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Biomedical subjects

J E Lemons

Publications and source records attributed to J E Lemons.

At least 19 recordsLinked to original sources
PubMed2001

Radioimaging of implants in rats using Tc-99m-MDP.

Radiopharmaceutical isotopes are widely used clinically to detect tumors of osteogenic origin. One example is Technetium-99m methylene diphosphonate (Tc-99m-MDP). When viewed with a gamma camera, the concentration of the isotope (increased gamma activity) indicates an area of increased bone activity. This technology provides an opportunity to measure bone growth around implants in vivo. The purpose of this study was to measure Tc-99m-MDP activity around titanium alloy implants placed in the tibiae of rats. Some implant sites were treated with a growth factor; other sites served as controls. The hypothesis tested was that implants placed with a growth factor would have greater associated Tc-99m-MDP activity. Twelve adult male Sprague-Dawley rats were anesthetized and surgical access to the medial proximal tibiae was obtained. Titanium alloy screw implants were placed in six animals along with 65 microgram of acidic fibroblast growth factor (FGF-1); the other six animals received implants only and served as controls. After five days, rats were injected with 1500 microCi of Tc-99m-MDP. After 3 hours, rats were imaged with a gamma camera. The Tc-99m-MDP intensity associated with each implant was quantified and the means for each group were compared using ANOVA. Implants treated with FGF-1 demonstrated significantly more Tc-99m-MDP activity than implants alone. This suggests that Tc-99m-MDP analysis may be a useful tool for determining bone growth around implants in laboratory animals in vivo.

Analysis of Variance↗
PubMed2001

Strength analysis of Le Fort I osteotomy fixation: titanium versus resorbable plates.

PURPOSE: The purpose of this study was to compare the biomechanical characteristics of metallic and polymeric fixation systems using a 3-dimensional skull model to simulate clinical conditions of maxillary advancement and loading. MATERIAL AND METHODS: Standard titanium, prebent titanium, and resorbable plates and mesh were applied to surgically altered polyurethane skulls. The constructs were loaded using an Instron machine (Instron Inc, Canton, MA) in anterior-posterior (AP) and inferior-superior (IS) directions. The load displacement, load to failure, and deformation magnitudes and modes of failure were recorded. Statistical studies included analysis of variance (ANOVA) at P <.05. RESULTS: Elastic stiffness was different among groups in the AP direction, but no significant difference was found in the IS direction. The IS loading direction load displacement (stiffness) was significantly greater than that on AP loading. The maximum load for permanent deformation was larger in the AP direction, while the maximum load for breaking was larger in the IS direction. CONCLUSION: The overall evaluation of the model and test analyses supported the relative value of this in vitro system and study procedure. All systems showed load capacity magnitudes above 285 N (64 lbs) and more elastic resistance in the IS direction. The resorbable systems showed lower elastic stiffness compared with the titanium systems, but they appear to be adequate for fixation and withstanding the forces of mastication.

Absorbable Implants↗
PubMed2001

Medical devices, health care, and consensus standards.

ASTM Committee F04 on Medical and Surgical Materials and Devices has been creating standards for this field since 1962. Dr. Jack Lemons provides a quick overview of the past, present, and future of this committee.

Decision Making↗
PubMed2000

Modulation of mechanical properties in multiple-component tissue adhesives.

In vitro, ex vivo, and in vivo studies were performed to investigate the effect of mixing upon the mechanical properties of a two-component tissue adhesive. The hypothesis investigated was that a more complete mixing of the two components would yield an increase in the mechanical performance of the adhesive. This in turn would be demonstrated by improved outcomes in models of clinical sealant application. In vitro stereological analysis of tissue adhesive mixed and delivered by several different applicators demonstrated variation in the amount of mixing provided by each type of delivery system. Ex vivo tensile adhesive strength showed that there was a correlation between the amount of mixing and bonding strength; that is, more thorough mixing demonstrated higher adhesive strength. No significant difference was seen, however, between the different applicator types and impact on in vivo dermal incisional closure strength. There was a correlation, though, in amount of mixing and in vivo hemostasis. In a rabbit spleen incision model, a more thoroughly mixed sealant corresponded with a decrease in time to obtain complete hemostasis, as well as less sealant used. The effects of mixing on tissue-adhesive mechanical performance were influenced somewhat by the amount of mixing provided by the applicator. This effect, however, was dependent upon the sealant formulation and the type of in vivo application.

Animals↗
PubMed1999

The development and characterization of a fracture-toughened acrylic for luting total joint arthroplasties.

