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Biomaterials. 1999 Jan;20(2):137-53.
Biaxial mechanical/structural effects of equibiaxial strain during crosslinking of bovine pericardial xenograft materials.
Langdon SE, Chernecky R, Pereira CA, Abdulla D, Lee JM.
Centre for Biomaterials, University of Toronto, Canada.
We have investigated the effect of biaxial constraint during glutaraldehyde crosslinking on the equibiaxial mechanical properties of bovine pericardium. Crosslinking of cruciate samples was carried out with: (i) no applied load, (ii) an initial 25 g ( approximately 30 kPa) equibiaxial load, or (iii) an initial 200 g (approximately 250 kPa) equibiaxial load. All loading during crosslinking was done under a defined initial equibiaxial load and subsequently fixed biaxial strain. Load changes during crosslinking were monitored. Mechanical testing and constraint during crosslinking were carried out in a custom-built biaxial servo-hydraulic testing system incorporating four actuators with phase-controlled waveform synthesis, high frame-rate video dimension analysis, and computer-interfaced data acquisition. The paired biaxial stress strain responses under equibiaxial loading at 1 Hz (before and after treatment) were evaluated for changes in anisotropic extensibility by calculation of an anisotropy index. Scanning electron microscopy (SEM) was performed on freeze-fractured samples to relate collagen crimp morphology to constraint during crosslinking. Fresh tissue was markedly anisotropic with the base-to-apex direction of the pericardium being less extensible and stiffer than the circumferential direction. After unconstrained crosslinking, the extensibility in the circumferential direction, the stiffness in the base-to-apex direction, and the tissue's anisotropy were all reduced. Anisotropy was preserved in the tissue treated with an applied 25 g load; however, tissue treated with an applied 200 g load became extremely stiff and nearly isotropic. SEM micrographs correlated well with observed extensibility in that the collagen fibre morphology changed from very crimped (unconstrained crosslinking), to straight (200 g applied load). Biaxial stress-fixation may allow engineering of bioprosthetic materials for specific medical applications.
online pharmacy ref. source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=10022783&dopt=Abstract
J Bone Miner Res. 1999 Mar;14(3):321-9.
Do more highly organized collagen fibrils increase bone mechanical strength in loss of mineral density after one-year running training?
Puustjarvi K, Nieminen J, Rasanen T, Hyttinen M, Helminen HJ, Kroger H, Huuskonen J, Alhava E, Kovanen V.
Department of Physical and Rehabilitation Medicine, University Hospital of Kuopio, Kuopio, Finland.
The aim of this study was to evaluate the effects of long-term running training on the structural properties of bone. Ten beagle dogs ran according to a strenuous progressive program (up to 40 km/day) for 1 year. At the end of the training program, there was a significant reduction in bone mineral density (up to 9.7%) in the vertebrae of the runner dogs as compared with 10 sedentary control dogs. Polarized light microscopy of the vertebral trabecular bone, however, displayed proportionally higher retardation values of the collagen network of the runner dogs than of the sedentary dogs, suggesting a reorganization in a more parallel manner in the collagen fibrils. The concentration and cross-linking of collagen in the bones remained similar in both groups. No differences were observed in the force to failure of bones of the two groups nor in the histomorphometric analysis of the bones. We suggest that the collagen network in the bones accounted for the maintenance of the strength properties in the bones of the runner dogs despite the loss of mineral density.
online pharmacy ref. source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=10027896&dopt=Abstract
Biomaterials. 1999 Jan;20(2):191-5.
Hydroxyapatite-collagen-hyaluronic acid composite.
Bakos D, Soldan M, Hernandez-Fuentes I.
Faculty of Chemical Technology, Slovak Technical University, Bratislava, Slovak Republic.
The new composite biomaterial made from hydroxyapatite and collagen conjugated with hyaluronic acid has been studied. The structure evaluation of the composite showed more dense arrangement due to the formation of collagen hyaluronic acid conjugate, and particles of inorganic component are closely anchored in the structure. Mechanical properties and model swelling of this composite are compared with properties of hydroxyapatite-collagen composite of similar material without hyaluronic acid. Higher cohesivity of the new biomaterial can give new possibilities for application as bone implant material. The test of contact cytotoxicity showed a very good biocompatibility of the biomaterial.
online pharmacy ref. source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=10022789&dopt=Abstract
J Bone Miner Res. 2003 Feb;18(2):222-30.
Cathepsin K mRNA and protein expression in prostate cancer progression.
Brubaker KD, Vessella RL, True LD, Thomas R, Corey E.
