Poly(Ethylene Furanoate) along Its Life-Cycle from a Polycondensation Approach to High-Performance Yarn and Its Recyclate.

We report on the pilot scale synthesis and melt spinning of poly(ethylene furanoate) (PEF), a promising bio-based fiber polymer that can heave mechanical properties in the range of commercial poly(ethylene terephthalate) (PET) fibers. Catalyst optimization and solid state polycondensation (SSP) allowed for intrinsic viscosities of PEF of up to 0.85 dL·g-1. Melt-spun multifilament yarns reached a tensile strength of up to 65 cN·tex-1 with an elongation of 6% and a modulus of 1370 cN·tex-1. The crystallization behavior of PEF was investigated by differential scanning calorimetry (DSC) and XRD after each process step, i.e., after polymerization, SSP, melt spinning, drawing, and recycling. After SSP, the previously amorphous polymer showed a crystallinity of 47%, which was in accordance with literature. The corresponding XRD diffractograms showed signals attributable to α-PEF. Additional, clearly assignable signals at 2θ > 30° are discussed. A completely amorphous structure was observed by XRD for as-spun yarns, while a crystalline phase was detected on drawn yarns; however, it was less pronounced than for the granules and independent of the winding speed.

Co-culture Model for Cutaneous Wound Healing to Assess a Porous Fiber-Based Drug Delivery System.

In vitro tissue-engineered cell culture models are an essential instrument to investigate physiological and pathophysiological wound healing mechanisms and to evaluate new beneficial wound dressing materials and therapeutics to identify possible drug targets and to improve regeneration processes in nonhealing and chronic wounds. In this study, the authors established an in vitro model for cutaneous wound healing, based on primary human dermal microvascular endothelial cells (HDMEC) and primary human dermal fibroblasts (HDF) to study wound healing-associated processes. Co-cultivation of HDMEC and HDF results in the formation of microvessel-like structures in long-term co-cultures. The proposed in vitro co-culture model can be easily modified by adding macrophages to simulate the process of inflammation, thus allowing in vitro investigation of pathophysiological wound healing processes present in nonhealing wounds. Furthermore, the beneficial in vitro wound healing model was used to evaluate a porous fiber-based drug delivery dressing material consisting of melt-spun porous fibers that were filled with a hydrogel carrier (gellan gum) containing vascular endothelial growth factor (VEGF). Angiogenic capability was chosen as functional parameter for improved wound healing, and release of deposited VEGF from the dressing material was evaluated up to 7 days of cultivation. The experiments demonstrated that the porous fiber-based drug delivery dressing material for dermal wound healing with incorporated VEGF strongly enhances the process of angiogenesis in the in vitro co-culture model through a release of VEGF over 7 days of cultivation. In conclusion, tissue-engineered human skin equivalents could contribute significantly to the understanding and improvement of drug releasing dressing materials in the context of treating chronic wounds.

Neuro tissue engineering of glial nerve guides and the impact of different cell types.

The aim of neuro tissue engineering is to imitate biological features in order to enhance regeneration. Following lesions of peripheral nerves, Schwann cells (SCs) reorganize to form longitudinal bands of Büngner (boB) which function as guides for regrowing axons. In order to imitate boB in synthetic implants designed to bridge nerve lesions, we developed resorbable, semipermeable nerve guide conduits with microstructured internal polymer filaments. We utilized a novel microcell chip and identified three extracellular matrix components conducive for coating non-permissive polymer surfaces. In order to maximize SC alignment, seven different microtopographies were investigated via the silicon chip technology. Special longitudinal microgrooves directed SC orientation and growing axons of dorsal root ganglia (DRG), thus achieving stereotropism. When these results were applied to microgrooved polymer filaments inside nerve guide conduits, we observed highly oriented axon growth without meandering. Since scar-forming fibroblasts could potentially interfere with axonal regrowth, triple cultures with fibroblasts, SC and DRG were conducted. Fibroblasts positioned on the outer nanopore containing conduit wall, did not hamper neuronal and glial differentiation inside the tube. In summary, for more rapid regrowth, functional boB can be induced by guided microtissue engineering. By considering both the negative and positive effects of cell interactions, a more rational design of nerve implants becomes feasible.