INVITRO STUDIES OF THE WEAR OF ARTICULAR-CARTILAGE .3. THE WEAR CHARACTERISTICS OF CHEMICALLY MODIFIED ARTICULAR-CARTILAGE WHEN WORN AGAINST A HIGHLY POLISHED CHARACTERIZED STAINLESS-STEEL SURFACE

The chemical modifications consisted of extracting some constituents of the tissue with aqueous solutions of either 2 M CaCl//2, 3 M MgCl//2, or 0. 5 M EDTA at pH 7. 4, or digesting it to various extents with either trypsin or testicular hyaluronidase. Samples of cartilage, subjected to the various procedures, were characterized for their hydroxyproline, hexosamine, and total protein contents, their amino acid compositions, their calcium and magnesium contents and their swelling ratios in equilibrium with 0. 03 M Tris-HCl at pH 7. 4 at 4 degree C. In addition, the fluid and hexosamine contents of trypsin digested cartilage were measured as a function of depth. As with normal cartilage, the tissue initially wore at higher rates than that finally attained at each pressure. After a period of time, characteristic for each treatment, the tissue wore at a constant, steady state rate (except for the case in which the tissue was subjected to digestion with trypsin for 18 hr at 37 degree C).