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Biomedical subjects

J A Szivek

Publications and source records attributed to J A Szivek.

At least 19 recordsLinked to original sources
PubMed2007

Sensate scaffolds can reliably detect joint loading.

Treatment of cartilage defects is essential to the prevention of osteoarthritis. Scaffold-based cartilage tissue engineering shows promise as a viable technique to treat focal defects. Added functionality can be achieved by incorporating strain gauges into scaffolds, thereby providing a real-time diagnostic measurement of joint loading. Strain-gauged scaffolds were placed into the medial femoral condyles of 14 adult canine knees and benchtop tested. Loads between 75 and 130 N were applied to the stifle joints at 30 degrees, 50 degrees, and 70 degrees of flexion. Strain-gauged scaffolds were able to reliably assess joint loading at all applied flexion angles and loads. Pressure sensitive films were used to determine joint surface pressures during loading and to assess the effect of scaffold placement on joint pressures. A comparison of peak pressures in control knees and joints with implanted scaffolds, as well as a comparison of pressures before and after scaffold placement, showed that strain-gauged scaffold implantation did not significantly alter joint pressures. Future studies could possibly use strain-gauged scaffolds to clinically establish normal joint loads and to determine loads that are damaging to both healthy and tissue-engineered cartilage. Strain-gauged scaffolds may significantly aid the development of a functional engineered cartilage tissue substitute as well as provide insight into the native environment of cartilage.

Animals↗
PubMed2006

An instrumented scaffold can monitor loading in the knee joint.

No technique has been consistently successful in the repair of large focal defects in cartilage, particularly in older patients. Tissue-engineered cartilage grown on synthetic scaffolds with appropriate mechanical properties will provide an implant, which could be used to treat this problem. A means of monitoring loads and pressures acting on cartilage, at the defect site, will provide information needed to understand integration and survival of engineered tissues. It will also provide a means of evaluating rehabilitation protocols. A "sensate" scaffold with calibrated strain sensors attached to its surface, combined with a subminiature radio transmitter, was developed and utilized to measure loads and pressures during gait. In an animal study utilizing six dogs, peak loads of 120N and peak pressures of 11 MPa were measured during relaxed gait. Ingrowth into the scaffold characterized after 6 months in vivo indicated that it was well anchored and bone formation was continuing. Cartilage tissue formation was noted at the edges of the defect at the joint-scaffold interfaces. This suggested that native cartilage integration in future formulations of this scaffold configured with engineered cartilage will be a possibility.

Animals↗
PubMed2005

TGF-beta1-enhanced TCP-coated sensate scaffolds can detect bone bonding.

Porous polybutylene terephthalate (PBT) scaffold systems were tested as orthopedic implants to determine whether these scaffolds could be used to detect strain transfer following bone growth into the scaffold. Three types of scaffold systems were tested: porous PBT scaffolds, porous PBT scaffolds with a thin beta-tricalcium phosphate coating (LC-PBT), and porous PBT scaffolds with the TCP coating vacuum packed into the scaffold pores (VI-PBT). In addition, the effect of applying TGF-beta1 to scaffolds as an enhancement was examined. The scaffolds were placed onto the femora of rats and left in vivo for 4 months. The amount of bone ingrowth and the strain transfer through various scaffolds was evaluated by using scanning electron microscopy, histology, histomorphometry, and cantilever bend testing. The VI-PBT scaffold showed the highest and most consistent degree of mechanical interaction between bone and scaffold, providing strain transfers of 68.5% (+/-20.6) and 79.2% (+/-8.7) of control scaffolds in tension and compression, respectively. The strain transfer through the VI-PBT scaffold decreased to 29.1% (+/-24.3) and 30.4% (+/-25.8) in tension and compression when used with TGF-beta1. TGF-beta1 enhancement increased the strain transfer through LC-PBT scaffolds in compression from 9.4% (+/-8.7) to 49.7% (+/-31.0). The significant changes in mechanical strain transfer through LC-PBT and VI-PBT scaffolds correlated with changes in bone ingrowth fraction, which was increased by 39.6% in LC-PBT scaffolds and was decreased 21.3% in VI-PBT scaffolds after TGF-beta1 enhancement. Overall, the results indicate that strain transfer through TCP-coated PBT scaffolds correlate with bone ingrowth after implantation, making these instrumented scaffolds useful for monitoring bone growth by monitoring strain transfer.

Animals↗
PubMed2001

Long-term measurement of bone strain in vivo: the rat tibia.

