Direct grafting of anti-fouling polyglycerol layers to steel and other technically relevant materials

Selective Quantification of Bacteria in Mixtures by Using Glycosylated Polypyrrole/Hydrogel Nanolayers

Here, we present a covalent nanolayer system that consists of a conductive and biorepulsive base layer topped by a layer carrying biorecognition sites. The layers are built up by electropolymerization of pyrrole derivatives that either carry polyglycerol brushes (for biorepulsivity) or glycoside moieties (as biorecognition sites). The polypyrrole backbone makes the resulting nanolayer systems conductive, opening the opportunity for constructing an electrochemistry-based sensor system. The basic concept of the sensor exploits the highly selective binding of carbohydrates by certain harmful bacteria, as bacterial adhesion and infection are a major threat to human health, and thus, a sensitive and selective detection of the respective bacteria by portable devices is highly desirable. To demonstrate the selectivity, two strains of Escherichia coli were selected. The first strain carries type 1 fimbriae, terminated by a lectin called FimH, which recognizes α-d-mannopyranosides, which is a carbohydrate that is commonly found on endothelial cells. The otherE. coli strain was of a strain that lacked this particular lectin. It could be demonstrated that hybrid nanolayer systems containing a very thin carbohydrate top layer (2 nm) show the highest discrimination (factor 80) between the different strains. Using electrochemical impedance spectroscopy, it was possible to quantify in vivo the type 1-fimbriated E. coli down to an optical density of OD600 = 0.0004 with a theoretical limit of 0.00005. Surprisingly, the selectivity and sensitivity of the sensing remained the same even in the presence of a large excess of nonbinding bacteria, making the system useful for the rapid and selective detection of pathogens in complex matrices. As the presented covalent nanolayer system is modularly built, it opens the opportunity to develop a broad band of mobile sensing devices suitable for various field applications such as bedside diagnostics or monitoring for bacterial contamination, e.g., in bioreactors.

Effect of the crosslinking agent on the biorepulsive and mechanical properties of polyglycerol membranes

Polyglycerol (PG) based surfaces materials and surfaces are well-established bio-compatible materials. Crosslinking of the dendrimeric molecules via their OH groups improves their mechanical stability up to the point that free-standing materials can be attained. Here, we investigate the effect of different crosslinkers on PG films regarding their biorepulsivity and mechanical properties. For this purpose, PG films with different thicknesses (15, 50 and 100 nm) were prepared by polymerizing glycidol in a ring-opening polymerization onto hydroxyl-terminated Si substrates. These films were then crosslinked using ethylene glycol diglycidyl ether (EGDGE), divinyl sulfone (DVS), glutaraldehyde (GA), 1,11-di(mesyloxy)-3,6,9-trioxaundecane (TEG-Ms₂) or 1,11-dibromo-3,6,9-trioxaundecane (TEG-Br₂), respectively. While DVS, TEG-Ms₂, and TEG-Br₂ resulted in slightly thinned films, presumably due to loss of unbound material, increase of film thickness was observed with GA and, in particular, EDGDE, what can be explained by the different crosslinking mechanisms. The biorepulsive properties of the crosslinked PG films were characterized by water contact angle (WCA) goniometry and various adsorption assays involving proteins (serum albumine, fibrinogen, γ-globulin) and bacteria (E. coli), showing that some crosslinkers (EGDGE, DVS) improved the biorepulsive properties, while others deteriorated them (TEG-Ms₂, TEG-Br₂, GA). As the crosslinking stabilized the films, it was possible to use a lift-off procedure to obtain free-standing membranes if the thickness of the films was 50 nm or larger. Their mechanical properties were examined with a bulge test showing high elasticities, with the Young's moduli increasing in the order GA ≈ EDGDE < TEG-Br₂ ≈ TEG-Ms₂ < DVS.

