The original plotting position concept was suggested more than a century ago. Since then, many alternative plotting position approaches have been developed. Despite a general lack of agreement around ...which plotting position is theoretically 'correct' and the 'best' to use, all plotting positions fail to adequately address outliers and data of similar magnitude. Hydrologists generally fail to acknowledge that the plotting position primarily offers an informative display of data, against which distributions can be compared, rather than an absolute measure of probability. This paper does not intend to challenge any of the many lengthy theoretical mathematical arguments, utilised to 'prove' why one plotting position is superior to the others. These theoretical arguments may very well be valid for a 'population' of flood peaks - the reality, however, is that hydrologists are confronted with the challenge of analysing very limited 'samples' of the population. Consequently, the plotting position issue demands a more pragmatic approach, rather than a purely theoretical approach. This paper illustrates various problems with existing plotting position techniques in use and offers an alternative approach and a more sensible plotting position technique, using Z-scores and referred to as the Z-set PP, against which distributions can be checked. The study further illustrates how effectively the Z-set PP deals with outliers and its robustness with various record lengths. Although derived from a study of flood peak data obtained from South African flow-gauging sites, it is deemed that it will be universally applicable.
Structural equation modeling (SEM) has a long history of representing models graphically as path diagrams. This article presents the freely available semPlot package for R, which fills the gap ...between advanced, but time-consuming, graphical software and the limited graphics produced automatically by SEM software. In addition, semPlot offers more functionality than drawing path diagrams: It can act as a common ground for importing SEM results into R. Any result usable as input to semPlot can also be represented in any of the 3 popular SEM frameworks, as well as translated to input syntax for the R packages sem (Fox, Nie, & Byrnes, 2013) and lavaan (Rosseel, 2012). Special considerations are made in the package for the automatic placement of variables, using 3 novel algorithms that extend the earlier work of Boker, McArdle, and Neale (2002). The article concludes with detailed instructions on these node-placement algorithms.
Constructing bioactive scaffolds with controllable architecture for bone tissue engineering and drug delivery still maintains a significant challenge. In this study, we have developed a composite ...material consisting of mesoporous bioactive glass (MBG) and concentrated alginate pastes for fabrication of hierarchical scaffolds by 3D plotting. The scaffold structure contains well-ordered nano-channels, micropores as well as controllable macropores beneficial for bone tissue engineering applications and drug delivery. The structural architecture of the scaffolds has been optimized by efficient designing of the plotting coordination. The effects of MBG on mechanical strength, apatite mineralization, cytocompatibility and drug delivery properties of the composite scaffolds have been systematically studied. Transmission electron microscopy, scanning electron microscopy and energy-dispersive spectrometry were used to characterize composition and microstructure of the composite scaffolds. The MBG/alginate pastes showed good processability in the 3D plotting process, in which stable MBG/alginate composite scaffolds with controllable architecture can be prepared. The incorporation of MBG particles significantly improved the mechanical properties and apatite-mineralization ability of alginate scaffolds as well as enhanced the attachment and alkaline phosphatase activity of human bone marrow-derived mesenchymal stem cells cultivated onto the scaffolds. Dexamethasone, used as a model drug, can be efficiently loaded in MBG particles and then incorporated into alginate scaffolds resulting in a more sustained release as a function of the MBG content. Our results have indicated that 3D-plotted MBG incorporated alginate scaffolds with well-ordered nano-pores, controllable large pores, and significantly improved physicochemical, biological and drug-delivery properties could be a platform for bone tissue engineering.
•A novel type of PCL scaffolds were produced using 3D plotting technique.•PCL scaffolds were comprised of tailored core/shell-structured filaments.•Core-shell structure was tailored by adjusting the ...water (W)/ethanol (E) ratio.•The thickness of the shell increased with an increase in W/E ratio.•The mechanical properties increased due to the dense shell layers.
This study presents a novel type of poly(ε-caprolactone) (PCL) scaffold comprised of tailored core/shell-structured filaments. The scaffold can be produced using a nonsolvent-induced phase separation phenomenon during the 3D plotting of PCL solutions in a coagulation bath. Specifically, a mixture of water and ethanol was employed as the nonsolvent, in order to tailor the phase separation behavior of a PCL/acetone solution. The addition of water to ethanol allowed for the creation of dense shells due to the fast exchange between acetone and water during the early stage of the 3D plotting process, while in the cores a number of micropores were formed. In addition, the thickness of the dense shell increased with an increase in water content in the water/ethanol mixture, increasing the mechanical properties (i.e., tensile strength, modulus, and strain at failure) of the porous PCL scaffolds with tailored core/shell-structured filaments remarkably.
