In JoVE (2)

Other Publications (24)

Articles by Delphine Dean in JoVE

Other articles by Delphine Dean on PubMed

Mechanical Compression of Cartilage Explants Induces Multiple Time-dependent Gene Expression Patterns and Involves Intracellular Calcium and Cyclic AMP

The Journal of Biological Chemistry. May, 2004  |  Pubmed ID: 14960571

Chondrocytes are influenced by mechanical forces to remodel cartilage extracellular matrix. Previous studies have demonstrated the effects of mechanical forces on changes in biosynthesis and mRNA levels of particular extracellular matrix molecules, and have identified certain signaling pathways that may be involved. However, the broad extent and kinetics of mechano-regulation of gene transcription has not been studied in depth. We applied static compressive strains to bovine cartilage explants for periods between 1 and 24 h and measured the response of 28 genes using real time PCR. Compression time courses were also performed in the presence of an intracellular calcium chelator or an inhibitor of cyclic AMP-activated protein kinase A. Cluster analysis of the data revealed four main expression patterns: two groups containing either transiently up-regulated or duration-enhanced expression profiles could each be subdivided into genes that did or did not require intracellular calcium release and cyclic AMP-activated protein kinase A for their mechano-regulation. Transcription levels for aggrecan, type II collagen, and link protein were up-regulated approximately 2-3-fold during the first 8 h of 50% compression and subsequently down-regulated to levels below that of free-swelling controls by 24 h. Transcription levels of matrix metalloproteinases-3, -9, and -13, aggrecanase-1, and the matrix protease regulator cyclooxygenase-2 increased with the duration of 50% compression 2-16-fold by 24 h. Thus, transcription of proteins involved in matrix remodeling and catabolism dominated over anabolic matrix proteins as the duration of static compression increased. Immediate early genes c-fos and c-jun were dramatically up-regulated 6-30-fold, respectively, during the first 8 h of 50% compression and remained up-regulated after 24 h.

Nanoscale Variation in Surface Charge of Synthetic Hydroxyapatite Detected by Chemically and Spatially Specific High-resolution Force Spectroscopy

Biomaterials. Jan, 2005  |  Pubmed ID: 15262469

The normal intersurface forces between nanosized probe tips functionalized with COO-- and NH3+-terminated alkanethiol self-assembling monolayers and dense polycrystalline phase pure synthetic hydroxyapatite (HA) were measured via a powerful nanomechanical technique called chemically specific high-resolution force spectroscopy. The data taken on approach of the probe tip to the HA surface was compared to the nonlinear Poisson-Boltzmann-based electrostatic double layer theory to predict the surface charge per unit area of the HA, sigmaHA (C/m2), as a function of ionic strength, position within a variety of grains, and across grain boundaries. The average sigmaHA was found to be approximately -0.02 C/m2 and to vary from -0.0037 to -0.072 C/m2 with nanoscale position in relation to grain boundaries and crystal planes up to -0.19 C/m2/microm. Positional measurement of nanoscale surface properties holds great promise in elucidating the molecular origins of physicochemical processes occurring at the biomaterial interface.

Nanomechanics of Opposing Glycosaminoglycan Macromolecules

Journal of Biomechanics. Sep, 2005  |  Pubmed ID: 16023465

In this study, the net intermolecular interaction force between a chondroitin sulfate glycosaminoglycan (GAG)-functionalized probe tip and an opposing GAG-functionalized planar substrate was measured as a function of probe tip-substrate separation distance in aqueous electrolyte solutions using the technique of high resolution force spectroscopy. A range of GAG grafting densities as near as possible to native cartilage was used. A long-range repulsive force between GAGs on the probe tip and substrate was observed, which increased nonlinearly with decreasing separation distance between probe tip and substrate. Data obtained in 0.1 M NaCl was well predicted by a recently developed Poisson-Boltzmann-based theoretical model that describes normal electrostatic double layer interaction forces between two opposing surfaces of end-grafted, cylindrical rods of constant volume charge density and finite length, which interdigitate upon compression. Based on these results, the nanomechanical data and interdigitated rod model were used together to estimate the electrostatic component of the equilibrium modulus of cartilage tissue, which was then compared to that of normal adult human ankle cartilage measured in uniaxial confined compression.

