SEARCH · Search PubMed

Results for “Matrix stiffness”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 775 records · Page 43Linked to original sources

PubMedDate not supplied

Effect of chelatants on gellan gel rheological properties and setting temperature for immobilization of living bifidobacteria.

The effect of various concentrations of sequestrants (sodium citrate, sodium metaphosphate, and EDTA) was studied on gellan gel (1.5-2.5% (w/v)) setting temperature and rheological properties. Addition of EDTA between 0 and 0.8% (w/v) led to a progressive decrease of setting temperature. Citrate and metaphosphate decreased this parameter when added up to 0.4 or 0.6%, depending on gellan gum concentration, eventually resulting in the absence of gel formation at room temperature for the 1.5% gellan solution containing 0.4% citrate. This effect was accompanied by a significant decrease of gel strength and stiffness and might be attributed to the binding of the divalent cations required for chain association during gelation by chelatants. With the aim of lowering the gel setting temperature during the cell entrapment process while maintaining high mechanical properties, a gel made of 2.5% gellan gum and 0.2% sodium citrate was used to entrap Bifidobacterium longum ATCC 15707. Ions and pH of the inoculum during the immobilization step influenced the long-term mechanical stability of the gel beads during continuous fermentation in a stirred tank reactor. High stability as well as high biocatalyst activity was obtained when a washed cell suspension was used as the inoculum. Gellan gel produced by dissolving gellan gum in a sodium citrate solution may be a promising entrapment matrix for temperature-sensitive cells such as mesophilic lactic acid bacteria and eukaryotic cells.

Bifidobacterium↗

PubMed2003

Effect of peroxisome proliferator-activated receptor-alpha and -gamma activators on vascular remodeling in endothelin-dependent hypertension.

OBJECTIVE: Peroxisome proliferator-activated receptors (PPARs) may modulate in vitro the vascular production of vasoactive peptides such as endothelin-1 (ET-1). Thus, we investigated in vivo the interaction between PPARs and ET-1 in deoxycorticosterone acetate (DOCA)-salt rats that overexpress vascular ET-1. METHODS AND RESULTS: Unilaterally nephrectomized 16-week-old Sprague-Dawley rats (Uni-Nx) were divided into 4 groups (n=6 each): control group, DOCA-salt group, DOCA-salt+PPAR-gamma activator (rosiglitazone, 5 mg x kg(-1) x d(-1)), or DOCA-salt+PPAR-alpha activator (fenofibrate, 100 mg x kg(-1) x d(-1)). Systolic blood pressure was significantly increased in the DOCA-salt group (240+/-11 vs 121+/-2 mm Hg in Uni-Nx, P<0.01). Progression of hypertension was partially prevented by coadministration of rosiglitazone (172+/-3 mm Hg vs DOCA-salt, P<0.05) but not by fenofibrate. Both PPAR activators abrogated the increase in prepro-ET-1 mRNA content in the mesenteric vasculature of DOCA-salt rats. The media-to-lumen ratio was increased in DOCA-salt rats (10.3+/-0.9% vs 4.9+/-0.5% in Uni-Nx rats, P<0.01). Rosiglitazone and fenofibrate prevented the hypertrophic remodeling observed in DOCA-salt rats without affecting vascular stiffness. Rosiglitazone but not fenofibrate prevented endothelial dysfunction in pressurized mesenteric arteries. Finally, both rosiglitazone and fenofibrate prevented the vascular increase in superoxide anion production induced in DOCA-salt animals. CONCLUSIONS: PPAR-alpha and -gamma activators were able to modulate endogenous production of ET-1 and had beneficial vascular effects in endothelin-dependent hypertension.

Animals↗

PubMed1981

Idiopathic familial chondrocalcinosis due to apatite crystal deposition.

