Biomedical subjects

S R Pollack

Publications and source records attributed to S R Pollack.

At least 37 records · Page 2Linked to original sources

PubMed1992

The effect of phase differences on the time-dependent variation of the zeta potential of hydroxyapatite.

The osteoconductive nature of calcium phosphate ceramics (CPC) follows from several proven effects, such as a direct bone attachment and enhanced bone tissue formation. Mechanisms leading to these phenomena are still largely undiscovered. Specifically, little is known about the CPC surface and cell-driven reactions. These atomic and molecular level events are involved in tissue attachment and enhanced tissue formation. It is hypothesized that the zeta potential of these ceramics is directly related to the surface reactivity governing osteoconductivity. As a first step in our analysis, the zeta potential of stoichiometric and Ca-deficient hydroxyapatite was determined as a function of immersion time. It is concluded that, under the conditions of the experiment, the observations support the hypothesis in a dual way. First, the absolute values of the zeta potential which were measured are related to electrokinetic potentials known to cause substantial effect on the cellular activities and bone tissue formation when applied exogenously. Second, the magnitude and duration of the changes in zeta potential are related to an ion exchange between the hydrated layer around the ceramic and the ceramic surface, and a net precipitation of new material. If these findings could be confirmed in other solutions, i.e., solutions with a substantially equivalent composition as the fluids in developing bone tissue, a basis would be provided to explain the bridging of the ceramic surface with the surrounding developing tissue.

Biocompatible Materials↗

PubMed1992

Comparison of asymmetrical and symmetrical pulse waveforms in electromagnetic stimulation.

Pulsing electromagnetic field (PEMF) stimulation is a noninvasive therapeutic modality that has been successfully used to stimulate healing of surgically resistant human bone fracture nonunions. Asymmetry of the stimulus pulse waveform was thought to be necessary for therapeutic effectiveness, but asymmetrical pulses require significant electrical energy that constrains clinical delivery systems to suboptimal designs. Development of low-energy consuming stimuli will enable clinical device improvements and may provide additional information about the interaction of electromagnetic fields with tissues. The objectives of this study were (a) to determine if asymmetry of the stimulus pulse waveform is needed for efficacy and (b) to determine if symmetrical pulse waveform stimuli also can produce a beneficial therapeutic response. The rabbit fibular osteotomy model was used to answer these questions and to identify which components of the clinically used asymmetrical PEMF produce the therapeutic response. The results suggest that asymmetry is not necessary and that a narrow pulse width, symmetrical square wave signal can also stimulate stiffness increases in this model. The data also suggest that the high-amplitude, narrow-pulse portion of the asymmetrical PEMF is the principal component of the signal pulse that is responsible for the clinical therapeutic effect.

Animals↗

PubMed1992

Field distributions in the rat tibia with and without a porous implant during electrical stimulation: a parametric modeling.

Expeditious post-operative ingrowth of bone is necessary for clinically successful fixation of porous joint prostheses. Electrical or electromagnetic fields to stimulate bone growth into porous implants have been used; however, they produced nonconvincing data. This was partially attributable to the lack of quantification of the localized electric fields produced in the pores of the implants. Therefore, this study set out: i) to quantify the local electric field values induced into the surface pores of nonconducting implants by "capacitive" coupling and to determine the magnitude of the macroscopically applied capacitively coupled electrical currents to induce specific electric field amplitudes in the pores, ii) to identify the important dielectric properties of the implant-tissue interface, and iii) to create the basis for successfully applying electrical fields in an animal model to stimulate bone ingrowth. A finite element method was used to calculate the electric field gradients and current densities present in a rat tibia modeled with a porous intramedullary implant when capacitively stimulated. Results indicated that while the current density in the pores are reduced in comparison to the region just outside the pore by about one order of magnitude, a significant current density still exists in the pore region. Furthermore, the presence of the implant increases the current densities in the trabecular bone while decreasing these values in the cortical bone. Replacing the trabecular bone in the pore by saline increases the current density in the pore by three-fold, but decreases the voltage gradient by a similar factor.

Animals↗

PubMed1992

Short-term effect of guided bone regeneration and electrical stimulation on bone growth in a surgically modelled resorbed dog mandibular ridge.

