Increasing Matrix Density Research Articles

Coupled effect of MWCNTs concentration and induced pore structures on compressive performance and elastic modulus of ultra-high toughness cementitious composites: Experimental and theoretical studies

Due to the superior mechanical properties and electrical conductivity of multi-walled carbon nanotubes (MWCNTs), their integration into cementitious composites can improve compressive strength and self-sensing capabilities. However, balancing high mechanical strength with high conductivity is challenging as high MWCNT dosages can impede strength development. We addressed this by studying the effect of MWCNTs concentration (0–1.1 wt% of cementitious binders) and induced pore structures on the compressive performance and elastic modulus of ultra-high toughness cementitious composites (UHTCC), both experimentally and theoretically. It was found that as the MWCNTs concentration increased, the porosity continued to increase, while the compressive strength fluctuated. Two failure patterns were identified, i.e., quasi-brittle failure and ductile failure. Analysis showed MWCNTs could promote cement binder hydration, increasing matrix density but the strength development was curbed by increased porosity. A balance was achieved at 0.7 wt% MWCNTs. Further investigations using the Eshelby-Mori-Tanaka method discussed how MWCNT concentration, mechanical properties, distribution, porosity, and pore geometry influenced the elastic modulus. Ultimately, we developed a UHTCC-MWCNT composite with 1.1 wt% MWCNTs, which exhibited substantial improvements in compressive strength (44.85 MPa) and conductivity (9.78✕10−3 S/m), showing increases of 22.18 % and 18,132.6 % respectively, compared to the reference group.

Up- and down-conversion photoluminescence properties of Ho2O3 doped YbAG single crystals prepared by optical floating zone method

Single crystals of garnets with composition Yb2.96-xYxHo0.04Al5O12 (x = 0, 2.92, 2.96) were grown by optical floating zone method, and shown by XRD measurements to be in the cubic phase. EDS spectra show that Ho3+ and Yb3+ were homogenously distributed in the structure. As shown by the transmission and absorption spectra, the Yb2.96-xYxHo0.04Al5O12 crystals are highly transparent and can function as excellent optical crystals. Compared to the Y2.96Ho0.04Al5O12 crystal, the Yb2.96Ho0.04Al5O12 crystal has an additional strong broad absorption in the 836–1070 nm range, which increases its absorption of 980 nm photons. The optical band gaps of the Yb2.96-xYxHo0.04Al5O12 crystals decrease with increasing Yb2O3 concentration. Furthermore, differences with Yb2O3 concentrations in the Yb2.96-xYxHo0.04Al5O12 crystals were observed for the first time in the up- and down-conversion photoluminescence. Under excitation with a 980 nm laser, the up-conversion PL spectra of the Yb2.96-xYxHo0.04Al5O12 crystals show several emission peaks at 548 nm, 665 nm and 775 nm, and their intensities increase with Yb2O3 concentrations. In the Yb2.96Ho0.04Al5O12 crystal, Yb3+ not only is a component of the garnet structure, but it also acts as a sensitizer. In regards of down-conversion, under excitation at 454 nm, the down-conversion PL spectra of the Yb2.96-xYxHo0.04Al5O12 crystals show strong emission peaks at 550 nm, and their intensities decrease with increasing Yb2O3 concentrations, which is considered to be the consequence of increasing matrix density.

Tunable PEG Hydrogels for Discerning Differential Tumor Cell Response to Biomechanical Cues.

Increased extracellular matrix (ECM) density in the tumor microenvironment has been shown to influence aspects of tumor progression such as proliferation and invasion. Increased matrix density means cells experience not only increased mechanical properties, but also a higher density of bioactive sites. Traditional in vitro ECM models like Matrigel and collagen do not allow these properties to be investigated independently. In this work, a poly(ethylene glycol)-based scaffold is used which modifies with integrin-binding sites for cell attachment and matrix metalloproteinase 2 and 9 sensitive sites for enzyme-mediated degradation. The polymer backbone density and binding site concentration are independently tuned and the effect each of these properties and their interaction have on the proliferation, invasion, and focal complex formation of two different tumor cell lines is evaluated. It is seen that the cell line of epithelial origin (Hs 578T, triple negative breast cancer) proliferates more, invades less, and forms more mature focal complexes in response to an increase in matrix adhesion sites. Conversely, the cell line of mesenchymal origin (HT1080, fibrosarcoma) proliferates more in 2D culture but less in 3Dculture, invades less, and forms more mature focal complexes in response to an increase in matrix stiffness.

