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PubMed1985

Mechanical properties of the rat colon: the effect of age, sex and different conditions of storage.

The mechanical properties of the rat colon were studied in old and young Sprague-Dawley rats which were also grouped by sex. Different storage media were used. Rings of colonic tissue were submitted to pulls on an Instron 1026 tensiometer. Gender did not affect the properties of the young rat colon. The rat colon has a tensile strength of around 50 g/mm2 (which places it between the dog and the cat). It increased in strength from proximal to distal, though the rectum was weaker than the colon. The pre-strain of the rat colon was 10% and it was capable of stretching to 200% of its original dimensions. The strength and ability to stretch fell with age, although it initially increased, in the first year of life. Physiological saline at 4 degrees C preserved the burst strength, percentage elongation, hysteresis and Young's modulus between 25 and 100 g stress for up to 1 week. Young's modulus between 125 and 200 g fell progressively with each day of storage. Stress relaxation rose in the first 24 h and thereafter remained constant. Salt appeared to be a good long-term storage medium. Irradiation of the colons before storage did not affect the mechanical properties.

Animals↗
PubMed1986

Energy stored and dissipated in skeletal muscle basement membranes during sinusoidal oscillations.

We subjected single skeletal muscle cells from frog semitendinosus to sinusoidal oscillations that simulated the strain experienced as the cells near the end of passive extension and begin active contraction in slow swimming. Other cells from which the basement membrane was removed by enzymatic and mechanical procedures were tested identically. Effectiveness of the basement membrane removal technique was evaluated by electron microscopy, by an electrophoretic and lectin-binding assay for depletion of cell surface glycoproteins, and by confirmation by means of electrophoretic and immunologic analyses that major intracellular, cytoskeletal proteins were not disrupted. Measurements of maximum stress, maximum strain, and phase lag between these maxima enabled the complex modulus (dynamic stiffness) and loss tangent (relative viscous losses to elastic energy storage) to be calculated for each mechanically tested preparation. We also calculated the amounts of energy stored and dissipated in each preparation. These calculations indicate that cells with intact basement membranes have complex moduli significantly greater than those of cells without basement membranes, and that cells with basement membrane store significantly more elastic energy than basement membrane depleted cells. However, when subjected to identical sinusoidal strains, energy dissipation in cells with intact basement membranes is over three times greater than dissipation in cells without basement membrane. The relative magnitudes of energy losses to energy storage, called the specific loss, is nearly three times greater for intact cells than for basement membrane depleted cells. Basement membranes may thereby serve as a brake for slowing passive extension of muscle before contraction begins.

Animals↗
PubMed1979

Viscoelastic and dynamic properties of soft liners and tissue conditioners.

The creep compliance and dynamic modulus of two tissue conditioners and five soft liners were determined after storage in water at 37 degrees C. Under static conditions the tissue conditioners functioned like viscous liquids, whereas the soft liners were more elastic. In general, linear viscoelasticity was not observed. Under dynamic conditions, the materials were stiffer.

Chemical Phenomena↗
PubMed1992

The effect of storage on the biomechanical behavior of articular cartilage--a large strain study.

The transplantation of stored shell osteochondral allografts is a potentially useful alternative to total joint replacements for the treatment of joint ailments. The maintenance of normal cartilage properties of the osteochondral allografts during storage is important for the allograft to function properly and survive in the host joint. Since articular cartilage is normally under large physiological stresses, this study was conducted to investigate the biomechanical behavior under large strain conditions of cartilage tissue stored for various time periods (i.e., 3, 7, 28, and 60 days) in tissue culture media. A biphasic large strain theory developed for soft hydrated connective tissues was used to describe and determine the biomechanical properties of the stored cartilage. It was found that articular cartilage stored for up to 60 days maintained the ability to sustain large compressive strains of up to 40 percent or more, like normal articular cartilage. Moreover, the equilibrium stress-strain behavior and compressive modulus of the stored articular cartilage were unchanged after up to 60 days of storage.

Animals↗
PubMed1975

[Mechanical-dynamic properties of prosthesis plastics].

