Malina Seyffertitz opened a general discussion of the paper by Adam P. Willard: Your simulations are based on a flat electrode geometry. How difficult would it be to introduce curved surfaces, i.e. porous electrodes? Adam P. Willard responded: It is certainly not impossible to si
Mammalian synovial joints are extremely efficient lubrication systems reaching friction coefficient μ as low as 0.001 at high pressures (up to 100 atm) and shear rates (up to 10(6) to 10(7) Hz); however, despite much previous work, the exact mechanism responsible for this behavior is still unknown. In this work, we study the molecular mechanism of synovial joint lubrication by emulating the articular cartilage superficial zone structure. Macromolecules extracted and purified from bovine hip joints using well-known biochemical techniques and characterized with atomic force microscope (AFM) have been used to reconstruct a hyaluronan (HA)--aggrecan layer on the surface of molecularly smooth mica. Aggrecan forms, with the help of link protein, supramolecular complexes with the surface-attached HA similar to those at the cartilage/synovial fluid interface. Using a surface force balance (SFB), normal and shear interactions between a HA--aggrecan-coated mica surface and bare mica have been examined, focusing, in particular, on the frictional forces. In each stage, control studies have been performed to ensure careful monitoring of the macromolecular surface layers. We found the aggrecan--HA complex to be a much better boundary lubricant than the HA alone, an effect attributed largely to the fluid hydration sheath bound to the highly charged glycosaminoglycan (GAG) segments on the aggrecan core protein. A semiquantitative model of the osmotic pressure is used to describe the normal force profiles between the surfaces and interpret the boundary lubrication mechanism of such layers.
The interactions between two mica surfaces bearing a fourth-generation carbosilane dendrimer (modified to expose −OH groups on its outer surface) were studied across a toluene medium, using a surface force balance capable of measuring shear as well as normal forces. Normal force measurements indicate that the dendrimers adsorb from dilute toluene solution (ca. 5 × 10-4 w/w) as a monolayer on each surface. Two such interacting surfaces experience a longer-ranged van der Waals attraction followed by strong short-range adhesion (probably of dipolar origin) as the adsorbed dendrimers come into contact. Within the range of our parameters, the dendrimer layers were incompressible normal to the surfaces. Friction versus load profiles were measured at different shear velocities, revealing marked stick-slip sliding, whereas the magnitude of the yield stress increased with longer times of contact and with normal pressure. This suggests that over time scales comparable with the experimental times the interacting layers rearrange to optimize their interfacial shear strength. The behavior of these −OH-exposing carbosilane dendrimers differs qualitatively from that of CH3-exposing poly(propyleneimine) dendrimers studied earlier, a difference attributable to the much more polar nature of the hydroxyl groups.
Articular joints in human body are uniquely efficient lubrication systems. While the cartilage surfaces slide past each other under physiological working conditions (pressure of tens of atmospheres and shear rates up to 106 – 107 Hz), the friction coefficient (μ) achieves extremely low values (down to 0.001) never successfully reached by mechanical prosthetic devices. Friction studies on polymer brushes attached to surfaces have recently demonstrated (17) their ability to reduce friction between the rubbing surfaces to extremely low values by means of the hydrated ions and the charges on the polymer chains. We propose that the extremely efficient lubrication observed in living joints arises from the presence of a brush-like phase of charged macromolecules at the surface of the cartilage superficial zone: hydration layers which surround the charges on the cartilage macromolecules might provide a lubricating ball-bearing-like effect as demonstrated for the synthetic polyelectrolytes (17). In this work macromolecules of the cartilage superficial zone (aggrecans) are extracted from human femoral heads and purified using well developed biochemical techniques (20). The extracted molecules are then characterized with atomic force microscope (AFM). By means of a surface force balance (SFB) normal and shear interactions between mica surfaces coated with these molecules are examined focusing on the frictional forces between such surfaces at normal stresses similar to those in human joints.
The original version of this Article contained an error throughout in which an incorrect symbol was used for the diffusion coefficient: it should be cambria math, italicized, and not bold. These have been corrected in both the PDF and HTML versions of the Article.
