As documented in Fig 1D and to assure that the dots represent gold particles we employed backscattering electron (BSE) mode showing material contrast in the SEM were we clearly identified the 18-nm gold particles. their hierarchical organized fiber architecture studied at high resolution at the authentic location within cartilage. We present electron micrographs of the collagenous cores of such fibers obtained by Diltiazem HCl an improved protocol for scanning electron microscopy (SEM). Articular cartilages are permeated by small prototypic fibrils with a homogeneous diameter of 18 5 nm that can align in their D-periodic pattern and merge into larger fibers by lateral association. Interestingly, these fibers have tissue-specific organizations in cartilage. They are twisted ropes in superficial regions of knee joints or assemble into parallel aligned cable-like structures in deeper regions of knee joint- or throughout hip joints articular cartilage. These novel observations contribute to an Diltiazem HCl improved understanding of collagen fiber biogenesis, function, and homeostasis in hyaline cartilage. Introduction Articular cartilage is usually a connective tissue that covers the ends of long bones and provides low-friction and wear-resistant joint motion. Cartilage is only 1C3 mm thin but is usually routinely loaded in compression, torsion and shear and allows to absorb and distribute loads generated in joint movements. Due to its compliance, it also prevents excessive loads and protects the subchondral bone from damage. These functions are engendered by two main interpenetrating suprastructural compartments, the collagen-containing fiber meshwork and the highly hydrated extrafibrillar proteoglycan-rich matrix that comprises the large, cartilage-specific proteoglycan aggrecan . Both aggrecan and the collagen networks Diltiazem HCl are highly ordered structures processed in a multi-step hierarchically self-assembly process. Structural changes of proteoglycans or collagens or loss of these structures may change the water content and affect tissue functional properties, which over time can damage the tissue and ultimately turn healthy into osteoarthritic cartilage. N-Shc There is general agreement that this development of osteoarthritis consists of a first, basically reversible loss of proteoglycans from the hydrated gel, followed by irreversible collagenolytic degradation of the fibrils, which then results in structural disintegration of the collagen meshwork, erosive tissue loss and ultimately to catastrophic failure of the joint. Articular cartilage comprises three structurally distinct zones distinguished by the predominant orientations of collagen fibers: (i) a surface layer representing about 10C20% of the overall thickness in which the fibers mainly run parallel to the joint surface, (ii) an intermediate layer of about 40C60% with the fibers in random orientation, and (iii) a deep layer of about 30% with fibers highly oriented along the longitudinal bone axis to anchor articular cartilage to the subchondral bone [2, 3]. These layers result into layer specific mechanical properties of articular cartilage . In addition, chondrocytes are guarded against compression by a so-called territorial matrix that contains a weave of small diameter fibrils oriented parallel to the cell surfaces. At some distance from the cells, the interterritorial matrix also contains large fibrils displaying a prominent banding pattern in addition to small fibrils similar to those of the territorial matrix . To obtain insight in greater detail of suprastructurally distinct cartilage fibrils we have investigated their organizations by scanning electron microscopy (SEM) at improved spatial resolution. We were especially interested in the suprastructural organization of the large fibers, i.e., how these collagen fibers are formed and how they are affected during disease. By the analysis of osteoarthritic articular cartilage, we obtained insights into Diltiazem HCl new aspects of the changes in fibers organization that relate to disease which point to the underlying mechanism of osteoarthritis progression. Results and Discussion Thick cartilage fibers are supramolecular composites of thin prototypic fibrils First, we inspected the surface, middle and deeper zones from normal human knee and hip articular cartilage with no signs of osteoarthritic damage (grade 0; see Materials.