Idiopathic familial chondrocalcinosis was found in five members of a family. The clinical features of the disease were morning stiffness, pain and limitation of motion of the dorsolumbar spine in four of the five members, associated with arthritis of the small joints of the hands in three, shoulder periarthritis in two and costal cartilage pain in one. Radiologically, four of the five patients had multiple intervertebral disk calcifications, mainly located at the nucleus pulposus area. Three of them also had periarticular calcific deposits, associated with costal cartilage calcifications and degenerative changes in the small joints of the hands in two. None of these cases showed cartilage calcification in the knees, public symphysis or triangular ligament of carpus. In the propositus, optical microscopy of a specimen of the second proximal interphalangeal joint obtained by open biopsy showed the presence of multiple calcified areas in the intercellular matrix and chondroid metaplasia with calcification of the matrix in the synovial membrane and capsule. X-ray diffraction studies, energy dispersive analysis, and infrared spectrophotometry of a costal cartilage sample obtained by open biopsy demonstrated the presence of carbonate calcium hydroxyapatite. In this study, no relation was found between HLA antigens, loci A, B and C, and this syndrome due to calcium hydroxyapatite crystal deposition.

Adult↗

PubMed2005

Design of scaffolds for blood vessel tissue engineering using a multi-layering electrospinning technique.

Aiming to develop a scaffold architecture mimicking morphological and mechanically that of a blood vessel, a sequential multi-layering electrospinning (ME) was performed on a rotating mandrel-type collector. A bi-layered tubular scaffold composed of a stiff and oriented PLA outside fibrous layer and a pliable and randomly oriented PCL fibrous inner layer (PLA/PCL) was fabricated. Control over the level of fibre orientation of the different layers was achieved through the rotation speed of the collector. The structural and mechanical properties of the scaffolds were examined using scanning electron microscopy (SEM) and tensile testing. To assess their capability to support cell attachment, proliferation and migration, 3T3 mouse fibroblasts and later human venous myofibroblasts (HVS) were cultured, expanded and seeded on the scaffolds. In both cases, the cell-polymer constructs were cultured under static conditions for up to 4 weeks. Environmental-scanning electron microscopy (SEM), confocal laser scanning microscopy (CLSM), histological examination and biochemical assays for cell proliferation (DNA) and extracellular matrix production (collagen and glycosaminoglycans) were performed. The findings suggest the feasibility of ME to design scaffolds with a hierarchical organization through a layer-by-layer process and control over fibre orientation. The resulting scaffolds achieved the desirable levels of pliability (elastic up to 10% strain) and proved to be capable to promote cell growth and proliferation. The electrospun PLA/PCL bi-layered tube presents appropriate characteristics to be considered a candidate scaffold for blood vessel tissue engineering.

3T3 Cells↗

PubMed2001

Denatured state thermodynamics: residual structure, chain stiffness and scaling factors.

A set of nine variants of yeast iso-1-cytochrome c with zero or one surface histidine have been engineered such that the N-terminal amino group is acetylated in vivo. N-terminal acetylation has been confirmed by mass spectral analysis of intact and proteolytically digested protein. The histidine-heme loop-forming equilibrium, under denaturing conditions (3 M guanidine hydrochloride), has been measured by pH titration providing an observed pK(a), pK(a)(obs), for each variant. N-terminal acetylation prevents the N-terminal amino group-heme binding equilibrium from interfering with measurements of histidine-heme affinity. Significant deviation is observed from the linear dependence of pK(a)(obs) on the log of the number of monomers in the loop formed, expected for a random coil denatured state. The maximum histidine-heme affinity occurs for a loop size of 37 monomers. For loop sizes of 37-83 monomers, histidine-heme pK(a)(obs) values are consistent with a scaling factor of -4.2+/-0.3. This value is much larger than the scaling factor of -1.5 for a freely jointed random coil, which is commonly used to represent the conformational properties of protein denatured states. For loop sizes of nine to 22 monomers, chain stiffness is likely responsible for the decreases in histidine-heme affinity relative to a loop size of 37. The results are discussed in terms of residual structure and sequence composition effects on the conformational properties of the denatured states of proteins.

Acetylation↗

PubMed1999

Role of collagenase in mediating in vitro alveolar epithelial wound repair.