Compressive Nanomechanics of Opposing Aggrecan Macromolecules

Journal of Biomechanics. 2006  |  Pubmed ID: 16289077

In this study, we have measured the nanoscale compressive interactions between opposing aggrecan macromolecules in near-physiological conditions, in order to elucidate the molecular origins of tissue-level cartilage biomechanical behavior. Aggrecan molecules from fetal bovine epiphyseal cartilage were chemically end-grafted to planar substrates, standard nanosized atomic force microscopy (AFM) probe tips (R(tip) approximately 50 nm), and larger colloidal probe tips (R(tip) approximately 2.5 microm). To assess normal nanomechanical interaction forces between opposing aggrecan layers, substrates with microcontact printed aggrecan were imaged using contact mode AFM, and aggrecan layer height (and hence deformation) was measured as a function of solution ionic strength (IS) and applied normal load. Then, using high-resolution force spectroscopy, nanoscale compressive forces between opposing aggrecan on the tip and substrate were measured versus tip-substrate separation distance in 0.001-1M NaCl. Nanosized tips enabled measurement of the molecular stiffness of 2-4 aggrecan while colloidal tips probed the nanomechanical properties of larger assemblies (approximately 10(4) molecules). The compressive stiffness of aggrecan was much higher when using a densely packed colloidal tip than the stiffness measured for using the nanosized tip with a few aggrecan, demonstrating the importance of lateral interactions to the normal nanomechanical properties. The measured stress at 0.1M NaCl (near-physiological ionic strength) increased sharply at aggrecan densities under the tip of approximately 40 mg/ml (physiological densities are approximately 20-80 mg/ml), corresponding to an average inter-GAG spacing of 4-5 Debye lengths (4-5 nm); this characteristic spacing is consistent with the onset of significant electrostatic interactions between GAG chains of opposing aggrecan molecules. Comparison of nanomechanical data to the predictions of Poisson-Boltzmann-based models further elucidated the regimes over which electrostatic and nonelectrostatic interactions affect aggrecan stiffness in compression. The most important aspects of this study include: the incorporation of experiments at two different length scales, the use of microcontact printing to enable quantification of aggrecan deformation and the corresponding nanoscale compressive stress vs. strain curve, the use of tips of differing functionality to provide insights into the molecular mechanisms of deformation, and the comparison of experimental data to the predictions of three increasingly refined Poisson-Boltzmann (P-B)-based theoretical models for the electrostatic double layer component of the interaction.

Silicon Addition to Hydroxyapatite Increases Nanoscale Electrostatic, Van Der Waals, and Adhesive Interactions

Journal of Biomedical Materials Research. Part A. Aug, 2006  |  Pubmed ID: 16646067

The normal intersurface forces between nanosized probe tips functionalized with COO(-)-terminated alkanethiol self-assembling monolayers and dense, polycrystalline silicon-substituted synthetic hydroxyapatite (SiHA) and phase pure hydroxyapatite (HA) were measured via a nanomechanical technique called chemically specific high-resolution force spectroscopy. A significantly larger van der Waals interaction was observed for the SiHA compared to HA; Hamaker constants (A) were found to be A(SiHA) = 35 +/- 27 zJ and A(HA) = 13 +/- 12 zJ. Using the Derjaguin-Landau-Verwey-Overbeek approximation, which assumes linear additivity of the electrostatic double layer and van der Waals components, and the nonlinear Poisson-Boltzmann surface charge model for electrostatic double-layer forces, the surface charge per unit area, sigma (C/m(2)), was calculated as a function of position for specific nanosized areas within individual grains. SiHA was observed to be more negatively charged than HA with sigma(SiHA) = -0.024 +/- 0.013 C/m(2), two times greater than sigma(HA) = -0.011 +/- 0.006 C/m(2). Additionally, SiHA was found to have increased surface adhesion (0.7 +/- 0.3 nN) compared to HA (0.5 +/- 0.3 nN). The characterization of the nanoscale variations in surface forces of SiHA and HA will enable an improved understanding of the initial stages of bone-biomaterial bonding.

