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Biomedical subjects

A Bettencourt

Publications and source records attributed to A Bettencourt.

12 recordsLinked to original sources
PubMed2004

Surface studies on acrylic bone cement.

Poly(methyl methacrylate) (PMMA) is used to fill the gap between the prosthesis and the surrounding bone in cemented arthroplasties. Biocompatibility problems related to bone cement application limit the clinical success of these cemented arthroplasties. Being the cement surface in close connection with the living bone, it is reasonable to assume that surface properties such as, surface composition and surface energy, will play a role in the biomaterial performance. X-ray photoelectron spectroscopy (XPS) analysis and surface energy studies were carried out during 4 months, in order to assess a possible correlation between aging time and surface changes. The aging of PMMA, in a biological model fluid, strongly influences the composition and wettability of the cement surface. These changes may be explained through the hydrolysis of PMMA ester groups and the subsequent hydrogen bonding. Although our study does not exactly reproduce the in vivo environment surrounding a prosthesis, it suggests that the changes in the composition and wettability of the surface may modulate the host response towards the implant, thus contributing to its loosening.

Bone Cements↗
PubMed2002

The effect of ethanol on acrylic bone cement.

Prosthesis loosening is a major problem associated with the use of poly(methyl methacrylate) (PMMA) bone cement that may be related to a peri-implant vacuolisation commonly observed at bone-cement interface. Methyl methacrylate (MMA) monomer may be one of the cement components partly responsible for the mentioned vacuolisation due to a cytotoxic effect associated to this compound. Alcoholism has been related to bone necrosis in predisposed individuals. Furthermore, ethanol has been shown to clean material with adherent cement debris during cleaning procedure in laboratory. Consequently, we have decided to study whether ethanol will also be related to an increased liberation of MMA from the polymer matrix. 'In vitro' release studies using PMMA plates were conducted to access the role of ethanol on the liberation of the monomer. Contact angle measurements and surface tension estimation were also carried out in order to find a possible effect of ethanol on surface cement properties. Results suggest that ethanol, even in small quantities, enhances the leaching of the monomer from the polymer matrix, but does not considerably change the wettability properties of the cement surface.

Acrylic Resins↗
PubMed2001

The influence of vacuum mixing on methylmethacrylate liberation from acrylic cement powder.

Polymethylmethacrylate (PMMA) bone cement is a biomaterial used to anchor prostheses during joint replacement surgery. Residual methylmethacrylate monomer (MMA) may be related with the cytotoxic effect of PMMA. The aim of the present paper was to investigate the effect of two different cement mixing methods: hand stirring at atmospheric pressure and under partial vacuum (0.330 and 0.154 bar) on residual monomer liberation in phosphate buffer saline solution from acrylic cement powder. Residual MMA content was determined by high-performance liquid chromatography. Mathematical models were applied to experimental dissolution data revealing that monomer release was significantly reduced in bone cement powder obtained at 0.154 bar vacuum pressure compared to the other mixing conditions. The kinetic models applied are consistent with a simple diffusion mechanism of the monomer from the polymer matrix.

Acrylates↗
PubMed2000

In vitro release studies of methylmethacrylate liberation from acrylic cement powder.

Bone cement or polymethylmethacrylate (PMMA) is commonly used for anchoring cemented prosthesis to the bone. Cytotoxic effect of culture media exposed to PMMA powder may be related with long term problems associated with acrylic cement application, being the monomer (methylmethacrylate) one of the cement's component partly responsible for the cytotoxic effect. The present work reports the studies of monomer release from acrylic bone cement powder under different experimental conditions: setting time of PMMA (in solution and air) and different culture media composition. High-performance liquid chromatography was used for the determination of residual monomer. Mathematical models were applied to experimental dissolution data revealing that monomer release is lightly affected by the studied variables. The monomer release seems to be a surface phenomena, suggesting that the possible actions of monomer will mainly be due to the initial loss of non polymerized monomer rather than to further depolymerization of the already polymerized cement.

Bone Cements↗
PubMed1999

Surgical treatment of lung metastases: prognostic factors for long-term survival.

BACKGROUND AND OBJECTIVES: Surgical resection of lung metastases is an established therapy for a large number of primary tumors, but there is some controversy about prognostic factors for long-term survival. METHODS: From 1968 to 1996, we performed a retrospective review of a series of 85 patients (100 operations) that have been operated for resection of lung metastases. The Kaplan-Meier method was used to estimate the probabilities of survival, the log-rank test for the univariate analysis of prognostic factors for survival, and the Cox model in the subsequent multivariate analysis. RESULTS: The operative mortality was 4% and the morbidity 18%. The mean follow-up after lung resection was 22.13 months (1-146). The actuarial 5-year survival rate was 29.2%. By univariate analysis, the following factors were associated with survival after resection: location and histology of the primary tumor, greatest dimension of the largest metastasis, radicality of the resection, involvement of the resection margins, and use of adjuvant therapy (P < 0.05). After multivariate analysis, only the dimension of the metastases and involvement of surgical margins have been found to be independently associated with survival. CONCLUSIONS: Surgical excision is a safe and effective therapy for lung metastases from a large number of primary tumors, provided a complete resection is feasible.