In the present work, gelatin/alginate and gelatin/alginate/hydroxyapatite (HAP) composite scaffolds were fabricated by 3D plotting based on high concentration gelatin/alginate pastes. At temperatures ...of 37 °C or above, the developed pastes could be easily processed into designed 3D structures; sequential crosslinking with Ca
2+
ions (effective for alginate) and the carbodiimide EDC (effective for gelatin) resulted in stable scaffolds. Mechanical testing demonstrated that the plotted composite scaffolds had a significantly higher strength and modulus compared to most reported gelatin scaffolds prepared by conventional methods. Cell experiments with human bone marrow-derived mesenchymal stem cells (hBMSC) revealed that the gelatin/alginate composite scaffolds favor cell adhesion and support proliferation. Furthermore, the cells showed a homogeneous distribution and excellent migration in the inner regions of the plotted composite scaffolds over 21 days. In conclusion, gelatin/alginate scaffolds, with or without HAP, fabricated by 3D plotting according to a predesigned CAD-model might be potential candidates for the repair of bony and chondral defects, especially in complex defect situations affecting the osteochondral tissue interface since biphasic scaffolds with a stable connection of the two parts can be easily fabricated by multi-channel 3D plotting.
Developed concentrated gelatin/alginate with/without HAP composites were plotted into pre-designed scaffolds, which showed good cells attachments and penetration.
In tissue engineering, additive manufacturing (AM) technologies have brought considerable progress as they allow the fabrication of three-dimensional (3D) structures with defined architecture. 3D ...plotting is a versatile, extrusion-based AM technology suitable for processing a wide range of biomaterials including hydrogels. In this study, composites of highly concentrated alginate and gellan gum were prepared in order to combine the excellent printing properties of alginate with the favorable gelling characteristics of gellan gum. Mixtures of 16.7 wt % alginate and 2 or 3 wt % gellan gum were found applicable for 3D plotting. Characterization of the resulting composite scaffolds revealed an increased stiffness in the wet state (15%⁻20% higher Young's modulus) and significantly lower volume swelling in cell culture medium compared to pure alginate scaffolds (~10%
~23%). Cytocompatibility experiments with human mesenchymal stem cells (hMSC) revealed that cell attachment was improved-the seeding efficiency was ~2.5⁻3.5 times higher on the composites than on pure alginate. Additionally, the composites were shown to support hMSC proliferation and early osteogenic differentiation. In conclusion, print fidelity of highly concentrated alginate-gellan gum composites was comparable to those of pure alginate; after plotting and crosslinking, the scaffolds possessed improved qualities regarding shape fidelity, mechanical strength, and initial cell attachment making them attractive for tissue engineering applications.
Scaffolds produced by rapid prototyping (RP) techniques have proved their value for tissue engineering applications, due to their ability to produce predetermined forms and structures featuring fully ...interconnected pore architectures. Nevertheless, low cell seeding efficiency and non-uniform distribution of cells remain major limitations when using such types of scaffold. This can be mainly attributed to the inadequate pore architecture of scaffolds produced by RP and the limited efficiency of cell seeding techniques normally adopted. In this study we aimed at producing scaffolds with pore size gradients to enhance cell seeding efficiency and control the spatial organization of cells within the scaffold. Scaffolds based on blends of starch with poly(ε-caprolactone) featuring both homogeneously spaced pores (based on pore sizes of 0.75 and 0.1mm) and pore size gradients (based on pore sizes of 0.1–0.75–0.1 and 0.75–0.1–0.75mm) were designed and produced by three-dimensional plotting. The mechanical performance of the scaffolds was characterized using dynamic mechanical analysis (DMA) and conventional compression testing under wet conditions and subsequently characterized using scanning electron microscopy and micro-computed tomography. Osteoblast-like cells were seeded onto such scaffolds to investigate cell seeding efficiency and the ability to control the zonal distribution of cells upon seeding. Scaffolds featuring continuous pore size gradients were originally produced. These scaffolds were shown to have intermediate mechanical and morphological properties compared with homogenous pore size scaffolds. The pore size gradient scaffolds improved seeding efficiency from ∼35% in homogeneous scaffolds to ∼70% under static culture conditions. Fluorescence images of cross-sections of the scaffolds revealed that scaffolds with pore size gradients induce a more homogeneous distribution of cells within the scaffold.
Structural properties of composite carbon with metal Cu (CCu) were analysis from the X-ray Diffraction (XRD) data by modified Williamson-Hall (W-H) and size-strain plotting methods. The effect of ...temperature shows influenced to increasing the resistance from 37.3% at room temperature to 66.4% for 600°C. By using the modified equation of Williamson-Hall, we found that the crystallite size about 40.78 nm. Modified Williamson-Hall (W-H) plotting and Gaussian distribution shows good correlation and accuration for determining the crystallite size from the XRD data in this study.
Porous scaffolds for tissue engineering applications consisting of hollow alginate fibers are presented. They are prepared using self-made shell/core nozzles and a 3D plotting device. Such materials ...open up the possibility to generate biodegradable tissue constructs with a preformed vascular system or can act as matrices for engineering of complex organs or 3D tissue models.
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