Rising to the surface: capturing and detecting bacteria by rationally-designed surfaces

Analytical microbiology has made substantial progress since its conception, starting from potato slices, through selective agar media, to engineered surfaces modified with capture probes. While the latter represents the dominant approach in designing sensors for bacteria detection, the importance of sensor surface properties is frequently ignored. Herein, we highlight their significant role in the complex process of bacterial transition from planktonic to sessile, representing the first and critical step in bacteria detection. We present the main surface features and discuss their effect on the bio-solid interface and the resulting sensing capabilities for both flat and particulate systems. The concepts of rationally-designed surfaces for enhanced bacterial detection are presented with recent examples of sensors (capture probe-free) relying solely on surface cues.

Carbon-based glyco-nanoplatforms: towards the next generation of glycan-based multivalent probes

Cell surface carbohydrates mediate a wide range of carbohydrate-protein interactions key to healthy and disease mechanisms. Many of such interactions are multivalent in nature and in order to study these processes at a molecular level, many glycan-presenting platforms have been developed over the years. Among those, carbon nanoforms such as graphene and their derivatives, carbon nanotubes, carbon dots and fullerenes, have become very attractive as biocompatible platforms that can mimic the multivalent presentation of biologically relevant glycosides. The most recent examples of carbon-based nanoplatforms and their applications developed over the last few years to study carbohydrate-mediate interactions in the context of cancer, bacterial and viral infections, among others, are highlighted in this review.

Surface Self-Assembly Construction of Therapeutic Contact Lens with Bacterial "Kill-Releasing" and Drug-Reloading Capabilities for Efficient Bacterial Keratitis Treatment

Bacterial keratitis, an ophthalmic emergency, can cause corneal perforation and even endophthalmitis, thus leading to severe visual impairment. To achieve effective treatment of bacterial keratitis, good bioavailability of antimicrobial drugs on the ocular surface is desired. In this investigation, a layer-by-layer (LBL) self-assembly combined with the host-guest recognition was used to construct an antibacterial coating on the surface of corneal contact lens (CLs) to improve drug bioavailability and achieve successful treatment of bacterial keratitis. First, a radical copolymerization of acrylic acid (AA) and 1-adamantan-1-ylmethyl acrylate (AdA) was carried out to synthesize a polyanionic copolymer P(AA-co-AdA) (defined as PAcA). Then, PAcA copolymer combined with poly(ethyleneimine) (PEI) was used for a layer-by-layer (LBL) self-assembly to fabricate multilayer films on the surface of CLs. An antibacterial conjugate, β-cyclodextrin-levofloxacin (β-CD-LEV), was successfully synthesized and utilized to generate antibacterial coating through a host-guest interaction between AdA and β-CD-LEV. The antibacterial ability and treatment effect of bacterial keratitis was evaluated by in vitro assay and in vivo test in an animal model of staphylococcal keratitis, demonstrating that the antibacterial coating had good antibacterial and germicidal efficacy both in vivo and in vitro. We believe that this work will provide a promising strategy for the treatment of bacterial keratitis.

Layer-by-layer assembly methods and their biomedical applications

Various biomedical applications arising due to the development of different LbL assembly methods with unique process properties.

A Dual-Responsive Peptide-Based Smart Biointerface with Biomimetic Adhesive Behaviors for Bacterial Isolation

As mimics of the extracellular matrix, surfaces with the capability of capturing and releasing specific cells in a smart and controllable way play an important role in bacterial isolation. In this work, we fabricated a dual-responsive smart biointerface via peptide self-assembly and reversible covalent chemistry biomimetic adhesion behavior for bacterial isolation. Compared with that of the biointerface based on a single reversible covalent bond, the bacterial enrichment efficiency obtained in this work was 2.3 times higher. Furthermore, the release of bacteria from the surface could be achieved by dual responsiveness (sugar and enzyme), which makes the biointerface more adaptable and compatible under different conditions. Finally, the reusability of the biointerface was verified via peptide self-assembly and the regenerated smart biointerface still showed good bacterial capture stability and excellent release efficiency, which was highly anticipated to be more widely applied in biomaterial science and biomedicine in the future.

