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Biomedical subjects

J R Parsons

Publications and source records attributed to J R Parsons.

At least 19 recordsLinked to original sources
PubMed2002

Dissolved organic carbon--contaminant interaction descriptors found by 3D force field calculations.

Enthalpies of transfer at 300 K of various partitioning processes were calculated in order to study the suitability of 3D force fields for the calculation of partitioning constants. A 3D fulvic acid (FA) model of dissolved organic carbon (DOC) was built in a MM+ force field using AMI atomic charges and geometrical optimization (GO). 3,5-Dichlorobiphenyl (PCB14), 4,4'-dichlorobiphenyl (PCB15), 1,1,1-trichloro-2,2-bis-(4-chlorophenyl)-ethane (PPDDT) and 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (Atrazine) were inserted into different sites and their interaction energies with FA were calculated. Energies of hydration were calculated and subtracted from FA-contaminant interactions of selected sites. The resulting values for the enthalpies of transfer from water to DOC were 2.8, -1.4, -6.4 and 0.0 kcal/mol for PCB 14, PCB15, PPDDT and Atrazine, respectively. The value of PPDDT compared favorably with the experimental value of -5.0 kcal/mol. Prior to this, the method was studied by the calculation of the enthalpies of vaporization and aqueous solution using various force fields. In the MM + force field GO predicted enthalpies of vaporization deviated by +0.7 (PCB14), +3.6 (PCB15) and -0.7 (PPDDT)kcal/mol from experimental data, whereas enthalpies of aqueous solution deviated by -3.6 (PCB14), +5.8 (PCB15) and +3.7 (PPDDT) kcal/mol. Only for PCB14 the wrong sign of this enthalpy value was predicted. Potential advantages and limitations of the approach were discussed.

Atrazine↗
PubMed2001

Three-dimensional printing and porous metallic surfaces: a new orthopedic application.

As-cast, porous surfaced CoCr implants were tested for bone interfacial shear strength in a canine transcortical model. Three-dimensional printing (3DP) was used to create complex molds with a dimensional resolution of 175 microm. 3DP is a solid freeform fabrication technique that can generate ceramic pieces by printing binder onto a bed of ceramic powder. A printhead is rastered across the powder, building a monolithic mold, layer by layer. Using these 3DP molds, surfaces can be textured "as-cast," eliminating the need for additional processing as with commercially available sintered beads or wire mesh surfaces. Three experimental textures were fabricated, each consisting of a surface layer and deep layer with distinct individual porosities. The surface layer ranged from a porosity of 38% (Surface Y) to 67% (Surface Z), whereas the deep layer ranged from 39% (Surface Z) to 63% (Surface Y). An intermediate texture was fabricated that consisted of 43% porosity in both surface and deep layers (Surface X). Control surfaces were commercial sintered beaded coatings with a nominal porosity of 37%. A well-documented canine transcortical implant model was utilized to evaluate these experimental surfaces. In this model, five cylindrical implants were placed in transverse bicortical defects in each femur of purpose bred coonhounds. A Latin Square technique was used to randomize the experimental implants left to right and proximal to distal within a given animal and among animals. Each experimental site was paired with a porous coated control site located at the same level in the contralateral limb. Thus, for each of the three time periods (6, 12, and 26 weeks) five dogs were utilized, yielding a total of 24 experimental sites and 24 matched pair control sites. At each time period, mechanical push-out tests were used to evaluate interfacial shear strength. Other specimens were subjected to histomorphometric analysis. Macrotexture Z, with the highest surface porosity, failed at a significantly higher shear stress (p = 0.05) than the porous coated controls at 26 weeks. It is postulated that an increased volume of ingrown bone, resulting from a combination of high surface porosity and a high percentage of ingrowth, was responsible for the observed improvement in strength. Macrotextures X and Y also had significantly greater bone ingrowth than the controls (p = 0.05 at 26 weeks), and displayed, on average, greater interfacial shear strengths than controls, although they were not statistically significant.

