Investigation and Validation of a Shape Memory Alloy Material Model Using Interactive Fibre Rubber Composites

The growing demand for intelligent systems with improved human-machine interactions has created an opportunity to develop adaptive bending structures. Interactive fibre rubber composites (IFRCs) are created using smart materials as actuators to obtain any desired application using fibre-reinforced elastomer. Shape memory alloys (SMAs) play a prominent role in the smart material family and are being used for various applications. Their diverse applications are intended for commercial and research purposes, and the need to model and analyse these application-based structures to achieve their maximum potential is of utmost importance. Many material models have been developed to characterise the behaviour of SMAs. However, there are very few commercially developed finite element models that can predict their behaviour. One such model is the Souza and Auricchio (SA) SMA material model incorporated in ANSYS, with the ability to solve for both shape memory effect (SME) and superelasticity (SE) but with a limitation of considering pre-stretch for irregularly shaped geometries. In order to address this gap, Woodworth and Kaliske (WK) developed a phenomenological constitutive SMA material model, offering the flexibility to apply pre-stretches for SMA wires with irregular profiles. This study investigates the WK SMA material model, utilizing deformations observed in IFRC structures as a reference and validating them against simulated models using the SA SMA material model. This validation process is crucial in ensuring the reliability and accuracy of the WK model, thus enhancing confidence in its application for predictive analysis in SMA-based systems.

Novel Weft-Knitted Strain Sensors for Motion Capture

Functional electrical stimulation (FES) aims to improve the gait pattern in cases of weak foot dorsiflexion (foot lifter weakness) and, therefore, increase the liveability of people suffering from chronic diseases of the central nervous system, e.g., multiple sclerosis. One important component of FES is the detection of the knee angle in order to enable the situational triggering of dorsiflexion in the right gait phase by electrical impulses. This paper presents an alternative approach to sensors for motion capture in the form of weft-knitted strain sensors. The use of textile-based strain sensors instead of conventional strain gauges offers the major advantage of direct integration during the knitting process and therefore a very discreet integration into garments. This in turn contributes to the fact that the FES system can be implemented in the form of functional leggings that are suitable for inconspicuous daily use without disturbing the wearer unnecessarily. Different designs of the weft-knitted strain sensor and the influence on its measurement behavior were investigated. The designs differed in terms of the integration direction of the sensor (wale- or course-wise) and the width of the sensor (number of loops) in a weft-knitted textile structure.

Electromechanical Properties of Silver-Plated Yarns and Their Relation to Yarn Construction Parameters

For signal transmission and sensing in stretchable structures for human motion monitoring or proprioception of soft robots, textiles with electronically conductive yarns are a promising option. Many recent publications employ silver-plated yarns in knits, braids, wovens for strain or pressure sensing purposes as well as heating fabrics or twisted string actuators. Silver-plated yarns are available in a wide range of base materials, yarn counts and twists. These structural properties significantly influence the electrical and electromechanical behavior of such yarns. However, until now little research has been carried out on the yarns themselves. To close this research gap, several variations of a single yarn type are electromechanically characterized. Additionally, tensile tests with synchronous resistance measurements are performed. From these measurements, sensor metrics are derived and calculated to compare the different variants quantitatively.

Advancing Smart Textiles: Structural Evolution of Knitted Piezoresistive Strain Sensors for Enabling Precise Motion Capture

Recently, there has been remarkable progress in the development of smart textiles, especially knitted strain sensors, to achieve reliable sensor signals. Stable and reliable electro-mechanical properties of sensors are essential for using textile-based sensors in medical applications. However, the challenges associated with significant hysteresis and low gauge factor (GF) values remain for using strain sensors for motion capture. To evaluate these issues, a comprehensive investigation of the cyclic electro-mechanical properties of weft-knitted strain sensors was conducted in the present study to develop a drift-free elastic strain sensor with a robust sensor signal for motion capture for medical devices. Several variables are considered in the study, including the variation of the basic knit pattern, the incorporation of the electrically conductive yarn, and the size of the strain sensor. The effectiveness and feasibility of the developed knitted strain sensors are demonstrated through an experimental evaluation, by determining the gauge factor, its nonlinearity, hysteresis, and drift. The developed knitted piezoresistive strain sensors have a GF of 2.4, a calculated drift of 50%, 12.5% hysteresis, and 0.3% nonlinearity in parts.

