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Dirk W. Schubert
Institute of Polymer Materials, Friedrich-Alexander University Erlangen-Nürnberg (FAU), Martensstraße 7, 91058 Erlangen, Germany

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Journal article
Published: 15 August 2021 in Cancers
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Alginate hydrogels have been used as a biomaterial for 3D culturing for several years. Here, gene expression patterns in melanoma cells cultivated in 3D alginate are compared to 2D cultures. It is well-known that 2D cell culture is not resembling the complex in vivo situation well. However, the use of very intricate 3D models does not allow performing high-throughput screening and analysis is highly complex. 3D cell culture strategies in hydrogels will better mimic the in vivo situation while they maintain feasibility for large-scale analysis. As alginate is an easy-to-use material and due to its favorable properties, it is commonly applied as a bioink component in the growing field of cell encapsulation and biofabrication. Yet, only a little information about the transcriptome in 3D cultures in hydrogels like alginate is available. In this study, changes in the transcriptome based on RNA-Seq data by cultivating melanoma cells in 3D alginate are analyzed and reveal marked changes compared to cells cultured on usual 2D tissue culture plastic. Deregulated genes represent valuable cues to signaling pathways and molecules affected by the culture method. Using this as a model system for tumor cell plasticity and heterogeneity, EGR1 is determined to play an important role in melanoma progression.

ACS Style

Melanie Kappelmann-Fenzl; Sonja K. Schmidt; Stefan Fischer; Rafael Schmid; Lisa Lämmerhirt; Lena Fischer; Stefan Schrüfer; Ingo Thievessen; Dirk W. Schubert; Alexander Matthies; Rainer Detsch; Aldo R. Boccaccini; Andreas Arkudas; Annika Kengelbach-Weigand; Anja K. Bosserhoff. Molecular Changes Induced in Melanoma by Cell Culturing in 3D Alginate Hydrogels. Cancers 2021, 13, 4111 .

AMA Style

Melanie Kappelmann-Fenzl, Sonja K. Schmidt, Stefan Fischer, Rafael Schmid, Lisa Lämmerhirt, Lena Fischer, Stefan Schrüfer, Ingo Thievessen, Dirk W. Schubert, Alexander Matthies, Rainer Detsch, Aldo R. Boccaccini, Andreas Arkudas, Annika Kengelbach-Weigand, Anja K. Bosserhoff. Molecular Changes Induced in Melanoma by Cell Culturing in 3D Alginate Hydrogels. Cancers. 2021; 13 (16):4111.

Chicago/Turabian Style

Melanie Kappelmann-Fenzl; Sonja K. Schmidt; Stefan Fischer; Rafael Schmid; Lisa Lämmerhirt; Lena Fischer; Stefan Schrüfer; Ingo Thievessen; Dirk W. Schubert; Alexander Matthies; Rainer Detsch; Aldo R. Boccaccini; Andreas Arkudas; Annika Kengelbach-Weigand; Anja K. Bosserhoff. 2021. "Molecular Changes Induced in Melanoma by Cell Culturing in 3D Alginate Hydrogels." Cancers 13, no. 16: 4111.

Article
Published: 25 January 2021 in Nano-Micro Letters
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In recently years, high-performance wearable strain sensors have attracted great attention in academic and industrial. Herein, a conductive polymer composite of electrospun thermoplastic polyurethane (TPU) fibrous film matrix-embedded carbon black (CB) particles with adjustable scaffold network was fabricated for high-sensitive strain sensor. This work indicated the influence of stereoscopic scaffold network structure built under various rotating speeds of collection device in electrospinning process on the electrical response of TPU/CB strain sensor. This structure makes the sensor exhibit combined characters of high sensitivity under stretching strain (gauge factor of 8962.7 at 155% strain), fast response time (60 ms), outstanding stability and durability (> 10,000 cycles) and a widely workable stretching range (0–160%). This high-performance, wearable, flexible strain sensor has a broad vision of application such as intelligent terminals, electrical skins, voice measurement and human motion monitoring. Moreover, a theoretical approach was used to analyze mechanical property and a model based on tunneling theory was modified to describe the relative change of resistance upon the applied strain. Meanwhile, two equations based from this model were first proposed and offered an effective but simple approach to analyze the change of number of conductive paths and distance of adjacent conductive particles.

ACS Style

Xin Wang; Xianhu Liu; Dirk W. Schubert. Highly Sensitive Ultrathin Flexible Thermoplastic Polyurethane/Carbon Black Fibrous Film Strain Sensor with Adjustable Scaffold Networks. Nano-Micro Letters 2021, 13, 1 -19.

AMA Style

Xin Wang, Xianhu Liu, Dirk W. Schubert. Highly Sensitive Ultrathin Flexible Thermoplastic Polyurethane/Carbon Black Fibrous Film Strain Sensor with Adjustable Scaffold Networks. Nano-Micro Letters. 2021; 13 (1):1-19.

Chicago/Turabian Style

Xin Wang; Xianhu Liu; Dirk W. Schubert. 2021. "Highly Sensitive Ultrathin Flexible Thermoplastic Polyurethane/Carbon Black Fibrous Film Strain Sensor with Adjustable Scaffold Networks." Nano-Micro Letters 13, no. 1: 1-19.