An autopolymerizing fracture-toughened acrylic lute was developed utilizing a toughened prepolymer and a gel-polymerization method. Samples for mechanical and chemical characterization were molded from this material and from untoughened controls. Mechanical testing showed that the mode I fracture toughness (K(IC)) of the toughened lute was increased by 163% over that of the untoughened acrylic controls while the compressive strength and modulus were decreased by 36% and 34%, respectively. The flexural properties of the experimental material were not adversely affected. Analysis of molecular weight and residual monomer data for the experimental and control materials demonstrated that the increase in toughness was due to the presence of the toughened prepolymer. The use of the gel polymerization process gave excellent homogeneity with very low porosity for the experimental polymer, but it resulted in a significant increase in the residual monomer concentration due to the absence of a dispersed phase of prepolymer remnants. This raises questions concerning tissue response to the experimental system.

Arthroplasty, Replacement↗
PubMed1998

Effect of surface treatment on unalloyed titanium implants: spectroscopic analyses.

Surgical implant finishing and sterilization procedures were investigated to determine surface characteristics of unalloyed titanium (Ti). All specimens initially were cleaned with phosphoric acid and divided into five groups for comparisons of different surface treatments (C = cleaned as above, no further treatment; CP = C and passivated in nitric acid; CPS = CP and dry-heat sterilized; CPSS = CPS and resterilized; CS = C and dry-heat sterilized). Auger (AES), X-ray photoelectron (XPS), and Raman spectroscopic methods were used to examine surface compositions. The surface oxides formed by all treatments primarily were TiO2, with some Ti2O3 and possibly TiO. Significant concentrations of carbonaceous substances also were observed. The cleaning procedure alone resulted in residual phosphorus, primarily as phosphate groups along with some hydrogen phosphates. A higher percentage of physisorbed water appeared to be associated with the phosphorus. Passivation (with HNO3) alone removed phosphorus from the surface; specimens sterilized without prior passivation showed the thickest oxide and phosphorus profiles, suggesting that passivation alters the oxide characteristics either directly by altering the oxide structure or indirectly by removing moieties that alter the oxide. Raman spectroscopy showed no crystalline order in the oxide. Carbon, oxygen, phosphorus, and nitrogen presence were found to correlate with previously determined surface energy.

Electron Probe Microanalysis↗
PubMed1998

Unanticipated outcomes: dental implants.

Dental surgical implant treatment modalities continue to be relatively successful within musculoskeletal restorative systems. Because available systems include a wide range of metallic and ceramic biomaterials plus multiple designs for the implant body, transgingival abutment, and intraoral crown constructs, failure analyses of explanted devices must include comprehensive information. The current opinions are based on approximately 4000 musculoskeletal implant device studies conducted from 1970 to 1997. As a subset, the dental systems with and without calcium phosphate ceramic on the endosteal portion of the implants will be considered at 0 to 1, 1 to 5, 5 to 10, and beyond 10 years in vivo. Observations will be reported and opinions provided about the advantages and disadvantages of ceramic coated implant systems.

Coated Materials, Biocompatible↗
PubMed1998

Proteoglycans at the bone-implant interface.

The widespread success of clinical implantology stems from bone's ability to form rigid, load-bearing connections to titanium and certain bioactive coatings. Adhesive biomolecules in the extracellular matrix are presumably responsible for much of the strength and stability of these junctures. Histochemical and spectroscopic analyses of retrievals have been supplemented by studies of osteoblastic cells cultured on implant materials and of the adsorption of biomolecules to titanium powder. These data have often been interpreted to suggest that proteoglycans permeate a thin, collagen-free zone at the most intimate contact points with implant surfaces. This conclusion has important implications for the development of surface modifications to enhance osseointegration. The evidence for proteoglycans at the interface, however, is somewhat less than compelling due to the lack of specificity of certain histochemical techniques and to possible sectioning artifacts. With this caveat in mind, we have devised a working model to explain certain observations of implant interfaces in light of the known physical and biological properties of bone proteoglycans. This model proposes that titanium surfaces accelerate osseointegration by causing the rapid degradation of a hyaluronan meshwork formed as part of the wound-healing response. It further suggests that the adhesive strength of the thin, collagen-free zone is provided by a bilayer of decorin proteoglycans held in tight association by their overlapping glycosaminoglycan chains.

Animals↗
PubMed1998

Intervertebral spacer as an adjunct to anterior lumbar fusion. Part I. Design, fabrication, and testing of three prototypes.

