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PubMed1993

Effects of nasal allergen challenge on dynamic viscoelasticity of nasal mucus.

The effects of nasal provocation on the rheologic properties of nasal mucus were investigated in patients with allergic rhinitis provoked by house dust. The elastic modulus (G') and the dynamic viscosity (eta') of nasal mucus were determined by an oscillating sphere magnetic rheometer. Before and after the allergen challenge, G' increased, whereas eta' decreased with increasing oscillatory frequency; these findings indicate that the nasal mucus under these conditions is a non-newtonian fluid and has the cross-linked gel-like nature typical of mucus. Both G' and eta' values after nasal provocation were significantly lower than before. The values of G' and eta' after allergen challenge were in the optimal viscoelasticity range for mucociliary transport.

Adolescent↗

PubMed1999

Dental composite resins containing silica-fused ceramic single-crystalline whiskers with various filler levels.

Currently available direct-filling composite resins are susceptible to fracture and hence are not recommended for use in large stress-bearing posterior restorations involving cusps. The glass fillers in composites provide only limited reinforcement because of the brittleness and low strength of glass. The aim of the present study was to use ceramic single-crystalline whiskers as fillers to reinforce composites, and to investigate the effect of whisker filler level on composite properties. Silica particles were fused onto the whiskers to facilitate silanization and to roughen the whiskers, thereby improving retention in the matrix. The composite flexural strength, elastic modulus, hardness, and degree of polymerization conversion were measured as a function of whisker filler mass fraction, which ranged from 0% to 70%. Selected composites were polished simulating clinical procedures, and the surface roughness was measured with profilometry. The whisker composite with a filler mass fraction of 55% had a flexural strength (mean +/- SD; n = 6) of 196+/-10 MPa, significantly higher than 83+/-14 MPa of a microfill and 120+/-16 MPa of a hybrid composite control (family confidence coefficient = 0.95; Tukey's multiple comparison). The composite modulus and hardness increased monotonically with filler level. The flexural strength first increased, then plateaued with increasing filler level. The degree of conversion decreased with increasing filler level. The whisker composite had a polished surface roughness similar to that of a conventional hybrid composite (p>0.1; Student's t). To conclude, ceramic whisker reinforcement can significantly improve the mechanical properties of composite resins; the whisker filler level plays a key role in determining composite properties; and the reinforcement mechanisms appear to be crack pinning by whiskers and friction from whisker pullout resisting crack propagation.

Ceramics↗

PubMed2006

Multifunctional Ti-(Ca,Zr)-(C,N,O,P) films for load-bearing implants.

Films of Ti-Ca-P-C-O-(N), Ti-Ca-C-O-(N) and Ti-Zr-C-O-(N) were deposited by DC magnetron sputtering or ion implantation-assisted magnetron sputtering of composite targets TiC0.5 + 10%Ca10(PO4)6(OH)2, TiC0.5 + 20%(CaO + TiO2) and TiC0.5 + 10%ZrO2 in an Ar atmosphere or reactively in a gaseous mixture of Ar + 14%N2. The microstructure, elemental and phase composition of films were studied by means of X-ray diffraction, transmission electron microscopy, scanning force microscopy, X-ray photoelectron spectroscopy and energy-dispersive X-ray spectroscopy. The films were characterized in terms of their hardness, Young's modulus, elastic recovery, adhesion strength, and friction and wear both in air and under physiological solution. Particular attention was paid to the analysis of deformation and fracture for various film/substrate systems during scratch testing. The biocompatibility of the films was evaluated by both in vitro and in vivo experiments. In vitro studies involved the investigation of adhesion, spreading, and proliferation of MC3T3-E1 osteoblasts and IAR-2 epithelial cells, morphometric analysis, actin cytoskeleton, focal contacts staining, alkaline phosphatase activity and von Kossa staining of osteoblastic culture. Cell culture experiments demonstrated an increase of osteoblastic proliferation on Ca- and P-incorporated films. In vivo studies were fulfilled by subcutaneous implantation of Teflon plates coated with the tested films in mice and analysis of the population of adherent cells on their surfaces. The results obtained show that multicomponent nanostructured Ti-(Ca, Zr)-(C, N, O, P) films possess a combination of high hardness, wear resistance and adhesion strength, reduced Young's modulus, low friction coefficient and high biocompatibility.

