Microstructure and In Vitro Evaluation of Extruded and Hot Drawn Alloy MgCa0.7 for Biodegradable Surgical Wires

The MgCa0.7 alloy may be a promising material for biodegradable surgical wires. In this paper, the technology for producing surgical wires from this alloy has been developed, based both on finite element modelling and experimental study. In particular, the extrusion and hot-drawing effects on the mechanical properties, microstructures, in-vitro rates of biocorrosion, and cytotoxicity to human cancer cells (SaOS-2) and healthy (hPDL) ones, have been determined. An approximately 30–40% increase in corrosion rate due to increasing hot-drawing temperature was observed. An effect of hot-drawing temperature on cytotoxicity was also found. Notably, at various stages of the final wires’ production, the MgCa0.7 alloy became toxic to cancer cells. This cytotoxicity depended on the alloys’ processing parameters and was maximal for the as-extruded rod and for the wires immediately after hot drawing at 440 °C. Thus, the careful selection of processing parameters makes it possible to obtain a product that is not only a promising candidate for biodegradable surgical wires, but one which also has intrinsic bioactive properties that produce antitumor activity.

Transient Confinement of the Quaternary Tetramethylammonium Tetrafluoroborate Salt in Nylon 6,6 Fibres: Structural Developments for High Performance Properties

A temporary confinement of the quaternary tetramethylammonium tetrafluoroborate (TMA BF4) salt among polyamide molecules has been used for the preparation of aliphatic polyamide nylon 6,6 fibres with high-modulus and high-strength properties. In this method, the suppression or the weakening of the hydrogen bonds between the nylon 6,6 segments has been applied during the conventional low-speed melt spinning process. Thereafter, after the complete hot-drawing stage, the quaternary ammonium salt is fully extracted from the drawn 3 wt.% salt-confined fibres and the nascent fibres are, subsequently, thermally stabilized. The structural developments that are acquired in the confined-nylon 6,6 fibres are ascribed to the developments of the overall fibres’ properties due to the confinement process. Surprisingly, unlike the neat nylon 6,6 fibres, the X-ray diffraction (XRD) patterns of the as-spun salt-confined fibres have shown diminishing of the (110)/(010) diffraction plane that obtained pseudohexagonal-like β’ structural phase. Moreover, the β’ pseudohexagonal-like to α triclinic phase transitions took-place due to the hot-drawing stage (draw-induced phase transitions). Interestingly, the hot-drawing of the as-spun salt-confined nylon 6,6 fibres achieved the same maximum draw ratio of 5.5 at all of the drawing temperatures of 120, 140 and 160 °C. The developments that happened produced the improved values of 43.32 cN/dtex for the tensile-modulus and 6.99 cN/dtex for the tensile-strength of the reverted fibres. The influences of the TMA BF4 salt on the structural developments of the crystal orientations, on the morphological structures and on the improvements of the tensile properties of the nylon 6,6 fibres have been intensively studied.

Study on the Crystallization Behavior of PAN Fibers during Hot-Drawing Process in Supercritical Carbon Dioxide Fluid with Different Strain

Hot-drawing of polyacrylonitrile (PAN) fibers is an important step in the production of carbon fibers. In this article, we investigated the effect of strain on the crystallization behavior and mechanical properties of PAN fibers treated in supercritical carbon dioxide (Sc-CO2) fluid. We mainly used the methods of X-ray diffraction (XRD), monofilament strength analysis and differential scanning calorimeter (DSC) to study the crystallization behavior, mechanical properties and thermal behavior of PAN fibers during hot-drawing process. The experimental results showed that the crystallinity and mechanical properties of PAN fibers both increased a lot under the action of strain during hot-drawing in Sc-CO2 fluid. This provides an important method for preparation of higher performance PAN precursor for PAN-based carbon fibers.