Dispersive Cells Research Articles

A Methodology for Quantifying Cell Density and Distribution in Multidimensional Bioprinted Gelatin–Alginate Constructs

Bioprinted tissue constructs can be produced by microextrusion-based materials processing or coprinting of cells and hydrogel materials. In this paper, a gelatin–alginate hydrogel material formulation is implemented as the bio-ink toward a three-dimensional (3D) cell-laden tissue construct. However, of fundamental importance during the printing process is the interplay between the various parameters that yield the final cell distribution and cell density at different dimensional scales. To investigate these effects, this study advances a multidimensional analytical framework to determine both the spatial variations and temporal evolution of cell distribution and cell density within a bioprinted cell-laden construct. In the one-dimensional (1D) analysis, the cell distribution and single printed fiber shape in the circular cross-sectional view are observed to be dependent on the process temperature and material concentration parameters, along with the initial bio-ink cell densities. This is illustrated by reliable fabrication verified by image line profile analyses of structural fiber prints. Round fiber prints with width 809.5 ± 52.3 μm maintain dispersive cells with a degree of dispersion (Dd) at 96.8 ± 6.27% that can be achieved at high relative material viscosities under low temperature conditions (21 °C) or high material concentrations (10% w/v gelatin). On the other hand, flat fiber prints with width 1102.2 ± 63.66 μm coalesce cells toward the fiber midline with Dd = 76.3 ± 4.58% that can be fabricated at low relative material viscosities under high temperature (24 °C) or low material concentrations (7.5% w/v gelatin). A gradual decrement of Dd (from 80.34% to 52.05%) is observed to be a function of increased initial bio-ink cell densities (1.15 × 106–16.0 × 106 cells/ml). In the two-dimensional (2D) analysis, a printed grid structure yields differential cell distribution, whereby differences in localized cell densities are observed between the strut and cross regions within the printed structure. At low relative viscosities, cells aggregate at the cross regions where two overlapping filaments fuse together, yielding a cell density ratio of 2.06 ± 0.44 between the cross region and the strut region. However, at high relative viscosities, the cell density ratio decreases to 0.96 ± 0.03. In the 3D analysis, the cell density attributed to the different layers is studied as a function of printing time elapsed from the initial bio-ink formulation. Due to identifiable cell sedimentation, the dynamics of cell distribution within the original bio-ink cartridge or material reservoir yield initial quantitative increases in the cell density for the first several printed layers, followed by quantitative decreases in the subsequent printed layers. Finally, during incubation, the evolution of cell density and the emergence of material degradation effects are studied in a time course study. Variable initial cell densities (0.6 × 106 cells/mL, 1.0 × 106 cells/mL, and acellular control group) printed and cross-linked into cell-laden constructs for a 48 h time course study exhibit a time-dependent increase in cell density owing to proliferation within the constructs that are presumed to affect the rate of bio-ink material degradation.

Nonscattering Waveguides Based on Tensor Impedance Surfaces

A tensor impedance surface waveguide is built using anisotropic unit cells. The waveguide can propagate a confined waveguide mode along its axis while waves incident to the guide at an orthogonal direction pass through as if the waveguides were not present. Both straight and curved implementations are demonstrated. Surface waves incident at an angle to the waveguide show reflection and refraction at the impedance interface. A theoretical model for tensor impedance surface waveguides is generalized to include dispersive unit cells and bending loss around curves. Dispersion results for modes propagating in the waveguide show agreement between the theory, simulation, and experimental measurements. A curved waveguide is also constructed which guides surface waves around a curve and is transparent to surface waves incident at an orthogonal angle.

A novel bicompartmental mathematical model of glioblastoma multiforme.

Glioblastoma multiforme (GBM) is the most common primary CNS neoplasm, and continues to have a dismal prognosis. A widely-used approach to the mathematical modeling of GBM involves utilizing a reaction-diffusion model of cell density as a function of space and time, which accounts for both the infiltrative nature of the tumor using a diffusion term, and the proliferation of tumor cells using a proliferation term. The current paper extends the standard models by incorporating an advection term to account for the so-called 'cell streaming' which is often seen with GBM, where some of the tumor cells seem to stream widely along the white matter pathways. The current paper introduces a bicompartmental GBM model in the form of coupled partial differential equations with a component of dispersive cells. The parameters needed for this model are explored. It is shown that this model can account for the rapid distant dispersal of GBM cells in the CNS, as well as such phenomena as multifocal gliomas with tumor foci distant from the core tumor site. The model suggests a higher percentage of tumor cells below the threshold of MRI images in comparison to the standard model. By incorporating an advection component, the proposed model is able to account for phenomena such as multicentric gliomas and rapid distant dispersion of a small fraction of tumor cells throughout the CNS, features important to the prognosis of GBM, but not easily accounted for by current models.

