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PubMed1996

Experimental and theoretical quantification of the development of damage in fatigue tests of bone and antler.

This study concerns the development of damage (as measured by a reduction in elastic modulus) in two kinds of bones differing considerably in their degrees of mineralisation: laminar bone from bovine femur and osteonal bone from red deer antler. Antler bone is much tougher than 'ordinary' bone and its failure properties have been investigated in: (i) monotonic tensile tests and (ii) creep rupture experiments. Tensile fatigue is another way of examining how damage develops in bone. The development of damage in the present fatigue tests was non-linear with the cycle number, the degree of non-linearity was dependent on the level of stress and followed a clearly different course for bone and antler. Antler was a more damage-tolerant material, being able to achieve a reduction in the final modulus of elasticity, just prior to failure, three times greater than 'ordinary' bone. The evolution of damage is quantified by an empirical and a graphical method and by the use of Continuum Damage Mechanics (CDM) expressions. The CDM method shows important conditions, found in antler, but not in bone, that seen necessary for achieving stable fractures and consequently producing very tough materials.

Animals↗
PubMed1995

Compaction assay: a rapid and simple in vitro method to assess the responsiveness of a biopolymer matrix to enzymatic modification.

A rapid and simple in vitro method is described which measures the extent of unrecoiled solids compression when a complex biopolymer is subjected to a centrifugal force. This method, termed the compaction assay, was used to assess the response of purulent cystic fibrosis (CF) sputum samples to the addition of recombinant human deoxyribonuclease I (rhDNase). Enzyme treatment resulted in a dramatic decrease in DNA size, a redistribution of total DNA content from the pellet to supernatant, a significant decrease in that pellet volume and a decrease in elastic modulus. Sample elasticity, measured by a dynamic cone and plate viscometer, could be related to compaction assay results. These results suggest that the compaction assay may be a useful in vitro method for rapidly assessing the actions of enzymatic disruption of a complex biopolymer, such as that observed for the actions of rhDNase on purulent airway secretions.

Biocompatible Materials↗
PubMed2004

Deformation mechanisms in free-standing nanoscale thin films: a quantitative in situ transmission electron microscope study.

We have added force and displacement measurement capabilities in the transmission electron microscope (TEM) for in situ quantitative tensile experimentation on nanoscale specimens. Employing the technique, we measured the stress-strain response of several nanoscale free-standing aluminum and gold films subjected to several loading and unloading cycles. We observed low elastic modulus, nonlinear elasticity, lack of work hardening, and macroscopically brittle nature in these metals when their average grain size is 50 nm or less. Direct in situ TEM observation of the absence of dislocations in these films even at high stresses points to a grain-boundary-based mechanism as a dominant contributing factor in nanoscale metal deformation. When grain size is larger, the same metals regain their macroscopic behavior. Addition of quantitative capability makes the TEM a versatile tool for new fundamental investigations on materials and structures at the nanoscale.

Journal Article↗
PubMed2002

Carotid and femoral artery stiffness in Takayasu's arteritis. An ultrasound study.

PURPOSE: To determine the stiffness of large arteries in patients with Takayasu's arteritis (TA). MATERIALS AND METHODS: A noninvasive ultrasonic method was used to measure Peterson's elastic modulus (Ep), Young's elastic modulus (YM). and the stiffness constant beta of the common carotid arteries in 13 and of the common femoral arteries in 16 patients with TA and in healthy control subjects. RESULTS: The median carotid artery Ep, YM, and stiffness index beta were statistically significantly higher in patients with TA than in controls (p=0.019, 0.013, and 0.004, respectively). The median femoral artery Ep and YM were also higher in patients with TA than in controls (p=0.005 and 0.039, respectively), and the stiffness constant beta (p=0.127) also tended to be higher in patients with TA relative to healthy persons. CONCLUSIONS: Carotid artery compliance is strongly diminished in patients with TA. A comparable but somewhat less conspicuous change is seen in the femoral arteries.

