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Biomedical subjects

J R Parsons

Publications and source records attributed to J R Parsons.

At least 55 records · Page 3Linked to original sources
PubMed1990

Investigation of a hydroxyapatite and calcium sulfate composite supplemented with an osteoinductive factor.

In the search for a suitable bone graft substitute, a study was conducted using a material that combined a proven osteoconductive composite, hydroxyapatite-calcium sulfate (HA/CS), with an osteoinductive factor, bovine osteogenic factor (OF). The initial study demonstrated the osteoinductive potential of OF in the rabbit muscle model. Once satisfied that the OF was active, it was added to the HA/CS composite and placed in 8-mm trephine defects in the rabbit cranium. This HA/CS/OF was directly compared to HA/CS augmented with a control protein, rabbit serum albumin (RSA). Animals were sacrificed at 4 and 8 weeks. Results demonstrated increased bone formation with the addition of the OF to the composite with bridging of the defects, in most cases, by 4 weeks. No bridging was seen, at this time period, in the other defects left unfilled or filled with HA/CS/RSA. Osteogenic factor, with the appropriate delivery system, can induce bone formation in the rabbit muscle. It may also increase the rate of bone formation at early time periods in a bony defect site when the delivery system is the osteoconductive composite HA/CS.

Animals↗
PubMed1990

Preliminary characterization of bioresorbable and nonresorbable synthetic fibers for the repair of soft tissue injuries.

Preliminary characterizations of two new synthetic fibers were performed to determine their potentials for use in soft tissue scaffolding devices. A slowly bioresorbing random copolymer of dimethyltrimethylene carbonate (DMTMC) and trimethylene carbonate (TMC) was the first fiber evaluated. The second was a nonresorbable high-strength synthetic fiber of highly oriented polyethylene. Their in vitro mechanical behavior was evaluated by loading fibers in uniaxial tension to determine mechanical properties in dry and wet (saline) environments. The polyethylene fiber had a dry strength of approximately 2.0 GPa, an ultimate strain of 3 to 4%, a tangent modulus of 57 GPa, and was not affected by the saline environment. The bioresorbable fiber had a dry strength of approximately 500 MPa, an ultimate strain of 35%, and tangent modulus of 5.4 GPa. The in vitro resorption of the bioresorbable fibers produced a 15% loss in strength over a 10-week period. In vitro cell-fiber compatibility studies were conducted to assay material biocompatibility and fiber substrate efficacy. Fibroblasts proliferated and migrated on both the polyethylene and bioresorbable fibers at rates similar to those previously found for other compatible fibers, thus demonstrating the new materials to be similar in their in vitro biocompatibility profiles. Morphological assessment with SEM also confirmed that these materials were suitable substrates for cell attachment. A rabbit Achilles tendon repair model using oriented polyethylene or bioresorbable fiber tows was evaluated after 12 and 26 weeks of implantation. The mechanical performances of both types of tendon repairs were similar to those found in previous studies using carbon or PET fibers. The polyethylene fibers elicited a low-grade chronic inflammatory tissue response. The bioresorbable fibers were still intact at 26 weeks and remained relatively inert in the host tissue, eliciting a minimal foreign body response.

Animals↗
PubMed1990

Degradation of halogenated aromatic compounds.

Due to their persistence, haloaromatics are compounds of environmental concern. Aerobically, bacteria degrade these compounds by mono- or dioxygenation of the aromatic ring. The common intermediate of these reactions is (halo)catechol. Halocatechol is cleaved either intradiol (ortho-cleavage) or extradiol (meta-cleavage). In contrast to ortho-cleavage, meta-cleavage of halocatechols yields toxic metabolites. Dehalogenation may occur fortuitously during oxygenation. Specific dehalogenation of aromatic compounds is performed by hydroxylases, in which the halo-substituent is replaced by a hydroxyl group. During reductive dehalogenation, haloaromatic compounds may act as electron-acceptors. Herewith, the halosubstituent is replaced by a hydrogen atom.

Bacteria↗
PubMed1990

Quantitative structure-activity relationships for biodegradation.

Quantitative structure-activity relationships (QSARs) between biodegradation rates of organic compounds and chemical structure parameters are reviewed. Although a number of such relationships have been developed, they in general only apply to restricted ranges of compounds, limiting their value as predictors of biodegradation rates. For many of these classes of chemicals relationships have been reported with different structural descriptors, varying from macroscopic physical properties to molecular structure parameters. More information on the mechanism and rate-determining steps of biodegradation, which can lead to a better-founded choice of descriptors, and more biodegradation rate data are required to further develop QSARs for biodegradation.