Failure of anterior lumbar fusions are common, because the bone graft is required to provide mechanical stability during creeping substitution and replacement with host bone. Support of the interspace with mesh, cages, plates, and rods results in an improved rate of fusion. The objective of this study was to develop an anterior interbody implant to stabilize adjacent vertebral segments during spinal fusion. Three prototypes of an intervertebral spacer for anterior lumbar stabilization were designed, fabricated, and tested in vitro. The implants were inserted vertically between adjacent vertebral bodies in fresh frozen cadaver swine and baboon spines after disc excision and vertebral body preparation. In vitro cyclic testing of the three prototypes implanted in porcine and baboon spines to 100,000 cycles showed no displacement of the implant at 560-N axial and 16-Nm torsional loading. Three-point bending cyclic fatigue testing of the porous coated cylindrical implants (prototype 3) showed a maximum strength of 9,700 N in axial compressions. Analysis of the motion profiles at the site of implantation confirmed less axial displacement at the implant level compared with the uninstrumented levels above and below, but similar torsional displacements. Biomechanical testing of the three prototypes of anterior implants as well as radiographic, microstructural, and motion analysis confirmed implant stability and structural integrity in vitro. Based on these findings, implantation of a porous coated implant in baboons was undertaken as described in Part II (Nasca et al., this issue).

Aluminum↗
PubMed1998

Intervertebral spacer as an adjunct to anterior lumbar fusion. Part II. Six-month implantation in baboons.

Failure of interbody fusions in the lumbar spine are common due to reliance on the graft for structural support during healing by creeping substitution. Support of the interspace with an implant should result in improved fusion success. The objective of this study was to evaluate the stability of the implant in vivo and its potential as an adjunct to promote interbody arthrodesis. Prototype 3, a porous coated intervertebral spacer with extension lugs made of Ti-6A1-4V, was implanted vertically between adjacent lumbar vertebrae anteriorly in four baboons undergoing anterior interbody fusion. The animals were allowed freedom of activity for 6 months before being killed. A transperitoneal approach was made exposing the L4-L5 or L5-L6 interspace. At time of killing, clinical evaluation of the implant-vertebral body construct showed stability to manual stresses applied in extension, flexion, and rotation. Serial radiographs taken during the 6 months of implantation showed no change in position or displacement of the implants. Axial and torsional cyclic loads were applied to each spine at 1 cycle/s for 20,000 cycles. Statistical analysis of the motion profiles for intact and implanted spines demonstrated no significant difference in axial or rotational displacements at the arthrodesis level or adjacent unoperated levels, L1 and L4. The in vivo 6-month study in baboons confirmed implant stability and maintenance of disc space height. Variable osseous healing was noted. Release of plasma spray beading may have resulted from improper application on the implant or micromotion within the construct. A better method to mechanically interlock the plungers is being studied. Clinical trials based on this work appear justified.

Aluminum↗
PubMed1997

Changes in patient screening for a clinical study of dental implants after increased awareness of tobacco use as a risk factor.

Independent external monitoring committees are an important part of scientific clinical trials. They monitor patient safety, study progress, investigators' performance, and accurate interpretation/reporting of the study data. Data trends observed by a study monitoring committee detected a change in the pattern of patient screening by investigators after an increased awareness that tobacco use could directly compromise the osseointegration of root-form dental implants. This increased awareness is believed to have altered the number of active smokers accepted into a multicenter prospective dental implant study. Recent data analyses indicate that the success ratios were improved by alterations in this discretionary inclusion-exclusion criterion.

Data Interpretation, Statistical↗
PubMed1996

Interfacial shear strength and histology of plasma sprayed and sintered hydroxyapatite implants in vivo.

The interfaces of bone with sintered hydroxyapatite (SHA) and plasma sprayed hydroxyapatite-coated (HAC) implants in the femora of six dogs were examined by light microscopy, scanning electron microscopy, energy dispersive X-ray analysis, and push-out tests. The results demonstrated that there was no significant difference at 12 and 24 weeks after insertion between the interfacial shear strengths with bone for the two types of implants, however, the histological characteristics of the bone around the plasma sprayed HA could be distinguished from that of the sintered HA. The HAC implants showed an early surface biodegradation as compared with the SHA implants. The observed differences in the interfacial zones may be attributed to different bone cell activities and variations in the dynamics of bone formation, possibly resulting from a higher level of dissolution/reprecipitation along the plasma sprayed HA surface.

Animals↗
PubMed1996

Ceramics: past, present, and future.

