Preparation of ceramic membranes from surface modified tin oxide nanoparticles

The preparation of crack-free SnO2 supported membranes requires the development of new strategies of synthesis capable to allow controlled changes of surface chemistry and to improve the processability of supported layers. In this way, the controlled modification of the SnO2 nanoparticle surface by adding capping molecules like Tiron(R) ((OH)(2)C6H2(SO3Na)(2)) during the sol-gel process was studied, aiming to obtain high performance membranes. Colloidal suspensions were prepared by hydrolyzing SnCl4.5H(2)O aqueous solution with NH4OH in presence of Tiron(R). The effect of the amount of Tiro(R) (from I to 20 wt.%) on the structural features of nanoparticles, powder redispersability and particle-solution interface properties was investigated by X-ray powder diffraction (XRPD), extended X-ray absorption fine structure (EXAFS), quasi-elastic light scattering and electrophoretic mobility measurements. XRPD and EXAFS results showed that the addition of Tiron(R) up to 20 wt.% to colloidal suspensions does not affect the crystallite size of SnO2 primary particles, determined around 2-3 nm. This value is comparable to the hydrodynamic size measured after redispersion of powder prepared with amount of Tiro(R) higher than 7.5 wt.%, indicating the absence of condensation reactions between primary particles after the initial precipitation step. As a consequence the powder with amount of Tiron(R) > 7.5 wt.%, can be fully redispersed in aqueous solution at pH greater than or equal to I I until a nanoparticle concentration of 6 vol.%. The electrophoresis measurements showed a decrease of the isoelectric point by increasing the amount of grafted Tiron(R) at the SnO2 nanoparticle surface, resulting in negatively charged particle-solution interface in all the studied pH range (2-11). These features govern the gelation process favoring the preparation of crack-free SnO2 supported membranes. The control exercised by Tiron(R) modifying agent in the aggregation process allows the fine-tuning of the porosity, from 0.124 to 0.065 cm(3) g(-1), and mean pore size, from 6.4 to 1.9 nm, as the amount of grafted molecules increases from 0 to 10 wt.%. In consequence, the membrane cut-off determined by filtration of polyethylene glycol standard solutions can be screened from 1500 to 3500 g mol(-1). (C) 2002 Elsevier B.V. B.V. All rights reserved.

Fertility-associated proteins in Nelore bull sperm membranes

The present study was undertaken to evaluate the protein composition of the sperm membranes (SM) of Nelore bulls, assessing protein markers associated with bull fertility, and whether these markers can be used for predicting bull fertility. Samples were obtained of 20 Nelore bulls, with fertility ranked and divided into three groups (greater, normal and least). To rank the bull's fertility weighted classification was used (according to the number of pregnant cows, number of AI cows and number of herds, considering three different breeding seasons), using the PROC GENMOD as a statistical model, with 99% significance. A total of 7897 Nelore cows, randomly distributed among 28 different farms, were considered in the statistical analyses. The bulls were divided into three fertility groups (pregnancy rates): greater (%F > 80), normal (79 <%F > 71) and least (< 68%F) with 3, 13 and 4 bulls, respectively. Two-dimensional gel electrophoresis (2DE) of sperm membranes indicated in 27 spots (SM40, SM53, SM69, SM93, SM102, SM111, SM137, SM138, SM189, SM196, SM201, SM202, SM204, SM225, SM236, SM237, SM239, SM241, SM246, SM247, SM275, SM283, SM342, SM346, SM355, SM372, SM391) was prevalent in the higher fertility group, and just one spot (SM244) was prevalent in the lower fertility group. Spots SM244 and SM239 had their identification defined by PMF/MALDI-MS, as BSP-A3 and aSFP, respectively. Both these proteins showed a great potential for predicting bull's fertility. The amount of aSFP was 8.5 times greater in the sperm membrane protein profile of the higher fertility groups of Nelore bulls. Besides that, the BSP-A3 was 2.5 times greater in the lower fertility group. For the other spots potentially associated with fertility not yet identified, additional tests will be necessary, but it is clear that the 2D electrophoresis of the sperm membrane can be used for a new approach to predict Nelore bull fertility. (c) 2005 Elsevier B.V. All rights reserved.

SPINDLE MEMBRANES DURING SPERMATOGENESIS IN DERMATOBIA-HOMINIS (DIPTERA, CUTEREBRIDAE)

During the mitotic and meiotic division in Dermatobia hominis spermatogenesis, the nuclear envelope is fragmented and membranes appear around the spindle. The membranes surrounding the mitotic spindle are formed by two layers of cisterns. The membranes of the meiotic spindle consist in at least 3 or 4 layers of long smooth cisterns which isolate the spindle from the remaining cytoplasm. The presence of this kind of membranes during meiosis seems to be usual in insect male germ cell.

