Thickness-Dependent Permeation Properties of Quenched and Standard Laser-Sintered Polyamide 12 Sheets

The laser sintering of polymers is an additive manufacturing technology that is becoming increasingly established in the industrial environment. This study investigated the thickness-dependent permeation properties of laser-sintered (LS) polymers as required to design and produce components with a special barrier performance to gaseous substances. Helium and oxygen permeation experiments were carried out on quenched and standard LS polyamide 12 (PA12) sheets generated with two, four, six, and eight layers at a constant powder layer thickness of 100 µm. The structural properties of the sheets were examined by differential scanning calorimetry, light microscopy, and X-ray micro-computed tomography. A reduction in thickness resulted in higher diffusion coefficients for both types of LS sheets. An explanation could be the large volume fraction of poorly sintered powder particles adhering to the surfaces and incomplete melting and low consolidation of the polymer at small thicknesses. The thickness-dependency of the solubility coefficients was the opposite, especially for the standard LS sheets, which might be related to the larger pore volume in thicker sheets. As both effects compensated for each other, nearly constant permeation coefficients for all thicknesses were observed. The results provide further insights into different material characteristics of thin LS PA12 structures and offer new information on factors relevant to their solution and diffusion behavior.

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Combination of µCT and light microscopy for generation-specific stereological analysis of pulmonary arterial branches: a proof-of-concept study

Histochemistry and Cell Biology ◽

10.1007/s00418-020-01946-x ◽

2020 ◽

Cited By ~ 1

Author(s):

Roman Grothausmann ◽

Jonas Labode ◽

Pablo Hernandez-Cerdan ◽

David Haberthür ◽

Ruslan Hlushchuk ◽

...

Keyword(s):

Blood Vessels ◽

Volume Fraction ◽

Pulmonary Vasculature ◽

Chronic Obstructive ◽

Micro Computed Tomography ◽

Vascular Perfusion ◽

Arterial Tree ◽

Color Code ◽

Rabbit Lung ◽

Stereological Analysis

AbstractVarious lung diseases, including pulmonary hypertension, chronic obstructive pulmonary disease or bronchopulmonary dysplasia, are associated with structural and architectural alterations of the pulmonary vasculature. The light microscopic (LM) analysis of the blood vessels is limited by the fact that it is impossible to identify which generation of the arterial tree an arterial profile within a LM microscopic section belongs to. Therefore, we established a workflow that allows for the generation-specific quantitative (stereological) analysis of pulmonary blood vessels. A whole left rabbit lung was fixed by vascular perfusion, embedded in glycol methacrylate and imaged by micro-computed tomography (µCT). The lung was then exhaustively sectioned and 20 consecutive sections were collected every 100 µm to obtain a systematic uniform random sample of the whole lung. The digital processing involved segmentation of the arterial tree, generation analysis, registration of LM sections with the µCT data as well as registration of the segmentation and the LM images. The present study demonstrates that it is feasible to identify arterial profiles according to their generation based on a generation-specific color code. Stereological analysis for the first three arterial generations of the monopodial branching of the vasculature included volume fraction, total volume, lumen-to-wall ratio and wall thickness for each arterial generation. In conclusion, the correlative image analysis of µCT and LM-based datasets is an innovative method to assess the pulmonary vasculature quantitatively.

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Study in performance and morphology of polyamide 12 produced by selective laser sintering technology

Rapid Prototyping Journal ◽

10.1108/rpj-01-2017-0010 ◽

2018 ◽

Vol 24 (5) ◽

pp. 813-820 ◽

Cited By ~ 9

Author(s):

Junjie Wu ◽

Xiang Xu ◽

Zhihao Zhao ◽

Minjie Wang ◽

Jie Zhang

Keyword(s):

Selective Laser Sintering ◽

Polarized Light ◽

Chain Scission ◽

High Energy ◽

Laser Sintering ◽

X Ray Diffraction ◽

Scanning Calorimetry ◽

Content Type ◽

X Ray ◽

Polyamide 12

Purpose The purpose of this paper is to investigate the effect of selective laser sintering (SLS) method on morphology and performance of polyamide 12. Design/methodology/approach Crystallization behavior is critical to the properties of semi-crystalline polymers. The crystallization condition of SLS process is much different from others. The morphology of polyamide 12 produced by SLS technology was investigated using scanning electron microscopy, polarized light microscopy, differential scanning calorimetry, X-ray diffraction and wide-angle X-ray diffraction. Findings Too low fill laser power brought about bad fusion of powders, while too high energy input resulted in bad performance due to chain scission of macromolecules. There were three types of crystal in the raw powder material, denoted as overgrowth crystal, ring-banded spherulite and normal spherulite. Originality/value In this work, SLS samples with different sintering parameters, as well as compression molding sample for the purpose of comparison, were made to study the morphology and crystal structure of sintered PA12 in detail.

