, so the polymerization of polyurea can be slowed down (over 1 h), which improves its wetting and adhesion to a substrate. The residual silanol groups on the nanocluster further increase the adhesion. Such polyurea exhibits high adhesion on various substrates, including glass, ceramic, steel, copper, titanium, wood, and natural rubber (∼2.35-14.64 MPa). Besides, the nanoclusters can cross-link the prepolymer into a tough network, endowing the polyurea with a high mechanical strength of ∼25 MPa, much higher than the traditional polyaspartic ester polyurea. On the other hand, the PEG segments enable the polyurea to have good fouling resistance against proteins (fibrinogen absorption was reduced by over 90%), bacteria (RBA of S. aureusE. coli and Pseudomonas sp. was less than 10%), as well as diatom (diatom density was less than 100 cells/mm2). The polyurea is expected to find applications in biomedical engineering and marine antifouling.

Fouling of mammalian hair fibres exposed to a titanium dioxide colloidal suspension

Fouling of surfaces in prolonged contact with liquid often leads to detrimental alteration of material properties and performance. A wide range of factors which include mass transport, surface properties and surface interactions dictate whether foulants are able to adhere to a surface. Passive means of foulant rejection, such as the microscopic patterns, have been known to develop in nature. In this work, we investigate the anti-fouling behaviour of animal fur and its apparent passive resistance to fouling. We compare the fouling performance of several categories of natural and manufactured fibres, and present correlations between contamination susceptibility and physio-mechanical properties of the fibre and its environment. Lastly, we present a correlation between the fouling intensity of a fibre and the cumulative impact of multiple interacting factors declared in the form of a dimensionless group. Artificial and natural hair strands exhibit comparable anti-fouling behaviour in flow, however, the absence of flow improves the performance of some artificial fibres. Among the plethora of factors affecting the fouling of fur hair, the dimensionless groups we present herein provide the best demarcation between fibres of different origin.

Industrial applications of immobilized nano-biocatalysts

Immobilized enzyme-based catalytic constructs could greatly improve various industrial processes due to their extraordinary catalytic activity and reaction specificity. In recent decades, nano-enzymes, defined as enzyme immobilized on nanomaterials, gained popularity for the enzymes' improved stability, reusability, and ease of separation from the biocatalytic process. Thus, enzymes can be strategically incorporated into nanostructured materials to engineer nano-enzymes, such as nanoporous particles, nanofibers, nanoflowers, nanogels, nanomembranes, metal-organic frameworks, multi-walled or single-walled carbon nanotubes, and nanoparticles with tuned shape and size. Surface-area-to-volume ratio, pore-volume, chemical compositions, electrical charge or conductivity of nanomaterials, protein charge, hydrophobicity, and amino acid composition on protein surface play fundamental roles in the nano-enzyme preparation and catalytic properties. With proper understanding, the optimization of the above-mentioned factors will lead to favorable micro-environments for biocatalysts of industrial relevance. Thus, the application of nano-enzymes promise to further strengthen the advances in catalysis, biotransformation, biosensing, and biomarker discovery. Herein, this review article spotlights recent progress in nano-enzyme development and their possible implementation in different areas, including biomedicine, biosensors, bioremediation of industrial pollutants, biofuel production, textile, leather, detergent, food industries and antifouling.

Physically Switchable Antimicrobial Surfaces and Coatings: General Concept and Recent Achievements

Bacterial environmental colonization and subsequent biofilm formation on surfaces represents a significant and alarming problem in various fields, ranging from contamination of medical devices up to safe food packaging. Therefore, the development of surfaces resistant to bacterial colonization is a challenging and actively solved task. In this field, the current promising direction is the design and creation of nanostructured smart surfaces with on-demand activated amicrobial protection. Various surface activation methods have been described recently. In this review article, we focused on the "physical" activation of nanostructured surfaces. In the first part of the review, we briefly describe the basic principles and common approaches of external stimulus application and surface activation, including the temperature-, light-, electric- or magnetic-field-based surface triggering, as well as mechanically induced surface antimicrobial protection. In the latter part, the recent achievements in the field of smart antimicrobial surfaces with physical activation are discussed, with special attention on multiresponsive or multifunctional physically activated coatings. In particular, we mainly discussed the multistimuli surface triggering, which ensures a better degree of surface properties control, as well as simultaneous utilization of several strategies for surface protection, based on a principally different mechanism of antimicrobial action. We also mentioned several recent trends, including the development of the to-detect and to-kill hybrid approach, which ensures the surface activation in a right place at a right time.

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.

