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- ItemGlycosaminoglycan-based hydrogels to modulate heterocellular communication in in vitro angiogenesis models(London : Nature Publishing Group, 2014) Chwalek, K.; Tsurkan, M.V.; Freudenberg, U.; Werner, C.Angiogenesis, the outgrowth of blood vessels, is crucial in development, disease and regeneration. Studying angiogenesis in vitro remains challenging because the capillary morphogenesis of endothelial cells (ECs) is controlled by multiple exogenous signals. Therefore, a set of in situ-forming starPEG-heparin hydrogels was used to identify matrix parameters and cellular interactions that best support EC morphogenesis. We showed that a particular type of soft, matrix metalloproteinase-degradable hydrogel containing covalently bound integrin ligands and reversibly conjugated pro-angiogenic growth factors could boost the development of highly branched, interconnected, and lumenized endothelial capillary networks. Using these effective matrix conditions, 3D heterocellular interactions of ECs with different mural cells were demonstrated that enabled EC network modulation and maintenance of stable vascular capillaries over periods of about one month in vitro. The approach was also shown to permit in vitro tumor vascularization experiments with unprecedented levels of control over both ECs and tumor cells. In total, the introduced 3D hydrogel co-culture system could offer unique options for dissecting and adjusting biochemical, biophysical, and cell-cell triggers in tissue-related vascularization models.
- ItemCorrelating the ancient Maya and modern european calendars with high-precision AMS 14C dating(London : Nature Publishing Group, 2013) Kennett, D.J.; Hajdas, I.; Culleton, B.J.; Belmecheri, S.; Martin, S.; Neff, H.; Awe, J.; Graham, H.V.; Freeman, K.H.; Newsom, L.; Lentz, D.L.; Anselmetti, F.S.; Robinson, M.; Marwan, N.; Southon, J.; Hodell, D.A.; Haug, G.H.The reasons for the development and collapse of Maya civilization remain controversial and historical events carved on stone monuments throughout this region provide a remarkable source of data about the rise and fall of these complex polities. Use of these records depends on correlating the Maya and European calendars so that they can be compared with climate and environmental datasets. Correlation constants can vary up to 1000 years and remain controversial.Wereport a series of high-resolution AMS14C dates on a wooden lintel collected from the Classic Period city of Tikal bearing Maya calendar dates. The radiocarbon dates were calibrated using a Bayesian statistical model and indicate that the dates were carved on the lintel betweenAD 658-696. This strongly supports the Goodman-Mart?nez-Thompson (GMT) correlation and the hypothesis that climate change played an important role in the development and demise of this complex civilization.
- ItemUltrafast high-resolution mass spectrometric finger pore imaging in latent finger prints(London : Nature Publishing Group, 2014) Elsner, C.; Abel, B.Latent finger prints (LFPs) are deposits of sweat components in ridge and groove patterns, left after human fingers contact with a surface. Being important targets in biometry and forensic investigations they contain more information than topological patterns. With laser desorption mass spectrometry imaging (LD-MSI) we record 'three-dimensional' finger prints with additional chemical information as the third dimension. Here we show the potential of fast finger pore imaging (FPI) in latent finger prints employing LD-MSI without a classical matrix in a high-spatial resolution mode. Thin films of gold rapidly sputtered on top of the sample are used for desorption. FPI employing an optical image for rapid spatial orientation and guiding of the desorption laser enables the rapid analysis of individual finger pores, and the chemical composition of their excretions. With this approach we rapidly detect metabolites, drugs, and characteristic excretions from the inside of the human organism by a minimally-invasive strategy, and distinguish them from chemicals in contact with fingers without any labeling. The fast finger pore imaging, analysis, and screening approach opens the door for a vast number of novel applications in such different fields as forensics, doping and medication control, therapy, as well as rapid profiling of individuals.
- ItemCommunication activity in a social network: Relation between long-term correlations and inter-event clustering(London : Nature Publishing Group, 2012) Rybski, D.; Buldyrev, S.V.; Havlin, S.; Liljeros, F.; Makse, H.A.Human communication in social networks is dominated by emergent statistical laws such as non-trivial correlations and temporal clustering. Recently, we found long-term correlations in the user's activity in social communities. Here, we extend this work to study the collective behavior of the whole community with the goal of understanding the origin of clustering and long-term persistence. At the individual level, we find that the correlations in activity are a byproduct of the clustering expressed in the power-law distribution of inter-event times of single users, i.e. short periods of many events are separated by long periods of no events. On the contrary, the activity of the whole community presents long-term correlations that are a true emergent property of the system, i.e. they are not related to the distribution of inter-event times. This result suggests the existence of collective behavior, possibly arising from nontrivial communication patterns through the embedding social network.