Cell density alters matrix accumulation in two distinct fractions and the mechanical integrity of alginate-chondrocyte constructs

Chondrocyte density in articular cartilage is known to change with the development and growth of the tissue and may play an important role in the formation of a functional extracellular matrix (ECM). The objective of this study was to determine how initial chondrocyte density in an alginate hydrogel affects the matrix composition, its distribution between the cell-associated (CM) and further removed matrix (FRM) fractions, and the tensile mechanical properties of the developing engineered cartilage. Alginate constructs containing primary bovine chondrocytes at densities of 0, 4, 16, and 64 million cells/ml were fabricated and cultured for 1 or 2 weeks, at which time structural, biochemical, and mechanical properties were analyzed. Both matrix content and distribution varied with the initial cell density. Increasing cell density resulted in an increasing content of collagen and sulfated-glycosaminoglycan (GAG) and an increasing proportion of these molecules localized in the CM. While the equilibrium tensile modulus of cell-free alginate did not change with time in culture, the constructs with highest cell density were 116% stiffer than cell-free controls after 2 weeks of culture. The equilibrium tensile modulus was positively correlated with total collagen (r2 = 0.47, p < 0.001) and GAG content (r2 = 0.68, p < 0.001), and these relationships were enhanced when analyzing only those matrix molecules in the CM fraction (r2 = 0.60 and 0.72 for collagen and GAG, respectively, each p < 0.001). Overall, the results of this study indicate that initial cell density has a considerable effect on the developing composition, structure, and function of alginate–chondrocyte constructs.

Personal epistemology and teacher education

A growing body of personal epistemology research shows that personal epistemologies influence student learning, particularly in academic contexts. However, we know little about how personal epistemologies relate to teaching, and even less about teacher education. This introductory chapter sets the stage for this book which brings together a range of international researchers in the field of personal epistemology, teaching, and teacher education. This introductory chapter explores personal epistemology as a construct in the field of teaching and teacher education. In particular, it focuses on teacher education a one contextual influence on personal epistemologies by exploring the nature of teachers' personal epistemologies, teachers' personal epistemologies and learning, teachers' personal epistemologies and teaching, and changing personal epistemology in teacher education programs.

Rare earth element geochemistry of scleractinian coral skeleton during meteoric diagenesis: A sequence through neomorphism of aragonite to calcite

Rare earth element geochemistry in carbonate rocks is utilized increasingly for studying both modern oceans and palaeoceanography, with additional applications for investigating water–rock interactions in groundwater and carbonate diagenesis. However, the study of rare earth element geochemistry in ancient rocks requires the preservation of their distribution patterns through subsequent diagenesis. The subjects of this study, Pleistocene scleractinian coral skeletons from Windley Key, Florida, have undergone partial to complete neomorphism from aragonite to calcite in a meteoric setting; they allow direct comparison of rare earth element distributions in original coral skeleton and in neomorphic calcite. Neomorphism occurred in a vadose setting along a thin film, with degradation of organic matter playing an initial role in controlling the morphology of the diagenetic front. As expected, minor element concentrations vary significantly between skeletal aragonite and neomorphic calcite, with Sr, Ba and U decreasing in concentration and Mn increasing in concentration in the calcite, suggesting that neomorphism took place in an open system. However, rare earth elements were largely retained during neomorphism, with precipitating cements taking up excess rare earth elements released from dissolved carbonates from higher in the karst system. Preserved rare earth element patterns in the stabilized calcite closely reflect the original rare earth element patterns of the corals and associated reef carbonates. However, minor increases in light rare earth element depletion and negative Ce anomalies may reflect shallow oxidized groundwater processes, whereas decreasing light rare earth element depletion may reflect mixing of rare earth elements from associated microbialites or contamination from insoluble residues. Regardless of these minor disturbances, the results indicate that rare earth elements, unlike many minor elements, behave very conservatively during meteoric diagenesis. As the meteoric transformation of aragonite to calcite is a near worst case scenario for survival of original marine trace element distributions, this study suggests that original rare earth element patterns may commonly be preserved in ancient limestones, thus providing support for the use of ancient marine limestones as proxies for marine rare earth element geochemistry.