Highly selective and antifouling electrochemical biosensors for sensitive MicroRNA assaying based on conducting polymer polyaniline functionalized with zwitterionic peptide

Ultrasensitive and low-fouling microRNA electrochemical biosensors were successfully constructed by introducing thiol-terminated antifouling molecules (peptide sequence, polyethylene glycol, or mercapto alcohol) onto the surface of polyaniline-modified electrodes. For the three kinds of antifouling materials investigated, the newly designed and synthesized peptide exhibited superior antifouling ability to others, and it could effectively reduce the nonspecific adsorption of proteins and even prevent the fouling effect of serum. Compared with microRNA biosensors without antifouling capability, or those modified with polyethylene glycol or mercapto alcohol, the biosensor modified with the designed zwitterionic peptide showed the highest specificity for single-base mismatch, three-base mismatch, and completely complementary microRNAs. Most interestingly, the experimental results indicated that the introduction of antifouling molecules to the sensing interfaces did not significantly change the sensitivity of the biosensor. The strategy of constructing antifouling biosensors based on newly synthesized zwitterionic peptides and conducting polymers can be promisingly extended to the development of other electrochemical sensors and biosensors without encountering biofouling. Graphical abstract Ultrasensitive and low-fouling microRNA electrochemical biosensors were constructed by introducing thiol-terminated antifouling molecules (peptide sequence, polyethylene glycol, or mercapto alcohol) onto the surface of polyaniline-modified electrodes. The biosensor modified with the designed zwitterionic peptide showed the highest specificity amongst four kinds of biosensors.

Surface Modification by Nano-Structures Reduces Viable Bacterial Biofilm in Aerobic and Anaerobic Environments

Bacterial biofilm formation on wet surfaces represents a significant problem in medicine and environmental sciences. One of the strategies to prevent or eliminate surface adhesion of organisms is surface modification and coating. However, the current coating technologies possess several drawbacks, including limited durability, low biocompatibility and high cost. Here, we present a simple antibacterial modification of titanium, mica and glass surfaces using self-assembling nano-structures. We have designed two different nano-structure coatings composed of fluorinated phenylalanine via the drop-cast coating technique. We investigated and characterized the modified surfaces by scanning electron microscopy, X-ray diffraction and wettability analyses. Exploiting the antimicrobial property of the nano-structures, we successfully hindered the viability of Streptococcus mutans and Enterococcus faecalis on the coated surfaces in both aerobic and anaerobic conditions. Notably, we found lower bacteria adherence to the coated surfaces and a reduction of 86–99% in the total metabolic activity of the bacteria. Our results emphasize the interplay between self-assembly and antimicrobial activity of small self-assembling molecules, thus highlighting a new approach of biofilm control for implementation in biomedicine and other fields.

Amyloid-Like Protein Aggregates: A New Class of Bioinspired Materials Merging an Interfacial Anchor with Antifouling

Surfaces that resist nonspecific protein adsorption in a complex biological milieu are required for a variety of applications. However, few strategies can achieve a robust antifouling coating on a surface in an easy and reliable way, regardless of material type, morphology, and shape. Herein, the preparation of an antifouling coating by one-step aqueous supramolecular assembly of bovine serum albumin (BSA) is reported. Based on fast amyloid-like protein aggregation through the rapid reduction of the intramolecular disulfide bonds of BSA by tris(2-carboxyethyl)phosphine, a dense proteinaceous nanofilm with controllable thickness (≈130 nm) can be covered on virtually arbitrary material surfaces in tens of minutes by a simple dipping or spraying. The nanofilm shows strong stability and adhesion with the underlying substrate, exhibiting excellent resistance to the nonspecific adsorption of a broad-spectrum of contaminants including proteins, serum, cell lysate, cells, and microbes, etc. In vitro and in vivo experiments show that the nanofilm can prevent the adhesion of microorganisms and the formation of biofilm. Compared with native BSA, the proteinaceous nanofilm coating exposes a variety of functional groups on the surface, which have more-stable adhesion with the surface and can maintain the antifouling in harsh conditions including under ultrasound, surfactants, organic solvents, and enzymatic digestion.

Designed Three-in-One Peptides with Anchoring, Antifouling, and Recognizing Capabilities for Highly Sensitive and Low-Fouling Electrochemical Sensing in Complex Biological Media

Nonspecific adsorption is of great concern for electrochemical biosensors performing in complex biological media, and various antifouling materials have been introduced into the sensing interfaces to improve the antifouling capability of different biosensors. However, for most of the biosensors with antifouling materials and sensing probes coexisting in the sensing interfaces, either the antifouling materials will impair the sensing performances or the sensing probes will affect the antifouling ability. Herein, a facile and efficient antifouling biosensor was developed based on a newly designed three-in-one peptide with anchoring, antifouling, and recognizing capabilities. One end of the designed peptide is a unique anchoring part that is rich in amine groups, and this part can be anchored to the poly(3,4-ethylenedioxythiophene) (PEDOT)-citrate film electrodeposited on a glassy carbon electrode. The other end of the peptide is a recognizing part that can specifically bind to the aminopeptidase N (APN) and human hepatocellular carcinoma cells (HepG2 cells). Meanwhile, the middle part of the peptide, together with the anchoring part, was designed to be antifouling. With this designed multifunctional peptide, highly sensitive and low-fouling biosensors capable of assaying target APN and HepG2 cells in complex biological media can be easily prepared, with detection limits of 0.4 ng·mL^-1 and 20 cells·mL^-1, respectively. This antifouling biosensor is feasible for practical target detection in real complex samples, and it is highly expected that this peptide designing strategy may be extended to the development of various antifouling biosensors.

