Reagents for lubrication testing materials were as described previously,2 (link),6 (link),33 (link) including HA in a 4000-kDa form (Healon; Advanced Medical Optics). The antibody to PRG4 was anti-Lubricin from AbCam,2 (link) nonspecific rabbit IgG was from Pierce, and mouse anti-rabbit IgG secondary antibody was from Jackson ImmunoResearch. Streptomyceshyaluronidase was from Seikagaku, SeaKem gold agarose was from Lonza; 50X TAE (2M Tris, 0.5 M ethylenediamine tetraacetic acid [EDTA]) electrophoresis buffer was from Life Technologies, Hybond-P polyvinylidene difluoride (PVDF) membrane for Western blotting was from GE Healthcare, and Stains-All was from Sigma-Aldrich.