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PubMed2007

Modified cellulose II powder: preparation, characterization, and tableting properties.

The reaction of UICEL-A/102, a cellulose II powder recently prepared from Avicel(R) PH-102 by treatment with an aqueous sodium hydroxide solution, with glutaraldehyde in 0.01 N HCl has been investigated to improve its binder properties, without adversely affecting the rapid disintegration characteristic. The results showed that UICEL-A/102 and glutaraldehyde when reacted in a 1:0.6 weight ratio at 100 degrees C for 8.5 h produces a product, (hereinafter referred to as UICEL-XL), that, compared to UICEL-A/102, had a lower degree of polymerization, higher crystallinity, lower bulk density, lower tapped density, and higher porosity. Further, it showed lower yield pressure and higher crushing strength, and tensile strength values, indicating that UICEL-XL is more compressible and compactable than the starting material, UICEL-A/102. A comparison of "in-die" and "out-of-die" Heckel data indicated UICEL-XL to be less elastic than UICEL-A/102. Both UICEL-XL and UICEL-A/102 showed similar moisture sorption isotherms, and their compacts disintegrated rapidly in water. In conclusion, the glutaraldehyde-treated cellulose II powder not only serves as good a disintegrant as the untreated cellulose powder but also possesses superior binder properties.

Cellulose↗

PubMed1980

A quantitative analysis of elastic, entropic, electrostatic, and osmotic forces within relaxed skinned muscle fibers.

The elastic behavior of mechanically skinned skeletal muscle fibers in relaxing solution is modelled using equations developed by Flory (1953) for the elasticity of non-biological polymers. Mechanically, the relaxed skinned fiber is considered to be a semi-crystalline network of inextensible polymer chains, which are periodically cross-linked and which are bathed in an aqueous medium. We consider (1) configurational elastic forces in the network, (2) entropic forces due to mixing of polymer and water, (3) electrostatic forces due to fixed charges on the muscle proteins and mobile charges in the bathing solution, and (4) compressive forces due to large colloids in the bathing solution. Van der Waals forces are not considered since calculations show that they are probably negligible under our conditions. We derive an expression which relates known quantities (ionic strength, osmotic compressive pressure, and fiber width), experimentally estimated quantities (fixed charge density and volume fraction of muscle proteins), and derived quantities (concentration of cross-links and a parameter reflecting the interaction energy between protein and water). The model was tested by comparison with observed changes in skinned fiber width under a variety of experimental conditions which included changes in osmotic compressive pressure, pH, sarcomere length, and ionic strength. Over a wide range of compressive pressure (0-36 atm) the theory predicted the nonlinear relation between fiber width and logarithm of pressure. The direction and magnitude of the decrease in width when pH was decreased to 4 could be modelled assuming the fixed charge density on the protein network was 0.34 moles of electrons per liter protein, a value in accordance with the estimates of others. The relation between width and sarcomere length over the complete range of compressive pressures could be modelled with the assumption that the number of cross-links increases somewhat with sarcomere length. Changes of width with ionic strength were modelled assuming that increasing salt concentration both increased the electrostatic shielding of fixed charges and decreased the number of cross-links. The decrease of fiber width in 1% glutaraldehyde was modelled by assuming that the concentration of crosslinks increased by some 10%. The theory predicted the order of magnitude but not the detailed shape of the passive tension-length relation which may indicate that, as with non-biological polymers, the theory does not adequately describe the behavior of semi-crystalline networks at high degrees of deformation. In summary, the theory provides a semiquantitative approach to an understanding of the nature and relative magnitudes of the forces underlying the mechanical behavior of relaxed skinned fibers. It indicates, for instance, that when fibers are returned to near their in vivo size with 3% PVP, the forces in order of their importance are: (elastic forces) approximately (entropic forces) greater than (electrostatic forces) approximately (osmotic compressive forces).

Animals↗

PubMed2001

Gray matter of the bovine cervical spinal cord is mechanically more rigid and fragile than the white matter.

