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PubMed2006

Nanoindentation derived stress-strain properties of dental materials.

OBJECTIVES: The aim of the study is to investigate the stress-strain response of different dental materials, especially dental brittle materials, and compare them with enamel. METHODS: A nano-based indentation system (Ultra Micro-Indentation System, UMIS-2000, CSIRO, Australia) was used to determine the indentation stress-strain response of two kinds of dental ceramics (Cerec 2 Mark II and Vita VM9), one kind of dental alloy (Wiron 99) and healthy enamel. A spherical indenter was used to test the materials with nanometer and micro-Newton displacement and force resolution. Assuming the elastic modulus remained constant, a plot of contact pressure versus contact strain, H-a/R, of each material was obtained. RESULTS: By comparing the H-a/R curve of the different materials with enamel, it can be concluded that only the metallic alloy, has similar stress-strain response as enamel. Dental ceramics showed much higher yield stress response than enamel. VM9, a porcelain veneer component of crown/bridge structure, is slightly softer than its core, Mark II. The yield point for Mark II and VM9 are nearly 10 and 7GPa, respectively, and approximately 2GPa for Wiron alloy and enamel. SIGNIFICANCE: H-a/R curves provide a new method to compare the mechanical properties of different dental materials. From the standpoint of structural reliability, strong and tough materials with primarily elastic response, such as toughened ceramics are required to enable dental crown/bridges to have long term reliability. On the other hand, materials with too high hardness or yield response may damage opposing teeth during occlusal contact. Future studies may establish a relationship between stress and strain property and abrasive wear of dental material.

Dental Alloys↗

PubMed1999

Short-term effects of bisphosphonates on the biomechanical properties of canine bone.

Periprosthetic osteolysis and aseptic loosening of total joint replacements are believed to be initiated often by abnormal bone resorption induced by prosthetic wear debris. Bisphosphonates can inhibit bone resorption and have been successfully used clinically to treat osteoporosis and Paget's disease. In a recent study it also was shown that a third generation bisphosphonate (alendronate) is effective in preventing wear debris-induced periprosthetic osteolysis. Since inhibition of bone resorption by alendronate may disrupt the delicate balance between bone resorption and formation in normal bone remodeling, it is possible that continuous alendronate therapy may have an adverse effect on the biomechanical properties of bone. Thus the purpose of the present study was to examine the effects of systemic alendronate administration on the biomechanical properties of normal bone using a canine total hip arthroplasty model. We evaluated the biomechanical properties of femora from canines that had received total hip replacements on one side and had been given oral alendronate daily for 23 weeks. The biomechanical properties assessed were fracture toughness, elastic modulus, tensile strength, microhardness, porosity, and weight fractions of the mineral and organic phases of bone. Also, bone microstructure was examined using optical microscopy. Our results indicate that in the short term alendronate therapy does not have any adverse effects on the intrinsic biomechanical properties of canine bone. However, the long-term effects of alendronate therapy still need to be investigated.

Alendronate↗

PubMed2000

[Properties and infiltration arts of machinable infiltration ceramic(MIC)].

