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Biomedical subjects

J R Parsons

Publications and source records attributed to J R Parsons.

At least 73 records · Page 4Linked to original sources
PubMed1985

Carbon fiber debris within the synovial joint. A time-dependent mechanical and histologic study.

The consequences of release of carbon debris within the synovial joint are of interest to surgeons contemplating the intra-articular repair of cruciate-deficient knees with a carbon fiber-based material. Coverage of carbon fiber implants with absorbable polymer as well as autogeneic graft material has resulted in surgical procedures that minimize potential fiber release. However, finite risk of release of fiber debris certainly exists. With this in mind, a controlled animal experiment to model debris release in the synovial joint was performed. As a positive control, magnesium tetrasilicate (talc) in suspension was injected into the knees of rabbits. Talc produced a transient synovitis severe enough to alter the mechanical properties of the joint cartilage. Carbon fiber debris, when similarly injected, also produced a synovitis. However, the synovitis induced by carbon particulate was not of sufficient severity or duration to alter the mechanical properties of the cartilage. Neither talc nor carbon fiber debris appeared to physically abrade cartilage.

Animals↗
PubMed1985

Pseudarthrosis after spinal fusion for scoliosis. A comparison of autogeneic and allogeneic bone grafts.

This study was undertaken to compare the incidence of pseudarthrosis in fusions supplemented with autogeneic and frozen allogeneic grafts. The records of 208 patients with adolescent idiopathic scoliosis who were treated by posterior fusion and Harrington instrumentation were studied. The fusion was supplemented by an autogeneic iliac bone graft in 114 patients and by an allogeneic bank bone graft in 94 patients. The fusion mass was explored in all patients with suspected pseudarthrosis; therefore, all pseudarthroses reported in this series were proved by surgical exploration. Pseudarthrosis developed in five patients (4.4%) receiving an autogeneic graft and in five patients (5.3%) receiving an allogeneic graft. The incidence of pseudarthrosis was not significantly different at the 95% level of certainty. Average blood loss and operative time were determined for all patients. The decreases in average blood loss and operative time in those patients receiving allogeneic grafts were significant (p less than .01). Thus, based on the incidence of pseudarthrosis, allogeneic frozen bank-stored bone is an attractive alternative to autogeneic iliac bone for fusion supplementation in the treatment of scoliosis. Total operative time and blood loss can be decreased, and possible complications associated with a donor site can be avoided.

Adolescent↗
PubMed1984

The electrical stimulation of bone using a filamentous carbon cathode.

Filamentous carbon fiber is an extremely compatible biomaterial. It does not corrode and elicits almost no foreign body response. In addition, this material is an efficient electrical conductor in vivo. These desirable characteristics suggest that carbon fiber may be of use as an electrode material for the stimulation of bone and/or soft tissue growth. This possibility has been investigated in a well established laboratory animal model. When used as a cathode material in conjunction with an implantable constant direct current device, carbon fiber was shown to be an effective electrode material for the stimulation of bone and fibrous tissue within the medullary canal of the tibia of the rabbit. Further, adjustment of current levels appear to allow some selectivity in terms of the amount and type of tissue produced. Currents in the 1 microA range produced a maximum amount of bone, whereas a 20 microA current produced a maximum amount of fibrous tissue. Intermediate current levels produced a proportional mix of bone and soft tissue.

Animals↗
PubMed1983

Absorbable polymer-filamentous carbon composites--a new class of tissue scaffolding materials.

The utility of filamentous carbon in tendon and ligament repair is limited by its premature mechanical degradation. When filamentous carbon is coated with an absorbable polymer, polylactic acid (PLA), a composite material results which serves as a tissue scaffold, maintaining its integrity long enough for new tissue to grow in and around it before it gradually degrades. Biocompatibility studies showed excellent tissue response to the PLA-carbon composite. Dog patellar tendons and medial collateral ligaments and rabbit Achilles tendons fashioned from the composite were then implanted. The implants allowed almost immediate resumption of activity and encouraged the growth of new structures histologically and mechanically similar to the natural structures. Its high initial strength, rapid ingrowth and benign tissue reaction suggest that this new composite material may be useful in the treatment of tendon and ligament injuries in humans. Consequently, the material was entered into limited clinical trials. To date, thirty patients have had implant surgery for the repair of extensor mechanisms, knee ligaments, Achilles tendons, and rotator cuffs. At this writing, seven month follow-up is available. Early results are encouraging.