Long-term, synergistic and high-efficient antibacterial polyacrylonitrile nanofibrous membrane prepared by "one-pot" electrospinning process

Enhancing long-term antibacterial activity of membrane materials is an effective strategy to reduce biological contamination. Herein, we developed a long-term, synergistic antibacterial polyacrylonitrile (PAN) nanofiber membrane by a "one-pot" electrospinning process. In the reaction solution of PAN and N, N-dimethylformamide (DMF), silver-silicon dioxide nanoparticles (Ag@SiO₂ NPs) are in-situ synthesized and stabilized using silane coupling agent; and [2-(methacryloyloxy)-ethyl] trimethylammonium chloride (MT) monomers are then in-situ cross-linked to obtain a polyquaternary ammonium salt (PMT). Subsequently, the casting solution is directly used to fabricate Ag@SiO₂/PMT-PAN nanofibrous membrane (NFM) via electrospinning. The antibacterial activity, reusability, synergy effect and biological safety of the Ag@SiO₂/PMT-PAN NFM are systematically investigated, and the synergistic antibacterial mechanism is also explored. Even at very low (0.3 wt%) content of silver, the Ag@SiO₂/PMT-PAN NFM exhibits excellent antibacterial activity against E. coli (99%) and S. aureus (99%). Also, the antibacterial ability of the NFM remains the same level after three cycles of antibacterial processes with the efficient synergy effects of Ag@SiO₂ and PMT components. When the Ag@SiO₂/PMT-PAN contacts with bacteria, the PMT attracts and kills the bacteria through electrostatic action. The bacteria with damaged cell membranes are deposited on the nanofibrous membrane, which could greatly promote the release of Ag⁺ and further enhance the antibacterial activity. Moreover, L929 fibroblasts are co-cultured with the extract of 4 mg/mL Ag@SiO₂/PMT-PAN for 5 days, which exhibits a low cytotoxicity with a cell proliferation ratio of 95%. This work opens new pathways for developing long-term effective and synergistic antibacterial nanofibrous membrane materials to prevent infections associated with biomedical equipment.

Dual-Functional Surfaces Based on an Antifouling Polymer and a Natural Antibiofilm Molecule: Prevention of Biofilm Formation without Using Biocides

Pathogenic biofilms formed on the surfaces of implantable medical devices and materials pose an urgent global healthcare problem. Although conventional antibacterial surfaces based on bacteria-repelling or bacteria-killing strategies can delay biofilm formation to some extent, they usually fail in long-term applications, and it remains challenging to eradicate recalcitrant biofilms once they are established and mature. From the viewpoint of microbiology, a promising strategy may be to target the middle stage of biofilm formation including the main biological processes involved in biofilm development. In this work, a dual-functional antibiofilm surface is developed based on copolymer brushes of 2-hydroxyethyl methacrylate (HEMA) and 3-(acrylamido)phenylboronic acid (APBA), with quercetin (Qe, a natural antibiofilm molecule) incorporated via acid-responsive boronate ester bonds. Due to the antifouling properties of the hydrophilic poly(HEMA) component, the resulting surface is able to suppress bacterial adhesion and aggregation in the early stages of contact. A few bacteria are eventually able to break through the protection of the anti-adhesion layer leading to bacterial colonization. In response to the resulting decrease in the pH of the microenvironment, the surface could then release Qe to interfere with the microbiological processes related to biofilm formation. Compared to bactericidal and anti-adhesive surfaces, this dual-functional surface showed significantly improved antibiofilm performance to prevent biofilm formation involving both Gram-negative Pseudomonas aeruginosa and Gram-positive Staphylococcus aureus for up to 3 days. In addition, both the copolymer and Qe are negligibly cytotoxic, thereby avoiding possible harmful effects on adjacent normal cells and the risk of bacterial resistance. This dual-functional design approach addresses the different stages of biofilm formation, and (in accordance with the growth process of the biofilm) allows sequential activation of the functions without compromising the viability of adjacent normal cells. A simple and reliable solution may thus be provided to the problems associated with biofilms on surfaces in various biomedical applications.

