Alignment maps of tissues: I. Microscopic elliptical polarimetry.
An automated method for generating a fiber alignment map in tissues, tissue-equivalents, and other fibrillar materials exhibiting linear and circular optical properties and scattering is presented. This method consists of interrogating the sample with elliptically polarized light from a rotated quarter-wave plate and an effective circular analyzer, and implementing nonlinear regression techniques to estimate parameters defining the optical properties of the optic train and the sample. Thus, an account is made for imperfect and misaligned optic elements. The optic train was modeled using the Mueller matrix representation and the combined sample properties by an exponential matrix. Because a sample's Mueller matrix does not uniquely determine the linear, circular, or scattering properties, the circular properties and effective scattering are estimated for a matched isotropic sample to determine and correct for the linear birefringence of an aligned sample. The method's utility is demonstrated by generating an alignment map of an arterial media-equivalent, a relevant test case because of its circumferential alignment and thus showing the method's sample orientation independence. (+info)
Ontogenetic changes in fibrous connective tissue organization in the oval squid, Sepioteuthis lessoniana Lesson, 1830.
Ontogenetic changes in the organization and volume fraction of collagenous connective tissues were examined in the mantle of Sepioteuthis lessoniana, the oval squid. Outer tunic fiber angle (the angle of a tunic collagen fiber relative to the long axis of the squid) decreased from 33.5 degrees in newly hatched animals to 17.7 degrees in the largest animals studied. The arrangement of intramuscular collagen fiber systems 1 (IM-1) and 2 (IM-2) also changed significantly during ontogeny. Because of the oblique trajectory of the IM-1 collagen fibers, two fiber angles were needed to describe their organization: (1) IM-1(SAG), the angle of an IM-1 collagen fiber relative to the squid's long axis when viewed from a sagittal plane and (2) IM-1(TAN), the angle of an IM-1 collagen fiber relative to the squid's long axis when viewed from a plane tangential to the outer curvature of the mantle. The sagittal component (IM-1(SAG)) of the IM-1 collagen fiber angle was lowest in hatchling squid (32.7 degrees ) and increased exponentially during growth to 43 degrees in squid with a dorsal mantle length (DML) of 15 mm. In squid larger than 15 mm DML, IM-1(SAG) fiber angle did not change. The tangential component (IM-1(TAN)) of IM-1 collagen fiber angle was highest in hatchling squid (39 degrees ) and decreased to 32 degrees in the largest squid examined. IM-2 collagen fiber angle (the angle of an IM-2 collagen fiber relative to the outer surface of the mantle) was lowest in hatchling squid (34.6 degrees ) and increased exponentially to about 50 degrees in 15-mm DML animals. In squid larger than 15 mm DML, IM-2 fiber angle increased slightly with size. The volume fraction of collagen in IM-1 and IM-2 increased 68 and 36 times, respectively, during growth. The ontogenetic changes in the organization of collagen fibers in the outer tunic, IM-1, and IM-2 may lead to ontogenetic differences in the kinematics of mantle movement and in elastic energy storage during jet locomotion. (+info)
Collagen of articular cartilage.
The extracellular framework and two-thirds of the dry mass of adult articular cartilage are polymeric collagen. Type II collagen is the principal molecular component in mammals, but collagens III, VI, IX, X, XI, XII and XIV all contribute to the mature matrix. In developing cartilage, the core fibrillar network is a cross-linked copolymer of collagens II, IX and XI. The functions of collagens IX and XI in this heteropolymer are not yet fully defined but, evidently, they are critically important since mutations in COLIX and COLXI genes result in chondrodysplasia phenotypes that feature precocious osteoarthritis. Collagens XII and XIV are thought also to be bound to fibril surfaces but not covalently attached. Collagen VI polymerizes into its own type of filamentous network that has multiple adhesion domains for cells and other matrix components. Collagen X is normally restricted to the thin layer of calcified cartilage that interfaces articular cartilage with bone. (+info)
Biological liquid crystal elastomers.
Liquid crystal elastomers (LCEs) have recently been described as a new class of matter. Here we review the evidence for the novel conclusion that the fibrillar collagens and the dragline silks of orb web spiders belong to this remarkable class of materials. Unlike conventional rubbers, LCEs are ordered, rather than disordered, at rest. The identification of these biopolymers as LCEs may have a predictive value. It may explain how collagens and spider dragline silks are assembled. It may provide a detailed explanation for their mechanical properties, accounting for the variation between different members of the collagen family and between the draglines in different spider species. It may provide a basis for the design of biomimetic collagen and dragline silk analogues by genetic engineering, peptide- or classical polymer synthesis. Biological LCEs may exhibit a range of exotic properties already identified in other members of this remarkable class of materials. In this paper, the possibility that other transversely banded fibrillar proteins are also LCEs is discussed. (+info)
Abnormal collagen fibrils in tendons of biglycan/fibromodulin-deficient mice lead to gait impairment, ectopic ossification, and osteoarthritis.