Continuous Wet Spinning of Regenerated Silk Fibers from Spinning Dopes Containing 4% Fibroin Protein

The wet spinning of fibers from regenerated silk fibroin has long been a research goal. Due to the degradation of the molecular structure of the fibroin protein during the preparation of the regenerated silk fibroin solution, fibroin concentrations with at least 10% protein content are required to achieve sufficient viscosity for wet spinning. In this study, a spinning dope formulation of regenerated silk fibroin is presented that shows a rheological behavior similar to that of native silk fibroin isolated from the glands of B. mori silkworm larvae. In addition, we present a wet-spinning process that enables, for the first time, the continuous wet spinning of regenerated silk fibroin with only 4% fibroin protein content into an endless fiber. Furthermore, the tensile strength of these wet-spun regenerated silk fibroin fibers per percentage of fibroin is higher than that of all continuous spinning approaches applied to regenerated and native silk fibroin published so far.

Investigation of the Bonding Mechanism between Overlapping Textile Layers for FRP Repair Based on Dry Textile Patches

Lots of damaged fiber-reinforced plastic (FRP) components are replaced by new components instead of repairing. Furthermore, only very labor-intensive repair methods are available on the market to fully restore the integrity of the structure. This requires a high level of experience or, alternatively, very cost-intensive technology, such as the use of computer tomography and robotics. The high costs and CO₂ emissions caused by the manufacture of FRP components then bear no relation to their service life. The research project IGF-21985 BR "FRP-Repair" aims to solve the named challenges. Using semiconductor oxide catalysts, the matrix can be locally depolymerized by ultraviolet (UV) radiation, and thus removed from the damaged area of the FRP component. Subsequently, the damaged fibers in this area can be detached. By using customized textile repair patches and local thermoset reinfiltration, the repair area is restored. With this process, the fiber structure can be repaired locally with new fibers on the textile level. The repair is similar to the original production of a fiber composite in an infusion process. No additional adhesive material is used. As a result, repaired FRP structures with restored mechanics and a near-original surface can be realized. This article provides an insight into the actual steps of the development of the FRP component repair process using dry textile patches. The empirical investigation of overlapped rovings and UD material showed the expected results. Residual fracture forces of up to 86% could be achieved. The most interesting approach on the roving level was splicing the overlapping fibers. The free ends of the fibers of the patch and part are mechanically bonded. This bond at the textile level is further strengthened by infusion with matrix.

Textile Design of an Intervertebral Disc Replacement Device from Silk Yarn

Low back pain is often due to degeneration of the intervertebral discs (IVD). It is one of the most common age- and work-related problems in today's society. Current treatments are not able to efficiently restore the full function of the IVD. Therefore, the aim of the present work was to reconstruct the two parts of the intervertebral disc-the annulus fibrosus (AF) and the nucleus pulposus (NP)-in such a way that the natural structural features were mimicked by a textile design. Silk was selected as the biomaterial for realization of a textile IVD because of its cytocompatibility, biodegradability, high strength, stiffness, and toughness, both in tension and compression. Therefore, an embroidered structure made of silk yarn was developed that reproduces the alternating fiber structure of +30° and -30° fiber orientation found in the AF and mimics its lamellar structure. The developed embroidered ribbons showed a tensile strength that corresponded to that of the natural AF. Fiber additive manufacturing with 1 mm silk staple fibers was used to replicate the fiber network of the NP and generate an open porous textile 3D structure that may serve as a reinforcement structure for the gel-like NP.

Simulation of Tetrahedral Profiled Carbon Rovings for Concrete Reinforcements

Textile reinforcements are increasingly establishing their position in the construction industry due to their high tensile properties and corrosion resistance for concrete applications. In contrast to ribbed monolithic steel bars with a defined form-fit effect, the conventional carbon rovings' bond force is transmitted primarily by an adhesive bond (material fit) between the textile surface and the surrounding concrete matrix. As a result, relatively large bonding lengths are required to transmit bond forces, resulting in inefficient material utilization. Novel solutions such as tetrahedral profiled rovings promise significant improvements in the bonding behavior of textile reinforcements by creating an additional mechanical interlock with the concrete matrix while maintaining the high tensile properties of carbon fibers. Therefore, simulative investigations of tensile and bond behavior have been conducted to increase the transmittable bond force and bond stiffness of profiled rovings through a defined roving geometry. Geometric and material models were thus hereby developed, and tensile and pullout tests were simulated. The results of the simulations and characterizations could enable the optimization of the geometric parameters of tetrahedral profiled rovings to achieve better bond and tensile properties and provide basic principles for the simulative modeling of profiled textile reinforcements.