Adult↗
PubMed1985

Structural implications of basilar membrane compliance measurements.

Static point-load measurements of basilar membrane compliance were made in the basal region of the excised guinea pig cochlea. Points on a radial line across the basilar membrane were displaced in one-half micron increments and the force required to maintain each increment recorded. The results are interpreted in terms of the material layers of the basilar membrane and displayed as compliance curves. In addition, a beam model of the basilar membrane, including the arches of Corti and the actual geometry of the pectinate zone, is constructed from anatomical data. The free parameters in this model are the modulus of elasticity of the transverse filaments and the effective spring stiffness of the arches. Compliance curves for the model are generated with a finite element approach and the parameters are obtained by requiring optimal agreement with the experimental measurements. The results show that the separation between fiber layers in the pectinate zone is relevant to the effective moment of inertia of the cross section and that the longitudinal coupling between the heads of the arches provides a rigidity to the arcuate zone not seen in the pectinate zone where longitudinal coupling is minimal. The elastic modulus calculated for the filaments is 1.8 GPa, approximately one-half that of keratin, while the cells and ground substance are five orders of magnitude softer.

Animals↗
PubMed2002

A caffeine diet can alter the mechanical properties of the bones of young ovariectomized rats.

The general public widely consumes caffeine which is contained in various foods, beverages, and over-the-counter medications. The relationships between caffeine intake and bone fractures is controversial. Therefore, the aim of the current study was to determine what effects, if any, caffeine intake in early life exerts on mechanical properties and mineral contents of bone in growing ovariectomized rats. A total of 8 dams with pups were divided into two groups. Group 1 was fed a 20% protein diet. Group 2 was fed a 20% protein diet supplemented with caffeine (4 mg/100 g). The respective diets were fed to the dams during lactation and to the pups continuously after weaning on day 22 until the end of the experimental period. On day 32, offspring from both groups were ovariectomized. On day 52, the rats were sacrificed and the femora removed. The biomechanical properties of the femora were determined by three-point bend testing to failure at a rate of 2 mm/min, with continuous data sampling at 10 samples/s. The properties determined included the modulus of elasticity, yield load, yield stress, ultimate load, ultimate stress, and the second moment of area. The caffeine group exhibited a decrease in the various mechanical properties (ranging from approximately 7 to 20%), except for yield strain and moment of inertia. The decreases in maximum stress and elastic modulus values were significant. Calcium, magnesium, and phosphorous values for the caffeine group were significantly decreased. These results suggest that the bone in the caffeine group is weaker and less stiff, with greater deformation under applied loading. It could be concluded that caffeine intake during the early growing period affects the mechanical properties of bone.

Animals↗
PubMed1981

Alterations in stress distributions around interalveolar pores after exposure to papain in dogs.

Electron microscopic examination of dog lungs after exposure to papain for as little as 30 min showed removal of surfactant material from the pores of Kohn, and significant enlargement of the pores. We analyzed these early events in terms of structural mechanics, and concluded that: (1) The approximate doubling of the average diameter indicates a lowering of the effective modulus of elasticity in the vicinity of the pores to less than 50% of its original value, which is consistent with the destruction of elastin. (2) The removal of the surfactant material, which normally occludes the pores, results in the loss of the force caused by surface tension, which normally acts at the rim of the pore, and alleviates maximal tissue stress. This lost force can result in a stress increase on the elastin by as much as 20 to 30% of its strength. (3) The whole lung volume pressure deflation curves obtained in hamsters after exposure to papain show a significant increase in compliance associated with papain treatment. Degradation in the elastic modulus of the tissue, caused by the papain, contributes to such an increase. On the other hand, surface tension measurements from canine lung extracts after exposure to papain yield results that should contribute to a decrease in compliance. Because papain treatment destroys the continuity of the lining layer, this contribution is minimized, and the effect on the tissue dominates, resulting in a net increase in compliance.