OBJECTIVE: The purpose of this study is to explore the infiltration arts of MIC and study the effects of different packing density of Al2O3 matrix on the properties of MIC. METHODS: alpha-Al2O3 specimens were fabricated by pouring alpha-Al2O3 slip with different powder/liquid ratios(P/L = 3.5, 7.5, 10.5) into a mold, and subsequently pre-fired at 1160 degrees C for 6 hours to form Al2O3 matrix. The packing density of the matrices were measured. Infiltration concepts were introduced into this study by infiltrating molten mica micro-crystalline glass into the porous Al2O3 matrix at 1160 degrees C for 6 hours to form a continuous interpenetrating composite. The composite then underwent micro-crystallization by nucleating at 550 degrees C for 1 hour and crystallizing at 900 degrees C for 1 hour, which resulted in the MIC. Mechanical properties including three point flexural strength, elastic modulus, Vicker's hardness, indentation fracture toughness and Weibull's modulus of flexural strength were determined. Parameters of machinability(H/KIC)2 of MIC were calculated. XRD and SEM were employed to study its microstructure. RESULTS: The resulted matrices reached packing densities of 63%, 76%, 78% with P/L of 3.5, 7.5 and 10.5. The MIC attained high strength and good machinability after infiltration. Three-point flexural strength and indentation fracture toughness were 342, 431, 374 MPa and 4.05, 4.14, 5.02 MPa m1/2 for MIC with packing density of 63%, 76%, 78% separately. And parameters of machinability were 5.41, 6.84 and 7.39 respectively. Packing density of Al2O3 matrix significantly influenced the mechanical properties. Maximum properties were obtained with a matrix packing density of 75%(P/L = 7.5), with a Weibull's modulus of flexural strength of 6.8. Machinability decreased with the increase of P/L ratio. Micro-crystallizing treatment resulted in the formation of evenly distributed mica crystalline in the composite, which contributed to the high strength of this composite material. CONCLUSION: MIC is a new infiltrated ceramic with favorable strength and machinability which can satisfy the prosthodontic requirements as all ceramic crown and bridge materials, it also shows promising outlook for future developments and clinical usage.

Aluminum Oxide↗

PubMed2004

Rheological studies of PLLA-PEO-PLLA triblock copolymer hydrogels.

We report detailed rheological data on aqueous gels formed from triblock copolymers of L-lactide and ethylene oxide including the dependence of the viscoelastic moduli on frequency and applied stress of these systems for the first time. We are able to create strong gels with elastic moduli greater than 10,000 Pa, which is an order of magnitude higher than previously achieved with related biocompatible physically associated gels of similar chemistry. Moreover, the value of the elastic modulus strongly depends on PLLA block length, offering a mechanism to control the mechanical properties as desired for particular applications. At the gel point, we observe scaling that is characteristic of a percolated network, G' approximately G" approximately omega(Delta), but with an exponent that is lower than predicted by percolation, Delta=0.36. Our results have implications for the design of new materials for soft tissue engineering, where native tissues have moduli in the kPa range.

Biocompatible Materials↗

PubMed2006

Matrices with compliance comparable to that of brain tissue select neuronal over glial growth in mixed cortical cultures.

Cortical neurons and astrocytes respond strongly to changes in matrix rigidity when cultured on flexible substrates. In this study, existing polyacrylamide gel polymerization methods were modified into a novel method for making substrates capable of engaging specific cell-adhesion receptors. Embryonic cortical dissociations were cultured on polyacrylamide or fibrin gel scaffolds of varying compliance. On soft gels, astrocytes do not spread and have disorganized F-actin compared to the cytoskeletons of astrocytes on hard surfaces. Neurons, however, extend long neurites and polymerize actin filaments on both soft and hard gels. Compared to tissue culture plastic or stiff gel substrates coated with laminin, on which astrocytes overgrow neurons in mixed cultures, laminin-coated soft gels encourage attachment and growth of neurons while suppressing astrocyte growth. The number of astrocytes on soft gels is lower than on hard even in the absence of mitotic inhibitors normally used to temper the astrocyte population. Dissociated embryonic rat cortices grown on flexible fibrin gels, a biomaterial with potential use as an implant material, display a similar mechano-dependent difference in cell population. The stiffness of materials required for optimal neuronal growth, characterized by an elastic modulus of several hundred Pa, is in the range measured for intact rat brain. Together, these data emphasize the potential importance of material substrate stiffness as a design feature in the next generation of biomaterials intended to promote neuronal regeneration across a lesion in the central nervous system while simultaneously minimizing the ingrowth of astrocytes into the lesion area.

Acrylic Resins↗

PubMed1987

In vitro restructuring effect of human airway immunoglobulins A and lysozyme on airway secretions.