Comparative studies on the mechanic and molecular properties of heat- and self-curing polymers (PMMA) showed the following results: 1. The glass-transition temperature of heat- and self-curing polymers clearly shows measurable differences also as a function of their storage conditions. However, this is hardly of any clinical or practical significance. 2. The modulus of elasticity values of heat and self-curing polymers are not significantly different in the range of the usually applied temperatures. However, water-uptake considerably reduces the rigidity. 3. Overloading or fatigue failures do not show any clear differences in morphological characteristics. The practical influence of smaller long-term inflation strength of self-curing polymers has not yet been sufficiently proven. 4. Heat and self-curing polymers are identical as basic materials for dentures from the point of view of material technology.

Cold Temperature↗
PubMed1987

Polymers for healing caps on titanium implants.

Healing caps are used during the healing period after abutment connection on titanium implants of the Branemark type. These healing caps consist of a screw embedded in polyamide-6 (PA-6) which is considerably weakened during this healing period. The properties of PA-6 and poly(4-methyl-1-pentene) (PMP) were studied. Storage in water at 37 degrees C led to a marked reduction in the flexural modulus of PA-6, but only a minor decrease for PMP. PA-6 showed a marked increase in volume due to water uptake, whereas PMP showed no significant change in volume. The improved properties of PMP compared to PA-6 when used for healing caps were demonstrated. The results of an agar overlay cytotoxicity test indicated that both PMP and PA-6 were nontoxic under laboratory controlled conditions.

Adsorption↗
PubMed1985

[Physical characteristics of stripping veins preserved at 4 degrees C and usable as artery substitutes].

The mechanical behavior of varicosis veins harvested during stripping and preserved at 4 degrees C has been investigated by measuring the compliance, the yield strain, the yield stress and the longitudinal Young's modulus. No relationship has been demonstrated between those parameters and external factors such as age, sex, storage duration and bacteremic contamination. The mechanical behavior of such veins is unpredictable. Therefore, it is mandatory to proceed through individual and non-destructive quality control tests to obtain a selection of grafts suitable for implantation. Moreover, implantation should be oriented towards patients who are able to visit the hospital frequently since the healing capacity of the venous homograft is unpredictable.

Arteries↗
PubMed1990

Effect of alternative crosslinking methods on the low strain rate viscoelastic properties of bovine pericardial bioprosthetic material.

Early failures of bovine pericardial heart valves have been due to leaflet perforation/tearing and calcification. Since glutaraldehyde fixation has been shown to produce marked changes in leaflet mechanics and has been linked to the development of calcification, alternative crosslinking techniques have been suggested as means to overcome these obstacles. We have examined the low strain rate viscoelastic behavior of bovine pericardium: (1) fresh; (2) chemically treated with glutaraldehyde, cyanimide, or polyglycidyl ether; or (3) physically treated by freeze-drying or heat-drying. Shrinkage temperature tests were conducted to assess intrahelical crosslinking. Polyglycidyl ether and glutaraldehyde both produced substantial crosslinking, with the shrinkage temperature rising above 80 degrees C. Mechanical changes were nearly equivalent, both showing decreased stress relaxation and increased extensibility consistent with intrahelical crosslinking and shrinkage during fixation. Cyanimide, known to crosslink pure collagen materials, showed no evidence of crosslinking intact tissue. Heat-drying, also effective in pure collagen preparations, produced an increase in UTS and tissue modulus, but otherwise left the tissue unchanged. Freeze-drying had no mechanical effect, and therefore provides an attractive means for the storage of connective tissues for later mechanical testing.

Animals↗
PubMed1992

Invasion of hereditary ovalocytes by Plasmodium falciparum in vitro and its relation to intracellular ATP concentration.