Animals↗
PubMed2001

Fluorene degradation by Sphingomonas sp. LB126 proceeds through protocatechuic acid: a genetic analysis.

Sphingomonas sp. LB126 is able to utilize fluorene as sole source of carbon and energy. In the present study, a mutagenic vector was constructed and a "plasmid rescue" strategy was set up to isolate a 16.5-kb DNA fragment containing genes required for fluorene degradation. A 14.5-kb portion of the cloned DNA was sequenced revealing thirteen open reading frames. Two encoded hypothetical proteins (FldE and FldY) similar to transcriptional regulators and one (ORF360) located on an IS-like element (ISSsp126) encoded a putative transposase. Three other putative proteins (FldB, FldU and FldV) displayed strong similarity with enzymes of the protocatechuate 4,5-degradation pathway utilized by Sphingomonaspaucimobilis SYK-6 for the degradation of lignin breakdown products. The remaining hypothetical proteins displayed only limited similarity with enzyme sequences available from databases. Suicide plasmid-directed mutagenesis and genetic complementations showed that integrity of the protocatechuate catabolic pathway was an absolute requirement for fluorene degradation to proceed. These findings were further supported by the analysis of metabolites in bacterial culture supernatants obtained from appropriate mutants. The results presented here demonstrated the suitability of the genetic tool constructed and supplied the first genetic evidence for the participation of a protocatechuate 4,5-degradation pathway in a bacterial fluorene degradation pathway.

Bacterial Proteins↗
PubMed2001

In vitro longitudinal assessment of coronal discoloration from endodontic sealers.

A major cause of tooth discoloration may be sealer remnants in the chamber. The objective of this study was to evaluate, longitudinally, coronal discoloration from four sealers. Extracted premolars were sectioned in the coronal third of the root. The chamber contents were removed and instrumentation was via the canal. The following sealers were bulk introduced into the chamber: AH26, Kerr Pulp Canal Sealer, Roths 801 (nonstaining), and Sealapex. The apical access was sealed with white sticky wax. Teeth were maintained in a moist environment at 37 degrees C. Initial (immediate pretreatment) digital images of the teeth were made for base line comparison. Subsequent images were at 1-, 3-, 9-, and 12-month intervals. Then images were mixed and descriptively evaluated blindly by trained evaluators. Discoloration was induced by the four sealers, with slight to moderate visible changes that increased through 12 months. There was slightly more discoloration with AH26 and Kerr Pulp Canal Sealer. In conclusion discoloration induced by the endodontic sealers produced slight to moderate and generally progressive discoloration over 12 months.

Bicuspid↗
PubMed2000

Mechanical environment affects allograft incorporation.

In a bilateral canine tibial model, the mechanical, radiologic, and histologic characteristics of intercalary allografts stabilized with locked intramedullary nails were compared with those of allografts fixed with compression plates. Both methods of fixation achieved healing to host bone. Tibiae that were plated had more callus with statistically greater mean torsional rigidity and strength than those treated with nails (paired t-test, p </= 0.05). On average, tibiae which had been plated had much higher bending rigidity than those fixed with locked nails; however, the difference in means was not statistically significant. Histomorphometric analysis showed an overall greater total bone formation in those limbs treated with plates compared to nails (paired t-test, p </= 0.04). The mechanical environment created by the different fixation methods are thought to be responsible for the observed differences in healing pattern. The traditional concept of fixation for allografts to achieve maximum rigidity of the construct may not necessarily promote the most appropriate host healing response in all situations. A less rigid fixation method (plates) produced more callus resulting in superior torsional and bending properties. These data show that in this canine intercalary allograft model, limbs fixed with plates produced more external callus resulting in stronger, more rigid healing.

Animals↗
PubMed2000

A chemostat system for investigating pesticide biodegradation in continuous mixed bacteria cultures originating from surface water.