The in vitro effects of different pure proteins: IgA, IgM and human airway lysozyme (HAL) on rheological and transport properties of airway secretions from patients with chronic bronchitis, were studied. The proteins were added to the reconstituted sputum samples in concentrations within the range present in sputa (IgA: 4% HAL: 1% and IgM: 0.5%). A significant (p less than 0.05) positive increase in apparent viscosity and in elastic modulus was observed after adding IgA or HAL. This suggests that these two secretory proteins contribute to the viscoelastic properties of airway secretions and may act as restructuring molecules. After protein overload of the sputum samples, opposite changes in mucociliary transport rate were observed according to whether the initial values of protein concentration and rheology were abnormally low or high. These results suggest that, as for mucus rheology, there is an intermediate range of IgA and HAL optimal for mucociliary transport rate.

Elasticity↗

PubMedDate not supplied

The mechanical properties of exposed human common carotid arteries in vivo.

In exposed common carotid arteries of 15 patients (36-74 years) undergoing neck surgery, the intra-arterial pressure (P) was recorded by means of a catheter-tip manometer and, at the same site, the external diameter (D) by means of a contact-free photoelectric device. On the average, the pulsatile diameter changes were 5.6% of the end-diastolic diameter at pulse pressures of about 50 mm Hg. Due to viscoelasticity, the P-D diagrams exhibited hysteresis loops. Using the criterion of loop elimination, an iterative procedure was applied which permitted, by the use of an appropriate computer program, the separation of the purely elastic and the purely viscous components of the P-D relationships. In all cases, the purely elastic P-D curves markedly deviated from linearity. The tangential elastic modulus (Et) and the pulse wave velocity (c) calculated from these curves were normalized by dividing these quantities by the respective end-diastolic values and plotted against the normalized external diameters. During each pulse cycle, Et increased, with increasing diameter, by a factor between 1.2 and 3.5, while c increased by a factor between 1.1 and 1.9 with reference to the respective end-diastolic values.

Adult↗

PubMed2003

Photopolymerized hyaluronic acid-based hydrogels and interpenetrating networks.

Hyaluronic acid (HA) was derivatized with methacrylic esters used for the preparation of hydrogels via photopolymerization. Poly(ethylene glycol) diacrylate (PEG-DA) with a molecular weight of 570 was also used as a comacromonomer to improve elastic modulus and swelling behavior. The hydrogels were readily degraded by hyaluronidase and their mechanical properties could be modulated by HA molecular weight and concentration of PEG-DA. The incorporation of RGD peptides allowed modulation of the HA properties from cell non-adhesive to adhesive. Human dermal fibroblasts were cultured on the RGD, RDG, and non-functionalized HA hydrogels for up to 7d, showing adhesion and proliferation only with incorporated RGD.

Amino Acid Sequence↗

PubMed1991

[Age, activity and strength of knee ligaments].

The cruciate ligaments of older persons are thought to have diminished biomechanical properties. On the other hand, joint immobilization also leads to similar functional losses in ligaments. It can be difficult to differentiate between these factors in older and immobile persons. The anterior and posterior cruciate ligaments of six younger (average age 30 years) and six older (average age 64.7 years) donors with similar levels of activity were subjected to biomechanical testing. Each sample had to meet the following conditions: appropriate age, no chronic vascular and cardiopulmonary disease found on autopsy, no signs of osteoarthrosis and no knee injuries. The material properties of maximum stress (e.g. ACL: young/old 24/21N/mm2), elastic modulus (e.g. ACL: young/old 144/129 MPa), and strain (e.g. ACL: young/old 25/28%), did not differ significantly (p less than 0.05). This indicates that older persons who are active do not necessarily show functional losses in the cruciate ligaments. Other data found in the literature can be ascribed to immobilization influences. In this data many of the older test persons had chronic vascular insufficiency, cardiopulmonary disease or malignancies.

Aged↗

PubMed1996

In vitro characterization of a fluoropassivated gelatin-impregnated polyester mesh for hernia repair.

