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J J van Loon

Publications and source records attributed to J J van Loon.

8 recordsLinked to original sources
PubMed2001

Hypergravity studies in the Netherlands.

It looks like that with the utilization phase of the International Space Station (ISS) scientists will have the possibility to perform long duration and more sophisticated microgravity experiments than could be performed previously. In preparation for these spaceflight studies, ground based experiment tools for simulated (or real) microgravity and hypergravity are important. To provide the infrastructure and user support necessary to perform these ground based studies we have setup the Dutch Experiment Support Center, DESC. This paper will focus on the three Dutch centrifuge facilities. It is shown that these hypergravity facilities can be used to show sounding rocket launch effects, identify alterations in body mass, bone parameters and matrix composition in rodents as well as to derive a test protocol for the Space Adaptation Syndrome in humans. DESC coordinates the use of these centrifuge facilities.

Adaptation, Physiological↗
PubMed2000

Plastid position in Arabidopsis columella cells is similar in microgravity and on a random-positioning machine.

In order to study gravity effects on plant structure and function, it may become necessary to remove the g-stimulus. On Earth, various instruments such as clinostats have been used by biologists in an attempt to neutralize the effects of gravity. In this study, the position of amyloplasts was assayed in columella cells in the roots of Arabidopsis thaliana (L.) Heynh. seedlings grown in the following conditions: on Earth, on a two-dimensional clinostat at 1 rpm, on a three-dimensional clinostat (also called a random-positioning machine, or an RPM), and in space (true microgravity). In addition, the effects of these gravity treatments on columella cell area and plastid area also were measured. In terms of the parameters measured, only amyloplast position was affected by the gravity treatments. Plastid position was not significantly different between spaceflight and RPM conditions but was significantly different between spaceflight and the classical two-dimensional clinostat treatments. Flanking columella cells showed a greater susceptibility to changes in gravity compared to the central columella cells. In addition, columella cells of seedlings that were grown on the RPM did not exhibit deleterious effects in terms of their ultrastructure as has been reported previously for seedlings grown on a two-dimensional clinostat. This study supports the hypothesis that the RPM provides a useful simulation of weightlessness.

Arabidopsis↗
PubMed1999

Virtues and drawbacks of titanium alloy aneurysm clips.

This report describes the imaging characteristics of titanium alloy aneurysm clips and our clinical experience with these clips in more than 300 patients. Phantom and clinical investigations showed that clip artifacts on CT and MR are minor as compared to the cobalt alloy clips used previously. Spiral CT angiography (CTA) in combination with titanium alloy clips could be shown to be a feasible mode of postoperative control and can be used to determine completeness of aneurysm elimination, patency of adjacent arteries as well as vasospasm. In contrast, magnetic resonance angiography (MRA) proved to be unfeasible as a method of postoperative vascular imaging since the titanium clips still produce a shadow in the order of size of the entire aneurysm. Therefore, completeness of aneurysm elimination cannot be judged on magnetic resonance angiography. The clinical experience in more than 300 cases showed that the titanium alloy clips essentially performed well. However, the limits of elastic deformation appear to be somewhat inferior to cobalt alloy clips. The standard appliers do not open the blades of the titanium clips quite as far as with the comparable cobalt alloy clips and the corresponding appliers. Therefore the titanium aneurysm clips are not quite as well suited for large broad based aneurysms. Furthermore, the increased susceptibility of the new clips with regard to abuse suggests to follow the recommendations of the manufacturer not to recycle and re-sterilize clips that have been tried but not permanently implanted.

Alloys↗
PubMed1997

Postoperative spiral computed tomography and magnetic resonance angiography after aneurysm clipping with titanium clips.

OBJECTIVE: To reduce morbidity and mortality after subarachnoid hemorrhage, it is imperative to evaluate the results of the surgical treatment of cerebral aneurysms. We investigated the usefulness of spiral computed tomography (CT) and magnetic resonance angiography as postoperative control examinations after cerebral aneurysms were clipped with titanium clips. METHODS: Eleven patients with 13 treated aneurysms were studied prospectively with postoperative digital subtraction angiography, spiral CT, and magnetic resonance angiography. The occlusion of the dome of the aneurysm, the presence of a remnant of the neck, the patency of the parent vessels and other major vessels, and the presence of vasospasm were investigated. RESULTS: The different parameters could all be well evaluated by postoperative spiral CT. The artifacts caused by the titanium clips, although relatively small compared with artifacts from other clips, precluded evaluating the dome and the neck of the aneurysm with magnetic resonance angiography. CONCLUSION: In our opinion, spiral CT promises to become a valuable aid in in the postoperative evaluation of clipped aneurysms, and we recommend its routine performance. Postoperative digital subtraction angiography remains the gold standard and has to be performed when spiral CT reveals abnormalities, when the neck of the aneurysm cannot be evaluated because the clip overlays it, or when, intraoperatively, imperfect clipping is suspected and intraoperative angiography cannot be performed.

Adolescent↗
PubMed1995

Polysulphone inhibits final differentiation steps of osteogenesis in vitro.

Biocompatibility is an important factor in the development of orthopedic implants as well as in the development of new tissue culture devices. Polysulphone has been used for orthopedic implants because of its mechanical properties, ease of sterilization, molding capacity, and biocompatibility. Therefore, polysulphone has been chosen as the prime material for the construction of tissue culture devices to be used for the cultivation of osteogenic cells (preosteoblast-like MN7 cells and primary bone marrow fragments), as well as complete fetal long bone explants under space flight conditions. Whereas polysulphone did not interfere with the proliferation in early stages of bone-forming cells, we show that leachable factors within the polysulphone polymer prevented the final steps of matrix formation as measured by collagen synthesis and matrix mineralization. These data argue against polysulphone as a material for orthopedic implants.

Animals↗
PubMed1994

Development of tissue culture techniques and hardware to study mineralization under microgravity conditions.

To study the effects of weightlessness on mouse fetal long bone rudiment growth and mineralization we have developed a tissue culture system for the Biorack facility of Spacelab. The technique uses standard liquid tissue culture medium, supplemented with NA-beta-glycerophosphate, confined in gas permeable polyethylene bags mounted inside ESA Biorack Type I experiment containers. The containers can be flushed with an air/5% CO2 gas mixture necessary for the physiological bicarbonate buffer used. Small amounts of fluid can be introduced at the beginning (e.g. radioactive labels for incorporation studies) or at the end of the experiment (fixatives). A certain form of mechanical stimulation (continuous compression) can be used to counteract the, possibly, adverse effect of microgravity. Using 16 day old metatarsals the in vitro calcification process under microgravity conditions can be studied for a 4 day period.

Animals↗
PubMed1994

Structure-activity relationship of isolated avenanthramide alkaloids and synthesized related compounds as oviposition deterrents for Pieris brassicae.

The structure-activity relationship was investigated of compounds isolated from the eggs of Pieris brassicae, the large white cabbage butterfly, and eight synthesized related compounds as oviposition deterrents for this insect. The activity of all compounds was tested in a dual-choice bioassay. The two most active oviposition deterrents for P. brassicae were trans-2- [3-(4-hydroxyphenylpropenoyl)amino]-3,5-dihydroxybenzoic acid [8] and trans-2-[3-(3,4-dihydroxyphenylpropenoyl)amino]-3,5-dihydroxybenzo ic acid [2]. Among members of this compound class, alteration of the substituents of the cinnamic acid part of the molecule affected the oviposition deterrent activity more profoundly than other structural changes. Modification of the anthranilic acid part of the molecule resulted in lower activity.

Alkaloids↗