The selection and application of synthetic materials for surgical implants has been directly dependent upon the biocompatibility profiles of specific prosthetic devices. The early rationale for ceramic biomaterials was based upon the chemical and biochemical inertness (minimal bioreactivity) of elemental compounds constituted into structural forms (materials). Subsequently, mildly reactive (bioactive), and partially and fully degradable ceramics were identified for clinical uses. Structural forms have included bulk solids or particulates with and without porosities for tissue ingrowth, and more recently, coatings onto other types of biomaterial substrates. The physical shapes selected were application dependent, with advantages and disadvantages determined by: (1) the basic material and design properties of the device construct; and (2) the patient-based functional considerations. Most of the ceramics (bioceramics) selected in the 1960s and 1970s have continued over the long-term, and the science and technology for thick and thin coatings have evolved significantly over the past decade. Applications of ceramic biomaterials range from bulk (100%) ceramic structures as joint and bone replacements to fully or partially biodegradable substrates for the controlled delivery of pharmaceutical drugs, growth factors, and morphogenetically inductive substances. Because of the relatively unique properties of bioceramics, expanded uses as structural composites with other biomaterials and macromolecular biologically-derived substances are anticipated in the future.

Ceramics↗
PubMed1996

Analysis of consecutively placed loaded root-form and plate-form implants in adult Macaca mulatta monkeys.

The present paper describes 36 consecutively treated non-human primates (Macaca mulatta) as part of a balanced block design study to examine osseointegration in root- and plate-form implants prepared by atraumatic preparation of bone. Clinical measurements around selected teeth and digital radiology were utilized to monitor periodontal disease and bone loss around root- and plate-form implants which were loaded with a fixed prosthesis. Results indicate that once monthly regimen of scaling and root planing can prevent attachment loss in natural teeth, serving as abutments of loaded bridges. Root-form implants exhibited a significant loss of crestal bone height during the first year (P < 0.03) while plate-form implants showed less loss in bone height. There was an increase in bone mass over time for root-form or plate-form implants. Both root-form and plate-form implants provided radiographic evidence of osseointegration in loaded bridges.

Alveolar Bone Loss↗
PubMed1994

Surface energy characterization of unalloyed titanium implants.

Osteointegration is dependent on a variety of biomechanical and biochemical factors. One factor is the wettability of an implant surface that is directly influenced by its surface energy. This investigation used the Zisman plot to determine critical surface tension as one representative measurement of surface energy. The effects of surface treatment, bulk grain size, and surface roughness on the critical surface tension of unalloyed titanium (Ti) were examined. Radio frequency glow discharge-treated Ti had the highest critical surface tension, followed by the passivated and heat-sterilized conditions. Titanium with no surface treatment had the lowest critical surface tension. The surface energy of Ti with an average grain size of 23 microns was not significantly different from that with a grain size of 70 microns. Surface roughness was shown to cause significant difference in measurements and definitely should be considered in studies of this kind.

Prostheses and Implants↗
PubMed1994

Evaluation of consecutively placed unloaded root-form and plate-form implants in adult Macaca mulatta monkeys.

The present paper describes 18 consecutively-treated non-human primates (Macaca mulatta) as part of a balanced block design study of 36 animals to examine osseointegration in root- and plate-form implants prepared by atraumatic preparation of bone. Clinical measurements around selected teeth and digital radiology were utilized to monitor periodontal disease and bone deposition around the unloaded implants. Once a month scaling procedures were utilized as a means of preventing further advance of periodontal disease. Results indicate that once-monthly regimen of scaling and root planing can prevent attachment loss of natural teeth and will not interfere with the healing of either type of implant; once-monthly scalings produce significant reduction in redness (P < .05) and reduced probing depths (P = .01). A second finding is that both root and blade implants show radiographic evidence of osseointegration in this primate model. The quantitative analysis demonstrates bone gain is not stabilized until 6 months after healing. The data may indicate that occlusal loading of mandibular implants at 3 months may be premature.

Alveolar Bone Loss↗
PubMed1994

Biomaterial and design concepts to minimize wear in total joint arthroplasties.

The evolution of high technology-based total joint arthroplasty (TJA) materials and designs has resulted in systems that provide significant advantages related to surgical procedures, functional mechanics, and short-term and long-term rehabilitation. The research and development community has been addressing key issues associated with attachment-to-tissues for force transfer and wear and debris from articulating surfaces. To minimize wear, multiple material and design technologies have been applied, with recent emphasis on surface and bulk modifications of alloys and polymers plus the reconsideration of ceramic and metallic articulations. This article provides an overview of the biomaterial considerations for articulating surfaces of existing TJA systems, efforts to control wear phenomena, and implications on the clinical aspects of long-term function.

Alloys↗