Some aspects of the surface chemistry of carbon blacks and other carbons

/pdf/the-surface-chemistry-of-amorphous-silica-zhuravlev-model-4kfs2lx66q.pdf

The surface chemistry of amorphous silica. Zhuravlev model

Tissues can be soft like fat, which bears little stress, or stiff like bone, which sustains high stress, but whether there is a systematic relationship between tissue mechanics and differentiation is unknown. Here, proteomics analyses revealed that levels of the nucleoskeletal protein lamin-A scaled with tissue elasticity, E, as did levels of collagens in the extracellular matrix that determine E. Stem cell differentiation into fat on soft matrix was enhanced by low lamin-A levels, whereas differentiation into bone on stiff matrix was enhanced by high lamin-A levels. Matrix stiffness directly influenced lamin-A protein levels, and, although lamin-A transcription was regulated by the vitamin A/retinoic acid (RA) pathway with broad roles in development, nuclear entry of RA receptors was modulated by lamin-A protein. Tissue stiffness and stress thus increase lamin-A levels, which stabilize the nucleus while also contributing to lineage determination.

/pdf/nuclear-lamin-a-scales-with-tissue-stiffness-and-enhances-m0l552r7vs.pdf

Nuclear lamin-A Scales With Tissue Stiffness and Enhances Matrix-Directed Differentiation

Soft connective tissues at steady state are dynamic; resident cells continually read environmental cues and respond to them to promote homeostasis, including maintenance of the mechanical properties of the extracellular matrix (ECM) that are fundamental to cellular and tissue health. The mechanosensing process involves assessment of the mechanics of the ECM by the cells through integrins and the actomyosin cytoskeleton, and is followed by a mechanoregulation process, which includes the deposition, rearrangement or removal of the ECM to maintain overall form and function. Progress towards understanding the molecular, cellular and tissue-level effects that promote mechanical homeostasis has helped to identify key questions for future research.

Mechanotransduction and extracellular matrix homeostasis

http://www.css.cornell.edu/faculty/lehmann/publ/OrgGeochem%2037,%201477-1488,%202006%20Cheng%20www.pdf

Oxidation of Black Carbon by Biotic and Abiotic Processes

To investigate how substrate properties influence stem-cell fate, we cultured single human epidermal stem cells on polydimethylsiloxane (PDMS) and polyacrylamide (PAAm) hydrogel surfaces, 0.1 kPa-2.3 MPa in stiffness, with a covalently attached collagen coating. Cell spreading and differentiation were unaffected by polydimethylsiloxane stiffness. However, cells on polyacrylamide of low elastic modulus (0.5 kPa) could not form stable focal adhesions and differentiated as a result of decreased activation of the extracellular-signal-related kinase (ERK)/mitogen-activated protein kinase (MAPK) signalling pathway. The differentiation of human mesenchymal stem cells was also unaffected by PDMS stiffness but regulated by the elastic modulus of PAAm. Dextran penetration measurements indicated that polyacrylamide substrates of low elastic modulus were more porous than stiff substrates, suggesting that the collagen anchoring points would be further apart. We then changed collagen crosslink concentration and used hydrogel-nanoparticle substrates to vary anchoring distance at constant substrate stiffness. Lower collagen anchoring density resulted in increased differentiation. We conclude that stem cells exert a mechanical force on collagen fibres and gauge the feedback to make cell-fate decisions.

Extracellular-matrix tethering regulates stem-cell fate

Collective movement of epithelial cells drives essential multicellular organization during various fundamental physiological processes encompassing embryonic morphogenesis, cancer and wound healing. Yet the molecular mechanism that ensures the coordinated movement of many cells remains elusive. Here we show that a tumour suppressor protein, merlin, coordinates collective migration of tens of cells, by acting as a mechanochemical transducer. In a stationary epithelial monolayer and also in three-dimensional human skin, merlin localizes to cortical cell-cell junctions. During migration initiation, a fraction of cortical merlin relocalizes to the cytoplasm. This relocalization is triggered by the intercellular pulling force of the leading cell and depends on the actomyosin-based cell contractility. Then in migrating cells, taking its cue from the intercellular pulling forces, which show long-distance ordering, merlin coordinates polarized Rac1 activation and lamellipodium formation on the multicellular length scale. Together, these results provide a distinct molecular mechanism linking intercellular forces to collective cell movements in migrating epithelia.

A molecular mechanotransduction pathway regulates collective migration of epithelial cells

An der Oberflache von Festkorpern sind haufig strukturfremde Atome oder Atomgruppierungen gebunden Die Chemie dieser „End-Gruppen” an der Festkorperoberflache wird an einigen Beispielen besprochen Bei Diamant und graphitischem Kohlenstoff und auch noch bei Siliciumdioxid sind die Fremdatome covalent gebunden, wahrend bei Titandioxid und Aluminiumoxid vorwiegend ionenartige Bindung der Oberflachengruppen vorliegt Oxide sind normalerweise mit einer monomolekularen Hydroxidschicht bedeckt Wertigkeitsanderungen der Metallatome fuhren zu Veranderungen der Aciditat der Oberflache; bei der Reduktion oberflachenstandiger Ti4+-Ionen bekommt die TiO2-Oberflache sauren Charakter

Funktionelle Gruppen an Festkörper-Oberflächen

Atoms or groups foreign to the structure of a solid are often bonded to its surface. On diamond, graphite, and even silicon dioxide, the foreign atoms are bonded covalently, whereas the bonding of the structural groups to titanium oxide and alumina is predominantly ionic. Oxides are normally covered with a monomolecular hydroxide layer. Changes in the valence of the metal atoms lead to changes in the acidity of the surface; for example, reduction of surface Ti4+ions gives the surface of TiO2 an acidic nature.

Functional Groups on the Surfaces of Solids

Bei der Oxydation graphitischen Kohlenstoffs bilden sich an den Randern der Kohlenstoffschichten saure Oberflachenoxyde (oder -hydroxyde bei Anwesenheit von Wasser). Mit mikrokristallinem Kohlenstoff ergab sich, das bei der Reaktion mit Sauerstoff bei 400 bis 450°C vier Gruppen unterschiedlicher Aciditat entstehen: Je eine starker saure und eine schwacher saure Carboxylgruppe sowie eine phenolische Hydroxylgruppe wurden nachgewiesen. Wahrscheinlich liegt auserdem eine Carbonylgruppe vor. Mit gelosten Oxydationsmitteln bildet sich bei Zimmertemperatur zusatzlich ein Aquivalent einer starker sauren Carboxylgruppe. — Die moglichen Konstitutionen der sauren Oberflachenoxyde werden diskutiert. Auch an der Oberflache des Diamanten werden Oberflachenoxyde gebildet, die sich chemisch nachweisen lassen. Beim Einwirken von Sauerstoff bei 800 bis 900°C unter geringem Druck wird Diamant in schwarzen Kohlenstoff umgewandelt. Dabei spielen Oberflachenoxyde eine Rolle.

Heike Boehm

Papers

Extracellular-matrix tethering regulates stem-cell fate

A molecular mechanotransduction pathway regulates collective migration of epithelial cells

Funktionelle Gruppen an Festkörper-Oberflächen

Functional Groups on the Surfaces of Solids

Oberflächenoxyde des Kohlenstoffs