Substitution of strontium for calcium in glass ionomer cements (Part 1): Glass synthesis and characterisation, and the effects on the cement handling variables and setting reaction

Objectives: To investigate the effects of substituting strontium for calcium in fluoroaluminosilicate glass on the handling variables and setting reaction of high-viscosity glass ionomer cements.Design: An exploratory, laboratory-based study.Setting: Dental biomaterials research laboratory, Dental Physical Sciences Unit, Barts and the London School of Medicine and Dentistry, Queen Mary, University of London.Subjects: A series of five glasses in which strontium substitutes for calcium and based on the general formula: 4.5SiO2 - 3Al2O3 – 1.25P2O5 – xSrO - ySrF,sub>2 – zCaO - yCaF2, where x = 0, 0.5, 1.5 or 3; y = 0, 1 or 2; and, z = 0, 1.5, 2.5 or 3 were synthesized, ground, sieved and the powders characterised by X-Ray Diffraction (XRD), particle size analysis and thermal analysis. Thereafter, they were mixed with poly (acrylic acid) (PAA) and aqueous tartaric acid to form glass ionomer cements, whose properties were investigated at different time points: working and setting times were determined by rheometry;  and, the setting reaction was studied by Fourier transform infra-red (FT-IR) spectroscopy. Results: XRD confirmed the amorphous nature of the glasses, while thermal analysis showed a mixed alkaline/entropic effect on the glass transition temperature. Working and setting times did not vary significantly with strontium content but the shortest times were recorded for the cement with the smallest particle size.Conclusion: The results suggest that substitution of strontium for calcium has insignificant effects on the manipulation and setting reaction of the cement; therefore, substitution can be optimised to produce restorative materials with beneficial anticariogenic properties

Stress modulation as a means to improve yeasts for lignocellulose bioconversion

The second-generation (2G) fermentation environment for lignocellulose conversion presents unique challenges to the fermentative organism that do not necessarily exist in other industrial fermentations. While extreme osmotic, heat, and nutrient starvation stresses are observed in sugar- and starch-based fermentation environments, additional pre-treatment-derived inhibitor stress, potentially exacerbated by stresses such as pH and product tolerance, exist in the 2G environment. Furthermore, in a consolidated bioprocessing (CBP) context, the organism is also challenged to secrete enzymes that may themselves lead to unfolded protein response and other stresses. This review will discuss responses of the yeast Saccharomyces cerevisiae to 2G-specific stresses and stress modulation strategies that can be followed to improve yeasts for this application. We also explore published –omics data and discuss relevant rational engineering, reverse engineering, and adaptation strategies, with the view of identifying genes or alleles that will make positive contributions to the overall robustness of 2G industrial strains