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Biomedical subjects

T D Stewart

Publications and source records attributed to T D Stewart.

At least 19 recordsLinked to original sources
PubMed2004

The wear and fracture behaviour of ultra high molecular weight polyethylene subjected to gamma-irradiation in an atmosphere of acetylene.

The wear and mechanical properties of GUR 1020 (Perplas IMP 2000-2) Ultra High Molecular Weight Polyethylene (UHMWPE) subjected to gamma-irradiation in an atmosphere of acetylene, were evaluated for a range of processing conditions of irradiation, annealing and ageing. The results were compared with those obtained for the virgin UHMWPE material and material processed using conventional gamma-irradiation in nitrogen. Cross-linking produced by irradiation in acetylene, followed by subsequent annealing was found to be significantly more effective in improving the mechanical and wear properties of UHMWPE compared to when the material was irradiated in nitrogen. Gel fraction analysis on its own, while being able to detect the degree of cross-linking, was found to be insufficient in determining the effectiveness of the cross-links and the resulting mechanical properties of the UHMWPE material. The results suggest that gamma-irradiation in an atmosphere of acetylene may provide significant advantages over conventional UHMWPE processing and irradiation cross-linking techniques.

Acetylene↗
PubMed2004

Carbon-carbon composite bearing materials in hip arthroplasty: analysis of wear and biological response to wear debris.

Ultra-high molecular weight polyethylene wear particles have been implicated as the major cause of osteolysis, implant loosening and late aseptic failure in total hip arthroplasties in vivo. This study initially screened 22 carbon-carbon composite materials as alternatives for UHMWPE in joint bearings. New bearing materials should satisfy certain criteria--they should have good wear properties that at least match UHMWPE, and produce wear particles with low levels of cytotoxic and osteolytic activity. Initial screening was based on wear resistance determined in short-term tribological pin-on-plate tests. Three materials (HMU-PP(s), HMU-RC-P(s), and SMS-RC-P(s)) which had superior wear resistance were selected for long-term testing. All materials had very low wear factors and SMS-RC-P(s), which had a wear factor of 0.08 +/- 0.56 x 10(-7) mm3/Nm, was selected for the subsequent biological testing and particle size analysis. SMS-RC-P(s) showed good biocompatibility in bulk material form and also the wear particles had low cytotoxicity for L929 fibroblasts in culture compared to metal wear particles. Wear debris size analysis by transmission electron microscopy showed that the particles were very small, with the vast majority being under 100 nm in size, similar to metal wear particles. The potential osteolytic effect of SMS-RC-P(s) wear particles was investigated by culturing particles with human peripheral blood mononuclear cells and measuring TNFalpha production. SMS-RC-P(s) did not significantly stimulate TNFalpha production at a particle volume to cell number ratio of 80:1, indicating that the debris had a low osteolytic potential. The results of this study suggest that carbon-carbon composites, particularly those composed of PAN-based fibers may be important biomaterials in the development of next generation bearing surfaces for use in total joint replacements that have very low wear rates and reduced osteolytic and cytotoxic potential.

Animals↗
PubMed2004

Wear of surface engineered metal-on-metal hip prostheses.

The wear of existing metal-on-metal (MOM) hip prostheses (1 mm3/million cycles) is much lower than the more widely used polyethylene-on-metal bearings (30-100 mm3/million cycles). However, there remain some potential concerns about the toxicity of metal wear particles and elevated metal ion levels, both locally and systemically in the human body. The aim of this study was to investigate the wear, wear debris and ion release of fully coated surface engineered MOM bearings for hip prostheses. Using a physiological anatomical hip joint simulator, five different bearing systems involving three thick (8-12 microm) coatings, TiN, CrN and CrCN, and one thin (2 microm) coating diamond like carbon (DLC) were evaluated and compared to a clinically used MOM cobalt chrome alloy bearing couple. The overall wear rates of the surface engineered prostheses were at least 18-fold lower than the traditional MOM prostheses after 2 million cycles and 36-fold lower after 5 million cycles. Consequently, the volume of wear debris and the ion levels in the lubricants were substantially lower. These parameters were also much lower than in half coated (femoral heads only) systems that have been reported previously. The extremely low volume of wear debris and concentration of metal ions released by these surface engineered systems, especially with CrN and CrCN coatings, have considerable potential for the clinical application of this technology.