Cell Deposition System Based on Laser Guidance

Biotechnology Journal. Sep, 2006  |  Pubmed ID: 16941447

We have designed a laser cell deposition system that employs the phenomenon of laser guidance to place single cells at specific points in a variety of in vitro environments. Here, we describe the components of the system: the laser optics, the deposition chamber, the microinjection cell feeding system and our custom system control software application. We discuss the requirements and challenges involved in laser guidance of cells and how our present system overcomes these challenges. We demonstrate that the patterning system is accurate within one micrometer by repeatedly depositing polymer microspheres and measuring their position. We demonstrate its ability to create highly defined living patterns of cells by creating a defined pattern of neurons with neurite extensions displaying normal function. We found that the positional accuracy of our system is smaller than the variations in cell size and pattern disruptions that occur from normal cell movement during substrate adhesion. The laser cell deposition system is a potentially useful tool that can be used to achieve site- and time-specific placement of an individual cell in a cell culture for the systematic investigation of cell-cell and cell-extracellular matrix interactions.

Lateral Nanomechanics of Cartilage Aggrecan Macromolecules

Biophysical Journal. Feb, 2007  |  Pubmed ID: 17142289

To explore the role of the brush-like proteoglycan, aggrecan, in the shear behavior of cartilage tissue, we measured the lateral resistance to deformation of a monolayer of chemically end-attached cartilage aggrecan on a microcontact printed surface in aqueous NaCl solutions via lateral force microscopy. The effects of bath ionic strength (IS, 0.001-1.0 M) and lateral displacement rate (approximately 1-100 microm/s) were studied using probe tips functionalized with neutral hydroxyl-terminated self-assembled alkanethiol monolayers. Probe tips having two different end-radii (R approximately 50 nm and 2.5 microm) enabled access to different length-scales of interactions (nano and micro). The measured lateral force was observed to depend linearly on the applied normal force, and the lateral force to normal force proportionality constant, mu, was calculated. The value mu increased (from 0.03 +/- 0.01 to 0.11 +/- 0.01) with increasing bath IS (0.001-1.0 M) for experiments using the microsized tip due to the larger compressive strain of aggrecan that resulted from increased IS at constant compressive force. With the nanosized tip, mu also increased with IS but by a smaller amount due to the fewer number of aggrecan involved in shear deformation. The variations in lateral force as a function of applied compressive strain epsilon(n) and changes in bath IS suggested that both electrostatic and nonelectrostatic interactions contributed significantly to the shear deformational behavior of the aggrecan layers. While lateral force did not vary with lateral displacement rate at low IS, where elastic-like electrostatic interactions between aggrecan dominated, lateral force increased significantly with displacement rate at physiological and higher IS, suggestive of additional viscoelastic and/or poroelastic interactions within the aggrecan layer. These data provide insights into molecular-level deformation of aggrecan macromolecules that are important to the understanding of cartilage behavior.

Nanoscale Shear Deformation Mechanisms of Opposing Cartilage Aggrecan Macromolecules

Biophysical Journal. Sep, 2007  |  Pubmed ID: 17586571

The nanoscale shear deformation behavior of two opposing end-grafted aggrecan layers was studied in aqueous solutions using atomic force microscopy, and was observed to depend markedly on bath ionic strength, the presence of calcium ions, and the applied lateral displacement rate. These results provide molecular-level insights into the contribution of aggrecan deformation mechanisms to cartilage tissue-level material properties.