The gray matter of the cervical spinal cord has been thought to be equally or less rigid than the white matter. Based on this assumption, various studies have been conducted on the changes of stress distributions within the spinal cord under mechanical compression, although the mechanical properties of the white and gray matters had not been fully elucidated. The present study measured the mechanical properties of the white and gray matter of bovine spinal cords. For both the white and gray matter, the stress-strain curves had a nonlinear region, followed by a linear region, and then a region where the stresses plateaued before failure. In the nonlinear region, stress was not significantly different between the gray and white matter samples (strain approximately 0-10%), while stress and Young's modulus in the gray matter was significantly higher than the white matter in the linear part of the curve. The gray matter ruptured at lower strains than the white matter. These findings demonstrated the gray matter is more rigid and fragile than the white matter, and the conventional assumption (i.e., the white matter is more rigid than the gray matter) is not correct. We then applied our data to computer simulations using the finite element method, and confirmed that simulations agreed with actual magnetic resonance imaging findings of the spinal cord under compression. In future computer simulations, including finite element method using our data, changes in stress and strain within the cervical spinal cord under compression would be clarified in more detail, and our findings would also help to elucidate the area which can easily receive histologic damage or which could have hemodynamic disorders under mechanical compression, as well as severity and location of biochemical and molecular biological changes.

Animals↗

PubMed2005

Effect of cyclic compressive loading on the bond strength of an adhesive system to dentin after collagen removal.

PURPOSE: The objective of this study was to verify the effect of cyclic compressive loading on the shear bond strength of an adhesive system following collagen removal. MATERIALS AND METHODS: Sixty bovine teeth were divided into 4 groups based on the adhesive procedure used: groups 1 and 2--etching with 35% phosphoric acid and application of the Single Bond adhesive system; groups 3 and 4--after etching, a 10% sodium hypochlorite solution was applied for 1 min before the application of the adhesive. In all the specimens, a Z100 resin cylinder was built up over the bond area. Groups 2 and 4 were submitted to 500,000 cycles with a load of 100 N. RESULTS: The mean values for the shear bond test (MPa) were: group 1: 7.37 +/- 1.15; group 2: 5.72 +/- 1.66; group 3: 5.95 +/- 1.21; group 4: 3.66 +/- 1.12. There was no difference between groups 1 and 2 (p > 0.01). Between groups 1 and 3, 2 and 4, and 3 and 4 there was a significant difference (p < 0.01). The majority of the specimens demonstrated an adhesive failure. CONCLUSION: The application of sodium hypochlorite on dentin decreased the values of shear bond strength, as did the load cycling in the group treated with sodium hypochlorite.

Acid Etching, Dental↗

PubMed2000

Influence of granulating method on physical and mechanical properties, compression behavior, and compactibility of lactose and microcrystalline cellulose granules.

The physical and mechanical properties of lactose (LC) and microcrystalline cellulose (MCC) granules prepared by various granulating methods were determined, and their effects on the compression and strength of the tablets were examined. From the force-displacement curve obtained in a crushing test on a single granule, all LC granules appeared brittle, and MCC granules were somewhat plastically deformable. Inter-granular porosity epsilon inter clearly decreased with greater spherical granule shape for both materials. Decrease in intragranular porosity epsilon intra enhanced the crushing force of a single granule Fg. Agitating granulation brought about the most compactness and hardness of granules. In granule compression tests, the initial slope of Heckel plots K1 appeared closely related to ease of filling voids in a granule bed by the slippage or rolling of granules. The reciprocal of the slope in the succeeding step 1/K2 in compression of MCC granules indicated positive correlation to Fg, while in LC granules, no such obvious relation was evident. 1/K2 differed only slightly among granulating methods. Tensile strength of tablets Tt obtained by compression of various LC granules was low as a whole and was little influenced by granulating method. For MCC granules, which are plastically deformable, tablet strength greatly depended on granulation. Granules prepared by extruding or dry granulation gave strong tablets. Tablets prepared from granules made by the agitating method showed particularly low Tt. From stereomicroscopic observation, the contact area between granule particles in a tablet appeared smaller; this would explain the decrease in inter-granular bond formation.

Cellulose↗

PubMed2004

Biocompatibility and osseointegration of beta-TCP: histomorphological and biomechanical studies in a weight-bearing sheep model.

