A Lab-on-Chip Analyzer for in Situ Measurement of Soluble Reactive Phosphate: Improved Phosphate Blue Assay and Application to Fluvial Monitoring.

Here, we present a new in situ microfluidic phosphate sensor that features an improved "phosphate blue" assay which includes polyvinylpyrrolidone in place of traditional surfactants-improving sensitivity and reducing temperature effects. The sensor features greater power economy and analytical performance relative to commercially available alternatives, with a mean power consumption of 1.8 W, a detection limit of 40 nM, a dynamic range of 0.14-10 µM, and an infield accuracy of 4 ± 4.5%. During field testing, the sensor was continuously deployed for 9 weeks in a chalk stream, revealing complex relations between flow rates and phosphate concentration that suggest changing dominance in phosphate sources. A distinct diel phosphorus signal was observed under low flow conditions, highlighting the ability of the sensor to decouple geochemical and biotic effects on phosphate dynamics in fluvial environments. This paper highlights the importance of high resolution in situ sensors in addressing the current gross under-sampling of aquatic environments.

Cartilage tissue engineering on fibrous chitosan scaffolds produced by a replica molding technique.

The biocompatibility of chitosan and its similarity with glycosaminoglycans make it attractive as a scaffold for cartilage engineering. Fibrous scaffolds may simulate cartilage extracellular matrix structure and promote chondrocyte functions. Our objectives were to produce chitosan fibers of different size and evaluate their potential for chondrogenesis. A novel replica molding technique was developed to produce chitosan nonwoven scaffolds made of fiber measuring 4, 13, or 22 mum in width. A polyglycolic acid mesh (PGA) served as a reference group. Controls were analyzed 48 h after seeding porcine chondrocytes via scanning electron microscopy (SEM), DNA, and glycosaminoglycan (GAG) quantifications. Constructs were cultured for 21 days prior to confocal microscopy, SEM, histology, and quantitative analysis (weight, water, DNA, GAG and collagen II). Chondrocytes maintained their phenotypic appearance and a viability above 85% on the chitosan scaffolds. Chondrocytes attach preferentially to PGA, resulting in a greater cellularity of these constructs. However, based on the GAG/DNA and Collagen II/DNA ratios, matrix production per chondrocyte was improved in chitosan constructs, especially on smaller fibers. The differences between PGA and chitosan are more likely to result from the chemical composition rather than their structural characteristics. Although chitosan appears to promote matrix formation, further studies should be aimed at improving its cell adhesion properties.