Computational Investigation of Antifouling Property of Polyacrylamide Brushes

Antifouling materials and coatings have broad fundamental and practical applications. Strong hydration at polymer surfaces has been proven to be responsible for their antifouling property, but molecular details of interfacial water behaviors and their functional roles in protein resistance remain elusive. Here, we computationally studied the packing structure, surface hydration, and protein resistance of four poly(N-hydroxyalkyl acrylamide) (PAMs) brushes with different carbon spacer lengths (CSLs) using a combination of molecular mechanics (MM), Monte Carlo (MC), and molecular dynamics (MD) simulations. The packing structure of different PAM brushes were first determined and served as a structural basis for further exploring the CSL-dependent dynamics and structure of water molecules on PAM brushes and their surface resistance ability to lysozyme protein. Upon determining an optimal packing structure of PAMs by MM and optimal protein orientation on PAMs by MC, MD simulations further revealed that poly(N-hydroxymethyl acrylamide) (pHMAA), poly(N-(2-hydroxyethyl)acrylamide) (pHEAA), and poly(N-(3-hydroxypropyl)acrylamide) (pHPAA) brushes with shorter CSLs = 1-3 possessed a much stronger binding ability to more water molecules than a poly(N-(5-hydroxypentyl)acrylamide) (pHPenAA) brush with CSL = 5. Consequently, CSL-induced strong surface hydration on pHMAA, pHEAA, and pHPAA brushes led to high surface resistance to lysozyme adsorption, in sharp contrast to lysozyme adsorption on the pHPenAA brush. Computational studies confirmed the experimental results of surface wettability and protein adsorption from surface plasmon resonance, contact angle, and sum frequency generation vibrational spectroscopy, highlighting that small structural variation of CSLs can greatly impact surface hydration and antifouling characteristics of antifouling surfaces, which may provide structural-based design guidelines for new and effective antifouling materials and surfaces.

Bioinspired surfaces with wettability for antifouling application

Wettability is a special character found in nature, including the superhydrophobicity of lotus leaves, the underwater superoleophobicity of fish scales and the slipperiness of pitcher plants. These surfaces exhibit unique properties such as resistance to icing, corrosion, and the like. The antifouling properties of the material surface have important applications in a variety of areas, such as in hulls, in medical equipment, in water pipes and underwater equipment. However, the traditional anti-fouling surface is usually combined with toxic substances or its manufacturing process is complicated and expensive, which cannot meet the current antifouling demand. These wettable surfaces have always exhibited good anti-biofouling and self-cleaning properties, and their use as antifouling surfaces can well solve the problems of the above-mentioned traditional antifouling surfaces. Here, we divided the wettable surfaces into superhydrophobic surfaces, underwater superoleophobic surfaces and slippery surfaces, respectively, summarizing their development in the field of antifouling. Their research progress in antibacterial, antibiotic flocculation and antiplatelet adhesion is highlighted. Furthermore, we provide our own insights into the shortcomings and development prospects of wettable surface applications in the field of antifouling.

Bioelectrocatalysis at carbon nanotubes

This paper summarizes several examples of enzyme immobilization and bioelectrocatalysis at carbon nanotubes (CNTs). CNTs offer substantial improvements on the overall performance of amperometric enzyme electrodes mainly due to their unique structural, mechanical and electronic properties such as metallic, semi-conducting and superconducting electron transport. Unfortunately, their water insolubility restrains the kick-off in some particular fields. However, the chemical functionalization of CNTs, non-covalent and covalent, attracted a remarkable interest over the past several decades boosting the development of electrochemical biosensors and enzymatic fuel cells (EFCs) based on two different types of communications: mediated electron transfer (MET)-type, where the use of redox mediators, small electroactive molecules (freely diffusing or bound to side chains of flexible redox polymers), which are able to shuttle the electrons between the enzyme active site and the electrode (second electron transfer generation system); direct electron transfer (DET)-type between the redox group of the enzyme and the electrode surface (third electron transfer generation system).

Nanomaterial-Supported Enzymes for Water Purification and Monitoring in Point-of-Use Water Supply Systems