Biomedical Engineering↗
PubMed2003

Biological response to wear debris generated in carbon based composites as potential bearing surfaces for artificial hip joints.

UHMWPE wear particles have been implicated in osteolysis, implant loosening, and long-term failure of total hip arthroplasties in vivo. This study examined four carbon-based composite materials as alternatives for UHMWPE in joint bearings. These materials were HMU-CVD, SMS-CVD, P25-CVD, and CFR-PEEK. New bearing materials should satisfy certain criteria: they should have good wear properties that at least match UHMWPE, and produce wear particles with low levels of biological activity. Of the four materials tested in multidirectional pin-on-plate tribological tests, SMS-CVD, P25-CVD, and CFR-PEEK showed lower volumetric wear factors than UHMWPE. P25-CVD had the lowest wear factor of 0.54 +/- 0.34 x 10(-7) mm(3)/Nm. Analysis of P25-CVD wear particles by transmission electron microscopy showed that the debris was very small, with the vast majority of particles being under 100 nm in size, which was similar in size to metal wear particles. The P25-CVD particles were isolated and cultured with L929 fibroblasts and U937 monocytic cells to assess their effect on cell viability. P25-CVD particles were significantly less cytotoxic (p < 0.01, ANOVA) to both cell types than CoCr metal wear particles. This work suggests that carbon-carbon composite materials may have potential for use in total hip replacement bearings. Of the materials tested P25-CVD had the lowest wear factor, and produced very small wear debris that had minimal cytotoxic effect on L929 and U937 cells in vitro. Therefore carbon-carbon composites, such as P25-CVD, may be important in the development of next-generation implants with lower wear rates and reduced cytotoxic potential.

Animals↗
PubMed2002

An in vitro study of the reduction in wear of metal-on-metal hip prostheses using surface-engineered femoral heads.

Although the wear of existing metal-on-metal (MOM) hip prostheses (1 mm3/10(6) cycles) is much lower than the more widely used polyethylene-on-metal bearings, there are concerns about the toxicity of metal wear particles and elevated metal ion levels, both locally and systemically, in the human body. The aim of this study was to investigate the possibility of reducing the volume of wear, the concentration of metal debris and the level of metal ion release through using surface-engineered femoral heads. Three thick (8-12 microm) coatings (TiN, CrN and CrCN) and one thin (2 microm) coating (diamond-like carbon, DLC), were evaluated on the femoral heads when articulating against high carbon content cobalt-chromium alloy acetabular inserts (HC CoCrMo) and compared with a clinically used MOM cobalt-chromium alloy bearing couple using a physiological anatomical hip joint simulator (Leeds Mark II). This study showed that CrN, CrCN and DLC coatings produced substantially lower wear volumes for both the coated femoral heads and the HC CoCrMo inserts. The TiN coating itself had little wear, but it caused relatively high wear of the HC CoCrMo inserts compared with the other coatings. The majority of the wear debris for all half-coated couples comprised small, 30 nm or less, CoCrMo metal particles. The Co, Cr and Mo ion concentrations released from the bearing couples of CrN-, CrCN- and DLC-coated heads articulating against HC CoCrMo inserts were at least 7 times lower than those released from the clinical MOM prostheses. These surface-engineered femoral heads articulating on HC CoCrMo acetabular inserts produced significantly lower wear volumes and rates, and hence lower volumetric concentrations of wear particles, compared with the clinical MOM prosthesis. The substantially lower ion concentration released by these surface-engineered components provides important evidence to support the clinical application of this technology.

Carbon↗
PubMed2000

Syndrome X, depression, and chaos: relevance to medical practice.

The low detection rate and undertreatment of depression in general medical practice is pervasive. The persistence of this problem suggests that doubt remains within elements of the medical profession that depression is a medical condition meriting medical treatment, as opposed to an existential state, inevitable for the human condition. Depression is a physical and psychological clinical disorder which affects every aspect of human physiology. As such it deserves consideration as a comorbid medical illness requiring treatment as does hypertension in relation to diabetes. This article will illustrate how clinical depression is a comorbid medical illness requiring detection and treatment through the analysis of depression's impact on two conditions called Syndrome X. Conditions labeled Syndrome X in endocrinology and cardiology demonstrate how depression amplifies the pathophysiology of endocrine and cardiac disease and diminishes functional variability (regularizes variance) found in normal physiology.

