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J C Knowles

Publications and source records attributed to J C Knowles.

At least 73 records · Page 4Linked to original sources
PubMed1996

Structural changes of thermally sprayed hydroxyapatite investigated by Rietveld analysis.

Hydroxyapatite (HA) coatings were prepared by three thermal spraying methods: flame spraying, high velocity oxygen fuel spraying and plasma spraying. The HA was then examined by Rietveld analysis using the General Structure Analysis Software package (GSAS) and the results compared with those for the precursor powder. A comparison between HA before and after spraying showed that all three spraying methods caused a distortion in the unit cell in the form of a unit cell a-axis length decrease and a c-axis increase. Overall unit cell volumes showed a difference between the three thermal methods, with flame spraying and high velocity oxygen fuel methods giving a unit cell volume increase and the air plasma spraying method showing a decrease, compared to the starting powders. The two different starting powders used each showed a high oxygen occupancy for the hydroxyl oxygen. When thermally sprayed, both powders gave a reduction in occupancy, which suggested carbonate substitution for the OH group, but this was subsequently removed when thermally processed. The spraying also formed oxyapatite, indicated both by spectral analysis showing a reduction in the hydroxyl peak and by the hydroxyl oxygen occupancy falling to a level below 0.5. Major differences between the three spraying methods could be seen in the distortion index calculations. The thermal spraying techniques gave an increase in the distortion index, but it was significantly higher for the plasma-sprayed coating.

Biocompatible Materials↗
PubMed1994

Microstructural characterization of glass-reinforced hydroxyapatite composites.

The influence of phosphate-based glasses and a bioactive silica glass on the sintering mechanism of hydroxyapatite was studied over a wide range of temperatures. The composites were microstructurally characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Small additions of phosphate-based glasses proved to be beneficial to the sintering process and fully dense materials were obtained. A significant improvement in mechanical properties was achieved. beta-TCP and alpha-TCP were found in the microstructure depending on the sintering temperature. Additions of bioactive glass led to the development of calcium phosphate silicate.

Biocompatible Materials↗
PubMed1993

Development of a glass reinforced hydroxyapatite with enhanced mechanical properties. The effect of glass composition on mechanical properties and its relationship to phase changes.

Utilizing glasses of the types xNa2O-(1-x)P2O5 and xCaO-(1-x)P2O5 (where x = 0.2, 0.3, and 0.5), a systematic study of the effect of increasing network modifying oxides in glasses was made on the mechanical properties of a glass reinforced hydroxyapatite, at glass additions of 2.5 and 5 wt%. For the soda type glass, phase changes were promoted much more readily compared to the lime type glass. This was true for both 2.5 and 5 wt% additions of glass. For the lime type glass, considerable differences between the effects of 2.5 and 5 wt% additions were seen. At 5 wt%, the increased amount of liquid phase present promotes an increased level of phase inversion to alpha and beta tricalcium phosphate. At 2.5 wt%, a larger percentage of the HA remains stable at higher temperatures. Furthermore, the effect of the composition may be seen. As the mol% of network forming oxide increases, (i.e., the Ca/P ratio moves towards 1.67, (the ratio for HA) the HA remains more stable. This is seen in the maintenance of both the HA phase and also the enhanced mechanical properties.

Biocompatible Materials↗
PubMed1992

Development of a degradable composite for orthopaedic use: in vivo biomechanical and histological evaluation of two bioactive degradable composites based on the polyhydroxybutyrate polymer.

As a direct method for the evaluation of tissue bonding to two polyhydroxybutyrate (PHB) based composites, a mechanical push-out test was performed on implants in the femur of mature Japanese White rabbits. Three composites were tested. The first, a hydroxyapatite/PHB (HA/PHB) composite showed an increase in interfacial shear strength (ISS) up to 8 wk, after which the ISS decreased due to degradation of the implant. The second composite was an HA/glass/PHB (HGP) composite and this gave lower values for the ISS attributed to ion release from the glass causing a soft tissue reaction at the interface. The third composite was a carbon fibre reinforced polysulfone (CFRP) and this showed high interfacial shear strength values, which continued to increase with time. These conclusions were supported by contact microradiography (CMR) and histology which showed enhanced endosteal bone growth for the HA/PHB but for the HGP, no periosteal or endosteal activity was detected. Interposed soft tissue for the HGP composite was difficult to discern, histologically, but it was proposed that this was the reason for the low ISS values. It was concluded that the high ISS values for the carbon fibre control were due to surface morphology allowing deep ingrowth of soft tissue and this was confirmed by SEM.

Animals↗
PubMed1991

In vitro degradation of a PHB/PHV copolymer and a new technique for monitoring early surface changes.

The use of polyhydroxbutyrate and its copolymers as degradable materials for surgical use is showing increasing promise due to their long degradation profile. Of considerable interest were the interfacial changes and their role in affecting the overall or bulk degradation pattern. The role of pH and its effect on the degradation pattern were examined as polymer degradation significantly altered, depending on whether it was subjected to an alkaline or an acidic medium. In vitro surface changes were monitored using two techniques (scanning electron microscopy and goniophotometry); bulk changes were monitored by gravimetric, mechanical and molecular weight techniques. It was concluded that the bimodal molecular weight distribution plays a significant part in the degradation pattern and that this pattern is also considerably altered by pH.

