scholarly journals Analysis of the mechanical stability and surface detachment of matureStreptococcus mutansbiofilms by applying a range of external shear forces

Biofouling ◽  
2014 ◽  
Vol 30 (9) ◽  
pp. 1079-1091 ◽  
Author(s):  
Geelsu Hwang ◽  
Marlise I. Klein ◽  
Hyun Koo
Keyword(s):  
Mechanical Stability ◽  
Shear Forces ◽  
Surface Detachment

scholarly journals Streptavidin/biotin: Tethering geometry defines unbinding mechanics

2020 ◽  
Vol 6 (13) ◽  
pp. eaay5999 ◽  
Author(s):  
Steffen M. Sedlak ◽  
Leonard C. Schendel ◽  
Hermann E. Gaub ◽  
Rafael C. Bernardi
Keyword(s):  
Single Molecule ◽  
Conformational Changes ◽  
Energy Barrier ◽  
Mechanical Stability ◽  
Binding Pocket ◽  
Entire System ◽  
Shear Forces ◽  
Single Molecule Force Spectroscopy ◽  
Force Loading ◽  
Applied Forces

Macromolecules tend to respond to applied forces in many different ways. Chemistry at high shear forces can be intriguing, with relatively soft bonds becoming very stiff in specific force-loading geometries. Largely used in bionanotechnology, an important case is the streptavidin (SA)/biotin interaction. Although SA’s four subunits have the same affinity, we find that the forces required to break the SA/biotin bond depend strongly on the attachment geometry. With AFM-based single-molecule force spectroscopy (SMFS), we measured unbinding forces of biotin from different SA subunits to range from 100 to more than 400 pN. Using a wide-sampling approach, we carried out hundreds of all-atom steered molecular dynamics (SMD) simulations for the entire system, including molecular linkers. Our strategy revealed the molecular mechanism that causes a fourfold difference in mechanical stability: Certain force-loading geometries induce conformational changes in SA’s binding pocket lowering the energy barrier, which biotin has to overcome to escape the pocket.

scholarly journals Cytoplasmic anchorage of L-selectin controls leukocyte capture and rolling by increasing the mechanical stability of the selectin tether

2001 ◽  
Vol 155 (1) ◽  
pp. 145-156 ◽  
Author(s):  
Oren Dwir ◽  
Geoffrey S. Kansas ◽  
Ronen Alon
Keyword(s):  
Mechanical Properties ◽  
Mechanical Stability ◽  
Dissociation Rate ◽  
Regulatory Mechanisms ◽  
Cytoskeletal Protein ◽  
Shear Stresses ◽  
Leukocyte Rolling ◽  
Shear Forces ◽  
Force Sensitivity ◽  
Selectin Ligands

L-selectin is a leukocyte lectin that mediates leukocyte capture and rolling in the vasculature. The cytoplasmic domain of L-selectin has been shown to regulate leukocyte rolling. In this study, the regulatory mechanisms by which this domain controls L-selectin adhesiveness were investigated. We report that an L-selectin mutant generated by truncation of the COOH-terminal 11 residues of L-selectin tail, which impairs association with the cytoskeletal protein α-actinin, could capture leukocytes to glycoprotein L-selectin ligands under physiological shear flow. However, the conversion of initial tethers into rolling was impaired by this partial tail truncation, and was completely abolished by a further four-residue truncation of the L-selectin tail. Physical anchorage of both cell-free tail-truncated mutants within a substrate fully rescued their adhesive deficiencies. Microkinetic analysis of full-length and truncated L-selectin–mediated rolling at millisecond temporal resolution suggests that the lifetime of unstressed L-selectin tethers is unaffected by cytoplasmic tail truncation. However, cytoskeletal anchorage of L-selectin stabilizes the selectin tether by reducing the sensitivity of its dissociation rate to increasing shear forces. Low force sensitivity (reactive compliance) of tether lifetime is crucial for selectins to mediate leukocyte rolling under physiological shear stresses. This is the first demonstration that reduced reactive compliance of L-selectin tethers is regulated by cytoskeletal anchorage, in addition to intrinsic mechanical properties of the selectin–carbohydrate bond.

