No abstract

In a versatile modular scaffold system, gradient nonwovens of in situ crosslinked gelatin nanofibers (CGN), fabricated by reactive electrospinning, are laminated with perforated layers and nonwovens of thermoplastic non‐crosslinked biodegradable polyesters. The addition of glyoxal to a gelatin solution in a non‐toxic solvent mixture consisting of acetic acid, ethyl acetate, and water (5:3:2 w/w/w) enables the in situ crosslinking of gelatin nanofibers during electrospinning. The use of this fluorine‐free crosslinking system eliminates the need of post‐treatment crosslinking and purification steps typical for conventional CGN scaffolds. The slowly progressing crosslinking of the dissolved gelatin in the presence of glyoxal increases the viscosity of the gelatin solution during electrospinning so that the average diameter of the crosslinked gelatin nanofibers gradually increases from 90 to 680 nm. During the subsequent lamination process, alternating layers of CGN and polycaprolactone (PCL) nonwovens, produced by 3D microextrusion of micrometer‐sized PCL fibers, are bonded together upon heating above the PCL melting temperature. In contrast to the water‐soluble gelatin nanofibers and the comparatively weak CGN, the CGN/PCL/CGN layered biocomposites are water‐resistant and very robust. In such modular scaffold systems, strength, biodegradation rate, and biological functions can be controlled by varying the type, composition, fiber diameter, porosity, number, and sequence of the individual layers. The CGN/PCL multilayer biocomposites can be cut into any desired scaffold shape and attached to tissue by surgical sutures in order to suit the needs of individual patients.

The determination of relevant rheological properties and parameters in a very broad frequency range can be achieved for a number of thermoplastic polymers, for example, polystyrene, by applying the time-temperature-superposition principle. In contrast, polyethylene can only be explored rheologically in a limited frequency range, due to its fast crystallization below the crystallization temperature and its weak viscosity temperature-dependence. In this paper, various commercially available polydisperse and narrowly distributed linear and branched polyethylenes and ethylene-vinylacetate-copolymers were characterized. A piezoelectric- and a new quartz (crystal resonator) rheometer (QR) with an extended frequency range were utilized for the characterization. Introduction of high frequency rheological techniques and implementation of these new measurement methods are shown. For the first time, the entanglement relaxation time in the higher MHz frequency range was determined by applying the QR-technique and compared with those obtained by an alternative experimental method and numerical calculations.

No abstract