[A biomechanical model of human knee-joint elastic articulate contact].

In this paper, based on the characterizations of human knee-joint anatomical structures and reports of the literature and experiments, a biomechanical model of the human knee-joint elastic articulate contact is developed under the conditions of sampling the human knee-joints. This model is believed to be a powerful tool for functional analysis of the knee, for evaluation of surgical and diagnostic procedures and for design of artificial joints.

A biomechanical and spectroscopic study of bone from rats with selenium deficiency and toxicity.

Selenium, being an essential mineral in the mammalian diet, is important in providing protection against oxidative damage. Numerous in vitro studies of selenium compounds reveal a very high correlation between catalytic activity of selenium compounds and toxicity. The present study was designed to investigate the effects of dietary selenium on the biomechanical properties of bone. New born rats of both sexes were fed with either a control, or a selenium- and vitamin E-deficient, or a selenium-excess and vitamin E-adequate diet. We obtained the stiffness (modulus of elasticity) of bones (femur and tibia) by tensile test for all groups considered. Both the deficient and the excess groups have decreased biomechanical strength with respect to the control group. To support our biomechanical results for both experimental groups, X-ray diffraction analysis and FTIR spectroscopic study were performed on the femurs and tibiae. The X-ray diffraction analysis showed that the intensities of the peak observed at around 2theta degrees = 31.820, in the control femur and tibia are stronger than the intensities of the corresponding peak of two experimental groups. In FTIR spectroscopy, the disappearance and/or reduction of the intensities of some carbonate bands in the two experimental groups indicate that there is a decrease in crystallinity and mineral contents which, together with X-ray diffraction analysis, correlate very well with the biomechanical data.

Fracture resistance of Class II approximal slot restorations.

STATEMENT OF PROBLEM: Determination of the fracture resistance of various restorative materials in Class II approximal slot restorations has not been studied. PURPOSE: This study evaluated the effects of retention grooves and different restorative materials in Class II approximal slot restorations. To explore the possibilities for further research, the probable effects of preparation size and loading angle were investigated in a limited manner. MATERIAL AND METHODS: Ninety sound, caries-free human maxillary premolars were divided into 9 groups. The cavities were prepared either by hand or in a computer-controlled CNC machine with or without retention grooves. Four were restored with adhesive amalgam, another 4 with composite, and a single group with Compomer resin. The gingival floor depth was 1.5 mm. The specimens were loaded at an angle of 13. 5 degrees to their longitudinal axes by using a computer-controlled material testing machine until failure occurred. For one specific preparation of adhesive amalgam, loading was applied at 0 and 30 degrees to determine the probable effects of the loading angle. For a specific composite, resin application, the effects of the change in gingival floor depth were analyzed by assigning the depth to 2.0 mm. RESULTS: Composite and Compomer resin and composite exhibited better performance than amalgam. The existence of the retention grooves proved to be effective for adhesive amalgam restorations but did not have any advantageous effect in composite and Compomer restoration. CONCLUSION: For improved fracture resistance in small approximal restorations, the use of composite was the appropriate choice. Compomer also gave satisfactory results. Use of amalgam restoration should be accompanied with retention grooves and an adhesive system to improve its performance.

The mechanical properties of intact and traumatized epidural catheters.

UNLABELLED: Comparative data on the mechanical properties of epidural catheters used clinically are not available. We performed a controlled laboratory investigation to assess the mechanical performance of three different intact or traumatized catheter types (Polyurethane, clear nylon, and radiopaque nylon catheters, designed for 18-gauge Tuohy needles). We studied a control (intact) and two trauma groups (needle bevel and surgical blade). Catheters were loaded to their breaking points by using a Lloyd LS500 material testing machine (Lloyd, Southampton, UK). Maximal load and extension values before breakage were measured, and modulus of elasticity and toughness values were calculated. Intact polyurethane catheters did not break within the limits of the experimental study (extension up to 3 times the original length of a specimen). The toughness values obtained from polyurethane and clear nylon catheters were significantly higher than those for the radiopaque catheters in intact specimens (P < 0.05). In the traumatized groups, polyurethane catheters had the highest toughness values (P < 0.05). Modulus of elasticity values were higher in both control and trauma groups of the radiopaque catheters when compared with the polyurethane and clear nylon catheters, which indicates a higher stiffness to elastic deformation (P < 0.05). In conclusion, polyurethane catheters are the most durable catheter type to tensile loading, either intact or traumatized. Mechanical properties can be used to predict complications related to the clinical use of these catheters. IMPLICATIONS: Using a computer-assisted material testing machine, we studied the mechanical properties of three different types of epidural catheters, either intact or traumatized, in a blinded, controlled study. This information may be vital to clinicians who implant epidural catheters by helping them choose a catheter that has the lowest probability of failure.