Glioblastoma‐associated stromal cells (GASCs) from histologically normal surgical margins have a myofibroblast phenotype and angiogenic properties

Glioblastoma (GB) displays diffusely infiltrative growth patterns. Dispersive cells escape surgical resection and contribute to tumour recurrence within a few centimeters of the resection cavity in 90% of cases. We know that the non-neoplastic stromal compartment, in addition to infiltrative tumour cells, plays an active role in tumour recurrence. We isolated a new stromal cell population from the histologically normal surgical margins of GB by computer-guided stereotaxic biopsies and primary culture. These GB-associated stromal cells (GASCs) share phenotypic and functional properties with the cancer-associated fibroblasts (CAFs) described in the stroma of carcinomas. In particular, GASCs have tumour-promoting effects on glioma cells in vitro and in vivo. Here, we describe a quantitative proteomic analysis, using iTRAQ labelling and mass spectrometry, to compare GASCs with control stromal cells derived from non-GB peripheral brain tissues. A total of 1077 proteins were quantified and 67 proteins were found to differ between GASCs and control stromal cells. Several proteins changed in GASCs are related to a highly motile myofibroblast phenotype, and to wound healing and angiogenesis. The results for several selected proteins were validated by western blotting or flow cytometry. Furthermore, the effect of GASCs on angiogenesis was confirmed using the orthotopic U87MG glioma model. In conclusion, GASCs, isolated from GB histologically normal surgical margins and found mostly near blood vessels, could be a vascular niche constituent establishing a permissive environment, facilitating angiogenesis and possibly colonization of recurrence-initiating cells. We identify various proteins as being expressed in GASCs: some of these proteins may serve as prognostic factors for GB and/or targets for anti-glioma treatment.

Single cell molecular recognition of migrating and invading tumor cells using a targeted fluorescent probe to receptor PTPmu

Detection of an extracellular cleaved fragment of a cell-cell adhesion molecule represents a new paradigm in molecular recognition and imaging of tumors. We previously demonstrated that probes that recognize the cleaved extracellular domain of receptor protein tyrosine phosphatase mu (PTPmu) label human glioblastoma brain tumor sections and the main tumor mass of intracranial xenograft gliomas. In this article, we examine whether one of these probes, SBK2, can label dispersed glioma cells that are no longer connected to the main tumor mass. Live mice with highly dispersive glioma tumors were injected intravenously with the fluorescent PTPmu probe to test the ability of the probe to label the dispersive glioma cells in vivo. Analysis was performed using a unique three-dimensional (3D) cryo-imaging technique to reveal highly migratory and invasive glioma cell dispersal within the brain and the extent of colabeling by the PTPmu probe. The PTPmu probe labeled the main tumor site and dispersed cells up to 3.5 mm away. The cryo-images of tumors labeled with the PTPmu probe provide a novel, high-resolution view of molecular tumor recognition, with excellent 3D detail regarding the pathways of tumor cell migration. Our data demonstrate that the PTPmu probe recognizes distant tumor cells even in parts of the brain where the blood-brain barrier is likely intact. The PTPmu probe has potential translational significance for recognizing tumor cells to facilitate molecular imaging, a more complete tumor resection and to serve as a molecular targeting agent to deliver chemotherapeutics to the main tumor mass and distant dispersive tumor cells.

Cooperative social clusters are not destroyed by dispersal in a ciliate

BackgroundThe evolution of social cooperation is favored by aggregative behavior to facilitate stable social structure and proximity among kin. High dispersal rates reduce group stability and kin cohesion, so it is generally assumed that there is a fundamental trade-off between cooperation and dispersal. However, empirical tests of this relationship are rare. We tested this assumption experimentally using ten genetically isolated strains of a ciliate, Tetrahymena thermophila.ResultsThe propensity for social aggregation was greater in strains with reduced cell quality and lower growth performance. While we found a trade-off between costly aggregation and local dispersal in phenotypic analyses, aggregative strains showed a dispersal polymorphism by producing either highly sedentary or long-distance dispersive cells, in contrast to less aggregative strains whose cells were monomorphic local dispersers.ConclusionHigh dispersal among aggregative strains may not destroy group stability in T. thermophila because the dispersal polymorphism allows social strains to more readily escape kin groups than less aggregative strains, yet still benefit from stable group membership among sedentary morphs. Such dispersal polymorphisms should be common in other social organisms, serving to alter the nature of the negative impact of dispersal on social evolution.

