Author
Mario B. Viani
Other affiliations: University of California, University of Göttingen, Oxford Instruments
Bio: Mario B. Viani is an academic researcher from University of California, Santa Barbara. The author has contributed to research in topics: Cantilever & Non-contact atomic force microscopy. The author has an hindex of 14, co-authored 21 publications receiving 2560 citations. Previous affiliations of Mario B. Viani include University of California & University of Göttingen.
Papers
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TL;DR: In this article, the authors used the atomic force microscope to stretch the organic molecules exposed on the surface of freshly cleaved nacre and found that the elongation events occur for forces of a few hundred piconewtons, which are smaller than the forces of over a nanonewton required to break the polymer backbone in the threads.
Abstract: Natural materials are renowned for their strength and toughness1,2,3,4,5. Spider dragline silk has a breakage energy per unit weight two orders of magnitude greater than high tensile steel1,6, and is representative of many other strong natural fibres3,7,8. The abalone shell, a composite of calcium carbonate plates sandwiched between organic material, is 3,000 times more fracture resistant than a single crystal of the pure mineral4,5. The organic component, comprising just a few per cent of the composite by weight9, is thought to hold the key to nacre's fracture toughness10,11. Ceramics laminated with organic material are more fracture resistant than non-laminated ceramics11,12, but synthetic materials made of interlocking ceramic tablets bound by a few weight per cent of ordinary adhesives do not have a toughness comparable to nacre13. We believe that the key to nacre's fracture resistance resides in the polymer adhesive, and here we reveal the properties of this adhesive by using the atomic force microscope14 to stretch the organic molecules exposed on the surface of freshly cleaved nacre. The adhesive fibres elongate in a stepwise manner as folded domains or loops are pulled open. The elongation events occur for forces of a few hundred piconewtons, which are smaller than the forces of over a nanonewton required to break the polymer backbone in the threads. We suggest that this ‘modular’ elongation mechanism might prove to be quite general for conveying toughness to natural fibres and adhesives, and we predict that it might be found also in dragline silk.
1,120 citations
TL;DR: In this article, a simple process was used to fabricate small rectangular cantilevers out of silicon nitride, with lengths of 9-50 μm, widths of 3-5 μm and thickness of 86 and 102 nm.
Abstract: We have used a simple process to fabricate small rectangular cantilevers out of silicon nitride. They have lengths of 9–50 μm, widths of 3–5 μm, and thicknesses of 86 and 102 nm. We have added metallic reflector pads to some of the cantilever ends to maximize reflectivity while minimizing sensitivity to temperature changes. We have characterized small cantilevers through their thermal spectra and show that they can measure smaller forces than larger cantilevers with the same spring constant because they have lower coefficients of viscous damping. Finally, we show that small cantilevers can be used for experiments requiring large measurement bandwidths, and have used them to unfold single titin molecules over an order of magnitude faster than previously reported with conventional cantilevers.
401 citations
TL;DR: This work suggests that the small cantilever atomic force microscope is a useful tool for studying protein dynamics at the single molecule level.
Abstract: We have used a prototype small cantilever atomic force microscope to observe, in real time, the interactions between individual protein molecules. In particular, we have observed individual molecules of the chaperonin protein GroES binding to and then dissociating from individual GroEL proteins, which were immobilized on a mica support. This work suggests that the small cantilever atomic force microscope is a useful tool for studying protein dynamics at the single molecule level.
291 citations
TL;DR: A prototype atomic force microscope with small cantilevers was used to produce stable tapping-mode images in liquid of DNA adsorbed onto mica in as little as 1.7 s per image as mentioned in this paper.
Abstract: Small cantilevers allow for faster imaging and faster force spectroscopy of single biopolymers than previously possible because they have higher resonant frequencies and lower coefficients of viscous damping. We have used a new prototype atomic force microscope with small cantilevers to produce stable tapping-mode images (1 μm×1 μm) in liquid of DNA adsorbed onto mica in as little as 1.7 s per image. We have also used these cantilevers to observe the forced unfolding of individual titin molecules on a time scale an order of magnitude faster than previously reported. These experiments demonstrate that a new generation of atomic force microscopes using small cantilevers will enable us to study biological processes with greater time resolution. Furthermore, these instruments allow us to narrow the gap in time between results from force spectroscopy experiments and molecular dynamics calculations.