Type II pneumocytes are essential for repair of the injured alveolar epithelium. The effect of two MMP collagenases, MMP-1 and MMP-13 on alveolar epithelial repair was studied in vitro. The A549 alveolar epithelial cell line and primary rat alveolar epithelial cell cultures were used. Cell adhesion and cell migration were measured with and without exogenous MMP-1. Wound healing of a cell monolayer of rat alveolar epithelial cell after a mechanical injury was evaluated by time lapse video analysis. Cell adhesion on type I collagen, as well as cytoskeleton stiffness, was decreased in the presence of exogenous collagenases. A similar decrease was observed when cell adhesion was tested on collagen that was first incubated with MMP-1 (versus control on intact collagen). Cell migration on type I collagen was promoted by collagenases. Wound healing of an alveolar epithelial cell monolayer was enhanced in the presence of exogenous collagenases. Our results suggest that collagenases could modulate the repair process by decreasing cell adhesion and cell stiffness, and by increasing cell migration on type I collagen. Collagen degradation could modify cell adhesion sites and collagen degradation peptides could induce alveolar type II pneumocyte migration. New insights regarding alveolar epithelial cell migration are particularly relevant to investigate early events during alveolar epithelial repair following lung injury.

Animals↗

PubMed1998

Differences in elasticity of vinculin-deficient F9 cells measured by magnetometry and atomic force microscopy.

We have investigated a mouse F9 embryonic carcinoma cell line, in which both vinculin genes were inactivated by homologous recombination, that exhibits defective adhesion and spreading [Coll et al. (1995) Proc. Natl. Acad. Sci. USA 92, 9161-9165]. Using a magnetometer and RGD-coated magnetic microbeads, we measured the local effect of loss and replacement of vinculin on mechanical force transfer across integrins. Vinculin-deficient F9Vin(-/-) cells showed a 21% difference in relative stiffness compared to wild-type cells. This was restored to near wild-type levels after transfection and constitutive expression of increasing amounts of vinculin into F9Vin(-/-) cells. In contrast, the transfection of vinculin constructs deficient in amino acids 1-288 (containing the talin- and alpha-actinin-binding site) or substituting tyrosine for phenylalanine (phosphorylation site, amino acid 822) in F9Vin(-/-) cells resulted in partial restoration of stiffness. Using atomic force microscopy to map the relative elasticity of entire F9 cells by 128 x 128 (n = 16,384) force scans, we observed a correlation with magnetometer measurements. These findings suggest that vinculin may promote cell adhesions and spreading by stabilizing focal adhesions and transferring mechanical stresses that drive cytoskeletal remodeling, thereby affecting the elastic properties of the cell.

Animals↗

PubMed1996

Development of a finite element model of the middle ear.

A representative finite element model of the healthy ear is developed commencing with a description of the decoupled isotropic tympanic membrane. This model was shown to vibrate in a manner similar to that found both numerically (1, 2) and experimentally (8). The introduction of a fibre system into the membrane matrix significantly altered the modes of vibration. The first mode "remains as a piston like movement as for the isotropic membrane. However, higher modes show a simpler vibration pattern similar to the second mode but with a varying axis of movement and lower amplitudes. The introduction of a malleus and incus does not change the natural frequencies or mode shapes of the membrane for certain support conditions. When constraints are imposed along the ossicular chain by simulation of a cochlear impedance term then significantly altered modes can occur. More recently a revised model of the ear has been developed by the inclusion of the outer ear canal. This discretisation uses geometries extracted from a Nuclear Magnetic resonance scan of a healthy subject and a crude inner ear model using stiffness parameters ultimately fixed through a parameter tuning process. The subsequently tuned model showed behaviour consistent with previous findings and should provide a good basis for subsequent modelling of diseased ears and assessment of the performance of middle ear prostheses.

Biomechanical Phenomena↗

PubMed1997

Fiber-matrix interface studies on bioabsorbable composite materials for internal fixation of bone fractures. I. Raw material evaluation and measurement of fiber-matrix interfacial adhesion.