This study compares the quantitative bone changes that occur in attempting to augment a resorbed mandibular ridge by electrical stimulation and by the guided bone regeneration technique. At the base line three defects resembling an atrophic ridge were created in the mandible of 5 beagle dogs. Concomitantly, a constant current generator producing 20 +/- 2 mA was implanted under the floor of the mouth. Six weeks later a titanium cathode was inserted in the first bony defect and connected to the generator (electrical stimulation = ES); another titanium cathode, not connected to the generator, was inserted in the second defect (non-electrical stimulation = non-ES); the third defect remained without an electrical device (membrane only = MO). All 3 defects were covered with an expanded polytetrafluorethylene membrane, so as to prevent soft tissue proliferation into the defects. Tetracycline bone labelling compounds were administered to mark new bone formation. Four weeks following stimulation, ground sections were prepared for fluorescent microscopy. Differences between ES vs MO and between non-ES vs MO mean scores were statistically significant, indicating that 4 weeks of electrical stimulation resulted in similar bone formation as with non- electrical stimulation when both are confined to a membrane isolated defects.

Animals↗

PubMed1992

In vitro bone-cell response to a capacitively coupled electrical field. The role of field strength, pulse pattern, and duty cycle.

Newborn rat calvarial bone cells were grown to confluence and subjected to a matrix of sine wave 60-kHz capacitively coupled electrical signals of various field strengths, pulse-burst patterns, and duty cycles. Both [3H] thymidine incorporation into DNA and alkaline phosphatase activity were evaluated in field strengths ranging from 0.0001 to 20 mV/cm, with pulse-burst patterns ranging from continuous to 5 milliseconds ON/495 milliseconds OFF, with daily duty cycles ranging from 0.25% to 25%. A significant increase in proliferation occurred in field strengths of 0.1, 1, and 20 mV/cm when the signal was applied continuously for six hours. Significant proliferation also occurred when the 20-mV/cm field was pulsed for six hours at 5 milliseconds ON/495 milliseconds OFF and at 5 milliseconds ON/245 milliseconds OFF. No change in alkaline phosphatase activity occurred in the 20-mV/cm field with any signal. At 1 mV/cm, there was a significant decrease in alkaline phosphatase activity in the continuous signal and in the 5 milliseconds ON/62 milliseconds OFF signal; in the lower fields evaluated, there was an actual decrease in alkaline phosphatase activity with some of the signals. The field strength plays a dominant role in determining the bone-cell's proliferative response, and to a lesser extent the alkaline phosphatase activity response, to a capacitively coupled electric field. The pulse configuration and the duty cycle are also important, but only if the proper field strength is being applied to the cell.

Alkaline Phosphatase↗

PubMed1991

The proliferative and synthetic response of isolated calvarial bone cells of rats to cyclic biaxial mechanical strain.

Isolated bone cells from the calvaria of newborn rats were grown in monolayer on polyurethane membranes in specially constructed culture chambers. These were subjected to cyclic biaxial mechanical strains of 0.02 per cent (200 microstrain), 0.04 per cent (400 microstrain), and 0.1 per cent (1000 microstrain) at a frequency of one hertz for periods ranging from fifteen minutes to seventy-two hours. DNA content, an index of proliferation, was significantly increased at a strain of 0.04 per cent applied for fifteen minutes and for twenty-four and forty-eight hours. DNA content was not increased at the other amplitudes of strain that were evaluated, nor was it increased after prolonged mechanical stimulation for forty-eight hours or longer. Synthesis of collagen, non-collagenous protein, and proteoglycan, as well as activity of alkaline phosphatase, all indicators of macromolecular synthesis, were significantly decreased at a strain of 0.04 per cent applied for fifteen minutes and for twenty-four, forty-eight, and seventy-two hours. Macromolecular synthesis was not affected by the other amplitudes of strain that were evaluated in this study. At a strain of 0.04 per cent, prostaglandin E2 content was significantly increased after five, fifteen, and thirty minutes of mechanical stimulation, whereas net cAMP content did not change significantly. This suggests that the described cellular events (increased proliferation and decreased macromolecular synthesis) that occur secondary to mechanical strain are mediated, at least in part, by prostaglandin E2.

Alkaline Phosphatase↗

PubMed1990

Theoretical determination of the current density distributions in human vertebral bodies during electrical stimulation.