Increasing pollution of global water sources and challenges in rapid detection and treatment of the wide range of contaminants pose considerable burdens on public health. The issue is particularly critical in rural areas, where building of centralized water treatment systems and pipe infrastructure to connect dispersed populations is not always practical. Point-of-use (POU) water supply systems provide cost-effective and energy-efficient approaches to store, treat, and monitor the quality of water. Currently available POU systems have limited success in dealing with the portfolio of emerging contaminants, particularly those present at trace concentrations. A site-to-site variation in contaminant species and concentrations also requires versatile POU systems to detect and treat contaminants and provide on-demand clean water. Among different technologies for developing rapid and sensitive water purification processes and sensors, enzymes offer one of the potential solutions because of their strong activity and selectivity toward chemical substrates. Many enzyme-nanomaterial composites have recently been developed that enhance enzymes' stability and activity and expand their functionality, thus facilitating the application of nanosupported enzymes in advanced POU systems. In this Account, we highlight the strengths and limitations of nanosupported enzymes for their potential applications in POU systems for water treatment as well as detection of contaminants, even at trace levels. We first summarize the mechanisms by which silica, carbon, and metallic nanosupports improve enzyme stability, selectivity, and catalysis. The unique immobilization properties and potential advantages of novel bioderived nanosupports over non-bioderived nanomaterials are emphasized. We illustrate prospective applications of nanosupported enzymes in POU systems with different roles: water purification, disinfection, and contaminant sensing. For each type of application, nanosupported enzymes offer higher performance than free enzymes. Nanosupports prolong enzymes' lifetimes and improve the rates of contaminant removal by concentrating contaminants near the enzymes. Nanosupports also stabilize antimicrobial enzymes while facilitating their attachment to bacterial surfaces, thereby increasing their potential uses for disinfection and prevention of biofouling in water purification and storage devices. As enzyme-based electrochemical sensors rely on electrochemical reactions of enzymatically generated species, the ability of conductive nanosupports to enhance enzyme activity and stability and to promote transfer of electrons onto the electrode greatly improves the sensitivity and durability of electroenzymatic contaminant sensors. Despite the promising results in laboratory settings, the application of nanosupported enzymes in real-world POU systems requires the implementation of multiple enzyme combinations and strategies for minimizing health risks associated with unintended releases of nanomaterials. Finally, we identify multidisciplinary research gaps in the development of nanosupported enzyme treatment systems and provide frameworks for the early adopters to make informed decisions on whether and how to use such POU systems.

Slow polymer diffusion on brush-patterned surfaces in aqueous solution

A model system for the investigation of diffusional transport in compartmentalized nanosystems is described. Arrays of "corrals" enclosed within poly[oligo(ethylene glycol)methyl ether methacrylate] (POEGMA) "walls" were fabricated using double-exposure interferometric lithography to deprotect aminosilane films protected by a nitrophenyl group. In exposed regions, removal of the nitrophenyl group enabled attachment of an initiator for the atom-transfer radical polymerization of end-grafted POEGMA (brushes). Diffusion coefficients for poly(ethylene glycol) in these corrals were obtained by fluorescence correlation spectroscopy. Two modes of surface diffusion were observed: one which is similar to diffusion on the unpatterned surface and a very slow mode of surface diffusion that becomes increasingly important as confinement increases. Diffusion within the POEGMA brushes does not significantly contribute to the results.

Seawater-Induced Healable Underwater Superoleophobic Antifouling Coatings

Creating an artificial surface, mimicking a live fish scale that repels oil underwater and with self-healing properties, would be significant for the development of nontoxic marine antifouling coatings. Here, we report a seawater-induced strategy to create in situ an underwater superoleophobic surface, starting from the coatings of a self-polishing polymer and seawater-responsive polymer-grafted SiO₂ nanoparticles. The coatings' surfaces were able to renew in artificial seawater through the hydrolysis of the superficial self-polishing polymer and its subsequent dissolution. Particularly, the grafted poly(triisopropylsilyl acrylate- co-3-methacryloxypropyltrimethoxysilane) chains could transform into hydrophilic ones via seawater-induced hydrolysis, which additionally strengthened the oil-repellency (zero oil adhesive force) and endowed the surface with excellent antiprotein adsorption characteristics. Because the hydrolysis was limited to the superficial layer of the coatings, it could avoid the water-swelling that instead occurs with conventional underwater superoleophobic coatings, with significant benefits to its durability. We believe that the seawater-induced renewal of underwater superoleophobic surfaces will be useful in extreme marine environments.

Antifouling properties of layer by layer DNA coatings

Fouling is a major concern for solid/liquid interfaces of materials used in different applications. One approach of fouling control is the use of hydrophilic polymer coatings made from poly-anions and poly-cations using the layer-by-layer (LBL) method. The authors hypothesized that the poly-anionic properties and the poly-phosphate backbone of DNA would provide anti-biofouling and anti-scaling properties. To this end, poly(ethyleneimine)/DNA LBL coatings against microbial and inorganic fouling were developed, characterized and evaluated. DNA LBL coatings reduced inorganic fouling from tap water by 90% when incubated statically or under flow conditions mimicking surfaces in heat exchangers. The coatings also impaired biofilm formation by 93% on stainless steel from tap water, and resulted in a 97% lower adhesion force and reduced initial attachment of the human pathogens Staphylococcus aureus, Staphylococcus epidermidis and Pseudomonas aeruginosa on glass. This study demonstrates a proof of concept that LBL coatings with poly-anions harboring phosphate groups can address fouling in several applications.