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Poly(δ-valerolactone)/Poly(ethylene-co-vinylalcohol)/β-Tricalcium Phosphate Composite as Scaffolds: Preparation, Properties, and In Vitro Amoxicillin Release

Polymers ◽

10.3390/polym13010046 ◽

2020 ◽

Vol 13 (1) ◽

pp. 46

Author(s):

Mohammed Badwelan ◽

Mohammed Alkindi ◽

Osama Alghamdi ◽

Waseem Sharaf Saeed ◽

Abdel-Basit Al-Odayni ◽

...

Keyword(s):

Hybrid Materials ◽

Tricalcium Phosphate ◽

Drug Carrier ◽

Human Mesenchymal Stem Cells ◽

In Vitro Study ◽

Micro Computed Tomography ◽

Scanning Calorimetry ◽

Sem Images ◽

Poly Ethylene

Two poly(δ-valerolactone)/poly(ethylene-co-vinylalcohol)/β-tricalcium phosphate (PEVAL/PDVAL/β-TCP) composites containing an equal ratio of polymer and filled with 50 and 70 wt% of β-TCP microparticles were prepared by the solvent casting method. Interconnected pores were realized using the salt leached technique, and the porosity of the resulted composites was evaluated by the scanning electron microscopy (SEM) method. The homogeneity of the hybrid materials was investigated by differential scanning calorimetry (DSC) and X-ray diffraction (XRD) analysis. The prepared materials’ SEM images showed interconnected micropores that respond to the conditions required to allow their uses as scaffolds. The porosity of each scaffold was determined from micro computed tomography (micro-CT) data, and the analysis of the mechanical properties of the prepared materials was studied through the stress-strain compressive test. The proliferation test results used human mesenchymal stem cells (MSCs) to grow and proliferate on the different types of prepared materials, reflecting that the hybrid materials were non-toxic and could be biologically acceptable scaffolds. The antibacterial activity test revealed that incorporation of amoxicillin in the specimens could inhibit the bacterial growth of S. aureus. The in vitro study of the release of amoxicillin from the PEVAL/PDVAL/amoxicillin and PEVAL/PDVAL/β-TCP/amoxicillin drug carrier systems in pH media 7.4, during eight days, gave promising results, and the antibiotic diffusion in these scaffolds obeys the Fickian model.

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Comparative study of thermoplastic liner materials with regard to mechanical and permeation barrier properties before and after cyclic thermal aging

Materials Testing ◽

10.1515/mt-2020-0051 ◽

2021 ◽

Vol 63 (4) ◽

pp. 311-316

Author(s):

Simon Backens ◽

Jan Siering ◽

Stefan Schmidt ◽

Nikolai Glück ◽

Wilko Flügge

Keyword(s):

Thermal Aging ◽

Barrier Properties ◽

Tensile Tests ◽

Polyamide 6 ◽

Pressure Vessels ◽

Cross Linking ◽

Polyamide 12 ◽

Type Iv ◽

Before And After ◽

Permeation Properties

Abstract Lightweight pressure vessels of type IV for hydrogen storage consist of a thermoplastic inner liner, commonly from polyethylene or polyamide. The liner is the permeation barrier against the compressed gas and must prevent the formation of cracks, also after temperature changes, for example after refueling processes. In the present work high-density polyethylene, cross-linked polyethylene, polyamide 6 and polyamide 12 were characterized by tensile tests, single notch impact tests and permeations measurements before and after a cyclic thermal aging process. The aging only lead to slight changes of mechanical properties due to post-crystallization, but to a significant decrease of permeation properties. This decrease was contributed to weakened, amorphous regions where chain splitting occurred. Considerable differences in properties resulted from different peroxide cross-linking times of polyethylene at the same temperature. A longer holding time at 200 °C led to an improvement in impact strength by a factor of more than three. However, the permeation properties decreased by about 50 %, indicating that peroxide cross-linking in the melt inhibited the formation of crystalline regions.