Adolescent↗
PubMed1995

[The curative surgery of periampullary tumors. The results of 48 resections].

Periampullary tumors form a clinical entity with common symptoms, similar therapeutic options, unsatisfactory resectability rates and unfavorable prognosis. From April 1970 until March 1994, one hundred and twenty-seven patients with periampullary carcinoma were operated by our surgical team. In 48 of these patients, a resection for cure was performed (38%). Resectability rates varied according to the origin of these tumors, i.e., pancreas-20%, ampulla-76%; distal bile duct-71%, periampullary duodenum-88%. Pancreatic tumors showed a different resectability rate from the other periampullary carcinomas (p = 0.04). Forty-two of these patients had a pancreatoduodenectomy and in the remaining 6 cases a total pancreatectomy was performed. Fifteen patients had major post-operative morbidity (31%) and 8 of these cases died in-hospital (17%). Follow-up data was available in 81% of the patients, survival estimates were calculated according to the Kaplan-Meier method and survival comparisons were made with the Log-rank test. Median survival for resected pancreatic carcinoma was 6 months and for resected tumors of the ampulla 37 months. In this group of patients, pancreatic tumors showed a different survival rate from the remaining periampullary tumors (Log-rank-p = 0.002). This work evidences the need to improve management of periampullary tumors, particularly in-hospital mortality and long-term survival. To achieve these goals, patients with periampullary tumors should be treated in specialized centers and research to improve local and systemic control of this disease should be pursued.

Aged↗
PubMed1993

[Palliative surgery in carcinoma of the stomach. Retrospective study of 112 consecutive cases].

From January 1980 until October 1991 we operated 112 patients with Gastric cancer in which Surgery was considered palliative by intra-operative criteria or by pathological analysis of the resected specimen. Locally irresectable tumour was found in 24.1% of the cases, peritoneal metastases (mets.) in 21.4%, liver mets. in 17%, lymphatic mets. in 16.1%, and other mets. in 21.4%. Resections were possible in 57 patients (50.8%), with a mortality rate of 10.5%, which was similar to the mortality in the non-resection group (7%) p = 0.2. Median survival for the entire group was 7 months, the non-resection group had a median survival of 4 months, and the resection group of 18 months (p = 6.480 e-0.7). Locally advanced tumors had a better outcome than the metastatic group (p = 0.05), but no difference was observed between patients with liver or peritoneal mets. Patients in stage 3 and 4 of the disease had a different prognosis (p = 0.03), and the resection group within each stage fared better.

Adult↗
PubMed1977

Gas chromatographic and mass fragmentographic assays of carcinogenic polycyclic hydrocarbon epoxide hydratase activity.

A specific and very sensitive procedure for the determination of epoxide hydratase activity in hepatic microsomes is described. Any polycyclic hydrocarbon epoxide can be used as a substrate; in this study, benzo(a)anthracene-5,6-oxide, benzo(a)pyrene-4,5-oxide and 3-methylcholanthrene-11,12-oxide were utilized. The corresponding trans-diols formed during incubation are separated and evaluated using either an electron-capture gas chromatographic method for the determination of their chloromethyldimethylsilylated derivatives or gas chromatographic-mass fragmentographic measurement of their trimethylsilylated derivatives. Concentrations as low as 1 ng per millilitre of incubation mixture can be estimated.

Animals↗
PubMedDate not supplied

Curative surgery for gastric cancer: study of 166 consecutive patients.

From January 1980 to December 1991 we operated on 295 patients with a gastric carcinoma. In 166 cases (56.3%) surgery was performed with curative intent. In 93 patients (56%) a subtotal gastrectomy was performed, and in 73 cases (44%) a total gastrectomy. In all the cases a D-2 type lymphadenectomy was used. The global morbidity rate was 23%, and in-hospital mortality was 3.6%. The morbidity and mortality rates of these two operations were statistically different. Global 5-year survival estimate for the whole series is 61.3%. Univariate and multivariate analysis according to T and N (TNM classification), the number of positive nodes resected, and the relation of positive per resected nodes, revealed statistically different outcomes. This kind of quantitative classification allowed identification of high risk groups irrespective of site of nodal involvement. Tumors classified as intestinal or diffuse type by the Lauren classification had similar survival curves and 5-year survival estimates (p = 0.834). By univariate and multivariate analysis this classification did not reveal a prognostic value in this group of patients. In our opinion, tumor penetration and lymph node involvement are at present the most reliable prognostic factors available.

Adult↗