Comorbidity↗
PubMed1990

Anomalous morphologic formation of deciduous and permanent teeth in a 5-year-old 15th century child: a variant of the Ekman-Westborg-Julin syndrome.

A gross morphologic anomaly affecting both the primary and secondary teeth of unknown cause is presented. A 5-year-old American Indian child exhibited macrodontia, extreme shovel-shaping, agenesis, three-rooted deciduous molars, dens invaginatus, and other less striking dental features. This case represents the earliest example of a variant of the Ekman-Westborg-Julin syndrome reported in the New World.

Anodontia↗
PubMed1989

Twenty neuroleptic rechallenges after neuroleptic malignant syndrome in 15 patients.

Neuroleptic medication was reintroduced to 15 patients who had suffered an episode of neuroleptic malignant syndrome (NMS). Thirteen (87%) were eventually able to take neuroleptics again, indicating that they did not have an inherent intolerance. The authors analyzed the ability of patients to tolerate rechallenge according to the time of reintroduction after resolution of a previous episode and the relative neuroleptic potency and dosage compared with the initial episode. Successful rechallenge was highly significantly related to the time that had elapsed following resolution of the previous episode. The choice of a neuroleptic lower in potency and dosage than that which precipitated the original NMS episode was not significantly related to successful outcome.

Adult↗
PubMed1987

Depression: a possible complication of orthognathic surgery.

Advances in the field of orthognathic surgery as well as increased experience on the part of surgeons have led to successful treatment of greater numbers of patients with maxillofacial deformities. Consequently, greater insight has been gained into not only the technical effects of surgery, but also into the psychological impact on the patients. This paper describes a small pilot study designed to evaluate possible psychiatric effects that may occur during the recuperative period of orthognathic surgery.

Adult↗
PubMed1985

Use of projective testing on a consultation-liaison service.

Projective psychological testing is a valuable but underrated tool in consultation-liaison psychiatry. By reviewing psychiatric consultations with supporting psychological testing done over a 12-month period at the Beth Israel Hospital, the authors pinpointed clinical problems where projective testing was particularly helpful. The authors found suicidality, depression, and regression to be diagnostic dilemmas in which use of the Rorschach and TAT was decisive in the crisis setting of some consultations. The psychodynamic information offered by these tests guided both proper medication selection and verbal interventions as well as facilitated medical education. 4 cases were selected to illustrate the relevance of projective testing to consultation-liaison work.

Adult↗
PubMed1985

Penile prostheses: potential value of medical psychiatric assessment and psychotherapy.

Impotence is often the expression of complex psychological and physiological dysfunction. Proper medical psychiatric assessment is essential to assure that treatment addresses the real problems. Advances in materials technology and surgical methods have made penile implants an increasingly popular solution for impotence. There are, however, other treatments which may provide relief. These include correction of endocrine dysfunction, change in medications, and psychotherapy. This article reviews the content of a proper medical work-up, prosthesis options, psychiatric assessment, and psychotherapeutic considerations in addressing this problem.

Erectile Dysfunction↗
PubMed1984

Pathologic changes in aging sacroiliac joints. A study of dissecting-room skeletons.

Pathologic changes of the sacroiliac joints were observed in 1986 skeletons from dissecting rooms in St. Louis, Missouri and Johannesburg, South Africa. In addition to being the largest population samples ever studied from this standpoint, these samples are the first to include blacks. Para-articular osteophytosis culminating in ankylosis is considered first, followed by the less common intraarticular changes that also occasionally culminate in ankylosis. Expressed as "average involvement" by decade, sex, laterality, and ethnic group, these joint changes are shown clearly to worsen progressively from the age of about 40 years. Osteophytosis especially becomes more common in black males, both American and African Bantu, than in American white males, and generally more common in males than in females. When occurring only (or mainly) unilaterally, the changes average out in favor of the right side, but only slightly. Joint mobility, or lack thereof, is assigned a large etiologic role.

Adult↗