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Biomedical subjects

J Lemaitre

Publications and source records attributed to J Lemaitre.

At least 19 recordsLinked to original sources
PubMed2003

Hydroxyapatite cement scaffolds with controlled macroporosity: fabrication protocol and mechanical properties.

Precipitated hydroxyapatite cement scaffolds with macroporosity of controlled size and shape were successfully built using a solid freeform fabrication process. The negative macroporosity was designed using CAD software and built with an inkjet machine. A slip casting process using a plaster mold was used to precipitate the cement and manufacture samples for mechanical testing. The negative macroporosity was then extracted from the samples using a thermal process. Compression, tension and torsion tests were completed successfully on the precipitated hydroxyapatite cement samples in moist condition. Elastic and strength properties were measured for these three loading cases and compared to the plain hydroxyapatite cement properties reported in a previous study. Homogenization theory was applied to estimate the elastic properties of the manufactured scaffolds. A good correlation was obtained between the experimental data and the theory.

Bone Cements↗
PubMed2002

Bone colonization of beta-TCP granules incorporated in brushite cements.

Injectable calcium phosphate hydraulic cements are known to have a high clinical potential in bone reconstruction for mini-invasive orthopaedic surgery, interventional radiology, and rheumatology. Previous in vivo experiments in rabbit have shown that the presence of beta-TCP granules in injectable bone cement help maintain the transient biomechanical function of the implanted bone and promote the formation of good-quality new bone. Histomorphometric analysis of two brushite hydraulic cement (BHC) mixtures selected from previous results (referred to in this work as BHC-A and BHC-B) was performed at three postoperative delays (0, 12, and 24 weeks): histomorphometric analysis of bone colonization within beta-TCP shows that, just before implantation, the beta-TCP granule area is significantly higher in BHC-B; the residual granule area decreases steadily over time in BHC-A, whereas it goes through a maximum of 30% at 12 weeks in BHC-B; the residual granule porosity increases steadily up to 35% in BHC-A, whereas it goes through a maximum of 35% at 12 weeks and decreases somewhat until 24 weeks in BHC-B. New bone formation within granules appears higher in BHC-A (58% Area) compared to BHC-B (38% area) at 12 weeks. At 24 weeks bone colonization levels off in both cements at about 50% area. Irrespective of the cement matrix composition, beta-TCP granules contribute actively to the conduction of new bone formation.

Animals↗
PubMed2000

Effect of several additives and their admixtures on the physico-chemical properties of a calcium phosphate cement.

Combinations of citrate (C6H5O(7)3-), pyrophosphate (P2O(7)4-) and sulfate (SO(4)2-) ions were used to modify the physico-chemical properties of a calcium phosphate cement (CPC) composed of beta-tricalcium phosphate (beta-TCP) and phosphoric acid (PA) solution. The results obtained with only one additive at a time are similar to those previously published. New facts are: the positive effect of C6H5O(7)3- ions on cement failure strain and their negative effect on cement pH. The position of the setting time maximum measured at an SO(4)2- concentration of 0.09 M was not displaced by the addition of C6H5O(7)3- and P2O(7)4- ions. However, the effect of SO(4)2- ions on the setting time was depressed by C6H5O(7)3- ions. Moreover, no increase in tensile strength was observed when increasing amounts of SO(4)2- were added into a C6H5O(7)3--containing cement. The latter results suggest a competitive effect of C6H5O(7)3- and SO(4)2- on setting time and tensile strength. Anhydrous dicalcium phosphate (DCP; CaHPO4) appeared in cement samples dried just after setting, but not in cement samples incubated for 24 h in deionized water before the drying step. It is believed that the setting reaction is stopped by the drying step, leaving a low internal pH in the sample, hence providing favorable conditions for the transformation of dicalcium phosphate dihydrate (DCPD) into DCP. Interestingly, even though C6H5O(7)3- ions dramatically lowered the equilibrium pH of the cement with 5 ml of deionized water, they still prevented the occurrence of the transformation of DCPD into DCP.

Journal Article↗
PubMed1999

[Post-traumatic carotid-cavernous sinus fistula].

