A review of tissue-engineered skin bioconstructs available for skin reconstruction

Situations where normal autografts cannot be used to replace damaged skin often lead to a greater risk of mortality, prolonged hospital stay and increased expenditure for the National Health Service. There is a substantial need for tissue-engineered skin bioconstructs and research is active in this field. Significant progress has been made over the years in the development and clinical use of bioengineered components of the various skin layers. Off-the-shelf availability of such constructs, or production of sufficient quantities of biological materials to aid rapid wound closure, are often the only means to help patients with major skin loss. The aim of this review is to describe those materials already commercially available for clinical use as well as to give a short insight to those under development. It seeks to provide skin scientists/tissue engineers with the information required to not only develop in vitro models of skin, but to move closer to achieving the ultimate goal of an off-the-shelf, complete full-thickness skin replacement.     

Micromechanical multiscale model for alkali activation of fly ash and metakaolin

The process of alkali activation of fly ash and metakaolin is examined in the view of micromechanics. Elasticity is predicted via semi-analytical homogenization methods, using a combination of intrinsic elastic properties obtained from nanoindentation, evolving volume fractions and percolation theory. A new quantitative model for volume fraction is formulated, distinguishing the evolution of unreacted aluminosilicate material, solid gel particles of N-A-S-H gel, and open porosity, which is partially filled with the activator. The stiffening of N-A-S-H gel is modeled by increasing the fraction of solid gel particles. Their packing density and intrinsic elasticity differ in N-A-S-H gels synthesized from both activated materials. Percolation theory helps to address the quasi-solid transition at early ages and explains a long setting time and the beneficial effect of thermal curing. The low ability of N-A-S-H gel to bind water chemically explains the high porosity of Ca-deficient activated materials. Micromechanical analysis matches well the elastic experimental data during the activation and elucidates important stages in the formation of the microstructure.     

StarSync: An extendable standard-cell mesochronous synchronizer

StarSync, a mesochronous synchronizer, enables low latency and full throughput crossing of clock domain boundaries having same frequency but different phases. Full back pressure is supported, where the receiver can start and stop accepting words without any data loss. Variable depth buffering is provided, supporting a wide range of short and long range communications and accommodating multi-cycle wire delays. Burst data can also be accommodated thanks to buffering. Dynamic phase shifting due to varying voltage and temperature are mitigated by increasing the separation between write and read pointers. The synchronizer is exposed to metastability risk only during reset. It is suitable for implementation using standard cell design and requires neither delay lines nor other full custom circuits. It is shown that a minimum of four buffer stages are required, to mitigate skew in reset synchronization, in contrast with previous proposals for three stages.     

Zirconium phase transformations observed by “in-situ” XRD analysis

The high temperature phase transformations of zirconium were investigated by “in-situ” X-ray diffraction analysis. The experiments were carried out in a high temperature chamber Anton Paar HTK 1200N mounted on powder diffractometer Panalytical X’Pert Pro. The chamber was evacuated by a turbo-molecular pump creating a pressure about 3 × 10⁻⁴ Pa at the temperature 1200 °C before the measurement. The experimental samples were uniformly heated without thermal gradients up to 1000 °C or 1200 °C and then exposed for 180 min. At high temperature four or six diffraction patterns of each sample were recorded for the illustration of the phase changes in the material structure. Chemical composition of some samples after the exposure was determined by secondary ion mass spectrometry and compared with composition of the material in its initial state.     

Laser-assisted processing of Ni-Al-Co-Ti under high pressure

Laser-assisted processing and in-situ characterization of a Ni_0.7-Al_0.1235-Co_0.15-Ti_0.0265 alloy were carried out under a range of simultaneous hydrostatic high pressures of ～30?GPa and high temperature conditions ～2000°C using a laser-assisted heating in diamond anvil cell with synchrotron X-ray micro-diffraction. The characterization of the microstructure and X-ray diffraction analysis at ambient conditions confirmed the formation of the cuboids of ordered γ′ phase in the disordered γ matrix. The isothermal bulk modulus (B₀) and its first-order derivative (B₀’) of the alloy were determined to be B₀?=?123?±?9?GPa and B₀’?=?5.7?±?2.8. The in-situ characterization of the alloy at high temperatures under high pressures revealed that the γ′ phase transforms into the tetragonaly distorted D0₂₂-type structure. This transformation is similar to the transformation that occurs in the ordered Ni₃Al, responsible for the improved strength at high temperatures. High pressure was found to increase the onset temperature of the structural distortion. The pressure–temperature phase diagram of the Ni_0.7-Al_0.1235-Co_0.15-Ti_0.0265 up to ～30?GPa and ～2000°C was determined and is reported here.     

Dialysate bicarbonate variation in maintenance hemodiafiltration patients: Impact on serum bicarbonate,intradialytic hypotension and interdialytic weight gain

Introduction: The dialysate bicarbonate (DB) influences the acid‐base balance in dialysis patients. Very low and high serum bicarbonate (SB) have been related with a higher mortality. Acid‐base balance also has been associated with hemodynamic effects in these patients. The trial aim was to compare the effect of DB concentration variation on SB levels in maintenance hemodiafiltration (HDF) patients and the effect on intradialytic hypotension and interdialytic weight gain. Methods: A prospective study, with 9 months of follow‐up, involving 93 patients, divided in two groups: group 1 and group 2 with a DB of 34 mmol/L and 30 mmol/L, respectively, with monitoring of pre and post HDF SB, intradialytic hypotension, and interdialytic weight gain. Findings: Pre dialysis SB was higher in group 1: median concentration of 22.7 mmol/L vs. 21.1 mmol/L (P < 0.001). Post dialysis SB levels were higher in group 1: median concentration of 28.0 mmol/L vs. 25.3 mmol/L (P < 0.001). Post dialysis SB in alkalotic range was only detected in group 1 (51.2% of the patients). No significant differences were detected in intradialytic hypotension rate [28.0 vs. 27.4 episodes per 1000 sessions in group 1 and 2, respectively, (P = 0.906)] or in average interdialytic weight gain [2.9% vs. 3.0% in group 1 and 2, respectively, (P = 0.710)]. Discussion: DB of 30 mmol/L appears to be associated with SB levels closer to physiological levels than 34 mmol/L. The bicarbonate dialysate, in the tested concentrations, did not appear to have a significant impact on intradialytic hypotension and interdialytic weight gain in maintenance HDF patients.