3T3 Cells↗

PubMed2004

The effect of hot pressing on the physical properties of glass reinforced hydroxyapatite.

Hydroxyapatite (HA), being of physiological importance, can be developed synthetically for implant application. A number of avenues have been explored in order to improve the physical and biological properties of a variety of hydroxyapatite composites. However, the fact remains, hydroxyapatite lacks the mechanical properties needed to sustain high loads. This study investigates the advantages of hot pressing on the physical properties of HA and glass reinforced HA (GR-HA). The results show a significant enhancement in the mechanical properties of GR-HA composites compared to HA e.g. flexural bending strength values were given at 91.75 and 88.87 M Nm(-2) for GR-HA (CP15F) and GR-HA (CP20F) respectively, compared to 78.9 M Nm(-2) for HA. The results for other properties such as elastic modulus, fracture toughness, Vicker's hardness, density and porosity also demonstrate the benefit of adding phosphate based glasses as a sintering aid. This is supported by XRD analysis, highlighting the presence of a secondary phase (beta-TCP) in GR-HA systems and the positive effect it has on the physical properties. It must be brought to attention that densification of hot pressed HA and GR-HA composites is reached at a lower temperature compared to a previous study on the same materials that have undergone pressureless sintering.

Biocompatible Materials↗

PubMed1997

Pregnancy-associated changes in material properties of the third metacarpal cortical bone in mares.

OBJECTIVE: To investigate the effect of late gestation, age, and parity on material properties of third metacarpal (MCIII) cortical bone in mares. ANIMALS: 8 healthy mares (treatment group) that died or were euthanatized within 24 hours after parturition because of foaling complications and 6 age-matched, healthy, nonpregnant mares (control group). PROCEDURES: After random assignment for mechanical testing and microradiography, the dorsal half of transverse mid-diaphyseal sections of each MCIII bone was divided into lateral, dorsal, and medial regions. Cylinders of bone from each of the 3 regions were tested in compression in a single cycle to failure. Contact microradiographic views were taken of 100-microns-thick sections prepared from methylmethacrylate-embedded transverse dorsal region specimens, which were further divided into periosteal, intracortical, and endosteal regions for assessment of bone mineral density and porosity. RESULTS: Postpartum mares had lower yield strain in the dorsal and medial regions and failure strain in the medial region. Increasing parity was associated with decreasing elastic modulus in the dorsal region and yield stress and failure stress in the lateral region. Age and parity were positively correlated (r = 0.865; P = 0.0001), but significant correlations were not found between treatment group and age or between treatment group and parity. Increasing age and parity were associated with increasing porosity in the periosteal region. CONCLUSIONS AND CLINICAL RELEVANCE: On the basis of the material properties evaluated for MCIII cortical bone in late pregnancy, any increased risk for fractures in mares in late gestation may be related to parity or age or both, and less likely to pregnancy pese.

Aging↗

PubMed2002

Micromechanical studies of mitotic chromosomes.

