Koch's postulates and the etiology of AIDS: an historical perspective.

This paper examines the debate over the human immunodeficiency virus (HIV) as the cause of acquired immunodeficiency syndrome (AIDS) from an historical perspective. The changing criteria for proving the link between putative pathological agents and diseases are discussed, beginning with Robert Koch's research on anthrax in the late nineteenth century. Various versions of 'Koch's postulates' are analyzed in relation to the necessity and sufficiency arguments of logical reasoning. In addition, alterations to Koch's postulates are delineated, specifically those required by the discovery of rickettsiae and viruses in the early twentieth century and by the immunological testing developed after mid-century to demonstrate the links between elusive viral agents and two diseases, hepatitis B and infectious mononucleosis. From this perspective, an examination of the AIDS debate is constructed. Molecular biologist Peter Duesberg's argument that HIV is not the cause of AIDS is analyzed in light of his contention that a version of Koch's postulates has not been satisfied. Additional research findings through 1990 relating to the etiology of AIDS are also noted.     

Rheological properties of cross-linked hyaluronan-gelatin hydrogels for tissue engineering

Hydrogels that mimic the natural extracellular matrix (ECM) are used in three-dimensional cell culture, cell therapy, and tissue engineering. A semi-synthetic ECM based on cross-linked hyaluronana offers experimental control of both composition and gel stiffness. The mechanical properties of the ECM in part determine the ultimate cell phenotype. We now describe a rheological study of synthetic ECM hydrogels with storage shear moduli that span three orders of magnitude, from 11 to 3 500 Pa, a range important for engineering of soft tissues. The concentration of the chemically modified HA and the cross-linking density were the main determinants of gel stiffness. Increase in the ratio of thiol-modified gelatin reduced gel stiffness by diluting the effective concentration of the HA component.