Cartilage Aggrecan Can Undergo Self-adhesion

Biophysical Journal. Nov, 2008  |  Pubmed ID: 18676640

Here it is reported that aggrecan, the highly negatively charged macromolecule in the cartilage extracellular matrix, undergoes Ca(2+)-mediated self-adhesion after static compression even in the presence of strong electrostatic repulsion in physiological-like solution conditions. Aggrecan was chemically end-attached onto gold-coated planar silicon substrates and gold-coated microspherical atomic force microscope probe tips (end radius R approximately 2.5 mum) at a density ( approximately 40 mg/mL) that simulates physiological conditions in the tissue ( approximately 20-80 mg/mL). Colloidal force spectroscopy was employed to measure the adhesion between opposing aggrecan monolayers in NaCl (0.001-1.0 M) and NaCl + CaCl(2) ([Cl(-)] = 0.15 M, [Ca(2+)] = 0 - 75 mM) aqueous electrolyte solutions. Aggrecan self-adhesion was found to increase with increasing surface equilibration time upon compression (0-30 s). Hydrogen bonding and physical entanglements between the chondroitin sulfate-glycosaminoglycan side chains are proposed as important factors contributing to aggrecan self-adhesion. Self-adhesion was found to significantly increase with decreasing bath ionic strength (and hence, electrostatic double-layer repulsion), as well as increasing Ca(2+) concentration due to the additional ion-bridging effects. It is hypothesized that aggrecan self-adhesion, and the macromolecular energy dissipation that results from this self-adhesion, could be important factors contributing to the self-assembled architecture and integrity of the cartilage extracellular matrix in vivo.

Role of Cytoskeletal Components in Stress-relaxation Behavior of Adherent Vascular Smooth Muscle Cells

Journal of Biomechanical Engineering. Apr, 2009  |  Pubmed ID: 19275430

A number of recent studies have demonstrated the effectiveness of atomic force microscopy (AFM) for characterization of cellular stress-relaxation behavior. However, this technique's recent development creates considerable need for exploration of appropriate mechanical models for analysis of the resultant data and of the roles of various cytoskeletal components responsible for governing stress-relaxation behavior. The viscoelastic properties of vascular smooth muscle cells (VSMCs) are of particular interest due to their role in the development of vascular diseases, including atherosclerosis and restenosis. Various cytoskeletal agents, including cytochalasin D, jasplakinolide, paclitaxel, and nocodazole, were used to alter the cytoskeletal architecture of the VSMCs. Stress-relaxation experiments were performed on the VSMCs using AFM. The quasilinear viscoelastic (QLV) reduced-relaxation function, as well as a simple power-law model, and the standard linear solid (SLS) model, were fitted to the resultant stress-relaxation data. Actin depolymerization via cytochalasin D resulted in significant increases in both rate of relaxation and percentage of relaxation; actin stabilization via jasplakinolide did not affect stress-relaxation behavior. Microtubule depolymerization via nocodazole resulted in nonsignificant increases in rate and percentage of relaxation, while microtubule stabilization via paclitaxel caused significant decreases in both rate and percentage of relaxation. Both the QLV reduced-relaxation function and the power-law model provided excellent fits to the data (R(2)=0.98), while the SLS model was less adequate (R(2)=0.91). Data from the current study indicate the important role of not only actin, but also microtubules, in governing VSMC viscoelastic behavior. Excellent fits to the data show potential for future use of both the QLV reduced-relaxation function and power-law models in conjunction with AFM stress-relaxation experiments.

Cell Damage Evaluation of Thermal Inkjet Printed Chinese Hamster Ovary Cells

Biotechnology and Bioengineering. Aug, 2010  |  Pubmed ID: 20589673

Thermal inkjet printing technology has been applied successfully to cell printing. However, there are concerns that printing process may cause cell damages or death. We conducted a comprehensive study of thermal inkjet printed Chinese hamster ovary (CHO) cells by evaluating cell viability and apoptosis, and possible cell membrane damages. Additionally, we studied the cell concentration of bio-ink and found optimum printing of concentrations around 8 million cells per mL. Printed cell viability was 89% and only 3.5% apoptotic cells were observed after printing. Transient pores were developed in the cell membrane of printed cells. Cells were able to repair these pores within 2 h after printing. Green fluorescent protein (GFP) DNA plasmids were delivered to CHO-S cells by co-printing. The transfection efficiency is above 30%. We conclude that thermal inkjet printing technology can be used for precise cell seeding with minor effects and damages to the printed mammalian cells. The printing process causes transient pores in cell membranes, a process which has promising applications for gene and macroparticles delivery to induce the biocompatibility or growth of engineered tissues.