Relation between mechanical stiffness and vibration transmission of fracture callus: an experimental study on rabbit tibia.

It has been suggested that the vibration transmission across a fracture is affected by the stages of healing of the fracture callus. This study aims to correlate the change in vibration transmission with mechanical stiffness of the callus measured by three-point bending. The right tibiae of male, three-month old local albino rabbits were osteotomized and stabilized by intramedullary fixation following open reduction. The intramedullary rods were removed on the 15th, 28th, 42nd and 90th days postoperatively and the tibiae were excised for vibration, three-point bending and bone mineral density analysis by quantitative computerized tomography (QCT). Optimum time for clinical weight bearing was determined by checking the convergence of the vibration parameters of the fractured tibia to those of the unfractured contralateral. The conclusions obtained from curvature analysis, based on vibration experiments, were in considerable correlation (Spearman's rank correlation coefficient r = 0.93, p = 0.003) with the conclusions obtained from the three-point bending test data which reflected the mechanical condition of the bone by direct means. However, no correlation between bone mineral density change and vibration transmission was noted.

Synthesis and mechanical properties of interpenetrating networks of polyhydroxybutyrate-co-hydroxyvalerate and polyhydroxyethyl methacrylate.

Naturally occurring, biocompatible, and biodegradable polyhydroxybutyrate-co-hydroxyvalerate (PHBV), and synthetic, non-degrading polyhydroxyethylmethacrylate (PHEMA) membranes were prepared and their mechanical properties were studied. Their performances were compared with the interpenetrating networks (IPN) prepared by photopolymerization of HEMA in the presence of PHBV. The modulus of elasticity, failure stress and failure strain indicated that the IPNs are viscoelastic with properties closer to PHEMA but much stronger than PHEMA homopolymers. Incorporation of PHBV (7, 14 and 22% HV) affected the mechanical properties positively. Increasing the PHBV content increased the modulus of elasticity and failure stress nearly in all samples tested. PHBV (7, 14, and 22% HV, 300 mg) samples showed an approximately 17-30 fold increase in terms of modulus of elasticity and 7-10 fold increase in terms of failure stress. The scanning electron micrographs of the membranes showed that the PHEMA membranes are more porous than the PHBV membranes but the IPN structure displayed channels on the membrane surface indicating that HEMA polymerization was achieved by using the PHBV as a scaffold. With the use of the present technique, it is possible to synthesize supramolecular structures from molecules that are not compatible and miscible with each other.

[A human knee articulate mathematical model on femur-tibia-patella 3-segmetents].

In this paper, based on the previous work of S. Turgut Tumer et al, a human knee articulate mathematical model on femur-tibia-patella 3-segments is established by introducing patella-femur joint. This model includes both rolling and slipping motions of femur-tibia joint and femur-patella joint. It can be employed in simulating the biodynamic response of human lower extremity.

Dietary selenium- and vitamin E-induced alterations in some rabbit tissues.

The present study was designed to investigate and compare the effects of dietary selenium (Se) and vitamin E on some physiological parameters and histological changes in liver, heart, and skin tissues, as well as the blood parameters and the related enzymes. Both sex young rabbits were fed with deficient (9.8 micrograms/kg diet), adequate (225 micrograms/kg diet), and rich (4.2 mg/kg diet) Se and vitamin E diets for 12-15 wk for this purpose. As the plasma Se levels and the erythrocyte glutathione (GSH) peroxidase activity decreased (79.8 +/- 9.4 ng/mL and 2.0 +/- 0.3 U/g Hb, respectively) in the deficient group, these values increased (100.4 +/- 2.7 ng/mL and 14.5 +/- 4.3 U/g Hb) in the rich group significantly with respect to the control group. The other antioxidant enzyme activities and the related element levels did not change significantly in either one of the experimental groups. Although the platelet counts of the two experimental groups were not different from the control values, the collagen and the adenosine diphosphate (ADP) stimulated platelet aggregation rate and intensity increased in the deficient group (p < 0.05) and decreased very significantly (p < 0.001) in the rich group. In both of the experimental groups, as the percentage values of the neutrophils decreased, the lymphocytes and the eosinophils increased significantly. According to the light microscopic investigations, the observed lesions of considerable intensity within the tissues that elicit cell degenerations were more pronounced in the animals fed with the rich diet than in those fed with the deficient diet. The deficiency as well as toxicity of Se and the deficiency of vitamin E caused several alterations in the physiological functions of the tissues, and these alterations were supported by the histological lesions within these tissues.