Collagen and Vitamin C Supplementation Increases Lower Limb Rate of Force Development.

Exercise and vitamin C-enriched collagen supplementation increase collagen synthesis, potentially increasing matrix density, stiffness, and force transfer. To determine whether vitamin C-enriched collagen (hydrolyzed collagen [HC] + C) supplementation improves rate of force development (RFD) alongside a strength training program. Using a double-blinded parallel design, over 3weeks, healthy male athletes (n = 50, 18-25years) were randomly assigned to the intervention (HC + C; 20g HC + 50mg vitamin C) or placebo (20g maltodextrin). Supplements were ingested daily 60min prior to training. Athletes completed the same targeted maximal muscle power training program. Maximal isometric squats, countermovement jumps, and squat jumps were performed on a force plate at the same time each testing day (baseline, Tests 1, 2, and 3) to measure RFD and maximal force development. Mixed-model analysis of variance compared performance variables across the study timeline, whereasttests were used to compare the change between baseline and Test 3. Over 3weeks, maximal RFD in the HC + C group returned to baseline, whereas the placebo group remained depressed (p = .18). While both groups showed a decrease in RFD through Test 2, only the treatment group recovered RFD to baseline by Test 3 (p = .036). In the HC + C group, change in countermovement jumps eccentric deceleration impulse (p = .008) and eccentric deceleration RFD (p = .04) wasimproved. A strong trend was observed for lower limb stiffness assessed in the countermovement jumps (p = .08). No difference was observed in maximal force or squat jump parameters. The HC + C supplementation improved RFD in the squat and countermovement jump alongside training.

Abstract P5-07-06: Investigating breast cancer dormancy in response to microenvironment cues with well-defined synthetic extracellular matrices

Abstract Breast cancer recurs in approximately 20% of disease-free patients 5+ years after successful treatment of the original tumor. These late recurrences often occur at metastatic sites, including the bone marrow and lungs, and are hypothesized to arise from disseminated tumor cells (DTCs) that reactivate after a long period dormancy. Interactions between DTCs and the microenvironment at these sites are thought to be important regulators of both breast cancer cell dormancy and reactivation. New approaches are needed to study this complex process and test hypotheses about key cell-microenvironment interactions in dormancy toward improved treatment strategies. In this work, we investigated the role of cell-matrix and cell-cell interactions on dormancy and activation of breast cancer cells utilizing well-defined materials to mimic the extracellular matrix (ECM) of metastatic sites and selectively introducing metastatic niche cells via dynamic co-culture. We established synthetic ECMs with well-defined properties that mimicked key aspects of the mechanical properties and biochemical content of bone marrow and lung metastatic sites (Young's modulus E˜0.5-5 kPa, respectively, and rich in collagen). These synthetic ECMs were constructed with a bioinert, multifunctional poly(ethylene glycol) crosslinked with a cell-degradable peptide and decorated with integrin-binding peptides derived from collagen and laminin, creating three-dimensional (3D) environments for the culture of breast cancer cells and niche cells. We cultured breast cancer cells of different metastatic potential (estrogen receptor positive [ER+, T47Ds] and triple negative [ER-, MDA-MB-231s]) within matrices, with or without co-culture of niche cells, and examined differences in markers of dormancy for up to 6 weeks. Both breast cancer cell types exhibited good viability in 3D culture (> 90%). Different degrees of cell proliferation (metabolic activity, EdU assay, cell/cluster number and volume) were observed over the first 2 weeks in culture, dependent upon matrix composition. Interestingly, ER- MDA-MB-231s were more responsive to differences in the biochemical content of the matrix, with increased elongation and proliferation observed within collagen mimic environments, whereas fewer differences were observed in the responses of the ER+ T47Ds to these same compositions. Further, both cell types exhibited significant decreases in proliferation in response to increased matrix density, mimicking the moduli of bone marrow to lung tissues. Dormant single cells or small cell clusters, reminiscent of micrometastases, were observed over weeks 2-6. Immunostaining and bioinformatics analyses revealed increased expression of autophagy markers for these dormant cells, suggesting a potential mechanism of survival. Additionally, co-culture with specific niche cells, including human mesenchymal stem cells and osteoblasts, was observed to enhance or suppress breast cancer cell proliferation within these well-defined environments. These studies have established a new controlled 3D breast cancer dormancy culture model, with on-going investigations examining cell re-activation for the identification of therapeutics to maintain dormancy and prevent recurrence. Citation Format: Kloxin AM, Ovadia EM, Pradhan L, Sawicki LA. Investigating breast cancer dormancy in response to microenvironment cues with well-defined synthetic extracellular matrices [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P5-07-06.