Evolution of Supramolecular Systems Towards Next-Generation Biosensors

Supramolecular materials, which rely on dynamic non-covalent interactions, present a promising approach to advance the capabilities of currently available biosensors. The weak interactions between supramolecular monomers allow for adaptivity and responsiveness of supramolecular or self-assembling systems to external stimuli. In many cases, these characteristics improve the performance of recognition units, reporters, or signal transducers of biosensors. The facile methods for preparing supramolecular materials also allow for straightforward ways to combine them with other functional materials and create multicomponent sensors. To date, biosensors with supramolecular components are capable of not only detecting target analytes based on known ligand affinity or specific host-guest interactions, but can also be used for more complex structural detection such as chiral sensing. In this Review, we discuss the advancements in the area of biosensors, with a particular highlight on the designs of supramolecular materials employed in analytical applications over the years. We will first describe how different types of supramolecular components are currently used as recognition or reporter units for biosensors. The working mechanisms of detection and signal transduction by supramolecular systems will be presented, as well as the important hierarchical characteristics from the monomers to assemblies that contribute to selectivity and sensitivity. We will then examine how supramolecular materials are currently integrated in different types of biosensing platforms. Emerging trends and perspectives will be outlined, specifically for exploring new design and platforms that may bring supramolecular sensors a step closer towards practical use for multiplexed or differential sensing, higher throughput operations, real-time monitoring, reporting of biological function, as well as for environmental studies.

Host-Pathogen Adhesion as the Basis of Innovative Diagnostics for Emerging Pathogens

Infectious diseases are an existential health threat, potentiated by emerging and re-emerging viruses and increasing bacterial antibiotic resistance. Targeted treatment of infectious diseases requires precision diagnostics, especially in cases where broad-range therapeutics such as antibiotics fail. There is thus an increasing need for new approaches to develop sensitive and specific in vitro diagnostic (IVD) tests. Basic science and translational research are needed to identify key microbial molecules as diagnostic targets, to identify relevant host counterparts, and to use this knowledge in developing or improving IVD. In this regard, an overlooked feature is the capacity of pathogens to adhere specifically to host cells and tissues. The molecular entities relevant for pathogen–surface interaction are the so-called adhesins. Adhesins vary from protein compounds to (poly-)saccharides or lipid structures that interact with eukaryotic host cell matrix molecules and receptors. Such interactions co-define the specificity and sensitivity of a diagnostic test. Currently, adhesin-receptor binding is typically used in the pre-analytical phase of IVD tests, focusing on pathogen enrichment. Further exploration of adhesin–ligand interaction, supported by present high-throughput “omics” technologies, might stimulate a new generation of broadly applicable pathogen detection and characterization tools. This review describes recent results of novel structure-defining technologies allowing for detailed molecular analysis of adhesins, their receptors and complexes. Since the host ligands evolve slowly, the corresponding adhesin interaction is under selective pressure to maintain a constant receptor binding domain. IVD should exploit such conserved binding sites and, in particular, use the human ligand to enrich the pathogen. We provide an inventory of methods based on adhesion factors and pathogen attachment mechanisms, which can also be of relevance to currently emerging pathogens, including SARS-CoV-2, the causative agent of COVID-19.

Capture and Kill: Selective Eradication of Target Bacteria by a Flexible Bacteria-Imprinted Chip

This paper reports an antibacterial chip that can selectively capture bacteria and kill them using low-voltage DC electricity. We prepared a bacteria-imprinted, flexible PDMS chip that can separate target bacteria from suspensions with high selectivity. The chip contained integrated electrodes that can kill the captured bacteria within 10 min by applying a low DC voltage. The used chip could be easily regenerated by solution immersion. Meanwhile, the PDMS chip showed good biocompatibility and inhibited adhesion of human blood cells. Our work points to a new strategy to address pathogenic bacterial contamination and infection.

