Force spectroscopy of hyaluronan by atomic force microscopy: from hydrogen-bonded networks toward single-chain behavior

The conformational behavior of hyaluronan (HA) polysaccharide chains in aqueous NaCl solution was characterized directly at the single-molecule level. This communication reports on one of the first single-chain atomic force microscopy (AFM) experiments performed at variable temperatures, investigating the influence of the temperature on the stability of the HA single-chain conformation. Through AFM single-molecule force spectroscopy, the temperature destabilization of a local structure was proven. This structure involved a hydrogen-bonded network along the polymeric chain, with hydrogen bonds between the polar groups of HA and possibly water, and a change from a nonrandom coil to a random coil behavior was observed when increasing the temperature from 29 +/- 1 to 46 +/- 1 degrees C. As a result of the applied force, this superstructure was found to break progressively at room temperature. The use of a hydrogen-bonding breaker solvent demonstrated the hydrogen-bonded water-bridged nature of the network structure of HA single chains in aqueous NaCl solution.     

Synthesis of functionalized amphiphilic polymers for coating quantum dots

Quantum dots (QDs) need to be attached to other chemical species if they are to be used as biomarkers, therapeutic agents or sensors. These materials also need to disperse well in water and have well-defined functional groups on their surfaces. QDs are most often synthesized in the presence of ligands such as trioctylphosphine oxide, which render the nanoparticle surfaces hydrophobic. We present a complete protocol for the synthesis and water solubilization of hydrophobic CdSe/ZnS QDs using designer amphiphilic polymeric coatings. The method is based on functionalization of an anhydride polymer backbone with nucleophilic agents. Small functional groups, bulky cyclic compounds and polymeric chains can be integrated into the coating prior to solubilization. We describe the preparation of acetylene- and azide-functionalized QDs for 'click' chemistry. The method is universal and applicable to any type of nanoparticle stabilized with hydrophobic ligands able to interact with the alkyl chains in the coating in water.     

An in situ study of the nanomechanical properties of barnacle (Balanus amphitrite) cyprid cement using atomic force microscopy (AFM)

Abstract

Cyprids are the final planktonic stage in the larval dispersal of barnacles and are responsible for surface exploration and attachment to appropriate substrata. The nanomechanical properties of barnacle (Balanus amphitrite) cyprid permanent cement were studied in situ using atomic force microscopy (AFM). Force curves were recorded from the cement disc continually over the course of its curing and these were subsequently analysed using custom software. Results showed a narrowing of the pull-off force distribution with time, as well as a reduction in molecular stretch length over time. In addition, there was a strong correlation between maximum pull-off force and molecular stretch length for the cement, suggesting ‘curing’ of the adhesive; some force curves also contained a ‘fingerprint’ of modular protein unfolding. This study provides the first direct experimental evidence in support of a putative ‘tanning’ mechanism in barnacle cyprid cement.     

An in situ study of the nanomechanical properties of barnacle (Balanus amphitrite) cyprid cement using atomic force microscopy (AFM)

Cyprids are the final planktonic stage in the larval dispersal of barnacles and are responsible for surface exploration and attachment to appropriate substrata. The nanomechanical properties of barnacle (Balanus amphitrite) cyprid permanent cement were studied in situ using atomic force microscopy (AFM). Force curves were recorded from the cement disc continually over the course of its curing and these were subsequently analysed using custom software. Results showed a narrowing of the pull-off force distribution with time, as well as a reduction in molecular stretch length over time. In addition, there was a strong correlation between maximum pull-off force and molecular stretch length for the cement, suggesting 'curing' of the adhesive; some force curves also contained a 'fingerprint' of modular protein unfolding. This study provides the first direct experimental evidence in support of a putative 'tanning' mechanism in barnacle cyprid cement.     

Preparation and Friction Force Microscopy Measurements of Immiscible,Opposing Polymer Brushes

Solvated polymer brushes are well known to lubricate high-pressure contacts, because they can sustain a positive normal load while maintaining low friction at the interface. Nevertheless, these systems can be sensitive to wear due to interdigitation of the opposing brushes. In a recent publication, we have shown via molecular dynamics simulations and atomic force microscopy experiments, that using an immiscible polymer brush system terminating the substrate and the slider surfaces, respectively, can eliminate such interdigitation. As a consequence, wear in the contacts is reduced. Moreover, the friction force is two orders of magnitude lower compared to traditional miscible polymer brush systems. This newly proposed system therefore holds great potential for application in industry. Here, the methodology to construct an immiscible polymer brush system of two different brushes each solvated by their own preferred solvent is presented. The procedure how to graft poly(N-isopropylacrylamide) (PNIPAM) from a flat surface and poly(methyl methacrylate) (PMMA) from an atomic force microscopy (AFM) colloidal probe is described. PNIPAM is solvated in water and PMMA in acetophenone. Via friction force AFM measurements, it is shown that the friction for this system is indeed reduced by two orders of magnitude compared to the miscible system of PMMA on PMMA solvated in acetophenone.     

Environmental benchmarks for buildings: needs,challenges and solutions—71st LCA forum,Swiss Federal Institute of Technology,Zürich, 18 June 2019

The International Journal of Life Cycle Assessment - The 71st LCA forum was held on 18 June 2019 in Zurich, Switzerland, to discuss the current status and future plans of environmental benchmarking...     

