A Nonintrusive Method of Measuring the Local Mechanical Properties of Soft Hydrogels Using Magnetic Microneedles

2008 ◽  
Vol 131 (2) ◽  
Author(s):  
Uday Chippada ◽  
Bernard Yurke ◽  
Penelope C. Georges ◽  
Noshir A. Langrana
Keyword(s):  
Magnetic Field ◽  
Mechanical Properties ◽  
Field Gradient ◽  
Type I Collagen ◽  
Zero Magnetic Field ◽  
Arbitrary Field ◽  
Type I ◽  
Collagen Gels ◽  
Field Gradients ◽  
The Magnetic Field

Soft hydrogels serving as substrates for cell attachment are used to culture many types of cells. The mechanical properties of these gels influence cell morphology, growth, and differentiation. For studies of cell growth on inhomogeneous gels, techniques by which the mechanical properties of the substrate can be measured within the proximity of a given cell are of interest. We describe an apparatus that allows the determination of local gel elasticity by measuring the response of embedded micron-sized magnetic needles to applied magnetic fields. This microscope-based four-magnet apparatus can apply both force and torque on the microneedles. The force and the torque are manipulated by changing the values of the magnetic field at the four poles of the magnet using a feedback circuit driven by LABVIEW. Using Hall probes, we have mapped out the magnetic field and field gradients produced by each pole when all the other poles are held at zero magnetic field. We have verified that superposition of these field maps allows one to obtain field maps for the case when the poles are held at arbitrary field values. This allows one to apply known fields and field gradients to a given microneedle. An imaging system is employed to measure the displacement and rotation of the needles. Polyacrylamide hydrogels of known elasticity were used to determine the relationship between the field gradient at the location of the needles and the force acting on the needles. This relationship allows the force on the microneedle to be determined from a known field gradient. This together with a measurement of the displacement of the needle in a given gel allows one to determine the stiffness (F∕δ) of the gel and the elastic modulus, provided Poison’s ratio is known. Using this method, the stiffness and the modulus of elasticity of type-I collagen gels were found to be 2.64±0.05nN∕μm and 284.6±5.9Pa, respectively. This apparatus is presently being employed to track the mechanical stiffness of the DNA-cross-linked hydrogels, developed by our group, whose mechanical properties can be varied on demand by adding or removing cross-linker strands. Thus a system that can be utilized to track the local properties of soft media as a function of time with minimum mechanical disturbance in the presence of cells is presented.

Effects of the magnetic field gradient on the wall power deposition of Hall thrusters

2017 ◽  
Vol 83 (2) ◽  
Author(s):  
Yongjie Ding ◽  
Peng Li ◽  
Xu Zhang ◽  
Liqiu Wei ◽  
Hezhi Sun ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Field Gradient ◽  
Discharge Channel ◽  
Magnetic Field Gradient ◽  
Zero Magnetic Field ◽  
Power Deposition ◽  
Neutral Gas ◽  
Channel Exit ◽  
Ionization Region ◽  
The Magnetic Field

The effect of the magnetic field gradient in the discharge channel of a Hall thruster on the ionization of the neutral gas and power deposition on the wall is studied through adopting the 2D-3V particle-in-cell (PIC) and Monte Carlo collisions (MCC) model. The research shows that by gradually increasing the magnetic field gradient while keeping the maximum magnetic intensity at the channel exit and the anode position unchanged, the ionization region moves towards the channel exit and then a second ionization region appears near the anode region. Meanwhile, power deposition on the walls decreases initially and then increases. To avoid power deposition on the walls produced by electrons and ions which are ionized in the second ionization region, the anode position is moved towards the channel exit as the magnetic field gradient is increased; when the anode position remains at the zero magnetic field position, power deposition on the walls decreases, which can effectively reduce the temperature and thermal load of the discharge channel.

Analytical and Experimental Study of Magnetomechanical Properties of Magnetic Porous PDMS Sponge Under Non-Uniform Magnetic Fields

2020 ◽  
Vol 87 (8) ◽  
Author(s):  
Ali Shademani ◽  
Mu Chiao
Keyword(s):  
Magnetic Field ◽  
Mechanical Properties ◽  
Experimental Study ◽  
Magnetic Fields ◽  
Field Gradient ◽  
Magnetic Field Gradient ◽  
Experimental Methods ◽  
Compression Tests ◽  
Magnetomechanical Coupling ◽  
The Magnetic Field

Abstract Magnetic elastomers (MEs) respond to an applied magnetic field through magnetomechanical coupling, where the mechanical properties of the MEs change with magnetic field strength. These phenomena have been mostly studied under homogenous magnetic fields due to the simplicity. In this work, the effects of the magnetic field gradient on the mechanical properties and the response of the MEs was examined. MEs are made by embedding carbonyl iron microparticles (CI) into a polydimethylsiloxane (PDMS) matrix, which is later rendered porous. The influence of the CI concentration was investigated by manipulating four different samples with CI/PDMS weight ratios of 0.2, 0.6, 1.0, and 1.4. An analytical method was proposed to further understand the interactions of the magnetic field gradient and the material’s response. The proposed theory was later verified with experimental results from compression tests in the presence of different magnetic fields. The proposed theoretical framework and experimental methods can be used to improve the design of MEs in the future.

