Peer Reviewed Papers on Scanning Force Microscopy

Natural Bactericidal Surfaces: Mechanical Rupture of Pseudomonas aeruginosa Cells by Cicada Wings

Elena P. Ivanova , * Jafar Hasan , Hayden K. Webb , Vi Khanh Truong ,
Gregory S. Watson , Jolanta A. Watson , Vladimir A. Baulin , Sergey Pogodin ,
James Y. Wang , Mark J. Tobin , Christian Löbbe , and Russell J. Crawford


Natural superhydrophobic surfaces are often thought to have antibiofouling potential due to their self-cleaning properties. However, when incubated on cicada wings, Pseudomonas aeruginosa cells are not repelled; instead they are penetrated by the nanopillar arrays present on the wing surface, resulting in bacterial cell death. Cicada wings are effective antibacterial, as opposed to antibiofouling, surfaces.

Assembly and Degradation of Low-Fouling Click-Functionalized Poly(ethylene glycol)-Based Multilayer Films and Capsules

Melissa K. M. Leung , Georgina K. Such , Angus P. R. Johnston , Dhee P. Biswas , Zhiyuan Zhu , Yan Yan , Jean-François Lutz , and Frank Caruso

 Small 7 (2011)1075-85


Nano-/micrometer-scaled films and capsules made of low-fouling materials such as poly(ethylene glycol) (PEG) are of interest for drug delivery and tissue engineering applications. Herein, the assembly and degradation of low-fouling, alkynefunctionalized PEG (PEG Alk ) multilayer films and capsules, which are prepared by combining layer-by-layer (LbL) assembly and click chemistry, are reported. A nonlinear, temperature-responsive PEG Alk is synthesized, and is then used to form hydrogen-bonded multilayers with poly(methacrylic acid) (PMA) at pH 5. The thermoresponsive behavior of PEG Alk is exploited to tailor film buildup by adjusting the assembly conditions. Using alkyne–azide click chemistry, PEG Alk /PMA multilayers are crosslinked with a bisazide linker that contains a disulfide bond, rendering these films and capsules redox-responsive. At pH 7, by disrupting the hydrogen bonding between the polymers, PEG Alk LbL films and PEG Alk -based capsules are obtained. These films exhibit specific deconstruction properties under simulated intracellular reducing conditions, but remain stable at physiological pH, suggesting potential applications in controlled drug release. The low-fouling properties of the PEG films are confirmed by incubation with human serum and a blood clot. Additionally, these capsules showed negligible toxicity to human cells.

Reversible Shape Memory of Nanoscale Deformations in Inherently Conducting Polymers without Reprogramming

Michael J. Higgins, Willo Grosse, Klaudia Wagner, Paul J. Molino, and Gordon G. Wallace

 J. Phys. Chem. B 115 (2011) 3371–3378


By using inherently conducting polymers, we introduce new shape memory functionality for stimuli-responsive polymers. The shape memory process is unique in that it utilizes electrochemical control of the polymer redox state to conceal, and temporarily store, preformed nanoscale surface patterns, which can later be recalled. Unlike classical thermoset and thermoplastic shape memory polymers, the electrochemical control does not completely perturb the low entropy state of the deformed polymer chains, thus enabling the concept of reversible transition between the permanent and temporary shapes. This is demonstrated using electrochemical-atomic force microscopy/quartz crystal microbalance to characterize the modulation of nanoscale deformations in electroactive polybithiophene films. Experimental results reveal that cation/solvent exchange with the electrolyte and its effect on reconfiguration of the film structure is the mechanism behind the process. In addition
to incorporating conductive properties into shape-memory polymers, the ability to reversibly modulate surface nanopatterns in a liquid environment is also of significant interest in tribology and biointerface applications.

Conducting polymers with immobilised fibrillar collagen for enhanced neural interfacing

Xiao Liu, Zhilian Yue, Michael J. Higgins, Gordon G. Wallace

 Biomaterials (2011), doi:10.1016/j.biomaterials.2011.06.047


Conducting polymers with pendant functionality are advantageous in various bionic and organic bioelectronic applications, as they allow facile incorporation of bio-regulative cues to provide bio-mimicry and conductive environments for cell growth, differentiation and function. In this work, polypyrrole substrates doped with chondroitin sulfate (CS), an extracellular matrix molecule bearing carboxylic acid moieties, were electrochemically synthesized and conjugated with type I collagen. During the coupling process, the conjugated collagen formed a 3-dimensional fibrillar matrix in situ at the conducting polymer interface, as evidenced by atomic force microscopy (AFM) and fluorescence microscopy under aqueous physiological conditions. Cyclic voltammetry (CV) and impedance measurement confirmed no significant reduction in the electroactivity of the fibrillar collagen-modified conducting polymer substrates. Rat pheochromocytoma (nerve) cells showed increased differentiation and neurite outgrowth on the fibrillar collagen, which was further enhanced through electrical stimulation of the underlying conducting polymer substrate. Our study demonstrates that the direct coupling of ECM components such as collagen, followed by their further self-assembly into 3-dimensional matrices, has the potential to improve the neural-electrode interface of implant electrodes by encouraging nerve cell attachment and differentiation.