To be able to predict the degradation (rate) of organic chemicals (e.g. pesticides) in the field, knowledge of the environmental conditions that are of influence on the degradation process are of importance. In the present study an experimental system is described which is used to study the degradation of organic pollutants in mixed bacteria cultures originating from surface water With this system the degradation of compounds can be followed for relatively long experimental periods (months). In addition, it is possible to vary different environmental parameters in order to investigate their influences on the degradation of the chemical. These preliminary experiments show that growth and 'composition' of the bacteria culture have comparable patterns in parallel experiments. The first order degradation rate constant for the test compound dichloran, as calculated from these experiments under these circumstances, is about 0.002 h(-1).

Aerobiosis↗
PubMed1999

Small changes in polymer chemistry have a large effect on the bone-implant interface: evaluation of a series of degradable tyrosine-derived polycarbonates in bone defects.

In a series of homologous, tyrosine-based polycarbonates, small changes in the chemical structure of the polymer pendent chain were found to affect the bone response in a long-term (1280 d) implantation study. Identically sized pins, prepared from poly(DTE carbonate), poly(DTB carbonate), poly(DTH carbonate), and poly(DTO carbonate) were implanted transcortically in the proximal tibia and the distal femur of skeletally mature New Zealand White Rabbits. The tissue response at the bone-implant interface was characterized in terms of the absence of a fibrous capsule (direct bone apposition, indicative of a bone bonding response) or the presence of a fibrous capsule (referred to as the encapsulation response). The relative frequency of direct bone apposition versus encapsulation was recorded for each polymer throughout the entire period of the study. While all four polymers were tissue compatible, there was a correlation between the chemical structure of the pendent chain and the type of bone response observed, with poly(DTE carbonate) having the highest tendency to elicit direct bone apposition. Based on in vivo degradation data and the ability of model polymers with carboxylate groups at their surface to chelate calcium ions, it is proposed that the ability of poly(DTE carbonate) to bond to bone is caused by the facile hydrolysis of the pendent ethyl ester groups which creates calcium ion chelation sites on the polymer surface. The incorporation of calcium chelation sites into the chemical structure of an implant material appears to be a key requirement if direct bone apposition/bone bonding is desired. This study demonstrates that very subtle changes in the chemical composition of an implant material can have significant effects on the long-term tissue response in a clinically relevant model.

Animals↗
PubMed1998

Pathologic supracondylar fracture due to osteolytic pseudotumor of knee following cementless total knee replacement.

Wear debris of polyethylene, polymethylmethacrylate, and metal have been recognized to be associated with foreign body reactions, osteolysis, and aseptic prosthetic loosening after joint replacement arthroplasty. Further, foreign body reaction due to the presence of extensive wear debris can cause aggressive granulomatous lesions and pathologic fracture. To our knowledge, there has been no previous report of pathologic fracture of the femur due to an agressive pseudotumor. This report describes a case of pathologic supracondylar fracture of the femur 6 years and 5 months after cementless total knee replacement arthroplasty. The fracture occurred through an aggressive expanding soft tissue mass that was a tumorlike lesion secondary to polyethylene wear debris. The lesion was associated with massive osteolysis around the femoral component of the total knee prosthesis.

Arthroplasty, Replacement, Knee↗
PubMed1998

Mechanical properties of bone in a paraplegic rat model.

Pathologic fractures may occur with minimal trauma after spinal cord injury (SCI) because of osteoporosis. Rats were evaluated to determine whether they could be used as an SCI animal model. Male Sprague-Dawley rats underwent spinal cord transection at the ninth thoracic vertebrae. Control rats underwent a sham procedure. Mechanical testing of the humeral shaft, femoral shaft, tibial shaft, femoral neck, distal femur, and proximal tibia was performed separately at 0, 8, and 24 weeks after surgery. At 24 weeks, significant differences between SCI and control rats were found in maximum torque needed to produce failure in the femoral shaft (63 percent of control, p < 0.05) and tibial shaft (63 percent, p < 0.01), and in compressive load to produce failure in cross-sectional specimens of the distal femur (51 percent, p < 0.05) and proximal tibia (50 percent, p < 0.01). No differences were found in the maximum torque needed to produce failure of the humeral shaft (106 percent, p = 0.77) between SCI and control rats. Reductions in relative bone strength in SCI rats at 24 weeks were similar in magnitude to bone mineral density changes reported in humans with chronic paraplegia. Thus, Sprague-Dawley rats appear to be good animal models in which to evaluate changes in bone strength following SCI.