Diblock Polymer Brush (PHEAA- b-PFMA): Microphase Separation Behavior and Anti-Protein Adsorption Performance

In this paper, a series of amphiphilic diblock polymers of poly(hydroxyethylacrylamide)- b-poly(1H,1H-pentafluoropropyl methacrylate) (PHEAA- b-PFMA) were grafted from silicon wafer via surface-initiated atom transfer radical polymerization (SI-ATRP). Surface wettability and chemical compositions of the modified surfaces were characterized by contact angle goniometer and X-ray photoelectron spectroscopy (XPS) respectively. Molecular weight and polydispersity of each block were measured using gel permeation chromatography (GPC). The topography and the microphase separation behavior of PHEAA- b-PFMA surfaces were investigated by atomic force microscope (AFM). The results show that only when the grafting density (σ) and thickness of PHEAA brush were in the range of 0.9-1.3 (chain/nm²) and 6.6-15.1 nm, respectively, and the ratio of PFMA/PHEAA varied from 89/42 to 89/94, could the diblock copolymer phase separate into nanostructures. Further, the antiprotein adsorption performance of the modified surfaces against BSA, fibrinogen, and lysozyme was studied. The results indicated the modified surfaces could reduce the protein adsorption compared to the pristine silicon wafer. For Fibrinogen, the antiadsorption effect of PHEAA- b-PFMA-modified surfaces with microphase segregation was better than that of corresponding PHEAA modified surfaces. The results provide further evidence that surface composition and microphase segregation of fluorinated moieties of block copolymer brushes significantly impact protein adsorption behaviors.

Low Fouling Protein Detection in Complex Biological Media Supported by a Designed Multifunctional Peptide

The construction of sensitive and selective biosensors capable of detecting specific targets in complex biological samples remains a challenge highly relevant to a range of sensor/diagnostic applications. Herein, we have utilized a multifunctional peptide to present an interface that supports the very specific recruitment of targets from serum. The novel peptide sequence designed contains an anchoring domain (CPPPP-), an antifouling domain (-NQNQNQNQDHWRGWVA), and a human immunoglobulin G (IgG) recognition domain (-HWRGWVA), and the whole peptide was designed to be antifouling. These were integrated into polyaniline nanowire arrays in supporting the quantification of IgG (with a limit of detection of 0.26 ng mL^-1) in neat serum and real clinical samples. The strategy of utilizing multisegment peptide films to underpin highly selective target recruitment is, of course, readily extended to a broad range of targets for which an affinity sequence can be generated.

(PtBA-co-PPEGMEMA-co-PDOMA)-g-PPFA polymer brushes synthesized by sequential RAFT polymerization and ATRP

This article reports the synthesis of semi-fluorinated (PtBA-co-PPEGMEMA-co-PDOMA)-g-PPFA polymer brushes for self-cleaning anti-fouling surfaces.

Mechanisms underlying interactions between PAMAM dendron-grafted surfaces with DPPC membranes

Biofouling is a pervasive problem which demands the creation of smart, antifouling surfaces. Towards this end, we examine the interactions between a dipalmitoylphosphatidylcholine (DPPC) lipid bilayer and a polyamidoamine (PAMAM) dendron-grafted surface. In addition, we investigate the impact of dendron generation on the system behavior. To resolve the multiscale dynamical processes occurring over a large spatial scale, we employ Molecular Dynamics simulations with a coarse-grained implicit solvent force field. Our results demonstrate the transient and equilibrium system dynamics to be determined by the PAMAM dendron generation along with the underlying mechanisms. Higher generation dendrons are observed to favor penetration of the DPPC molecules into the dendron branches, thereby enabling sustained interactions between the membrane and the dendron-grafted surface. Under equilibrium, the membrane adopts a bowl-shaped morphology whose dimensions are determined by the dendron generation and density of interactions. The results from our study can be used to guide the design of novel surfaces with selective antifouling properties which can prevent the adsorption of microorganisms onto lipid membranes.

The interactions between a DPPC lipid membrane and a PAMAM dendron-grafted surface.

Tuning Bacterial Attachment and Detachment via the Thickness and Dispersity of a pH-Responsive Polymer Brush

We investigated the effect of two brush parameters, thickness and dispersity in the molecular weight distribution, on the adhesion of bacteria to pH-responsive poly(acrylic acid) (PAA) brushes synthesized using surface-initiated atom transfer radical polymerization. The attachment and detachment of Staphylococcus epidermidis to PAA brushes at pH 4 and pH 9, respectively, were examined with confocal microscopy. An optimal range of brush thickness, 13-18 nm, was identified for minimizing bacterial adhesion on PAA brushes at pH 4, and bacterial attachment did not depend on the brush dispersity. Increasing either the brush thickness or dispersity detached bacteria from the brushes when the pH was increased from 4 to 9. Bacterial detachment likely arose from an enhanced actuation effect in thick or high-dispersity brushes, as PAA brushes change conformation from collapsed to extended states when the pH is increased from 4 to 9. These results suggest that manipulating the molecular weight distribution provides a route to separately tune the attachment and detachment of bacteria.

Multifunctional Mesoporous Carbon Capsules and their Robust Coatings for Encapsulation of Actives: Antimicrobial and Anti-bioadhesion Functions

We present the synthesis and applications of multifunctional hollow porous carbon spheres with well-ordered pore architecture and ability to encapsulate functional nanoparticles. In the present work, the applications of hollow mesoporous carbon capsules (HMCCs) are illustrated in two different contexts. In the first approach, the hollow capsule core is used to encapsulate silver nanoparticles to impart antimicrobial characteristics. It is shown that silver-loaded HMCCs (concentration ∼100 μg/mL) inhibit the growth and multiplication of bacterial colonies of Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive) up to 96% and 83%, respectively. In the second part, the fabrication of hierarchical micro- and nanostructured superhydrophobic coatings of HMCCs (without encapsulation with silver nanoparticles) is evaluated for anti-bioadhesion properties. Studies of protein adsorption and microorganism and platelet adhesion have shown a significant reduction (up to 100%) for the HMCC-based superhydrophobic surfaces compared with the control surfaces. Therefore, this unique architecture of HMCCs and their coatings with the ability to encapsulate functional materials make them a promising candidate for a variety of applications.