Hereditary ovalocytes (stomatocytic ovalocytes), when examined within 1-2 days from the time that the blood sample is drawn, are invaded by Plasmodium falciparum in culture to the extent of at least 55% of normal control cells. The ovalocytes have extremely rigid membranes, characterised by a shear elastic modulus some 3-4 times greater than that of normal cells. The extent of invasion falls off very much more rapidly than that into normal cells on storage, and we surmise that this is the reason for earlier reports of resistance of ovalocytes to malarial invasion in vitro. The initial loss of susceptibility to invasion with time is not accompanied by any change in membrane rigidity, but is primarily a consequence of a rapid decline in intracellular ATP concentration: this falls to below the threshold level required for invasion (approx. 0.1 mM) over a period in which the ATP in normal cells remains almost constant. Incubation in a metabolic regenerating medium leads to a rise in the intracellular ATP concentration and invasion by P. falciparum is recovered, though to a much lower extent than in normal cells. The resistance of ovalocytes to invasion becomes irreversible, due possibly to degradative processes in the membrane, on further storage. The developing parasites in ovalocytes have a reduced number of merozoites and show distinct morphological abnormalities.

Adenosine Triphosphate↗
PubMed1985

Biomechanics of fruits and vegetables.

The scope of fruit and vegetable biomechanics is reviewed. Sources of mechanical injury to produce in harvesting, processing, storage, packaging and transportation are briefly described. A survey of produce handling and transportation environments was conducted, whereby an envelope model encompassing composite spectra of trucks, railroad, marine and cargo aircraft is presented. The protective quality, i.e. strength of shipping containers is quantified in static and dynamic loading such as encountered in storage, handling and transportation. Mechanical response of fruits and vegetables in quasistatic and dynamic loading are formulated by a nonlinear rheological model, whereby a time and deformation dependent relaxation modulus is defined. A realistic link is established between the model and real fruits and vegetables by test procedures for determination of the parameters in the governing nonlinear equations. Based on the nonlinear relaxation modulus, mechanical damage of fruits and vegetables is quantified for static compression, transients and vibration loading as well as for combined static and dynamic loading, by equations of contact circle diameter, bruise depth and contact pressure. Distribution of loads over a maximal number of contact points per fruit is linked to geometrical patterns of produce packs. The application of Shock Damage Boundary techniques for produce-package testing is described along with a case study comparing the protective qualities of two types of apple packs. Produce damage quantification by direct fruit inspection in terms of a 'Bruise Index' is described, including a practical example, comparing the protective qualities of three types of apple packs in shipping tests. Indirect methods of mechanical injury evaluation, based on weight loss and CO2 emission differences between bruised and wholesome fruits are also briefly discussed.

Biomechanical Phenomena↗
PubMed1978

[Studies on orthodontic polyurethane ringlets. (Part 1) Examination of its physical properties (author's transl)].

The purpose of this study was to develop orthodontic ringlets from polyurethane which have maximum flow resistance. The two types of polyurethane involved were thermoplastic and thermosetting polyurethane. The former included Paraprene 22, 25, 4805 + 4806, Biomer, Elastollan 585 (E-585) and improved Elastollan 590 (E-590). Thermosetting type incorporated Adiprene, Loyler 2170, Colonate 4080 and DC-4978. Using these materials as its base, a ring device was developed. Under two conditions, tests were conducted for tensile strength, aging effects on 50% and 100% modulus and permanent elongation. One group was stored in air at 20 degrees C and the other in water at 37 degrees C. The results were as follows; It was found that the thermoplastic polyurethane possessed high tensile strength. However, the modulus upon aging resulted in a lower reading with the exception of E-590 and Biomer. In the thermosetting polyurethane group, most of the rings except DC-4978 broke down during storage at 100% elongation in water at 37 degrees C. In the case of DC-4978, there was maximum flow resistance. Upon comparing it with E-590 and Biomer, it appeared that DC-4978 was the most effective for orthodontic purposes.

Elasticity↗
PubMed1987

Preoperative metabolic analysis of donor corneas using magnetic resonance spectroscopy.

Successful corneal transplantation was accomplished following metabolic phosphorus magnetic resonance analysis. Four cat corneas were analyzed using phosphorus-31 magnetic resonance following storage in modified McCarey-Kaufman (M-K) medium for 24 h. Corneas were re-stored in M-K medium and transplanted 24 h after MR analysis. Four control corneas (contralateral eye, no magnetic resonance analysis performed) were also transplanted following storage in M-K medium under identical conditions. Successful corneal transplantation was accomplished with minimal ATP tissue levels. Corneas stored for 48 h maintained a pH of 7.3. The phosphorus-31 spectral modulus, which is the ratio of the high-energy phosphates to the low-energy phosphates, was calculated using the spectral integral (range, 0.49-0.77). No difference in endothelial cell density or morphology was detected between corneas following magnetic resonance analysis and control corneas when evaluated by specular microscopy.