Small leucine-rich proteoglycans (SLRPs) regulate extracellular matrix organization, a process essential in development, tissue repair, and metastasis. In vivo interactions of biglycan and fibromodulin, two SLRPs highly expressed in tendons and bones, were investigated by generating biglycan/fibromodulin double-deficient mice. Here we show that collagen fibrils in tendons from mice deficient in biglycan and/or fibromodulin are structurally and mechanically altered resulting in unstable joints. As a result, the mice develop successively and progressively 1) gait impairment, 2) ectopic tendon ossification, and 3) severe premature osteoarthritis. Forced use of the joints increases ectopic ossification and osteoarthritis in the double-deficient mice, further indicating that structurally weak tendons cause the phenotype. The study shows that mutations in SLRPs may predispose to osteoarthritis and offers a valuable and unique animal model for spontaneous osteoarthritis characterized by early onset and a rapid progression of the disease. (+info)
Ultrastructure of the human intra-articular disc of the temporomandibular joint.
The ultrastructural appearance of the human intra-articular disc (IAD) was investigated in three discs that had been surgically removed due to disease from three female patients aged 47, 50, and 54 years of age. Regions of the IAD were selected from central areas that appeared to be least affected by disease. Sections were fixed in 2.5 per cent glutaraldehyde in 0.1 M phosphate buffer, pH 7.3 immediately after surgery. The regions examined showed no obvious signs of inflammation. The cells showed moderate amounts of the intracellular organelles associated with protein synthesis and secretion, and possessed considerable amounts of microfilamentous material, thus resembling those described in other mammals. Despite the large number of cells examined, only one cell showed evidence of a chondrocyte-like morphology in that it possessed an incomplete pericellular zone of microfilamentous material separating the cell membrane from the adjacent collagen bundles of the extracellular matrix (ECM). Thus, on morphological grounds, fibrocartilage was virtually non-existent in the specimens examined. The mean collagen fibril diameter was 43.9 nm and the fibril diameter distribution was not unimodal. Although the majority of fibrils had a relatively small diameter, two of the three specimens possessed many fibrils with diameters of over 100 nm, this being consistent with tissue subjected to tension. The mean area of a fibre bundle occupied by collagen (as opposed to the ground substance) was approximately 56 per cent. (+info)
Altered collagen fibril formation in the sclera of lumican-deficient mice.
PURPOSE: To better understand the role of lumican (corneal keratan sulfate proteoglycan) in the scleral extracellular matrix, collagen fibril size, shape, and organization were evaluated in the sclera of wild-type mice and in mice homozygous or heterozygous for a null mutation in the lumican gene. METHODS. Anterior and posterior sclera from 6-month-old wild-type (lum+/lum+) and lumican-deficient mice (lum+/lum- and lum-/lum-) were analyzed by transmission electron microscopy. In addition, lumican was characterized in the sclera of wild-type and lumican-deficient mice by Western blot analyses. RESULTS: Lumican was present in the mouse sclera as an approximately 48-kDa core protein containing short glycosaminoglycan side chains consisting of moderate- to low-sulfated keratan sulfate. The wild-type mouse sclera consisted of irregularly arranged lamellae of collagen fibrils with an average diameter of 47.37 +/- 0.648 nm in the anterior sclera and 54.68 +/- 0.342 nm the posterior sclera. Collagen fibrils in the sclera of lumican mutant mice (lum+/lum- and lum-/lum-) were significantly larger in diameter in anterior (72.61 +/- 0.445 and 84.47 +/- 0.394 nm, respectively) and posterior (75.92 +/- 0.361 and 80.90 +/- 0.490 nm, respectively) scleral regions compared with wild-type mice (P < 0.001). CONCLUSIONS: The results of the present study indicate that null mutations in one or both alleles of the lumican gene result in significant defects in scleral collagen fibril formation that could lead to alterations in ocular shape and size and severely affect vision. (+info)
Reaction diffusion model of the enzymatic erosion of insoluble fibrillar matrices.
Predicting the time course of in vivo biodegradation is a key issue in the design of an increasing number of biomedical applications such as sutures, tissue analogs and drug-delivery devices. The design of such biodegradable devices is hampered by the absence of quantitative models for the enzymatic erosion of solid protein matrices. In this work, we derive and simulate a reaction diffusion model for the enzymatic erosion of fibrillar gels that successfully reproduces the main qualitative features of this process. A key aspect of the proposed model is the incorporation of steric hindrance into the standard Michaelis-Menten scheme for enzyme kinetics. In the limit of instantaneous diffusion, the model equations are analogous to the standard equations for enzymatic degradation in solution. Invoking this analogy, the total quasi-steady-state approximation is used to derive approximate analytical solutions that are valid for a wide range of in vitro conditions. Using these analytical approximations, an experimental-theoretical method is derived to unambiguously estimate all the kinetic model parameters. Moreover, the analytical approximations correctly describe the characteristic hyperbolic dependence of the erosion rate on enzyme concentration and the zero-order erosion of thin fibers. For definiteness, the analysis of published experimental results of enzymatic degradation of fibrillar collagen is demonstrated, and the role of diffusion in these experiments is elucidated. (+info)