Despite the importance of strain in regulating bone metabolism, knowledge of strains induced in bone in vivo during normal activities is limited to short-term studies. Biodegeneration of the bond between gauge and bone is the principle cause of this limitation. To overcome the problem of bond degeneration, a unique calcium phosphate ceramic (CPC) coating has been developed that permits long-term attachment of microminiature strain gauges to bone. Using this technique, we report the first long-term measurements of bone strain in the rat tibia. Gauges, mounted on the tibia, achieved peak or near peak bonding at 7 weeks. Measurements were made between 7-10 weeks. Using ambulation on a treadmill, the pattern and magnitude of strain measured in the tibia remained relatively constant between 7-10 weeks post implantation. That strain levels were similar at 7 and 10 weeks suggests that gauge bonding is stable. These data demonstrate that CPC-coated strain gauges can be used to accurately measure bone strain for extended periods, and provide an in vivo assessment of tibial strain levels during normal ambulation in the rat.

Animals↗
PubMed2001

Strain transfer between a CPC coated strain gauge and cortical bone during bending.

The finite element method was used to simulate strain transfer from bone to a calcium phosphate ceramic (CPC) coated strain gauge. The model was constructed using gross morphometric and histological measurements obtained from previous experimental studies. Material properties were assigned based on experiments and information from the literature. Boundary conditions simulated experimental cantilever loading of rat femora. The model was validated using analytical solutions based on the theory of elasticity as well as direct comparison to experimental data obtained in a separate study. The interface between the bone and strain gauge sensing surface consisted of layers of polysulfone, polysulfone/CPC, and CPC/bone. Parameter studies examined the effect of interface thickness and modulus, gauge geometry, partial gauge debonding, and waterproofing on the strain transfer from the bone to the gauge sensing element. Results demonstrated that interface thickness and modulus have a significant effect on strain transfer. Optimal strain transfer was achieved for an interface modulus of approximately 2 GPa. Strain transfer decreased consistently with increasing interface thickness. Debonding along the lateral edges of the gauge had little effect, while debonding proximal and distal to the sensing element decreased strain transfer. A waterproofing layer decreased strain transfer, and this effect was more pronounced as the modulus or thickness of the layer increased. Based on these simulations, specific recommendations were made to optimize strain transfer between bone and CPC coated gauges for experimental studies.

Biocompatible Materials↗
PubMed2001

Surface enhancements accelerate bone bonding to CPC-coated strain gauges.

Calcium phosphate ceramic (CPC)-coated strain gauges have been used for in vivo bone strain measurements for up to 18 weeks, but they require 6 to 9 weeks for sufficient bonding. Osteogenic protein-1 (OP-1), PepTite (a proprietary ligand), calcium sulfate dihydrate (CSD), transforming growth factor beta-1 (TGF-beta1 ), and an endothelial cell layer with and without TGF-beta1 were used as surface enhancements to accelerate bone-to-CPC bonding. Young male Sprague-Dawley rats were implanted with unenhanced and enhanced CPC-coated gauges. Animals were allowed normal activity for 3 weeks and then calcein labeled. Femurs were explanted following euthanasia. A gauge was attached with cyanoacrylate to the opposite femur in the same position as the CPC-coated gauge. Bones were cantilever-loaded to assess strain transfer. They were sectioned and stained with mineralized bone stain (MIBS) and examined with transmitted and ultraviolet light. Mechanical testing indicated increased sensing accuracy for TGF-beta1 and OP-1 enhancements to 105 +/- 14% and 92 +/- 12% versus 52 +/- 44% for the unenhanced gauges. The PepTite and the endothelial-cell-layer-enhanced gauges showed lower sensing accuracy, and histology revealed a vascular layer near CPC particles. TGF-beta1 increased bone formation when used prior to endothelial cell sodding. CSD prevented strain transfer to the femur. TGF-beta1 and OP-1 surface enhancements produced accurate in vivo strain sensing on the rat femur after 3 weeks.

Animals↗
PubMed2000

A comparison of in vitro and in vivo degradation of two CPC strain gauge coatings.