Influence of membrane-solution interface on the selectivity of SnO2 ultrafiltration membranes

SnO2 supported membranes, presenting 3.0 nm average pore size, have been produced by sol casting on alumina tubular substrate using aqueous colloidal suspensions prepared by sol-gel route. The selectivity and flux throughout SnO2 membrane were analyzed by permeation experiments, using a laboratory tangential filtration pilot equipped with a monotubular membrane. To evaluate the effect of the surface charge at the membrane-solution interface, aqueous salt solutions (NaCl, Na2SO4, CaCl, and CaSO4) of different ionic strength have been filtered and the results correlated with the values of zeta potential measured at several pH. The results show that the retention coefficient is dependent on the electrolyte present in aqueous solution decreasing as: (dication, monoanion) > (monocation, monoanion) approximate to (monocation, dianion) > (dication, dianion). The surface charge and the cation adsorption capacity play a determinant role in these selectivity sequences. (C) 2001 Elsevier B.V. B.V. All rights reserved.

Study of the selectivity of SnO2 supported membranes prepared by a sol-gel route

In this work the sol-gel process was used to prepare SnO2 supported membranes with an average pore size of 2.5 nm. The effects of salt concentration (NaCl or CaCl2) and of the pH of the aqueous solutions used on the flux and selectivity through the SnO2 membrane were analyzed by permeation experiments and the results interpreted taking account of the zeta potential values determined from the electrophoretic mobility of the SnO2 powder aqueous dispersion. The results show that the ion flux (Na+, Ca2+ and Cl-) throughout the membrane is determined by the electrostatic repulsion among these species and the surface charge at the tin oxide-solution interface.

Collagen membranes at immediate implants: a histomorphometric study in dogs

AimTo evaluate the influence of resorbable membranes on hard tissue alterations and osseointegration at implants placed into extraction sockets in a dog model.Material and methodsIn the mandibular premolar region, implants were installed immediately into the extraction sockets of six Labrador dogs. Collagen-resorbable membranes were placed at the test sites, while the control sites were left uncovered. Implants were intended to heal in a submerged mode. After 4 months of healing, the animals were sacrificed, and ground sections were obtained for histomorphometric evaluation.ResultsAfter 4 months of healing, a control implant was not integrated (n=5). Both at the test and at the control sites, bone resorption occurred. While the most coronal bone-to-implant contact was similar between the test and the control sites, the alveolar bone crest outline was maintained to a higher degree at the buccal aspect of the test sites (loss: 1.7 mm) compared with the control sites (loss: 2.2 mm).ConclusionsThe use of collagen-resorbable membranes at implants immediately placed into extraction sockets contributed to a partial (23%) preservation of the buccal outline of the alveolar process.To cite this article:Caneva M, Botticelli D, Salata LA, Souza SLS, Carvalho Cardoso L, Lang NP. Collagen membranes at immediate implants: a histomorphometric study in dogs.Clin. Oral Impl. Res. 21, 2010; 891-897.doi: 10.1111/j.1600-0501.2010.01946.x.

Use of Biopolymeric Membranes for Adsorption of Paraquat Herbicide from Water

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Pore size distribution of unsupported SnO2 membranes prepared by sol-gel process - Code: EP21

Unsupported SnO2 membranes were prepared by sol-gel process and characterized by N2 adsorption-desorption isotherms and X-ray diffraction. Results show that the texture of dried samples does not change appreciably with the concentration of electrolyte. All of the pore size range used in ultrafiltration process was screened using sintering temperature between 300 and 700°C. © 1994 Kluwer Academic Publishers.

Influence of viscoelastic characteristics of the colloidal suspensions on the formation of SnO2 supported membranes

SnO2 supported membranes have been prepared by sol-casting on alumina tubular substrate, using aqueous colloidal suspensions prepared by sol-gel route. The viscoelastic behaviour during sol ageing was analyzed by dinamic rheologial measurements. The complex viscosity and the storage and loss moduli have been followed during the sol-gel transition and the results have been correlated with the linear aggregates growth and the scalar percolation models. The scanning electron microscopy has evidenced that the homogeneity and thickness of the membrane depend on the sol ageing time. Crack-free and homogeneous membranes have been obtained for coated layers of 0.5μm thickness. © 1997 Trans Tech Publications.

