Biomedical subjects

N Guzelsu

Publications and source records attributed to N Guzelsu.

14 recordsLinked to original sources

PubMed2000

The effects of interphase and bonding on the elastic modulus of bone: changes with age-related osteoporosis.

A simple shear lag model is developed to analyze the physics of the stress transfer between the organic and mineral constituents of bone tissue in the presence of an interphase and changes in bonding. The analytical model is developed assuming interactions between overlapped bone mineral platelets. The platelets are assumed to carry the axial stresses while the organic matrix transfers the stresses from one platelet to another by shear. A decrease in the interphase mechanical properties decreases the elastic modulus due to increased shear between the overlapped platelets. A decrease in bonding decreases the elastic modulus due to an increase in the axial stress transferred from the ends of the platelet. The implications of the changes in parameters on the age-related disorders of bone (osteoporois) are discussed. It is suggested that the aspect ratio and volume fraction of the mineral in the remaining bone tissue would increase due to a reduction in the density of the bone. The mechanical properties of the organic are hypothesized to increase due to a reduction in the density of bone leading to an increased tendency for damage within the organic.

Blood Platelets↗

PubMed1999

Adaptation of passive rat left ventricle in diastolic dysfunction.

This article deals with providing a theoretical explanation for quantitative changes in the geometry, the opening angle and the deformation parameters of the rat ventricular wall during adaptation of the passive left ventricle in diastolic dysfunction. A large deformation theory is applied to analyse transmural stress and strain distribution in the left ventricular wall considering it to be made of homogeneous, incompressible, transversely isotropic, non-linear elastic material. The basic assumptions made for computing stress distributions are that the average circumferential stress and strain for the adaptive ventricle is equal to the average circumferential stress and strain in the normotensive ventricle, respectively. All the relevant parameters, such as opening angle, twist per unit length, axial extension, internal and external radii and others, in the stress-free, unloaded and loaded states of normotensive, hypertensive and adaptive left ventricle are determined. The circumferential stress and strain distribution through the ventricular wall are also computed. Our analysis predicts that during adaptation, wall thickness and wall mass of the ventricle increase. These results are consistent with experimental findings and are the indications of initiation of congestive heart failure.

Adaptation, Physiological↗

PubMed1998

Optimal patterns for suturing wounds.

A mathematical model for computing stresses in sutured human skin wounds is presented. The model uses the incremental law of elasticity and elastic constants valid for in vivo orthotropic skin. The model is applied to compute the principal stress and displacements resulting from suturing small elliptical and circular wounds in a large flat sheet of skin, in order to determine the optimal suturing patterns. It is observed that the average stress index for a circular wound sutured toward the center is almost double that of a wound sutured transverse to the diameter. Thus, the latter type of suturing pattern is preferable. Similarly, suturing an elliptical wound transversely produces a lower average stress index than a circular wound of the same area. It is also found that the optimal ratio of semi-major to semi-minor axis of an elliptical wound is near 3 (for abdominal wounds), i.e., this ratio produces the most uniform stresses along the wound edges, where wound healing is slowest. Since high stresses have adverse effects on healing and blood flow, this work, depicting regions of high stresses, may be used along with other biological factors to help predict regions of slower healing in sutured wounds.

Algorithms↗

PubMed1998

Varying the mechanical properties of bone tissue by changing the amount of its structurally effective bone mineral content.

The effect of fluoride ions on the mechanical properties of bone tissue in tension was investigated with an in vitro model. Structurally effective Bone Mineral Content (BMC) of bovine bone tissue was changed by fluoride ion treatment. First, bovine cortical bone specimens were treated with a detergent solution in order to increase the diffusion rates of the treatment ions across the samples. After the initial treatment, different ion solutions were used to treat the tension samples (fluoride, sodium and chloride). Ionic strength and pH were varied. Experimental results showed that the sodium chloride solutions of different ionic strengths, at physiological and high pH, do not affect the mechanical properties of bone tissue in tension. However, uniform fluoride treatment across the samples reduced the mechanical strength of bone tissue by converting small amounts of bone mineral to mostly calcium fluoride. This action reduces the structurally effective BMC and also possibly effects the interface bonding between the bone mineral and the organic matrix of the bone tissue.