Frictional Behavior of Individual Vascular Smooth Muscle Cells Assessed By Lateral Force Microscopy

Materials. Sep, 2010  |  Pubmed ID: 21686041

With the advancement of the field of biotribology, considerable interest has arisen in the study of cell and tissue frictional properties. From the perspective of medical device development, the frictional properties between a rigid surface and underlying cells and tissues are of a particular clinical interest. As with many bearing surfaces, it is likely that contact asperities exist at the size scale of single cells and below. Thus, a technique to measure cellular frictional properties directly would be beneficial from both a clinical and a basic science perspective. In the current study, an atomic force microscope (AFM) with a 5 μm diameter borosilicate spherical probe simulating endovascular metallic stent asperities was used to characterize the surface frictional properties of vascular smooth muscle cells (VSMCs) in contact with a metallic endovascular stent. Various treatments were used to alter cell structure, in order to better understand the cellular components and mechanisms responsible for governing frictional properties. The frictional coefficient of the probe on VSMCs was found to be approximately 0.06. This frictional coefficient was significantly affected by cellular crosslinking and cytoskeletal depolymerization agents. These results demonstrate that AFM-based lateral force microscopy is a valuable technique to assess the friction properties of individual single cells on the micro-scale.

Variation of Surface Charge Along the Surface of Wool Fibers Assessed by High-Resolution Force Spectroscopy

Journal of Engineered Fibers and Fabrics. 2011  |  Pubmed ID: 21866220

In this study, we have mapped the surface charge of wool fibers using chemically specific high-resolution force spectroscopy in order to better understand the dispersion of amino acids in relation to fiber morphology. The inter-surface forces between standard atomic force microscopy (AFM) probe tips (tip radius ~ 50 nm) functionalized with COOH and NH(3) terminated alkanethiol self assembling monolayers and the wool surface were used to estimate the surface charge per unit area using linear Poisson-Boltzmann-based electrostatic double layer theory. The positional measurement of nano-scale surface charge showed a correlation between the surface charge and fiber morphology, indicated that basic amino acids are located near the scale edges.

Effect of Matrix on Cardiomyocyte Viscoelastic Properties in 2D Culture

Molecular & Cellular Biomechanics : MCB. Sep, 2012  |  Pubmed ID: 23285736

Cardiomyocyte phenotype changes significantly in 2D culture systems depending on the substrate composition and organization. Given the variety of substrates that are used both for basic cardiac cell culture studies and for regenerative medicine applications, there is a critical need to understand how the different matrices influence cardiac cell mechanics. In the current study, the mechanical properties of neonatal rat cardiomyocytes cultured in a subconfluent layer upon aligned and unaligned collagen and fibronectin matrices were assessed over a two week period using atomic force microscopy. The elastic modulus was estimated by fitting the Hertz model to force curve data and the percent relaxation was determined from stress relaxation curves. The Quasilinear Viscoelastic (QLV) and Standard Linear Solid (SLS) models were fit to the stress relaxation data. Cardiomyocyte cellular mechanical properties were found to be highly dependent on matrix composition and organization as well as time in culture. It was observed that the cells stiffened and relaxed less over the first 3 to 5 days in culture before reaching a plateau in their mechanical properties. After day 5, cells on aligned matrices were stiffer than cells on unaligned matrices and cells on fibronectin matrices were stiffer than cells on collagen matrices. No such significant trends in percent relaxation measurements were observed but the QLV model fit the data very well. These results were correlated with observed changes in cellular structure associated with culture on the different substrates and analyzed for cell-to-cell variability.