Animals↗
PubMedDate not supplied

A biomechanical analysis of matched bone-patellar tendon-bone and double-looped semitendinosus and gracilis tendon grafts.

Biomechanical testing was done on 15 matched pairs of central-third bone-patellar tendon-bone and double-looped semitendinosus-gracilis grafts harvested from 15 cadaveric knees. Load to failure, composite graft stiffness, and the modulus of elasticity were calculated for each graft. Specimens were from 2 female and 13 male donors (average age, 40 years; range, 17 to 53). Average load to failure for the patellar tendon grafts was 1784 N (+/- 580), compared with 2422 N (+/- 538) for the hamstring tendon grafts (significantly different). There was no statistically significant difference in stiffness between grafts (patellar tendon, 210 N/mm; hamstring tendon, 238 N/mm). The elastic modulus was 225 MPa (+/- 129) for the patellar tendon grafts and 145 MPa (+/- 58) for the hamstring tendon grafts (significantly different). The average cross-sectional area for the hamstring tendon grafts was 57 mm2, compared with the 45 mm2 for the patellar tendon grafts. The hamstring tendon grafts were significantly stronger than the matched central-third patellar tendon grafts, but the two grafts were similar in stiffness. The patellar tendon grafts had a higher modulus than the hamstring tendon grafts.

Adult↗
PubMed1996

The creep behavior of acrylic denture base resins.

The creep behavior of acrylic dental base resins, at room temperature and at different loading conditions, has been examined. The behaviors of these resins are similar to that of "commercial perspex" at room temperature over a period of 1000 seconds. The pseudo-elastic moduli of the blends of PMMA VC show a significant increase compared with PMMA alone. The addition of the PVC powder to the heat-cured acrylic resin increased the time-dependent elastic modulus. This increase in elastic modulus is advantageous in the production of denture based resins of improv mechanical properties.

Acrylic Resins↗
PubMed1995

Titanium as the material of choice for cementless femoral components in total hip arthroplasty.

Modern total hip arthroplasty has been performed using femoral stems manufactured from stainless steel, cobalt-chrome molybdenum alloy (CoCrMb), titanium aluminum vanadium alloy (TiAlV), and, on a limited basis, low-elastic modulus composites. Today, only CoCrMb and TiAlV are used in significant numbers. There is ample theoretical, experimental, and clinical evidence to support Ti-AlV as the material of choice for cementless femoral stems, based on superior mechanical compatibility and biocompatibility. The primary advantage of TiAlV over CoCrMb is a lower modulus of elasticity. This results in decreased stress shielding and subsequent favorable femoral remodeling. This effect is more significant with the smaller stem sizes used in primary surgery but persists even with larger stem sizes used in revision surgery. The second advantage of TiAlV is its biocompatibility. Titanium aluminum vanadium alloy is of relatively low toxicity in concentrations found clinically, and TiAlV is inert in the physiologic environment. With regard to fixation in cementless total hip arthroplasty, TiAlV has been shown to achieve excellent bone ingrowth into porous surfaces. In addition, there is evidence of superior bony ingrowth into TiAlV as compared with CoCrMb. Titanium aluminum vanadium alloy is presently the material of choice to be used in conjunction with hydroxyapatite coating. Prosthetic design, stem diameter, and porous-coating applications play significant roles in bony response regardless of metal composition.

Biocompatible Materials↗
PubMed2000

Evaluation of mucoadhesion for two polyelectrolyte gels in simulated physiological conditions using a rheological method.