Photothermal bactericidal surfaces: killing bacteria using light instead of biocides

Recent developments of photothermal bactericidal surfaces based on immobilized photothermal agents to kill bacteria through hyperthermia effects are reviewed.

Design and applications of protein delivery systems in nanomedicine and tissue engineering

Proteins are biological macromolecules involved in a wide range of biological functions, which makes them very appealing as therapeutics agents. Indeed, compared to small molecule drugs, their endogenous nature ensures their biocompatibility and biodegradability, they can be used in a large range of applications and present a higher specificity and activity. However, they suffer from unfolding, enzymatic degradation, short half-life and poor membrane permeability. To overcome such drawbacks, the development of protein delivery systems to protect, carry and deliver them in a controlled way have emerged importantly these last years. In this review, the formulation of a wide panel of protein delivery systems either in the form of polymer or inorganic nanoengineered colloids and scaffolds are presented and the protein loading and release mechanisms are addressed. A section is also dedicated to the detection of proteins and the characterization methods of their release. Then, the main protein delivery systems developed these last three years for anticancer, tissue engineering or diabetes applications are presented, as well as the major in vivo models used to test them. The last part of this review aims at presenting the perspectives of the field such as the use of protein-rich material or the sequestration of proteins. This part will also deal with less common applications and gene therapy as an indirect method to deliver protein.

A Reusable Column Method Using Glycopolymer-Functionalized Resins for Capture-Detection of Proteins and Escherichia coli

The use of glycopolymer-functionalized resins (Resin-Glc), as a solid support, in column mode for bacterial/protein capture and quantification is explored. The Resin-Glc is synthesized from commercially available chloromethylated polystyrene resin and glycopolymer, and is characterized by fourier transform infrared spectroscopy, thermogravimetry, and elemental analysis. The percentage of glycopolymer functionalized on Resin-Glc is accounted to be 5 wt%. The ability of Resin-Glc to selectively capture lectin, Concanavalin A, over Peanut Agglutinin, reversibly, is demonstrated for six cycles of experiments. The bacterial sequestration study using SYBR (Synergy Brands, Inc.) Green I tagged Escherichia coli/Staphylococcus aureus reveals the ability of Resin-Glc to selectively capture E. coli over S. aureus. The quantification of captured cells in the column is carried out by enzymatic colorimetric assay using methylumbelliferyl glucuronide as the substrate. The E. coli capture studies reveal a consistent capture efficiency of 10⁵  CFU (Colony Forming Units) g^-1 over six cycles. Studies with spiked tap water samples show satisfactory results for E. coli cell densities ranging from 10² to 10⁷  CFU mL^-1 . The method portrayed can serve as a basis for the development of a reusable solid support in capture and detection of proteins and bacteria.

Cyclodextrin-Based Functional Glyconanomaterials

Cyclodextrins (CDs) have long occupied a prominent position in most pharmaceutical laboratories as "off-the-shelve" tools to manipulate the pharmacokinetics of a broad range of active principles, due to their unique combination of biocompatibility and inclusion abilities. The development of precision chemical methods for their selective functionalization, in combination with "click" multiconjugation procedures, have further leveraged the nanoscaffold nature of these oligosaccharides, creating a direct link between the glyco and the nano worlds. CDs have greatly contributed to understand and exploit the interactions between multivalent glycodisplays and carbohydrate-binding proteins (lectins) and to improve the drug-loading and functional properties of nanomaterials through host-guest strategies. The whole range of capabilities can be enabled through self-assembly, template-assisted assembly or covalent connection of CD/glycan building blocks. This review discusses the advancements made in this field during the last decade and the amazing variety of functional glyconanomaterials empowered by the versatility of the CD component.