An improved design for an Scanning Tunnelling Microscope (STM) for use in a Transmission Electron Microscope (TEM)

1991 ◽  
Vol 49 ◽  
pp. 384-385
Author(s):  
W.K. Lo ◽  
J.C.H. Spence
Keyword(s):  
Electron Microscope ◽  
Transmission Electron Microscope ◽  
Mechanical Stability ◽  
Scanning Tunnelling Microscope ◽  
Reflection Mode ◽  
Specimen Holder ◽  
Transmission Electron ◽  
Scanning Tunnelling ◽  
Improved Design

An improved design for a combination Scanning Tunnelling Microscope/TEM specimen holder is presented. It is based on earlier versions which have been used to test the usefulness of such a device. As with the earlier versions, this holder is meant to replace the standard double-tilt specimen holder of an unmodified Philips 400T TEM. It allows the sample to be imaged simultaneously by both the STM and the TEM when the TEM is operated in the reflection mode (see figure 1).The resolution of a STM is determined by its tip radii as well as its stability. This places strict limitations on the mechanical stability of the tip with respect to the sample. In this STM the piezoelectric tube scanner is rigidly mounted inside the endcap of the STM holder. The tip coarse approach to the sample (z-direction) is provided by an Inchworm which is located outside the TEM vacuum.

Experiments with a scanning tunneling microscope (STM) mounted in a scanning electron microscope (SEM)

1986 ◽  
Vol 44 ◽  
pp. 636-639
Author(s):  
Oliver C. Wells ◽  
Mark E. Welland
Keyword(s):  
Electron Microscope ◽  
Scanning Electron Microscope ◽  
Mechanical Stability ◽  
Tunneling Current ◽  
Feedback System ◽  
Scanning Tunneling ◽  
Surface Profiling ◽  
Close Proximity ◽  
Metal Tip ◽  
Scanning Electron

Scanning tunneling microscopes (STM) exist in two versions. In both of these, a pointed metal tip is scanned in close proximity to the specimen surface by means of three piezos. The distance of the tip from the sample is controlled by a feedback system to give a constant tunneling current between the tip and the sample. In the low-end STM, the system has a mechanical stability and a noise level to give a vertical resolution of between 0.1 nm and 1.0 nm. The atomic resolution STM can show individual atoms on the surface of the specimen.A low-end STM has been put into the specimen chamber of a scanning electron microscope (SEM). The first objective was to investigate technological problems such as surface profiling. The second objective was for exploratory studies. This second objective has already been achieved by showing that the STM can be used to study trapping sites in SiO2.

Electron microscopy of keratinocytes cultured on a collagen substrate used as an allograft for the treatment of chronic wounds

1992 ◽  
Vol 50 (2) ◽  
pp. 1104-1105
Author(s):  
Debby A. Jennings ◽  
Michael J. Morykwas ◽  
Louis C. Argenta
Keyword(s):  
Electron Microscopy ◽  
Cell Suspension ◽  
Single Cell ◽  
Chronic Wounds ◽  
Mechanical Stability ◽  
Uv Light ◽  
Type I ◽  
Single Cell Suspension ◽  
Collagen Substrate ◽  
Dermal Collagen

Grafts of cultured allogenic or autogenic keratlnocytes have proven to be an effective treatment of chronic wounds and burns. This study utilized a collagen substrate for keratinocyte and fibroblast attachment. The substrate provided mechanical stability and augmented graft manipulation onto the wound bed. Graft integrity was confirmed by light and transmission electron microscopy.Bovine Type I dermal collagen sheets (100 μm thick) were crosslinked with 254 nm UV light (13.5 Joules/cm2) to improve mechanical properties and reduce degradation. A single cell suspension of third passage neonatal foreskin fibroblasts were plated onto the collagen. Five days later, a single cell suspension of first passage neonatal foreskin keratinocytes were plated on the opposite side of the collagen. The grafts were cultured for one month.The grafts were fixed in phosphate buffered 4% formaldehyde/1% glutaraldehyde for 24 hours. Graft pieces were then washed in 0.13 M phosphate buffer, post-fixed in 1% osmium tetroxide, dehydrated, and embedded in Polybed 812.