Journal article
Published: 21 January 2021 in Materials
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Novel hemp fiber reinforced geopolymer composites were fabricated. The matrix was a new geopolymer based on a mixture of red mud and fly ash. Chopped, randomly oriented hemp fibers were used as reinforcement. The mechanical properties of the geopolymer composite, such as diametral tensile (DTS) (or Brazilian tensile) strength and compressive strength (CS), were measured. The geopolymer composites reinforced with 9 vol.% and 3 vol.% hemp fiber yielded average DTS values of 5.5 MPa and average CS values of 40 MPa. Scanning electron microscopy (SEM) studies were carried out to evaluate the microstructure and fracture surfaces of the composites. The results indicated that the addition of hemp fiber is a promising approach to improve the mechanical strength as well as to modify the failure mechanism of the geopolymer, which changed from brittle to “pseudo- ductile.”

ACS Style

Eyerusalem Taye; Judith Roether; Dirk Schubert; Daniel Redda; Aldo Boccaccini. Hemp Fiber Reinforced Red Mud/Fly Ash Geopolymer Composite Materials: Effect of Fiber Content on Mechanical Strength. Materials 2021, 14, 511 .

AMA Style

Eyerusalem Taye, Judith Roether, Dirk Schubert, Daniel Redda, Aldo Boccaccini. Hemp Fiber Reinforced Red Mud/Fly Ash Geopolymer Composite Materials: Effect of Fiber Content on Mechanical Strength. Materials. 2021; 14 (3):511.

Chicago/Turabian Style

Eyerusalem Taye; Judith Roether; Dirk Schubert; Daniel Redda; Aldo Boccaccini. 2021. "Hemp Fiber Reinforced Red Mud/Fly Ash Geopolymer Composite Materials: Effect of Fiber Content on Mechanical Strength." Materials 14, no. 3: 511.

Full paper
Published: 12 January 2021 in Advanced Engineering Materials
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Blends of PCL with two different molar masses were deliberately varied to change viscosity independent of polymer concentration enabling to separate viscosity and a direct concentration dependence of the fiber diameter in the electrospinning process. Multiple distributions as a result of jet splitting were determined and analyzed. The existence of essentially two modes in fiber diameter frequency distribution, the base mode and split mode, was revealed, while the scaling laws for each mode could be validated according to the latest theory. Finally, the theoretical predicted upper limit 2 2 , of the ratio of standard deviation of fiber diameter and average fiber diameter was validated. This article is protected by copyright. All rights reserved.

ACS Style

Dirk W. Schubert; Vincent Allen; Ursula Dippel. Revealing Novel Power Laws and Quantization in Electrospinning Considering Jet Splitting—Toward Predicting Fiber Diameter and Its Distribution Part II Experimental. Advanced Engineering Materials 2021, 23, 1 .

AMA Style

Dirk W. Schubert, Vincent Allen, Ursula Dippel. Revealing Novel Power Laws and Quantization in Electrospinning Considering Jet Splitting—Toward Predicting Fiber Diameter and Its Distribution Part II Experimental. Advanced Engineering Materials. 2021; 23 (3):1.

Chicago/Turabian Style

Dirk W. Schubert; Vincent Allen; Ursula Dippel. 2021. "Revealing Novel Power Laws and Quantization in Electrospinning Considering Jet Splitting—Toward Predicting Fiber Diameter and Its Distribution Part II Experimental." Advanced Engineering Materials 23, no. 3: 1.

Journal article
Published: 25 August 2020 in Polymers
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Thermoplastic Polyurethane (TPU) is a unique tailorable material due to the interactions of hard and soft segments within the block-copolymer chain. Therefore, various products can be created out of this material. A general trend towards a circular economy with regards to sustainability in combination with TPU being comparably expensive is of high interest to recycle production as well as post-consumer wastes. A systematic study investigating the property changes of TPU is provided, focusing on two major aspects. The first aspect focuses on characterizing the change of basic raw material properties through recycling. Gel permeation chromatography (GPC) and processing load during extrusion indicate a decrease in molar mass and consequently viscosity with an increasing number of recycling cycles. This leads to a change in morphology at lower molar mass, characterized by differential scanning calorimetry (DSC) and visualized by atomic force microscope (AFM). The change in molar mass and morphology with increasing number of recycling cycles has an impact on the material performance under tensile stress. The second aspect describes processing of the recycled TPU to nonwoven fabrics utilizing melt blowing, which are evaluated with respect to relevant mechanical properties and related to molecular characteristics. The molar mass turns out to be the governing factor regarding mechanical performance and processing conditions for melt blown products.

ACS Style

Bastian Wölfel; Andreas Seefried; Vincent Allen; Joachim Kaschta; Christopher Holmes; Dirk W. Schubert. Recycling and Reprocessing of Thermoplastic Polyurethane Materials towards Nonwoven Processing. Polymers 2020, 12, 1917 .

AMA Style

Bastian Wölfel, Andreas Seefried, Vincent Allen, Joachim Kaschta, Christopher Holmes, Dirk W. Schubert. Recycling and Reprocessing of Thermoplastic Polyurethane Materials towards Nonwoven Processing. Polymers. 2020; 12 (9):1917.

Chicago/Turabian Style

Bastian Wölfel; Andreas Seefried; Vincent Allen; Joachim Kaschta; Christopher Holmes; Dirk W. Schubert. 2020. "Recycling and Reprocessing of Thermoplastic Polyurethane Materials towards Nonwoven Processing." Polymers 12, no. 9: 1917.