The objective of this study was to characterize and evaluate the performance of various fiber-matrix composite systems by studying the mechanical, thermal, and physical properties of the fiber and matrix components, and by studying the fiber-matrix interface adhesion strength using both microbond and fragmentation methods. The composites studies were poly(L-lactic acid) (PLLA) matrix reinforced with continuous fibers of either nonabsorbable AS4 carbon (C), absorbable calcium phosphate (CaP), poly(glycolic acid) (PGA), or chitin. Carbon and CaP single fibers had high Young's moduli and failed in a brittle manner. PGA and chitin single fibers had relatively lower Young's moduli and relatively higher ductility. Upon in vitro hydrolysis, CaP fibers retained 17% of their tensile strength and 39% of their Young's modulus after 12 h, PCA fibers retained 10% of their tensile strength and 52% of their Young's modulus after 16 days, and chitin fibers retained 87% of their tensile strength and 130% of their Young's modulus after 25 days. PLLA films had much lower strength and Young's moduli, but much higher ductility relative to the single fibers. Using the microbond method, the initial fiber-matrix interfacial shear strength (IFSS) of C/PLLA and CaP/PLLA microcomposites was 33.9 and 12.6 MPa, respectively. Upon in vitro hydrolysis, C/PLLA retained 49% of IFSS after 15 days and CaP/PLLA retained 46% of IFSS after 6 h. Using a fiber fragmentation method, the initial IFSS of C/PLLA, CaP/PLLA, and chitin/ PLLA was 22.2, 15.6, and 28.3 MPa, respectively. The performance of carbon fibers and C/PLLA composites was superior to the other fibers and fiber/PLLA systems, but the carbon fiber was nonabsorbable. CaP had the most suitable modulus of the absorbable fibers for fixing cortical bone fracture, but its rapid deterioration of mechanical properties and loss of IFSS limits its use. PGA and chitin fibers had suitable mechanical properties and their retention for fixing cancellous bone fractures, but likely had insufficient stiffness for applications such as bone plates for fixing cortical bone fractures.

Adhesiveness↗

PubMed2005

Current understanding and review of the literature: vocal fold scarring.

Vocal fold scarring is the greatest cause of poor voice after vocal fold injury. Scarring causes a disruption of the viscoelastic layered structure of the lamina propria, an increase in stiffness of the vibratory structure, and glottic incompetence. Current treatments for this complex condition are inconsistent and often produce suboptimal results. Research investigating this condition has dramatically increased over the last several years. The literature has been directed toward understanding vocal fold scarring at the biological level and translating this to the clinical forum. We present an up-to-date, thorough, and scholarly review of the literature in vocal fold scarring since 1996.

Adjuvants, Immunologic↗

PubMed1996

Endothelin antagonism in end-organ damage of spontaneously hypertensive rats. Comparison with angiotensin-converting enzyme inhibition and calcium antagonism.

High blood pressure results in cardiac hypertrophy and fibrosis, increased thickness and stiffness of large artery walls, and decreased renal function. The objective of our study was to assess the role of endothelin, angiotensin II, and high blood pressure in the end-organ damage observed in spontaneously hypertensive rats (SHR). For this purpose, SHR were treated for 10 weeks with either a mixed endothelin-A and endothelin-B receptor antagonist, bosentan (100 mg/kg per day), an angiotensin-converting enzyme inhibitor, enalapril (10 mg/kg per day), or a long-acting calcium antagonist, mibefradil (20 mg/kg per day). A group of SHR was left untreated, and a group of normotensive Wistar rats was used as control. At the end of treatment, maximal coronary blood flow was measured in isolated perfused hearts. Cardiac hypertrophy and fibrosis, aortic medial thickness, and extracellular matrix content were evaluated by quantitative morphometry. Proteinuria and urea and creatinine clearances were measured, and renal histopathology was assessed. SHR exhibited cardiac hypertrophy, perivascular fibrosis, and decreased maximal coronary blood flow. Aortic medial thickness was increased, whereas elastin density was decreased. Finally, SHR showed decreased urinary excretion and decreased urea and creatinine clearances. No renal histological lesions were observed. Although bosentan did not affect blood pressure, it normalized renal function and slightly decreased left ventricular hypertrophy and fibrosis. Enalapril and mibefradil were both effective in significantly decreasing blood pressure, left ventricular hypertrophy, and aortic medial thickness and improving coronary blood flow, but in contrast to bosentan, they did not improve creatinine clearance. We conclude that in SHR, high blood pressure plays a major role in end-organ damage and that endothelin may partly mediate renal dysfunction and cardiac remodeling independently of a direct hemodynamic effect.