Distribution of ghrelin-like immunoreactive cells in amphioxus, Branchiostoma belcheri – A study of immunohistochemistry

The distribution of ghrelin-like immunoreactive cells in amphioxus ( Branchiostoma belcheri) was investigated by using immunohistochemical staining with rabbit antiserum against synthetical mammalian ghrelin. The results showed that ghrelin-like immunoreactive cells were distributed widely in the nervous system, Hatschek’s pit, wheel organ, digestive tract and gonads (ovary and testis). In nervous system, ghrelin-like immunoreactive neurons and their protrusions were distributed specifically on the dorsal side, ventral side and funnel part of brain vesicle, with a few dispersive immunoreactive nerve cells and their fibers in nerve tube. Ghrelin-like immunoreactivities were also detected in Hatschek’s pit epithelial cells and wheel organ cells, with positive substance located along cell membrane. In digestive tract, ghrelin-like immunoreactive cells existed in hepatic diverticulum, anterior and posterior region of midgut, and could be classified into two types, closed- and opened-type endocrine cells. The number of positive cells was most in hepatic diverticulum, secondary in posterior region of midgut and least in anterior region of midgut. In gonads, ghrelin-like immunoreactive substance was detected in oogonia, oocytes and follicle cells in ovary at the small and large growth stages and in early spermatogenic cells and Sertoli cells in testis. The extensive distribution of ghrelin-like cells in amphioxus suggested that these kinds of cells are conservative in evolution and diversified in function. At the same time, we found for the first time that ghrelin-like immunoreactive cells existed in brain vesicle and Hatschek’s pit, which provided new morphological evidence for the existence of an activation pathway between brain vesicle and Hatschek’s pit for the regulation of growth hormone excretion.

Electric field distribution and energy absorption in anisotropic and dispersive red blood cells

We have studied the influence of the anisotropic and dispersive nature of the red blood cell structure on the energy absorption and electric field distribution within the cell exposed to electromagnetic fields of frequencies in the range from 50 kHz to 10 GHz. For this purpose we have generated a realistic model of a multilayered erythrocyte cell from a set of parametric equations in terms of Jacobi elliptic functions. The effect of dipole relaxations and anisotropic conductivities is taken into account in the dispersion equations for the conductivity and permittivity of each layer (cytoplasmic and extra-cellular bound waters, membrane, cytoplasm and external medium). Using a finite element numerical technique, we have found that the electric field distribution and the energy absorbed in the membrane show well-defined maxima for both normal and parallel orientations of the external field with respect to the symmetry axis of the cell. The normal and tangential conductivities and permittivities of the membrane are shown to be responsible for the different peak amplitudes and frequency shifts of the maxima. A previously unnoticed effect is that the cell shape combined with the dispersion of the membrane permittivity and the influence of bound water layers leads to a very high amplification factor (greater than 300) of the electric field in the membrane at frequencies in the megahertz range.

Feasibility of TFEL application of Ce-doped CaGa 2S 4 and SrGa 2S 4 films prepared by flash evaporation method

Ce-doped CaGa 2S 4 and SrGa 2S 4 thin films were prepared for the first time by the flash evaporation method. The films were characterized before and after annealing in H 2S(10%)+Ar gas stream by measuring photoluminescence and absorption spectra, X-ray diffraction and electron probe micro analyses. X-ray diffraction curves and absorption spectra before annealing show amorphous behaviour, whereas the annealing leads to a significant crystallization and improves the stoichiometry of the films. Based on the performance data obtained from dispersive type EL cells using CaGa 2S 4:Eu powder together with photoluminescence property comparison between CaGa 2S 4:Eu and CaGa 2S 4:Ce powders, the annealed films prepared by flash evaporation can be considered to become one of the candidates for TFEL flat panel devices.

A nonlinear model for auroral density cavities

A nonlinear model for the short‐scale auroral density cavity (SSADC) is presented. Specifically, it is shown that the SSADC is associated with nonlinear short wavelength (in comparison with the collisionless electron skin depth) dispersive convective cells (DCCs) whose frequencies are much smaller than the ion gyrofrequency. In a stationary frame, the relevant equations governing the dynamics of the nonlinear DCCs are put in the form of an energy integral with an effective potential. The latter is analyzed to demonstrate the existence of density cavities (or holes). Larger amplitude cavities are necessarily quasi‐stationary. The present theoretical model is capable of describing the salient features of SSADCs that are seen in data from the Freja satellite.