Biodegradation, Environmental↗
PubMed1990

The influence of growth hormone on the reversibility of articular cartilage degeneration in rabbits.

Growth hormone has chondrogenic affects on normal as well as on damaged articular cartilage. In this study, the influence of growth hormone is investigated on early degenerative changes in the articular cartilage in 72 New Zealand white rabbits. Cartilage lesions were created in femoral condyles using an immobilization model. Cartilage damage was assessed using biochemical, histologic, and biomechanical criteria. Growth hormone had no influence on prevention of immobilization abnormalities but had a significant affect on healing of established lesions.

Animals↗
PubMed1990

Perioperative blood loss associated with total knee arthroplasty. A comparison of procedures performed with and without cementing.

We reviewed the cases of thirty-four patients (thirty-eight knees) in whom prostheses with an identical design were used for primary total knee arthroplasty, and we compared the perioperative blood loss between the eleven knees in which cement was used and the twenty-seven knees in which cement was not used. The patients who had an uncemented prosthesis had a significantly greater mean blood loss, both intraoperatively (p less than or equal to 0.05) and during each subsequent eight-hour interval on the first postoperative day (p less than or equal to 0.05). The total for the forty-eight-hour postoperative collection also was greater (p less than or equal to 0.01), as was the cumulative loss for the entire study (p less than or equal to 0.01). When patients who had rheumatoid arthritis and osteoarthrosis were considered separately, the results were similar; that is, there was a significantly greater total postoperative blood loss in each of the two groups when cement was not used (p less than or equal to 0.025). A minimum postoperative hemoglobin concentration of ninety-five grams per liter was maintained; a greater percentage of patients (sixteen of twenty-seven) in whom cement was not used needed a transfusion as compared with two of eleven in the group in whom cement was not used (p less than or equal to 0.025), and they also needed more packed red-blood cells (1062 compared with 750 milliliters) (p less than or equal to 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1989

An evaluation of purified reconstituted type 1 collagen fibers.

Collagen fibers composed of type I collagen molecules were studied for biocompatibility and mechanical properties. These fibers were crosslinked using two different processes: 1) glutaraldehyde, 2) dehydration followed by exposure to cyanamide (DHT/C); the latter method produces only urea as a by-product of the crosslinking process and is postulated to be more biocompatible. An in vitro model using rat tendon fibroblasts growing on individual fibers was used to evaluate outgrowth rates, cell/fiber interactions, and cell morphology. These studies showed an advantage with DHT/C crosslinking, relative to glutaraldehyde crosslinking, in promoting fibroblast growth. In vivo intramuscular implantation in rats showed excellent biocompatibility for both kinds of collagen implants. In addition, aligned ingrowth into the implant from the medial collateral ligament when applied in that location was demonstrated. Mechanical testing demonstrated the higher strength of dry fibers; however, upon hydration, there was a marked decrease in stress to failure. This reduction in strength was due principally to an increase in cross section due to swelling. These collagen fibers appear to be very biocompatible even in the presence of low concentrations of glutaraldehyde. They promote fibrous aligned ingrowth in a setting of ligament healing. Thus, they represent a strong candidate as a scaffold ligament or tendon prosthesis if crosslink density can be increased.

Animals↗
PubMed1989

Long-term follow-up of achilles tendon repair with an absorbable polymer carbon fiber composite.

In this cooperative multicenter study for surgical repair of Achilles tendon rupture using a composite implant, 48 patients underwent 52 procedures. This implant is composed of filamentous uniaxially aligned carbon fibers coated with an absorbable polymer. This highly biocompatible implant acts as a scaffold for regrowth of collagenous tissue. The early strength of this repair is provided by the composite implant and by the rapid ingrowth and attachment of new tissue, which allows for an earlier and more vigorous rehabilitation program. Patients with a minimum follow-up of 1 year form the basis of this article. The overall average follow-up is 2.1 years. Three cohort groups were observed on a temporal basis and quantitatively evaluated at 1 year (N = 29), 18 months (N = 22), and 2 years (N = 20), respectively. These three groups demonstrated continuous improvement during the first postoperative year. A high level of function was maintained throughout the second year. Repair of chronic injuries (N = 15) was compared with repair of acute injuries (N = 12) at 1 year following surgery. Both groups greatly improved. However, the acute group had more serious preoperative deficits but improved to a slightly better overall level. Of the patients having at least 1 year follow-up, 86% had a good or excellent result. There was no increased morbidity associated with the use of the carbon implant.