A rheological method to measure mucoadhesion was evaluated for two ion-sensitive polymers, Carbopol 934 and Gelrite((R)) (deacetylated gellan gum), in a simulated physiological environment using two commercially available mucins. The method simulates the interpenetration layer in the mucoadhesion process. The elastic modulus for a polymer/mucin mixture is compared with the elastic modulus for the polymer alone, and an increase in the elastic modulus for the mixture compared to the polymer is interpreted as a positive interaction caused by mucoadhesion. In this study the influence of polymer concentration, type of mucin and experimental rheological factors, such as gap width, were examined. The choice of polymer concentration was crucial, especially with the porcine gastric mucin. We found that one is more likely to obtain positive interactions with weak gels. It was also shown that the choice of mucin has a large influence on the results obtained. Carbopol 934 interacted more strongly with the bovine submaxillary gland mucin than with the porcine gastric mucin, whereas the gel structure of Gelrite((R)) was destroyed when mixed with the bovine mucin. Furthermore, it was concluded that with hydrogels consisting of gel particles (such as Carbopol 934), rheological measurements can give highly varying results, depending on, for example, the concentration and ion-sensitivity of the polymer, the quantity of ions present, as well as the gap width of the measuring system.

Acrylic Resins↗
PubMed2003

Biaxial flexural strength, elastic moduli, and x-ray diffraction characterization of three pressable all-ceramic materials.

STATEMENT OF PROBLEM: Before the release of an advanced ceramic material, independent assessment of its strength, elastic modulus, and phase composition is necessary for comparison with peer materials. PURPOSE: This study compared the biaxial flexural strength, elastic moduli, and crystalline phases of IPS Empress and Empress 2 with a new experimental ceramic. MATERIAL AND METHODS: Twenty standardized disc specimens (14 x 1.1 mm) per material were used to measure the biaxial strength. With a universal testing machine, each specimen was supported on 3 balls and loaded with a piston at a crosshead speed of 0.5 mm/min until fracture. Three standardized bars (30 x 12.75 x 1.1 mm) for each material were prepared and excited with an impulse tool. The resonant frequencies (Hz) of the bars were used to calculate the elastic moduli with the equation suggested by the standard ASTM (C 1259-94). X-ray diffraction with Cu Kalpha at a diffraction angle from 20 to 40 degrees was used to identify the crystalline phases by means of a diffractometer attached to computer software. The data were analyzed with 1-way analysis of variance followed by pairwise t tests (P<.05). RESULTS: Mean biaxial strengths were 175 +/- 32, 407 +/- 45, and 440 +/- 55 MPa for IPS Empress, Empress 2, and the experimental ceramic, respectively. Elastic modulus results were 65, 103, and 91 GPa for the same materials, respectively. There was no significant difference in strength and elastic modulus between Empress 2 and the experimental ceramic. Both materials demonstrated a significantly higher elastic modulus and strength than IPS Empress. X-ray diffraction revealed leucite as the main crystalline phase for IPS Empress and lithium disilicate for both Empress 2 and the experimental ceramic. CONCLUSION: Within the limitations of this study, the improved mechanical properties of Empress 2 and experimental ceramic over those of IPS Empress were attributed to the nature and amount of their crystalline content lithium disilicate.

Aluminum Silicates↗
PubMed1999

Viscoelastic properties of f-actin, microtubules, f-actin/alpha-actinin, and f-actin/hexokinase determined in microliter volumes with a novel nondestructive method.