Animals↗
PubMed1989

Histological and biomechanical assessment of articular cartilage from stored osteochondral shell allografts.

Normal and stored articular cartilage from the medial tibial plateaus of mature canine knee joints were evaluated histologically and biomechanically. The medial plateaus from the right knee (control) were assessed fresh, while the left (stored) were preserved in culture media at 4 degrees C for 3, 7, 14, or 28 days and then evaluated. Biomechanically, confined compression tests were performed on all specimens to determine the aggregate modulus and apparent permeability of the articular cartilage. Histologically, Safranin O- and hematoxylin and eosin (H&E)-stained sections were evaluated. All stored cartilage specimens had an aggregate modulus on average lower than normal, but the differences were not significant (p greater than 0.10). The apparent permeability was on average higher than but also not significantly different from normal (p greater than 0.10). Time in storage (up to 28 days) did not have a significant effect on the biomechanical properties of stored cartilage normalized by control values (p greater than 0.50). Safranin O and H&E histological evaluation also showed no overall changes in cell appearance or staining of the stored cartilage when compared with control for the time periods studied.

Animals↗
PubMedDate not supplied

Viscoelastic properties of solutions of ovine submaxillary mucin.

The linear viscoelastic and rheological properties of high molecular weight ovine submaxillary mucin (OSM) solution have been investigated in terms of the Newtonian steady-flow viscosity [eta(gamma)], the complex oscillatory viscosity [eta*(omega)], and the storage and loss shear moduli [G'(omega) and G"(omega)]. It was observed that tau(gamma), eta*(omega), and G'(omega) are always higher when OSM is dissolved in 0.1M NaCl than when at the same concentration in 6M GdnHCl. This is consistent with previous observations that submaxillary mucins self-associate in 0.1M NaCl to form large aggregates, which are disrupted in 6M GdnHCl. As the OSM concentration increases, the appearance of a plateau shear modulus indicates the formation of a gel network in both solvents. The results suggest gelation involves specific intermolecular interactions, perhaps due to hydrophobic forces between interdigitated oligosaccharide side chains. The viscoelastic behavior of OSM solution at high concentration is thus similar to that reported in the literature for porcine gastric mucin (PGM). However, the OSM gels are mechanically weaker, having moduli that are an order of magnitude lower than those for PGM gels of comparable concentration. The oligosaccharide side chains of OSM consist of only 1-2 sugar units compared to 10-15 for PGM, but it appears that this is sufficient to allow for intermolecular interaction and the formation of weak gels.

Animals↗
PubMed1990

Effect of vacuum mixing on the mechanical properties of antibiotic-impregnated polymethylmethacrylate bone cement.

Polymethylmethacrylate bone cement, containing either no added antibiotic, 0.5 g of Vancomycin, 1.0 g of Vancomycin, or 1.0 g of Tobramycin, was mixed either in air or a vacuum chamber. Following storage in a water bath at 37 degrees C for 48 h, the specimens were tested in four-point bending. The porosity of the specimens was assessed radiographically, and their antibacterial activity was monitored for 21 days. The bending strength of the vacuum mixed specimens containing no antibiotic was 40% greater than that of similar air-mixed specimens. However, there were no significant differences in the bending strength of either the air- or vacuum-mixed specimens when any of the antibiotic dosages were added. The bending modulus of the vacuum-mixed specimens, containing no antibiotic, was significantly greater than the moduli of all the other specimen groups which did not differ from each other. Vacuum mixing reduced the apparent porosity of the specimens fivefold, and while the addition of antibiotic did not effect porosity of the air-mixed specimens, that of the vacuum-mixed specimens was doubled. Although initial rapid decreases were seen, leaching of antibiotic from the cement and antibacterial activity continued through the 21-day monitoring period.

Biomechanical Phenomena↗
PubMed1986

The effect of resin formulation on the degree of conversion and mechanical properties of dental restorative resins.