Biocompatible Materials↗
PubMed1988

An evaluation of serum CA 50 levels in cancer using a time-resolved fluoroimmunoassay.

The CA 50 levels in serum samples from 440 patients were estimated using a dissociated enhanced lanthanide immunofluorimetric assay. The distribution was similar to CA 50-RIA assays. Raised levels (greater than 14 U/ml) were present in 95% pancreatic cancer, 68% hepatoma, 54% advanced colorectal cancer, 58% advanced breast cancer and 48% lung cancer. High values were observed in adenocarcinoma of the lung, and were related to tumour mass in small cell lung cancer. CA 50 is independent of CEA. The marker is of considerable potential in pancreatic cancer where the majority of patients express the Can 50 Ag.

Antigens, Tumor-Associated, Carbohydrate↗
PubMed1986

Pulp innervation after radiation therapy.

Decreased sensitivity was observed in teeth within and adjacent to an irradiated field. Mandibular teeth outside the field and distal to the irradiated mandibular nerve trunk showed an immediate decrease in sensitivity, Maxillary teeth outside the field showed a delayed decrease in sensitivity. Blood flow rates and nutrition were also related to time. Neurons are though to be relatively radio-resistant and few changes were seen histologically after radiation therapy. However, functional impairment was observed in histologically normal tissue.

Dental Pulp↗
PubMed1986

Alpha 1-protease inhibitor in serous effusions: differences in lectin crossed immuno-affinoelectrophoresis precipitin profiles between benign and malignant disease.

Differences in the lectin crossed immuno-affinoelectrophoresis (LCIE) precipitin profile of the antiprotease alpha 1-protease inhibitor (alpha 1-PI) have been detected between serous effusions of benign and malignant origin. Extra proteins with antigenicity towards anti-human alpha 1-PI appear in both malignant pleural effusions and malignant ascitic fluid caused by ovarian cancer that are not detected in effusions of benign origin. These compounds may be protease-antiprotease complexes caused by tumour excretion of proteases into the serous effusions.

Ascitic Fluid↗
PubMed1984

A functional speech impression used to fabricate a maxillary speech prosthesis for a partial glossectomy patient.

Surgery for cancer of the floor of the mouth often results in alteration of the muscles of the tongue and floor of the mouth. Both primary and secondary surgical procedures often result in scar formation with reduced mobility of the tongue during speech and deglutition. Speech is often used as a diagnostic tool in the placement of the anterior teeth during fabrication of a prosthesis. Speech can similarly be used to help determine the proper placement of a speech portion of the prosthesis. The prosthetic rehabilitation approach described lowers the palatal vault with a false palate to enable the tongue to function against it during speech (Fig. 15). Group studies have shown that the design and fabrication of speech prostheses for partial glossectomy patients have significantly improved speech and swallowing for these patients. A speech pathologist is helpful during diagnosis, and speech therapy is necessary for significant speech improvement. Prosthetic rehabilitation alone cannot be expected to improve speech.

Adenocarcinoma↗
PubMed1982

Electron microscopy of superficial bladder tumours and urothelium after intravesical doxorubicin.

The effects of intravesical doxorubicin on cells in superficial transitional cell carcinomas and adjacent urothelium were studied by electron microscopy. Nucleolar segregation, vacuolation of the cytoplasms, mitochondrial abnormalities and the breakdown of secondary lysosomes leading to autolysis were the main patterns of damage. Cell loss was by desquamation from the surface and random cell death in the deeper cell layers of the tumour and urothelium.

Carcinoma, Transitional Cell↗
PubMed1981

Kaufman syndrome (hydrometrocolpos, polydactyly, and congenital heart disease) with pituitary dysplasia, choanal atresia, and vertebral anomalies.

An infant was found to have the previously known manifestations of the Kaufman syndrome (hydrometrocolpos, postaxial polydactyly, and congenital heart disease) but also imperforate anus, malrotation of gut, congenital hip dislocation, and urogenital sinus. All of these anomalies have been separately reported in other cases of the syndrome. Three previously unreported problems present in this case were choanal atresia, pituitary dysplasia, and vertebral anomalies; these may well be component manifestations of the syndrome and not sporadic occurrences in our patient. Of particular clinical importance were the hypoglucocorticism and the hypoglucocorticism secondary to the pituitary dysplasia.

Abnormalities, Multiple↗
PubMed1973

Evaluation of dimethylhydrazine induced tumours in mice as a model system for colorectal cancer.

The evolution and structure of adenomatous polyps and adenocarcinomata of the colon in NMRI mice induced by dimethylhydrazine are described. Severe toxic reactions in the liver and other organs are produced by dimethylhydrazine (DMH), but tumours are induced only in the colon and around the anus. The 100% incidence and growth characteristics of the tumours make it potentially a good model system, but investigators should take into account the widespread nonspecific cellular injury induced by this carcinogen.

Adenocarcinoma↗