Aerosol-to-Hydrosol Sampling and Simultaneous Enrichment of Airborne Bacteria For Rapid Biosensing

Rapid monitoring of biological particulate matter (Bio-PM, bioaerosols) requires an enrichment technique for concentrating the Bio-PM dispersed in the air into a small volume of liquid. In this study, an electrostatic air sampler is employed to capture aerosolized test bacteria in a carrier liquid (aerosol-to-hydrosol (ATH) enrichment). Simultaneously, the captured bacteria are carried into a fluid channel for hydrosol-to-hydrosol (HTH) enrichment with Concanavalin A coated magnetic particles (CMPs). The ATH enrichment capacity of the air sampler was evaluated with an aerosol particle counter for the following test bacteria: Staphylococcus aureus, Bacillus cereus, Escherichia coli, and Acinetobacter baumannii. Then, the HTH enrichment capacity for the ATH-collected sample was evaluated using the colony-counting method, scanning electron microscopy based image analysis, fluorescence microscopy, electrical current measurements, and real-time quantitative polymerase chain reaction (qPCR). The ATH and HTH enrichment capacities for the given operation conditions were up to 80 000 and 14.9, respectively, resulting in a total enrichment capacity of up to 1.192 × 10⁶. Given that air-to-liquid enrichment required to prepare detectable bacterial samples for real-time qPCR in field environments is of the order of at least 10⁶, our method can be used to prepare a detectable sample from low-concentration airborne bacteria in the field and significantly reduce the time required for Bio-PM monitoring because of its enrichment capacity.

New solutions to capture and enrich bacteria from complex samples

Current solutions to diagnose bacterial infections though reliable are often time-consuming, laborious and need a specific laboratory setting. There is an unmet need for bedside accurate diagnosis of infectious diseases with a short turnaround time. Moreover, low-cost diagnostics will greatly benefit regions with poor resources. Immunoassays and molecular techniques have been used to develop highly sensitive diagnosis solutions but retaining many of the abovementioned limitations. The detection of bacteria in a biological sample can be enhanced by a previous step of capture and enrichment. This will ease the following process enabling a more sensitive detection and increasing the possibility of a conclusive identification in the downstream diagnosis. This review explores the latest developments regarding the initial steps of capture and enrichment of bacteria from complex samples with the ultimate goal of designing low cost and reliable diagnostics for bacterial infections. Some solutions use specific ligands tethered to magnetic constructs for separation under magnetic fields, microfluidic platforms and engineered nano-patterned surfaces to trap bacteria. Bulk acoustics, advection and nano-filters comprise some of the most innovative solutions for bacteria enrichment.

"Three-in-One" SERS Adhesive Tape for Rapid Sampling, Release, and Detection of Wound Infectious Pathogens

The traditional colony culture method for detection of pathogens is subjected to the laborious and tedious experimental procedure, which limits its application in point-of-care (POC) testing and quick diagnosis. This work designs an intelligent adhesive tape as a "three-in-one" platform for rapid sampling, photocontrolled release, and surface-enhanced Raman scattering (SERS) detection of pathogens from infected wounds. This tape is constructed by encapsulating densely packed gold nanostars as SERS substrates between two pieces of graphene and modified with a synthetic o-nitrobenzyl derivative molecule to form an artificial biointerface for highly efficient pathogen capture via electrostatic interaction. The captured targets can be conveniently released onto a solid culture medium by UV cleavage of o-nitrobenzyl moiety for pathogen growth and in situ SERS detection. As a proof of strategy, this "three-in-one" platform has been used for detecting the concurrent infection of Pseudomonas aeruginosa and Staphylococcus aureus by pasting the tape on a skin burn wound. The impressive detection performance with an analytical time of only several hours for these pathogens at an early growth stage demonstrates its great potential as a POC testing device for health care.