Journal article
Published: 17 August 2020 in Cancers
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Bioprinting offers the opportunity to fabricate precise 3D tumor models to study tumor pathophysiology and progression. However, the choice of the bioink used is important. In this study, cell behavior was studied in three mechanically and biologically different hydrogels (alginate, alginate dialdehyde crosslinked with gelatin (ADA–GEL), and thiol-modified hyaluronan (HA-SH crosslinked with PEGDA)) with cells from breast cancer (MDA-MB-231 and MCF-7) and melanoma (Mel Im and MV3), by analyzing survival, growth, and the amount of metabolically active, living cells via WST-8 labeling. Material characteristics were analyzed by dynamic mechanical analysis. Cell lines revealed significantly increased cell numbers in low-percentage alginate and HA-SH from day 1 to 14, while only Mel Im also revealed an increase in ADA–GEL. MCF-7 showed a preference for 1% alginate. Melanoma cells tended to proliferate better in ADA–GEL and HA-SH than mammary carcinoma cells. In 1% alginate, breast cancer cells showed equally good proliferation compared to melanoma cell lines. A smaller area was colonized in high-percentage alginate-based hydrogels. Moreover, 3% alginate was the stiffest material, and 2.5% ADA–GEL was the softest material. The other hydrogels were in the same range in between. Therefore, cellular responses were not only stiffness-dependent. With 1% alginate and HA-SH, we identified matrices that enable proliferation of all tested tumor cell lines while maintaining expected tumor heterogeneity. By adapting hydrogels, differences could be accentuated. This opens up the possibility of understanding and analyzing tumor heterogeneity by biofabrication.

ACS Style

Rafael Schmid; Sonja K. Schmidt; Jonas Hazur; Rainer Detsch; Evelyn Maurer; Aldo R. Boccaccini; Julia Hauptstein; Jörg Teßmar; Torsten Blunk; Stefan Schrüfer; Dirk W. Schubert; Raymund E. Horch; Anja K. Bosserhoff; Andreas Arkudas; Annika Kengelbach-Weigand. Comparison of Hydrogels for the Development of Well-Defined 3D Cancer Models of Breast Cancer and Melanoma. Cancers 2020, 12, 2320 .

AMA Style

Rafael Schmid, Sonja K. Schmidt, Jonas Hazur, Rainer Detsch, Evelyn Maurer, Aldo R. Boccaccini, Julia Hauptstein, Jörg Teßmar, Torsten Blunk, Stefan Schrüfer, Dirk W. Schubert, Raymund E. Horch, Anja K. Bosserhoff, Andreas Arkudas, Annika Kengelbach-Weigand. Comparison of Hydrogels for the Development of Well-Defined 3D Cancer Models of Breast Cancer and Melanoma. Cancers. 2020; 12 (8):2320.

Chicago/Turabian Style

Rafael Schmid; Sonja K. Schmidt; Jonas Hazur; Rainer Detsch; Evelyn Maurer; Aldo R. Boccaccini; Julia Hauptstein; Jörg Teßmar; Torsten Blunk; Stefan Schrüfer; Dirk W. Schubert; Raymund E. Horch; Anja K. Bosserhoff; Andreas Arkudas; Annika Kengelbach-Weigand. 2020. "Comparison of Hydrogels for the Development of Well-Defined 3D Cancer Models of Breast Cancer and Melanoma." Cancers 12, no. 8: 2320.

Journal article
Published: 12 June 2020 in Additive Manufacturing
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Polypropylene (PP) powder is treated in a fluidized bed reactor with an atmospheric Ar/O2 plasma jet to investigate the influence of the plasma treatment on the coloring of the powders. The oxygen concentration in the plasma gas and duration of the treatment was varied. Contact angle and X-ray photoelectron spectroscopy measurements confirmed and quantified the formation of surface functionalities and their dependence on the process parameters. The plasma treatment contributes to a significant improvement of the dispersibility and coloring of PP. Powder bulk properties such as particle size distribution and flowability were not modified by the process. Effects of the plasma treatment on the material bulk properties are also negligible.

ACS Style

Gómez Bonilla Juan S; Tim Szymczak; Xuemei Zhou; Stefan Schrüfer; Maximilian A. Dechet; Patrik Schmuki; Dirk W. Schubert; Jochen Schmidt; Wolfgang Peukert; Andreas Bück. Improving the coloring of polypropylene materials for powder bed fusion by plasma surface functionalization. Additive Manufacturing 2020, 34, 101373 .

AMA Style

Gómez Bonilla Juan S, Tim Szymczak, Xuemei Zhou, Stefan Schrüfer, Maximilian A. Dechet, Patrik Schmuki, Dirk W. Schubert, Jochen Schmidt, Wolfgang Peukert, Andreas Bück. Improving the coloring of polypropylene materials for powder bed fusion by plasma surface functionalization. Additive Manufacturing. 2020; 34 ():101373.

Chicago/Turabian Style

Gómez Bonilla Juan S; Tim Szymczak; Xuemei Zhou; Stefan Schrüfer; Maximilian A. Dechet; Patrik Schmuki; Dirk W. Schubert; Jochen Schmidt; Wolfgang Peukert; Andreas Bück. 2020. "Improving the coloring of polypropylene materials for powder bed fusion by plasma surface functionalization." Additive Manufacturing 34, no. : 101373.