Sex differentiation in the crabEriocheir japonicus(Decapoda, Grapsidae)

Summary The sex differentiation of the crab Eriocheir japonicus was studied histologically and morphologically from the first zoeal stage to the fifth crab stage. The gonoducts were the first sexual characteristic that underwent sex differentiation. As early as the crab was at the megalopa stage, gender could be determined on the basis of two different orientations of the gonoducts. One orientation was toward the eighth thoracic sternite in the males and the other was toward the sixth thoracic sternite in the females. The second sexual characteristic that underwent sex differentiation was found in the pleopods at the third crab stage. No remarkable morphological or structural difference was observed between the gonia in males and those in females. We compared our findings with those in the crabs studied in previous research regarding the sequences of the sex differentiation of sexual characteristics and the development of gonoducts and gonopores. We also discussed the timing of the appearance of the androgenic gland in the sex differentiation of decapods and other malacostracans. Unlike isopods and amphipods, no androgenic gland is visible prior to sex differentiation in E. japonicus. This finding is consistent with those reported in other decapods. We hypothesize that in decapods, before the androgenic gland cells form a gland, they already exist dispersively in both sexually undifferentiated genetic males and females. In the genetic males, these dispersive androgenic gland cells may be activated by the male sex-determining genes to produce androgenic gland hormones inducing sex differentiation.

Editorial comment

The distribution of ghrelin-like immunoreactive cells in amphioxus (Branchiostoma belcheri) was investigated by using immunohistochemical staining with rabbit antiserum against synthetical mammalian ghrelin. The results showed that ghrelin-like immunoreactive cells were distributed widely in the nervous system, Hatschek’s pit, wheel organ, digestive tract and gonads (ovary and testis). In nervous system, ghrelin-like immunoreactive neurons and their protrusions were distributed specifically on the dorsal side, ventral side and funnel part of brain vesicle, with a few dispersive immunoreactive nerve cells and their fibers in nerve tube. Ghrelin-like immunoreactivities were also detected in Hatschek’s pit epithelial cells and wheel organ cells, with positive substance located along cell membrane. In digestive tract, ghrelin-like immunoreactive cells existed in hepatic diverticulum, anterior and posterior region of midgut, and could be classified into two types, closed- and opened-type endocrine cells. The number of positive cells was most in hepatic diverticulum, secondary in posterior region of midgut and least in anterior region of midgut. In gonads, ghrelin-like immunoreactive substance was detected in oogonia, oocytes and follicle cells in ovary at the small and large growth stages and in early spermatogenic cells and Sertoli cells in testis. The extensive distribution of ghrelin-like cells in amphioxus suggested that these kinds of cells are conservative in evolution and diversified in function. At the same time, we found for the first time that ghrelin-like immunoreactive cells existed in brain vesicle and Hatschek’s pit, which provided new morphological evidence for the existence of an activation pathway between brain vesicle and Hatschek’s pit for the regulation of growth hormone excretion.

Summing-up of laser physics, laser technology, and industrial and scientific applications

Ultra short optical pulses of only a few wavelengths or a few femto seconds duration have proven to be very valuable for the understanding of elementary processes. The technology to generate tuneble short pulses with dye lasers in the colliding pulse configuration has been well developed. The further compression by means of self phase modulation in filters and dispersive cells to synchronize the frequency spectrum results in pulses of only a few wavelengths. The technique was reviewed by Kafka and Ippen. The measurements of the optical lengths are done by auto-correlations in a nonlinear cyrstal like KDP. A very important scientific application of these femto second pulses have been presented by Ippen. He reported on the electron relaxations in semi-conductors and metals. Using GaAs and heating the electrons with about 0.5 eV relaxation phenomena of the order of 200 fs are observed. In gold electron heating up to 1000 K and the speed of energy transport by the electrons of about 10 s cm/sec was observed. His measurements were based on an adjustable delay of a second probe pulse that follows the pump pulse. Although molecular laser systems may have many lasing transitions the linewdiths i.e. the continuous tunebility is in general poor compared with dye and solid state systems. However, the range of lasing frequencies is considerable due to optical pumping of many lasing gases. Especially the well devloped high power CO2 systems have shown to be very useful as pumping sources. A review of many optically pumped systems were presented by Gupta. The quantum efficiency can be as high as 28%. Several gases like NH 3 and CF 4 will also oscillate in continuous operation. The attractive features are the selective excitation, the non-destructive active medium and the adaptability. Furthermore, the gain anisotropy by pumping off center allows unidirectional amplification in ring lasers. To get full profit out of laser science the realization of reliabIe systems is a basic requirement. As long as laboratory studies are concerned with the prove of principle, the stability reproducibility may be poor. For further development also the engineering aspects with respect to scaling parameters, excitation efficiency, simplicity, optimization, etc. become important. Several aspects of laser construction and their performances have been presented by Witteman. He discussed the stability of a transition selective three mirror configuration, single discharge pulsed systems, and a table top e-beam pumped excimer laser construction.