244 citations
TL;DR: In this paper, the authors measured the spring constant as a function of the spot along the length of the cantilever and observed systematic variation in the spring constants of this position.
Abstract: One of the most popular methods for calibrating the spring constant of an atomic force microscope cantilever is the thermal noise method The usual implementation of this method has been to position the focused optical spot on or near the end of the cantilever, acquire a force curve on a hard surface to characterize the optical lever sensitivity and to then measure the thermal motion of the cantilever The equipartition theorem then allows the spring constant to be calculated In this work, we measured the spring constant as a function of the spot along the length of the cantilever The observed systematic variation in the spring constant as a function of this position ranged from 15% for a short 60 μm cantilever up to 50% for a 225 μm cantilever we examined In addition, the thermally calibrated spring constants systematically disagreed with spring constants calibrated using the Sader and Cleveland methods: by 50% for the short 60 μm cantilever and by 25% for the longest, 225 μm cantilever By using a model that accounts for the spot diameter and position on the cantilever, the thermally measured spring constants were brought into better than 10% agreement with the other methods
242 citations
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TL;DR: The atomic force microscope (AFM) is not only used to image the topography of solid surfaces at high resolution but also to measure force-versus-distance curves as discussed by the authors, which provide valuable information on local material properties such as elasticity, hardness, Hamaker constant, adhesion and surface charge densities.
3,281 citations
TL;DR: The common design motifs of a range of natural structural materials are reviewed, and the difficulties associated with the design and fabrication of synthetic structures that mimic the structural and mechanical characteristics of their natural counterparts are discussed.
Abstract: Natural structural materials are built at ambient temperature from a fairly limited selection of components. They usually comprise hard and soft phases arranged in complex hierarchical architectures, with characteristic dimensions spanning from the nanoscale to the macroscale. The resulting materials are lightweight and often display unique combinations of strength and toughness, but have proven difficult to mimic synthetically. Here, we review the common design motifs of a range of natural structural materials, and discuss the difficulties associated with the design and fabrication of synthetic structures that mimic the structural and mechanical characteristics of their natural counterparts.
3,083 citations
TL;DR: In this paper, the basic principles involved in designing hierarchical biological materials, such as cellular and composite architectures, adapative growth and as well as remodeling, are discussed, and examples that are found to utilize these strategies include wood, bone, tendon, and glass sponges.
2,274 citations
TL;DR: The specific transduction, via surface stress changes, of DNA hybridization and receptor-ligand binding into a direct nanomechanical response of microfabricated cantilevers is reported, demonstrating the wide-ranging applicability of nanomechamical transduction to detect biomolecular recognition.
Abstract: We report the specific transduction, via surface stress changes, of DNA hybridization and receptor-ligand binding into a direct nanomechanical response of microfabricated cantilevers. Cantilevers in an array were functionalized with a selection of biomolecules. The differential deflection of the cantilevers was found to provide a true molecular recognition signal despite large nonspecific responses of individual cantilevers. Hybridization of complementary oligonucleotides shows that a single base mismatch between two 12-mer oligonucleotides is clearly detectable. Similar experiments on protein A-immunoglobulin interactions demonstrate the wide-ranging applicability of nanomechanical transduction to detect biomolecular recognition.
1,729 citations
TL;DR: It is demonstrated how the physics of ice formation can be used to develop sophisticated porous and layered-hybrid materials, including artificial bone, ceramic-metal composites, and porous scaffolds for osseous tissue regeneration with strengths up to four times higher than those of materials currently used for implantation.
Abstract: Materials that are strong, ultralightweight, and tough are in demand for a range of applications, requiring architectures and components carefully designed from the micrometer down to the nanometer scale. Nacre, a structure found in many molluscan shells, and bone are frequently used as examples for how nature achieves this through hybrid organic-inorganic composites. Unfortunately, it has proven extremely difficult to transcribe nacre-like clever designs into synthetic materials, partly because their intricate structures need to be replicated at several length scales. We demonstrate how the physics of ice formation can be used to develop sophisticated porous and layered-hybrid materials, including artificial bone, ceramic-metal composites, and porous scaffolds for osseous tissue regeneration with strengths up to four times higher than those of materials currently used for implantation.
1,696 citations