Angiotensin-Converting Enzyme Inhibitors↗

PubMed1993

Changes in the structure and mechanical properties of pulmonary arteries of rats exposed to cigarette smoke.

The effect of cigarette smoke on the structure and mechanical properties of pulmonary arteries was studied in 2- and 3-month smoke-exposed rats. The animals were exposed to cigarette smoke in a smoke-generating system 10 times per day with one cigarette each time. The smoke density and the puffing duration and frequency of the system were regulated in accordance with reference values measured from human smokers. The volume fractions of the cells, including smooth muscle cells and fibroblasts, and extracellular matrix components, including collagen, elastin, and remainder (components not specified in this study), of the pulmonary arteries of approximately 450 microns in external diameter (at zero pressure) were determined in smoke-exposed and control rats by using an electron microscopic method. It was found that the volume fractions of the fibroblasts, the collagenous bundles, and the elastic laminae of the pulmonary arteries were increased significantly, whereas those of the smooth muscle cells and the remainder were decreased significantly in both the 2- and 3-month smoke-exposed rats in comparison with those of the corresponding control rats. The mechanical properties of the pulmonary arteries were determined based on the in vitro dimensional measurement of the vessels at various inflation pressures and zero-stress state. An increase in the stiffness of the pulmonary arteries was found in both the 2- and 3-month smoke-exposed rats. We conclude that cigarette smoke can induce structural and mechanical remodeling in the pulmonary arteries of rats.

Animals↗

PubMed1999

Porous bioactive glass matrix in reconstruction of articular osteochondral defects.

BACKGROUND AND AIMS: This study was carried out to investigate the use of porous bioactive glass implants in promotion of articular cartilage and subchondral bone repair in large osteochondral joint defects. MATERIAL AND METHODS: Two conical osteochondral defects (top diameter 3.0-3.2 mm) were drilled into the patellar grooves of the distal femurs in the rabbit. The defects, extending (approximately 6-7 mm) from the surface of the articular cartilage to the subchondral marrow space, were reconstructed with size-matched porous conical implants made of sintered bioactive glass microspheres (microsphere diameter 250-300 microm, structural implant compression strength 20-25 MPa) using press-fit technique. The implant surface was smoothened to the level of the surrounding articular cartilage. One of the two defects in each femur was left empty to heal naturally and to serve as the control. At 8 weeks, the defect healing was analyzed with use of a semiquantitative histological grading system, histomorphometry of subchondral bone repair, back-scattered electron imaging of scanning electron microscopy (BEI-SEM), and a microindentation test for characterization for the stiffness properties of the cartilage repair tissue. RESULTS: The porous structure of the bioactive glass implants, extending from the articular defect of the patellar groove into the posterior cortex of the femur, was extensively filled by new bone. Cartilage repair varied from near-complete healing by hyaline cartilage to incomplete healing predominantly by fibrocartilage or fibrous tissue. There were, however, no statistical differences in the histological scores of repair between the glass-filled and control defects, although the sum of the averages of each category was lowest for the bioactive glass filled defects. The indentation stiffness values of all the defects were also significantly lower than that of normal cartilage on the patellar groove. CONCLUSIONS: Porous textures made by sintering bioactive glass microspheres may expand the opportunities in reconstruction of deep osteochondral defects of weight-bearing joints. The implants act mechanically as a supporting scaffold and facilitate the penetration of stromal bone marrow cells and their chondrogenic and osteogenic differentiation. Ionic properties of the bioactive glasses make the substances highly potential even as delivery systems for adjunct growth factor therapy.