Green Synthesis of Robust, Biocompatible Silver Nanoparticles Using Garlic Extract

Journal of Nanomaterials. 2012  |  Pubmed ID: 24683414

This paper details a facile approach for the synthesis of stable and monodisperse silver nanoparticles performed at ambient/low temperature where Allium sativum (garlic) extract functions as the silver salt reducing agent during nanoparticle synthesis as well as the post-synthesis stabilizing ligands. Varying the synthesis conditions provides control of particle size, size-distribution, and kinetics of particle formation. Infrared spectroscopy, energy dispersive x-ray chemical analysis, and high performance liquid chromatography indicated that the carbohydrates present in the garlic extract are the most likely nanoparticle stabilizing chemistry. The synthesized silver nanoparticles also demonstrate potential for biomeical applications, owing to the 1) enhanced stability in biological media, 2) resistance to oxidation by the addition of H2O2, 3) ease and scalability of synthesis, and 4) lack of harsh chemicals required for synthesis. Cytotoxicity assays indicated no decrease in cellular proliferation for vascular smooth muscle cells and 3T3 fibroblasts at a concentration of 25 μg/ml, confirming that garlic extract prepared silver nanoparticles are ideal candidates for future experimentation and implementation into biomedical applications.

A Computational Approach to Understand Phenotypic Structure and Constitutive Mechanics Relationships of Single Cells

Annals of Biomedical Engineering. Mar, 2013  |  Pubmed ID: 23180027

The goal of this study is to construct a representative 3D finite element model (FEM) of individual cells based on their sub-cellular structures that predicts cell mechanical behavior. The FEM simulations replicate atomic force microscopy (AFM) nanoindentation experiments on live vascular smooth muscle cells. Individual cells are characterized mechanically with AFM and then imaged in 3D using a spinning disc confocal microscope. Using these images, geometries for the FEM are automatically generated via image segmentation and linear programming algorithms. The geometries consist of independent structures representing the nucleus, actin stress fiber network, and cytoplasm. These are imported into commercial software for mesh refinement and analysis. The FEM presented here is capable of predicting AFM results well for 500 nm indentations. The FEM results are relatively insensitive to both the exact number and diameter of fibers used. Despite the localized nature of AFM nanoindentation, the model predicts that stresses are distributed in an anisotropic manner throughout the cell body via the actin stress fibers. This pattern of stress distribution is likely a result of the geometric arrangement of the actin network.

Fluid Flow Forces and RhoA Regulate Fibrous Development of the Atrioventricular Valves

Developmental Biology. Feb, 2013  |  Pubmed ID: 23261934

Fibrous development of the extracellular matrix (ECM) of cardiac valves is necessary for proper heart function. Pathological remodeling of valve ECM is observed in both pediatric and adult cardiac disorders. It is well established that intracardiac hemodynamics play a significant role in the morphogenesis of cardiovascular tissues. However, the mechanisms that transduce mechanical forces into morphogenetic processes are not well understood. Here, we report the development of a three-dimensional, in vitro culture system that allows for culture of embryonic valve tissue under specific pulsatile flow conditions. This system was used to investigate the role that fluid flow plays in fibrous ECM expression during valve formation and to test the underlying cellular mechanisms that regulate this mechanotransduction. When cultured under pulsatile flow, developing valve tissues upregulated fibrous ECM expression at both the transcript and protein levels in comparison to no-flow controls. Flow-cultured valve tissues also underwent morphological development, as cushions elongated into leaflet-like structures that were absent in no-flow controls. Furthermore, rhoA, a member of the cytoskeletal actin-regulating GTPase family of proteins, was upregulated and activated by flow culture. Inhibition of the downstream rhoA effector kinase, ROCK, blocked flow-driven fibrous ECM accumulation and tissue stiffening, while the addition of lysophosphatidic acid (LPA), a rhoA activator, stimulated fibrous ECM deposition and tissue stiffening. These results support a prominent role for the rhoA pathway in the mechanotransduction of hemodynamic forces during fibrous remodeling of developing valve tissue. Our results also point to a potential link between regulation of the actinomyosin cytoskeleton and fibrous ECM synthesis in cardiovascular tissues.