We review micromechanical experiments on mitotic chromosomes. We focus on work where chromosomes were extracted from prometaphase amphibian cells, and then studied by micromanipulation and microfluidic biochemical techniques. These experiments reveal that chromosomes have well-behaved elastic response over a fivefold range of stretching, with an elastic modulus similar to that of a loosely tethered polymer network. Perturbation by microfluidic 'spraying' of various ions reveals that the mitotic chromosome can be rapidly and reversibly decondensed or overcondensed, i.e. that the native state is not maximally compacted. Finally, we discuss microspraying experiments of DNA-cutting enzymes which reveal that the element which gives mitotic chromosomes their mechanical integrity is DNA itself. These experiments indicate that chromatin-condensing proteins are not organized into a mechanically contiguous 'scaffold', but instead that the mitotic chromosome is best thought of as a cross-linked network of chromatin. Preliminary results from restriction-enzyme digestion experiments indicate a spacing between chromatin 'cross-links' of roughly 15 kb, a size similar to that inferred from classical chromatin-loop-isolation studies. We compare our results to similar experiments done by Houchmandzadeh and Dimitrov (J Cell Biol 145: 215-213 (1999)) on chromatids reconstituted using Xenopus egg extracts. Remarkably, while the stretching elastic response of the reconstituted chromosomes is similar to that observed for chromosomes from cells, the reconstituted chromosomes are far more easily bent. This result suggests that reconstituted chromatids have a large-scale structure which is quite different from chromosomes in somatic cells. More generally our results suggest a strategy for the use of micromanipulation methods for the study of chromosome structure.

Animals↗

PubMed2006

Histological and biomechanical evaluation of implanted graft materials in a rabbit vaginal and abdominal model.

OBJECTIVE: The objective of the study was to describe the histologic and biomechanical changes of implanted dermal collagen graft materials. STUDY DESIGN: Twenty rabbits were randomized into 2 groups (6 and 12 weeks, respectively). Each rabbit had 4 graft segments (human dermis, porcine dermis, porcine collagen-coated polypropylene mesh, and autologous fascia) randomly implanted into the abdomen and the vagina. Biomechanical testing and histologic analysis was performed after recovery of graft segments. RESULTS: Dermal graft segments showed a marked decrease in ultimate strength (84% to 86%) and elastic modulus (73% to 82%) that was significantly different from the decrease seen in autologous fascia or coated synthetic mesh (P < .0008 and P < .0001, respectively). The decrease in ultimate strength was associated with vaginal implantation (P = .057). Dermal graft materials had moderate inflammation and minimal collagen infiltration. CONCLUSION: The mechanical properties of dermal graft materials decline after implantation. Vaginal implantation may cause a different tissue response to graft material than abdominal implantation. Dermal graft material caused moderate inflammation and minimal collagen ingrowth remote from implantation.

Abdomen↗

PubMed2002

Mechanical properties of skeletal bone in gene-mutated stöpsel(dtl28d) and wild-type zebrafish (Danio rerio) measured by atomic force microscopy-based nanoindentation.

An atomic force microscopy (AFM)-based nanoindenter was used to evaluate the mechanical properties of skeletal bones in wild-type and gene-mutated zebrafish (Danio rerio), stöpsel(dtl28d). Both skeletons were isolated from adult zebrafish and tested under a load of 5 mN. It was found that stp/stp bone has a similar nanohardness but significantly greater elastic modulus compared with that of wild-type bone. The residual indenter impressions using AFM and the fracture surfaces of both bones using scanning electron microscopy were examined and showed that the bone of zebrafish becomes more brittle after the stp mutation. This first observation of the alteration of bone mechanical behavior by gene mutation in zebrafish system is of scientific and clinical relevance to many areas of study, such as bone fracture and fragility mechanisms in human heritable disorders and bone-materials fabrication via gene engineering.

Animals↗

PubMed1996

Fracture of articular cartilage.

Crack formation and propagation is a significant element of the degeneration process in articular cartilage. In order to understand this process, and separate the relative importance of structural overload and material failure, methods for measuring the fracture toughness of cartilage are needed. In this paper, two such methods are described and used to measure fracture properties of cartilage from the canine patella. A modified single edge notch (MSEN) specimen was used to measure J, and a trouser tear test was used to measure T, both measures of fracture toughness with units of kN/m. A pseudo-elastic modulus was also obtained from the MSEN test. Several potential error sources were examined, and results for the MSEN test compared with another method for measuring the fracture parameter for urethane rubber. Good agreement was found. The two test methods were used to measure properties of cartilage from the patellae of 12 canines: 4-9 specimens from each of 12 patellae, with 5 right-left pairs were tested. Values of J ranged from 0.14-1.2 kN/m. J values correlated with T and were an average of 1.7 times larger than T. A variety of failure responses was seen in the MSEN tests, consequently a grade of 0 to 3 was assigned to each test, where 0 represented a brittle-like crack with minimal opening and 3 represented plastic flow with no crack formation. The initial cracks in 12/82 specimens did not propagate and were assigned to grade 3. The method for reducing data in the MSEN test assumed pseudo-elastic response and could not be used for the grade 3 specimens. Stiffness did not correlate with J. Neither J nor T was statistically different between right-left pairs, but varied between animals. The test methods appear useful for providing a quantitative measure of fracture toughness for cartilage and other soft materials.