The surgical management of abdominal hernias requires prosthetic grafting in situations where the defect is too large or the surrounding tissue is not available for repair. Flat patches made of different biomaterials have been used in textile or microporous forms. The present work describes the results of an in vitro study comparing the morphological, mechanical, and chemical characteristics of a new textile prototype, Fluoropassiv, made of polyester fibers treated with a fluoropolymer and impregnated with gelatin to those of seven existing commercial meshes and patches made from polypropylene, polyester, polytetrafluoroethylene (PTFE) yarns, and expanded microporous PTFE graft. The morphological study revealed a diversity of structures having a minimal relative porosity of 70%, high bursting, and suture retention strengths in comparison with natural muscular tissue. Elasticmoduli proved to depend more on the direction of the textile the rigidity was higher for those materials having tight structure, like the Fluoropassiv and the Surgipro meshes (> 30 MPa), whereas those with more open structures, such as the Marlex, Trelex, Lars, Bard Teflon, and GoreTex structures, showed lower elastic modulus (10 mPa). In addition, chemical analyses confirmed no irregularities in the polymers used in all prostheses and demonstrated that the fluoropolymer coating of the Fluoropassiv was uniformly distributed. The innovative aspects in the construction of the knitted fabric Fluoropassiv appears to make it suitable for repairing hernias, and the inclusion of both continuous fluoropolymer surface treatment of polyester fibers and gelatin impregnation appears to improve the healing process.

Biocompatible Materials↗

PubMed1996

Geometric properties of the fractured tibia stabilized by unreamed interlocking nail: development of a three-dimensional finite element model.

Based upon magnetic resonance scans of five human tibiae a three-dimensional finite element model using eight nodal isoparametric elements was developed to analyze the biomechanical properties of fracture fixation by an unreamed interlocking nail. Tension phenomena and bone implant translations occurring in the borderlines of the fracture zone, bone-implant interface, and the fixation site of the interlocking screws were analyzed with the help of link elements. The proximal fracture segment was fixed with a link element so as to produce exclusively translatory shifts corresponding to the vector of the load applied. Under condition of static load F = 500 N or axial torsion MT = 15 Nm the biomechanical properties of a nailed horizontal fracture (42-A3), a three fragment lesion (42-B2), and a comminuted midshaft fracture (42-C3) were evaluated. On condition of axial load maximum dislocations of 0.1549 mm are induced in the direction of the x-axis due to the asymmetric geometry of the human tibia which promotes medially directed translations. Independent from the fracture type present a homogenous tension profile was calculated for the whole tibia diaphysis with a sigmaEQV ranging from 24.18 to 121.14 MPa due to the relative low elastic modulus of the cortical bone compared to material characteristics of the implant. However, application of a torsional moment MT = 15 Nm induces significantly increased tension maxima in the nail-interlocking screw interface with a sigmaEQV = 7, 626 MPa. Maximum translatory movements ux = 12.59 mm and uy = 23.53 mm in the x and y plane indicate that these load conditions bear a high risk of an implant failure.

Biomechanical Phenomena↗

PubMed2006

Ex vivo measurement of brain tissue viscoelasticity in postischemic brain edema.

Knowledge of the biomechanical properties of postischemic brain tissue is important for understanding the mechanisms of postischemic secondary brain tissue injury. We describe the method and results of biomechanical property measurement in ex vivo postischemic brain tissue by applying an indentation method. Mongolian gerbils were subjected to a transient unilateral hemispheric ischemia. At day 1 after ischemia, multi-parametric MRI was performed, the brain was removed under anesthesia, sliced, and kept in a container with silicone oil for the measurement. A compression probe attached to a pressure transducer was inserted to a pre-determined depth at the regions of interest and maintained at a constant speed. A pressure relaxation curve was recorded for the calculation of elasticity modulus (E) and viscosity modulus (eta) according to Maxwell-Voigt's 3-element model. One day after ischemia, E and eta decreased to 78.7% and 73.1% of the control level, respectively. This decrease corresponded to a mild decrease in apparent diffusion coefficient (ADC) and magnetization transfer ratio, and an increase in T2 value. Tissue water content increased to 105.1% of control. Microvacuolation with demyelination and axonal disruption was evident in the postischemic brain tissue.