A Linear Programming Approach to Reconstructing Subcellular Structures from Confocal Images for Automated Generation of Representative 3D Cellular Models

Medical Image Analysis. Apr, 2013  |  Pubmed ID: 23395283

This paper presents a novel computer vision algorithm to analyze 3D stacks of confocal images of fluorescently stained single cells. The goal of the algorithm is to create representative in silico model structures that can be imported into finite element analysis software for mechanical characterization. Segmentation of cell and nucleus boundaries is accomplished via standard thresholding methods. Using novel linear programming methods, a representative actin stress fiber network is generated by computing a linear superposition of fibers having minimum discrepancy compared with an experimental 3D confocal image. Qualitative validation is performed through analysis of seven 3D confocal image stacks of adherent vascular smooth muscle cells (VSMCs) grown in 2D culture. The presented method is able to automatically generate 3D geometries of the cell's boundary, nucleus, and representative F-actin network based on standard cell microscopy data. These geometries can be used for direct importation and implementation in structural finite element models for analysis of the mechanics of a single cell to potentially speed discoveries in the fields of regenerative medicine, mechanobiology, and drug discovery.

Increased Extracellular Matrix Density Decreases MCF10A Breast Cell Acinus Formation in 3D Culture Conditions

Journal of Tissue Engineering and Regenerative Medicine. Feb, 2013  |  Pubmed ID: 23404906

The extracellular matrix (ECM) contributes to the generation and dynamic of normal breast tissue, in particular to the generation of polarized acinar and ductal structures. In vitro 3D culture conditions, including variations in the composition of the ECM, have been shown to directly influence the formation and organization of acinus-like and duct-like structures. Furthermore, the density of the ECM appears to also play a role in the normal mammary tissue and tumour formation. Here we show that the density of the ECM directly influences the number, organization and function of breast acini. Briefly, non-malignant human breast MCF10A cells were incubated in increasing densities of a Matrigel®-collagen I matrix. Elastic moduli near and distant to the acinus structures were measured by atomic force microscopy, and the number of acinus structures was determined. Immunochemistry was used to investigate the expression levels of E-cadherin, laminin, matrix metalloproteinase-14 and ß-casein in MCF10A cells. The modulus of the ECM was significantly increased near the acinus structures and the number of acinus structures decreased with the increase in Matrigel-collagen I density. As evaluated by the expression of laminin, the organization of the acinus structures present was altered as the density of the ECM increased. Increases in both E-cadherin and MMP14 expression by MCF10A cells as ECM density increased were also observed. In contrast, MCF10A cells expressed lower ß-casein levels as the ECM density increased. Taken together, these observations highlight the key role of ECM density in modulating the number, organization and function of breast acini. Copyright © 2013 John Wiley & Sons, Ltd.

Effects of Low Dose X-ray Irradiation on Porcine Articular Cartilage Explants

Journal of Orthopaedic Research : Official Publication of the Orthopaedic Research Society. Nov, 2013  |  Pubmed ID: 23913833

Ionizing radiation therapy is a crucial treatment for cancer, but can damage surrounding normal tissues. Damage to articular cartilage leading to arthropathy can occur at irradiated sites. It is unclear whether this response is due to damaging surrounding skeletal structures or direct effects on cartilage. In this study, we showed that irradiation with 2 Gy of X-rays causes a significant reduction in the stiffness of porcine explants 1 week post-irradiation. By using both microindentation and indentation-type atomic force microscopy, ionizing radiation reduces stiffness in both the superficial zone, and throughout the entire thickness of the tissue. Young's modulus values were 75% and 60% lower in 2 Gy irradiated samples when compared with controls using microindentation and nanoindentation, respectively. Glycosaminoglycans (GAGs) released into the culture media of irradiated samples was nearly 100% greater at 24 h after exposure. While collagen content in the tissue is similar between groups, GAG content is 55% lower in irradiated explants compared with controls 7 days after exposure. Therefore, the irradiated explants are unable to recover from the initial loss of GAGs by 1 week. This acute loss of GAGs is a likely contributor to the reduction in modulus seen after exposure to ionizing radiation.