Skeletal muscle cell proliferatinio and differentiation on polypyrrole substrates doped with extracellular matrix components

Kerry J. Gilmore, Magdalena Kita, Yao Han, Amy Gelmi, Michael J. Higgins, Simon E. Moulton, Graeme M. Clark, Robert Kapsa and Gordon G. Wallace

 Biomaterials 30 (2009) 5292-5304


Conducting polymers have been developed as substrates for in vitro studies with a range of cell types including electrically-excitable cells such as nerve and smooth muscle. The goal of this study was to optimise and characterise a range of polypyrrole materials to act as substrates for electrical stimulation of differentiating skeletal myoblasts. Although all of the polymer materials provided suitable substrates for myoblast adhesion and proliferation, significant differences became apparent under the low-serum conditions used for differentiation of primary myoblasts. The significance of the work lies in the design and control of polymer materials to facilitate different stages of skeletal muscle cell proliferation and/or differentiation, opening up opportunities for engineering of this tissue. This paper therefore constitutes not just a biocompatibility assessment but a comprehensive study of how synthesis conditions affect the final outcome in terms of cell response.

Combined AFM-Confocal Microscopy of Oil Droplets: Absolute Separations and Forces in Nanofilms

Rico F. Tabor, Hannah Lockie, Douglas Mair, Rogerio Manica, Derek Y. C. Chan, Franz Grieser, and Raymond R. Dagastine

 J. Phys. Chem. Lett.  2 (2011) 961-965


Quantitative interpretation of the dynamic forces between micrometer-sized deformable droplets and bubbles has previously been limited by the lack of an independent measurement of their absolute separation. Here, we use in situ confocal fluorescence microscopy to directly image the position and separation of oil droplets in an atomic force microscopy experiment. Comparison with predicted force vs. separation behavior to describe the interplay of force and deformation showed excellent agreement with continuum hydrodynamic lubrication theory in aqueous films less than 30 nm thick. The combination of force measurement and 3D visualization of geometric separation and surface deformation is applicable to interactions between other deformable bodies.

The effect of unlocking RGD-motifs in collagen I on pre-osteoblast adhesion and differentiation

Anna V. Taubenberger, Maria A. Woodruff, Huifen Bai, Daniel J. Muller, Dietmar W. Hutmacher

 Biomaterials 31 (2010) 2878-2835


Denaturation of extracellular matrix proteins exposes cryptic binding sites. It is hypothesized that
binding of cell adhesion receptors to these cryptic binding sites regulates cellular behaviour during tissue
repair and regeneration. To test this hypothesis, we quantify the adhesion of pre-osteoblastic cells to
native (Col) and partially-denatured (pdCol) collagen I using single-cell force spectroscopy. During early
stages of cell attachment (<=180 s) pre-osteoblasts (MC3T3-E1) adhered significantly stronger to pdCol
compared to Col. RGD (Arg-Gly-Asp)-containing peptides suppressed this elevated cell adhesion. We
show that the RGD-binding alpah5beta1- and alpha(v)-integrins mediated pre-osteoblast adhesion to pdCol, but not to Col. On pdCol pre-osteoblasts had a higher focal adhesion kinase tyrosine-phosphorylation level that
correlated with enhanced spreading and motility. Moreover, pre-osteoblasts cultured on pdCol showed
a pronounced matrix mineralization activity. Our data suggest that partially-denatured collagen exposes
RGD-motifs that trigger binding of a5b1- and av-integrins. These integrins initiate cellular processes that
stimulate osteoblast adhesion, spreading, motility and differentiation. Taken together, these quantitative
insights reveal an approach for the development of alternative collagen I- based surfaces for tissue
engineering applications.

Single-molecule biophysics: at the interface of biology, physics and chemistry

Ashok A. Deniz, Samrat Mukhopadhyay and Edward A. Lemke

J. R. Soc. Interface (2008) 5, 15–45


Single-molecule methods have matured into powerful and popular tools to probe the complex
behaviour of biological molecules, due to their unique abilities to probe molecular structure,
dynamics and function, unhindered by the averaging inherent in ensemble experiments. This
review presents an overview of the burgeoning field of single-molecule biophysics, discussing
key highlights and selected examples from its genesis to our projections for its future.
Following brief introductions to a few popular single-molecule fluorescence and manipulation
methods, we discuss novel insights gained from single-molecule studies in key biological areas
ranging from biological folding to experiments performed in vivo.
Keywords: single-molecule fluorescence; force; FRET; tracking; AFM; optical tweezers

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