Biomedical subjects

M Amaral

Publications and source records attributed to M Amaral.

6 recordsLinked to original sources

PubMed2002

Densification route and mechanical properties of Si3N4-bioglass biocomposites.

The processing route and the final microstructural and mechanical characteristics of a novel biomaterial composite are described. This new material is composed of 70 wt% Si3N4 ceramic phase and 30 wt% bioglass, the later performing as a liquid sintering aid system and simultaneously providing bioactivity characteristics to the composite. The conditions for fabrication of an almost fully dense material (approximately 98% of relative density) were pursued. Optimised parameters were 1350 degrees C-40 min-30 MPa by hot-pressing technique. The very fast densification rate of the process avoided the crystallisation of the bioglass intergranular phase and therefore its intrinsic properties were maintained. Also, the large amount of glassy phase assured the densification by liquid phase assisted grain rearrangement without Si3N4 phase transformation. The final mechanical properties of the Si3N4 bioglass were as follows: fracture toughness, K(IC) = 4.4 MPa m(1/2); Vickers hardness, Hv = 10.3 GPa; Young's modulus, E = 197 GPa; bending strength, sigma(g) = 383 MPa; Weibull modulus, m = 8.3. These values provide an attractive set of properties among other bioactive materials, namely by upgrading the main drawback of bioceramcs and bioglasses for high-load medical applications, which is the lack of satisfactory fracture toughness.

Biocompatible Materials↗

PubMed2002

Wettability and surface charge of Si3N4-bioglass composites in contact with simulated physiological liquids.

Wettability and surface charge studies were performed on a novel Si3N4-30wt% bioglass biocomposite. Contact angle and surface tension variation with time were determined at 25 degrees C, respectively, by the sessile and pendant drop techniques, for distinct testing liquids: water, diiodomethane, simulated body fluid (SBF) and bovine serum albumin (BSA) dissolved in SBF solution. This biocomposite revealed a hydrophilic character (theta = 26.6 +/- 2.0 degrees) and a surface tension value (66.6 mJ m(-2)) comparatively higher than those of the most common bioceramics. An important characteristic is the high work of adhesion towards SBF + BSA (96.4 +/- 0.2mJ m(-2)) that was measured. The Si3N4-bioglass material is negatively surface charged above the pH(IEP) = 2.5 in aqueous SBF + BSA solution, as a result of the presence at the surface of unsaturated Si-O bonds and Si-OH groups. The very high negative zeta potential at pH approximately 7 (-58.6 +/- 5.5mV) influenced albumin adsorption and mechanisms are discussed in terms of entropy and enthalpy gains from conformational unfolding and cations coadsorption.

Glass↗

PubMed2002

Si(3)N(4)-bioglass composites stimulate the proliferation of MG63 osteoblast-like cells and support the osteogenic differentiation of human bone marrow cells.

The in vitro osteocompatibility of a novel Si(3)N(4)-bioglass composite (70-30% weight proportion) with improved mechanical properties (fracture toughness = 4.4 M Pa m(1/2); bending strength = 383 +/- 47 MPa) is reported. Immersion of the composite samples in culture medium (30 min to 7 days) resulted in rapid protein adsorption to the surface and, also, dissolution of the intergranular phase of bioglass (time-dependent process) with the formation of different size cavities. "As-received" and pre-treated material samples presented a similar behaviour concerning the proliferation of MG63 osteoblast-like cells, evaluated during a 5-day culture period. Seeded materials showed a higher cell growth rate as compared to cultures performed on the standard plastic culture plates. To assess the osteogenic potential of the composite, "as-received" material samples were seeded with human bone marrow cells and cultured for 35 days in experimental conditions that favour the development of the osteoblastic phenotype. The cell adhesion process was similar to that observed in control cultures. Cells successfully adapted to the irregularities of the surface and were able to grow towards inside the cavities; in addition, osteogenic differentiation occurred with the formation of abundant cell-mediated mineralised deposits. Results suggest that this Si(3)N(4)-bioglass composite seems to be a promising candidate for high-stress medical applications.

Adsorption↗

PubMed1996

Complex cystic fibrosis allele R334W-R1158X results in reduced levels of correctly processed mRNA in a pancreatic sufficient patient.

CFTR alleles containing two mutations have been very rarely found in cystic fibrosis (CF) patients. They provide an opportunity to study the effect of two in cis-interacting gene defects on gene expression. Here, we describe a three-generation CF family with a complex CFTR allele that has not been previously described, containing the missense mutation R334W in exon 7 and the nonsense mutation R1158X in exon 19. Lymphocyte RNA analysis showed that (1) the mRNA corresponding to the complex allele is present although at markedly reduced levels; and (2) the nonsense mutation does not lead to detectable skipping of exon 19. The clinical picture of the patients with the genotype R334W-R1158X/delta F508 is characterized by pancreatic sufficiency and an atypical course of the disease.

Alleles↗

PubMed1995

Implementation and evaluation of computerized patient management problems.

We developed and implemented computerized patient management problems (CPMP) for medical school education as a simulation of case management and evaluated its efficacy in the School of Medicine at Chiba University. PMP was first developed in the USA; it was used for examinations by the board of American College of Physicians and then introduced to Japan for examination purposes. This test is a practical clinical test for decision making in various medical situations. PMP is, however, a kind of case simulation from a doctor's point of view; it is also a sophisticated tool in training medical students. PMP had many disadvantages in the past, but by computerizing PMP, we solved many problems. We developed the CPMP system for bedside teaching and evaluated its efficiency in terms of education by giving the same test twice and analyzing a survey.

Audiovisual Aids↗

PubMedDate not supplied

Diagnostic value of serum antibody and antigen detection in heroin addicts with systemic candidiasis.

The diagnostic value of antibody detection by indirect hemagglutination (IHA), indirect immunofluorescence (IFA), and counterimmunoelectrophoresis (CIE) and of Candida albicans mannan antigen detection by latex agglutination was studied in 36 cases of systemic candidiasis in heroin addicts. The IHA and IFA techniques were highly sensitive (97% and 91%, respectively), but their specificity was low (60% and 50%). When a titer of greater than or equal to 1:2,560 was used as a criterion for IHA positivity, the specificity of the test rose to 87%, with sensitivity at 75%. CIE had a high degree of specificity (96%) but a low degree of sensitivity (58%). A good correlation was found between clinical evolution of infection and serologic data. Two of 12 patients who could be followed for 9-16 months had a rise in antibody titer detected either by IFA or by IHA and CIE. These two patients had a persistent chondrocostal tumor and C. albicans endocarditis, respectively. All of the other patients, who were cured, had a decrease in titer detected by IHA and IFA and had negative CIE results at the end of follow-up. Serum mannan antigen was not found in any case. The detection of antibody to C. albicans may be useful for diagnosis and follow-up of such patients.

Adult↗