Reversible, High-Affinity Surface Capturing of Proteins Directed by Supramolecular Assembly

The ability to design surfaces with reversible, high-affinity protein binding sites represents a significant step forward in the advancement of analytical methods for diverse biochemical and biomedical applications. Herein, we report a dynamic supramolecular strategy to directly assemble proteins on surfaces based on multivalent host-guest interactions. The host-guest interactions are achieved by one-step nanofabrication of a well-oriented β-cyclodextrin host-derived self-assembled monolayer on gold (β-CD-SAM) that forms specific inclusion complexes with hydrophobic amino acids located on the surface of the protein. Cytochrome c, insulin, α-chymotrypsin, and RNase A are used as model guest proteins. Surface plasmon resonance and static time-of-flight secondary ion mass spectrometry studies demonstrate that all four proteins interact with the β-CD-SAM in a specific manner via the hydrophobic amino acids on the surface of the protein. The β-CD-SAMs bind the proteins with high nanomolar to single-digit micromolar dissociation constants ( K_D). Importantly, while the proteins can be captured with high affinity, their release from the surface can be achieved under very mild conditions. Our results expose the great advantages of using a supramolecular approach for controlling protein immobilization, in which the strategy described herein provides unprecedented opportunities to create advanced bioanalytic and biosensor technologies.

Zwitterionic Reduction-Activated Supramolecular Prodrug Nanocarriers for Photodynamic Ablation of Cancer Cells

An adamantane-containing zwitterionic copolymer poly(2-(methacryloyloxy)ethyl phosphorylcholine)- co-poly(2-(methacryloyloxy)ethyl adamantane-1-carboxylate) (poly(MPC- co-MAda)) was prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization. The hydrophobic photosensitizer chlorin e6 (Ce6) was conjugated to β-cyclodextrin (β-CD) by glutathione (GSH)-sensitive disulfide bonds. The Ce6 conjugated supramolecular prodrug nanocarriers were fabricated due to the host-guest interaction between adamantane and β-CD, which was confirmed by dynamic light scattering (DLS) and transmission electron microscopy (TEM). The Ce6 conjugated prodrug nanocarriers showed reduction-responsive release of Ce6, which could result in the activation of Ce6. The generation of cytotoxic reactive oxygen species (ROS) was significantly enhanced due to the activation of Ce6. In additiona, the Ce6 conjugated prodrug nanocarriers could effectively inhibit the proliferation of cancer cells upon light irradiation.

Responsive and Synergistic Antibacterial Coatings: Fighting against Bacteria in a Smart and Effective Way

Antibacterial coatings that eliminate initial bacterial attachment and prevent subsequent biofilm formation are essential in a number of applications, especially implanted medical devices. Although various approaches, including bacteria-repelling and bacteria-killing mechanisms, have been developed, none of them have been entirely successful due to their inherent drawbacks. In recent years, antibacterial coatings that are responsive to the bacterial microenvironment, that possess two or more killing mechanisms, or that have triggered-cleaning capability have emerged as promising solutions for bacterial infection and contamination problems. This review focuses on recent progress on three types of such responsive and synergistic antibacterial coatings, including i) self-defensive antibacterial coatings, which can "turn on" biocidal activity in response to a bacteria-containing microenvironment; ii) synergistic antibacterial coatings, which possess two or more killing mechanisms that interact synergistically to reinforce each other; and iii) smart "kill-and-release" antibacterial coatings, which can switch functionality between bacteria killing and bacteria releasing under a proper stimulus. The design principles and potential applications of these coatings are discussed and a brief perspective on remaining challenges and future research directions is presented.

Fabrication of Supramolecular Bioactive Surfaces via β-Cyclodextrin-Based Host-Guest Interactions