Synthesis and Characterization of Dendritic and Linear Glycol Methacrylates and Their Performance as Marine Antifouling Coatings

Dendritic polyglycerol (PG) was covalently coupled to 2-hydroxyethyl methacrylate (HEMA) by an anionically catalyzed ring-opening polymerization generating a dendritic PG-HEMA with four PG repetition units (PG₄MA). Coatings of the methacrylate monomer were prepared by grafting-through and compared against commercially available hydrophilic monomers of HEMA, poly(ethylene) glycol methacrylate (PEGMA), and poly(propylene) glycol methacrylate (PPGMA). The obtained coatings were characterized by modern surface analytical techniques, including water contact angle goniometry (sessile and captive bubble), attenuated total internal reflection Fourier transform infrared spectroscopy, and atomic force microscopy. The antifouling (AF) and fouling-release (FR) properties of the coatings were tested against the model organisms Cobetia marina and Navicula perminuta in laboratory-scale dynamic accumulation assays as well as in a dynamic short-term field exposure (DSFE) in the marine environment. In addition, the hydration of the coatings and their susceptibility toward silt uptake were evaluated, revealing a strong correlation between water uptake, silt incorporation, and field assay performance. While all glycol derivatives showed good resistance in laboratory settlement experiments, PPGMA turned out to be less susceptible to silt incorporation and outperformed PEGMA and PG₄MA in the DSFE assay.

Smart Molecular Nanosheets for Advanced Preparation of Biological Samples in Electron Cryo-Microscopy

Transmission electron cryo-microscopy (cryoEM) of vitrified biological specimens is a powerful tool for structural biology. Current preparation of vitrified biological samples starts off with sample isolation and purification, followed by the fixation in a freestanding layer of amorphous ice. Here, we demonstrate that ultrathin (∼10 nm) smart molecular nanosheets having specific biorecognition sites embedded in a biorepulsive layer covalently bound to a mechanically stable carbon nanomembrane allow for a much simpler isolation and structural analysis. We characterize in detail the engineering of these nanosheets and their biorecognition properties employing complementary methods such as X-ray photoelectron and infrared spectroscopy, atomic force microscopy as well as surface plasmon resonance measurements. The desired functionality of the developed nanosheets is demonstrated by in situ selection of a His-tagged protein from a mixture and its subsequent structural analysis by cryoEM.

Antifouling Properties of Dendritic Polyglycerols against Marine Macrofouling Organisms

Dendritic polyglycerols (PGs) were synthesized and postmodified by grafting of poly(ethylene glycol) (PEG) and polypropylene glycol (PPG) diglycidyl ether groups, and their antifouling and fouling-release properties were tested. Coating characterization by spectroscopic ellipsometry, contact angle goniometry, attenuated total internal reflection-Fourier transform infrared spectroscopy (ATR-FTIR), and atomic force microscopy showed brushlike morphologies with a high degree of microscale roughness and the ability to absorb large amounts of water within seconds. PGs with three different thicknesses were tested in laboratory assays against settlement of larvae of the barnacle Balanus improvisus and against the settlement and removal of zoospores of the alga Ulva linza. Very low coating thicknesses, e.g., 11 nm, reduced the settlement of barnacles, under static conditions, to 2% compared with 55% for an octadecyltrichlorosilane reference surface. In contrast, zoospores of U. linza settled readily but the vast majority were removed by exposure to a shear force of 52 Pa. Both PEG and PPG modification increased the antifouling properties of the PG films, providing a direct comparison of the ultralow fouling properties of all three polymers. Both, the modified and the nonmodified PGs are promising components for incorporation into amphiphilic fouling-resistant coatings.

Noncovalent Functionalization of Carbon Substrates with Hydrogels Improves Structural Analysis of Vitrified Proteins by Electron Cryo-Microscopy

In electron cryo-microscopy, structure determination of protein molecules is frequently hampered by adsorption of the particles to the support film material, typically amorphous carbon. Here, we report that pyrene derivatives with one or two polyglycerol (PG) side chains bind to the amorphous carbon films, forming a biorepulsive hydrogel layer so that the number of protein particles in the vitreous ice drastically increases. This approach could be extended by adding a hydrogel-functionalized carbon nanotube network (HyCaNet, the hydrogel again being formed from the PG-pyrene derivatives), which stabilized the protein-containing thin ice films during imaging with the electron beam. The stabilization resulted in reduced particle motion by up to 70%. These substrates were instrumental for determining the structure of a large membrane protein complex.