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The Role of Nuclear Stiffness and Resilience in Mechanotransduction

ASME 2010 Summer Bioengineering Conference, Parts A and B ◽

10.1115/sbc2010-19514 ◽

2010 ◽

Author(s):

Kris Noel Dahl ◽

Elizabeth A. Booth-Gauthier ◽

Alexandre J. S. Ribeiro ◽

Zhixia Zhong

Keyword(s):

Gene Expression ◽

Cell Fate ◽

Live Cell Imaging ◽

Volume Fraction ◽

Direct Role ◽

Intact Cells ◽

Large Volume Fraction ◽

Nuclear Mechanics ◽

Model Cell

Mechanical force is found to be increasingly important during development and for proper homeostatic maintenance of cells and tissues. The nucleus occupies a large volume fraction of the cell and is interconnected with the cytoskeleton. Here, to determine the direct role of the nucleus itself in converting forces to changes in gene expression, also known as, mechanotransduction, we examine changes in nuclear mechanics and gene reorganization associated with cell fate and with extracellular force. We measure mechanics of nuclei in many model cell systems using micropipette aspiration to show changes in nuclear mechanics. In intact cells we characterize the rheological changes induced in the genome organization with live cell imaging and particle tracking, and we suggest how these changes relate to gene expression.

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Uniformity of Grain Coarsening in Submicron Grained Al-Sc Alloy Containing Local Variations in Texture

Materials Science Forum ◽

10.4028/www.scientific.net/msf.495-497.609 ◽

2005 ◽

Vol 495-497 ◽

pp. 609-614

Author(s):

Michael Ferry

Keyword(s):

Grain Size ◽

Size Distribution ◽

Grain Size Distribution ◽

Fine Particles ◽

Volume Fraction ◽

Marked Change ◽

Grain Coarsening ◽

Large Volume Fraction ◽

Orientation Gradient ◽

Distribution Boundary

The effect of fine particles on the uniformity of grain coarsening in a submicron grained Al-Sc alloy containing significant local variations in texture has been investigated using high resolution EBSD. The alloy was processed by severe plastic deformation and low temperature ageing to generate a fine-grained (0.8 µm diameter) microstructure containing either a dispersion of nanosized Al3Sc particles or a particle-free matrix. The initial processing generated a uniform grain size distribution, but the distribution of grain orientations was inhomogeneous with the microstructure containing colonies of grains consisting predominantly of either HAGBs or LAGBs with the latter possessing orientation gradients of up to 10 o/µm. Despite the marked differences in boundary character between these regions, the alloy undergoes slow and uniform grain coarsening during annealing at temperatures up to 500 oC with no marked change in the grain size distribution, boundary distribution and texture. A model of grain coarsening that takes into account the influence of fine particles on the kinetics of grain growth within an orientation gradient is outlined. The model predicts that a large volume fraction of fine particles (large f/r-value) tends to homogenize the overall rate of grain coarsening despite the presence of orientation gradients in the microstructure.

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Insight into the Formation of Ultrafine Nanostructures in Bulk Amorphous Zr54.5 Ti7.5Al10Cu20Ni8

MRS Proceedings ◽

10.1557/proc-703-v5.4 ◽

2001 ◽

Vol 703 ◽

Author(s):

André Heinemann ◽

Helmut Hermann ◽

Albrecht Wiedenmann ◽

Norbert Mattern ◽

Uta Kühn ◽

...

Keyword(s):

Electron Microscopy ◽

Volume Fraction ◽

High Volume ◽

High Resolution Electron Microscopy ◽

Scattering Data ◽

Scanning Calorimetry ◽

Enhanced Diffusion ◽

Resolution Electron ◽

The Mean ◽

Interparticle Interference

ABSTRACTBulk amorphous Zr54.5 Ti7.5Al10Cu20Ni8 is investigated by means of smal-angle neutron scattering (SANS), differential-scanning calorimetry (DSC), high-resolution electron microscopy (HREM) and other methods. The formation of ultrafine nanostructures in the glassy phase is observed and explained by a new model. Structura fluctuations of randomly distributed partialy ordered domains grow during annealing just below the glass transition temperature by local re-ordering. During anneaing the DSC gives evidence for a increasing volume fraction of the localy ordered domains. At high volume fractions of impinging domains a percolation threshold on the interconnected domain boundaries occurs and enhanced diffusion becomes possible. At that stage SANS measurements lead to satistically significant scattering data. The SANS signals are anayzed in terms of a model taking into account spherica particles surrounded by diffusion zones and interparticle interference effects. The mean radius of the nanocrystaline particles is determined to 1 nm and the mean thickness of the depletion zone is 2 nm. The upper limit for the volume fraction after annealing at 653 K for 4hours is about 20 %. Electron microscopy confirms the size and shows that the particle are crystaline.