Effect of dietary selenium and vitamin E on the biomechanical properties of rabbit bones.

It is generally agreed that combined deficiency of selenium and vitamin E leads to several abnormalities including Kashin-Beck disease which is an endemic and chronic degenerative osteoarthrosis. The abnormalities can be reversed by the administration of various forms of selenium and vitamin E. The present study was designed to investigate the effects of dietary selenium and vitamin E on bone tissue and on the biomechanical properties of bone. Young rabbits of both sexes were fed with either a selenium- and vitamin E-adequate diet (control group), or a selenium- and vitamin E-deficient diet or a selenium-excess diet. The selenium-deficient diet resulted in a significant decrease in plasma selenium level and the selenium-excess diet resulted in a significant increase in the plasma selenium level with respect to the corresponding control values (p < 0.05). The diets did not affect the blood cell counts considerably but erythrocyte glutathione peroxidase activity increased (decreased) relatively when the plasma selenium level increased (decreased) (p < 0.05). The light microscopic investigations of the bone tissues of the two experimental groups indicate that the findings of the present work are compatible with osteomalacia. The biomechanical properties of the bones from the three groups were determined experimentally with bending tests. Both the Se- and vitamin E-deficient diet and the Se-excess diet decreased the biomechanical strength of the bones significantly while the bones belonging to the control group always had the largest modulus of elasticity (p < 0.05).

Reduction of restrictive adhesions by local aprotinin application and primary sheath repair in surgically traumatized flexor tendons of the rabbit.

The effects of microsurgical and medical treatments on reduction of adhesions in surgically traumatized flexor tendons of rabbits are quantified in this study. The effects of the mentioned techniques were investigated for the following 4 groups: (1) neither primary sheath repair nor aprotinin application was done, (2) primary sheath repair was done but no aprotinin was used, (3) primary sheath repair was not done but local aprotinin (15,000 IU/kg) was applied, and (4) primary sheath repair was done and local aprotinin was applied. At the sixth and twelfth postoperative weeks, the flexor digitorum profundus tendons of the second and the third digits were subjected to biomechanical tests. Only the third digit was used in macroscopic and histopathologic evaluations. There were 6 digits included in each subgroup of biomechanical tests and 4 digits per subgroups in macroscopic and histopathologic evaluations. Work of flexion (WOF) values were obtained by calculating the area under the load-displacement curve. Percent resistive work of flexion (PRWOF) was obtained by calculating the difference between the WOF value for the repaired right digit and the WOF value for the contralateral corresponding nonrepaired digit. Combined primary sheath repair and medical treatment yielded the best results in reducing the restrictive adhesions in injured tendons. The differences between the PRWOF values of group 4 were 33.7% +/- 8.2% and 15.8% +/- 7.7% for the sixth and twelfth postoperative weeks, respectively. The corresponding values for group 1 were 95.7% +/- 13.8% and 51.75% +/- 10.25%.

An investigation of the chemical synthesis and high-temperature sintering behaviour of calcium hydroxyapatite (HA) and tricalcium phosphate (TCP) bioceramics.

The experimental conditions for the synthesis of sub-micrometre, spherical particles of calcium hydroxyapatite [Ca10(PO4)6(OH)2] (HA) and tricalcium phosphate [Ca3(PO4)2] (TCP) are investigated through chemical coprecipitation from the aqueous solutions of calcium nitrate and di-ammonium hydrogen phosphate salts. The precipitation process employed was also found to be suitable for the production of sub-micrometre HA/TCP composite powders in situ. The synthesized pure HA and TCP powders were found to be stable even at 1300 degrees C in air for prolonged heating times. Bioceramic sample characterization was achieved by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and density and surface area measurements. Crystallographic analyses of HA powders were performed by the Rietveld method on the powder XRD data.

