Cell traction forces on soft biomaterials. I. Microrheology of type I collagen gels

A laser-trap microrheometry technique was used to determine the local shear moduli of Type I collagen gels. Embedded 2.1 microm polystyrene latex particles were displaced 10-100 nm using a near-infrared laser trap with a trap constant of 0.0001 N/m. The trap was oscillated transversely +/- 200 nm using a refractive glass plate mounted on a galvanometric scanner. The displacement of the microspheres was in phase with the movement of the laser trap at frequencies less than 1 rad/s, indicating that at least locally, the gels behaved as elastic media. The local shear modulus was measured at various positions throughout the gel, and, for gels at 2.3 mg/mL and 37 degrees C, values ranged from G = 3 to 80 Pa. The average shear modulus G = 55 Pa, which compares well with measurements from parallel plate rheometry.     

I. I. Mechnikoff's contribution to immunology

I. I. Mechnikoff's contribution to various aspects of immunology is evaluated. The 25 years' struggle of this scientist for the existence of phagocytosis theory is briefly described. Works of I. I. Mechnikoff dealing with several factors of humoral immunity and cytotoxins are reviewed. The significance of I. I. Mechnikoff's studies providing analysis of immune processes in the phylogenetic sense as well as his ideas about the nervous system role in immunity processes is stressed.