A nondestructive method to determine viscoelastic properties of gels and fluids involves an oscillating glass fiber serving as a sensor for the viscosity of the surrounding fluid. Extremely small displacements (typically 1-100 nm) are caused by the glass rod oscillating at its resonance frequency. These displacements are analyzed using a phase-sensitive acoustic microscope. Alterations of the elastic modulus of a fluid or gel change the propagation speed of a longitudinal acoustic wave. The system allows to study quantities as small as 10 microliters with temporal resolution >1 Hz. For 2-100 microM f-actin gels a final viscosity of 1.3-9.4 mPa s and a final elastic modulus of 2.229-2.254 GPa (corresponding to 1493-1501 m/s sound velocity) have been determined. For 10- to 100-microM microtubule gels (native, without stabilization by taxol), a final viscosity of 1.5-124 mPa s and a final elastic modulus of 2.288-2. 547 GPa (approximately 1513-1596 m/s) have been determined. During polymerization the sound velocity in low-concentration actin solutions increased up to +1.3 m/s (approximately 1.69 kPa) and decreased up to -7 m/s (approximately 49 kPa) at high actin concentrations. On polymerization of tubulin a concentration-dependent decrease of sound velocity was observed, too (+48 to -12 m/s approximately 2.3-0.1 MPa, for 10- to 100-microM tubulin). This decrease was interpreted by a nematic phase transition of the actin filaments and microtubules with increasing concentration. 2 mM ATP (when compared to 0.2 mM ATP) increased polymerization rate, final viscosity and elastic modulus of f-actin (17 microM). The actin-binding glycolytic enzyme hexokinase also accelerated the polymerization rate and final viscosity but elastic modulus (2.26 GPa) was less than for f-actin polymerized in presence of 0.2 mM ATP (2.28 GPa).

Acoustics↗
PubMedDate not supplied

The flexural properties of fiber-reinforced composite with light-polymerized polymer matrix.

PURPOSE: The aim of this study was to measure the flexural strength and the elastic modulus of composite resin with and without reinforcing fibers and to evaluate the reinforcing effect of various fibers. MATERIALS AND METHODS: A polyethylene fiber (Ribbond), a polyaramid fiber (Fibreflex), and three glass fibers (FibreKor, GlasSpan, Vectris) were used to reinforce composite resins. The flexural strength and elastic modulus of specimens in the three-point bending mode were measured using a universal testing machine at a cross-head speed of 1 mm/min after storage in water at 37 degrees C for 24 hours. All tests were carried out in a water bath at 37 degrees C. The data were analyzed using analysis of variance and the Sheffé test at P= 0.05. After testing, the fractured surface was evaluated using a scanning electron microscope at 50x, 500x, and 3,000x magnifications. RESULTS: Yield flexural strengths of nonreinforced resins were 48 to 56 MPa, and those of reinforced resins were 56 to 134 MPa. Ultimate flexural strengths of nonreinforced specimens were 96 to 119 MPa, and those of reinforced ones were 203 to 386 MPa. Elastic modulus of nonreinforced resin was 6 to 9 GPa, and fiber reinforcing increased the value to 9 to 15 GPa, while it had no effect in Ribbond. CONCLUSION: Most of the fibers used in this study increased both yield and ultimate flexural strengths of composite resins, with the exception of the yield strength of Vectris. GlasSpan, Fibreflex, and FibreKor were effective in reinforcing elastic modulus, while Ribbond had no effect on it. Unidirectional glass fibers and polyaramid fiber were effective in reinforcing both flexural strength and elastic modulus of composite resin.

Analysis of Variance↗
PubMedDate not supplied

Aortic elastic properties with transesophageal echocardiography with automated border detection: validation according to regional differences between proximal and distal descending thoracic aorta.

We have previously described the use of transesophageal echocardiography with automated border detection to quantify regional aortic elastic properties. The purpose of this study was to validate this technique further by measuring regional variations of aortic elastic properties and comparing them with previously published data acquired by invasive methods. In nine anesthetized, closed-chest dogs, aortic pressure and lumenal area (transesophageal echocardiography with automated border detection) signals were recorded simultaneously at two aortic sites: just distal to the branching site of the left subclavian artery (proximal) and at the level of the diaphragm (distal). Instantaneous wall thickness was estimated by combining M-mode measurement of aortic end-diastolic thickness with instantaneous lumenal area. Data were acquired over a wide range of loading conditions, generated by inferior vena caval balloon occlusion. Aortic compliance per unit length, midwall radius, midwall stress, and incremental elastic modulus were computed. Aortic midwall radius and incremental elastic modulus values for proximal and distal aortic sites were compared at a common level of midwall stress. Compliance per unit length was higher in the proximal compared with the distal descending thoracic aorta (0.013 +/- 0.003 versus 0.008 +/- 0.003 cm2/mm Hg; mean +/- SD; p = 0.0011). Midwall radius was larger at the proximal location (0.76 +/- 0.07 cm versus 0.64 +/- 0.07 cm; p = 0.0001), whereas incremental elastic modulus was greater distally (0.799 +/- 0.052 dynes x 10(6)/cm2 versus 0.912 +/- 0.130 dynes x 10(6)/cm2; p = 0.02). Lower compliance values at the distal site of the descending thoracic aorta resulted from greater wall stiffness and a smaller radius. Transesophageal echocardiography with automated border detection provides reliable measurements of instantaneous aortic areas necessary for quantifying regional elastic properties.