Supramolecular host-guest interactions provide a facile and versatile basis for the construction of sophisticated structures and functional assemblies through specific molecular recognition of host and guest molecules to form inclusion complexes. In recent years, these interactions have been exploited as a means of attaching bioactive molecules and polymers to solid substrates for the fabrication of bioactive surfaces. Using a common host molecule, β-cyclodextrin (β-CD), and various guest molecules as molecular building blocks, we fabricated several types of bioactive surfaces with multifunctionality and/or function switchability via host-guest interactions. Other groups have also taken this approach, and several intelligent designs have been developed. The results of these investigations indicate that, compared to the more common covalent bonding-based methods for attachment of bioactive ligands, host-guest based methods are simple, more broadly ("universally") applicable, and allow convenient renewal of bioactivity. In this Spotlight on Applications, we review and summarize recent developments in the fabrication of supramolecular bioactive surfaces via β-CD-based host-guest interactions. The main focus is on the work from our laboratory, but highlights on work from other groups are included. Applications of the materials are also emphasized. These surfaces can be categorized into three types based on: (i) self-assembled monolayers, (ii) polymer brushes, and (iii) multilayered films. The host-guest strategy can be extended from material surfaces to living cell surfaces, and work along these lines is also reviewed. Finally, a brief perspective on the developments of supramolecular bioactive surfaces in the future is presented.

Sweet Switch: Sugar-Responsive Bioactive Surfaces Based on Dynamic Covalent Bonding

Smart bioactive surfaces that can modulate interactions with biological systems are of great interest. In this work, a surface with switchable bioactivity in response to sugars has been developed. It is based on dynamic covalent bonding between phenylboronic acid (PBA) and secondary hydroxyls on the "wide" rim of β-cyclodextrin (β-CD). The system reported consists of gold surface modified with PBA-containing polymer brushes and a series of functional β-CD derivatives conjugated to diverse bioactive ligands (CD-X). CD-X molecules are attached to the surface to give specified bioactivity such as capture of a specific protein or killing of attached bacteria. Subsequent treatment with cis-diol containing biomolecules having high affinity for PBA (e.g. fructose) leads to the release of CD-X together with the captured proteins, killed bacteria, and so forth from the surface. The surface bioactivity is thereby "turned off". Effectively, this constitutes an on-off bioactivity switch in a mild and noninvasive way, which has the potential in the design of dynamic bioactive surfaces for biomedical applications.

A facile method to prepare a versatile surface coating with fibrinolytic activity, vascular cell selectivity and antibacterial properties

Clot and thrombus formation on surfaces that come into contact with blood is still the most serious problem for blood contacting devices. Despite many years of continuous efforts in developing hemocompatible materials, it is still of great interest to develop multifunctional materials to enable vascular cell selectivity (to favor rapid endothelialization while inhibiting smooth muscle cell proliferation) and improve hemocompatibility. In addition, biomaterial-associated infections also cause the failure of biomedical implants and devices. However, it remains a challenging task to design materials that are multifunctional, since one of their functions will usually be compromised by the introduction of another function. In the present work, the gold substrate was first layer-by-layer (LbL) deposited with a multilayered polyelectrolyte film containing chitosan (positively charged) and a copolymer of sodium 4-vinylbenzenesulfonate (SS) and the "guest" adamantane monomer 1-adamantan-1-ylmethyl methacrylate (P(SS-co-Ada), negatively charged) via electro-static interactions, referred to as Au-LbL. The chitosan and P(SS-co-Ada) were intended to provide, respectively, resistance to bacteria and heparin-like properties. Then, "host" β-cyclodextrin derivatives bearing seven lysine ligands (CD-L) were immobilized on the Au-LbL surface by host-guest interactions between adamantane residues and CD-L, referred to as Au-LbL/CD-L. Finally, a versatile surface coating with fibrinolytic activity (lysis of nascent clots), vascular cell selectivity and antibacterial properties was developed.

A highly efficient bactericidal surface based on the co-capture function and photodynamic sterilization

Bacterial infection is posing a great threat to human life, and constructing a platform to capture or kill the bacteria attached on a material surface is of particular significance.

A supramolecular approach for versatile biofunctionalization of magnetic nanoparticles

A convenient and versatile approach for biofunctionalization of magnetic nanoparticles was developed based on supramolecular host–guest interaction.

Bacterial adaptability of enzyme and pH dual-responsive surface for infection resistance

A major challenge in antibacterial surface preparation is the elaborated implement of controlled antibacterial agent delivery on demand. We present a bacterial hyaluronidase (HAase) and pH dual-responsive antimicrobial surface, with excellent biocompatibility under physiological conditions and releasing vancomycin (Van) once bacteria invade.