Improved Tensile and Bond Properties through Novel Rod Constructions Based on the Braiding Technique for Non-Metallic Concrete Reinforcements

Textile reinforcements have established themselves as a convincing alternative to conventional steel reinforcements in the building industry. In contrast to ribbed steel bars that ensure a stable mechanical interlock with concrete (form fit), the bonding force of smooth carbon rovings has so far been transmitted primarily by an adhesive bonding with the concrete matrix (material fit). However, this material fit does not enable the efficient use of the mechanical load capacity of the textile reinforcement. Solutions involving surface-profiled rods promise significant improvements in the bonding behavior by creating an additional mechanical interlock with the concrete matrix. An initial analysis was carried out to determine the effect of a braided rod geometry on the bonding behavior. For this purpose, novel braided rods with defined surface profiling consisting of several carbon filament yarns were developed and characterized in their tensile and bond properties. Further fundamental examinations to determine the influence of the impregnation as well as the application of a pre-tension during its consolidation in order to minimize the rod elongation under load were carried out. The investigations showed a high potential of the impregnated surface-profiled braided rods for a highly efficient application in concrete reinforcements. Hereby, a complete impregnation of the rod with a stiff polymer improved the tensile and bonding properties significantly. Compared to unprofiled reinforcement structures, the specific bonding stress could be increased up to 500% due to the strong form-fit effect of the braided rods while maintaining the high tensile properties.

Development of an Innovative Glass/Stainless Steel/Polyamide Commingled Yarn for Fiber-Metal Hybrid Composites

Fiber-metal hybrid composites are widely used in high-tech industries due to their unique combination of mechanical, toughness and ductile properties. Currently, hybrid materials made of metals and high-performance fibers have been limited to layer-by-layer hybridization (fiber-metal laminates). However, layer-by-layer hybridization lacks in fiber to fiber mixing, resulting in poor inter-laminar interfaces. The objective of this paper was to establish the fundamental knowledge and application-related technological principles for the development and fabrication of air-textured commingled yarn composed of glass (GF), stainless steel (SS) and polyamide-6 (PA-6) filaments for fiber-metal hybrid composites. For this purpose, extensive conceptual, design and technological developments were carried out to develop a novel air-texturing nozzle that can produce an innovative metallic commingled yarn. The results show that an innovative metallic commingled yarn was developed using fiber-metal hybrid composites with a composite tensile strength of 700 ± 39 MPa and an E-modulus of 55 ± 7. This shows that the developed metallic commingled yarn is a suitable candidate for producing metal-fiber hybrid composites.

Influence of Spinning Method on Shape Memory Effect of Thermoplastic Polyurethane Yarns

Shape memory polymers are gaining increasing attention, especially in the medical field, due to their ability to recover high deformations, low activation temperatures, and relatively high actuation stress. Furthermore, shape memory polymers can be applied as fiber-based solutions for the development of smart devices used in many fields, e.g., industry 4.0, medicine, and skill learning. These kind of applications require sensors, actors, and conductive structures. Textile structures address these applications by meeting requirements such as being flexible, adaptable, and wearable. In this work, the influence of spinning methods and parameters on the effect of shape memory polymer yarns was investigated, comparing melt and wet spinning. It is shown that the spinning method can significantly influence the strain fixation and generated stress during the activation of the shape memory effect. Furthermore, for wet spinning, the draw ratio could affect the stress conversion, influencing its efficiency. Therefore, the selection of the spinning process is essential for the setting of application-specific shape-changing properties.

Bond Modification of Carbon Rovings through Profiling

The load-bearing behavior and the performance of composites depends largely on the bond between the individual components. In reinforced concrete construction, the bond mechanisms are very well researched. In the case of carbon and textile reinforced concrete, however, there is still a need for research, especially since there is a greater number of influencing parameters. Depending on the type of fiber, yarn processing, impregnation, geometry, or concrete, the proportion of adhesive, frictional, and shear bond in the total bond resistance varies. In defined profiling of yarns, we see the possibility to increase the share of the shear bond (form fit) compared to yarns with a relatively smooth surface and, through this, to reliably control the bond resistance. In order to investigate the influence of profiling on the bond and tensile behavior, yarns with various profile characteristics as well as different impregnation and consolidation parameters are studied. A newly developed profiling technique is used for creating a defined tetrahedral profile. In the article, we present this approach and the first results from tensile and bond tests as well as micrographic analysis with profiled yarns. The study shows that bond properties of profiled yarns are superior to conventional yarns without profile, and a defined bond modification through variation of the profile geometry as well as the impregnation and consolidation parameters is possible.