Enzymatic waterborne polyurethane towards a robust and environmentally friendly anti-biofouling coating

A simple, green, robust and efficient method has been developed for the preparation of an anti-biofouling coating by directly mixing antifouling enzymes with a castor oil-based waterborne polyurethane (WPU) dispersion.

Under the lens: carbon nanotube and protein interaction at the nanoscale

The combination of the very different chemical natures of carbon nanotubes (CNTs) and proteins gives rise to systems with unprecedented performance, thanks to a rich pool of very diverse chemical, electronic, catalytic and biological properties. Here we review recent advances in the field, including innovative and imaginative aspects from a nanoscale point of view. The tubular nature of CNTs allows for internal protein encapsulation, and also for their external coating by protein cages, affording bottom-up ordering of molecules in hierarchical structures. To achieve such complex systems it is imperative to master the intermolecular forces between CNTs and proteins, including geometry effects (e.g. CNT diameter and curvature) and how they translate into changes in the local environment (e.g. water entropy). The type of interaction between proteins and CNTs has important consequences for the preservation of their structure and, in turn, function. This key aspect cannot be neglected during the design of their conjugation, be it covalent, non-covalent, or based on a combination of both methods. The review concludes with a brief discussion of the very many applications intended for CNT-protein systems that go across various fields of science, from industrial biocatalysis to nanomedicine, from innovative materials to biotechnological tools in molecular biology research.

A remotely operated drug delivery system with an electrolytic pump and a thermo-responsive valve

Implantable drug delivery devices are becoming attractive due to their abilities of targeted and controlled dose release. Currently, two important issues are functional lifetime and non-controlled drug diffusion. In this work, we present a drug delivery device combining an electrolytic pump and a thermo-responsive valve, which are both remotely controlled by an electromagnetic field (40.5 mT and 450 kHz). Our proposed device exhibits a novel operation mechanism for long-term therapeutic treatments using a solid drug in reservoir approach. Our device also prevents undesired drug liquid diffusions. When the electromagnetic field is on, the electrolysis-induced bubble drives the drug liquid towards the Poly (N-Isopropylacrylamide) (PNIPAM) valve that consists of PNIPAM and iron micro-particles. The heat generated by the iron micro-particles causes the PNIPAM to shrink, resulting in an open valve. When the electromagnetic field is turned off, the PNIPAM starts to swell. In the meantime, the bubbles are catalytically recombined into water, reducing the pressure inside the pumping chamber, which leads to the refilling of the fresh liquid from outside the device. A catalytic reformer is included, allowing more liquid refilling during the limited valve's closing time. The amount of body liquid that refills the drug reservoir can further dissolve the solid drug, forming a reproducible drug solution for the next dose. By repeatedly turning on and off the electromagnetic field, the drug dose can be cyclically released, and the exit port of the device is effectively controlled.

An adaptive biointerface from self-assembled functional peptides for tissue engineering

A self-assembled peptide-based biointerface is demonstrated with triple functional layers that can significantly improve the tissue self-healing process or prevent biofilm-mediated chronic inflammation. This smart biointerface is composed of three functional moieties (i.e., a cell-adhesive peptide, an infectious environment-responsive peptide, and an antifouling hexaethylene glycol (HEG) layer), and the resulting interface coated onto prosthetic replacements can smartly respond to the surrounding physiological or pathological microenvironment.

Role of arginine in mediating protein-carbon nanotube interactions

Arginine-rich proteins (e.g., lysozyme) or poly-L-arginine peptides have been suggested as solvating and dispersing agents for single-wall carbon nanotubes (CNTs) in water. In addition, protein structure-function in porous and hydrophobic materials is of broad interest. The amino acid residue, arginine (Arg(+)), has been implicated as an important mediator of protein/peptide-CNT interactions. To understand the structural and thermodynamic aspects of this interaction at the molecular level, we employ molecular dynamics (MD) simulations of the protein lysozyme in the interior of a CNT, as well as of free solutions of Arg(+) in the presence of a CNT. To dissect the Arg(+)-CNT interaction further, we also perform simulations of aqueous solutions of the guanidinium ion (Gdm(+)) and the norvaline (Nva) residue in the presence of a CNT. We show that the interactions of lysozyme with the CNT are mediated by the surface Arg(+) residues. The strong interaction of Arg(+) residue with the CNT is primarily driven by the favorable interactions of the Gdm(+) group with the CNT wall. The Gdm(+) group is not as well-hydrated on its flat sides, which binds to the CNT wall. This is consistent with a similar binding of Gdm(+) ions to a hydrophobic polymer. In contrast, the Nva residue, which lacks the Gdm(+) group, binds to the CNT weakly. We present details of the free energy of binding, molecular structure, and dynamics of these solutes on the CNT surface. Our results highlight the important role of Arg(+) residues in protein-CNT or protein-carbon-based material interactions. Such interactions could be manipulated precisely through protein engineering, thereby offering control over protein orientation and structure on CNTs, graphene, or other hydrophobic interfaces.

