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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).

Net Shape Nonwoven: a novel technique for porous three-dimensional nonwoven hybrid scaffolds

Textile structures made of biocompatible, osteoconductive and resorbable chitosan-filaments provide excellent preconditions as scaffolds for Bone Tissue Engineering applications. The novel Net Shape Nonwoven (NSN) technique that enables short fibers to be processed into three-dimensional net-shaped nonwoven structures with adjustable pore size distributions is described. NSN scaffolds made of pure chitosan fibers were fabricated. NSN hybrid scaffolds for improved initial cell adhesion were realized by combining the NSN technique with electrospinning and dip-coating with collagen, respectively. Scanning electron microscopy and liquid displacement porosimetry revealed an interconnecting open porous scaffold structure. The novel chitosan-hybrid scaffolds provide proper conditions for adhesion, proliferation and differentiation of the seeded human bone marrow stromal cells, proving that they are suitable for usage in hard-tissue regeneration.

PCL/Chitosan bLended nanofibrous tubes made by duaL syringe eLeCtrosPinning

Abstract 3D tubular scaffolds made from Poly-(Ɛ-caprolactone) (PCL)/chitosan (CS) nanofibres are very promising candidate as vascular grafts in the field of tissue engineering. In this work, the fabrication of PCL/CS-blended nanofibrous tubes with small diameters by electrospinning from separate PCL and CS solutions is studied. The influence of different CS solutions (CS/polyethylene glycol (PEO)/glacial acetic acid (AcOH), CS/trifluoroacetic acid (TFA), CS/ AcOH) on fibre formation and producibility of nanofibrous tubes is investigated. Attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) is used to verify the presence of CS in the blended samples. Tensile testing and pore size measurements are done to underline the good prerequisites of the fabricated blended PCL/ CS nanofibrous tubes as potential scaffolds for vascular grafts. Tubes fabricated from the combination of PCL and CS dissolved in AcOH possesses properties, which are favourable for future cell culture studies.

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.

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.

Analysis and prediction of air permeability of woven barrier fabrics with respect to material, fabric construction and process parameters

Air permeability is one of the important properties of conventional as well as technical fabrics such as protective garments, filters, and fabrics for airbags and parachutes. In case of surgical textiles, air permeability is an effective measure of thermo-physiological comfort. This study is aimed to analyze PES barrier fabrics and to develop correlation between permeability and influential material, construction and process parameters. Not only the individual effects of yarn, fabric and loom parameters but also the underlying complex interactions between fewer or several of these influencing factors exert significant influence on fabric porosity and permeability. Artificial neural network (ANN) is the suitable tool to map such complex input-output relationships, since a direct analytical solution is not possible. Feedforward neural network models were trained with combination of Levenberg-Marquardt algorithm and Bayesian regularization support incorporated in backpropagation. Based on the number of input variables, three ANN models were optimized. It was observed that the model which was trained with all selected inputs delivered promising results on test data, i.e., R2=0.985 and mean absolute error of 1.8%. To eliminate any doubt of overfitting, 10 % cross-validation was also performed for selected final model. Furthermore, to investigate the relative importance of input variables in the optimized ANN model, the rank analysis was also carried out. Research outcomes reveal that ANN can be used to tailor barrier fabric permeability depending on the requirements quickly without trials and error by adjusting loom, fabric and yarn parameters.

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.

Prediction of yarn crimp in PES multifilament woven barrier fabrics using artificial neural network

Abstract This research was aimed to develop artificial neural network (ANN) models to predict yarn crimp in woven barrier fabrics. For ANN training, 52 polyester (PES) multifilament barrier fabrics were produced by varying weft yarn and filament fineness, yarn type, weft density, weave type, and loom parameters. The supervised training of neural network was performed using Matlab® ANN toolbox function ‘trainbr’ which is the incorporation of Levenberg-Marquardt (LM) optimization and automated Bayesian regularization into backpropagation. From modeling outcomes, it was observed that both warp and weft yarn crimp models have generalized well with excellent coefficient of determination and trivial mean absolute error when tested on novel data. Moreover, input rank analysis of optimized network provided important information about model stability with respect to input variables, and trend analysis elucidated the input-crimp behavior using different input levels.

Prediction of the Porosity of Barrier Woven Fabrics with Respect to Material, Construction and Processing Parameters and Its Relation with Air Permeability

Porosity is one of the most important characteristics of fabrics that dictate the permeability and retention properties of fabrics. Several technical uses require textiles with a combination of definite permeability and retention properties. Besides filtration, surgical textiles require these contrary properties to offer an effective barrier against particle laden fluids, such as bacteria and viruses, together with added wearer comfort. Pore size and pore size distribution are important characteristics to determine the permeability and retention behaviour of multifilament barrier textiles by influencing the effective porosity, which can be tailored according to end use requirements by material, weave construction and processing factors. The present research was aimed at developing the relationship that material, construction and loom parameters have with porosity in terms of the mean pore size and mean flow pore size of the fabric, and thereby with air permeability. To map such nonlinear complex relations, an artificial neural network (ANN) was employed. From the findings, it was observed that the porosity of barrier fabrics can be predicted with excellent accuracy using an ANN.

New Image Analysis Method for Determination of the Inter-Fibre Pore Size Intensity of Polyester Woven Barrier Fabrics

Porosity is an important characteristic of a filter textile, which affects permeability and retention properties. Determination of the inter-yarn and inter-fibre pore sizes of barrier textiles is also required to assess the filter behaviour of these textiles. In this study, a software tool was developed to detect the inter-fibre pore size distribution and pore size intensity of multifilament woven barrier fabrics using cross-section images. Fabrics were chosen according to their fabric construction parameters, such as the fabric index, weft yarn filament fineness and weft yarn structure (flat or textured). Microscopic cross-section images of weft yarns were taken, processed to binary images, and analysed with respect to the pore size distribution, number of pore lengths and pore intensity. It was also analysed how the fabric index, filament cross-section and filament fineness affect the inter-fibre pore lengths and separation level proposed. It was found that weft yarns with wider lengths and lower height showed wider inter-fibre pores. Inter-fibre pores decreased with a decrease in filament fineness. Moreover the separation level proposed deviated from the 90% level depending on the fabric index. This deviation was very small in samples with reduced filament fineness and textured samples. The separation level proposed will be useful to understand the effect of fabric construction parameters to obtain targeted properties regarding inter-fibre and inter-yarn pore size.