Hinged Adaptive Fiber-Rubber Composites Driven by Shape Memory Alloys-Development and Simulation

Adaptive structures based on fiber-rubber composites with integrated Shape Memory Alloys are promising candidates for active deformation tasks in the fields of soft robotics and human-machine interactions. Solid-body hinges improve the deformation behavior of such composite structures. Textile technology enables the user to develop reinforcement fabrics with tailored properties suited for hinged actuation mechanisms. In this work, flat knitting technology is used to create biaxially reinforced, multilayer knitted fabrics with hinge areas and integrated Shape Memory Alloy wires. The hinge areas are achieved by dividing the structures into sections and varying the configuration and number of reinforcement fibers from section to section. The fabrics are then infused with silicone, producing a fiber-rubber composite specimen. An existing simulation model is enhanced to account for the hinges present within the specimen. The active deformation behavior of the resulting structures is then tested experimentally, showing large deformations of the hinged specimens. Finally, the simulation results are compared to the experimental results, showing deformations deviating from the experiments due to the developmental stage of the specimens. Future work will benefit from the findings by improving the deformation behavior of the specimens and enabling further development for first applications.

Development of electrospun, biomimetic tympanic membrane implants with tunable mechanical and oscillatory properties for myringoplasty

Most commonly, autologous grafts are used in tympanic membrane (TM) reconstruction. However, apart from the limited availability and the increased surgical risk, they cannot replicate the full functionality of the human TM properly. Hence, biomimetic synthetic TM implants have been developed in our project to overcome these drawbacks. These innovative TM implants are made from synthetic biopolymer polycaprolactone (PCL) and silk fibroin (SF) by electrospinning technology. Static and dynamic experiments have shown that the mechanical and oscillatory behavior of the TM implants can be tuned by adjusting the solution concentration, the SF and PCL mixing ratio and the electrospinning parameters. In addition, candidates for TM implants could have comparable acousto-mechanical properties to human TMs. Finally, these candidates were further validated in in vitro experiments by performing TM reconstruction in human cadaver temporal bones. The reconstructed TM with SF-PCL blend membranes fully recovered the acoustic vibration when the perforation was smaller than 50%. Furthermore, the handling, medium adhesion and transparency of the developed TM implants were similar to those of human TMs.

Pure Chitosan-Based Fibers Manufactured by a Wet Spinning Lab-Scale Process Using Ionic Liquids

Ionic liquids offer alternative methods for the sustainable processing of natural biopolymers like chitosan. The ionic liquid 1-butyl-3-methylimidazolium acetate (BmimOAc) was successfully used for manufacturing of pure chitosan-based monofilaments by a wet spinning process at lab-scale. Commercial chitosan with 90% deacetylation degree was used for the preparation of spinning dopes with solids content of 4–8 wt.%. Rheology tests were carried out for the characterization of the viscometric properties. BmimOAc was used as a solvent and deionized water as coagulation and washing medium. Optical (scanning electron microscope (SEM), light microscope) and textile physical tests were used for the evaluation of the morphological and mechanical characteristics. The manufactured chitosan monofilaments a homogeneous structure with a diameter of ~150 μm and ~30 tex yarn count. The mechanical tests show tensile strengths of 8 cN/tex at Young’s modulus up to 4.5 GPa. This work represents a principal study for the manufacturing of pure chitosan fibers from ionic liquids and provides basic knowledge for the development of a wet spinning process.

Development of an Elastic, Electrically Conductive Coating for TPU Filaments

Electrically conductive filaments are used in a wide variety of applications, for example, in smart textiles and soft robotics. Filaments that conduct electricity are required for the transmission of energy and information, but up until now, most electrically conductive fibers, filaments and wires offer low mechanical elongation. Therefore, they are not well suited for the implementation into elastomeric composites and textiles that are worn close to the human body and have to follow a wide range of movements. In order to overcome this issue, the presented study aims at the development of electrically conductive and elastic filaments based on a coating process suited for multifilament yarns made of thermoplastic polyurethane (TPU). The coating solution contains TPU, carbon nanotubes (CNT) and N-Methyl-2-pyrrolidone (NMP) with varied concentrations of solids and electrically conductive particles. After applying the coating to TPU multifilament yarns, the mechanical and electrical properties are analyzed. A special focus is given to the electromechanical behavior of the coated yarns under mechanical strain loading. It is determined that the electrical conductivity is maintained even at elongations of up to 100%.

A Fast and Reliable Process to Fabricate Regenerated Silk Fibroin Solution from Degummed Silk in 4 Hours

Silk fibroin has a high potential for use in several approaches for technological and biomedical applications. However, industrial production has been difficult to date due to the lengthy manufacturing process. Thus, this work investigates a novel procedure for the isolation of non-degraded regenerated silk fibroin that significantly reduces the processing time from 52 h for the standard methods to only 4 h. The replacement of the standard degumming protocol by repeated short-term microwave treatments enabled the generation of non-degraded degummed silk fibroin. Subsequently, a ZnCl₂ solution was used to completely solubilize the degummed fibroin at only 45 °C with an incubation time of only 1 h. Desalting was performed by gel filtration. Based on these modifications, it was possible to generate a cytocompatible aqueous silk fibroin solution from degummed silk within only 4 h, thus shortening the total process time by 48 h without degrading the quality of the isolated silk fibroin solution.