Full paper
Published: 08 June 2020 in Macromolecular Materials and Engineering
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In this study, poly(methyl methacrylate) (PMMA)/carbon black (CB), PMMA/carbon fiber (CF), and PMMA/carbon nanotube (CNT) conductive composite films with different filler concentrations are prepared using the solution casting technique. Both perpendicular and in‐plane direction conductivity of all the binary composite films are investigated, percolation thresholds (ϕc) of both directions of PMMA/CB, PMMA/CF, and PMMA/CNT composite films are investigated and the experimental data are fitted using McLachlan’s equation. For all the three investigated films, the perpendicular ϕc,⊥ and in‐plane ϕc,∥ with different fillers show totally different behaviors. Pristine CB, CF, and CNT as well as PMMA/CB, PMMA/CF, and PMMA/CNT composite films are discussed. The gravity effect of the fillers is found to be most significant in the PMMA/CB system. A schematic diagram of PMMA composite films with CB, CF, and CNT as filler prepared from solution casting process is presented to explain the distribution gradient of the fillers in the perpendicular direction of the film after solution casting. A power law behavior is revealed for different filler types (CB, CF, CNT) correlating the exponent t for McLachlan’s equation and corresponding ϕc for in‐plane and perpendicular directions.

ACS Style

Huagen Xu; Dirk W. Schubert. Perpendicular and In‐Plane Conductivity of Poly(methyl methacrylate) Composite Films Filled with Carbon‐Based Fillers Prepared from Solution Casting Process. Macromolecular Materials and Engineering 2020, 305, 1 .

AMA Style

Huagen Xu, Dirk W. Schubert. Perpendicular and In‐Plane Conductivity of Poly(methyl methacrylate) Composite Films Filled with Carbon‐Based Fillers Prepared from Solution Casting Process. Macromolecular Materials and Engineering. 2020; 305 (7):1.

Chicago/Turabian Style

Huagen Xu; Dirk W. Schubert. 2020. "Perpendicular and In‐Plane Conductivity of Poly(methyl methacrylate) Composite Films Filled with Carbon‐Based Fillers Prepared from Solution Casting Process." Macromolecular Materials and Engineering 305, no. 7: 1.

Journal article
Published: 03 June 2020 in Polymers
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When characterizing the viscoelastic properties of polymers, shear rheological measurements are commonly the method of choice. These properties are known to affect extrusion and nozzle-based processes such as fiber melt spinning, cast film extrusion and 3D-printing. However, an adequate characterization of shear thinning polymers can be challenging and still insufficient to not only describe but predict process relevant influences. Furthermore, the evaluation of rheological model systems in literature is mostly based on stress–relaxation experiments, which are rarely available for various polymeric materials. Therefore, a simple approach is presented, that can be used to evaluate and benchmark a wide range of rheological model systems based on commonly accessible frequency sweep data. The approach is validated by analyzing alginate PH176 solutions of various concentrations, a thermoplastic poly-urethane (TPU) Elastollan 1180A melt, the liquid silicon rubber Elastosil 7670 and a polycaprolactone (PCL) fiber-alginate composite system. The used rheological model systems, consisting of simple springs and dashpots, are suitable for the description of complex, viscoelastic material properties that can be observed for polymer solutions and gel-like systems. After revealing a suitable model system for describing those material properties, the determination and evaluation of relevant model parameters can take place. We present a detailed guideline for the systematic parameter revelation using alginate solutions of different concentrations as example. Furthermore, a starting point for future correlations of strut spreading in 3D-bioprinting and model parameters is revealed. This work establishes the basis for a better understanding and potential predictability of key parameters for various fabrication techniques.

ACS Style

S. Schrüfer; D. Sonnleitner; G. Lang; D. W. Schubert. A Novel Simple Approach to Material Parameters from Commonly Accessible Rheometer Data. Polymers 2020, 12, 1276 .

AMA Style

S. Schrüfer, D. Sonnleitner, G. Lang, D. W. Schubert. A Novel Simple Approach to Material Parameters from Commonly Accessible Rheometer Data. Polymers. 2020; 12 (6):1276.

Chicago/Turabian Style

S. Schrüfer; D. Sonnleitner; G. Lang; D. W. Schubert. 2020. "A Novel Simple Approach to Material Parameters from Commonly Accessible Rheometer Data." Polymers 12, no. 6: 1276.

Full paper
Published: 08 May 2020 in Advanced Engineering Materials
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A novel theoretical approach, which yields a non‐linear differential equation for the mechanical properties of fiber filled composites as a function of the volume fraction of the filler and the fiber orientation, is shown. Furthermore, the transfer to polymer solutions is shown and gives a physical explanation for various well‐known empirical relations and numerical values including the Huggins constant and the exponent of power‐law molar mass dependence of the polymer melt viscosity. This article is protected by copyright. All rights reserved.

ACS Style

Dirk W. Schubert. Novel Theoretical Self‐Consistent Mean‐Field Approach to Describe the Conductivity of Carbon Fiber‐Filled Thermoplastics: Part III—Application of the Concept to Mechanical Properties of Composites and Polymer Solutions. Advanced Engineering Materials 2020, 22, 1 .