Tunable synthetic extracellular matrices to investigate breast cancer response to biophysical and biochemical cues.

The extracellular matrix (ECM) is thought to play a critical role in the progression of breast cancer. In this work, we have designed a photopolymerizable, biomimetic synthetic matrix for the controlled, 3D culture of breast cancer cells and, in combination with imaging and bioinformatics tools, utilized this system to investigate the breast cancer cell response to different matrix cues. Specifically, hydrogel-based matrices of different densities and modified with receptor-binding peptides derived from ECM proteins [fibronectin/vitronectin (RGDS), collagen (GFOGER), and laminin (IKVAV)] were synthesized to mimic key aspects of the ECM of different soft tissue sites. To assess the breast cancer cell response, the morphology and growth of breast cancer cells (MDA-MB-231 and T47D) were monitored in three dimensions over time, and differences in their transcriptome were assayed using next generation sequencing. We observed increased growth in response to GFOGER and RGDS, whether individually or in combination with IKVAV, where binding of integrin β1 was key. Importantly, in matrices with GFOGER, increased growth was observed with increasing matrix density for MDA-MB-231s. Further, transcriptomic analyses revealed increased gene expression and enrichment of biological processes associated with cell-matrix interactions, proliferation, and motility in matrices rich in GFOGER relative to IKVAV. In sum, a new approach for investigating breast cancer cell-matrix interactions was established with insights into how microenvironments rich in collagen promote breast cancer growth, a hallmark of disease progression in vivo, with opportunities for future investigations that harness the multidimensional property control afforded by this photopolymerizable system.

Effect of fibre surface coating on the mechanical properties of natural fibre-reinforced soil

ABSTRACT The application of natural fibres in soil reinforcement is cost-effective and environmentally friendly. However, natural fibres exhibit dimensional instability when exposed to moisture. Their hydrophilic characteristics affect mechanical performance and durability of natural fibre-reinforced composites. In this study, the effects of fibre surface coating on the mechanical properties of soil–fibre composite were investigated. Natural-based water repellent was coated onto sisal fibres to prevent water absorption. The single-fibre pull-out tests were conducted with varying soil matrix moisture contents and densities. Unconfined compression tests were performed on the soil composite containing 25 mm coated fibres at 0.75% fibre content. The results showed that interfacial shear strength (IFSS) of coated fibres was lower than uncoated fibres at the matrix optimum moisture content. This was attributed to the presence of thin film of moisture at fibre–matrix interface, which suppressed adhesion and mechanical interlock between fibre and soil matrix. Increasing matrix density led to high IFSS of both fibre types due to the enhanced interfacial frictional resistance. The composite with coated fibres exhibited higher rate of moisture loss due to the hydrophobic characteristics of fibres. Shear lag model was used to predict axial load transfer of fibres. The model prediction accuracy was dependent on the material properties, geometry and friction at fibre–matrix interface. Rosin can effectively be used to prevent water absorption of natural fibres and enhance long-term strength properties of natural fibre-reinforced soil.