Animals↗

PubMed2004

Surface-induced dissociation of ions produced by matrix-assisted laser desorption/ionization in a fourier transform ion cyclotron resonance mass spectrometer.

Intermediate pressure matrix-assisted laser desorption/ionization (MALDI) source was constructed and interfaced with a 6-T Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR MS) specially configured for surface-induced dissociation (SID) studies. First MALDI-SID results in FT-ICR are presented, demonstrating unique advantages of SID over conventional FT-ICR MS ion activation techniques for structural characterization of singly protonated peptide ions. Specifically, we demonstrate that SID on a diamond surface results in a significantly better sequence coverage for singly protonated peptides than SORI-CID. A combination of two effects contributes to the improved sequence coverage: shattering of peptide ions on surfaces opens up a variety of dissociation channels at collision energies above 40 eV, and second, wide internal energy distribution deposited by collision with a stiff diamond surface provides an efficient mixing between the primary reaction channels that are dominant at low internal energies and extensive fragmentation at high internal excitation that results from shattering. Activation of MALDI-generated ions by collisions with surfaces in FT-ICR MS is a new powerful method for characterization and identification of biomolecules

Journal Article↗

PubMed2006

The effects of the Maillard reaction on the physical properties and cell interactions of collagen.

The non-enzymic glycation of collagen occurs as its turnover decreases during maturation, with complex carbohydrates accumulating slowly and the end-products of these reactions being permanent. The nature of these advanced glycation end-reaction products (AGEs) can be categorised as: 1) cross-linking: intermolecular cross-linking may occur between two adjacent molecules and involve lysine to lysine or lysine to arginine residues. Several compounds have been characterised. They are believed to be located between the triple helical domains of adjacent molecules in the fibre resulting in major changes of the physical properties, primarily, fibre stiffness, thermal denaturation temperature and enzyme resistance, all of which increase slowly with age but the rate is accelerated in diabetes mellitus due to high glucose levels: 2) side-chain modifications: these changes alter the charge profile of the molecule affecting the interactions within the fibre and if they occur at specific sites can affect the cell-collagen interaction. Modification of arginine within the sites RGD and GFOGER recognised by the two specific integrins (alpha1beta2 and alpha2beta1) for collagen reduce cell interactions during turnover and for platelet interactions (alpha1beta2). These changes can ultimately affect repair of, for example, vascular damage and dermal wound healing in diabetes mellitus. Both types of modification are deleterious to the optimal properties of collagen as a supporting framework structure and as a controlling factor in cell matrix interactions. Glycation during ageing and diabetes is therefore responsible for malfunctioning of the diverse collagenous tissues throughout the body.

Aging↗

PubMed2003

Long-term intermittent shear deformation improves the quality of cartilaginous tissue formed in vitro.

The formation of cartilaginous tissue in vitro is a promising alternative to repair damaged articular cartilage. However, recent attempts to tissue-engineer articular cartilage that has similar properties to the native tissue have proven to be difficult. The in vitro-formed cartilaginous tissue typically has a similar proteoglycan content to native cartilage, but has a reduced collagen content and only a fraction of the mechanical properties. In this study, we investigated whether the intermittent application of cyclic shearing forces during tissue formation would improve the tissue quality. Chondrocyte cultures were stimulated at a 2% shear strain amplitude at a frequency of 1 Hz for 400 cycles every 2nd day. At one week, both collagen and proteoglycan synthesis increased (23+/-6% and 20+/-6%, respectively) over the unstimulated, static controls. At four weeks, an increased amount of tissue formed (stimulated: 1.85+/-0.08, unstimulated: 1.58+/-0.07 mg dry wt.). This tissue contained approximately 40% more collagen (stimulated: 511+/-23, unstimulated: 367+/-24 microg/construct) and 35% more proteoglycans (stimulated: 376+/-21, unstimulated: 279+/-26 microg/construct). Tissues that formed in the presence of shearing forces also displayed a 3-fold increase in compressive load-bearing capacity (stimulated: 16+/-5, unstimulated: 5+/-1 kPa max. equilibrium stress) and a 6-fold increase in stiffness (stimulated: 112+/-36, unstimulated: 20+/-6 kPa max. equilibrium modulus) compared to the static controls. These results demonstrate that intermittent application of dynamic shearing forces over a four-week period improves the quality of cartilaginous tissue formed in vitro. Interestingly, low amplitudes of shear stimulation for short periods of time (6 min of stimulation applied every 2nd day) produced these changes.