Thermoplastic Composites for Integrally Woven Pressure Actuated Cellular Structures: Design Approach and Material Investigation

The use of pressure-actuated cellular structures (PACS) is an effective approach for the application of compliant mechanisms. Analogous to the model in nature, the Venus flytrap, they are made of discrete pressure-activated rows and can be deformed with high stiffness at a high deformation rate. In previous work, a new innovative approach in their integral textile-based manufacturing has been demonstrated based on the weaving technique. In this work, the theoretical and experimental work on the further development of PACS from simple single-row to double-row PACS with antagonistic deformation capability is presented. Supported by experimental investigations, the necessary adaptations in the design of the textile preform and the polymer composite design are presented and concretized. Based on the results of pre-simulations of the deformation capacity of the new PACS, their performance was evaluated, the results of which are presented.

Isotropic and Anisotropic Scaffolds for Tissue Engineering: Collagen, Conventional, and Textile Fabrication Technologies and Properties

In this review article, tissue engineering and regenerative medicine are briefly explained and the importance of scaffolds is highlighted. Furthermore, the requirements of scaffolds and how they can be fulfilled by using specific biomaterials and fabrication methods are presented. Detailed insight is given into the two biopolymers chitosan and collagen. The fabrication methods are divided into two categories: isotropic and anisotropic scaffold fabrication methods. Processable biomaterials and achievable pore sizes are assigned to each method. In addition, fiber spinning methods and textile fabrication methods used to produce anisotropic scaffolds are described in detail and the advantages of anisotropic scaffolds for tissue engineering and regenerative medicine are highlighted.

Anisotropic Chitosan Scaffolds Generated by Electrostatic Flocking Combined with Alginate Hydrogel Support Chondrogenic Differentiation

The replacement of damaged or degenerated articular cartilage tissue remains a challenge, as this non-vascularized tissue has a very limited self-healing capacity. Therefore, tissue engineering (TE) of cartilage is a promising treatment option. Although significant progress has been made in recent years, there is still a lack of scaffolds that ensure the formation of functional cartilage tissue while meeting the mechanical requirements for chondrogenic TE. In this article, we report the application of flock technology, a common process in the modern textile industry, to produce flock scaffolds made of chitosan (a biodegradable and biocompatible biopolymer) for chondrogenic TE. By combining an alginate hydrogel with a chitosan flock scaffold (CFS+ALG), a fiber-reinforced hydrogel with anisotropic properties was developed to support chondrogenic differentiation of embedded human chondrocytes. Pure alginate hydrogels (ALG) and pure chitosan flock scaffolds (CFS) were studied as controls. Morphology of primary human chondrocytes analyzed by cLSM and SEM showed a round, chondrogenic phenotype in CFS+ALG and ALG after 21 days of differentiation, whereas chondrocytes on CFS formed spheroids. The compressive strength of CFS+ALG was higher than the compressive strength of ALG and CFS alone. Chondrocytes embedded in CFS+ALG showed gene expression of chondrogenic markers (COL II, COMP, ACAN), the highest collagen II/I ratio, and production of the typical extracellular matrix such as sGAG and collagen II. The combination of alginate hydrogel with chitosan flock scaffolds resulted in a scaffold with anisotropic structure, good mechanical properties, elasticity, and porosity that supported chondrogenic differentiation of inserted human chondrocytes and expression of chondrogenic markers and typical extracellular matrix.

Silk Fiber-Reinforced Hyaluronic Acid-Based Hydrogel for Cartilage Tissue Engineering

A continuing challenge in cartilage tissue engineering for cartilage regeneration is the creation of a suitable synthetic microenvironment for chondrocytes and tissue regeneration. The aim of this study was to develop a highly tunable hybrid scaffold based on a silk fibroin matrix (SM) and a hyaluronic acid (HA) hydrogel. Human articular chondrocytes were embedded in a porous 3-dimensional SM, before infiltration with tyramine modified HA hydrogel. Scaffolds were cultured in chondropermissive medium with and without TGF-β1. Cell viability and cell distribution were assessed using CellTiter-Blue assay and Live/Dead staining. Chondrogenic marker expression was detected using qPCR. Biosynthesis of matrix compounds was analyzed by dimethylmethylene blue assay and immuno-histology. Differences in biomaterial stiffness and stress relaxation were characterized using a one-step unconfined compression test. Cell morphology was investigated by scanning electron microscopy. Hybrid scaffold revealed superior chondro-inductive and biomechanical properties compared to sole SM. The presence of HA and TGF-β1 increased chondrogenic marker gene expression and matrix deposition. Hybrid scaffolds offer cytocompatible and highly tunable properties as cell-carrier systems, as well as favorable biomechanical properties.