Animals↗

PubMed1994

Effect of electromagnetic stimulation with different waveforms on cultured chick tendon fibroblasts.

An energy efficient electromagnetic stimulator device for fracture healing was compared to a commercially available device in stimulating cell growth in tissue cultures. The energy efficient device, which conserves energy by using a bidirectional time-dependent magnetic wave form, and the commercially available stimulator, which uses a unidirectional time-dependent magnetic wave form, were tested on chick tendon fibroblasts in primary culture. Comparing non-stimulated control and cells electromagnetically stimulated with unidirectional and bidirectional waveforms showed that at the growth phase between days 2 and 3, both electrical stimulation techniques increased cell division as measured by DNA synthesis. When cells were dividing rapidly, collagen synthesis was reduced. When the cells reached the confluence there was no difference among the groups (control, unidirectionally stimulated, and bidirectionally stimulated) in terms of number of cells or collagen produced.

Animals↗

PubMed1994

Compressive properties of cortical bone: mineral-organic interfacial bonding.

Bone tissue is an anisotropic non-homogeneous composite material composed of inorganic, bone mineral fibres (hydroxyapatite) embedded in an organic matrix (type I collagen and non-collagenous proteins). Factors contributing to the overall mechanical behaviour include constituent volume fraction, mechanical properties, orientation and interfacial bonding interactions. Interfacial bonding between the mineral and organic constituents is based, in part, on electrostatic interactions between negatively charged organic domains and the positively charged mineral surface. Phosphate and fluoride ions have been demonstrated to alter mineral-organic interactions, thereby influencing the mechanical properties of bone in tension. The present study explores the effects of phosphate and fluoride ions on the compressive properties of cortical bone.

Analysis of Variance↗

PubMed1993

Ion concentration effects on bone streaming potentials and zeta potentials.

Electrical potentials are dependent on the properties of the solid and fluid phases of bone. The solid phase in bone is composed of an organic matrix and inorganic bone mineral fibre, while the fluid phase is separated into compartments associated with the vascular channel system and mineralized matrix. Recently, a piezoelectric and electrokinetic response following mechanical deformation was demonstrated in fully hydrated bone. However, alterations in the fluid phase and the effects on streaming potentials where flow through the sample due to pressure on the fluid phase without prior solid matrix mechanical deformation have not been examined. Streaming potentials in high ionic strength solutions reveal a flow-dependent streaming potential in the absence of mechanical deformation not previously observed in stress-generated potentials. Streaming potentials in high ionic strength sodium chloride solutions (0.75 M) of control and deproteinized samples suggest that organic molecules and ions in the electrical double layer may be susceptible to flow-induced alterations which can modify the streaming potentials generated. Alterations in properties of the fluid phase can modify the streaming and zeta potentials and may play a role in the biofeedback response to bone tissue.

Animals↗

PubMed1993

The role of ions and mineral-organic interfacial bonding on the compressive properties of cortical bone.

Bone tissue is a composite material composed of an inorganic stiff mineral phase embedded in a compliant organic matrix. Similar to other composites, the mechanical properties of bone depend upon the properties, volume fraction, and orientation of its constituents as well as the bonding interactions. Interfacial bonding between the mineral and organic constituents are based, in part, on electrostatic interactions between negatively charged organic domains and positively charged mineral surface. Phosphate and fluoride ions can alter mineral-organic interfacial causing a permutation in the mechanical properties. Partial debonding between the mineral and organic constituents of bone may play an important role in the mechanical properties of aged and diseased bone. The present study examines the effects of phosphate and fluoride ion treatment on the compression properties of cortical bone and the reversibility of the effect.

Animals↗

PubMed1991

Electrokinetic behavior of intact wet bone: compartmental model.

Streaming potential experiments were performed on chemically-treated intact wet bone plugs equilibrated in potential-determining ion buffers. Comparison of calculated zeta (zeta) potentials from intact wet bone streaming potentials and bone particle electrophoresis indicates different values. Intact streaming potential experiments, where fluid is forced through the samples, represents flow, primarily through the vascular channel system, and contribution of the organically-lined channels to the electrokinetic zeta potential. Bone particle electrophoresis represents mainly the electrokinetic contribution of exposed mineralized matrix. The organic linings present in the vascular channel system limit potential-determining ions' access to the mineralized matrix. These linings may have an important role in mineral homeostasis and control of ion fluxes between bone compartments.

