Biomedical subjects

Mark E Welland

Publications and source records attributed to Mark E Welland.

5 recordsLinked to original sources

PubMed2006

Characterization of the nanoscale properties of individual amyloid fibrils.

We report the detailed mechanical characterization of individual amyloid fibrils by atomic force microscopy and spectroscopy. These self-assembling materials, formed here from the protein insulin, were shown to have a strength of 0.6 +/- 0.4 GPa, comparable to that of steel (0.6-1.8 GPa), and a mechanical stiffness, as measured by Young's modulus, of 3.3 +/- 0.4 GPa, comparable to that of silk (1-10 GPa). The values of these parameters reveal that the fibrils possess properties that make these structures highly attractive for future technological applications. In addition, analysis of the solution-state growth kinetics indicated a breakage rate constant of 1.7 +/- 1.3 x 10(-8) s(-1), which reveals that a fibril 10 mum in length breaks spontaneously on average every 47 min, suggesting that internal fracturing is likely to be of fundamental importance in the proliferation of amyloid fibrils and therefore for understanding the progression of their associated pathogenic disorders.

Amyloid↗

PubMed2006

Spatial persistence of angular correlations in amyloid fibrils.

Using atomic force microscopy height maps, we resolve and quantify torsional fluctuations in one-dimensional amyloid fibril aggregates self-assembled from three different representative polypeptide systems. Furthermore, we show that angular correlation in these nanoscale structures is maintained over several microns, corresponding to many thousands of molecules along the fibril axis. We model disorder in the fibril in respect of both thermal fluctuations and structural defects, and determine quantitative values for the defect density, as well as the energy scales involved in the fundamental interactions stabilizing these generic structures.

Amyloid↗

PubMed2006

Highly reversible and multi-stage cantilever actuation driven by polyelectrolyte brushes.

Microcantilever bending can be reversibly driven by conformational changes of phosphate containing polyelectrolyte brushes when exposed to different pH or salt solutions. The deflection of the cantilevers allows a detailed analysis of the properties of polymer brushes, while these systems are also a first step toward polymer-based nanoactuators.

Journal Article↗

PubMed2005

DNA molecular motor driven micromechanical cantilever arrays.

The unique ability of living systems to translate biochemical reactions into mechanical work has inspired the design of synthetic DNA motors which generate nanoscale motion via controlled conformational change. However, while Nature has evolved intricate mechanisms to convert molecular shape change into specific micrometer-scale mechanical cellular responses, the integration of artificial DNA motors with mechanical devices presents a major challenge. Here we report the direct integration between an ensemble of DNA motors and an array of microfabricated silicon cantilevers. The forces exerted by the precise duplex to nonclassical i-motif conformational change were probed via differential measurements using an in-situ reference cantilever coated with a nonspecific sequence of DNA. Fueled by the addition of protons, the open to close stroke of the motor induced 32 +/- 3 mN/m compressive surface stress, which corresponds to a single motor force of approximately 11 pN/m, an order of magnitude larger than previous classical hybridization studies. Furthermore, the surface-tethered conformational change was found to be highly reversible, in contrast to classical DNA motors which typically suffer rapid system poisoning. The direction and amplitude of motor-induced cantilever motion was tuneable via control of buffer pH and ionic strength, indicating that electrostatic forces play an important role in stress generation. Hybrid devices which directly harness the multiple accessible conformational states of dynamic oligonucleotides and aptamers, translating biochemical energy into micromechanical work, present a radical new approach to the construction of "smart" nanoscale machinery and mechano-biosensors.

Biomechanical Phenomena↗

PubMed2005

Dynamic shadow mask technique: a universal tool for nanoscience.

A comprehensive instrument, designed for fabricating nanostructures by evaporation through a dynamic shadow mask in ultrahigh vacuum, is described. The versatility and performance of the instrument is demonstrated through a series of examples, allowing for applications that are impossible to achieve with traditional nanopatterning methods. Clean nanostructures or entire devices made of different materials and on various substrates can be fabricated. The technique is compatible with fundamental surface science and can be easily interfaced with other fabrication and characterization techniques.

Journal Article↗