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Biomedical subjects

J Snauwaert

Publications and source records attributed to J Snauwaert.

18 recordsLinked to original sources
PubMed2005

Roughness and hydrophobicity studies of nanofiltration membranes using different modes of AFM.

Determination of the surface roughness by AFM is crucial to the study of particle fouling in nanofiltration. It is, however, very difficult to compare the different roughness values reported in the literature because of a lack in uniformity in the methods applied to determine surface roughness. AFM is used in both noncontact mode and tapping mode; moreover, the size of the scan area is highly variable. This study compares, for six different nanofiltration membranes (UTC-20, N30F, Desal 51HL, Desal 5DL, NTR7450, NF-PES-10), noncontact mode AFM with tapping mode AFM for several sizes of the scan area. Although the absolute roughness values are different for noncontact AFM and tapping mode AFM, no difference is found between the two modes of AFM in ranking the nanofiltration membranes with respect to their surface roughness. NTR 7450 and NF-PES-10 are the smoothest membranes, while the roughest surface can be found with Desal 51HL and Desal 5DL. UTC-20 and N30F are characterized by an intermediate roughness value. An increase in roughness with increasing scan area is observed for both AFM modes. Larger differences between the roughnesses of the membranes are obtained with tapping mode AFM because of the tapping of the tip on the surface. Phase imaging is an extension of tapping mode AFM, measuring the phase shift between the cantilever oscillation and the oscillation of the piezo driver. This phase shift reflects the interaction between the cantilever and the membrane surface. A comparison with contact angle measurements proves that a small phase shift corresponds to a large contact angle, representing a hydrophobic membrane surface.

Journal Article↗
PubMed2005

Monomer-solvent phase separation in one-step self-etch adhesives.

One-step adhesives bond less effectively to enamel/dentin than do their multi-step versions. To investigate whether this might be due to phase separation between adhesive ingredients, we characterized the interaction of 5 experimental and 3 commercial self-etch adhesives with dentin using transmission electron microscopy. All adhesives were examined for homogeneity by light microscopy. Bonding effectiveness to dentin was determined with the use of a micro-tensile bond-strength protocol. The lower bond strength of the one-step adhesives was associated with light-microscopic observation of multiple droplets that disappeared slowly. Interfacial analysis confirmed the entrapment of droplets within the adhesive layer. The prompt disappearance of droplets upon application of a small amount of HEMA (2-hydroxyethyl methacrylate) or a HEMA-containing bonding agent, as well as the absence of droplets at the interface of all HEMA-containing adhesives, strongly suggests that the adhesive monomers separate from water upon evaporation of ethanol/acetone. Upon polymerization, the droplets become entrapped within the adhesive, potentially jeopardizing bond durability. This can be avoided by strong air-drying of the adhesive, thereby removing interfacial water and thus improving bonding effectiveness.

Acid Etching, Dental↗
PubMed2001

Adhesion to and decalcification of hydroxyapatite by carboxylic acids.

Fundamental to the processes of decalcification of or adhesion to mineralized tissues is the molecular interaction of acids with hydroxyapatite. This study was undertaken to chemically analyze the interaction of 1 mono-, 2 di-, 1 tri-, and 2 polycarboxylic acids with hydroxyapatite in an attempt to elucidate the underlying mechanism. Maleic, citric, and lactic acid decalcified hydroxyapatite, in contrast to oxalic acid and the two polycarboxylic acids that were chemically bonded to hydroxyapatite. Solubility tests showed that the calcium salts of the former were very soluble, whereas those of the latter could hardly be dissolved in the respective acid solutions. Based on these data, an adhesion/decalcification concept was advanced that predicts that carboxylic acids, regardless of concentration/pH, either adhere to or decalcify hydroxyapatite, depending on the dissolution rate of the respective calcium salts in the acid solution. This contrasting behavior of organic acids most likely results from their differential structural conformations.

Acrylic Resins↗
PubMed2000

Assessment of decontamination methods as pretreatment of silanization of composite glass fillers.

In terms of mechanical properties and durability, the surface of glass fillers should be decontaminated in order to optimize the silanization process for the production of resin composites. The objective of this study was to evaluate the decontamination efficiency of 18 cleaning methods on glass fillers as pretreatment of silane coupling. X-ray photoelectron spectroscopy revealed that SiO(2) boiled with a 5% sodium peroxodisulfate aqueous solution for 15 min, followed by ultrasonic rinsing with acetone for 30 min was most effective among all the decontamination methods investigated. In addition, nano-indentation measurements on SiO(2) treated by the above-mentioned method revealed that the surface was not significantly weakened as compared to untreated SiO(2). The results of this study should lead to an improved filler-matrix coupling and thus contribute to the development of better wear and fatigue-resistant composites. Therefore, sodium peroxodisulfate is proposed as a presilanization filler decontamination step in the production process of resin composites.