Calcium phosphate ceramic (CPC) coated strain gauges have been used to measure bone strain in animal models for up to 16 weeks and are being developed to collect measurements in patients for periods of 1 year or more. A published surface roughening and heat treating procedure produced improved dry strength and in vivo stability of CPC-gauge interfaces after 16 weeks. The long term bond strength of two CPC-gauge interfaces prepared using the roughening and heat treating process were evaluated after up to 1 year in vitro and in vivo using a lap shear test. The feasibility of using an in vitro test to predict long term in vivo interface changes was established. A blended tricalcium phosphate + hydroxyapatite had a CPC-gauge interface strength which decreased from 6.07 +/- 2.64 MPa at 16 weeks to 4.71 +/- 1.840 MPa after 1 year in Hanks Balanced Salts (HBS). The same coating had a strength that decreased from 8.51 +/- 2.63 MPa at 16 weeks to 5.35 +/- 1 MPa after 1 year in vivo. A soluble calcium enhanced hydroxyapatite had an interface strength of 4.83 +/- 1.106 MPa after 16 weeks and 4.51+/- 1.100 MPa after 1 year in HBS. The same coating had an interface strength of 8.34 +/- 2.40 MPa after 16 weeks and 5.20 +/- 2.00 MPa after 1 year in vivo. Although interface strengths decreased slightly with time in vivo, after 1 year they were in the same strength range as published CPC-bone interface strengths of 4.8 +/- 2.4 MPa. Comparison of in vitro with in vivo results indicated that in vitro results were a good predictor of strength change in the blended CPC coating, but a poorer predictor of strength changes in the soluble calcium-enhanced coating.

Animals↗
PubMed2000

An experimental method for the application of lateral muscle loading and its effect on femoral strain distributions.

Experimental models that have been used to evaluate hip loading and the effect of hip implants on bone often use only a head load and abductor load. Anatomic considerations and in vivo measurements have lead several investigators to suggest that these models are inaccurate because they do not incorporate the loads imposed by additional muscles. The aim of this study was to evaluate the strains in the proximal and mid diaphysis of the femur for five hip loading models, one with a head load and abductor load only and four which incorporated lateral muscle loads as well. Head load to body weight load ratios were used to evaluate the physiologic accuracy of these models and strains were compared to determine the extent of strain changes as a function of model complexity. All models which incorporated additional lateral muscle loads more accurately simulated head load to body-weight load ratios than the simple abductor-only model. The model which incorporated a coupled vastus lateralis and iliotibial band load in addition to the abductor load provided the simplest configuration with a reasonable body-weight to head-load ratio.

Biomedical Engineering↗
PubMed1999

Bone bonding strength of calcium phosphate ceramic coated strain gauges.

Although strain transfer from bone to gauge has been used as an indication of the extent of bone bonding to calcium phosphate ceramic (CPC) coated strain gauges, interface strength measurements have not been reported. In order to develop bone-bonded gauges that remain attached to bone surfaces for long periods, the strength of the CPC-bone interface must be optimized. A shear test to assess the interface strength of the CPC-bone interface was developed using the femora of 120-day-old male rats. The mean interface strength of a blended CPC coating bonded to the femora of the rats for 6 weeks in vivo was 4.8+/-2.4 MPa, and one specimen achieved a strength of nearly 10 MPa. This mean strength value is higher then the CPC-gauge interface strength reported in early studies, but it is lower than recently developed heat treated CPC-gauge interfaces that have average strengths of approximately 7.0+/-2.0 MPa.

Animals↗
PubMed1999

Polyethylene particle morphology in synovial fluid of failed knee arthroplasty.

Synovial fluid from the knees of 16 patients undergoing revision knee arthroplasty for aseptic failure was subjected to base digestion and ultrafiltration. Filtered particles were scanned using scanning electron microscopy and analyzed with an image program. Polyethylene particles were identified visually and confirmed with the use of electron diffraction spectroscopy. Averaging more than 1500 particles per patient sample, 25,148 particles were analyzed. This corresponded to a concentration of 3000 polyethylene particles per milliliter of synovial fluid. Three populations of wear debris were identified in the fluid. Small globular particles with a mean area of 75 mu 2 represented 94% of all particles observed. The particles averaged 10 mu in diameter and often were seen in clumps. Long fibrous particles with a mean area of 1164 mu 2 made up 4% of the particle population. Large rhomboidal particles with an area of 557 mu 2 were observed least commonly and comprised the remainder of the particles visualized. All three particle types were observed in each fluid sample regardless of the wear pattern of the retrieved polyethylene liner. There were no differences in absolute particle counts, particle morphologic characteristics, or particle size between patients with and without gross polyethylene wear.

Aged↗
PubMed1998

Interface strength studies of calcium phosphate ceramic coated strain gauges.

In vivo strain gauging has been used to understand physiological loading and bone remodeling. In early studies, a cyanoacrylate adhesive was used to bond gauges to bone, even though this adhesive is susceptible to biodegradation that results in rapid debonding. Calcium phosphate ceramic (CPC) coated gauges have been successfully bonded to bone for long periods. However, earlier studies noted occasional debonding of coatings from gauges. The goals of this project were to develop a technique to securely bond particles to gauge backings and develop an in vitro test and assess its accuracy in simulating in vivo degradation of this interface. Gauges were heated for different time intervals, roughened with carbide papers, and prepared using layered coatings of polysulfone and CPC particles that varied in size, shape, and crystallinity. They were soaked in solution or placed in muscle pouches of rats for up to 16 weeks. They were then epoxied to fixtures, mounted on an MTS machine, and loaded to failure. Heating and roughening gauge surfaces increased the interface strengths by up to 2000%. In vivo and in vitro testing showed an initial drop in the interface strength, which leveled off to approximately 7.0+/-2.0 MPa.