Electrical stimulation with a 60 kHz sinewave input signal, supplied via external plate electrodes on the skin surface, is presently being studied as a treatment for human systemic osteoporosis. In this paper, Maxwell's equations were solved for voltage and current density values at nodal points in a three-dimensional, anatomically-based, finite element grid model of the human trunk constructed from T5 to L5. Based on the dose response results from Luessenhop's castrated Sprague Dawley breeder rat experiment and our theoretical determination, the magnitude of the input current to the electrodes necessary to induce a response in the human vertebral body was determined. Four different electrode systems in current clinical use were evaluated, and the optimal input current determined. In addition, the effect of subcutaneous fat was studied.

Adipose Tissue↗

PubMed1989

Proliferative and synthetic response of bovine growth plate chondrocytes to various capacitively coupled electrical fields.

In vitro monolayer cultures of growth plate chondrocytes isolated from newborn calf costochondral junctions were subjected to capacitively coupled electrical fields for 48 h. In part A, the electrical signal was a 60-kHz sine wave applied at different voltages so as to produce electrical fields at the pericellular level of 7, 20, 50, and 126 mV/cm. Incorporations of [3H]thymidine and [35S]sulfate were assayed to determine the effect of the above fields on cells proliferation and matrix synthesis, respectively. Proliferation was increased by 47% in the 20 mV/cm field whereas the same field decreased [35S]sulfate incorporation by 21%. These changes were significant at p less than 0.05 in both instances. In part B, the 20 mV/cm field was applied in a pulsed fashion to produce daily duty cycles of 100, 25, 2, and 0.25%. Incorporation of [3H]thymidine, [35S]sulfate, and [14C]proline per DNA were assayed. Results indicated that the 100, 25, and 0.25% percent duty cycles showed significantly (p less than 0.01-0.05) increased proliferation, whereas the 0.25% signal (5 ms on/495 ms off for 6 h/day) significantly decreased [14C]proline incorporation. We conclude that the biologic response of cells in vitro is signal specific, and that the total amount of electrical energy required to stimulate the growth plate chondrocyte to increased proliferation is very small since the total time the 0.25% duty cycle signal was only 3.6 min of a 24-h period.

Animals↗

PubMed1989

Field distributions in vertebral bodies of the rat during electrical stimulation: a parametric study.

The electrical field and current density distributions were found in the various tissues of a mathematical model of the experimental rat used to study systemic osteoporosis. The finite element method was used to solve the boundary value problem derived from Maxwell's equations using a quasistatic approximation for a 60 kHz external output signal applied via skin electrodes. A parametric study was done initially to determine the principle factors which effect the solution of the field in the vertebral bodies. Grid coarseness, model length, and intervertebral space width had little effect on the solution while trabecular bone and abdominal cavity conductivity values had strong effects. The two pair of transversely placed electrodes spaced by at least three vertebral bodies produced the most uniform field distributions and was used in the experimental rat model. The range of current density values in the trabecular bone was determined to be 3.0-5.0 microA/cm2 at the external output signal where evidence of a reversal of bone loss due to castration osteoporosis had been found in the experimental rat.

Animals↗

PubMed1989

Treatment of castration-induced osteoporosis by a capacitively coupled electrical signal in rat vertebrae.

Castrated male Sprague Dawley rats were subjected to various capacitively coupled electrical fields for six and eight weeks at two and 4.5 months after castration, respectively, with pairs of electrodes that were located paraspinally on the surface of the skin dorsally at the eleventh thoracic and fourth lumbar levels. When the animals were killed, dry and ash weights per unit of volume (apparent density), elastic modulus, ultimate stress, work to failure, trabecular area fraction, and mean trabecular width were determined for selected vertebrae. The results indicated that a sixty-kilohertz, 100-microampere signal (a calculated current density of five microamperes root-mean-square per square centimeter and a field of twelve millivolts root-mean-square per centimeter) significantly reversed the castration-induced osteoporosis in the lumbar vertebrae and restored bone mass per unit of volume in rats that had been stimulated for eight weeks after castration.

Animals↗

PubMed1988

Pulsing electromagnetic field stimulation of the in vitro growth plate.