Bisphenol A-Glycidyl Methacrylate↗
PubMed2000

Evidence of chemical bonding at biomaterial-hard tissue interfaces.

For many years, glass-polyalkenoate cements have been described as possessing the unique properties of self-adherence to human hard tissues, such as bones or teeth. However, direct experimental evidence to prove the existence of chemical bonding has not been advanced. X-ray Photoelectron Spectroscopy (XPS) was used to analyze the chemical interaction of a synthesized polyalkenoic acid with enamel and synthetic hydroxyapatite. For both enamel and hydroxyapatite, the peak representing the carboxyl groups of the polyalkenoic acid was detected to have significantly shifted to a lower binding energy. De-convolution of this shifted peak disclosed two components with a peak representing unreacted carboxyl groups and a peak suggesting chemical bonding to hydroxyapatite. On average, 67.5% of the carboxyl groups of the polyalkenoic acid were measured to have bonded to hydroxyapatite. XPS of hydroxyapatite also disclosed its surface to be enriched in calcium and decreased in phosphorus, indicating that phosphorus was extracted at a relatively higher rate than calcium. Analysis of these data supports the mechanism in which carboxylic groups replace phosphate ions (PO4(3-)) of the substrate and make ionic bonds with calcium ions of hydroxyapatite. It is concluded that an ultrathin layer of a polyalkenoic acid can be prepared on a hydroxyapatite-based substrate by careful removal of non-bonded molecules. With this specimen-processing method, XPS not only provided direct evidence of chemical bonding, but also enabled us to quantify the percentages of functional groups of the polyalkenoic acids that bonded to calcium of hydroxyapatite.

Binding Sites↗
PubMed1999

A novel approach to AFM characterization of adhesive tooth-biomaterial interfaces.

A novel approach is proposed for studying tooth-biomaterial interactions with high resolution. Thus far, polished interfaces examined by AFM have not disclosed much detail, mainly due to the destruction of soft surface texture and the smearing of polishing debris across the interface that obscures the actual ultra-structure. Therefore the practical utility of diamond-knife microtomy as a sample preparation technique for imaging tooth-biomaterial interfaces by AFM with high resolution was tested in this study and compared to that of ultra-fine mechanical polishing techniques. The AFM images clearly demonstrated the enhanced potential of diamond-knife microtomy for nondestructively producing clean cross-sections through interfaces that allow the interfacial ultra-structure to be imaged by AFM with a resolution equaling that of TEM. This novel approach opens the field to the full range of scanning probe microscopy, including physical and chemical surface characterization of interfaces with a mix of soft and hard substrates.

Dental Cements↗
PubMed1999

Hybridization effectiveness of a two-step versus a three-step smear layer removing adhesive system examined correlatively by TEM and AFM.

PURPOSE: The objectives of this study were (1) to compare the hybridization effectiveness of two adhesive systems that are applied in respectively three and two steps, and (2) to determine the best resin-dentin interface preparation technique for atomic force microscopy (AFM). MATERIALS AND METHODS: The resin-dentin interface produced by the three-step OptiBond Dual-Cure (Kerr) and its simplified two-step successor OptiBond Solo (Kerr) was ultramorphologically examined using transmission electron microscopy (TEM) and AFM. Four different methods were used to prepare interface specimens for AFM: (1) polishing to a 0.1-micron finish with a silicon oxide suspension, (2) polishing to a 0.05-micron finish with an aluminum oxide suspension, (3) argon-ion etching, and (4) sectioning with a diamond knife. RESULTS: Both TEM and AFM demonstrated that some collapse of the exposed collagen fibril network, due to gentle postconditioning air-drying of the dentin surface, may not have been totally recovered through hybridization by the two-step adhesive formulation as opposed to the three-step precursor. From the four interface preparation methods, only diamond-knife sectioning revealed sufficient ultramorphologic detail and high resolution that can capitalize on the high resolution offered by AFM. CONCLUSION: First, the findings suggest that simplifying the application procedure of adhesives by combining the primer and adhesive resin into a single application step may reduce hybridization effectiveness. Future research should confirm this effect for other two- versus three-step adhesive systems. Second, diamond-knife sectioning should be used for future topographic imaging and physicomechanical testing of resin-dentin interfaces by AFM.

Bisphenol A-Glycidyl Methacrylate↗
PubMed1998

Strong enhancement of nonlinear optical properties through supramolecular chirality

A new approach to second-order nonlinear optical (NLO) materials is reported, in which chirality and supramolecular organization play key roles. Langmuir-Blodgett films of a chiral helicene are composed of supramolecular arrays of the molecules. The chiral supramolecular organization makes the second-order NLO susceptibility about 30 times larger for the nonracemic material than for the racemic material with the same chemical structure. The susceptibility of the nonracemic films is a respectable 50 picometers per volt, even though the helicene structure lacks features commonly associated with high nonlinearity. Susceptibility components that are allowed only by chirality dominate the second-order NLO response.