The authors report the case of a 51 year-old man who developed a carotid-cavernous sinus fistula after a blunt trauma. In view of an exophthalmia, an impressive chemosis, a pupillary dilatation due to parasympathetic paralysis and a bruit over the right orbit, a carotid-cavernous sinus fistula was diagnosed. The existence of the fistula was confirmed by a brain CT scan and a cerebral angiogram. Carotid-cavernous sinus fistulas are rare. They are spontaneous or posttraumatic. Cerebral angiography is the diagnostic procedure of choice. The authors review the signs and symptoms, diagnostic procedures, treatment, and prognosis of this complication.

Arteriovenous Fistula↗
PubMed1998

Adsorption of Catalase on Hydroxyapatite.

The adsorption of catalase on calcium hydroxyapatite is reported in this study. In all the solutions investigated, catalase adsorption takes place under conditions where the adsorbent and the adorbate are both negatively charged and is accompanied by the release of phosphate ions. This suggests that electrostatic attraction does not play a leading role in the adsorption process. However, electrostatic repulsion does play a role as evidenced by the influence of the solution composition on the maximum amount adsorbed. In fact, the amount adsorbed increases when the surface charge tends to be less negative (decrease of pH and phosphate concentration, presence of calcium) or when the electrical charges are screened as a result of the ionic strength increase. This was confirmed by the electrophoretic mobility which becomes more negative after protein adsorption. The rate of catalase adsorption is extremely low; the time required to reach a stationary concentration is 60 and 125 h in potassium nitrate and phosphate solution, respectively. The reversibility of catalase was examined with respect to changes in the bulk solution concentration. No significant desorption was obtained after several days of observation. The adsorption, desorption, and kinetic aspects have been discussed in relation to changes in the the protein structure upon interaction and to the microstructural characteristics of the mineral. Copyright 1998 Academic Press.

Journal Article↗
PubMed1998

[Development of a model which makes it possible to test injectable bone substitutes and evaluation of a calcium phosphate cement].

New percutaneous filling techniques are beginning to be used in bone tumor pathology. The purpose of this study was to develop a reproducible model for testing new injectable bone substitutes. A closed cancellous bone defect was created in the distal femoral condyles of rabbit. Bone defect was filled by a percutaneous injection. Several situations were tested: spontaneous evolution of unfilled cavities, evolution of cavities filled either with a conventional orthopedic cement (PMMA), either with a mixed collagen-hydroxyapatite material, either with a biomaterial derived from the vegetal protein zein, either with a calcium phosphate cement brushite type. The new bone formation was quantified in the defect for each group in which several delays were tested. A bone defect of reproducible size was obtained consistently. A partial bone formation was observed in the unfilled group. The best bone formation rate was obtained in the phosphate cement group. This model showed the interest of injectable biomaterials and more precisely the interest of the phosphate calcium cements as brushite.

Animals↗
PubMed1998

Löeffler endomyocarditis: a clinical presentation as right ventricular tumor.

A four-year-old girl presented with an apical mass of the right ventricle, pulmonary embolism and hypereosinophilia, and was shown to be infected with Toxocara canis. Cardiac involvement was represented by endomyocardial fibrosis, mainly at the apex of the right ventricle, mural thrombi and tricuspid regurgitation. Hypereosinophilia appears to be the head point at the basis of multiple organ damage in Löeffler endomyocarditis. The disease mechanism proposed is the eosinophilic production of peroxidases, which are cytotoxic when released in large amounts into the blood flow. Treatment is based on etiologic and corticosteroid therapy (prednisolone 1-2 mg/kg/day); surgical therapy is indicated in the end stages of the pathologic process.

Animals↗
PubMed1998

Leiomyosarcoma of the mesocolon.

Retroperitoneal sarcomas are rare tumours. Although exceptional in the mesocolon, they can yet be considered as a special kind of retroperitoneal tumours. Leiomyosarcoma represents from 25 to 30% in this location. Clinical features are rarely obvious because the symptomatology depends upon displaced or compressed adjacent organs. Most authors agree on using the CT-scanner or MRI as diagnostic tools. However, the diagnosis is made after a histologic examination permitting the establishment of its grade and margins. Only a surgical treatment can offer prolonged survival and this can be improved if there is a low histological grade and total excision. The mesocolic location facilitates a radical removal and may therefore offer a better long-term prognosis.

Female↗
PubMed1997

Composition effects on the pH of a hydraulic calcium phosphate cement.