Animals↗
PubMed1997

The biomechanical analysis of sublaminar wires and cables using luque segmental spinal instrumentation.

STUDY DESIGN: Data was gathered from biomechanical testing of 10 thoracic human cadaveric spines. Spines were tested intact and with a Luque rectangle fixed with wire or cable. OBJECTIVES: To compare the rigidity of fixation and intraspinal penetration of sublaminar monofilament wire and multistrand cable under identical conditions using human cadaveric spines. SUMMARY OF BACKGROUND DATA: Reports of neurologic and mechanical complications associated with sublaminar wiring techniques have led to the recent development of more flexible multistrand cable systems. The relative performance of flexible cable versus monofilament wire has not been explored fully in a controlled mechanical environment. METHODS: A servohydraulic mechanical testing machine was used to measure the static mechanical stiffness of sublaminar wire or cable fixation in conjunction with a Luque rectangle for thoracic human cadaveric spine segments in flexion-extension and torsion modes. Cyclic testing was performed in the flexion-extension mode. Intraspinal penetration of wires and cables was measured. RESULTS: Spine fixation with sublaminar wire and cable resulted in constructs of equal stiffness in flexion-extension and torsion modes. Cyclic testing also indicated similar fatigue profiles for wire- and cable-instrumented spines. Wire and cable fixed spines displayed greater stiffness than the intact spines. Cable encroachment of the spinal canal was less than that seen with wire. CONCLUSIONS: Sublaminar multistrand cable may be a rational alternative to monofilament wire in segmental spinal instrumentation because it provides less encroachment into the spinal canal. Further, cadaveric spines instrumented with wire and cable display equivalent mechanical behavior, statically and under cyclic loading. The potential advantages of cable, however, must be balanced against a substantial increase in cost relative to wire.

Biomechanical Phenomena↗
PubMed1997

A biomechanical study of a cervical spine stabilization device: Roy-Camille plates.

STUDY DESIGN: Three-hole Roy-Camille posterior plates (Howmedica, Inc., Rutherford, NJ) were used to fix severely destabilized fresh cadaveric cervical spines. Fixed spine constructs were tested mechanically in flexion-extension and torsion, and the results were compared with the same characteristics in the intact spine before destabilization. Stainless steel and titanium plates and screws were evaluated. OBJECTIVES: To determine if the application of Roy-Camille posterior plates provided suitably strong and rigid fixation of a severe, surgically created three-column instability. SUMMARY OF BACKGROUND DATA: Controversy still remains regarding the exclusive use of posterior cervical plating in the face of three-column instability. Posterior plating has been evaluated biomechanically in severely destabilized calf spines; however, posterior plating of similarly destabilized human cadaveric cervical spines using the Roy-Camille system has not been examined. METHODS: The authors chose to test the main motions of the neck (flexion, extension, and torsion) in the intact and the plated state using a servohydraulic materials testing system. Testing the surgically altered spine before fixation proved to be futile because of drastic instability, which is characteristic of the chosen defect. Once fixed, the spines were tested, and the rigidity of the constructs were compared with that of the intact state. Strength and failure mechanisms were evaluated. RESULTS: The rigidity of the plated spine constructs surpassed that of the intact spines; the stainless steel and titanium systems were mechanically equivalent. Thus, application of the Roy-Camille plates of either type dramatically reduced the motion of the unstable spine. Strength of the fixed spine constructs was limited by screw pull-out at theoretically predictable levels of force. CONCLUSIONS: Posterior application of Roy-Camille plates can fix cervical spines with severe destabilizing defects rigidly. Screw pull-out of the most proximal or distal screw was always the mechanism of failure.