Animals↗

PubMed1995

Surfactant incorporation markedly alters mechanical properties of a fibrin clot.

Intra-alveolar clot formation is a common finding in acute and chronic inflammatory lung diseases. Incorporation of lipophilic surfactant components into a growing fibrin clot has recently been reported (Am. J. Respir. Cell Mol. Biol. 1993; 9:213-220). In the present study, we investigated the influence of such surfactant incorporation on the elastic properties and water permeability of the fibrin polymer. Thrombelastography and compaction experiments were employed for assessment of the elastic properties, and the permeability characteristics of the clot material were addressed in fibrin-packed columns. Two calf lung surfactant extracts (CLSE and Alveofact), Curosurf, and a synthetic phospholipid mixture (dipalmitoylphosphatidylcholine, phosphatidylglycerol, and palmitic acid at a ratio of 68.5:22.5:9 [wt/wt]) were used. The presence of surfactant did not affect the cleavage of fibrinopeptide A upon incubation of fibrinogen with thrombin (enzyme-linked immunosorbent assay technique). Similarly, kinetics and extent of factor XIII-induced covalent crosslinkage of the fibrin network remained unchanged in the presence of surfactant (sodium dodecyl sulfate polyacrylamide gel electrophoresis and D-Dimer quantification upon subsequent clot lysis). All surfactants, however, dose-dependently decreased the elastic modulus of the arising fibrin polymer. The maximal amplitude in thrombelastography was reduced, and the recovery of fluid after centrifugation of the fibrin clot increased. Fibrin clots embedding natural surfactant material displayed reduced permeability for saline as compared with control fibrin polymers. Subsequent washout of lipids from these clots with Triton X-100 resulted in increased hydraulic conductivity. This was accompanied by an increase in pore size, suggesting altered architecture of the fibrin matrix generated in the presence of surfactant.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1998

Influence of plasticizers on tableting properties of polymers.

This study relates tablet formation with relaxation properties of two polymers on the basis of the stress-deformation curve. The mechanical properties of the polymers were varied by changing tableting temperature, adding varying amounts of plasticizer, and incorporating a monomer with plasticizer effect on the polymer chain. The crucial parameter appeared to be the difference between the glass transition temperature and the tableting temperature. This temperature difference was found to determine the amount of energy stored during densification. The energy is manifested as the stress relaxation propensity of the material. Large stress relaxation yields porous and consequently weak tablets. At a low temperature difference (i.e., tableting temperature is much lower than the glass transition temperature), the amount of stored energy is large. An increase in tableting temperature, or a decrease in glass transition temperature, yields a decrease in stored energy as a result of a decrease in yield strength. Consequently, production of less porous and stronger tablet is possible. However, if the tableting temperature is higher than the glass transition temperature, the stress relaxation propensity of the deformed polymers is extremely high because the elastic modulus of the materials is low under these circumstances. This results is porous and even capped tablets. From the data it is concluded that, independent of the type of polymer and the method of plasticizing, compaction at a temperature of about 20 K under the glass transition temperature yields circumstances for which the amount of stored energy has a minimum. Consequently, tablet porosity has a minimum and tablet strength has a maximum. These circumstances are created by changing both the tableting temperature and the glass transition temperature of the powder.