Animals↗

PubMed2005

Effect of raloxifene on aortic elasticity in healthy postmenopausal women.

BACKGROUND: The effect of raloxifene on aortic elasticity in healthy postmenopausal women is unknown. The purpose of the present study was to examine the effect of raloxifene on aortic elasticity and cardiovascular structure and function in healthy postmenopausal women. METHODS: A randomized, crossover, double-blind, placebo-controlled clinical trial was performed. Fourteen healthy postmenopausal women received treatment with raloxifene 60 mg daily and matching placebo for 8 weeks with an 8-week washout period in between the 2 treatment periods. Cardiovascular magnetic resonance imaging was used to assess ascending thoracic and abdominal aortic elasticity and cardiovascular structure and function (left ventricular volumes, ejection fraction, and mass and mitral annular displacement) before and at the end of each treatment period. RESULTS: Administration of raloxifene had no significant effect on either heart rate or systemic blood pressure. Raloxifene treatment was associated with a small decrease of the ascending aorta wall thickness (pretreatment 2.4 +/- 0.3 vs posttreatment 2.2 +/- 0.2 mm, P = .01). Consequently, there was an increase in the Young's elastic modulus after raloxifene treatment at the ascending thoracic aorta but not the abdominal aorta. There were no significant differences in aortic compliance or any cardiac indexes after raloxifene treatment. CONCLUSIONS: Raloxifene administration in healthy postmenopausal women over an 8-week period may decrease the aortic wall thickness but has no significant effects on aortic compliance or cardiac structure and function.

Aorta↗

PubMed1984

Rheological properties of living cytoplasm: a preliminary investigation of squid axoplasm (Loligo pealei).

A magnetic sphere viscoelastometer has been developed to perform rheological experiments in living axoplasm of Loligo pealei. The technique includes the use of a calibrated magnetic sphere viscoelastometer on surgically implanted ferro-magnetic spheres in intact squid giant axons. The axoplasm was discerned to be "living" by the biological criterion of tubulovesicular organelle motility, which was observed before and after experimentation. From these in vivo experiments, new structural characteristics of the axoplasm have been identified. First, analysis of magnetic sphere trajectories has shown the axoplasm to be a complex viscoelastic fluid. Directional experimentation showed that this material is structurally anisotropic, with a greater elastic modulus in the direction parallel to the axon long axis. Second, both magnetic sphere and in vivo capillary experiments suggested that the axoplasm is tenaciously anchored to the axolemma. Third, it was found that axoplasm could be modelled as a linear viscoelastic material in the low shear rate range of 0.0001 to 0.004 s-1. The simplest mechanical model incorporating the discovered properties of the material in this range is Burger's model.

Animals↗

PubMed2004

Relationship between reduced elasticity of extracardiac vessels and left main stem coronary artery disease.

OBJECTIVES: To investigate the elastic properties of medium-size extracardiac arteries and veins between patients with and without left main stem coronary artery disease. METHODS: The compliance, distensibility, and incremental elastic modulus (iEmod) of the internal thoracic arteries (n=53), long saphenous veins (n=38), and radial arteries (n=35) from 74 patients undergoing coronary surgery were studied in organ baths. Twenty-four patients had left main stem (LMS) disease and 50 non-LMS coronary disease. RESULTS: Internal thoracic arteries from patients with LMS presented significantly lower compliance (-17%) and distensibility (-18%) and significantly higher iEmod (19%) than internal thoracic arteries from patients with non-LMS disease. Radial arteries from patients with LMS presented higher iEmod (50%) than radial arteries from patients with non-LMS disease. Furthermore, long saphenous veins from patients with LMS had reduced compliance (-45%), reduced distensibility (-40%) and increased iEmod (34%) compared to those from patients with non-LMS disease. CONCLUSIONS: LMS coronary disease is associated with a significantly reduced elasticity of extracardiac arteries and veins compared to non-LMS coronary disease. This finding suggests that widespread vascular elasticity defects may play a role in the development of LMS disease and be responsible for the higher incidence of early and late cardiovascular morbidity observed in this condition.