Bone Remodeling↗
PubMed1998

Contact areas and pressures between native patellas and prosthetic femoral components.

Contact areas and pressures between native patellas and a prosthetic condylar design femoral component were measured at flexion angles of 30 degrees, 60 degrees, and 90 degrees. These were compared to measurements obtained with a domed all-polyethylene patellar component. Mean native patellar contact areas were found to be fourfold greater than seen with the prosthetic patellar component. Contact stresses in the native patellas were below the yield strength of articular cartilage in 80% of the contact area. By contrast, stresses measured in the prosthetic patella exceeded the yield strength of ultrahigh molecular weight polyethylene in 64% of the measured contact area. Contact areas and stresses were not significantly effected by flexion angle. Although contact areas and stresses reflect only a part of the dynamics of the patellofemoral articulation this information would support the selective retention of the native patella in total knee arthroplasty.

Aged↗
PubMed1997

Pullout strengths of cannulated and noncannulated cancellous bone screws.

The pullout strengths of large diameter cannulated and noncannulated cancellous screws were tested in a synthetic polyurethane foam. The foam was fabricated to have mechanical properties equivalent to human cancellous bone and was characterized by compression testing before screw pullout. Long and short thread commercially available screws from four manufacturers were tested. In screws with short threads (16-22 mm), there was no difference in holding power among the four cannulated screw designs. However, the short thread noncannulated screw performed significantly better than the short thread cannulated screw with the lowest pullout strength. There were statistically significant differences in holding power among the different long thread (32-40 mm) cannulated screw designs. Additionally, the long thread noncannulated screw had better holding power than several of the long thread cannulated screws. No differences in pullout strengths between comparably sized cannulated and noncannulated screws produced by the same manufacturer were found, and all long thread screws had significantly greater holding power than all short thread screws. There was no demonstrable effect on holding power when screws were inserted with or without tapping. Thread surface area was found to be a reasonable predictor of holding power.

Bone Screws↗
PubMed1996

Bilateral symmetry of biomechanical properties in rat femora.

In many studies, bone healing and remodeling have been examined in various animal models using one femur as a control for the contralateral femur based on the assumption that they are bilaterally symmetrical. Symmetry studies have been limited mainly to geometrical properties. The purpose of this study was to determine whether or not there is symmetry in the mechanical properties of rat femora. Two strain gauges were attached to the anterior surface parallel to the long axis of explanted femora of retired female breeder and 120-day-old male Sprague Dawley rats. Femora were mechanically tested in cantilever bending and the strain values were recorded. Moments of inertia, cortical areas, and moduli of elasticity were determined from strains and cross-sectional properties. Female femora showed a bilateral strain difference of less than 2.2% and an elastic modulus difference of less than 8.7%. Males had less than 2.0% and 7.9% differences for strain and elastic moduli, respectively. Statistical analysis showed no significant difference between left and right femoral strain values for the females, but modulus differences were significant different at the p = 0.05 level. There was no significant difference in strain and modulus values for the males, indicating mechanical and geometrical symmetry of their femora.

Analysis of Variance↗
PubMed1996

Evaluation of factors affecting bonding rate of calcium phosphate ceramic coatings for in vivo strain gauge attachment.