Fabrication of polymer brush surfaces with highly-ordered perfluoroalkyl side groups at the brush end and their antibiofouling properties

The protein-resistant performance was enhanced greatly by constructing a polymer brush surface with perfectly close-packed perfluoroalkyl groups.

Peptide-induced affinity binding of carbonic anhydrase to carbon nanotubes

Although affinity binding between short chain peptides and carbon nanotube (CNT) has been reported, little is known for the study of proteins with CNT recognition and specific binding capabilities. Herein, carbonic anhydrase (CA) was functionalized via protein fusion with a single-walled carbon nanotube (SWNTs)-binding peptide, thereby forming a bioactive protein with high affinity binding capability. TEM and AFM analyses showed that the fusion CA could firmly coat to SWNTs with a surface coverage over 51%, while the enzyme maintained its catalytic activity. Structural analysis revealed that slight conformation changes were induced as a result of the fusion; however, the affinity binding of CA to the hydrophobic surface of SWNTs restored the native structure of the protein, with the conformation of the SWNT-bound CA largely resembling that of the native parent enzyme. Interfacial interactions between the fusion CA and SWNT were further investigated with Raman spectrometry and microscopic analysis. The results suggested that such peptide-induced CNT-protein binding allows the development of bioactive hybrid materials with the native structures of the protein moieties largely undisrupted.

Ethylenediamine-assisted preparation of carbon nanofiber supported nickel oxide electrocatalysts for sensitive and durable detection of insulin

Facile preparation of a carbon nanofibers/nickel oxide nanocomposite and its sensitive and durable performance for insulin electrocatalytic oxidation.

Self-repairing nonfouling polyurethane coatings via 3D-grafting of PEG-b-PHEMA-b-PMPC copolymer

Long-lasting nonfouling polyurethane coatings via 3D-grafting of a triblock copolymer showed inhibition ability for the adhesion of protein and human platelets.

A Systematic Study of the Catalytic Behavior at Enzyme–Metal-Oxide Nanointerfaces

Metal-oxide nanoparticles with high surface area, controllable functionality and thermal and mechanical stability provide high affinity for enzymes when the next generation of biosensor applications are being considered. We report on the synthesis of metal-oxide-based nanoparticles (with different physical and chemical properties) using hydrothermal processing, photo-deposition and silane functionalization. Physical and chemical properties of the user-synthesized nanoparticles were investigated using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and Raman scattering, respectively. Thus, characterized metal-oxide-based nanoparticles served as nanosupports for the immobilization of soybean peroxidase enzyme (a model enzyme) through physical binding. The enzyme–nanosupport interface was evaluated to assess the optimum nanosupport characteristics that preserve enzyme functionality and its catalytic behavior. Our results showed that both the nanosupport geometry and its charge influence the functionality and catalytic behavior of the bio-metal-oxide hybrid system.

Fabrication and cyto-compatibility of Fe3O4/SiO2/graphene-CdTe QDs/CS nanocomposites for drug delivery

Synthesis of magnetic Fe3O4/SiO2/graphene-CdTe QDs/chitosan nanocomposites (FGQCs) is investigated with respect to their potential of improving the drug loading content above that of magnetic/fluorescent bifunctional nanocomposites. To evaluate the performance of the FGQCs, their surface morphology was thoroughly assessed. The in vitro interaction between the FGQCs and heptoma cell line smmc-7721 cells was observed for the first time by TEM ultrathin section imaging. At an excitation wavelength of 365 nm, the graphene-QDs exhibit a strong luminescence in aqueous environments. The loading content and entrapment efficiency of the FGQCs were 70% and 50%, respectively. The cytotoxicity of this novel drug delivery system was evaluated in vitro using heptoma cell line smmc-7721 and quantified by the 3-(4,5-dimethylthiazol-z-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. The results show that FGQCs are a promising new multifunctional material for drug delivery in biological and medical applications.