The aim of the study was to investigate the biocompatibility, degradation, and biomechanical properties of beta-TCP (Cerasorb) in a weight-bearing sheep model. beta-TCP implant prototypes were implanted in the tibial head of adult merino sheep. After 6 and 12 months material explants were harvested for biomechanical, histological, and histomorphometrical analysis. Corresponding bone specimens of the intact bone of the contralateral leg were used as controls in the biomechanical test. Compression tests showed higher values for maximum fracture load, yield strength, and compression modulus after 6 and 12 months compared to control. Microscopically, the implants showed good osteoconduction and were incorporated into the bone; however, relevant amounts of beta-TCP were still present after 12 months. Histomorphological results revealed that beta-TCP had partially degraded between implantation and 6 months, but its share remained constant between 6 and 12 months. The bone volume fraction in the area of the implant (46% +/- 6.5%) was initially higher than in the corresponding bone area of the contralateral leg (31% +/- 9.6%), but after 12 months declined to 29% +/- 9.4% (control: 33% +/- 8.3%), while the share of beta-TCP remained constant at 36% +/- 12.2%. These findings were supported by microradiographic data. In conclusion, in a weight bearing implantation model beta-TCP showed good biocompatibility, osseointegration and beginning degradation, even though it was not further degraded between 6 and 12 months.

Animals↗

PubMedDate not supplied

Hydrogels for an accommodating intraocular lens. An explorative study.

In this study it was investigated whether hydrogels could be used for an accommodating lens. The requirements of such a hydrogels are a low modulus, high refractive index, transparency, and strength. Since conventional hydrogels do not possess this combination of properties, a novel preparation method and new polymers are introduced. As starting materials poly(1-hydroxy-1,3-propanediyl), poly(ethylene-co-vinyl alcohol), poly(vinyl alcohol), and poly(allyl alcohol) were used. The first three were cross-linked with a number of diisocyanate compounds. Network formation was performed at low concentrations in a good solvent. Mixing of the polymer solution and cross-linker appeared to be crucial for transparency. Poly(1-hydroxy-1,3-propanediyl), cross-linked with a slow reacting diisocyanate block, shows the most promising properties with respect to refractive index, transparency, tensile strength, and modulus. Poly(allyl alcohol) hydrogel was made by compression molding. The hydrogel was transparent and had a high refractive index and low modulus. It was concluded that hydrogels could be used as accommodating lens material.

Accommodation, Ocular↗

PubMed2000

Influence of crystal habit on the surface free energy and interparticulate bonding of L-lysine monohydrochloride dihydrate.

The objective of the present study was to apply a technique to measure the surface energy of crystalline powders without changing the surface properties by compaction, and to relate such measurements to crystal habit and orientation. The surface free energy of uncompacted L-lysine monohydrochloride dihydrate (LH), determined using a modified sessile-drop method, reflected a combined value for the various faces, and was influenced by the relative size of the faces and the orientation of the crystals. The surface free energy values obtained from contact angle measurements were within the possible range calculated from the crystal structure. Discrepancies between the theoretical estimates of interparticulate cohesive strengths and those measured from the tensile strength of powder compacts were used to estimate the flaw sizes (or gaps between the particles) that act as stress concentrators and reduce the tensile strength of the compacts. The flaw sizes indicate packing and compressibility of the various crystal habits. In the absence of compressive load, compacts made out of the equidimensional crystals have the larger flaw sizes (wider cracks or wider gaps between the particles). At higher compaction pressures, the compacts from long rod-shaped crystals have longer crack lengths. The weakness of the compacts made from the long rods at the higher compaction pressures may be because of the longer crack length along the interparticulate boundary, which may result in a higher stress intensity at the crack tip and increased fracture propensity.

Chemistry, Pharmaceutical↗

PubMed2006

The effect of damage on the viscoelastic behavior of human vertebral trabecular bone.

The present study examines the viscoelastic behavior of cancellous bone at low strains and the effects of damage on this viscoelastic behavior. It provides experimental evidence of interaction between stress relaxation behavior and the effect of accumulated damage. The results suggest that damage is at least orthotropic in trabecular bone specimens under uniaxial loading. Simple linear models of viscoelasticity described the time-dependent stress-strain behavior at low strains before and after specimen damage, although better fits of these models were obtained prior to damage. Modeling the observed changes in relaxation times with damage accumulation appears necessary to successfully predict the post-damage viscoelastic response.

Anisotropy↗

PubMedDate not supplied

Strength characteristics of glass-ionomer cements.

The purpose of this investigation was to compare the compressive and diametral tensile strengths of two silver-reinforced and three conventional glass-ionomer cements of different powder-to-liquid ratios at 1 and 24 hours. ANOVA (P < 0.001) and Tukey's Studentized Multiple Range Test indicated significant differences between the compressive strengths of several of the cements tested (P < 0.05). No significant differences were noted between any of the cements for the diametral tensile strength test (alpha = 0.05).

