Biomedical subjects

E Groenendijk

Publications and source records attributed to E Groenendijk.

4 recordsLinked to original sources

PubMed2005

Novel approach to quantify immobilized-enzyme distributions.

The quantitative intraparticle enzyme distribution of Assemblase, an industrially employed polydisperse immobilized penicillin-G acylase, was measured. Because of strong autofluorescence of the carrier, the generally applied technique of confocal scanning microscopy could not be used; light microscopy was our method of choice. To do so, Assemblase particles of various sizes were sectioned, labeled with antibodies specifically against the enzyme, and analyzed light microscopically. Image analysis software was developed and used to determine the intraparticle enzyme distribution, which was found to be heterogeneous, with most enzyme located in the outer regions of the particles. Larger particles showed steeper gradients than smaller ones. A mathematical representation of the intraparticle profiles, based on in-stationary enzyme diffusion into the particles, was validated successfully for a broad range of particle sizes using data for volume-averaged particle size and enzyme loading. The enzyme gradients determined in this work will be used as input for a physical model that quantitatively describes the complex behavior of Assemblase. Such a physical model will lead to identification of the current bottlenecks in Assemblase and can serve as a starting point for the design of improved biocatalysts that also may be based on intelligent use of enzyme gradients.

Catalysis↗

PubMed2003

[Dental ingenuity 2. Implant treatment using transitional implants].

The applications in oral implantology are strongly increased due to the advance in the field of osseointegration and in material technology. As a result of this gained knowledge the area of indications increased in both edentulous and partially dentate patients. With the extension of the indications of dental implants there also is a growing patients' demand for direct replacement of lost tooth. Sometimes it is possible to fulfill the expressed wish of immediate loading. In case of poor bone quantity or quality this is impossible. Transitional implants supply the prosthodontist with an additional possibility to fulfill the need for uninterrupted healing as well as patients' demands for immediate functional and esthetic restorations.

Dental Implantation, Endosseous↗

PubMed2001

Development of in vivo sponge cultures: particle feeding by the tropical sponge Pseudosuberites aff. andrewsi.

The rate of food particle uptake of the tropical sponge Pseudosuberites aff. andrewsi was studied in relation to particle concentrations and particle size. A range of different concentrations of either the marine microalga Dunaliella tertiolecta (approximately 5-8 microm) or the marine cyanobacterium Synechococcus sp. (approximately 1 microm) was supplied to the sponges. D. tertiolecta had a pronounced effect on the filtration activity of the sponges: at concentrations higher than approximately 4 x 10(5) cells/cm(3), the filtration rates dropped dramatically. Such a clear effect was not found for Synechococcus sp. The results further showed that the maximal amount of food (when expressed in organic carbon) that can be taken up per cubic centimeter of sponge volume per unit of time should in principle be sufficient to enable growth (irrespective of the food particle type). At the maximal food particle concentration that did not affect the filtration rates, the uptake of organic carbon is already highly in excess of the amount of organic carbon that the sponges need to cope with their respiratory demand. Based on these findings, a series of growth experiments was carried out in which the sponges were subjected to a constant concentration of different types of food particles (Synechococcus sp. and the microalgae Chlorella sorokiniana and Nannochloropsis sp). Although initial growth was sometimes observed, continuous growth at a constant rate could not be obtained. It is concluded that qualitative aspects of feeding rather than quantitative aspects are the key to successful in vivo sponge culture.

Journal Article↗

PubMed1988

Improvement of the caries resistance of human dental roots by a two-step conversion of the root mineral into fluoridated hydroxylapatite.

Roots of extracted human molars were treated for both 10 and 30 min with a saturated solution of dicalcium phosphate dihydrate (DCPD) of pH 2.4 and subsequently with a 5.3 mmol.L-1 solution of sodium fluoride of pH 7.0. The objective of these combined treatments was to convert the highly-soluble root mineral into the less-soluble fluoridated hydroxylapatite, with DCPD as an intermediate, to improve caries resistance. The mineral content of the surface layer was not affected in a significant way. Roots treated in this way were subjected to 50 mmol.L-1 acetate buffer solutions of pH 5.5 and with pIOHA-values of 112, 116, and 122. The proportional reduction of the rate of demineralization (Vdem) of similarly treated roots subjected to buffer solutions of pIOHA 112 and 116 appeared to be equal initially. Since fluoridated hydroxylapatite is insoluble under these conditions, these findings are in agreement with expectations. The reduction of V dem amounted to about 45 and 70% for roots treated for 10 and 30 min, respectively. When roots were treated for 10 and 30 min and then exposed to buffer solutions with a pIOHA 122, reductions of V dem of about 30 and 55%, respectively, were found. Conversion of the root mineral into fluoridated hydroxylapatite can eliminate, in principle, the existing difference in caries susceptibility of the root and of the dental enamel.

Calcium Phosphates↗