AMA Style

Dirk W. Schubert. Novel Theoretical Self‐Consistent Mean‐Field Approach to Describe the Conductivity of Carbon Fiber‐Filled Thermoplastics: Part III—Application of the Concept to Mechanical Properties of Composites and Polymer Solutions. Advanced Engineering Materials. 2020; 22 (9):1.

Chicago/Turabian Style

Dirk W. Schubert. 2020. "Novel Theoretical Self‐Consistent Mean‐Field Approach to Describe the Conductivity of Carbon Fiber‐Filled Thermoplastics: Part III—Application of the Concept to Mechanical Properties of Composites and Polymer Solutions." Advanced Engineering Materials 22, no. 9: 1.

Full paper
Published: 21 April 2020 in Advanced Engineering Materials
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Fibrous scaffolds can be employed to mimic the structure of cartilage extracellular matrix aiming at cartilage regeneration through optimal utilization of such scaffolds and chondrogenic cells. In this study, different types of fibrous structures were manufactured through electrospinning of blends of Polyethylene Oxide (PEO) and Polycaprolactone (PCL) and the physical and chemical characteristics of the produced fiber mats were investigated. The amount of PEO influenced hydrophilicity, biodegradibility and mechanical properties of the blend fibers. To assess the cytotoxicity and biocompatibility of the scaffolds as well as the effect of fiber orientation, in vitro cell culture studies with a chondrogenic cell line (ATDC5) were performed. The results showed no cytotoxicity of the developed fibrous structures. The work presents a promising fibrous scaffold technology with potential applications in cartilage tissue engineering. This article is protected by copyright. All rights reserved.

ACS Style

Zeynab Mirzaei; Soheila S. Kordestani; Sonja Kuth; Dirk W. Schubert; Rainer Detsch; Judith A. Roether; Torsten Blunk; Aldo R. Boccaccini. Preparation and Characterization of Electrospun Blend Fibrous Polyethylene Oxide:Polycaprolactone Scaffolds to Promote Cartilage Regeneration. Advanced Engineering Materials 2020, 22, 1 .

AMA Style

Zeynab Mirzaei, Soheila S. Kordestani, Sonja Kuth, Dirk W. Schubert, Rainer Detsch, Judith A. Roether, Torsten Blunk, Aldo R. Boccaccini. Preparation and Characterization of Electrospun Blend Fibrous Polyethylene Oxide:Polycaprolactone Scaffolds to Promote Cartilage Regeneration. Advanced Engineering Materials. 2020; 22 (9):1.

Chicago/Turabian Style

Zeynab Mirzaei; Soheila S. Kordestani; Sonja Kuth; Dirk W. Schubert; Rainer Detsch; Judith A. Roether; Torsten Blunk; Aldo R. Boccaccini. 2020. "Preparation and Characterization of Electrospun Blend Fibrous Polyethylene Oxide:Polycaprolactone Scaffolds to Promote Cartilage Regeneration." Advanced Engineering Materials 22, no. 9: 1.

Short communication
Published: 24 January 2020 in Polymer Testing
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15 micro-textured silicone breast explants are investigated in cyclic compression tests regarding their mechanical behavior. Initially a maximum load of 2.5 kN was applied to the explants in a repetitive way until failure happened. Finally the results are shown on the one hand as a correlation between the number of endured loading cycles and the implantation time. On the other hand the correlation to the explants’ mass was analyzed and described by using a power law.

ACS Style

Harald Von Hanstein; Raymund E. Horch; Dirk W. Schubert. Resistance of silicone breast explants under cyclic compressive load as a function of implantation time and explant mass. Polymer Testing 2020, 84, 106377 .

AMA Style

Harald Von Hanstein, Raymund E. Horch, Dirk W. Schubert. Resistance of silicone breast explants under cyclic compressive load as a function of implantation time and explant mass. Polymer Testing. 2020; 84 ():106377.

Chicago/Turabian Style

Harald Von Hanstein; Raymund E. Horch; Dirk W. Schubert. 2020. "Resistance of silicone breast explants under cyclic compressive load as a function of implantation time and explant mass." Polymer Testing 84, no. : 106377.

Journal article
Published: 20 December 2019 in Additive Manufacturing
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In this work, the development and processing behavior of poly(L-lactide) (PLLA) particles for powder bed fusion (PBF) of polymers obtained via a green and sustainable process route are thoroughly studied. Liquid-liquid phase separation and precipitation from triacetin, a non-toxic solvent, are applied for the production of highly spherical PLLA particles of excellent flowability. Starting from the measured cloud-point diagram of the PLLA-triacetin system, appropriate temperature profiles for the precipitation process are derived. The effect of process parameters on the product properties is addressed in detail; the PLLA particles are characterized regarding their size distribution and morphology. Furthermore, material properties including thermal behavior (c.f. processing window for powder bed fusion (PBF)) and powder flowability are assessed. The spherical PLLA particles of narrow size distribution display a wide sintering window of 59 K and an excellent flowability due to the intrinsic surface roughness of the particles. Thus, tensile test bars and complex porous gyroid specimens were successfully manufactured via PBF without the need for any additional surface functionalization of the particles with flow agents. The high potential of the newly developed PLLA powders produced via an environmentally friendly approach omitting the use of halogenated or toxic solvents, as well as flowing aids, is demonstrated by mechanical testing of the printed specimens.