Biomechanical analysis of the effects of single high-dose vitamin D3 on fracture healing in a healthy rabbit model.

In a previous ultrastructural study, the benefit of a single high dose of vitamin D3 on fracture healing in a healthy animal model was demonstrated. This study examined the biomechanical consequences of applying a single high dose of vitamin D3 in a healthy rabbit model subsequent to femoral fracture. The fracture load, the values of energy absorbed until fracture and the flexural rigidity values of the vitamin D group were significantly higher than the corresponding ones of the control group in the case of fracture. On the other hand, for intact bones, those values did not differ significantly between the two groups. It was concluded that single high-dose vitamin D3 application had positive effects on fracture healing in a healthy animal model, as far as the parameters related to mechanical strength are concerned.

Biomechanics of the Gazi type pelvis external skeletal fixator.

External skeletal fixation is an alternative method of treatment to conventional therapy and open surgical procedures in pelvis fractures. The appropriate type of frame and the configuration of the connecting bars of these fixators are under investigation. In the Gazi type pelvis external fixator (GPEF) which has been developed, a 70 degree angulation is applied to the connecting bars of the anterior quadrangular frame. This configuration, which is expected to improve the stability of the posterior column of the pelvis, was evaluated biomechanically on a phantom with various types of pelvic fractures and separations. The results suggest that the GPEF effectively controls anterior column pelvis fractures such as unilateral pubic ramus fractures, unilateral ischium pubis rami fractures and symphysis pubis separations under vertical loads. The fixator is partially capable of stabilizing the posterior column; however, loads above 700 N cause separation at the fracture site. Further studies and clinical trials are essential to determine the GPEF's effectiveness in reducing blood loss and in providing stability at the posterior column.

Effect of medication on biomechanical properties of rabbit bones: heparin induced osteoporosis.

The aim of this controlled study is to investigate the effect of heparin on osteoporosis initiation and of calcitonin and tamoxifen on the progress of osteoporosis induced by heparin through biomechanical means and, thus, to assist in clinical usage of these drugs. 32 four-month-old female New Zealand white rabbits were divided into four different experimental groups. The animals in group A were administered heparin (Liquemine) intraperitoneally at the dosage of 1000 IU/kg/day. The animals in group B were injected the same amount of heparin as those of group A, and in addition, were given calcitonin at the dosage of 100 IU/kg/day. The animals in group C were medicated the same way as group B but 2 mg/kg/day tamoxifen (Nolvadex) was orally added into their intestine via cannula, one side connected to the injector. The animals in group D were the control. The experiment lasted 8 weeks. The animals in all experimental groups showed the same growth pattern as that of the control group. Whole-bone femur, humerus and tibia specimens were subjected to 3-point bending tests while sections from the proximal ends of the same specimens were subjected to compression tests. The data, recorded as load vs deflection, were converted into stress vs strain using the strength of materials formulae. The data obtained from the bending and the compression experiments were treated separately. The stiffness of the bones of the medicated groups were compared with those of the control groups. Our data indicated that the tamoxifen treated humera, femora and tibiae attained the largest bending stiffness in all cases investigated. However, this was not the case for compression. None of the drug administered groups attained the stiffness of the control group except for the case of tamoxifen treated femora which attained stiffness close to that of the controls. The results show that heparin altered the mechanical properties of bones indicating osteoporosis, tamoxifen was effective in reducing the effect of heparin while calcitonin yielded no conclusive result.

Do porous calcium hydroxyapatite ceramics cause porosis in bone? A bone densitometry and biomechanical study on cortical bones of rabbits.