Molecular Adhesion Between Cartilage Extracellular Matrix Macromolecules

Biomacromolecules. Mar, 2014  |  Pubmed ID: 24491174

In this study, we investigated the molecular adhesion between the major constituents of cartilage extracellular matrix, namely, the highly negatively charged proteoglycan aggrecan and the type II/IX/XI fibrillar collagen network, in simulated physiological conditions. Colloidal force spectroscopy was applied to measure the maximum adhesion force and total adhesion energy between aggrecan end-attached spherical tips (end radius R ≈ 2.5 μm) and trypsin-treated cartilage disks with undamaged collagen networks. Studies were carried out in various aqueous solutions to reveal the physical factors that govern aggrecan-collagen adhesion. Increasing both ionic strength and [Ca(2+)] significantly increased adhesion, highlighting the importance of electrostatic repulsion and Ca(2+)-mediated ion bridging effects. In addition, we probed how partial enzymatic degradation of the collagen network, which simulates osteoarthritic conditions, affects the aggrecan-collagen interactions. Interestingly, we found a significant increase in aggrecan-collagen adhesion even when there were no detectable changes at the macro- or microscales. It is hypothesized that the aggrecan-collagen adhesion, together with aggrecan-aggrecan self-adhesion, works synergistically to determine the local molecular deformability and energy dissipation of the cartilage matrix, in turn, affecting its macroscopic tissue properties.

Enzyme-etching Technique to Fabricate Micropatterns of Aligned Collagen Fibrils

Biotechnology Letters. Jun, 2014  |  Pubmed ID: 24562408

A technique to tailor-make pre-coated, pre-aligned bovine collagen fibrils, derived from neonatal cardiomyocytes, on the surface of a glass slide into a designated pattern is reported. The unwanted collagen-coated area was erased by a collagenase solution and the tailored area was retained by attaching a microfabricated polydimethylsiloxane stamp directly to the collagen-coated surface. Using this technique, collagen patterns with designated orientations and with clear pattern boundaries and defined shapes were fabricated.

A Low-Cost Inkjet-Printed Glucose Test Strip System for Resource-Poor Settings

Journal of Diabetes Science and Technology. Jun, 2015  |  Pubmed ID: 26071426

The prevalence of diabetes is increasing in low-resource settings; however, accessing glucose monitoring is extremely difficult and expensive in these regions. Work is being done to address the multitude of issues surrounding diabetes care in low-resource settings, but an affordable glucose monitoring solution has yet to be presented. An inkjet-printed test strip solution is being proposed as a solution to this problem.

Comparative Limb Bone Loading in the Humerus and Femur of the Tiger Salamander: Testing the 'mixed-chain' Hypothesis for Skeletal Safety Factors

The Journal of Experimental Biology. Feb, 2016  |  Pubmed ID: 26596535

Locomotion imposes some of the highest loads upon the skeleton, and diverse bone designs have evolved to withstand these demands. Excessive loads can fatally injure organisms; however, bones have a margin of extra protection, called a 'safety factor' (SF), to accommodate loads that are higher than normal. The extent to which SFs might vary amongst an animal's limb bones is unclear. If the limbs are likened to a chain composed of bones as 'links', then similar SFs might be expected for all limb bones because failure of the system would be determined by the weakest link, and extra protection in other links could waste energetic resources. However, Alexander proposed that a 'mixed-chain' of SFs might be found amongst bones if: (1) their energetic costs differ, (2) some elements face variable demands, or (3) SFs are generally high. To test whether such conditions contribute to diversity in limb bone SFs, we compared the biomechanical properties and locomotor loading of the humerus and femur in the tiger salamander (Ambystoma tigrinum). Despite high SFs in salamanders and similar sizes of the humerus and femur that would suggest similar energetic costs, the humerus had lower bone stresses, higher mechanical hardness and larger SFs. SFs were greatest in the anatomical regions where yield stresses were highest in the humerus and lowest in the femur. Such intraspecific variation between and within bones may relate to their different biomechanical functions, providing insight into the emergence of novel locomotor capabilities during the invasion of land by tetrapods.

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