ACS Style

Maximilian A. Dechet; Anna Demina; Lea Römling; Juan S. Gómez Bonilla; Franz J. Lanyi; Dirk W. Schubert; Andreas Bück; Wolfgang Peukert; Jochen Schmidt. Development of poly(L-lactide) (PLLA) microspheres precipitated from triacetin for application in powder bed fusion of polymers. Additive Manufacturing 2019, 32, 100966 .

AMA Style

Maximilian A. Dechet, Anna Demina, Lea Römling, Juan S. Gómez Bonilla, Franz J. Lanyi, Dirk W. Schubert, Andreas Bück, Wolfgang Peukert, Jochen Schmidt. Development of poly(L-lactide) (PLLA) microspheres precipitated from triacetin for application in powder bed fusion of polymers. Additive Manufacturing. 2019; 32 ():100966.

Chicago/Turabian Style

Maximilian A. Dechet; Anna Demina; Lea Römling; Juan S. Gómez Bonilla; Franz J. Lanyi; Dirk W. Schubert; Andreas Bück; Wolfgang Peukert; Jochen Schmidt. 2019. "Development of poly(L-lactide) (PLLA) microspheres precipitated from triacetin for application in powder bed fusion of polymers." Additive Manufacturing 32, no. : 100966.

Journal article
Published: 09 December 2019 in Composites Part A: Applied Science and Manufacturing
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In this study, a triple-layered coaxial fibre structure was fabricated for strain sensor applications. The core consisted of melt-spun poly (ethylene terephthalate) (PET) where in a subsequent step carbon black (CB) particles were coated onto the surface of the PET fibre to build the conductive pathways by a dissolving-coating method. For the outer protective sheath, a thermoplastic polyurethane (TPU) with a thickness of about 7 μm was generated using a layer-by-layer assembly technique. Compared with other investigated CB-coated fibres, the novel triple hierarchic PET/CB/TPU composite fibres exhibit a high Young’s modulus and tensile strength, as well as a doubled sensing range. The fabrication process can be directly used in the textile industry for the production of wearable and flexible sensors due to its efficacy and low cost. Moreover, a model based on tunnelling theory utilizing only two adjustable parameters was modified based on the actual experimental data, which could precisely describe the relative change of resistance upon the applied strain. Meanwhile, an empirical equation was first proposed and this model offers an effective but simple approach towards quantitative analysis of strain sensors.

ACS Style

Yijing Qin; Muchao Qu; Yamin Pan; Chunhua Zhang; Dirk W. Schubert. Fabrication, characterization and modelling of triple hierarchic PET/CB/TPU composite fibres for strain sensing. Composites Part A: Applied Science and Manufacturing 2019, 129, 105724 .

AMA Style

Yijing Qin, Muchao Qu, Yamin Pan, Chunhua Zhang, Dirk W. Schubert. Fabrication, characterization and modelling of triple hierarchic PET/CB/TPU composite fibres for strain sensing. Composites Part A: Applied Science and Manufacturing. 2019; 129 ():105724.

Chicago/Turabian Style

Yijing Qin; Muchao Qu; Yamin Pan; Chunhua Zhang; Dirk W. Schubert. 2019. "Fabrication, characterization and modelling of triple hierarchic PET/CB/TPU composite fibres for strain sensing." Composites Part A: Applied Science and Manufacturing 129, no. : 105724.

Full paper
Published: 04 October 2019 in Advanced Engineering Materials
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While the influence of fiber strength and calendering parameters on the mechanical strength of polypropylene spunbond nonwovens have been investigated extensively, only a few non‐systematic studies are available on the influence of bonding point size and bonding point fraction. Therefore, systematic investigations of the influence of bonding point fraction, bonding point size and spacing on the tensile properties of nonwovens are carried out. Additionally the influence of fiber orientation and cloudiness on the strength is evaluated. It is demonstrated that an increase in the bonding‐fraction leads to an increase in stiffness and strength, although this effect is weakened due to fiber damage at the edges of bonding points, when many small bonding points are used. An increase in bonding point size and distance between the points with a constant bonding fraction initially leads to an increase in strength. Only when the distance between the points exceeds the size of the local non‐uniformities the strength decreases again, whereas the stiffness decreases continuously with increasing distance between the bonding points. In addition, it is shown that the stress‐strain behaviour of nonwovens can be described using a Maxwell model and that the strengths can be modelled using statistical modelling with optically accessible parameters. This article is protected by copyright. All rights reserved.

ACS Style

Karsten Leucker; Dirk W. Schubert. Analysis and Modeling of the Influence of the Size and Fraction of Bonding Points onto the Mechanical Behavior of Polypropylene Spunbond Nonwovens. Advanced Engineering Materials 2019, 22, 1 .

AMA Style

Karsten Leucker, Dirk W. Schubert. Analysis and Modeling of the Influence of the Size and Fraction of Bonding Points onto the Mechanical Behavior of Polypropylene Spunbond Nonwovens. Advanced Engineering Materials. 2019; 22 (9):1.

Chicago/Turabian Style

Karsten Leucker; Dirk W. Schubert. 2019. "Analysis and Modeling of the Influence of the Size and Fraction of Bonding Points onto the Mechanical Behavior of Polypropylene Spunbond Nonwovens." Advanced Engineering Materials 22, no. 9: 1.