Analysis of Variance↗

PubMed2001

Mechanical strength testing of compacted powders.

Alternative test specimens for the determination of the fracture stress of brittle materials (eg. compacted powders) are described and discussed, and a statistical approach to the processing of strength test data is outlined.

Compressive Strength↗

PubMed2002

Distribution of crushing strength of tablets.

The distribution of a given set of data is important since most parametric statistical tests are based on the assumption that the studied data are normal distributed. In analysis of fracture mechanics the Weibull distribution is widely used and the derived Weibull modulus is interpreted as a material constant. However, the estimation of this parameter is laborious and subject to estimation problems. It is shown that the Weibull modulus is inherently connected to the coefficient of variation and that the information obtained from the modulus is unclear. The distribution of crushing strength data from nine model tablet formulations and four commercial tablets are shown to follow the normal distribution. The importance of proper cleaning of the crushing strength apparatus is demonstrated.

Compressive Strength↗

PubMed2002

Use of rubble from building demolition in mortars.

Because of increasing waste production and public concerns about the environment, it is desirable to recycle materials from building demolition. If suitably selected, ground, cleaned and sieved in appropriate industrial crushing plants, these materials can be profitably used in concrete. Nevertheless, the presence of masonry instead of concrete rubble is particularly detrimental to the mechanical performance and durability of recycled-aggregate concrete and the same negative effect is detectable when natural sand is replaced by fine recycled aggregate fraction. An alternative use of both masonry rubble and fine recycled material fraction could be in mortars. These could contain either recycled instead of natural sand or powder obtained by bricks crushing as partial cement substitution. In particular, attention is focused on the modification that takes place when either polypropylene or stainless steel fibers are added to these mortars. Polypropylene fibers are added in order to reduce shrinkage of mortars, stainless steel fibers for improving their flexural strength. The combined use of polypropylene fibers and fine recycled material from building demolition could allow the preparation of mortars showing good performance, in particular when coupled with bricks. Furthermore, the combined use of stainless steel fibers and mortars containing brick powder seems to be an effective way to guarantee a high flexural strength.

Compressive Strength↗

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

Pulmonary function tests, respiratory muscle strength, and endurance of patients with osteoporosis.

BACKGROUND: It has been shown that patients with thoracic kyphosis due to osteoporosis have diminished pulmonary function. The aim of this study was to determine the pulmonary function, respiratory muscle strength, and endurance of patients with osteoporosis who did not have compression fractures. METHODS: The patient group consisted of 88 recently diagnosed postmenopausal osteoporotic women without spinal fractures. They were matched for age and body mass index with 54 healthy women, who formed the control group. Bone mineral density, pulmonary function test (PFT), maximum voluntary ventilation (MVV), maximal inspiratory pressure (MIP), and maximal expiratory pressure (MEP) measurements of both groups were performed. RESULTS: There were no significant differences between the two groups regarding PFT parameters and MIP and MEP. However, osteoporotic patients had significantly lower MW values. CONCLUSION: Women with postmenopausal osteoporosis without spinal compression fractures have normal PFT, MIP, and MEP values, but they have reduced respiratory muscle endurance.

Aged↗

PubMed1997

Effect of compression speeds on the compaction properties of a 1:1 paracetamol-microcrystalline cellulose mixture prepared by single compression and by combinations of pre-compression and main-compression.

A 1:1 blend of paracetamol and microcrystalline cellulose was compacted at different compression speeds by single compression or combinations of pre- and main-compression. The tensile strengths of the tablets decreased from 0.74+/-0.01 to 0.44+/-0.05 MPa as the compression speed was increased from 78 to 390 mm/s when a single compression pressure of 80 MPa was used to compress the tablets. When combinations of pre- and main-compression of 320 and 240 MPa were used to compress the tablets, tensile strengths decreased from 3.12+/-0.67 MPa at a compression speed of 78 mm/s to 1.24+/-0.36 MPa when the compression speed was 390 mm/s. The energies of compression and the ratio of elastic to plastic energies increased with increase in compression speed. This was because the material was becoming more elastic and more energy was required for the elastic expansion leading to a reduction in the energy available for plastic deformation and bond formation which resulted in a decrease in tensile strengths. Pre-compression played a major role at high compression speeds. The tensile strengths of tablets (1.2+/-0.08 MPa) compressed with a pre-compression of 160 MPa followed by a main-compression of 80 MPa (compression speed of 390 mm/s) were similar to the tensile strengths of tablets (1.1+/-0.10 MPa) compressed using a single compression of 320 MPa at the same compression speed of 390 mm/s. Thus, combinations of lower pressures can be employed to compress the material to the same tensile strength as a high single compression.