Microfluidic channels with renewable and switchable biological functionalities based on host–guest interactions

Microfluidic channels with renewable and switchable biological functionalities were prepared using host–guest interactions.

Self-assembled proteinaceous wound dressings attenuate secondary trauma and improve wound healing in vivo

Stimuli-responsive gauze coated with a phase-transitioned lysozyme nanofilm (PTLF@gauze) has been developed, which exhibits great potential for clinical applications by reducing secondary trauma and relieving the pain of patients.

Smart Antibacterial Surfaces with Switchable Bacteria-Killing and Bacteria-Releasing Capabilities

The attachment and subsequent colonization of bacteria on the surfaces of synthetic materials and devices lead to serious problems in both human healthcare and industrial applications. Therefore, antibacterial surfaces that can prevent bacterial attachment and biofilm formation have been a long-standing focus of considerable interest and research efforts. Recently, a promising "kill-release" strategy has been proposed and applied to construct so-called smart antibacterial surfaces, which can kill bacteria attached to their surface and then undergo on-demand release of the dead bacteria and other debris to reveal a clean surface under an appropriate stimulus, thereby maintaining effective long-term antibacterial activity. This Review focuses on the recent progress (particularly over the past 5 years) on such smart antibacterial surfaces. According to the different design strategies, these surfaces can be divided into three categories: (i) "K + R"-type surfaces, which have both a killing unit and a releasing unit; (ii) "K → R"-type surfaces, which have a surface-immobilized killing unit that can be switched to perform a releasing function; and (iii) "K + (R)"-type surfaces, which have only a killing unit but can release dead bacteria upon the addition of a release solution. In the end, a brief perspective on future research directions and the major challenges in this promising field is also presented.

Surface-Assembled Mechanically Interlocked Architectures

Since the advent of supramolecular chemistry, there has been keen interest in the synthesis of interlocked molecules, given their unique potential to act as receptors, molecular machines and even motors. Despite advances in the complexity of molecular machines that can be synthesised and operated in solution, reports of the operation or even attachment of complex supramolecular systems on solid surfaces are less common. Synthetic challenges and a lack of adequate characterisation techniques to monitor the thermodynamic and kinetic influences governing assembly at the solution-surface interface has slowed progress in this area of research. This Review looks at the developments in the field of covalently assembled interlocked architectures on gold, silica and polymer surfaces, highlighting the differences observed between solution and surface assembly of these unique structures.

Supramolecular Platform with Switchable Multivalent Affinity: Photo-Reversible Capture and Release of Bacteria

Surfaces having dynamic control of interactions at the biological system-material interface are of great scientific and technological interest. In this work, a supramolecular platform with switchable multivalent affinity was developed to efficiently capture bacteria and on-demand release captured bacteria in response to irradiation with light of different wavelengths. The system consists of a photoresponsive self-assembled monolayer containing azobenzene (Azo) groups as guest and β-cyclodextrin (β-CD)-mannose (CD-M) conjugates as host with each CD-M containing seven mannose units to display localized multivalent carbohydrates. Taking the advantage of multivalent effect of CD-M, this system exhibited high capacity and specificity for the capture of mannose-specific type 1-fimbriated bacteria. Moreover, ultraviolet (UV) light irradiation caused isomerization of the Azo groups from trans-form to cis-form, resulting in the dissociation of the host-guest Azo/CD-M inclusion complexes and localized release of the captured bacteria. The capture and release process could be repeated for multiple cycles, suggesting good reproducibility. This platform provides the basis for development of reusable biosensors and diagnostic devices for the detection and measurement of bacteria and exhibits great potential for use as a standard protocol for the on-demand switching of surface functionalities.

Promoting neural differentiation of embryonic stem cells using β-cyclodextrin sulfonate

Promoting neural differentiation of embryonic stem cells using inclusion complexes formed between β-cyclodextrin sulfonate and all-trans retinoic acid.