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Intracellular CalciumWaves in Bone Cell Networks Under Single Cell Nanoindentation
In this study, bone cells were successfully cultured into a micropatterned network with dimensions close to that of in vivo osteocyte networks using microcontact printing and self-assembled monolyers (SAMs). The optimal geometric parameters for the formation of these networks were determined in terms of circle diameters and line widths. Bone cells patterned in these networks were also able to form gap junctions with each other, shown by immunofluorescent staining for the gap junction protein connexin 43, as well as the transfer of gap-junction permeable calcein-AM dye.
No need to worry about gravity at the atomic-/nano-scale
When a metal is grown onto a substrate of itself (homoepitaxy), the growth front is typically smooth, or at most is roughened by the formation of shallow hills (called surface mounds). The underlying reason for the roughening has been recognized to be of kinetic nature: Atoms landed on an upper terrace do not have enough time to overcome the "road blocks" provided by the steps and fill all the valleys (known as the Villian instability).
Molecular and Cellular Biomechanics Journal
A new journal dedicated to the field of Molecular and Cellular Biomechanics has been formed for about a year. Many members in this community (such as Ning Wang, Cheng Zhu, Phil LeDuc) are on the board of editors. You may want to check it out....
Micro cantilever pre-stress
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Dear all,
Im a PhD student in Cambridge Uni, UK working in the field of MEMS, and as part of my work, of late Ive been looking at deriving materials properties of MEMS thin film materials by means of resonant testing. The basic outline of the experiment is first creating free standing rectangular cantilevers of the material under test, evaporate with gold to increase reflectivity (when needed), then (under reasonable vacuum) applying a base excitation using a chirp signal into a piezo actuator and logging the cantilever tip response using a laser/photodetector setup. The frequency response is then calculated and the modal frequencies noted.
To determine the materials' properties, both an analytical model (with bending/torsion modes) and finite element model (using 2D mindlin) are created with similar geometry as the sample, and by minimising the squared relative error between the measured modes and those from the models, the value of Young's modulus (known density) and poissons ratio may be determined iteratively. These yield fairly consistent results.
To take the work further I now feel I should also include the effects of residual stress in the cantilevers. The method Ive been looking at is by using finite element (via COMSOL) - the beam geometry is created and loaded with the stress model ('surface stress' as a force tangential to the top boundary, and gradient stress as a 'tangential' force that varies from +F to -F from top to bottom boundary of the cantilever). The model is solved statically, and the deformed shape is then saved as the linearisation point for the next model, which then computes the eigenfrequencies. Btw I can only do this in 3D FE, which makes computation times quite long hence using iteration to quantify this stress highly unlikely.
In any case, is there an analytical model I can use to model the effect of this stress on multiple modes of a cantilever. Id like to verify whether the FE is giving me anything close to ball park numbers before I work out a means to compare them with experimental results. I was thinking of using the Rayleigh method by representing the effect of prestress as an additional term in the potential energy. The original mode shapes, with some modification will be used to evaluate the two energy integrals. The potential energy due to stress is worked out by measuring the static deflected shape using a zygo inteferometer - some rough model is used, with the beam curvature and peak deflection as input to work out the amount of this energy. Not having much experience in mechanics (i was an electronics undergrad!), Im not sure how good an estimate this would be, if at all its a useable or even possible one. Will the extra energy factor in to the torsion modes just the same?
The iMechanica Journal Club (iMech jClub)
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2025 Themes and Discussion Leaders
Mass sensing by using a resonating microcantilever
We recently reported the mass sensing by using resonating microcantilevers. The characterization of mass-sensing and its related sensitivity was suggested on the basis of elasticity theory.
Model Reduction of Large Proteins for Normal Mode Studies
Recently, I reported the model reduction method for large proteins for understanding large protein dynamics based on low-frequency normal modes. This work was pubslihed at Journal of Computational Chemistry (click here).
Coarse-Graining of protein structures for the normal mode studies
Abstracts
Quantum Stability of Metallic Thin Films and Nanostructures
When a metal system shrinks its dimension(s), the conduction electrons inside the metal feel the squeezing, and are forced into (discrete) quantum states. Such confined motion of the conduction electrons may influence the global or local stability of the low dimensional systems, and in the case of a thin film on a foreign substrate this "quantum energy" of electronic origin can easily overwhelm the strain effects in definging the film stability, thereby severely influencing the preferred growth mode (see, e.g., Suo and Zhang, Phys. Rev. B 58, 5116 (1998)).
Mechanics and deformation of the nucleus in micropipette aspiration experiment
Robust biomechanical models are essential for studying the nuclear mechanics and can help shed light on the underlying mechanisms of stress transition in nuclear elements. Here, we develop a computational model for an isolated nucleus undergoing micropipette aspiration. Our model includes distinct components representing the nucleoplasm and the nuclear envelope. The nuclear envelope itself comprises three layers: inner and outer nuclear membranes and one thicker layer representing the nuclear lamina.