Abstract P5-03-07: Probing breast cancer cell activation in response to extracellular cues using well-defined synthetic microenvironments

Abstract Interactions between breast cancer cells and their microenvironments are essential in tumor growth, metastasis, and recurrence. The tumor stroma undergoes constant structural changes, including degradation, redeposition, and crosslinking of collagens with gradients in matrix stiffness and composition that drive invasion and metastasis. At metastatic sites, similar remodeling events that occur with injury and aging are hypothesized to promote reactivation of dormant tumor cells in recurrence. Approaches are needed for testing hypotheses about pivotal cell-matrix interactions in the progression of breast cancer for identifying key regulators and improving treatment strategies. In this work, we have designed well-defined materials to mimic key aspects of tumor microenvironments toward studying such complex phenomena in vitro. Specifically, we have created synthetic extracellular matrices with well-defined biophysical and biochemical properties that enable three-dimensional (3D) culture of breast cancer cells and niche cells over weeks. A bioinert polymer, multiarm poly(ethylene glycol) functionalized with thiols (Mn ˜ 20 kDa), was reacted with integrin-binding and cell-degradable peptides decorated with one and two allyloxycarbonyl protecting groups, respectively, by rapid light-triggered thiol-ene polymerization for independent control of matrix density and composition. The elasticity, or 'stiffness', of these matrices has been tuned to mimic a variety of soft tissues (Young's modulus E˜0.5-20 kPa), from healthy and cancerous mammary tissues to metastatic site bone marrow and lung tissues. Further, the biochemical content has been tuned with receptor-binding peptides derived from laminin (IKVAV, laminin receptor), collagen ((POG)3POGFOGER(POG)4, α2β1 and α1β1), and fibronectin/vitronectin (RGDS, αVβ3 and α5β1 amongst others) and a crosslinking peptide derived from collagen (GPQG↓IWGQ, degraded MMP-1, -2, and -9 amongst others). We hypothesized that a microenvironment rich in collagen and fibronectin/vitronectin, mimicking aspects of remodeled tissues, would activate breast cancer cells relative to a laminin-rich epthelium-like microenvironment, building upon seminal studies in naturally-derived matrices and in vivo. To test this, we cultured breast cancer cells of different metastatic potential (estrogen receptor positive [ER+, T47Ds] and triple negative [ER-, MDA-MB-231s]) within different matrix densities and compositions. Both cell types exhibited high viability (> 90%), and cell activation in response to different matrix compositions was assayed by examining proliferation (metabolic activity, Ki-67, cell/cluster number and volume) and phenotype (morphology; E-cadherin, vimentin). Increased matrix density decreased elongation of ER- cells and proliferation of both cell types. Increased collagen content increased the proliferation of the ER+ cells and proliferation and elongation of ER- with mass and stellate morphologies, respectively, like observed in naturally-derived matrices. These studies demonstrate a new tool for controlled 3D culture of breast cancer cells relevant for both fundamental and applied research, with on-going investigations incorporating niche cells and triggered matrix changes. Citation Format: Kloxin AM, Sawicki LA, Ovadia EM. Probing breast cancer cell activation in response to extracellular cues using well-defined synthetic microenvironments [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P5-03-07.

Evaluating the potential of endothelial cells derived from human induced pluripotent stem cells to form microvascular networks in 3D cultures

A major translational challenge in the fields of therapeutic angiogenesis and regenerative medicine is the need to create functional microvasculature. The purpose of this study was to assess whether a potentially autologous endothelial cell (EC) source derived from human induced pluripotent stem cells (iPSC-ECs) can form the same robust, stable microvasculature as previously documented for other sources of ECs. We utilized a well-established in vitro assay, in which endothelial cell-coated (iPSC-EC or HUVEC) beads were co-embedded with fibroblasts in a 3D fibrin matrix to assess their ability to form stable microvessels. iPSC-ECs exhibited a five-fold reduction in capillary network formation compared to HUVECs. Increasing matrix density reduced sprouting, although this effect was attenuated by distributing the NHLFs throughout the matrix. Inhibition of both MMP- and plasmin-mediated fibrinolysis was required to completely block sprouting of both HUVECs and iPSC-ECs. Further analysis revealed MMP-9 expression and activity were significantly lower in iPSC-EC/NHLF co-cultures than in HUVEC/NHLF co-cultures at later time points, which may account for the observed deficiencies in angiogenic sprouting of the iPSC-ECs. Collectively, these findings suggest fundamental differences in EC phenotypes must be better understood to enable the promise and potential of iPSC-ECs for clinical translation to be realized.