Journal Article↗

PubMed2001

Laboratory strength of glass ionomer and zinc phosphate cements.

PURPOSE: The present in vitro study examined 3 mechanical properties, namely compressive, flexural, and diametral tensile strength, of various commercially available cements and core materials as a function of time after mixing. MATERIALS AND METHODS: The examined materials were 2 cermet cements (Ketac Silver [ESPE, Seefeld, Germany] and Chelon Silver [ESPE]), 1 metal-reinforced glass ionomer cement (Miracle Mix [GC Dental Industrial Corp, Tokyo, Japan]), 2 conventional glass ionomer cements (Ketac Bond [ESPE] and Ketac Cem [ESPE]), 1 standard cure zinc phosphate cement (Harvard Cement [Richter and Hoffmann, Berlin, Germany]), and 1 zinc phosphate cement with the addition of 30% silver amalgam alloy powder (Harvard Cement 70% with Dispersalloy 30% [Richter and Hoffmann/Johnson and Johnson, East Windsor, NJ]). Properties were measured using a universal testing machine at 15 minutes, 1 hour, and 24 hours after first mixing. RESULTS: Compressive strengths varied widely between the 3 times of measurement from 5.8 +/- 6.6 MPa for Ketac Cem to 144.3 +/- 10.2 MPa for Ketac Silver. Twenty-four hours after mixing, the Bonferroni test showed significant (p <or= .01) differences between Ketac Silver and all other materials tested. Diametral tensile strengths ranged widely from 4.4 +/- 0.9 MPa for Ketac Cem to 11.5 +/- 2.2 MPa for Chelon Silver. At 15 minutes, 1 hour, and 24 hours after first mixing, the analysis of variance did not show any significant differences between Ketac Silver, Chelon Silver, and Miracle Mix. The 3-point flexural strength of Ketac Silver showed, at 15 minutes with 13.5 +/- 3.9 MPa and at 24 hours with 27.2 +/- 7.4 MPa, the highest values. CONCLUSIONS: Setting time influences the mechanical properties of the materials tested in this study. Ketac Silver, a glass ionomer cement reinforced with sintered glass-silver particles, showed the highest mechanical properties of the examined materials.

Analysis of Variance↗

PubMed2002

The effects of graded compression of the median nerve in the carpal canal on grip force.

The relationship between tactile hypoesthesia and precision grip force was examined using compression of the median nerve in healthy adults. Hypoesthesia was graded by varying the pressure that an external clamp exerted over the carpal canal. Electrical stimulation of the median nerve in the forearm evoked a compound sensory nerve action potential (SNAP) that we recorded from the digital nerves of the index finger. Clamp pressure was varied to achieve SNAPs that were 75%, 50%, and 25% of precompression amplitude (100%). Grip force and tactile sensibility (Semmes-Weinstein filaments, cotton wisps, sharp/dull) did not change in parallel with reductions of the SNAP. Subjects reported paresthesias at the thumb and index finger at 75% SNAP. Tactile pressure thresholds increased to the clinical range of 'diminished light touch', but subjects detected cotton wisps stroked along the finger. At 75% SNAP grip force did not change compared to 100% SNAP. Simple prehension can proceed efficiently despite these modest reductions in tactile signals. At 50% SNAP the digits remained sensate, but were reported to feel "thick, like cardboard". No subject could detect cotton wisps and tactile thresholds increased by one filament. Sharp/dull distinctions remained. Grip force increased by 55% compared to grip force at SNAPs of 100% and 75%. There were no changes in skin slipperiness, so the increased grip force represented elevated 'safety margin' (grip force exceeding that needed to prevent slip). At 25% SNAP subjects described the skin innervated by the median nerve as feeling "numb", but grip force increased little compared to 50% SNAP. Grip force continued to reflect changes in grip surface friction, and mechanical transients from setting the object on the table triggered coordinated reductions in grip force. We suspect that the loss of information from SA I and FA I, but not FA II, tactile afferents provoked the increased grip force.

Action Potentials↗