Animals↗

PubMed1990

The origin of electrokinetic potentials in bone tissue: the organic phase.

The purpose of this study was to determine the relative contributions of the organic and mineral phases of cow cortical bone to its electrokinetic response at room temperature. The technique of particle electrophoresis permitted electrokinetic (zeta) potentials to be calculated and plotted as a function of pH. Control and demineralized bone particles exhibited similar isoelectric points at pH approximately 5.1 (pH at which the zeta potential is zero), well below the isoelectric point of the bone mineral (pH approximately 8.6). In addition, the use of phosphate-containing buffers resulted in a zeta potential sign reversal of the bone mineral but had no effect on both the control and demineralized bone. These key results form the basis from which we suggest that the bone mineral lies within the organic phase (e.g., the mineral is not exposed to the fluid phase) and that the electrokinetic behavior of bone tissue is dominated by its organic ultrastructure.

Animals↗

PubMed1990

Streaming potential of intact wet bone.

The conversion of mechanical loads to bioelectrical signals in bone have been suggested to control repair and remodeling. These signals in wet bone are attributed to the electrokinetic behavior where mechanical forces cause electrical signals due to motion of an ion carrying extracellular fluid in the bone matrix (streaming potentials). Streaming potential experiments were performed on control and chemically treated intact wet bone plugs in aphosphate and phosphate buffers to examine the contribution of bone constituents to the electrokinetic behavior of bone tissue. Data indicate that the organic constituents of bone dominate streaming potentials. Slopes of streaming potential vs pressure are related to the electrokinetic (zeta) potential. The slopes should be analyzed in the low pressure region where data is mainly linear. Comparisons of estimated zeta potentials from streaming potentials with existing data obtained by particle electrophoresis showed similar trends.

Animals↗

PubMed1984

Electro-mechanical behavior of wet bone--Part I: Theory.

The remodeling properties of bones due to various stimuli have been of substantial interest to the scientists. Examination of electro-mechanical properties of bone and their relation to remodeling and osteogenesis have been investigated mainly by experimental means. In this study, by using continuum physics, it is shown that the remodeling of bones can be formulated theoretically in terms of electrical and mechanical effects. The interactions among the constituents of bone (bone matrix, bone salts, electrolytes and hydrogen ions) and effects of various stimuli (mechanical, electrical and chemical) on the remodeling mechanism of bone tissue are interpreted with this model. Moreover, the stimulation of osteogenesis by electrical means is predicted.

Biomedical Engineering↗

PubMed1984

Electro-mechanical behavior of wet bone--Part II: Wave propagation.

In this study, a general mixture model, which was developed for wet bone, has been used to analyze the flexural wave propagation in long bones. The electrical conduction is taken into account as well as the piezo-electric properties of bone tissue. The general formulation is simplified and certain assumptions made to yield a particular set of equations. The solution of the magnetic induction vector outside the bone due to the mechanical wave propagation is obtained. The results are compared with a similar problem using dry bone. The results indicate that the electro-mechanical properties of bone tissue could be used for monitoring the rate of fracture healing in long bones.

Biomedical Engineering↗

PubMedDate not supplied

The effect of in vitro fluoride ion treatment on the ultrasonic properties of cortical bone.

The mechanical properties of composites are influenced, in part, by the volume fraction, orientation, constituent mechanical properties, and interfacial bonding. Cortical bone tissue represents a short-fibered biological composite where the hydroxyapatite phase is embedded in an organic matrix composed of type I collagen and other noncollagenous proteins. Destructive mechanical testing has revealed that fluoride ion treatment significantly lowers the Z-axis tensile and compressive properties of cortical bone through a constituent interfacial debonding mechanism. The present ultrasonic data indicates that fluoride ion treatment significantly alters the longitudinal velocity in the Z-axis as well as the circumferential and radial axes of cortical bone. This suggests that the distribution of constituents and interfacial bonding amongst them may contribute to the anisotropic nature of bone tissue.

Animals↗