Matrix stiffening promotes a tumor vasculature phenotype

Tumor microvasculature tends to be malformed, more permeable, and more tortuous than vessels in healthy tissue, effects that have been largely attributed to up-regulated VEGF expression. However, tumor tissue tends to stiffen during solid tumor progression, and tissue stiffness is known to alter cell behaviors including proliferation, migration, and cell-cell adhesion, which are all requisite for angiogenesis. Using in vitro, in vivo, and ex ovo models, we investigated the effects of matrix stiffness on vessel growth and integrity during angiogenesis. Our data indicate that angiogenic outgrowth, invasion, and neovessel branching increase with matrix cross-linking. These effects are caused by increased matrix stiffness independent of matrix density, because increased matrix density results in decreased angiogenesis. Notably, matrix stiffness up-regulates matrix metalloproteinase (MMP) activity, and inhibiting MMPs significantly reduces angiogenic outgrowth in stiffer cross-linked gels. To investigate the functional significance of altered endothelial cell behavior in response to matrix stiffness, we measured endothelial cell barrier function on substrates mimicking the stiffness of healthy and tumor tissue. Our data indicate that barrier function is impaired and the localization of vascular endothelial cadherin is altered as function of matrix stiffness. These results demonstrate that matrix stiffness, separately from matrix density, can alter vascular growth and integrity, mimicking the changes that exist in tumor vasculature. These data suggest that therapeutically targeting tumor stiffness or the endothelial cell response to tumor stiffening may help restore vessel structure, minimize metastasis, and aid in drug delivery.

Cone-beam CT to assess bony fusion following anterior cervical interbody fusion

Assessment of bony fusion following anterior cervical interbody fusion (ACIF) is usually done by plain film or CT. We present the first clinical application of Cone-Beam CT (CBCT) to evaluate bony fusion after ACIF. A 56-year-old man with disc herniation at C6-C7 underwent ACIF surgery using a compressed nanocrystalline hydroxyapatite interbody device (nanOss-C, Pioneer Surgical Marquette, MI, USA) and a nanocrystalline hydroxyapatite bone graft filler (nanOss Bioactive, Pioneer Surgical Marquette, MI, USA). Imaging follow-up was performed by CBCT (NewTom 5G, QR Srl, Verona, Italy) at 1day, 6weeks, 3and 9months post-operatively. Two independent assessors quantitatively measured the greyscale changes of the bone graft filler and qualitatively evaluated the bony fusion process. Quantitative analysis of the images showed a steadily increasing matrix density of the bone graft filler over the 9months follow-up, suggesting increasing calcification. Qualitative evaluation demonstrated different stages of the bone fusion process within the disc space around the cage, at the interface between cage and endplates, and at the interface between bone graft filler and the endplates. CBCT provides high-resolution cross-sectional imaging of the cervical spine after ACIF. For the first time, in vivo evaluation of the bone graft filler within the centre of the circumferentially radiodense cage and detailed cross-sectional evaluation of bone fusion was achieved. Confirmation of these promising outlooks of CBCT in a large cohort of ACIF patients is needed with regard to routine clinical application and evaluation of different interbody devices.

Matrix density alters zyxin phosphorylation, which limits peripheral process formation and extension in endothelial cells invading 3D collagen matrices

This study was designed to determine the optimal conditions required for known pro-angiogenic stimuli to elicit successful endothelial sprouting responses. We used an established, quantifiable model of endothelial cell (EC) sprout initiation where ECs were tested for invasion in low (1mg/mL) and high density (5mg/mL) 3D collagen matrices. Sphingosine 1-phosphate (S1P) alone, or S1P combined with stromal derived factor-1α (SDF) and phorbol ester (TPA), elicited robust sprouting responses. The ability of these factors to stimulate sprouting was more effective in higher density collagen matrices. S1P stimulation resulted in a significant increase in invasion distance, and with the exception of treatment groups containing phorbol ester, invasion distance was longer in 1mg/mL compared to 5mg/mL collagen matrices. Closer examination of cell morphology revealed that increasing matrix density and supplementing with SDF and TPA enhanced the formation of multicellular structures more closely resembling capillaries. TPA enhanced the frequency and size of lumen formation and correlated with a robust increase in phosphorylation of p42/p44 Erk kinase, while S1P and SDF did not. Also, a higher number of significantly longer extended processes formed in 5mg/mL compared to 1mg/mL collagen matrices. Because collagen matrices at higher density have been reported to be stiffer, we tested for changes in the mechanosensitive protein, zyxin. Interestingly, zyxin phosphorylation levels inversely correlated with matrix density, while levels of total zyxin did not change significantly. Immunofluorescence and localization studies revealed that total zyxin was distributed evenly throughout invading structures, while phosphorylated zyxin was slightly more intense in extended peripheral processes. Silencing zyxin expression increased extended process length and number of processes, while increasing zyxin levels decreased extended process length. Altogether these data indicate that ECs integrate signals from multiple exogenous factors, including changes in matrix density, to accomplish successful sprouting responses. We show here for the first time that zyxin limited the formation and extension of fine peripheral processes used by ECs for matrix interrogation, providing a molecular explanation for altered EC responses to high and low density collagen matrices.