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Microstructure and mechanical properties of slowly cooled Cu47.5Zr47.5Al5

Journal of Materials Research ◽

10.1557/jmr.2007.0033 ◽

2007 ◽

Vol 22 (2) ◽

pp. 326-333 ◽

Cited By ~ 42

Author(s):

J. Das ◽

S. Pauly ◽

C. Duhamel ◽

B.C. Wei ◽

J. Eckert

Keyword(s):

Mechanical Properties ◽

Fracture Strain ◽

Volume Fraction ◽

Spherical Shape ◽

High Yield ◽

High Yield Strength ◽

Scanning Calorimetry ◽

Arc Melting ◽

Martensite Matrix

Cu47.5Zr47.5Al5 was prepared by arc melting and solidified in situ by suction casting into 2–5-mm-diameter rods under various cooling rates (200–2000 K/s). The microstructure was investigated along the length of the rods by electron microscopy, differential scanning calorimetry and mechanical properties were investigated under compression. The microstructure of differently prepared specimens consists of macroscopic spherical shape chemically inhomogeneous regions together with a low volume fraction of randomly distributed CuZr B2 phase embedded in a 2–7 nm size clustered “glassy-martensite” matrix. The as-cast specimens show high yield strength (1721 MPa), pronounced work-hardening behavior up to 2116 MPa and large fracture strain up to 12.1–15.1%. The fracture strain decreases with increasing casting diameter. The presence of chemical inhomogenities and nanoscale “glassy-martensite” features are beneficial for improving the inherent ductility of the metallic glass.

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Trabecular bone patterning in the hominoid distal femur

PeerJ ◽

10.7717/peerj.5156 ◽

2018 ◽

Vol 6 ◽

pp. e5156 ◽

Cited By ~ 6

Author(s):

Leoni Georgiou ◽

Tracy L. Kivell ◽

Dieter H. Pahr ◽

Matthew M. Skinner

Keyword(s):

Trabecular Bone ◽

Distal Femur ◽

Volume Fraction ◽

Reaction Force ◽

Intraspecific Variability ◽

Trabecular Structure ◽

Trabecular Architecture ◽

Micro Computed Tomography ◽

Bone Volume Fraction ◽

Distal Epiphysis

BackgroundIn addition to external bone shape and cortical bone thickness and distribution, the distribution and orientation of internal trabecular bone across individuals and species has yielded important functional information on how bone adapts in response to load. In particular, trabecular bone analysis has played a key role in studies of human and nonhuman primate locomotion and has shown that species with different locomotor repertoires display distinct trabecular architecture in various regions of the skeleton. In this study, we analyse trabecular structure throughout the distal femur of extant hominoids and test for differences due to locomotor loading regime.MethodsMicro-computed tomography scans ofHomo sapiens(n= 11),Pan troglodytes(n= 18),Gorilla gorilla(n= 14) andPongosp. (n= 7) were used to investigate trabecular structure throughout the distal epiphysis of the femur. We predicted that bone volume fraction (BV/TV) in the medial and lateral condyles inHomowould be distally concentrated and more anisotropic due to a habitual extended knee posture at the point of peak ground reaction force during bipedal locomotion, whereas great apes would show more posteriorly concentrated BV/TV and greater isotropy due to a flexed knee posture and more variable hindlimb use during locomotion.ResultsResults indicate some significant differences between taxa, with the most prominent being higher BV/TV in the posterosuperior region of the condyles inPanand higher BV/TV and anisotropy in the posteroinferior region inHomo. Furthermore, trabecular number, spacing and thickness differ significantly, mainly separatingGorillafrom the other apes.DiscussionThe trabecular architecture of the distal femur holds a functional signal linked to habitual behaviour; however, there was more similarity across taxa and greater intraspecific variability than expected. Specifically, there was a large degree of overlap in trabecular structure across the sample, andHomowas not as distinct as predicted. Nonetheless, this study offers a comparative sample of trabecular structure in the hominoid distal femur and can contribute to future studies of locomotion in extinct taxa.

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3D MORPHOLOGICAL ANALYSIS OF COMPOSITE MATERIALS WITH AGGREGATES OF SPHERICAL INCLUSIONS

Image Analysis & Stereology ◽

10.5566/ias.v22.p153-161 ◽

2011 ◽

Vol 22 (1) ◽

pp. 153 ◽

Cited By ~ 14

Author(s):

Arnaud Delarue ◽

Dominique Jeulin

Keyword(s):

Composite Materials ◽

Volume Fraction ◽

Empirical Distribution ◽

Geodesic Distance ◽

Shortest Paths ◽

Morphological Properties ◽

3D Images ◽

Spherical Inclusions ◽

New Information ◽

The Matrix

Composite materials containing aggregates of spherical inclusions are studied from 3D images obtained by X-ray microtomography. Using two point statistics in different directions, and the empirical distribution of orientations of pairs of inclusions, interesting details concerning the anisotropy of the distribution of inclusions are obtained and are related to the method of construction for these materials. Some 3D morphological properties, available on the 3D images, give new information on the shape and the distribution of aggregates: tortuosity of shortest paths in the matrix, local volume fraction, geodesic distance function, local histograms of numbers of objects.

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