Animals↗

PubMed1996

Pyridoxine deficiency affects biomechanical properties of chick tibial bone.

The mechanical integrity of bone is dependent on the bone matrix, which is believed to account for the plastic deformation of the tissue, and the mineral, which is believed to account for the elastic deformation. The validity of this model is shown in this study based on analysis of the bones of vitamin B6-deficient and vitamin B6-replete chick bones. In this model, when B6-deficient and control animals are compared, vitamin B6 deficiency has no effect on the mineral content or composition of cortical bone as measured by ash weight (63 +/- 6 vs. 58 +/- 3); mineral to matrix ratio of the FTIR spectra (4.2 +/- 0.6 vs. 4.5 +/- 0.2), line-broadening analyses of the X-ray diffraction 002 peak (beta 002 = 0.50 +/- 0.1 vs. 0.49 +/- 0.01), or other features of the infrared spectra. In contrast, collagen was significantly more extractable from vitamin B6-deficient chick bones (20 +/- 2% of total hydroxyproline extracted vs. 10 +/- 3% p < or = 0.001). The B6-deficient bones also contained an increased amount of the reducible cross-links DHLNL, dehydro-dihydroxylysinonorleucine, (1.03 +/- 0.07 vs. 0.84 +/- 0.13 p < or = 0.001); and a nonsignificant increase in HLNL, dehydro-hydroxylysinonorleucine, (0.51 +/- 0.03 vs. 0.43 +/- 0.03, p < or = 0.10). There were no significant changes in bone length, bone diameter, or area moment of inertia. In four-point bending, no significant changes in elastic modulus, stiffness, offset yield deflection, or fracture deflection were detected. However, fracture load in the B6-deficient animals was decreased from 203 +/- 35 MPa to 151 +/- 23 MPa, p < or = 0.01, and offset yield load was decreased from 165 +/- 9 MPa to 125 +/- 14 MPa, p < or = 0.05. Since earlier histomorphometric studies had demonstrated that the B6-deficient bones were osteopenic, these data suggest that although proper cortical bone mineralization occurred, the alterations of the collagen resulted in changes to bone mechanical performance.

Animals↗

PubMed1985

Properties of microfilled composite resins as influenced by filler content.

Two series of composite resins were prepared with a light-cured urethane dimethacrylate matrix to which varying amounts of two types of silanated silica particles were added. One series contained volume fractions ranging from 15.8 to 28.8% silica particles of 20 nm in diameter (Type I filler) and the other series volume fractions of from 24 to 49.4% of an agglomerated silica particle of 40 nm in diameter (Type II filler). Tests were conducted to determine the effect of filler level on: depth of cure as determined by hardness measurements; color stability in both UV light and water; water sorption with time; hardness; compressive strength; strain behavior in slow compression; and resistance to toothbrush abrasion and wear by hydroxyapatite. Analysis of the data obtained for these two microfilled series indicate that increased filler levels result in trends for increased depth of cure, color stability, hardness, compressive strength, and stiffness, while water sorption and resistance to both toothbrush abrasion and wear by hydroxyapatite were reduced. These trends were more pronounced for the Type II filler series than for the Type I filler series. However, there was a greater differential in filler levels within the Type II series than within the Type I series.

Acrylates↗