Extracellular Matrix Density Regulates the Rate of Neovessel Growth and Branching in Sprouting Angiogenesis

Angiogenesis is regulated by the local microenvironment, including the mechanical interactions between neovessel sprouts and the extracellular matrix (ECM). However, the mechanisms controlling the relationship of mechanical and biophysical properties of the ECM to neovessel growth during sprouting angiogenesis are just beginning to be understood. In this research, we characterized the relationship between matrix density and microvascular topology in an in vitro 3D organ culture model of sprouting angiogenesis. We used these results to design and calibrate a computational growth model to demonstrate how changes in individual neovessel behavior produce the changes in vascular topology that were observed experimentally. Vascularized gels with higher collagen densities produced neovasculatures with shorter vessel lengths, less branch points, and reduced network interconnectivity. The computational model was able to predict these experimental results by scaling the rates of neovessel growth and branching according to local matrix density. As a final demonstration of utility of the modeling framework, we used our growth model to predict several scenarios of practical interest that could not be investigated experimentally using the organ culture model. Increasing the density of the ECM significantly reduced angiogenesis and network formation within a 3D organ culture model of angiogenesis. Increasing the density of the matrix increases the stiffness of the ECM, changing how neovessels are able to deform and remodel their surroundings. The computational framework outlined in this study was capable of predicting this observed experimental behavior by adjusting neovessel growth rate and branching probability according to local ECM density, demonstrating that altering the stiffness of the ECM via increasing matrix density affects neovessel behavior, thereby regulated vascular topology during angiogenesis.

Mechanisms of Three-Dimensional Tumor Cell Motility in Dense Extracellular Matrices

Tumor cell invasion requires navigation of tissue barriers of varying architecture. For instance, the extreme invasiveness of glioma cells is facilitated by their ability to migrate diffusely through brain parenchyma and approach guidance tracks along blood vessels. Brain parenchyma has a distinct physical structure characterized by densely packed neural cell processes and sub-micron extracellular space, and is largely devoid of the fibrillar collagen scaffolding typically found in stromal tissue. Consequently, glioma cells migrating in brain slices exhibit a distinct type of motility, with branched protrusions and hourglass-shaped cell-body deformations that help squeeze cells through tight spaces (Beadle et al., Mol. Biol. Cell 2008; 19(8):3357-68). However, the mechanistic details of this unique mode of motility remain incompletely understood. To address this question, we synthesized brain-mimetic nanoporous, non-fibrillar extracellular matrices (ECMs) based on cross-linked hyaluronic acid (HA), and verified that three-dimensional glioma cell motility in these ECMs strikingly recapitulated the phenotype seen in brain slices (Ananthanarayanan et al. Biomaterials 2011; 32(31):7913-23). Eliminating RGD peptides from the ECM abolished invasion, suggesting a requirement for integrin-mediated adhesions for this mode of motility. Increasing matrix density, or inhibiting myosin-based cellular contractility by blebbistatin or shRNA-induced knockdown of Myosin IIA severely impaired motility. We report preliminary results from two sets of studies: First, we investigate the balance of protrusive and contractile forces in glioma cell motility by pharmacologically and genetically manipulating the Rho GTPases RhoA, Rac1, and Cdc42. Second, we explore the involvement of actin-nucleating proteins such as Arp2/3 and formins in the protrusive dynamics observed in this mode of motility. Our studies help define the signaling mechanisms underlying the distinctive glioma cell motility observed in dense matrices.