Magnetostrictive gradient in Tb0.27Dy0.73Fe1.95 induced by high magnetic field gradient applied during solidification

2016 ◽  
Vol 09 (01) ◽  
pp. 1650003 ◽  
Author(s):  
Pengfei Gao ◽  
Tie Liu ◽  
Meng Dong ◽  
Yi Yuan ◽  
Kai Wang ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Field Gradient ◽  
High Magnetic Field ◽  
Applied Magnetic Field ◽  
Magnetic Field Gradient ◽  
Gradient Distribution ◽  
Field Gradients ◽  
Magnetic Field Gradients ◽  
The Magnetic Field

We investigated how high magnetic field gradients affected the magnetostrictive performance of Tb[Formula: see text]Dy[Formula: see text]Fe[Formula: see text] during solidification. At high applied magnetic field gradients, the magnetostriction exhibited a gradient distribution throughout the alloy. Increasing the magnetic field gradient also increased the magnetostriction gradient. We attributed the graded magnetostrictive performance to the gradient distribution of (Tb, Dy)Fe2 phase in the alloy and its orientation.

Guiding Stem Cell Differentiation Into Neural Lineages With Tunable Collagen Biomaterials

2009 ◽  
Author(s):  
Gary A. Monteiro ◽  
David I. Shreiber
Keyword(s):  
Mechanical Properties ◽  
Stem Cells ◽  
Stem Cell ◽  
Cell Differentiation ◽  
Type I Collagen ◽  
Striated Muscle ◽  
Stem Cell Differentiation ◽  
Type I ◽  
Collagen Gels ◽  
Biomaterial Scaffolds

The long-term objective of this research is to develop tunable collagen-based biomaterial scaffolds for directed stem cell differentiation into neural lineages to aid in CNS diseases and trauma. Type I collagen is a ubiquitous protein that provides mechanostructural and ligand-induced biochemical cues to cells that attach to the protein via integrin receptors. Previous studies have demonstrated that the mechanical properties of a substrate or tissue can be an important regulator of stem cell differentiation. For example, the mechanical properties polyacrylamide gels can be tuned to induce neural differentiation from stem cells [1, 2]. Mesenchymal stem cells (MSCs) cultured on ployacrylamide gels with low elastic modulus (0.1–1 kPa) resulted in a neural like population. MSCs on 10-fold stiffer matrices that mimic striated muscle elasticity (Emuscle ∼8–17 kPa) lead to spindle-shaped cells similar in shape to myoblasts. Still stiffer gels (25–40 kPa) resulted in osetoblast differentiation. Based on these observations, collagen gels may provide an ideal material for differentiation into neural lineages because of their low compliance.

Photo-Cross-Linking of Type I Collagen Gels in the Presence of Smooth Muscle Cells:  Mechanical Properties, Cell Viability, and Function

2003 ◽  
Vol 4 (4) ◽  
pp. 890-895 ◽  
Author(s):  
William T. Brinkman ◽  
Karthik Nagapudi ◽  
Benjamin S. Thomas ◽  
Elliot L. Chaikof
Keyword(s):  
Mechanical Properties ◽  
Smooth Muscle ◽  
Smooth Muscle Cells ◽  
Cell Viability ◽  
Type I Collagen ◽  
Muscle Cells ◽  
Cross Linking ◽  
Type I ◽  
Collagen Gels ◽  
And Function

Intrinsic mechanical properties of the extracellular matrix affect the behavior of pre-osteoblastic MC3T3-E1 cells

2006 ◽  
Vol 290 (6) ◽  
pp. C1640-C1650 ◽  
Author(s):  
Chirag B. Khatiwala ◽  
Shelly R. Peyton ◽  
Andrew J. Putnam
Keyword(s):  
Mechanical Properties ◽  
Type I Collagen ◽  
Focal Adhesions ◽  
Microscopic Analysis ◽  
Maximal Activity ◽  
Type I ◽  
Cell Functions ◽  
Collagen Density ◽  
Cells Cultured ◽  
In Cells

Mechanical cues present in the ECM have been hypothesized to provide instructive signals that dictate cell behavior. We probed this hypothesis in osteoblastic cells by culturing MC3T3-E1 cells on the surface of type I collagen-modified hydrogels with tunable mechanical properties and assessed their proliferation, migration, and differentiation. On gels functionalized with a low type I collagen density, MC3T3-E1 cells cultured on polystyrene proliferated twice as fast as those cultured on the softest substrate. Quantitative time-lapse video microscopic analysis revealed random motility speeds were significantly retarded on the softest substrate (0.25 ± 0.01 μm/min), in contrast to maximum speeds on polystyrene substrates (0.42 ± 0.04 μm/min). On gels functionalized with a high type I collagen density, migration speed exhibited a biphasic dependence on ECM compliance, with maximum speeds (0.34 ± 0.02 μm/min) observed on gels of intermediate stiffness, whereas minimum speeds (0.24 ± 0.03 μm/min) occurred on both the softest and most rigid (i.e., polystyrene) substrates. Immature focal contacts and a poorly organized actin cytoskeleton were observed in cells cultured on the softest substrates, whereas those on more rigid substrates assembled mature focal adhesions and robust actin stress fibers. In parallel, focal adhesion kinase (FAK) activity (assessed by detecting pY397-FAK) was influenced by compliance, with maximal activity occurring in cells cultured on polystyrene. Finally, mineral deposition by the MC3T3-E1 cells was also affected by ECM compliance, leading to the conclusion that altering ECM mechanical properties may influence a variety of MC3T3-E1 cell functions, and perhaps ultimately, their differentiated phenotype.

