Search

Many biological structures such as nerves, blood and lymphatic vessels, and muscle fibres exhibit longitudinal geometries with distinct cell types extending along both the length and width of internal linear axes. Modelling these three-dimensional structures in vitro is challenging: the best-defined stem-cell differentiation systems are mono-layer cultures or organoids using pluripotent stem cells. Pluripotent stem cells can differentiate into functionally mature cells depending on the signals received, holding great promise for regenerative medicine. However, the integration of in vitro differentiated cell types into diseased tissue remains a challenge. Engineered scaffolds can bridge this gap if the appropriate signalling systems are incorporated into the scaffold. Here, we have taken a biomimicry approach to generate longitudinal structures in vitro . In this approach, mouse embryonic stem cells are directed to differentiate to specific cell types on the surface of polycaprolactone (PCL) fibres treated by plasma-immersion ion implantation and to which with lineage-specifying molecules have been covalently immobilised. We demonstrate the simplicity and utility of our method for efficiently generating high yields of the following cell types from these pluripotent stem cells: neurons, vascular endothelial cells, osteoclasts, adipocytes, and cells of the erythroid, myeloid, and lymphoid lineages. Strategically arranged plasma-treated scaffolds with differentiated cell types could ultimately serve as a means for the repair or treatment of diseased or damaged tissue. [ABSTRACT FROM AUTHOR]

In the past two decades, high entropy alloy (HEA) coatings have attracted great attention due to their superior mechanical properties, outstanding corrosion and oxidation resistance, and exceptionally high thermal stability. In comparison to HEA thin films, high entropy nitrides (HENs) exhibit higher mechanical strength and chemical inertness. In this work, AlCrFeCoNiCu0.5 HEA and HEN thin films were fabricated using a filtered cathodic arc. By regulating the deposition pressure from 0.0005 Pa (HEA thin film) to 0.05 Pa, the nitrogen concentration in each thin film was precisely controlled to tune the mechanical properties. Scanning transmission electron microscopy-energy dispersive spectroscopy revealed that the nitrogen concentration of the films was up to 21.2 at. % at the pressure of 0.05 Pa. The reduced effect of preferential sputtering increased aluminum concentration from 8.3 ± 1.5 to 12.9 ± 2.2 at. % as pressure increased up to 0.05 Pa. X-ray photoelectron spectroscopy further confirmed the formation of AlN and CrN at pressures of 0.01–0.05 Pa. The highest hardness and elastic modulus of the HEN film were 12.4 ± 0.6 and 347.3 ± 17.7 GPa, respectively, which were 84.8% and 131.4% higher than those of the HEA thin film. [ABSTRACT FROM AUTHOR]

AlCrFeCoNiCu0.5 thin films were fabricated by cathodic arc deposition under different substrate biases. Detailed characterization of the chemistry and structure of the film, from the substrate interface to the film surface, was achieved by combining high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, and atomic force microscopy. Computer simulations using the transport of ions in matter model were applied to understand the ion surface interactions that revealed the key mechanism of the film growth. The final compositions of the films are significantly different from that of the target used. A trend of elemental segregation, which was more pronounced with higher ion kinetic energy, was observed. The XPS results reveal the formation of Al 2 O 3 and Cr 2 O 3 on the thin film surface. The grain size is shown to increase with the increasing of the ion kinetic energy. The growth of equiaxed grains contributed to the formation of a flat surface with a relatively low surface roughness as shown by atomic force microscopy. [ABSTRACT FROM AUTHOR]

The highly organized extracellular matrix (ECM) of musculoskeletal tissues, encompassing tendons, ligaments and muscles, is structurally anisotropic, hierarchical and multi-compartmental. These features collectively contribute to their unique function. Previous studies have investigated the effect of tissue-engineered scaffold anisotropy on cell morphology and organization for musculoskeletal tissue repair and regeneration, but the hierarchical arrangement of ECM and compartmentalization are not typically replicated. Here, we present a method for multi-compartmental scaffold design that allows for physical mimicry of the spatial architecture of musculoskeletal tissue in regenerative medicine. This design is based on an ECM-inspired macromolecule scaffold. Polycaprolactone (PCL) scaffolds were fabricated with aligned fibers by electrospinning and mechanical stretching, and then surface-functionalized with the cell-supporting ECM protein molecule, tropoelastin (TE). TE was attached using two alternative methods that allowed for either physisorption or covalent attachment, where the latter was achieved by plasma ion immersion implantation (PIII). Aligned fibers stimulated cell elongation and improved cell alignment, in contrast to randomly oriented fibers. TE coatings bound by physisorption or covalently following 200 s PIII treatment promoted fibroblast proliferation. This represents the first cytocompatibility assessment of novel PIII-treated TE-coated PCL scaffolds. To demonstrate their versatility, these 2D anisotropic PCL scaffolds were assembled into 3D hierarchical constructs with an internally compartmentalized structure to mimic the structure of musculoskeletal tissue. [ABSTRACT FROM AUTHOR]

Competition between target erosion and compound layer formation during pulse cycles in reactive HiPIMS opens up the possibility of tuning discharge conditions and the properties of deposited films by varying the duty cycle in situ without altering the reactive gas mixture. Three different reactive systems, hafnium in oxygen, tungsten in oxygen, and tungsten in oxygen/nitrogen, are studied in which amorphous films of hafnium oxide (HfO2), tungsten oxide (WO3), and tungsten oxynitride (WOxNy) are deposited. We show that the cyclic evolution of the target surface composition depends on the properties of the target including its affinity for the reactive gas mix and the compound layer melting point and volatility. We find that pulse length variations modulate the target compound layer and hence the discharge chemistry and properties of the films deposited. The refractive indices of HfO2 and WO3 were progressively reduced with the duty cycle, whereas that of WOxNy increased. These variations were found to be due to changes in the chemical composition and/or densification. We present and validate a phenomenological model that explains these findings in terms of a compound layer on the target surface that undergoes evolution during each pulse resulting in a cyclic equilibrium. The end points of the composition of the target surface depend on the duty cycle. Tuning the pulse characteristics holds great promise for the fabrication of multilayer films with through thickness graded properties. [ABSTRACT FROM AUTHOR]