Preparation and characterization of agarose–nickel nanoporous composite particles customized for liquid expanded bed adsorption

Agarose–nickel nanoporous composite matrices with a series of densities, named Ag–Ni, were prepared herein for expanded bed adsorption of nanobioproduct/bioproduct by a water-in-oil emulsification method. The optical microscope (OM), scanning electronic microscope (SEM) and particle size analyzer (PSA) were utilized in order to characterize the structure and morphology of the agarose–nickel composite. The results indicated that the matrices prepared had a spherical appearance, appropriate wet density of 1.73–2.56g/ml, water content of 32.2–58.5% and porosity of 79.4–96.37% and pore size of about 100–150nm. All the Ag–Ni beads follow logarithmic normal size distribution with the range of 60–230μm and average diameter of 133.68–148.4μm. One of the useful properties of the Ag–Ni particles is the high wet density up to 2.56g/ml, which shows a potential for the operation in an expanded bed at high flow rate. The impact of nickel powder addition on the physical and hydrodynamic properties was also investigated. In addition, the fluidization behavior of the Ag–Ni particles under various conditions was characterized by the measurement of bed expansion and axial dispersion coefficients for the liquid phase when operated in a standard fluidized bed contactor. It was observed that the expansion factors were decreased with the increasing matrix density under the same velocity. The bed expansion and fluid velocity were correlated with Richardson–Zaki equation for all particles prepared and the correlation parameters (the terminal settling velocity Ut and expansion index n) were investigated. Using measurements of residence time distributions, hydrodynamic properties in the expanded beds were investigated and were compared with reported matrices in other literatures. In addition, the impact of the flow velocity, bed expansion degree and density of adsorbent on hydrodynamic properties in the expanded beds were investigated. The results indicated that the expansion factor showed little effect on the hydrodynamic properties while the fluid velocity was the most essential factor on this regard. Furthermore, the results indicated that the heavy matrices of Ag–Ni-3, Ag–Ni-4 and Ag–Ni-5, were more suited for high operation fluid velocity. In addition, even the light matrices, i.e. Ag–Ni-1 and Ag–Ni-2, seem to be superior to other matrices in hydrodynamic properties, which made them promising adsorbents for further use in EBA processes.

Neuronal and Glial Alterations Due to Focal Cortical Hypoxia Induced by Direct Cobalt Chloride (CoCl2) Brain Injection

Ischemic brain injury is a dynamic process that involves oxidative stress, inflammation, and cell death, as well as activation of endogenous adaptive and regenerative mechanisms depending on activation of transcription factors such as hypoxia inducible factor 1-alpha (HIF-1alpha). Because CoCl2 activates HIF-1alpha, we described a new focal-hypoxia model by direct intracerebral CoCl2 injection. Adult male Wistar rats were intracerebrally injected with CoCl2 (2 microl-50 mM), in frontoparietal cortex of right hemisphere, and saline (2 microl) in the contralateral hemisphere. In slides of fixed brains at 1, 6, 9, 24 h or 5 day after treatment, TTC, histochemistry (toluidine blue, Hoescht-33342, TUNEL), immunostaining (HIF-1alpha, GFAP), Lycopersicon esculentum lectin staining, and electron microscopy (EM) were performed. Immediately after 1 h post CoCl2 injection, HIF-1alpha stabilization and neuronal nuclear shrinkage and cromathin condensation were observed by immunostaining and EM, respectively. Neuronal apoptotic nuclear morphology and GFAP immunoreactivity and lectin maximal reactivity were detected during 6-9 h. Ultrastructural alterations of morphology included edematous perinuclear cytoplasm, organelles and endoplasmic reticulum (RE) enlargement, mitochondrial swelling with increased matrix density, and deposits of electron-dense material. Neurons showed particular nuclear indentations. Astrocytes and oligodendrocytes presented alterations in both nuclei and RE with dilated lumen and altered mitochondrias, and all these ultrastructural changes became detectable at day 5. CoCl2 cortical injection mimics focal brain ischemia, inducing neuronal death and glial activation. This model brings the opportunity to develop focal ischemia in selected brain areas to study their functional consequences and potential pharmacological therapies for in vivo models of stroke.