Biomechanical Phenomena↗
PubMed1996

Ecological hazard assessment of dioxins: hazards to organisms at different levels of aquatic food webs (fish-eating birds and mammals, fish and invertebrates).

An ecological hazard assessment was performed for 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin in the aquatic environment, taking into account four different classes of species which differ with respect to their positions in aquatic food webs: invertebrates, fish, birds preying on aquatic organisms, and mammals preying on aquatic organisms. The most sensitive toxicological endpoints for each class were selected from the literature. These endpoints were extrapolated to no effect concentrations (NECs) in water with a two-level food chain model as indicator for secondary poisoning. From the results it is concluded that fish-eating birds and mammals experience larger hazards from dioxins and related compounds than fish. The limited data available appear to indicate that invertebrates are rather insensitive to dioxins. The study indicates that assessment of secondary poisoning affects environmental quality criteria setting and risk assessment.

Animals↗
PubMed1996

RP4::Mu3A-mediated in vivo cloning and transfer of a chlorobiphenyl catabolic pathway.

Chromosomal DNA fragments encoding the ability to utilize biphenyl as sole carbon source (Bph+) were mobilized by means of plasmid RP4::Mu3A from strain JB1 (tentatively identified as Burkholderia sp.) to Alcaligenes eutrophus CH34 at a frequency of 10(-3) per transferred plasmid. The mobilized DNA integrated into the recipient chromosome or was recovered as catabolic prime plasmids. Three Bph+ prime plasmids were transferred from A. eutrophus to Escherichia coli and back to A. eutrophus without modification of the phenotype. The transferred Bph+ DNA segments allowed metabolism of biphenyl, 2-, 3- and 4-chlorobiphenyl, and diphenylmethane. Genes involved in biphenyl degradation were identified on the prime plasmids by DNA-DNA hybridization and by gene cloning. Bph+ prime plasmids were transferred to Burkholderia cepacia, Pseudomonas aeruginosa, Comamonas testosteroni and A. eutrophus and the catabolic genes were expressed in those hosts. Transfer of the plasmid to the 3-chlorobenzoate-degrading bacterium Pseudomonas sp. B13 allowed the recipient to mineralize 3-chlorobiphenyl. Other catabolic prime plasmids were obtained from JB1 by selection on m-hydroxybenzoate and tyrosine as carbon sources. 16S rRNA sequence data demonstrated that the in vivo transfer of bph was achieved between bacteria belonging to two different branches of the beta-Proteobacteria.

Alcaligenes↗
PubMed1995

Materials and design concepts for an intervertebral disc spacer. II. Multidurometer composite design.

The main function of the intervertebral disc is to transmit and attenuate compressive and torsional forces, and stabilize the intervertebral joint. Unfortunately, the disc may be displaced or damaged due to trauma or disease causing the nucleus to herniate and protrude into the vertebral canal or intervertebral foramen. Pressure on the spinal nerve may cause pain or paralysis in the area of its distribution. At present, the surgical procedures used to alleviate this condition include disc excision, and/or spinal fusion. A more desirable situation would involve removing the nucleus pulposus and part or all of the annulus fibrosis and implanting a suitable biofunctional equivalent. Such a prosthesis should attenuate stresses and prevent abnormal stress at adjacent intervertebral joints. Maintenance of normal disc height would prevent impingement of the posterior facet joints and facet joint syndrome. In a previous companion paper (J. Applied Biomat. 5:125-132; 1994), the mechanical behavior of disc prostheses manufactured from fiber reinforced, elastomeric thermoset resins were examined. In order to develop devices which were more practical from a manufacturing standpoint and extremely reproducible, the fiber reinforced thermoset resins were replaced by multi-durometer thermoplastic elastomeric materials. In the present paper, the mechanical properties of thermoplastic multicomponent designs have been investigated.