Chapter
Published: 27 September 2019 in Textile Science and Clothing Technology
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In this chapter, poly(ethylene terephthalate) (PET) melt-spun fibres from five different PET materials were fabricated by a capillary rheometer, which was equipped with an air aspirator for aerodynamic stretching. Two recycled PET of coloured rPET-A and clear rPET-B from waste PET bottle flakes were used, and three virgin PET with different grades of the bottle-grade vPET-2, fibre-grade vPET-1 and fibre-grade vPET-3 were chosen as reference benchmark. During the extrusion process, two processing temperatures of 270 and 280 °C in the capillary rheometer were applied, combined with six different take-up pressures from 0.5 to 3.0 bar for fibre stretching during the spinning process. An empirical equation was given, to predict the water content of PET materials under the specific drying temperature and drying time. Afterwards, the characteristics of the raw materials and drawn PET fibres were discussed comprehensively from the perspective of thermal behaviour, molar mass characteristic, rheological properties, surface morphology, diameter, tenacity and elongation at break. rPET-B and vPET-1 materials yielded optimal spinnability and demonstrated to be the most suitable materials to fabricate fibres with a desirable tenacity, an outstanding elongation at break and an excellent fibre fineness. Crystallinity and orientation of fibres from these two materials were explored to give a potential explanation for the higher tenacity. Furthermore, performance-reliability plots were applied, and a semi-empirical equation was suggested for the first time relating the tenacity and elongation at break of fibres. This study proves the possibility to produce PET fibres from bottle-grade recycled co-polymer PET material, which have similar properties as fibres produced from fibre-grade virgin homo-polymer PET. All the specific information of the five investigated PET materials, especially rPET-B and vPET-1, can provide guidance for melt spinning process in the future.

ACS Style

Yijing Qin; Muchao Qu; Joachim Kaschta; Vincent Allen; Dirk W. Schubert. Studies on Recycled Polyester. Textile Science and Clothing Technology 2019, 29 -67.

AMA Style

Yijing Qin, Muchao Qu, Joachim Kaschta, Vincent Allen, Dirk W. Schubert. Studies on Recycled Polyester. Textile Science and Clothing Technology. 2019; ():29-67.

Chicago/Turabian Style

Yijing Qin; Muchao Qu; Joachim Kaschta; Vincent Allen; Dirk W. Schubert. 2019. "Studies on Recycled Polyester." Textile Science and Clothing Technology , no. : 29-67.

Journal article
Published: 08 September 2019 in Coatings
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Electrophoretic deposition (EPD) was used to produce a multilayer coatings system based on chitosan/curcumin coatings on poly-ether-ether-ketone (PEEK)/bioactive glass (BG)/hexagonal boron nitride (h-BN) layers (previously deposited by EPD on 316L stainless steel) to yield bioactive and antibacterial coatings intended for orthopedic implants. Initially, PEEK/BG/h-BN coatings developed on 316L stainless steel (SS) substrates were analyzed for wear studies. Then, the EPD of chitosan/curcumin was optimized on 316L SS for suspension stability, thickness, and homogeneity of the coatings. Subsequently, the optimized EPD parameters were applied to produce chitosan/curcumin coatings on the PEEK/BG/h-BN layers. The multilayered coatings produced by EPD were characterized in terms of composition, microstructure, drug release kinetics, antibacterial activity, and in vitro bioactivity. Scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) confirmed the deposition of chitosan/curcumin on the multilayer coating system. The release of curcumin upon immersion of multilayer coatings in phosphate-buffered saline (PBS) was confirmed by ultraviolet/visible (UV/VIS) spectroscopic analysis. The antibacterial effect of chitosan/curcumin as the top coating was determined by turbidity tests (optical density measurements). Moreover, the multilayer coating system formed an apatite-like layer upon immersion in simulated body fluid (SBF), which is similar in composition to the hydroxyapatite component of bone, confirming the possibility of achieving close bonding between bone and the coating surface.

ACS Style

Ranjot Singh Virk; Muhammad Atiq Ur Rehman; Muhammad Azeem Munawar; Dirk W. Schubert; Wolfgang H. Goldmann; Ján Dusza; Aldo R. Boccaccini. Curcumin-Containing Orthopedic Implant Coatings Deposited on Poly-Ether-Ether-Ketone/Bioactive Glass/Hexagonal Boron Nitride Layers by Electrophoretic Deposition. Coatings 2019, 9, 572 .

AMA Style

Ranjot Singh Virk, Muhammad Atiq Ur Rehman, Muhammad Azeem Munawar, Dirk W. Schubert, Wolfgang H. Goldmann, Ján Dusza, Aldo R. Boccaccini. Curcumin-Containing Orthopedic Implant Coatings Deposited on Poly-Ether-Ether-Ketone/Bioactive Glass/Hexagonal Boron Nitride Layers by Electrophoretic Deposition. Coatings. 2019; 9 (9):572.

Chicago/Turabian Style

Ranjot Singh Virk; Muhammad Atiq Ur Rehman; Muhammad Azeem Munawar; Dirk W. Schubert; Wolfgang H. Goldmann; Ján Dusza; Aldo R. Boccaccini. 2019. "Curcumin-Containing Orthopedic Implant Coatings Deposited on Poly-Ether-Ether-Ketone/Bioactive Glass/Hexagonal Boron Nitride Layers by Electrophoretic Deposition." Coatings 9, no. 9: 572.