Department of Urology, University of Washington School of Medicine, Seattle, Washington 98195, USA. kbrubak.washington.edu
Prostate cancer (CaP) is the most commonly diagnosed malignancy in men and is often associated with bone metastases, which cause much of the morbidity associated with CaP. Lesions associated with CaP generally exhibit increased bone formation and resorption. Increased bone resorption may release factors from the extracellular matrix that contribute to tumor growth. Cathepsin K (cat K) is a cysteine protease that exhibits strong degradative activity against the extracellular matrix and is involved in osteoclast-mediated bone destruction. In this study, we analyzed the expression of cat K in CaP cell lines and patient samples. Cat K message was detected in CaP cell lines by reverse transcription-polymerase chain reaction (RT-PCR) and in primary CaP and metastases by in situ hybridization. Immunohistochemistry revealed variable expression of cat K in primary CaP samples, as well as nonosseous metastases, whereas expression in bone metastases was significantly higher than in primary CaP, and normal prostate tissues were negative. Cat K protein was detected in CaP cell lines by Western blotting after immunoprecipitation. Cat K enzymatic activity was also detected in CaP cell lines by a fluorogenic assay and by an assay for degradation of collagen type I. Increased levels of NTx, a marker of bone matrix degradation mediated primarily by cat K, were also detected in sera of patients with CaP bone metastases. We hypothesize that CaP-expressed cat K may contribute to the invasive potential of CaP, while increased expression in bone metastases is consistent with a role in matrix degradation.
online pharmacy ref. source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=12568399&dopt=Abstract
J Biol Chem. 1999 Feb 26;274(9):5777-81.
Association of the aggrecan keratan sulfate-rich region with collagen in bovine articular cartilage.
Hedlund H, Hedbom E, Heineg rd D, Mengarelli-Widholm S, Reinholt FP, Svensson O.
Department of Orthopedics, Karolinska Institutet, Huddinge University Hospital, SE-141 86 Huddinge, Sweden. Hakan.Hedlunaro.ki.se
Aggrecan, the predominant large proteoglycan of cartilage, is a multidomain macromolecule with each domain contributing specific functional properties. One of the domains contains the majority of the keratan sulfate (KS) chain substituents and a protein segment with a proline-rich hexapeptide repeat sequence. The function of this domain is unknown but the primary structure suggests a potential for binding to collagen fibrils. We have examined binding of aggrecan fragments encompassing the KS-rich region in a solid-phase assay. A moderate affinity (apparent Kd = 1.1 microM) for isolated collagen II, as well as collagen I, was demonstrated. Enzymatic digestion of the KS chains did not alter the capacity of the peptide to bind to collagen, whereas cleavage of the protein core abolished the interaction. The distribution of the aggrecan KS-rich region in bovine tarsometatarsal joint cartilage was investigated using immunoelectron microscopy. Immunoreactivity was relatively low in the superficial zone and higher in the intermediate and deep zones of the uncalcified cartilage. Within the pericellular and territorial matrix compartments the epitopes representing the aggrecan KS-rich region were detected preferentially near or at collagen fibrils. Along the fibrils, epitope reactivity was non-randomly distributed, showing preference for the gap region within the D-period. Our data suggest that collagen fibrils interact with the KS-rich regions of several aggrecan monomers aligned within a proteoglycan aggregate. The fibril could therefore serve as a backbone in at least some of the aggrecan complexes.
online pharmacy ref. source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=10026199&dopt=Abstract
The average human scalp is covered by approximatey 100,000 hair follicles. Each hair undergoes
Loss of hair itself does not pose critical health problems because biological role of human hair is relatively marginal. Hair on our scalp protects the head from mechanical shock, heat loss, and exposure to UV-light. The eyelashes and eyebrowes protect the eyes, and hair in the ear canal or the nasal passages help filter out particles and pathogens, thus protecting our internal organs.
However, hair does play important social role: it is one of the major determinants of our appearance and identity in daily life. Fullness of hair also implicates or manifests physical integrity and youthfulness of the person. Losing hair could have more than just emotional impacts on individuals.
The hair is a unique organ that goes through a characteristic cycle consisting of an immature phase, a growing phase called anagen, a transitional phase between the growing phase and the resting phase called catagen, and finally a resting phase called telogen in which the hair stops growing, waiting to fall out. 85-90% of hairs on our body are in anagen phase or growing phase, which lasts anywhere from two to five years. This phase is followed by a short regression phase, or catagen, which lasts 2-3 weeks. Approximately 1% of hair follicles are in catagen. Approximately 10-15% of hair follicles are in the resting phase, the telogen, which lasts about 3-5 months. Hair follicles typically goes through 10-20 asynchronous cycles during the lifetime.
Persistent loss of more than 150 hairs would consist a state of hair loss, or alopecia, albeit it could be temporary.
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