Achilles Tendon↗
PubMed1989

Hydroxyapatite ceramics and the nature of the bone-ceramic interface.

Hydroxyapatite ceramics have been used as bone implants in a number of experimental systems and clinical applications. We have developed a unique experimental model that allows study of the interface between bone and implant materials. A comparison of titanium and hydroxyapatite materials, using this model, has demonstrated the osteoconductive nature of hydroxyapatite and its ability to bond directly to bone.

Animals↗
PubMed1989

Bone attachment to hydroxyapatite coated polymers.

Bone attachment to two classes of hydroxyapatite (HA) coated polymers was evaluated mechanically and histologically. Particulate HA was molded into the surface of thermoplastic implants and cast into the surface of thermoset implants. Coated and uncoated implants of both types were implanted in the distal femurs of rabbits for four and twelve weeks. After sacrifice, the bone/implant interface was evaluated mechanically via a push-out test with a servohydraulic test system. Paired statistical analysis revealed significantly greater shear strengths for coated vs. uncoated implants for both polymer systems at both time periods. Mixed mode of failure occurred with particle removal from the polymer surface and from the bone. One animal at each time period was saved for histology. Histology at both time periods indicated direct bone apposition to the HA coating as compared to a fibrous encapsulation about the uncoated implants. This was confirmed with backscatter scanning electron microscopy and scanning acoustic microscopy. Hydroxyapatite coatings significantly improve the bond strength between polymers and bone by allowing direct bone apposition and some mechanical interlocking with the bone.

Animals↗
PubMed1988

Osteoconductive composite grouts for orthopedic use.

A composite of HA particulate and calcium sulfate hemihydrate has been developed. When this dry material is mixed with either sterile saline or water, the resulting mixture begins to gel. While in the gel or dough state, the composite can be manually inserted or injected under pressure into a bone defect where it sets in situ. The calcium sulfate acts as a binder to hold the HA particles in place. The subsequent resorption of the calcium sulfate leaves controlled porosity for bone ingrowth and attachment to the nonresorbable HA particulate. The combination of calcium sulfate and HA results in a composite with handling properties superior to those of HA alone. Calcium sulfate has a long history of medical use as an implant material. The biocompatibility of the material has been clearly established. The combination of HA and calcium sulfate is likewise extremely compatible as demonstrated in the present studies. Bone ingrowth concomitant with resorption occurs rapidly with efficient conduction of bone from particle to particle. Based on the experiments presented herein, the composite of HA and calcium sulfate may be a useful alternative or adjunct to autogenous bone grafting. Many questions, however, remain regarding long-term tissue response and bone remodeling as well as the efficacy of this material relative to bone grafting.

Alveolar Process↗
PubMed1988

Deconvoluted X-ray diffraction analysis of bone and mixtures of bone and particulate hydroxyapatite.

Recent evidence suggests that bone phosphate exists almost entirely as hydroxyapatite (HA). The relative deficiency of calcium and presence of substantial HPO2-4 in bone phosphate indicates modification of the ideal HA structure, however. An inability to resolve closely spaced lines in fine grained materials, coupled with the limited periodicity of the thin mineral crystals of bone have prevented definitive characterization of the structure of bone mineral using standard X-ray diffraction (XRD) techniques. We have applied computer deconvolution XRD techniques to aid in the resolution of component overlapped profiles from bone, synthetic hydroxyapatite (HA) and mixtures of bone and synthetic HA resulting from implantation studies. In the course of this resolution process separate profiles were resolved from the (002) profile of bone derived HA. The ratio of integrated intensities of these profiles to the intensity of the profile of synthetic HA appears to provide an approximate measure of the ratio of bone to synthetic HA in a given sample. The finding of shoulders on the (002) peak of bone provides the basis for resolution into separate profiles. The asymmetry of these shoulders in mature bone cannot be attributed to crystallinity, particle size, or computer artifact. The same finding has been previously reported in hydrolyzed, deproteinated bone. Further work will be needed to resolve the question of whether the structural heterogeneity implied by profile geometry is the result of multiple HA phases, surface layer structure involving hydrolysis and calcium absences, or some other factor.