Absorption↗
PubMed1983

Iron repletion decreases maximal exercise lactate concentrations in female athletes with minimal iron-deficiency anemia.

We studied the effect of 2 weeks of iron therapy on exercise performance and exercise-induced lactate production in trained women athletes: six control subjects with normal parameters of iron status and nine with mild iron-deficiency anemia defined by low Fe/TIBC, ferritin, and minimally decreased Hgb values. Iron therapy improved the abnormal measures of iron status and low Hgb in the second group to normal. Exercise performance in a progressive work-exercise protocol on a bicycle ergometer to exhaustion was unchanged after iron therapy in both groups; however, blood lactate levels at maximum exercise in the iron-deficient group decreased significantly from 10.3 +/- 0.6 mmol/L before therapy to 8.42 +/- 0.7 after therapy (p less than 0.03). The control subjects did not significantly alter lactate levels after maximal exercise on iron compared to placebo: 8.3 +/- 0.8 mmol/L vs. 8.5 +/- 0.7. Although there was not a significant difference in maximum exercise performance after iron therapy, these data support animal experiments implying that iron may play a role in oxidative metabolism and that minimal decreases in Hgb may impair arterial oxygen content enough to affect aerobic metabolism. In addition, these findings may have important implications for competitive women athletes in whom mild iron deficiency may go unnoticed.

Acidosis↗
PubMed1981

Soft tissue attachment of a filamentous carbon-absorbable polymer tendon and ligament replacement.

Soft tissue structures can be replaced by a filamentous carbon-polylactic acid polymer tissue scaffold. A successful replacement requires a secure bond between the synthetic material and living soft tissue. This attachment has been investigated in a rabbit model. In 23 male, white New Zealand rabbits, the proximal third of the Achilles tendon of the hind leg was resected. Seventeen of these rabbits received composite tendon implants; six received no implants and served as shams. In all cases, the contralateral limb served as a unoperated control. Biological fixation of the synthetic material to the tendinous and myotendinous tissues of the rabbit gastrocnemius system was achieved. This occurred by ingrowth of soft tissue into the 7 mu carbon fiber network. This bond developed rapidly and was mechanically secure under physiologic loading conditions. The anastomoses' strengths were tested in tension over a 12-week period and compared to the breaking strengths of their contralateral, unoperated gastrocnemius systems and the sham systems. After four weeks, the systems with implants had strengths equivalent to those of the unoperated systems. Sham systems were significantly weaker throughout the test period. Histologically, the ingrowth process was associated with little inflammatory response. The ingrown tissue was found to be highly cellular with collagen oriented longitudinally to the tendon. After 12 weeks, the volume of collagenous tissue making up the regrown tendon section appeared nearly normal. Secure biological fixation of the carbon-polylactic acid scaffold to soft tissues may allow it application in repair or replacement of tendon or ligament deficits.

Achilles Tendon↗
PubMed1980

The role of bioengineering in orthopedics.

Orthopedic bioengineering is an example of professionals in distinct disciplines applying their skills to problems that require an interdisciplinary approach. Two current research projects, the development of replacement ligaments and tendons and of an absorbable fracture fixation device, illustrate this integrated approach.

Biocompatible Materials↗
PubMed1979

Articular cartilage preservation and storage. II. Mechanical indentation testing of viable, stored articular cartilage.

Mature rabbit articular cartilage in the form of distal femoral condyles, composite osteoarticular structures, were incubated in the presence of alpha-tocopherol (200 micrograms/ml) over a period of time. Indentation testing and 35S uptake indicate preservation of sustained load carrying capacity and viability, respectively, in the presence of alpha-tocopherol for up to 30 days in organ culture. Condylar cartilage stored in the absence of alpha-tocopherol as well as frozen cartilage demonstrated progressive inability to resist sustained loading over time. Nonoptimal synthetic function apparently occurred in these latter two groups when compared to alpha-tocopherol stored material.