Enzymatic surface erosion of poly(trimethylene carbonate) films studied by atomic force microscopy

In this article, the surface erosion of spin-coated poly(trimethylene carbonate) (PTMC) films by lipase solutions from Thermomyces lanuginosus was studied using atomic force microscopy (AFM). PTMC films (23-48 nm thick) were stable in water at 37 degrees C for 16 h, while after immersion in lipase solutions at 37 degrees C for 30 s and 1 min, the average thickness of the film decreased in time at a rate of 11.0 +/- 3.7 nm/min. The initially smooth films became significantly rougher during the erosion process. When the immersion time of the films in the lipase solutions was limited to less than 5 s, degradation of the surface was minimal and individual lipase molecules adsorbed on PTMC films could be discerned. By microcontact printing of the PTMC surfaces using a patterned PDMS stamp and lipase solution for 30 s, a predefined micropattern consisting of parallel, 5-microm-wide lines lying 5-nm deep and separated at a distance of 2 microm was formed. Friction images showed differences in surface properties between the recessed and protruding lines in the pattern.     

Reactive thin polymer films as platforms for the immobilization of biomolecules

Spin-coated thin films of poly(N-hydroxysuccinimidyl methacrylate) (PNHSMA) on oxidized silicon and gold surfaces were investigated as reactive layers for obtaining platforms for biomolecule immobilization with high molecular loading. The surface reactivity of PNHSMA films in coupling reactions with various primary amines, including amine-terminated poly(ethylene glycol) (PEG-NH2) and fluoresceinamine, was determined by Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), fluorescence microscopy, and ellipsometry measurements, respectively. The rate constants of PEG-NH2 attachment on the PNHSMA films were found to be significantly increased compared to the coupling on self-assembled monolayers (SAMs) of 11,11'-dithiobis(N-hydroxysuccinimidylundecanoate) (NHS-C10) on gold under the same conditions. More significantly, the PEG loading observed was about 3 times higher for the polymer thin films. These data indicate that the coupling reactions are not limited to the very surface of the polymer films, but proceed into the near-surface regions of the films. PNHSMA films were shown to be stable in contact with aqueous buffer; the swelling analysis, as performed by atomic force microscopy (AFM), indicated a film thickness independent swelling of approximately 2 nm. An increased loading was also observed by surface plasmon resonance for the covalent immobilization of amino-functionalized probe DNA. Hybridization of fluorescently labeled target DNA was successfully detected by fluorescence microscopy and surface plasmon resonance enhanced fluorescence spectroscopy (SPFS), thereby demonstrating that thin films of PNHSMA comprise an attractive and simple platform for the immobilization of biomolecules with high densities.     

The effects of a serine protease,Alcalase®, on the adhesives of barnacle cyprids (Balanus amphitrite)

Barnacles are a persistent fouling problem in the marine environment, although their effects (eg reduced fuel efficiency, increased corrosion) can be reduced through the application of antifouling or fouling-release coatings to marine structures. However, the developments of fouling-resistant coatings that are cost-effective and that are not deleterious to the marine environment are continually being sought. The incorporation of proteolytic enzymes into coatings has been suggested as one potential option. In this study, the efficacy of a commercially available serine endopeptidase, Alcalase® as an antifoulant is assessed and its mode of action on barnacle cypris larvae investigated. In situ atomic force microscopy (AFM) of barnacle cyprid adhesives during exposure to Alcalase supported the hypothesis that Alcalase reduces the effectiveness of the cyprid adhesives, rather than deterring the organisms from settling. Quantitative behavioural tracking of cyprids, using Ethovision? 3.1, further supported this observation. Alcalase removed cyprid ‘footprint’ deposits from glass surfaces within 26 min, but cyprid permanent cement became resistant to attack by Alcalase within 15 h of expression, acquiring a crystalline appearance in its cured state. It is concluded that Alcalase has antifouling potential on the basis of its effects on cyprid footprints, un-cured permanent cement and its non-toxic mode of action, providing that it can be successfully incorporated into a coating.     

The effects of a serine protease, Alcalase, on the adhesives of barnacle cyprids (Balanus amphitrite)

Barnacles are a persistent fouling problem in the marine environment, although their effects (eg reduced fuel efficiency, increased corrosion) can be reduced through the application of antifouling or fouling-release coatings to marine structures. However, the developments of fouling-resistant coatings that are cost-effective and that are not deleterious to the marine environment are continually being sought. The incorporation of proteolytic enzymes into coatings has been suggested as one potential option. In this study, the efficacy of a commercially available serine endopeptidase, Alcalase as an antifoulant is assessed and its mode of action on barnacle cypris larvae investigated. In situ atomic force microscopy (AFM) of barnacle cyprid adhesives during exposure to Alcalase supported the hypothesis that Alcalase reduces the effectiveness of the cyprid adhesives, rather than deterring the organisms from settling. Quantitative behavioural tracking of cyprids, using Ethovision 3.1, further supported this observation. Alcalase removed cyprid 'footprint' deposits from glass surfaces within 26 min, but cyprid permanent cement became resistant to attack by Alcalase within 15 h of expression, acquiring a crystalline appearance in its cured state. It is concluded that Alcalase has antifouling potential on the basis of its effects on cyprid footprints, un-cured permanent cement and its non-toxic mode of action, providing that it can be successfully incorporated into a coating.