A core-softened fluid model in disordered porous media. Grand canonical Monte Carlo simulation and integral equations

We have studied the microscopic structure and thermodynamic properties of a core-softened fluid model in disordered matrices of Lennard-Jones particles by using grand canonical Monte Carlo simulation. The dependence of density on the applied chemical potential (adsorption isotherms), pair distribution functions, as well as the heat capacity in different matrices are discussed. The microscopic structure of the model in matrices changes with density similar to the bulk model. Thus one should expect that the structural anomaly persists at least in dilute matrices. The region of densities for the heat capacity anomaly shrinks with increasing matrix density. This behavior is also observed for the diffusion coefficient on density from independent molecular dynamics simulation. Theoretical results for the model have been obtained by using replica Ornstein–Zernike integral equations with hypernetted chain closure. Predictions of the theory generally are in good agreement with simulation data, except for the heat capacity on fluid density. However, possible anomalies of thermodynamic properties for the model in disordered matrices are not captured adequately by the present theory. It seems necessary to develop and apply more elaborated, thermodynamically self-consistent closures to capture these features.

Mesenchymal Stem Cells Enhance Angiogenesis in Mechanically Viable Prevascularized Tissues via Early Matrix Metalloproteinase Upregulation

Angiogenesis, the sprouting of new blood vessels from existing vasculature, is a complex biological process of interest to both the treatment of numerous pathologies and the creation of thick engineered tissues. In the context of tissue engineering, one potential solution to the diffusion limitation is to create a vascular network in vitro that can subsequently anastomose with the host after implantation, allowing the implantation of thicker, more complex tissues. In this study, the ability of endothelial cells to sprout and form stable vascular networks in 3-dimensional (3D) fibrin matrices was investigated as a function of matrix density in a prevascularized tissue model. The results demonstrate that while increasing matrix density leads to a nearly 7-fold increase in compressive stiffness, vascular sprouting is virtually eliminated in the most dense matrix condition. However, the addition of human mesenchymal stem cells (HMSCs) to the denser matrices reverses this effect, resulting in an up to a 7-fold increase in network formation. Although the matrix metalloproteinases (MMPs) MMP-2, MMP-9, and MT1-MMP are all upregulated early on with the addition of HMSCs, MT1-MMP appears to play a particularly important role in the observed angiogenic response among these proteases. This study provides a means to design stiffer prevascularized tissues utilizing naturally derived substrates, and its results may yield new mechanistic insights into stem cell-based angiogenic therapies.

Mitochondrial Damage as an Early Event of Monensin‐induced Cell Injury in Cultured Fibroblasts L929

The present study was designed to identify, submicroscopically, the primary organelle or target structure for monensin in cultured murine fibroblasts L929. In addition, the effect of the drug on cell size and surface membranes of the cells were analysed; cellular proliferation, collagen secretion, and necrosis and apoptosis were re-evaluated. At the lowest concentration of monensin the foremost ultrastructural alteration occurred in the mitochondria, characterized by increased matrix density with disorganized and less distinct crystae. Incubation with monensin at higher concentrations resulted in severe mitochondrial damage and marked dilatation of the Golgi apparatus and rough endoplasmic reticulum cisternae. Fibroblasts exposed to higher concentrations of monensin were enlarged with decreased number of filopodia and hollows in the surface membrane. Moreover, monensin inhibited the cell proliferation, increased immunohistochemical positiveness for collagen type I in a dose-dependent manner, and, at high concentrations, caused cell necrosis whereas apoptosis was not induced. Taken together, these results show that monensin induces early mitochondrial damage, possibly causing an energy deficit that led to inhibition of fibroblasts proliferation and accumulation of collagen causing dilatation of Golgi apparatus and rough endoplasmic reticulum. Moreover, the mitochondrial damage would also explain the monensin-induced necrosis.

Hard sphere fluids at surfaces of porous media.

An adsorbate fluid of hard spheres is brought into contact with a semi-infinite porous matrix modeled by immobilized configurations of freely overlapping spheres with a sharp kink one-body density distribution. Comparison of results from a recent density-functional approach to those of our computer simulations yields good agreement for the adsorbate density profile across the matrix surface. We show how the matrix can be replaced by a fictitious external potential that only depends on the distance from the interface, and that leads to the same adsorbate density profile. This potential is found to be a smooth function of distance, due to the geometry of the matrix particles. For high matrix densities, the porous medium becomes practically impenetrable, and its surface behaves like a rough hard wall whose roughness decreases with increasing matrix density.