Journal Article↗
PubMed1996

Imaging red blood cells with the atomic force microscope.

A novel technique for the reproduction of ultramorphological images and details of the surface of normal and pathological red blood cells (RBC) was investigated. The atomic force microscope (AFM) provided high-resolution images of cell surfaces. The RBC dimensions obtained by this technique revealed differences between native red cells in smears and glutaraldehyde-fixed red cells. It was shown that fixed red blood cells were best suited for the ultramorphological imaging of the cell surface.

Erythrocytes↗
PubMed1992

Protein engineering of xylose (glucose) isomerase from Actinoplanes missouriensis. 2. Site-directed mutagenesis of the xylose binding site.

Site-directed mutagenesis in the active site of xylose isomerase derived from Actinoplanes missouriensis is used to investigate the structural and functional role of specific residues. The mutagenesis work together with the crystallographic studies presented in detail in two accompanying papers adds significantly to the understanding of the catalytic mechanism of this enzyme. Changes caused by introduced mutations emphasize the correlation between substrate specificity and cation preference. Mutations in both His 220 and His 54 mainly affect the catalytic rate constant, with catalysis being severely reduced but not abolished, suggesting that both histidines are important, but not essential, for catalysis. Our results thus challenge the hypothesis that His 54 acts as an obligatory catalytic base for ring opening; this residue appears instead to be implicated in governing the anomeric specificity. With none of the active site histidines acting as a catalytic base, the role of the cations in catalyzing proton transfer is confirmed. In addition, Lys 183 appears to play a crucial part in the isomerization step, by assisting the proton shuttle. Other residues also are important but to a lesser extent. The conserved Lys 294 is indirectly involved in binding the activating cations. Among the active site aromatic residues, the tryptophans (16 and 137) play a role in maintaining the general architecture of the substrate binding site while the role of Phe 26 seems to be purely structural.

Actinomycetales↗
PubMed1987

Immunohistochemical study of epidermal Langerhans cells and dermal dendritic cells in benign and malignant skin lesions characterized by a dermal lymphoid infiltrate consisting either of B-cells or T-cells.

Skin biopsies from 43 patients with a rather dense dermal lymphoid infiltrate of either inflammatory or neoplastic nature have been investigated. We studied the number, distribution and immunophenotype of epidermal Langerhans cells and dermal dendritic cells. As previously reported, differences in epidermal Langerhans cell and dermal dendritic cell numbers between skin biopsies with a B-cell infiltrate and skin biopsies with a T-cell infiltrate were found, dendritic cells being more numerous in the latter. The main finding of this study was an uneven distribution of epidermal Langerhans cells and dermal dendritic cells in skin biopsies with a T-cell infiltrate: in skin lesions with an inflammatory lymphoid infiltrate, small clusters of epidermal and dermal dendritic cells admixed with T-lymphocytes (predominantly T-helper/inducer cells) and small blood vessels were present at areas of exocytosis. In skin lesions with a neoplastic lymphoid infiltrate larger, more loosely arranged aggregates of dendritic cells and T-cells were seen. These cell aggregations composed of activated (inflammatory or neoplastic) T-cells and dendritic cells may represent the cutaneous homologue of the secondary T-nodule in the lymph node. Both types of cell aggregates may correspond to the dendritic cell-T cell clusters observed in in vitro induced immune responses.

B-Lymphocytes↗
PubMed1986

Polycations reduce vasopressin-induced water flow by endocytic removal of water channels.

Several polycations added to the luminal solution were found to inhibit the vasopressin (ADH)-induced water flow in toad urinary bladder but not the ADH-induced increase in sodium transport or in urea permeability. Ultrastructural studies were conducted to evaluate the uptake of cationized ferritin. It was found that endocytosis of cationized ferritin by luminal cells was strikingly enhanced on exposure to ADH; this increased endocytosis was concomitant with inhibition of transepithelial ADH-induced water flow. Various maneuvers preventing endocytosis were also found to counteract the polycation-induced inhibition of the ADH effect. It is suggested that polycations are endocytosed in vesicles whose walls contain the water channels but not the urea or sodium channels.

Animals↗
PubMed1984

Bleomycin-induced Raynaud's phenomenon and acral sclerosis.

This study presents a case of two of the more uncommon side effects of bleomycin therapy for a metastasized testicular carcinoma: Raynaud's phenomenon and acral sclerosis. It is suggested that this association indicates a common pathogenic mechanism. These side effects may serve as an experimental model in the study of Raynaud's phenomenon and acral sclerosis.

Adult↗