Tensile Behavior of High-Strength, Strain-Hardening Cement-Based Composites (HS-SHCC) Reinforced with Continuous Textile Made of Ultra-High-Molecular-Weight Polyethylene

The paper at hand presents an investigation of the tensile behavior of high-strength, strain-hardening cement-based composites (HS-SHCC), reinforced with a single layer of continuous, two-dimensional textile made of ultra-high molecular weight polyethylene (UHMWPE). Uniaxial tension tests were performed on the bare UHMWPE textiles, on plain HS-SHCC, and on the hybrid fiber-reinforced composites. The bond properties between the textile yarns and the surrounding composite were investigated in single-yarn pullout experiments. In order to assess the influence of bond strength between the yarn and HS-SHCC on the tensile behavior of the composites with hybrid fiber reinforcement, the textile samples were analyzed both with, and without, an additional coating of epoxy resin and sand. Compared to the composites reinforced with carbon yarns in previous studies by the authors, the high elongation capacity of the UHMWPE textile established the higher strain capacity of the hybrid fiber-reinforced composites, and showed superior energy absorption capacity up to failure. The UHMWPE textile limited the average crack width in comparison with that of plain HS-SHCC, but led to slightly larger crack widths when compared to equivalent composites reinforced with carbon textile, the reason for which was traced back to the lower Young's modulus and the higher elongation capacity of the polymer textile.

Techniques and Processes for the Realization of Electrically Conducting Textile Materials from Intrinsically Conducting Polymers and Their Application Potential

This review will give an overview on functional conducting polymers, while focusing on the integration of intrinsically conducting, i.e., self-conducting, polymers for creating electrically conducting textile materials. Thus, different conduction mechanisms as well as achievable electrical properties will be introduced. First, essential polymers will be described individually, and secondly, techniques and processes for the realization of electrically conducting textile products in addition to their application potential will be presented.

Numerical Modelling of the Mechanical Behaviour of Biaxial Weft-Knitted Fabrics on Different Length Scales

Weft-knitted fabrics offer an excellent formability into complex shapes for composite application. In biaxial weft-knitted fabric, additional yarns are inserted in the warp (wale-wise) and weft (course-wise) directions as a reinforcement. Due to these straight yarns, the mechanical properties of such fabrics are better than those of unreinforced weft-knitted fabrics. The forming process of flat fabrics into 3D preforms is challenging and requires numerical simulation. In this paper, the mechanical behavior of biaxial weft-knitted fabrics is simulated by means of macro- and meso-scale finite element method (FEM) models. The macro-scale modelling approach is based on a shell element formulation and offers reasonable computational costs but has some limitations by the description of fabric mechanical characteristics and forming behavior. The meso-scale modelling approach based on beam elements can describe the fabric’s mechanical and forming characteristics better at a higher computational cost. The FEM models were validated by comparing the results of various simulations with the equivalent experiments. With the help of the parametric models, the forming of biaxial weft-knitted fabrics into complex shapes can be simulated. These models help to predict material and process parameters for optimized forming conditions without the necessity of costly experimental trials.

Collagen multifilament spinning

The benefits of fiber based implants and scaffolds for tissue engineering applications are their anisotropic, highly porous, and controllable macro-, micro-, and nanostructure. Collagen is one of the most commonly used material for the fabrication of scaffolds, as this biopolymer is present in the natural extracellular matrix. For textile processing and textile scaffold fabrication methods, multifilament yarns are required, however, only monofilaments can be generated by state-of-the-art collagen spinning. Hence, the research presented in here aimed at the development of a collagen multifilament wet-spinning process in reproducible quality as well as the characterization of non-crosslinked and crosslinked wet-spun multifilament yarns. Wet spun collagen yarns were comprised of 6 single filaments each having a fineness of 5 tex and a diameter of 80 μm. The tensile strength of the glutaraldehyde crosslinked yarns was 169 MPa (Young's modulus 3534 MPa) in the dry state and 40 MPa (Young's modulus 281 MPa) in the wet state. Furthermore, wet spun collagen filaments showed a characteristic fibrillar structure, which was similar the morphological structure of natural collagen fibers. The textile processing of collagen multifilament yarn was demonstrated by means of knitting technology.

