Tracking the hydrophobicity recovery of PDMS compounds using the adhesive force determined by AFM force distance measurements

Polydimethylsiloxane (PDMS) materials show the unique phenomenon that when exposed to electrical discharge, such as corona discharge, their hydrophobic surface becomes hydrophilic. However, after a certain relaxation time they gradually regain their hydrophobicity. In this study the adhesive force obtained by AFM force distance measurements using a hydrophilic Si₃N₄ probe is used to track the recovery of the hydrophobicity. The time constant of the recovery can be determined by measuring the adhesive force as a function of the recovery time after corona exposure. It is shown how these time constants can be used to monitor the recovery rate as a function of corona treatment time for both filled and unfilled PDMS compounds.     

Probing the morphology of polypropylene fibres by scanning probe microscopy

This paper highlights the application of scanning probe microscopy, notably atomic force microscopy in contact mode supported by lateral force microscopy, to the investigation of changes in the morphology of polypropylene (PP) monofilaments during melt-extrusion and subsequent drawing. A gradual deformation at the fibre surface from a spherulitic structure to a shish-kebab type structure is observed for the gravity spun and as-spun variants. In the drawn PP filaments, the surface structure is predominantly fibrillar in character, though the nature of the fibrillar structure is influenced by the drawing conditions. Wide angle X-ray scattering analysis, in conjunction with SPM, indicates contrasting features of surface and bulk crystal structure both at the as-spun and drawn stages of production. In addition, an unusual WAXS diffraction pattern is observed for the cold drawn PP filament. Studies of the bulk structures of the fibres by investigating fibre cross-sections using SPM will be the subject of a companion paper.     

Determination of the influence of the polymer structure and particle size on the film formation process of polymers by atomic force microscopy

The particle size and morphology of a synthetic polymer latex were shown to influence the film formation behavior. Theoretical models predict that small particles coalesce more easily than large colloids do.The influence of particle size and morphology of differently structured lattices on the film-formation process was investigated by atomic force microscopy (AFM). Sequences of AFM images were acquired over a certain temperature range or at room temperature as a function of time. From the resulting images the average particle diameter of the latex particles in the surface layer was determined as a function of the time or temperature. The resulting curves could be compared to observe differences in the film formation kinetics of the different lattices. These AFM studies confirmed that the film formation behavior is influenced by the particle size and particle morphology, but that the core/shell ratio of core-shell particles has no significant influence on the film formation kinetics.     

Investigation of encapsulation of pancreatic beta cells and curcumin within alginate microcapsules

Cell encapsulation is an ideal approach for the replacement of pancreatic function in Type 1 diabetes. Poor biocompatibility of microcapsules generates an inflammatory response in the implantation site and induces fibrosis infiltration, which causes microencapsulated cell death and graft failure. To prevent inflammation after implantation, composite microcapsules that exhibit anti-inflammatory properties were designed. This study is about encapsulating beta cells and curcumin within 1.5% alginate by the jet-breaking regime of the syringe pump. The microcapsules’ size distribution and rate of the alginate solution were characterized to find uniform particles. Micro-size particles were attained at a rate of 25 mL/min. Uniform spherical microcapsules (200–300 μm) were created in large amounts in a short period. Microcapsule breakage was less than 3% during 7 days, which demonstrated the stability of the encapsulation method. Insulin secretion and cell viability assays were performed 1, 3, and 7 days after microencapsulation by glucose-stimulated insulin secretion (GSIS) and 3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide (MTT) assays. No significant differences in the amount of insulin secretion and beta cell viability were observed among free cells, alginate microcapsules, and curcumin-alginate microcapsules during 7 days (p > 0.05). Therefore, the curcumin and alginate membrane did not show any harmful impacts on the function and survival of the beta cells.     