The pH of a hydraulic calcium phosphate cement (HCPC) made of monocalcium phosphate monohydrate (Ca(H2PO4)2.H2O; MCPM), beta-tricalcium phosphate (beta-(Ca3(PO4)2; beta-TCP) and water was measured as a function of reaction time and composition at room temperature. During setting, the cement pH varies from very acidic pH values, i.e., 2.5, to almost neutral pH values, i.e., 6. The cement pH profile significantly depends on the initial cement composition. However, all profiles are characterized by a sharp initial decrease of the pH due to the dissolution of MCPM crystals and the precipitation of dicalcium phosphate dihydrate (CaHPO4. 2H2O; DCPD) crystals. With an excess of MCPM, the final pH stays low, and its value can be predicted from the initial composition of the cement and solubility data. With an excess of beta-TCP, the end pH is close to 5, which is much lower than 5.9, the value predicted by calculation. Results suggest that the difference may be due to the presence of impurities in the cement. Replacing MCPM by phosphoric acid renders the cement paste very acidic for the initial 30 s, but then the pH profile follows that obtained with MCPM. Adding pyrophosphate ions into the cement paste postpones the position of the pH minimum. The delay, which is proportional to the concentration of pyrophosphate ions, is thought to be due to the inhibiting action of pyrophosphate ions on the precipitation of DCPD crystals.

Journal Article↗
PubMed1996

[Transsexualism and legal proceedings].

One may not ignore the legal problem to which the transsexuals are exposed, once they have to search medical care. In Belgium, there does not exist any laws, which deal with the change of sex, although such laws would be very important for transsexual patients. On the other hand, change of the first name has been regulated by law. The actual knowledge of this problem is reviewed in this paper.

Female↗
PubMed1992

Setting, hardening and resorption of calcium phosphate hydraulic cements.

Two examples of calcium phosphate hydraulic cements (CPHC) are presented. Type I cements consist in mixtures of beta-tricalcium phosphate (beta-TCP) and monocalcium phosphate monohydrate (MCPM), to which some plaster of Paris (CSH) is added as a setting retardant. Type II cements consist in mixtures of beta-TCP, dicalcium phosphate dihydrate (DCPD) and calcium carbonate (CC), to which some hydroxyapatite (HAP) is added as a setting accelerator. The setting time of these cements ranges from a few minutes up to a few hours, according to their composition and the amount of mixing water. Tensile strengths ranging from 1.2 up to 3.5 MPa have been recorded on cements which porosity ranged from 38 up to 55 vol%. In-vivo experiments on dogs have shown the perfect biocompatibility and resorbability of cement I.

Animals↗
PubMed1989

Calcium phosphate cements: study of the beta-tricalcium phosphate--monocalcium phosphate system.

The possibility of making cements based on beta-tricalcium phosphate (beta-TCP), a promising bone graft material, was investigated. Upon admixture with water, beta-TCP/monocalcium phosphate monohydrate (MCPM) mixtures were found to set and harden like conventional hydraulic cements. Beta-TCP powders with larger particle size, obtained by sintering at higher temperatures, increased the ultimate strength of the cement. Results show that setting occurs after dissolution of MCPM, as a result of the precipitation of dicalcium phosphate dihydrate (DCPD) in the paste. The ultimate tensile strength of the hardened cement is proportional to the amount of DCPD formed. Upon ageing above 40 degrees C, DCPD transforms progressively into anhydrous dicalcium phosphate (DCP), thereby decreasing the strength. Ageing of the pastes in 100% r.h. results in a decay of the mechanical properties. This can be ascribed to an intergranular dissolution of the beta-TCP aggregates as a result of the pH lowering brought about by the MCPM to DCPD conversion.

Biocompatible Materials↗
PubMed1989

Evidence for the production of an interleukin-like protein by Asterias rubens (axial organ cells) in mixed leukocyte cultures.

Cells from the axial organ of the sea star may be separated into two subpopulations, depending on adherence to nylon wool. The non-adherent cells are morphologically and physiologically similar to Th. lymphocytes and produce an MLR-like reaction in a xenogeneic system involving two different species of sea stars. On the second day of such a MLC, these cells released molecules which were probably glycoproteins and which produced a mitogenic effect on all the axial organ cells. No effect occurred when the supernatant was tested on adherent or non-adherent cells separately, suggesting that a cellular cooperation is necessary in order to produce the response. These soluble mediators produced by T-like cells with a mitogenic effect on lymphocyte-like cells resemble the interleukin proteins produced by vertebrate leukocytes.

Animals↗