Animals↗
PubMed1976

Long-term effects of chondrocyte death on rabbit articular cartilage in vivo.

The effects of freezing localized areas of rabbit articular cartilage in vivo were studied at two to twelve months morphologically (gross and microscopic examination, including scanning electron microscopy), histochemically (toluidine blue and safranin O), and metabolically (35S uptake). Up to six months the frozen cartilage was intact but appeared to be dead, as shown by the absence of stainable chondrocytes, severely decreased acid mucopolysaccharide content, and absence of significant uptake of 35S. At twelve months fibrillation and softening were evident, clusters of new chondrocytes with surrounding acid mucopolysaccharides were visible microscopically, and scanning electron microscopy revealed an irregular pattern of collagen fibers which were larger than normal, of varying thickness, and broken in some areas. These changes resembled those seen in degenerative joint disease.

Animals↗
PubMedDate not supplied

Morphological characteristics of tendon cells cultured on synthetic fibers.

Filamentous carbon is currently being used as an implant material for tendon and ligament repair in humans. This material acts as a scaffold for the organization of new fibrous tissue growth. Primary cultures of rat tendon fibroblast cells (1 degrees RTF cells) were grown on carbon, Dacron, polyethylene and Nylon fibers in vitro. The morphological characteristics of these cells were examined. The process of cell migration from tendon explant to fiber substrate was similar for all four materials. Three morphological categories of cells were observed on these materials. (1) spherical dividing cells, (2) spindle-shaped migrating cells, (3) sheath-like migrating or stationary cells. The morphological characteristics and orientational behavior of cultured fibroblasts on these fiber materials were strongly influenced by the diameters of the fibers and by fiber surface characteristics such as longitudinal striations. The possible mechanisms of cell response to substrate geometric configuration are discussed along with the clinical significance of these experiments.

Animals↗
PubMedDate not supplied

Aerobic degradation of polychlorinated biphenyls by Alcaligenes sp. JB1: metabolites and enzymes.

In contrast to the degradation of penta- and hexachlorobiphenyls in chemostat cultures, the metabolism of PCBs by Alcaligenes sp. JB1 was shown to be restricted to PCBs with up to four chlorine substituents in resting-cell assays. Among these, the PCB congeners containing ortho chlorine substituents on both phenyl rings were found to be least degraded. Monochloro-benzoates and dichlorobenzoates were detected as metabolites. Resting cell assays with chlorobenzoates showed that JB1 could metabolize all three monochlorobenzoates and dichlorobenzoates containing only meta and para chlorine substituents, but not dichlorobenzoates possessing an ortho chlorine substituent. In enzyme activity assays, meta cleaving 2,3-dihydroxybiphenyl 1,2-dioxygenase and catechol 2,3-dioxygenase activities were constitutive, whereas benzoate dioxygenase and ortho cleaving catechol 1,2-dioxygenase activities were induced by their substrates. No activity was found for pyrocatechase II, the enzyme that is specific for chlorocatechols. The data suggest that complete mineralization of PCBs with three or more chlorine substituents by Alcaligenes sp. JB1 is unlikely.

Aerobiosis↗
PubMedDate not supplied

Biodegradation pathway of 2-chlorodibenzo-p-dioxin and 2-chlorodibenzofuran in the biphenyl-utilising strain JB1.

The biphenyl-utilising Burkholderia (previously Alcaligenes) strain JB1 is also able to degrade a number of chlorinated dibenzo-p-dioxins and dibenzofurans. In this study, 4-chlorocatechol and a chlorotrihydroxydiphenyl ether were identified as metabolites of 2-chlorodibenzo-p-dioxin. 5-Chlorosalicylic acid and a chlorotrihydroxybiphenyl were metabolites of 2-chlorodibenzofuran. These results show that degradation of these compounds follows pathways in which the initial reaction is angular dioxygenation, followed by cleavage of an ether bridge. This pathway is similar to that used by dibenzofuran-degrading strains such as Sphingomonas sp. strain RW1.

Benzofurans↗