Factors affecting the mechanical and geometrical properties of electrostatically flocked pure chitosan fiber scaffolds

The field of articular cartilage tissue engineering has developed rapidly, and chitosan has become a promising material for scaffold fabrication. For this paper, wet-spun biocompatible chitosan filament yarns were converted into short flock fibers and subsequently electrostatically flocked onto a chitosan substrate, resulting in a pure, highly open, porous, and biodegradable chitosan scaffold. Analyzing the wet-spinning of chitosan revealed its advantages and disadvantages with respect to the fabrication of the fiber-based chitosan scaffolds. The scaffolds were prepared using varying processing parameters and were analyzed in regards to their geometrical and mechanical properties. It was found that the pore sizes were adjustable between 65 and 310 µm, and the compressive strength was in the range 13–57 kPa

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

Thermoresponsive Shape Memory Fibers for Compression Garments

Their highly deformable properties make shape memory polymers (SMP) a promising component for the development of new compression garments. The shape memory effect (SME) can be observed when two polymers are combined. In here, polycaprolactone (PCL) and thermoplastic polyurethane (TPU) were melt spun in different arrangement types (blend, core-sheath, and island-in-sea), whereas the best SME was observed for the blend type. In order to trigger the SME, this yarn was stimulated at a temperature of 50 °C. It showed a strain fixation of 62%, a strain recovery of 99%, and a recovery stress of 2.7 MPa

Targeted partial finishing of barrier textiles with microparticles, and their effects on barrier properties and comfort

Woven barrier fabrics for filtration and operating room textiles feature permeable pore channels between yarn interlocking points (mesopores), which create an increased risk of penetration by contaminated fluids and particles. These pore channels can be reduced in size by high-density weaving. This, however, results in deteriorated drapability and performance characteristics. To meet the requirements made on the barrier effect without impairing the physiological properties of the textile, fluid-tight and particle-tight woven fabrics with adjustable porosity are being developed. This research aim could be realized by the targeted and partial application of microparticles into the mesopores. There, they form a meshed structure in the pores, whose size is thus reduced without them being entirely obstructed. The simultaneous retention of the micropores (pores between the individual filaments) in the woven fabric guarantees preservation of the physiological characteristics of the textile. The efficiency of the finishing was examined by an extensive physiological and physical characterization of the woven fabrics before and after particle application. Regarding the test method used to monitor the barrier effect and the channel paths, a test device was modified to simulate the demands of later, practical use

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

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

Approaches for process and structural finite element simulations of braided ligament replacements

To prevent the renewed rupture of ligaments and tendons prior to the completed healing process, which frequently occurs in treated ruptured tendons, a temporary support structure is envisaged. The limitations of current grafts have motivated the investigation of tissue-engineered ligament replacements based on the braiding technology. This technology offers a wide range of flexibility and adjustable geometrical and structural parameters. The presented work demonstrates the possible range for tailoring the mechanical properties of polyester braids and a variation of the braiding process parameters. A finite element simulation model of the braiding process was developed, which allows the optimization of production parameters without the performance of further experimental trials. In a second modelling and simulation step, mechanical properties of the braided structures were virtually determined and compared with actual tests. The digital element approach was used for the yarns in the numerical model. The results show very good agreement for the process model in terms of braiding angles and good agreement for the structural model in terms of force-strain behaviour. With a few adaptions, the models can, thus, be applied to actual ligament replacements made of resorbable polymers

Methods for a permanent binding of functionalized micro-particle on polyester fabric for the improvement of the barrier effect

Polyethylene terephthalate multifilament fabrics used as filtration and operating room textiles possess through-thickness pore channels at the yarn intersections (mesopores). These pore channels pose a risk for the penetration of contaminated fluids and particles. The size of pore channels may be reduced by high-density weaving. However, this leads to reduced drapability and thus to degraded application properties of the fabric. To satisfy the requirements without impeding the physiological properties of the textile, fluid- and particle-tight fabrics are developed. This was realized by partial immobilization of functionalized micro particles into the meso-pores. A reduction of the pore size without complete pore-closure is achieved by establishing a net-like particle structure in the meso-pores. To match the requirements of intensive use, permanent particle-bonding to the fiber surface is necessary. This can be achieved by suitable polyethylene terephthalate fabric surface-modification, dependent on the particle functionalization. The investigations have shown that functionalized particles establish a very good inter particle bonding as well as to the fiber surface. An increased permanent bonding can be realized by a modification of the fabric surface which is tuned to the functionalization of the particle

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

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