Solvent effects on the elasticity of polysaccharide molecules in disordered and ordered states by single-molecule force spectroscopy

Single-molecule force spectroscopy, especially as implemented on an atomic force microscopy (AFM) platform is unique in its ability to apply small (F<10 pN) and large (F>1000 pN) stretching forces to individual polymer chains and in this way examines their elasticity and also reports force-induced conformational transitions in whole polymers and in their building blocks. In this paper, we briefly review recent applications of single-molecule force spectroscopy to the study of polysaccharides elasticity. We provide examples illustrating AFM measurements of solvent effects on the hydrogen bonding and the elasticity of individual polysaccharides and how molecular dynamics simulation can aid the interpretation of AFM results. We also discuss the use of single-molecule force spectroscopy in exploring ordered secondary structures of individual polysaccharide chains and their multi-strand complexes.     

Study of the surface of the water treated cellulose acetate membrane by atomic force microscopy

Water treated cellulose acetate (CA) membrane's surface was studied by atomic force microscopy (AFM). It was observed that when CA membrane (water untouched) was treated with water, the morphology of the surface change was detected by AFM. The roughness parameter of the surface was increased. No significant change was observed on the surface on drying the water treated membrane at room temperature for four days. The results were discussed on the basis that CA membrane contains continuous channels (network pores), which were formed in water-swollen polymer matrix. These water channels are responsible for the rejection of salt in reverse osmosis (RO) phenomenon.     

Measurement of the Interaction Between Recombinant I-domain from Integrin alpha 2 beta 1 and a Triple Helical Collagen Peptide with the GFOGER Binding Motif Using Molecular Force Spectroscopy

The role of the collagen-platelet interaction is of crucial importance to the haemostatic response during both injury and pathogenesis of the blood vessel wall. Of particular interest is the high affinity interaction of the platelet transmembrane receptor, alpha 2 beta 1, responsible for firm attachment of platelets to collagen at and around injury sites. We employ single molecule force spectroscopy (SMFS) using the atomic force microscope (AFM) to study the interaction of the I-domain from integrin alpha 2 beta 1 with a synthetic collagen related triple-helical peptide containing the high-affinity integrin-binding GFOGER motif, and a control peptide lacking this sequence, referred to as GPP. By utilising synthetic peptides in this manner we are able to study at the molecular level subtleties that would otherwise be lost when considering cell-to-collagen matrix interactions using ensemble techniques. We demonstrate for the first time the complexity of this interaction as illustrated by the complex multi-peaked force spectra and confirm specificity using control blocking experiments. In addition we observe specific interaction of the GPP peptide sequence with the I-domain. We propose a model to explain these observations.     

Atomic force microscope study of the rejection of colloids by membrane pores

An atomic force microscope (AFM) in conjunction with the colloid probe technique has been used to study the electrical double layer interactions between a 0.75 μm silica sphere and a polymeric microfiltration track etch Cyclopore membrane (nominally 1 μm) in aqueous solutions. The silica colloid probe was used to image the membrane surface (using the double layer mode) at different imaging forces in high purity water and at constant imaging force in sodium chloride solutions of different ionic strengths at pH 8. Force-distance measurements show clearly how the sphere detects the membrane surface. Quality of images produced from scanning the 0.75 μm silica particle across the surface deteriorates with increasing distance between the silica sphere and membrane surface. Such images were compared with those obtained from scanning a sharp silicon nitride tip over the membrane surface.     

An Atomic Force Microscopy Study of the Wetting of an Inorganic Surface by Latex Particles

Atomic Force Microscopy is used to investigate the wetting of a calcium carbonate crystal surface by latex particles when dried from dispersion. The measured particle heights are found to depend on the scanning rate and on the force of the probe tip acting on the sample. The analysis of the particle profile shows that the spreading is not governed by capillary forces. Below their glass temperature, the latex particles have weak adhesion to the crystal and are moved easily by the probe tip. This results in tip-induced organization of particles. Above their glass temperature, the particles spread on the surface and they are no longer moved by the probe tip.