Early healing pattern of autogenous bone grafts with and without e-PTFE membranes: A histomorphometric study in rats

Objective. The aim of this study was to perform quantitative and qualitative analyses of the initial repair pattern of an autogenous bone block graft when covered or not with e-PTFE membranes. Study design. Sixty male Wistar rats received a bone graft plus an e-PTFE membrane (MB) or just the graft (B). A block graft was harvested from the animal's calvarium and was laid and stabilized on the external cortical area near the angle of the mandible. Descriptive histology and histomorphometric analyses were carried out and the data were analyzed statistically by ANOVA and the Tukey test, with the level of significance set at 5%. Results. The results for group B showed that there was bone loss during the healing period (B0 = 1.38, B45 = 1.05, F = 7.91 > F C = 3.02), that is, the initial volume of the graft decreased in time. Bone tissue loss was about 24%. In contrast, the MB group showed bone tissue gain along the observation period (MB0 = 1.54, MB45 = 2.40, F = 7.91 > FC = 3.02), meaning that the total volume of newly formed bone was greater than the original graft area. Bone tissue gain was approximately 55%. MB showed significantly greater bone gain when compared to B (B45 = 1.05, MB45 = 2.40, F = 39.86 > FC = 1.90). These significant differences between B and MB could already be observed after 21 days. Conclusions. The bone block graft underwent resorption at an early healing stage, while additional new bone formation was observed when the bone graft was covered with an e-PTFE membrane. © 2005 Mosby, Inc. All rights reserved.

Reconstruction of Mandibular Segmental Defects Using the Guided-Bone Regeneration Technique With Polylactide Membranes and/or Autogenous Bone Graft: A Preliminary Study on the Influence of Membrane Permeability

Purpose: Bone maintenance after mandibular reconstruction with autogenous iliac crest may be disappointing due to extensive resorption in the long term. The potential of the guided-bone regeneration (GBR) technique to enhance the healing process in segmental defects lacks comprehensive scientific documentation. This study aimed to investigate the influence of polylactide membrane permeability on the fate of iliac bone graft (BG) used to treat mandibular segmental defects. Materials and Methods: Unilateral 10-mm-wide segmental defects were created through the mandibles of 34 mongrel dogs. All defects were mechanically stabilized, and the animals were divided into 6 treatment groups: control, BG alone, microporous membrane (poly L/DL-lactide 80/20%) (Mi); Mi plus BG; microporous laser-perforated (15 cm2 ratio) membrane (Mip), and Mip plus BG. Calcein fluorochrome was injected intravenously at 3 months, and animal euthanasia was carried out at 6 months postoperatively. Results: Histomorphometry showed that BG protected by Mip was consistently related to larger amounts of bone compared with other groups (P ≤ .0001). No difference was found between defects treated with Mip alone and BG alone. Mi alone rendered the least bone area and reduced the amount of grafted bone to control levels. Data from bone labeling indicated that the bone formation process was incipient in the BG group at 3 months postoperatively regardless of whether or not it was covered by membrane. In contrast, GBR with Mip tended to enhance bone formation activity at 3 months. Conclusions: The use of Mip alone could be a useful alternative to BG. The combination of Mip membrane and BG efficiently delivered increased bone amounts in segmental defects compared with other treatment modalities. © 2008 American Association of Oral and Maxillofacial Surgeons.

Luminescent multifunctional biocellulose membranes

Luminescent biocellulose membranes were obtained by incorporation of ethanolic solutions of the europium compounds [Eu(BTFAC)3(H2O)2], [Eu(BTFA) 3(DBSO)2], [Eu(BTFA)3(PTSO)2] and [Eu(BTFA)3(FSO)2] (BTFAC- 4,4,4-Trifluoro-1- phenyl-1,3-butanedione DBSO- dibenzyl sulfoxide, PTSO- p-Tolyl sulfoxide and FSO- phenyl sulfoxide). Selfsustainable semi-transparent composite membranes were obtained showing strong emission under UV exctiation. The antenna hole played by the ligands was observed to be more efficient in the composite membranes than in the precursor complexes which by themselves are also strong red emitter compounds. These new multifuctional membranes could find application in different areas as phosphors and UV→Visible energy converting devices. © 2011 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).

When small is different: The case of membranes inside tubes

Recently, classical elasticity theory for thin sheets was used to demonstrate the existence of a universal structural behavior describing the confinement of sheets inside cylindrical tubes. However, this kind of formalism was derived to describe macroscopic systems. A natural question is whether this behavior still holds at nanoscale. In this work, we have investigated through molecular dynamics simulations the structural behavior of graphene and boron nitride single layers confined into nanotubes. Our results show that the class of universality observed at macroscale is no longer observed at nanoscale. The origin of this discrepancy is addressed in terms of the relative importance of forces and energies at macro and nano scales. © 2012 Materials Research Society.