Porous calcium hydroxyapatite (CHA) ceramics are biocompatible and present osteoconductive properties. These ceramics are widely used in orthopaedic surgery; however, it is not yet known whether they have some adverse effects on bone and bone marrow healing. Our previous radiological study revealed possible local porosis at the adjacent sites of the CHA ceramic. Histological findings of the same study revealed bone marrow swelling and depletion at the implantation site. Osteoclasts removed particles of the implant that may be the cause of local porosis. In the present study, possible local osteoporosis was evaluated by bone densitometry analyses, and compression and three-point bending tests. CHA particles were implanted into the left limbs and a sham operation was utilized on the right limbs of 75 white rabbits. The animals were followed up for 23 weeks for bone mineral density and for 6 months for biomechanical analyses. The CHA implanted area and its distal or proximal adjacent areas were evaluated with a Hologic QDR-2000 bone densitometer. Three-point bending and compression tests were performed with an M-30 K material testing device. The results revealed a time-dependent bone density increase at the CHA implantation site and no significant porosis at adjacent areas of the implant. The stiffness of CHA-implanted bones in three-point bending is larger than that of the control group. CHA-implanted rabbit bones presented a different fracture pattern from the control group. The stiffness of the control and CHA-implanted bones generally increased with time indicating no adverse effects of porous CHA ceramics in bone and bone marrow healing. The clinical relevance of this work is that porous CHA ceramics do not cause local porosis at adjacent areas when implanted into osseous sites.(ABSTRACT TRUNCATED AT 250 WORDS)

Mechanical behavior of fetal dura mater under large deformation biaxial tension.

The mechanical behavior of fetal dura mater was investigated by means of a biaxial tension test designed to simulate the constraints imposed on the membrane by the cranial bones. The experimental results are compared with the theoretical results obtained by using two published strain energy functions: one defined by Mooney and Rivlin (MR) and the other by Skalak, Tozeren, Zarda and Chien (STZC). The latter constitutive relations fit the experimental results consistently well. The STZC stiffness values from this series of tests are compared with those from membrane inflation tests performed previously and reported elsewhere by the authors.

Biomechanics of virus-to-cell and cell-to-cell fusion.

A biomechanical model of virus-to-cell and cell-to-cell fusion is presented. Virus and the cells are modelled as initially spherical membranes of nonlinear elastic material that undergo large deformations. The membranes are connected by a cytoplasmic bridge which expands, resulting in the formation of a larger single sphere. In virus-to-cell fusion, a smaller spherical membrane is connected to a much larger one. Fusion is completed when the smaller membrane is completely incorporated into the larger one. The numerical results predict the existence of a ring force in the so-called furrow plane. It is possible that the microfilaments of the cortical layer form the furrow band which may provide this ring force.

Etiology and biomechanics of hernial sac formation.

This paper, to the authors' best knowledge, presents the first attempt on the understanding of the biomechanics of hernial sac formation. First, a brief survey of the selected etiological factors and their related theories on hernia is given. Next, the results of some preliminary tensile tests conducted on normal and sac peritoneum are discussed. The third part of the paper is concerned with a theoretical model which incorporates both material and geometric nonlinearities by considering deformation of circular membrane under internal fluid pressure. The influence of the material properties of the peritoneal sac, its thickness and its initial radius of curvature, as well as the internal fluid pressure on the growth of the sac are illustrated. The existence of a critical value for a non-dimensional parameter is shown and it is proposed that the herniation process can be viewed as a biomechanically unstable phenomenon in the light of the present model.

Mechanical behavior of fetal dura mater under large axisymmetric inflation.

The nonlinear mechanical behavior of fetal dura mater was tested experimentally and compared to two published nonlinear material strain energy functions, the Mooney-Rivlin and the Skalak, Tozeren, Zarda, and Chien (STZC). The STZC constitutive relations best fit the behavior of the dura mater and were used to describe quantitatively its stiffness. Runge-Kutta numerical procedures were used to fit the theoretical data to the experimental results. The material's stiffness was positively correlated with fetal weight (r = 0.67, p less than 0.05). These results are discussed and directions for future research indicated.

Two-dimensional dynamic modelling of human knee joint.

A mathematical dynamic model of the two-dimensional representation of the knee joint is presented. The profiles of the joint surfaces are determined from X-ray films and they are represented by polynomials. The joint ligaments are modelled as nonlinear elastic springs of realistic stiffness properties. Nonlinear equations of motion coupled with nonlinear constraint conditions are solved numerically. Time derivatives are approximated by Newmark difference formulae and the resulting nonlinear algebraic equations are solved employing the Newton-Raphson iteration scheme. Several dynamic loads are applied to the center of mass of the tibia and the ensuing motion is investigated. Numerical results on ligament forces, contact point locations between femur and tibia, and the orientation of tibia relative to femur are presented. The results are shown to be consistent with the anatomy of the knee joint.