Assembly of type I collagen: fusion of fibril subunits and the influence of fibril diameter on mechanical properties

2000 ◽  
Vol 19 (5) ◽  
pp. 409-420 ◽  
Author(s):  
David L. Christiansen ◽  
Eric K. Huang ◽  
Frederick H. Silver
Keyword(s):  
Mechanical Properties ◽  
Type I Collagen ◽  
Type I ◽  
Fibril Diameter

scholarly journals Magnetophonons & type-B Goldstones from hydrodynamics to holography

2020 ◽  
Vol 2020 (9) ◽  
Author(s):  
Matteo Baggioli ◽  
Sebastian Grieninger ◽  
Li Li
Keyword(s):  
Magnetic Field ◽  
2D Materials ◽  
Goldstone Boson ◽  
Quasinormal Modes ◽  
Effective Field ◽  
Zero Magnetic Field ◽  
Type B ◽  
Hydrodynamic Modes ◽  
Pinning Mechanism ◽  
The Magnetic Field

Abstract We perform a detailed analysis of a large class of effective holographic models with broken translations at finite charge density and magnetic field. We exhaustively discuss the dispersion relations of the hydrodynamic modes at zero magnetic field and successfully match them to the predictions from charged hydrodynamics. At finite magnetic field, we identify the presence of an expected type-B Goldstone boson Re[ω] ∼ k2, known as magnetophonon and its gapped partner — the magnetoplasmon. We discuss their properties in relation to the effective field theory and hydrodynamics expectations. Finally, we compute the optical conductivities and the quasinormal modes at finite magnetic field. We observe that the pinning frequency of the magneto-resonance peak increases with the magnetic field, in agreement with experimental data on certain 2D materials, revealing the quantum nature of the holographic pinning mechanism.

Abstract 418: Co-Culture of Endothelial Cells, Smooth Muscle Cells and Monocytes in Collagen Scaffold: A Novel i n vitro Model of Atherosclerosis

2017 ◽  
Vol 37 (suppl_1) ◽  
Author(s):  
Martin Liu ◽  
Angelos Karagiannis ◽  
Matthew Sis ◽  
Srivatsan Kidambi ◽  
Yiannis Chatzizisis
Keyword(s):  
Endothelial Cells ◽  
Smooth Muscle ◽  
Smooth Muscle Cells ◽  
Type I Collagen ◽  
Smooth Muscle Actin ◽  
Muscle Cells ◽  
Type I ◽  
Collagen Gels ◽  
Human Coronary Artery

Objectives: To develop and validate a 3D in-vitro model of atherosclerosis that enables direct interaction between various cell types and/or extracellular matrix. Methods and Results: Type I collagen (0.75 mg/mL) was mixed with human artery smooth muscle cells (SMCs; 6x10 5 cells/mL), medium, and water. Human coronary artery endothelial cells (HCAECs; 10 5 /cm 2 ) were plated on top of the collagen gels and activated with oxidized low density lipoprotein cholesterol (LDL-C). Monocytes (THP-1 cells; 10 5 /cm 2 ) were then added on top of the HCAECs. Immunofluorescence showed the expression of VE-cadherin by HCAECs (A, B) and α-smooth muscle actin by SMCs (A). Green-labelled LDL-C particles were accumulated in the subendothelial space, as well as in the cytoplasm of HCAECs and SMCs (C). Activated monocytes were attached to HCAECs and found in the subendothelial area (G-I). Both HCAECs and SMCs released IL-1β, IL-6, IL-8, PDGF-BB, TGF-ß1, and VEGF. Scanning and transmission electron microscopy showed the HCAECs monolayer forming gap junctions and the SMCs (D-F) and transmigrating monocytes within the collagen matrix (G-I). Conclusions: In this work, we presented a novel, easily reproducible and functional in-vitro experimental model of atherosclerosis that has the potential to enable in-vitro sophisticated molecular and drug development studies.

scholarly journals Mechanical Properties of Native and Cross-linked Type I Collagen Fibrils

2008 ◽  
Vol 94 (6) ◽  
pp. 2204-2211 ◽  
Author(s):  
Lanti Yang ◽  
Kees O. van der Werf ◽  
Carel F.C. Fitié ◽  
Martin L. Bennink ◽  
Pieter J. Dijkstra ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Type I Collagen ◽  
Collagen Fibrils ◽  
Type I
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