Specific pulsing electromagnetic fields (PEMFs) have been used to stimulate growth and repair of osteogenic tissues; however, the basis for this specificity is unknown. Previously, we determined the relevant electromagnetic field parameters of the clinically used PEMF and independently verified the beneficial effects of PEMFs on the rabbit fibula fracture healing model. The goal of the present study was to develop an in vitro model that would permit the effectiveness of various electric and magnetic field components of the PEMF to be determined. The costochondral junction (CCJ) of the 21-day-old rat was exposed in vitro to PEMFs with various electric and magnetic field component amplitudes. Response of this model to PEMFs was determined by nondestructive macrophotographic measurement of CCJ growth. Preliminary data indicated that temperature effects were present in this in vitro system. Subsequent experiments designed to separate the effects of temperature and PEMFs on the growth of CCJs in tissue culture were performed. Results indicate that accurate and frequent temperature measurements must be made for in vitro models being used to study effects of PEMFs. Small temperature differences induced by the coils used to produce PEMFs in the CCJ experimental system can have significant stimulatory effects, and the combined effects of temperature and PEMFs are not linearly additive in this model. Furthermore, our results suggest that thermal and PEMF stimuli could affect macrophotographically measured growth of the CCJ by separate mechanisms or could have a synergistic effect. Therefore, PEMF stimulation experiments should be performed under strictly "athermal" conditions.

Animals↗

PubMed1988

Treatment of denervation/disuse osteoporosis in the rat with a capacitively coupled electrical signal: effects on bone formation and bone resorption.

Utilizing a sciatic neurectomy model of disuse osteoporosis, the effects on rates of bone formation and bone resorption were examined when a capacitively coupled electrical signal was applied to the denervated tibia in the rat. It was found that a low-voltage, symmetrical sine wave, 60-kHz, capacitively coupled signal had no significant effect on the amount of bone resorption occurring in denervated right tibiae in rats previously labeled with [3H]tetracycline. This was true whether the signal was applied while osteoporosis was developing (prevention of osteoporosis) or after it had been established (treatment of osteoporosis). If a similar capacitively coupled signal was applied to rats in which osteoporosis was well established, and the rats were labeled with [3H]tetracycline daily during a 12-day treatment period, it was found that there was statistically significant enhancement of the amount of new bone formation (increased [3H]tetracycline incorporation) in the tibiae that received the signal as compared with that of the controls. These results indicate that prevention or amelioration of disuse osteoporosis that occurs with a capacitively coupled electrical signal is due not to a change in the rate of bone resorption, but to an increase in the rate of bone formation.

Animals↗

PubMed1987

Electromechanical potentials in cortical bone--I. A continuum approach.

An electrokinetic model to characterize the electromechanical effect in cortical bone has been developed using the basic principles of the biphasic theory of porous materials and a simple model for permeability and charge distribution for cortical bone. The model is developed analytically in Part I of this paper and is shown to account qualitatively for the principal experimental results reported to date. Part II of this paper concerns experimental analysis of this model, reporting results of low frequency testing of the dynamic characteristics of stress-generated potentials. Quantitative analysis of these results indicates that the microporosity of bone, made up of the channels around the hydroxyapatite encrusting the collagen matrix, is the compartment responsible for the electromechanical effects in fluid-saturated cortical bone. This microporous compartment would seem to be the obvious source of the electrokinetic effect, because it has the greatest surface area in bone and constitutes the rate limiting fluid flow compartment in deformation-induced fluid flow at low frequency.

Animals↗

PubMed1987

Electromechanical potentials in cortical bone--II. Experimental analysis.

The electrokinetic model developed in Part 1 of this paper is used to characterize the electromechanical effect in cortical bone. Low frequency characteristics of stress-generated potentials are measured to provide insight into the origin and generation of these potentials induced in fluid-filled cortical bone. The results support the proposed model and indicate that fluid movement within the microporosity of bone is responsible for observed potentials whose origin is electrokinetic. The microporosity in bone, composed of the fluid spaces in and around mineral crystals encrusting collagen fibrils, constitutes an enormous surface area and appears to dominate surface-related phenomena at low frequencies. Previous experimental results, reported by many researchers, are also supported by this mechanism.

Animals↗

PubMed1986

Ion concentration effects on the zeta potential of bone.