Coronary Artery Disease↗

PubMed2001

Mechanics of the antebrachial interosseous membrane: response to shearing forces.

The interosseous membrane functions to maintain the structural integrity of the forearm; however, the age-related mechanical properties of the intact membrane are incompletely defined. The purpose of this study is to quantify the mechanical properties of the interosseous membrane by applying a quasi-equilibrium shearing force between the radius and ulna. A 5-cm section of the central (main and accessory bundles) fiber from 11 (5 male and 6 female) fresh-frozen cadaver arms (age, 74 +/- 6.9 years) was isolated with the radial and ulnar attachments, measured, and positioned into the testing apparatus. A shear force was applied at 12.7 mm/min to produce a quasi-equilibrium state, and the applied force and elongation were monitored. The average ultimate force, ultimate strength, and elastic modulus were 1101 +/- 191 N, 13.98 +/- 4.85 MPa, and 135.29 +/- 41.57 MPa, respectively. Age-related changes were also noted with an increase in thickness by 0.056 mm per year of age and a decrease in fiber stiffness of 4.78 MPa/yr. The age-related mechanical properties of the intact interosseous membrane are necessary for modeling forearm stability in normal and pathologic conditions. This information is required for analysis of repair or reconstructive procedures.

Aged↗

PubMed2002

Measurements of endothelial cell-to-cell and cell-to-substrate gaps and micromechanical properties of endothelial cells during monocyte adhesion.

The interaction between monocytes and endothelial cells is considered to play a major role in the early stage of atherosclerosis, and the involved endothelial cell micromechanics may provide us with important aspects of atherogenesis. In the present study, we evaluated (i) the endothelial cell-to-cell and cell-to-substrate gaps with the electric cell-substrate impedance sensing system, which can detect the nanometer order changes of cell-to-cell and cell-to-substrate distances separately, and (ii) the endothelial cell micromechanical properties with an atomic force microscope after application of monocytes to endothelial cells. Application of monocytic THP-1 cells to IL-1beta-stimulated human umbilical vein endothelial cells immediately decreased the electrical resistance of the endothelial cell-to-substrate (increase of the cell-to-substrate gap), whereas the endothelial cell-to-cell resistance (cell-to-cell gap) did not change. The elastic modulus of the endothelial cells decreased after 2-h monocyte application, indicating an increase of endothelial cell deformability. In conclusion, the interaction of the monocytes to the endothelial cells reduced the adhesiveness to the substrate and increased the deformability of endothelial cells. These changes in the adhesiveness and the deformability may facilitate migration of monocytes, a key process of atherogenesis in the later stage.

Actins↗

PubMed1991

Length dependence of passive stiffness in single cardiac myocytes.

Passive elastic properties have been studied in detergent-skinned isolated single cardiac myocytes of rat, guinea pig, and rabbit in an attempt to determine whether a measurable difference exists in passive cellular elastic characteristics of these mammalian species. Although the cross-sectional area of isolated cardiac myocytes is complex, a small but statistical difference appears to exist in the elastic modulus of detergent-skinned mammalian cardiac myocytes at 2.2 microns sarcomere length (SL) in the order rat is greater than rabbit, which is greater than guinea pig. The stiffness of rat cells increases least rapidly with increases in SL, and that of the rabbit cells increases most rapidly. In comparison with intact cardiac tissue in the literature, the proportion of stress contributed by skinned myocytes may be as much as half that of the trabeculae at 2.2 microns SL and approximately 10% of that of papillary muscles. Below 2.2 microns SL, the relative cellular proportion increases such that cellular elements may be a major contributor at 1.9 microns SL. Above 2.2 microns SL, the relative cellular contribution declines such that by 2.4 microns SL the cellular contribution is insignificant. It is concluded that at functional SLs intracellular elastic elements may contribute measurably to total cardiac passive elasticity, but at extended lengths the extracellular structures constitute the major limitation to extension.

Animals↗