Algorithms↗

PubMed1989

Properties of a glass-ionomer/resin-composite hybrid material.

A small percentage of the liquid resin used in commercial dental composites was added to the liquid used in a commercial glass-ionomer restorative in order to produce a fluoride-containing hybrid restorative-type material that would adhere to dentin while being stronger, less brittle, and less sensitive to desiccation in the oral cavity than glass ionomer. Compressive strength, yield strength, elastic modulus, fracture toughness, and tensile strength were analyzed for this hybrid, light-cured material. In addition, the solubility in water, adhesion to dentin, and surface roughness were also examined in vitro. The results suggest that the early (one-hour) mechanical properties of the hybrid material exceed those of glass ionomer. In addition, the brittleness and solubility of the material are less than those of commercial glass ionomer, while adhesion to dentin is unaffected. Most importantly, surface crazing, a documented problem with some glass ionomers when they become desiccated, is alleviated with this hybrid formulation.

Composite Resins↗

PubMed2005

Biosynthetic hydrogel scaffolds made from fibrinogen and polyethylene glycol for 3D cell cultures.

Tissue engineering scaffolds are fabricated from either biological materials, which provide biofunctional signals and interact well with cells, or from synthetic polymers, which provide precise control over their structural properties. We describe a biosynthetic hybrid scaffold comprised of a fibrinogen backbone and crosslinked with difunctional polyethylene glycol (PEG) side chains. Denatured fibrinogen fragments are PEGylated with PEG-diacrylates, mixed with photoinitiator and exposed to UV light to form a hydrogel material in the presence of a cell suspension. This unique hydrogel material provides a distinct advantage over other scaffold materials because its mechanical properties are highly malleable while the biological functionality is maintained by the backbone of the polymeric network. The elastic modulus of the PEG-fibrinogen hydrogel is dependent on the molecular weight of the PEG constituent and proportional to the percent polymeric composition. The biological domains in the fibrinogen backbone provide attachment motifs for endothelial cell and smooth muscle cell adhesion as well as proteolytic sensitivity for biodegradation. Smooth muscle cells demonstrate the ability to proteolytically penetrate through the hydrogel material and form interconnecting networks of cells. Our efforts to develop novel biodegradable scaffolds for cultivating cells in a 3D environment are beneficial for tissue regeneration therapies.

Absorbable Implants↗

PubMed2002

Effect of bone graft characteristics on the mechanical behavior of the lumbar spine.

There is little information about the influence of bone graft size, position and elasticity on the mechanical behavior of the lumbar spine. Intersegmental motion, intradiscal pressure and stresses in the lumbar spine were calculated using a three-dimensional, nonlinear finite element model which included an internal spinal fixation device and a bone graft. Cross-sectional area, position, and elastic modulus of the graft were varied in this study. Bone grafts, especially very stiff ones, increase stresses on adjacent endplates. Though larger grafts lead to less contact pressure, it is difficult to judge the quality of different bone graft positions. In general, ventral flexion results in lower maximum contact pressure than lateral bending. There is always little intersegmental rotation in the bridged region compared with that of an intact spine.A larger graft with low stiffness should be favored from a mechanical point of view. Patients should avoid lateral bending of the upper body shortly after surgery.

Biomechanical Phenomena↗

PubMed2001

Comparative rheological behavior of hyaluronan from bacterial and animal sources with cross-linked hyaluronan (hylan) in aqueous solution.