Journal article
Published: 05 September 2019 in Polymer
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A simplified mathematical model was given based on the actual experimental data from a laboratory-scale poly (ethylene terephthalate) (PET) melt spinning. PET fibres were produced using three virgin and two recycled PET materials at two different processing temperatures of 270 °C and 280 °C. Filament emerging from a spinneret was drawn by high-velocity air moving through an aspirator, where six take-up pressures were used. It was proved that the model with only two adjustable parameters could effectively predict the variation of PET fibre diameter as a function of take-up pressure, and one of the parameters could be estimated using the zero shear viscosity of materials.

ACS Style

Yijing Qin; Dirk W. Schubert. Simple model to predict the effect of take-up pressure on fibre diameter of PET melt spinning. Polymer 2019, 181, 121769 .

AMA Style

Yijing Qin, Dirk W. Schubert. Simple model to predict the effect of take-up pressure on fibre diameter of PET melt spinning. Polymer. 2019; 181 ():121769.

Chicago/Turabian Style

Yijing Qin; Dirk W. Schubert. 2019. "Simple model to predict the effect of take-up pressure on fibre diameter of PET melt spinning." Polymer 181, no. : 121769.

Journal article
Published: 04 June 2019 in Materials
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Calcareous biominerals typically feature a hybrid nanogranular structure consisting of calcium carbonate nanograins coated with organic matrices. This nanogranular organisation has a beneficial effect on the functionality of these bioceramics. In this feasibility study, we successfully employed a flow-chemistry approach to precipitate Mg-doped amorphous calcium carbonate particles functionalized by negatively charged polyelectrolytes—either polyacrylates (PAA) or polystyrene sulfonate (PSS). We demonstrate that the rate of Mg incorporation and, thus, the ratio of the Mg dopant to calcium in the precipitated amorphous calcium carbonate (ACC), is flow rate dependent. In the case of the PAA-functionalized Mg-doped ACC, we further observed a weak flow rate dependence concerning the hydration state of the precipitate, which we attribute to incorporated PAA acting as a water sorbent; a behaviour which is not present in experiments with PSS and without a polymer. Thus, polymer-dependent phenomena can affect flow-chemistry approaches, that is, in syntheses of functionally graded materials by layer-deposition processes.

ACS Style

Benedikt Demmert; Frank Schinzel; Martina Schüßler; Mihail Mondeshki; Joachim Kaschta; Dirk W. Schubert; Dorrit E. Jacob; Stephan E. Wolf. Polymer-Functionalised Nanograins of Mg-Doped Amorphous Calcium Carbonate via a Flow-Chemistry Approach. Materials 2019, 12, 1818 .

AMA Style

Benedikt Demmert, Frank Schinzel, Martina Schüßler, Mihail Mondeshki, Joachim Kaschta, Dirk W. Schubert, Dorrit E. Jacob, Stephan E. Wolf. Polymer-Functionalised Nanograins of Mg-Doped Amorphous Calcium Carbonate via a Flow-Chemistry Approach. Materials. 2019; 12 (11):1818.

Chicago/Turabian Style

Benedikt Demmert; Frank Schinzel; Martina Schüßler; Mihail Mondeshki; Joachim Kaschta; Dirk W. Schubert; Dorrit E. Jacob; Stephan E. Wolf. 2019. "Polymer-Functionalised Nanograins of Mg-Doped Amorphous Calcium Carbonate via a Flow-Chemistry Approach." Materials 12, no. 11: 1818.

Journal article
Published: 29 May 2019 in e-Polymers
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This study deals with the subject of optimizing the melt electrospinning process of polypropylene with the aim of producing nanoscale fibers. A feasibility study with two polypropylene types and different additives to adapt the material composition is performed. The polypropylene types are of different molar masses to adapt the viscosity to the process. The used additives, sodium stearate and Irgastat®P 16, have a positive effect on the electrical conductivity of the polymer melt. In addition, process parameter optimization is done by varying the climate chamber temperature, using different collector voltages and varying the nozzle-collector distance. A strong influence of the climate chamber temperature has been proven and leads to a desired temperature of 100°C. The fiber diameter is dependent on process parameters, material melt viscosity and electrical conductivity. With optimized process and material parameters, the fiber diameter could be minimized to a median value of 210 nm.

ACS Style

Jonas Daenicke; Michael Lämmlein; Felix Steinhübl; Dirk W. Schubert. Revealing key parameters to minimize the diameter of polypropylene fibers produced in the melt electrospinning process. e-Polymers 2019, 19, 330 -340.

AMA Style

Jonas Daenicke, Michael Lämmlein, Felix Steinhübl, Dirk W. Schubert. Revealing key parameters to minimize the diameter of polypropylene fibers produced in the melt electrospinning process. e-Polymers. 2019; 19 (1):330-340.

Chicago/Turabian Style

Jonas Daenicke; Michael Lämmlein; Felix Steinhübl; Dirk W. Schubert. 2019. "Revealing key parameters to minimize the diameter of polypropylene fibers produced in the melt electrospinning process." e-Polymers 19, no. 1: 330-340.