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTMutual diffusion in blends of long and short entangled polymer chainsElizabeth A. Jordan, Robin C. Ball, Athene M. Donald, Lewis J. Fetters, Richard A. L. Jones, and Jacob KleinCite this: Macromolecules 1988, 21, 1, 235–239Publication Date (Print):January 1, 1988Publication History Published online1 May 2002Published inissue 1 January 1988https://pubs.acs.org/doi/10.1021/ma00179a045https://doi.org/10.1021/ma00179a045research-articleACS PublicationsRequest reuse permissionsArticle Views259Altmetric-Citations56LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts
Article1 May 1937THE RELATION OF FUNGUS INFECTION OF GRAIN CROPS TO VASOMOTOR DISTURBANCES IN MANJACOB E. KLEIN, M.D.JACOB E. KLEIN, M.D.Search for more papers by this authorAuthor, Article, and Disclosure Informationhttps://doi.org/10.7326/0003-4819-10-11-1708 SectionsAboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissions ShareFacebookTwitterLinkedInRedditEmail ExcerptThe relationship of diseases of plants to human health has not received the detailed consideration which it deserves. Although botanists and agriculturists have made intensive studies of plant pathology, there has been no systematic effort to correlate plant disease with human pathology. On perusing the literature with a historical perspective it is interesting to note that the ancients ascribed disease conditions to contaminated cereal crops. Thus Galen refers to the "morbus cerealis," a disease due to eating spoiled cereal. There are also on record epidemics from eating bread made of rye infected with the fungus, Claviceps purpurea.1Robertson and Ashby2...Bibliography1. HIRSCH A: Handbook of geographic and historical pathology, 1885. Google Scholar2. ROBERTSONASHBY JHT: Ergot poisoning among rye bread consumers, Brit. Med. Jr., 1928, i, 302-303. CrossrefGoogle Scholar3. KLEIN JE: The etiologic relationship of certain grain fungi to acrodynia, thromboangiitis obliterans, and related conditions, Ill. Med. Jr., 1932, lxi, 254. Google Scholar4. KAUNITZ J: The pathological similarity of thromboangiitis obliterans and endemic ergotism, Am. Jr. Path., 1930, vi, 299-316. Google Scholar5. MELLANBY E: Nutrition and disease, 1934, London, p. 126. Google Scholar6. KOEHLERHOLBERT BJ: Corn diseases in Illinois, University of Illinois Agricultural Experiment Station, Bulletin No. 354. Google Scholar7. STEVENSHALL FLJB: Diseases of economic plants, 1922, Macmillan Co., New York. Google Scholar8. MAYERHOFER E: Über Fälle von kindlicher Akrodynie und ihre Stellung zur Feerschen Neurose, Ztschr. f. Kinderheilk., 1930, xlix, 579-588. CrossrefGoogle Scholar9. SOLLMANN T: A manual of pharmacology, p. 457, 1926, W. B. Saunders Co., Philadelphia. Google Scholar10. MARIE A: In Oxford system of medicine, Vol. 4, p. 311, 1920-21. Google Scholar11. DALE HH: The action of ergot, Jr. Physiol., 1906, xxxiv, 163. CrossrefGoogle Scholar12. STOLLSPIRO AK: Über die wirksamen Substanzen des Mutterkorns, Schweiz. med. Wchnschr., 1921, lii, 525. Google Scholar13. FEER E: Eine eigenartige Neurose des vegetativen Systems beim kleinen Kinde, Ergebn. inn. Med. u. Kinderheilk., 1923, xxiv, 100-122. CrossrefGoogle Scholar This content is PDF only. To continue reading please click on the PDF icon. Author, Article, and Disclosure InformationAuthors: JACOB E. KLEIN, M.D.Affiliations: Chicago, Illinois*Received for publication May 1, 1936.From department of Pediatrics, Northwestern University Medical School, and the Laboratory of Pathology and Bacteriology, Northwestern University Dental School. PreviousarticleNextarticle Advertisement FiguresReferencesRelatedDetails Metrics 1 May 1937Volume 10, Issue 11 Page: 1708-1715 Keywords Bacteriology Bread Eating Pediatrics Research laboratories ePublished: 1 December 2008 Issue Published: 1 May 1937 PDF downloadLoading ...
'%3e%3cpath fill='%23012169' d='M0 0v30h60V0z'/%3e%3cpath stroke='%23fff' stroke-width='6' d='m0 0 60 30m0-30L0 30'/%3e%3cpath stroke='%23C8102E' stroke-width='4' d='m0 0 60 30m0-30L0 30' clip-path='url(%23b)'/%3e%3cpath stroke='%23fff' stroke-width='10' d='M30 0v30M0 15h60'/%3e%3cpath stroke='%23C8102E' stroke-width='6' d='M30 0v30M0 15h60'/%3e%3c/g%3e%3c/svg%3e)
'/%3e%3cuse xlink:href='%23a' transform='rotate(23.036 .093 25.536)'/%3e%3cuse xlink:href='%23a' transform='rotate(45.87 1.273 16.18)'/%3e%3cuse xlink:href='%23a' transform='rotate(69.945 .996 12.078)'/%3e%3cuse xlink:href='%23a' transform='rotate(20.66 -19.689 31.932)'/%3e%3c/svg%3e)