The devil and holy water: protein and carbon nanotube hybrids

Integrating carbon nanotubes (CNTs) with biological systems to form hybrid functional assemblies is an innovative research area with great promise for medical, nanotechnology, and materials science applications. The specifics of molecular recognition and catalytic activity of proteins combined with the mechanical and electronic properties of CNTs provides opportunities for physicists, chemists, biologists, and materials scientists to understand and develop new nanomachines, sensors, or any of a number of other molecular assemblies. Researchers know relatively little about the structure, function, and spatial orientation of proteins noncovalently adsorbed on CNTs, yet because the interaction of CNTs with proteins depends strongly on the tridimensional structure of the proteins, many of these questions can be answered in simple terms. In this Account, we describe recent research investigating the properties of CNT/protein hybrids. Proteins act to solvate CNTs and may sort them according to diameter or chirality. In turn, CNTs can support and immobilize enzymes, creating functional materials. Additional applications include proteins that assemble ordered hierarchical objects containing CNTs, and CNTs that act as protein carriers for vaccines, for example. Protein/CNT hybrids can form bioscaffolds and can serve as therapeutic and imaging materials. Proteins can detect CNTs or coat them to make them biocompatible. One of the more challenging applications for protein/CNT hybrids is to make CNT substrates for cell growth and neural interfacing applications. The challenge arises from the structures' interactions with living cells, which poses questions surrounding the (nano)toxicology of CNTs and whether and how CNTs can detect biological processes or sense them as they occur. The surface chemistry of CNTs and proteins, including interactions such as π-π stacking interactions, hydrophobic interactions, surfactant-like interactions, and charge-π interactions, governs the wealth of structures, processes, and functions that appear when such different types of molecules interact. Each residue stars in one of two main roles, and understanding which residues are best suited for which type of interaction can lead to the design of new hybrids. Nonlocally, the peptide or protein primary, secondary, and tertiary structures govern the binding of proteins by CNTs. The conjugation of proteins with CNTs presents some serious difficulties both experimentally and culturally (such as bridging the "jargon barrier" across disciplines). The intersection of these fields lies between communities characterized by distinctly different approaches and methodologies. However, the examples of this Account illustrate that when this barrier is overcome, the exploitation of hybrid CNT-protein systems offers great potential.

Carbon Nanotubes: A Review on Structure and Their Interaction with Proteins

Carbon nanotubes (CNTs) are allotropes of carbon with a nanostructure that can have a length-to-diameter ratio greater than 1,000,000. Techniques have been developed to produce nanotubes in sizeable quantities, including arc discharge, laser ablation, and chemical vapor deposition. Developments in the past few years have illustrated the potentially revolutionizing impact of nanomaterials, especially in biomedical imaging, drug delivery, biosensing, and the design of functional nanocomposites. Methods to effectively interface proteins with nanomaterials for realizing these applications continue to evolve. The high surface-to-volume ratio offered by nanoparticles resulted in the concentration of the immobilized entity being considerably higher than that afforded by other materials. There has also been an increasing interest in understanding the influence of nanomaterials on the structure and function of proteins. Various immobilization methods have been developed, and in particular, specific attachment of enzymes on carbon nanotubes has been an important focus of attention. With the growing attention paid to cascade enzymatic reaction, it is possible that multienzyme coimmobilization would be one of the next goals in the future. In this paper, we focus on advances in methodology for enzyme immobilization on carbon nanotubes.

Cell micropatterning on superhydrophobic diamond nanowires

Cell micropatterning was achieved in a spatially controlled manner based on heterogeneously wetted superhydrophilic/superhydrophobic diamond nanowire (NW) surfaces. Diamond NWs were synthesized on boron-doped diamond substrates using reactive ion etching and functionalized with octadecyltrichlorosilane to achieve superhydrophobicity. Superhydrophilic motifs of 400×400 μm(2) and 10×10 μm(2) single cell-sized motifs, surrounded by superhydrophobic regions, were then generated by selectively exposing the substrates to UV light. This design allowed successful patterning of single HeLa and MCF-10A cells within the superhydrophilic regions without additional surface modification. To add a further level of complexity, micropatterned co-cultures were obtained using bovine serum albumin to promote cell adhesion. This method is simple and does not require any complicated processing steps such as mask deposition or template removal. Potential applications are in the development of cell-based biological assays in well-controlled and biologically relevant environments.

Superhydrophobicity for antifouling microfluidic surfaces

Fouling of surfaces is often problematic in microfluidic devices, particularly when using protein or -enzymatic solutions. Various coating methods have been investigated to reduce the tendency for protein molecules to adsorb, mostly relying on hydrophobic surface chemistry or the antifouling ability of -polyethylene glycol. Here we present the potential use of superhydrophobic surfaces to not only reduce the amount of surface contamination but also to induce self-cleaning under flow conditions. The methodology is presented in order to prepare superhydrophobic surface coatings having micro- and nanoscale feature dimensions, as well as a step-by-step guide to quantify adsorbed protein down to nanogram levels. The fabrication of these surfaces as coatings via silica sol-gel and copper nano-hair growth is presented, which can be applied within microfluidic devices manufactured from various materials.

Grafting polymer brushes on biomimetic structural surfaces for anti-algae fouling and foul release

Sylgard-184 silicone elastomer negative replica and resorcinol-formaldehyde (RF) positive replica were made by biomimicking the patterns of natural Trifolium and three other kinds of leaves using the micromolding lithography. An effective antifouling (AF) polymer, poly(3-sulfopropyl methacrylate) (PSPMA), was then grafted on these replica surfaces via the surface-initiated atom transfer radical polymerization (SI-ATRP). The AF property of the modified biomimetic surfaces was tested via the settlement assay with two microalgae in different sizes, and their fouling-release (FR) property was evaluated by the removal assay. The results indicate that the structure of microspines on Trifolium leaf can inhibit settlement of microalgae and facilitate the cell release. The AF property was improved by modification with PSPMA brushes.