Bioinspired calcium phosphate mineralization on Net-Shape-Nonwoven chitosan scaffolds stimulates human bone marrow stromal cell differentiation

Chitosan fibers were processed using the Net-Shape-Nonwoven (NSN) technique in order to create porous scaffolds which were functionalized in two bioinspired ways: collagen type I coating and unique mineralization with organically modified hydroxyapatite (ormoHAP). While collagen is common to enhance cell attachment on surfaces, the electric-field assisted migration and deposition of ormoHAP on the surface of the NSN-scaffolds is a novel technique which enables sub-micrometer sized mineralization while maintaining the original pore structure. Microscopy revealed fast attachment and morphological adaptation of the cells on both, the pure and the functionalized NSN-scaffolds. Remarkably, the cell number of osteogenically induced hBMSC on ormoHAP-modified NSN-scaffolds increased 3.5-5 fold compared to pure NSN-scaffolds. Osteogenic differentiation of hBMSC/osteoblasts was highest on collagen-functionalized NSN-scaffolds. RT-PCR studies revealed gene expression of ALP, BSP II, and osteocalcin to be high for all NSN-scaffolds. Overall, the NSN-scaffold functionalization with collagen and ormoHAP improved attachment, proliferation, and differentiation of hBMSC and therefore revealed the remarkable potential of their application for the tissue engineering of bone.

Design of Complexly Graded Structures inside Three-Dimensional Surface Models by Assigning Volumetric Structures

An innovative approach for designing complex structures from STL-datasets based on novel software for assigning volumetric data to surface models is reported. The software allows realizing unique complex structures using additive manufacturing technologies. Geometric data as obtained from imaging methods, computer-aided design, or reverse engineering that exist only in the form of surface data are converted into volumetric elements (voxels). Arbitrary machine data can be assigned to each voxel and thereby enable implementing different materials, material morphologies, colors, porosities, etc. within given geometries. The software features an easy-to-use graphical user interface and allows simple implementation of machine data libraries. To highlight the potential of the modular designed software, an extrusion-based process as well as a two-tier additive manufacturing approach for short fibers and binder process are combined to generate three-dimensional components with complex grading on the material and structural level from STL files.

In silico modeling of structural and porosity properties of additive manufactured implants for regenerative medicine

Additive manufacturing technologies are a promising technology towards patient-specific implants for applications in regenerative medicine. The Net-Shape-Nonwoven technology is used to manufacture structures from short fibers with interconnected pores and large functional surfaces that are predestined for cell adhesion and growth. The present study reports on a modeling approach with a particular focus on the specific structural properties. The overall porosities and mean pore-sizes of the digital models are simulated according to liquid-displacement porosity in a tool implemented in the modeling software. This allows adjusting the process parameters fiber length and fiber diameter to generate biomimetic structures with pore-sizes adapted to the requirements of the tissue that is to be replaced. Modeling the structural and porosity properties of scaffolds and implants leads to an efficient use of the processed biomaterials as the trial-and-error method is avoided.

Electrostatic flocking of chitosan fibres leads to highly porous, elastic and fully biodegradable anisotropic scaffolds

Electrostatic flocking - a common textile technology which has been applied in industry for decades - is based on the deposition of short polymer fibres in a parallel aligned fashion on flat or curved substrates, covered with a layer of a suitable adhesive. Due to their highly anisotropic properties the resulting velvet-like structures can be utilised as scaffolds for tissue engineering applications in which the space between the fibres can be defined as pores. In the present study we have developed a fully resorbable compression elastic flock scaffold from a single material system based on chitosan. The fibres and the resulting scaffolds were analysed concerning their structural and mechanical properties and the biocompatibility was tested in vitro. The tensile strength and Young's modulus of the chitosan fibres were analysed as a function of the applied sterilisation technique (ethanol, supercritical carbon dioxide, γ-irradiation and autoclaving). All sterilisation methods decreased the Young's modulus (from 14GPa to 6-12GPa). The tensile strength was decreased after all treatments - except after the autoclaving of chitosan fibres submerged in water. Compressive strength of the highly porous flock scaffolds was 18±6kPa with a elastic modulus in the range of 50-100kPa. The flocked scaffolds did not show any cytotoxic effect during indirect or direct culture of human mesenchymal stem cells or the sarcoma osteogenic cell line Saos-2. Furthermore cell adhesion and proliferation of both cell types could be observed. This is the first demonstration of a fully biodegradable scaffold manufactured by electrostatic flocking.

STATEMENT OF SIGNIFICANCE

Most tissues possess anisotropic fibrous structures. In contrast, most of the commonly used scaffolds have an isotropic morphology. By utilising the textile technology of electrostatic flocking, highly porous and clearly anisotropic scaffolds can be manufactured. Flocking leads to parallel aligned short fibres, glued on the surface of a substrate. Such structures are characterised by a high and adjustable porosity, accompanied by distinct stiffness in fibre direction. The present article describes for the first time a fully biodegradable flock scaffold, solely made of chitosan. Utilisation of only one material for manufacturing of flock substrate, adhesive and fibres allow a uniform degradation of the whole construct. Such a new type of scaffold can be of great interest for a variety of biomedical applications.