Animals↗
PubMed1987

Mechanical and histological studies of acute joint hemorrhage.

In this study, a simple animal model has been used to gather data on the mechanical and histologic changes in cartilage and the histologic changes in synovium attendant to acute joint hemorrhage. The continuous presence of autologous blood in the experimental joints for 10 days results in cartilage which is significantly more compliant than normal. These changes are attributed to loss of proteoglycan. Further, the study demonstrates a consistent pathology of the synovial tissues. Elaboration of degenerative enzymes from iron-laden synovial or subsynovial macrophages must be considered a primary mechanism of cartilage damage.

Acute Disease↗
PubMed1987

Mechanical behavior of articular cartilage quantitative changes with enzymatic alteration of the proteoglycan fraction.

The in-vitro viscoelastic mechanical response of normal rabbit articular cartilage is strongly dependent on the quantity and integrity of the proteoglycan fraction of the tissue matrix. Experimental results demonstrate that specific functional relationships exist between shear moduli, retardation time spectra, and proteoglycan content. Quantitative enzymolysis of the proteoglycan fraction of the tissue alters the form of these relationships in a fashion consistent with the altered physiochemical make-up of the tissue. The observed changes in mechanical behavior with controlled enzymolysis are similar to those associated with the early stages of osteoarthritis, rheumatoid arthritis, joint sepsis, and synovitis in animal models.

Animals↗
PubMed1987

The design and analysis of a laminated partially degradable composite bone plate for fracture fixation.

During the early stages of fracture healing, rigid internal fixation maintains alignment and promotes primary osseous union. Unfortunately, as healing progresses rigid fixation from bone plating can cause bone in the region of the plate to undergo stress protection atrophy. This can result in significant loss of bone mass and osteoporosis. Refracture of the bone upon device removal is a widely reported complication. In an effort to minimize or eliminate stress protection atrophy, we have designed a partially absorbable, fiber-reinforced bone plate. Ideally, such a plate gradually loses rigidity as the fracture heals, increasingly transferring stress to the bone. Stress protection may be avoided and removal of the device after healing may be unnecessary. Composite theory was used to determine an optimum fiber layup for a composite bone plate. Composite analysis suggested the mechanical superiority of a 0 degree/ +/ -45 degree laminae layup. Given this laminated design, a thermoplastic absorbable polymer (polylactic acid polymer) was reinforced with high-modulus carbon fiber to produce a semiabsorbable composite. Implant evaluation included optimizing fabrication techniques, thorough mechanical device testing, and implantation on canine femurs to determine biocompatibility and efficacy. The composite design proved to have superior static and fatigue properties to laminated or random fiber designs used previously. Two techniques for hole fabrication were tested. The production of screw holes during the molding process rather than machining postmolding, improved the mechanical integrity of the finished plate. Although the 0 degree/ +/- 45 degree carbon/polylactic acid composite possessed superior mechanical properties, it was unsuccessful in the in vivo environment. Water absorption and subsequent delamination made the plate flexible. Hypertrophic nonunions developed. Further development to prevent water intrusion and premature loss of mechanical properties is necessary.

Absorption↗
PubMed1986

Ligament and tendon repair with an absorbable polymer-coated carbon fiber stent.

Ribbon-like composite structures of filamentous carbon fiber and absorbable polymers have been used in the repair and replacement of both tendons and ligaments. The composite acts as a scaffold upon which new collagenous tissue can grow and has proved successful in a variety of animal models. The results of the first three years of human clinical trials have revealed ingrowth potential similar to that seen in the animal studies. Most patients have shown significant improvement, with many demonstrating good to excellent stability and function.

Animals↗
PubMed1985

Resorbable materials and composites. New concepts in orthopedic biomaterials.

For the last several decades, research in orthopedic biomaterials has remained focused on homogeneous plastics and metals. Initial research resulted in rapid improvements and a number of standardized materials emerged. With time, development of these materials has become a slower, more deliberate process. Recently, however, investigators have sought to broaden the scope of orthopedic biomaterials research. New materials systems are now under consideration. These systems include natural and synthetic resorbable polymerics and resorbable ceramics. A variety of composite materials are under primary investigation or in clinical trials. Our emerging understanding of these new materials is rapidly leading to new surgical applications not possible with conventional metals and plastics.

Animals↗