Biocompatible Materials↗
PubMed1995

Evaluation of poly(DTH carbonate), a tyrosine-derived degradable polymer, for orthopedic applications.

The polymerization of desaminotyrosinetyrosylhexyl ester (DTH) with phosgene gives rise to poly(DTH carbonate), a new pseudopoly(amino acid). To evaluate the performance of this bioabsorbable material in orthopedic applications, the tissue responses elicited by compression-molded pins of poly(DTH carbonate) and clinically used polydioxanone pins (PDS; Orthosorb) were compared. The two types of pins were implanted in the paravertebral muscle and in the metaphyseal proximal tibia and distal femur of 10 White New Zealand Rabbits for 1, 2, 4, and 26 weeks. The tissue response was evaluated using histologic staining of soft- and hard-tissue sections, fluorescent bone marker of incorporation, and backscattered electron imaging. In soft tissue, both poly(DTH carbonate) and PDS elicited a mild inflammatory response resulting in encapsulation. During the disintegration phase, the PDS implants triggered a foreign body response involving the phagocytosis of polymeric debris by histiocytes and giant cells. No such response was observed for poly(DTH carbonate). In hard tissue, close bone apposition was observed throughout the 26-week test period for poly(DTH carbonate) implants. At the 26-week time point, the poly(DTH carbonate) implants exhibited surface erosion and were penetrated by new bone. In contrast, an intervening fibrous tissue layer was always present between the PDS pins and the bone. At 26 weeks, the PDS implants had partially resorbed and a foreign body response characterized by infiltration in several of the implantation sites. This study indicates that poly(DTH carbonate) and PDS exhibit fundamentally different interactions with hard tissue, and that poly(DTH carbonate) is a promising orthopedic implant material.

Absorption↗
PubMed1995

Effect of demineralized bone matrix on bone growth within a porous HA material: a histologic and histometric study.

Coralline hydroxyapatite (cHA) is an osteoconductive material currently being used as a bone graft substitute. Created by the hydrothermal conversion of the calcium carbonate skeleton of coral to hydroxyapatite, this material has a porous structure similar to cancellous bone. Addition of demineralized bone matrix (DBM) would conceivably create a composite with both osteoconductive and osteoinductive properties. This pilot study evaluated the healing of rabbit cranial defects that had been filled with cHA or cHA augmented with a DBM gel formed by adding glycerol to the DBM particulate. Data from these were then compared to unfilled defects from a previous study. Results indicated enhancement of new bone formation and an increase in the rate of healing in the defects filled with the cHA-DBM gel composite. Further studies are warranted.

Animals↗
PubMed1995

The porous-coated anatomic (PCA) total hip arthroplasty: a review of 73 uncemented cases with 2-year follow up.

A total of 73 hips in 62 patients who underwent non-cemented total hip arthroplasties (THA) with porous-coated anatomic (PCA, Howmedica) prostheses have been reviewed. A complete evaluation including preoperative and postoperative Harris hip scores (HHSs), a complete radiographic study, and complication determination has been completed with greater than 2-year follow up. Diagnoses included osteoarthritis (74.0%), rheumatoid arthritis (4.1%), avascular necrosis (15.1%), and posttraumatic arthritis following fracture (6.8%). The complication rate was 10.9% (8 complications/73 arthroplasties); 20 patients (35.6%) received bilateral implants. The mean preoperative HHS for the entire group was 38.7, and the mean postoperative score, irrespective of postoperative time, was 93.6. Key findings regarding the consecutive radiographic review of each arthroplasty included: 9.6% lucencies, 43.8% stress shielding, stable fibrous ingrowth in 74.0%, tip sclerosis in 19.2%, and cortical widening in 4.1%. The finding of loose beads from the pore ingrowth area of the prosthesis was minimal (7 beads in 6 patients). These results demonstrate the efficacy of the PCA prosthesis.

Activities of Daily Living↗