Stressed bone generates an electrical potential, the sign of which reverses in the presence of specific concentrations of sodium, potassium, or calcium ions. A study was designed to test the hypotheses, drawn from stress-generated potential (SGP) studies, that the reversal in polarity of the zeta potential of bone is the cause of this SGP polarity reversal. The zeta potential of bone particles, prepared from fresh bovine metatarsals as homogeneous 5 microns dispersions, was measured by free-fluid electrophoresis in different concentrations of sodium chloride. The zeta potential of bone particles reversed sign at a sodium ion concentration that was the same as that found to reverse measured SGPs, namely 0.74 molar. This finding is consistent with the hypothesis that streaming potentials are the cause of SGPs in fluid-saturated bone. It was possible to obtain electrophoretic mobility histograms, and hence zeta-potential histograms, of bone particles by using a Pen Kem, Inc. (Bedford Hills, NY, U.S.A.) "3000" Automated Electrokinetic Analyzer. At sodium ion concentrations at which bone particles were nearly neutral, the zeta-potential histograms indicated a broad distribution of particle charge, with some particles being negative, some positive, and some neutral. In addition, it was found that particles prepared from Formalin-fixed bone produced the same electrokinetic results as those prepared from fresh bone, and that the addition of MOPS buffer caused the zeta potential to invert sign from negative to positive values at ion concentrations exceeding 3.0 molar.

Animals↗

PubMed1985

Fracture healing in the rabbit fibula when subjected to various capacitively coupled electrical fields.

The effect of capacitively coupled electrical stimulation on the healing of midshaft transverse osteotomies of the rabbit fibula is assessed roentgenographically, mechanically, and histologically. The results show that a dose-response curve for capacitive coupling and fracture healing exists and that a 220 mV, 250 microA, 60 kHz applied electrical signal (0.33 V/cm internal electric field) is the most effective signal for fracture stimulation in this model.

Animals↗

PubMed1985

Prevention and treatment of sciatic denervation disuse osteoporosis in the rat tibia with capacitively coupled electrical stimulation.

Osteoporosis in the sciatic-denervated rat tibia was both prevented and reversed with a capacitively coupled electrical field. In both the prevention of the development of osteoporosis and the reversal of a previously established osteoporosis, a statistically significant enhancement of wet weight, dry weight, ashed weight, ultimate strength, cortical area, cortical thickness, and a concomitant decrease in cortical porosity occurred in the stimulated, denervated tibiae of the experimental animals compared with the nonstimulated, denervated tibiae of the control animals. These effects exhibited dose-response characteristics. A 60 kHz symmetrical sinewave signal was effective in preventing osteoporosis at a range of 5-10 peak-to-peak, and it was effective in reversing osteoporosis at 10 V peak-to-peak. Reversal of a well-established osteoporosis in laboratory animals has not been reported previously. Continued investigation into the use of a capacitively coupled electrical field in the prevention and treatment of osteoporosis seems warranted from these studies.

Animals↗

PubMed1985

Treatment of recalcitrant non-union with a capacitively coupled electrical field. A preliminary report.

Twenty-two well established non-unions in twenty patients were treated with a capacitively coupled electrical signal (sine wave, sixty kilohertz, five volts peak to peak) that was applied non-invasively through stainless-steel capacitor plates placed on the skin surface overlying the approximate site of the non-union. The average age of the eleven female and nine male patients in this series was 38.4 years, and the average duration of the twenty-two non-unions was 3.3 years. Seventeen of the non-unions were labeled recalcitrant, meaning that they had failed to heal after either previous bone-grafting or another type of electrical stimulation, or both. Five of the non-unions had not been previously treated. Seventeen (77.3 per cent) of the non-unions achieved solid osseous union after an average of 22.5 weeks of treatment with capacitive coupling. The results in this small series were not affected by the non-union being recalcitrant, by the fact that one patient bore full weight on the extremity in a cast, by the presence of osteomyelitis, or by the presence of remaining metallic internal-fixation devices in the bone. Since capacitive coupling is non-invasive, involves portable equipment, allows full weight-bearing on the lower extremity in a cast, is easy to apply, and does not require precise localization of the capacitor plates, it has distinct advantages over other methods of treating non-union with electricity.

Adolescent↗