P20 phosphor on polyimide as a large area high-resolution transmission screen for slow scan CCD systems

1995 ◽  
Vol 53 ◽  
pp. 20-21
Author(s):  
C. C. Ahn ◽  
S. Karnes ◽  
M. Lvovsky ◽  
C. M. Garland ◽  
H. A. Atwater ◽  
...  
Keyword(s):  
Mechanical Stability ◽  
High Energy ◽  
Practical Implementation ◽  
Line Pair ◽  
Modulation Transfer ◽  
Large Area ◽  
Ccd Imaging ◽  
Transmission Electron ◽  
The One ◽  
Beam Broadening

The bane of CCD imaging systems for transmission electron microscopy at intermediate and high voltages has been their relatively poor modulation transfer function (MTF), or line pair resolution. The problem originates primarily with the phosphor screen. On the one hand, screens should be thick so that as many incident electrons as possible are converted to photons, yielding a high detective quantum efficiency(DQE). The MTF diminishes as a function of scintillator thickness however, and to some extent as a function of fluorescence within the scintillator substrates. Fan has noted that the use of a thin layer of phosphor beneath a self supporting 2μ, thick Al substrate might provide the most appropriate compromise for high DQE and MTF in transmission electron microcscopes which operate at higher voltages. Monte Carlo simulations of high energy electron trajectories reveal that only little beam broadening occurs within this thickness of Al film. Consequently, the MTF is limited predominantly by broadening within the thin phosphor underlayer. There are difficulties however, in the practical implementation of this design, associated mostly with the mechanical stability of the Al support film.

A conduction-cooled stage for high-resolution Cryo-SEM

1992 ◽  
Vol 50 (2) ◽  
pp. 1282-1283
Author(s):  
John G. Sheehan
Keyword(s):  
High Resolution ◽  
Liquid Nitrogen ◽  
Mechanical Stability ◽  
Cooling System ◽  
Cold Trap ◽  
Nitrogen Gas ◽  
Particulate Suspensions ◽  
Advantages And Disadvantages ◽  
Convection Cooling ◽  
Styrene Butadiene

The goal is to examine with high resolution cryo-SEM aqueous particulate suspensions used in coatings for printable paper. A metal-coating chamber for cryo-preparation of such suspensions was described previously. Here, a new conduction-cooling system for the stage and cold-trap in an SEM specimen chamber is described. Its advantages and disadvantages are compared to a convection-cooling system made by Hexland (model CT1000A) and its mechanical stability is demonstrated by examining a sample of styrene-butadiene latex.In recent high resolution cryo-SEM, some stages are cooled by conduction, others by convection. In the latter, heat is convected from the specimen stage by cold nitrogen gas from a liquid-nitrogen cooled evaporative heat exchanger. The advantage is the fast cooling: the Hexland CT1000A cools the stage from ambient temperature to 88 K in about 20 min. However it consumes huge amounts of liquid-nitrogen and nitrogen gas: about 1 ℓ/h of liquid-nitrogen and 400 gm/h of nitrogen gas. Its liquid-nitrogen vessel must be re-filled at least every 40 min.

SiO2 Entrapment of Animal Cells for Hybrid Bioartificial Organs

2000 ◽  
Vol 628 ◽  
Author(s):  
Giovanni Carturan ◽  
Renzo Dal Monte ◽  
Maurizio Muraca
Keyword(s):  
Gas Phase ◽  
Mechanical Stability ◽  
Porous Silica ◽  
Collagen Matrix ◽  
Homogeneous Layer ◽  
Animal Cells ◽  
Bioartificial Organs ◽  
Liver And Pancreas ◽  
Encapsulation Method ◽  
Metabolic Activities

ABSTRACTSi-alkoxides in gas phase are reactive towards the surface of animal cells, depositing a homogeneous layer of porous silica. This encapsulation method preserves cell viability and does not alter the hindrance of the biological load.In the prospective use for the design of a hybrid bioartificial liver, hepatocytes in a collagen matrix can be entrapped by the siliceous deposit which provides definite mechanical stability to the collagen matrix and molecular cutoff vs. high molecular weight proteins, including immunoglobulins. The functionality of the encapsulated cell load is maintained for the expressions of typical liver and pancreas metabolic activities.

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