Effects of (Oxy-)Fluorination on Various High-Performance Yarns

In this work, typical high-performance yarns are oxy-fluorinated, such as carbon fibers, ultra-high-molecular-weight polyethylene, poly(p-phenylene sulfide) and poly(p-phenylene terephthalamide). The focus is on the property changes of the fiber surface, especially the wetting behavior, structure and chemical composition. Therefore, contact angle, XPS and tensile strength measurements are performed on treated and untreated fibers, while SEM is utilized to evaluate the surface structure. Different results for the fiber materials are observed. While polyethylene exhibits a relevant impact on both surface and bulk properties, polyphenylene terephthalamide and polyphenylene sulfide are only affected slightly by (oxy-)fluorination. The wetting of carbon fiber needs higher treatment intensities, but in contrast to the organic fibers, even its textile-physical properties are enhanced by the treatment. Based on these findings, the capability of (oxy-)fluorination to improve the adhesion of textiles in fiber-reinforced composite materials can be derived.

Textile cell-free scaffolds for in situ tissue engineering applications

In this article, the benefits offered by micro-fibrous scaffold architectures fabricated by textile manufacturing techniques are discussed: How can established and novel fiber-processing techniques be exploited in order to generate templates matching the demands of the target cell niche? The problems related to the development of biomaterial fibers (especially from nature-derived materials) ready for textile manufacturing are addressed. Attention is also paid on how biological cues may be incorporated into micro-fibrous scaffold architectures by hybrid manufacturing approaches (e.g. nanofiber or hydrogel functionalization). After a critical review of exemplary recent research works on cell-free fiber based scaffolds for in situ TE, including clinical studies, we conclude that in order to make use of the whole range of favors which may be provided by engineered fibrous scaffold systems, there are four main issues which need to be addressed: (1) Logical combination of manufacturing techniques and materials. (2) Biomaterial fiber development. (3) Adaption of textile manufacturing techniques to the demands of scaffolds for regenerative medicine. (4) Incorporation of biological cues (e.g. stem cell homing factors).

Ulvan and ulvan/chitosan polyelectrolyte nanofibrous membranes as a potential substrate material for the cultivation of osteoblasts

A new generation of biomaterials composed of the natural polysaccharides, ulvans extracted from the green seaweed Ulva rigida and chitosan have been investigated. Ulvan, chitosan alone and ulvan/chitosan polyelectrolyte membranes have been synthesised and characterised. The structure of the membranes was altered by the weight ratio of the polyion components. Fibrous and nanofibrous morphology was created, in accordance with a supramolecular self assembly. ATR-FTIR measurements suggested the presence of both polycationic chitosan and polyanionic ulvan in the polyelectrolyte membranes. The cytocompatibility of these new materials was examined by fluorescence microscopy. The results show that ulvan as well as ulvan/chitosan membranes promoted the attachment and proliferation of 7F2 osteoblasts and maintained the cell morphology and viability. Thus, ulvan and chitosan which possess unique properties might have high impact in biomedical applications as potential scaffold materials.

Inorganic/organic (SiO₂)/PEO hybrid electrospun nanofibers produced from a modified sol and their surface modification possibilities

Ceramic silica (SiO(2)) hybrid nanofibers were prepared by electrospinning of solutions containing biocompatible polymer and modified silica precursors. The new hybrid nanofibers are based on polyethylene oxide (PEO) and a new solution of modified sol-gel particles of mixture containing tetraethoxysilane (TEOS) and 3-glycidyloxypropyltriethoxysilane (GPTEOS) in a weight ratio of 3:1. Adding high-molecular-weight PEO into the silica sol is found to enhance the formation of the silica nanofibers and leads to reduce the water-soluble carrying polymer down to 1.2%wt. Transmission electron microscopy (TEM) and attenuated total reflection fourier transformation infrared ATR-FTIR measurements are suggested that PEO is encapsulated by the silica component. This excellent formulation renders electrospinning of SiO(2) a robust process for an easy production of controllable silicate nanofibrous matrices. For instance, nanofibers with average diameter down to 400 nm are accessible by varying the weight ratio between the polymer and the inorganic precursor. These are reduced to 120 nm after the pyrolysis process. Moreover, the surface of the nanofibers could be easily modified, either by Al(3+) leading to aluminium silicate coatings, or by incorporation of Ca(2+) ions and subsequent bioactive hydroxyl carbonate apatite (HAP) formation. These hybrid silica nanofibers are possess a unique collective properties can have a great impact either in high-temperature reinforced materials and filtration or in biomedical applications such as in dentistry and bone tissue engineering.