The aim of this study was to compare the bone-bonding rates of eight calcium phosphate ceramic (CPC) coatings attached to strain gauges, alone and in conjunction with an OP1 device (Creative BioMolecules, Hopkinton, MA) and autologous concentrated pericyte cells. These coatings were studied to develop faster bone bonding to long-term in vivo strain sensors. Characterization of the CPC powders using electron microscopy and X-ray diffraction showed that they had shapes ranging from spherical to rocklike and properties ranging from highly crystalline to amorphous. CPC coated gauges were placed on the femora of young male dogs during aseptic surgery and were initially held in place using resorbable sutures. Test groups were euthanized after 3, 9, and 12 weeks. Both femora of the dogs were explanted and cantilever loaded. Response of the implanted hydroxyapatite (HA) coated gauges were compared to the response of bench-top glued sets of gauges (controls) attached to the contralateral femur and reported as a percentage of the control values. One CPC coating type showed an average response of 30% of controls after 3 weeks, four showed average responses higher than 75% after 9 weeks, and three showed averages higher than 82% after 12 weeks in vivo. Amorphous CPC coatings bonded more quickly than crystalline ones and particle shape had less effect than crystal structure on bonding rates. When either OP1 or autologous concentrated pericyte cells were placed on selected CPC coated gauge surfaces, the CPC5 coated gauges bonded best after 3 weeks with a response of 59%. After the same time period in vivo, CPC3 and CPC7 provided responses of 40 and 16%, respectively. Comparison of a soluble calcium-coated CPC with an uncoated one that had identical crystal structure and similar particle shape indicated that the calcium coating slowed bone bonding substantially in the young dog model. Optical microscopy of stained undecalcified bone sections and backscattered electron imaging indicated bone formation at all bone-HA interfaces and an increase in the number of areas of bone remodeling adjacent to the gauge at all time periods. Gross bone remodeling due to strain gauge placement was only observed near the distalmost cell-seeded strain gauges. Selection of the type of coating and enhancement system can accelerate bone bonding to strain sensors but must be tailored to the bone of the model in which it is being used. Augmentation of CPC coatings with cells or OP1 resulted in variable enhancement of the bonding rate and depended on the CPC and the enhancement system.

Animals↗
PubMed1996

Average and peak contact stress distribution evaluation of total knee arthroplasties.

Seven total knee arthroplasty systems were tested to determine contact stress patterns and contact areas using a calibrated Fuji film stress analysis technique. Knees were loaded to 2,000 N (204 kg) at 15 degrees, 60 degrees, 90 degrees, and 135 degrees flexion at 24 and 37 degrees C. Evaluation of stresses at 37 degrees C at 15 degrees and 60 degrees using an average contact stress assessment technique indicated that the LCS meniscal bearing knee system, (DePuy, Warsaw, IN), the AMK knee with a constrained insert (DePuy), and the PFC knee with a posterior-lipped insert (Johnson and Johnson, Raynham, MA) had the lowest average contact stresses (near or below 10 MPa). The PFC with a regular insert (Johnson and Johnson) the Ortholoc II (Dow Corning Wright, Arlington, TN), and the AMK with a regular insert (DePuy) had intermediate contact stresses. The AMK with a Hylamer-M insert (DePuy) and the MG II (Zimmer, Warsaw, IN) had the highest average contact stresses (near or above 20 MPa). A stress-calibrated Fuji film measurement technique has shown that an assessment of ranges of contact stress provides much more information about regions of expected wear than an assessment of average contact stresses. Testing of the tibiofemoral articulation of artificial knees revealed that all knees had some areas of contact with maximum stresses in excess of 15 MPa. As the yield strength of ultrahigh-molecular-weight polyethylene is approximately 15 MPa, all tibial inserts could wear to some extent. Peak contact stresses at four test angles of the AMK, Series 7000 (Osteonics, Allendale, NJ:) Genesis (Smith & Nephew Orthopaedics, Memphis, TN), and MG II patellofemoral articulations were high (above 30 MPa). Contact areas varied from line-shaped to bilateral circular or elliptical shapes. The LCS knee system experienced substantially lower patellofemoral contact stresses and larger contact areas. Changes in conformity of knee designs are warranted to overcome wear problems. Peak contact stresses measured from the LCS meniscal bearing tibiofemoral and patellofemoral joint were in excess of 30 MPa in some areas at low flexion angles. This design does create large areas of contact at very low contact pressures, however, and for this reason is expected to wear less than other designs.

Humans↗
PubMed1995

Characterization of three formulations of a synthetic foam as models for a range of human cancellous bone types.

Porous polyurethane foams were prepared from Daro foam components with a range of mechanical properties to simulate human trabecular bone. Ratios of 10.0:5.0, 10.0:7.9, and 10.0:10.0 isocyanate to resin were mixed, cured, and cut into cubes. Properties were determined from uniaxial compression to 50% of the original cube height at a strain rate of 1.2 mm/s. Electron microscopy was used to characterize the foam structure. Average compressive yield stress values, ultimate compressive stresses, and elastic moduli ranged from 4.44 to 2.79, 5.61 to 3.28, and 134.0 to 110.1 MPa, respectively, for the three formulations. The foam materials showed a similar morphology of spherical bubbles, and the average bubble size tended to decrease as the ratio of isocyanate to resin increased even though the bubble size differences were not statistically significant. The results indicate that large blocks of foam can be prepared with consistent mechanical properties simulating a range of trabecular bone properties so that implants can be tested for various patient populations.

Biocompatible Materials↗