Using a variety of rheological techniques, the behavior of hyaluronan (M(w) 0.8-2.2 x 10(6)), cross-linked hyaluronan (hylan) (M(w) 1.8-12.5 x 10(6)), and Healon (M(w) approximately 5 x 10(6)) (a proprietary hyaluronan) was studied over a large range of molecular weights. The object was to study the effect of the cross-links in hylan on the various rheological parameters, in comparison with linear hyaluronan. There are significant differences. The Huggins constant and the critical overlap parameter C*[eta] are considerably lower for hylan and an increase in moduli at low frequencies was observed for hylan compared with the hyaluronan samples at all molecular weights studied. The results point to a difference in structure in dilute solution for hylan due to the ability to form networks, which can be removed by pressure filtration. In contrast, we do not find an increase of the steady shear viscosity and elastic modulus at higher concentrations when a homogeneous entangled network is reached. We attribute this behavior to the semirigid character of the hyaluronan chain and to the predominance of entanglements over the cross-link points present in hylan in the semidilute domain. Due to the higher apparent molecular weights that are possible with hylan structures but not with the hyaluronans currently available, a wider range of applications can be achieved with hylans when viscoelasticity is required, particularly for the viscosupplementation of synovial fluid damaged by osteoarthritis.

Animals↗

PubMed1990

Mechanical properties of mammalian single smooth muscle cells. III. Passive properties of pig detrusor and human a terme uterus cells.

Cells isolated from pig urinary bladders and pregnant full term human uteruses were attached longitudinally between a microforce transducer and a length displacement apparatus. Cells were stretched by applying a series of ramp-like length changes of 0.2 s duration and 10.0 microns amplitude at intervals of 15 min. Passive forces upon straining were as high as 70-100 microNs. Following these peak forces stress relaxation occurred, levelling off approximately 50% of the maximum peak force. The maximum elastic modulus estimated for single cells was found to be at least a tenfold higher than was previously estimated from intact bladder strips. The relation between the increase in length and the increase in initial force increment was found to be approximately linear. An exponential equation was fitted to a selected number of stress relaxation curves. Relaxation curves of bladder cells show a clearly different time course as compared to bladder tissue strips, suggesting that a significant amount of relaxation in strips has to be contributed to the connective tissue components or to structural changes in these strips.

Animals↗

PubMed2004

Heterogeneous nanomechanical properties of superficial and zonal regions of articular cartilage of the rabbit proximal radius condyle by atomic force microscopy.

Articular chondrocytes have been thought to reside in a homogenous matrix. The physical characteristics of the intercellular matrix of articular cartilage are not well characterized, especially at a nanoscopic scale. The present work tested the hypothesis that the nanomechanical properties of the intercellular matrices of articular cartilage in both the articulating surface and various cellular zones are non-homogeneous. Nanoindentation by atomic force microscopy was applied to the geometric center of the medial, lateral and groove regions of the superficial zone of the rabbit proximal radius cartilage, and then the intercellular matrices of chondrocytes from the superficial to calcifying zones in 40 microm increments. The elastic modulus of the articular surface of the medial condyle (1.46+/-0.11 MPa) was significantly higher than the lateral condyle (1.18+/-0.10 MPa), and the groove (0.96+/-0.07 MPa). There is a significant gradient increase in Young's moduli from the superficial zone (0.52+/-0.05 MPa) to calcifying zone (1.69+/-0.12 MPa). Thus, the nanomechanical properties of the intercellular matrices of the articulating surface are region-specific and likely related to articular function. Heterogeneous biophysical properties of intercellular matrices along the depth from the superficial to calcifying zones suggest that chondrocytes likely reside in a heterogeneous matrix.

Animals↗

PubMed2006

Carotid intima-media thickness is increased and related to arterial stiffening in patients with beta-thalassaemia major.

An increased iron store has been linked to the risk of atherosclerosis. The carotid intima-media thickness (IMT), stiffness index, Young's elastic modulus (YEM), and augmentation index were determined in 20 patients with beta-thalassaemia major. Compared with controls, patients had greater IMT (P < 0.001), YEM (P = 0.005), and stiffness (P = 0.009) and augmentation (P = 0.03) indices. The odds ratio for increased IMT in patients was 39. Carotid IMT correlated with YEM (P = 0.036), stiffness index (P = 0.036) and augmentation index (P = 0.006). Multivariate analysis identified patient status (P < 0.001) as the only significant determinant of IMT. These findings suggest the possibility of premature atherosclerosis in beta-thalassaemia major patients.

Adult↗