Fouling-Release Properties of Dendritic Polyglycerols against Marine Diatoms

Dendritic polyglycerols (PGs) were grafted onto surfaces using a ring-opening polymerization reaction, and the fouling-release properties against marine organisms were determined. The coatings were characterized by spectroscopic ellipsometry, contact angle goniometry, ATR-FTIR, and stability tests in different aqueous media. A high resistance toward the attachment of different proteins was found. The PG coatings with three different thicknesses were tested in a laboratory assay against the diatom Navicula incerta and in a field assay using a rotating disk. Under static conditions, the PG coatings did not inhibit the initial attachment of diatoms, but up to 94% of attached diatoms could be removed from the coatings after exposure to a shear stress of 19 Pa. Fouling release was found to be enhanced if the coatings were sufficiently thick. The excellent fouling-release properties were supported in dynamic field-immersion experiments in which the samples were continually exposed to a shear stress of 0.18 Pa.

Development of Antifouling Hyperbranched Polyglycerol Layers on Hydroxyl Poly-p-xylylene Coatings

Antifouling surfaces that are resistant to protein adsorption and cell adhesion are desirable for many biomedical devices, such as diagnostic devices, biosensors, and implants. In this study, we developed an antifouling hyperbranched polyglycerol (hPG) surface on hydroxyl poly-p-xylylene (PPX-OH). PPX-OH was deposited via chemical vapor deposition (CVD), and an hPG film was then developed via the ring-opening reaction of glycidol. The hPG film greatly reduced the adhesion of L929 cells and platelets as well as protein adsorption. The addition of alkenyl groups in the hPG layer allows the conjugation of biomolecules, such as peptides and biotin, and elicits specific biological interactions. Since the CVD deposition of PPX-OH could be applied to most types of materials, our approach makes it possible to decorate an antifouling hPG film on most types of materials. Our method could be applied to biosensors, diagnostics, and biomedical devices in the future.

Polyglycerol mediated covalent construction of magnetic mesoporous silica nanohybrid with aqueous dispersibility for drug delivery

Construction of nanohybrids with chemical and colloidal stability is of great importance for the exploration of their potential applications in biomedical field. In this work, a versatile strategy based on polyglycerol (PG) mediated covalent linkage is developed to fabricate a core-satellite nanohybrid, termed MMSN, consisting of a mesoporous silica nanoparticle (MSN) as a core and many superparamagnetic iron oxide nanoparticles (SPION) on the outer surface. In this synthetic strategy, the PG grafted SPION is derivatized to convert partial periphery hydroxyl groups to carboxyl moieties, followed by attachment to aminated MSN through amide bonds. The PG layer accounting for ~17wt% of MMSN not only serves as a tether to connect the two nanoparticles but also greatly enhances the colloidal stability of the nanohybrid, resulting in no significant change in hydrodynamic diameter and zeta potential during four months. Taking advantage of the combined porosity and magnetic property of the nanohybrid, a photosensitizer chlorin e6 (Ce6) is loaded on MMSN and efficiently delivered into target cells under magnetic guidance, leading to an enhanced efficacy of photodynamic therapy (PDT). The versatile strategy presented here opens up a new route to rational design and fabrication of multifunctional nanohybrids for various biomedical purposes.

Self-Perforated Hydrogel Nanomembranes Facilitate Structural Analysis of Proteins by Electron Cryo-Microscopy

We developed a method to improve specimen preparation for electron cryo-microscopy of membrane proteins. The method features a perforated hydrogel nanomembrane that stabilizes the thin film of aqueous buffer spanning the holes of holey carbon films, while at the same time preventing the depletion of protein molecules from these holes. The membrane is obtained by cross-linking of thiolated polyglycerol dendrimer films on gold, which self-perforate upon transfer to holey carbon substrates, forming a sub-micron-sized hydrogel network. The perforated nanomembrane improves the distribution of the protein molecules in the ice considerably. This facilitates data acquisition as demonstrated with two eukaryotic membrane protein complexes.

Antimicrobial Polymers and Surfaces – Natural Mimics or Surpassing Nature?