Animals↗
PubMed1998

[Bio-mechanical property changes of long bone in ovariectomized goats].

This paper presents the biomechanical property changes of long bone in goats at 180 days after ovariectomy. 10 female goats at the age of 1.5 +/- years(average body wight 22 kg) were randomly divided into the control group and ovariectomized group. These goats were sacrificed at 180 days after ovariectomy and the femora, tibiae, metatarsus, humeri, radius and metacarpus were taken out bilaterally. The structural mechanical properties of these bones were measured with the three-point bending method. The material mechanical properties of flexura, compress and tensile in the compact bone specimens taken from the two broken ends were also measured. The results showed that the bone density, bone thickness in broken ends, and the break load of three-point bending for the long bones in the OVX group were obviously lower than those in the control group (P < 0.05). And compared with the control group all the long bones in the OVX group, except the femur, had significantly lower ultimate bending strength, bending elastic modulus; ultimate flexural strength, flexural elastic modulus; ultimate compressing strength, and compressing elastic moduus. Some long bones in the OVX group had significantly decreased ultimate tensile strength (P < 0.05). These indicated that the mechanical properties of long bone in OVX group at 180 days after ovariectomy were reduced in varying degrees and were liable to fracture. This result is in accord with the clinical findings in osteoporosis resulting from post-menopausal estrogen fall and is also consistent with the osteoporotic model of ovariectomized rats. The authors conclude that the bone biomechanical properties are important parameters in assessing osteoporosis and the ovariectomized goat can possible be a good big animal model of osteoporosis.

Animals↗
PubMed2003

Mechanical response of the porcine temporomandibular joint disc to an impact event and repeated tensile loading.

AIMS: To test for orthotropy in the stress-strain behavior of the temporomandibular joint (TMJ) disc under repeated physiologic loading before and after an impact event. METHODS: Two groups, each consisting of 10 discs, were subjected to repeated tensile cycling in the dorsoventral (group 1) and mediolateral (group 3) direction. Two additional groups, each consisting of 10 discs, had preconditioning in the form of a 1.18 N.s impulsive load before tensile cycling in either the dorsoventral (group 2) or mediolateral (group 4) direction. Physiologic loads of 1 to 3 N were cycled at 0.1 Hz, and stress-strain responses were recorded every cycle between 1 to 10 cycles, and then periodically at 50, 100, 500, 750, and 1,000 cycles. The properties of elastic modulus, residual strain upon unloading, and area contained within the hysteresis loop were measured. RESULTS: Dorsoventral loading produced 5-fold higher elastic modulus, 5-fold lower residual strain, and 5-fold lower hysteresis compared to mediolateral tensile loading (P < or = .001). Repeated loading effectively reduced the viscous response for all discs, as the elastic modulus increased while residual strain and hysteresis decreased. Impulsive loading caused elastic modulus to increase for dorsoventrally cycled discs, whereas hysteresis decreased for mediolaterally cycled discs (P < or = .05). CONCLUSION: The findings suggest that damage from the impact load may have increased the porosity of the extracellular matrix, which ultimately resulted in additional stress transfer to the collagen fibers during loading. Impulsive loads may be an important preconditioning factor in the fatigue failure of the TMJ disc in vivo.

Analysis of Variance↗