The goal of this study was to determine the effects of resin formulation variables, such as diluent concentration, catalyst type and concentration and cure mode, on the degree of conversion of carbon double bonds and mechanical properties of dental restorative resins. Diametral tensile strength, compressive strength, hardness, flexural modulus and strength, and dynamic mechanical properties were tested, and the results were correlated to the degree of conversion results obtained by infrared analysis. The results showed a significant correlation between increased mechanical properties and higher degrees of conversion. Enhanced conversions were achieved by incorporating higher diluent and lower inhibitor concentrations into the resins. Ambient temperature properties were similarly enhanced by lower inhibitor concentrations, but were not enhanced by higher diluent concentration. Dynamic mechanical properties testing at oral and elevated temperatures elucidated possible differences in resin microstructure and network quality. The storage moduli decreased over the dental temperature range and was lower at all temperatures for resins with lower conversions. The glass transition temperature was also lower in resins with poorer conversions, suggesting that these resins may be more unstable at oral temperatures than more highly converted resins. Dynamic mechanical properties were most closely correlated to degree of conversion in these polymeric systems.

Acrylic Resins↗
PubMed1991

[Biomechanical properties of heat and irradiation treated spongiosa].

Cylindrical specimens of trabecular pig bone were tested to uniaxial compressive strain levels of 30% to study the influence of various sterilization techniques and methods of HIV-inactivation on the mechanical properties characterized by compressive modulus, yield point, energy absorption and maximum stress. Heat inactivation at 60 degrees C (Lactated Ringer, 1 h) showed no effect; 80 degrees C (Lactated Ringer, 1 h) resulted in a diminution of the yield point and the maximum stress (p less than 0.005), while energy absorption and compressive modulus were not affected. No reduction in the stability was seen when ethanol was used instead of Lactated Ringer. At a temperature of 100 degrees C, all measured parameters were reduced to approximately 60% compared with the control group. A decrease to 13% to 25% was seen after autoclavation (120 degrees C, 2 bar, 20 min and 134 degrees C, 3 bar, 12 min). Irradiation (60Co) with 3 respectively 10kGy did not impair the stability, whereas a dose of 25 kGy led to a reduction to 61% to 69%. No additional effect was seen when irradiation was followed by storage at -80 degrees C for one week. These effects on bone stability should be considered when choosing a method of bone preparation to obtain HIV-inactivated bone grafts. Autoclavation should be used with caution when stability of the bone graft is essential. In this case, irradiation seems to be a safe method of sterilizing bone grafts ensuring both a high degree of safety and stability.

Animals↗
PubMed1979

Thermoelasticity of red blood cell membrane.

The elastic properties of the human red blood cell membrane have been measured as functions of temperature. The area compressibility modulus and the elastic shear modulus, which together characterize the surface elastic behavior of the membrane, have been measured over the temperature range of 2-50 degrees C with micropipette aspiration of flaccid and osmotically swollen red cells. In addition, the fractional increase in membrane surface area from 2-50 degrees C has been measured to give a value for the thermal area expansivity. The value of the elastic shear modulus at 25 degrees C was measured to be 6.6 X 10(-3) dyne/cm. The change in the elastic shear modulus with temperature was -6 X 10(-5) dyne/cm degrees C. Fractional forces were shown to be only on the order of 10-15%. The area compressibility modulus at 25 degrees C was measured to be 450 dyne/cm. The change in the area compressibility modulus with temperature was -6 dyne/cm degrees C. The thermal area expansivity for red cell membrane was measured to be 1.2 X 10(-3)/degrees C. With this data and thermoelastic relations the heat of expansion is determined to be 110-200 ergs/cm2; the heat of extension is 2 X 10(-2) ergs/cm2 for unit extension of the red cell membrane. The heat of expansion is of the order anticipated for a lipid bilayer idealized as twice the behavior of a monolayer at an oil-water interface. The observation that the heat of extension is positive demonstrates that the entropy of the material increases with extension, and that the dominant mechanism of elastic energy storage is energetic. Assuming that the red cell membrane shear rigidity is associated with "spectrin," unit extension of the membrane increases the configurational entropy of spectrin by 500 cal/mol.

Elasticity↗