Fighting pathogenic microbes is one of the great current challenges of mankind. Nature has developed several techniques to counteract microbial attacks. Science has also yielded several technologies, including antimicrobial polymers as biocides and polymers used for microbe killing and repelling surfaces. Recent scientific antimicrobial approaches are mimicking natural concepts. In this chapter, current developments in antimicrobial and antifouling polymers and surfaces are reviewed and discussed regarding the question whether they mimic nature or surpass it.

Bio-inspired strategies for designing antifouling biomaterials

Contamination of biomedical devices in a biological medium, biofouling, is a major cause of infection and is entirely avoidable. This mini-review will coherently present the broad range of antifouling strategies, germicidal, preventive and cleaning using one or more of biological, chemical and physical techniques. These techniques will be discussed from the point of view of their ability to inhibit protein adsorption, usually the first step that eventually leads to fouling. Many of these approaches draw their inspiration from nature, such as emulating the nitric oxide production in endothelium, use of peptoids that mimic protein repellant peptides, zwitterionic functionalities found in membrane structures, and catechol functionalities used by mussel to immobilize poly(ethylene glycol) (PEG). More intriguing are the physical modifications, creation of micropatterns on the surface to control the hydration layer, making them either superhydrophobic or superhydrophilic. This has led to technologies that emulate the texture of shark skin, and the superhyprophobicity of self-cleaning textures found in lotus leaves. The mechanism of antifouling in each of these methods is described, and implementation of these ideas is illustrated with examples in a way that could be adapted to prevent infection in medical devices.

Dual-function antibacterial surfaces for biomedical applications

Bacterial attachment and the subsequent formation of biofilm on surfaces of synthetic materials pose a serious problem in both human healthcare and industrial applications. In recent decades, considerable attention has been paid to developing antibacterial surfaces to reduce the extent of initial bacterial attachment and thereby to prevent subsequent biofilm formation. Briefly, there are three main types of antibacterial surfaces: bactericidal surfaces, bacteria-resistant surfaces, and bacteria-release surfaces. The strategy adopted to develop each type of surface has inherent advantages and disadvantages; many efforts have been focused on the development of novel antibacterial surfaces with dual functionality. In this review, we highlight the recent progress made in the development of dual-function antibacterial surfaces for biomedical applications. These surfaces are based on the combination of two strategies into one system, which can kill attached bacteria as well as resisting or releasing bacteria. Perspectives on future research directions for the design of dual-function antibacterial surfaces are also provided.

Antibiofouling polymer interfaces: poly(ethylene glycol) and other promising candidates

This review highlights antibiofouling polymer interfaces with emphasis on the latest developments using poly(ethylene glycol) and the design new polymeric structures.

Polyglycerol coated polypropylene surfaces for protein and bacteria resistance

Polyglycerol coated polypropylene films were prepared in two steps by plasma bromination and grafting of polyglycerol. Films were characterized and their bioinertness against proteins and bacteria was investigated.

Fabrication of a photocontrolled surface with switchable wettability based on host-guest inclusion complexation and protein resistance

A novel surface-modification strategy has been developed for the construction of a photocontrolled silicon wafer surface with switchable wettability based on host-guest inclusion complexation. The silicon wafer was first modified by guest molecule azobenzene (Azo) via a silanization reaction. Subsequently, a series of polymers with different polarities were attached to host molecule β-cyclodextrin (β-CD) to prepare β-CD-containing hemitelechelic polymers via click chemistry. Finally, a photocontrolled silicon wafer surface modified with polymers was fabricated by inclusion complexation between β-CD and Azo, and the surface properties of the substrate are dependent on the polymers we used. The elemental composition, surface morphology, and hydrophilic/hydrophobic property of the modified surfaces were characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscope, and contact angle measurements, respectively. The antifouling property of the PEG-functionalized surface was evaluated by a protein adsorption assay using bovine serum albumin, which was also characterized by XPS. The results demonstrate that the surface modified with PEG possesses good protein-resistant properties.

A high efficiency approach for a titanium surface antifouling modification: PEG-o-quinone linked with titanium via electron transfer process

The stability and long-term antifouling properties of the electro-assembly monolayers of PEG-o-quinone are better than that of the self-assembly monolayers of PEG-catechol.