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Biomedical subjects

K de Groot

Publications and source records attributed to K de Groot.

At least 145 records · Page 8Linked to original sources
PubMed1991

Plasma-sprayed coatings of tetracalciumphosphate, hydroxyl-apatite, and alpha-TCP on titanium alloy: an interface study.

In order to study the interaction of calcium phosphate coatings with bone tissue, coated titanium cylinders with a standard size were implanted in dog femora. Coatings were made by plasma spraying powders of hydroxylapatite, beta-whitlockite, and tetracalciumphosphate particles. The plasma spraying process turns beta-whitlockite into alpha-TCP. Bone bonding and bone formation were evaluated by mechanical push-out tests and histological observations. Hydroxylapatite and tetracalciumphosphate coatings show an interface strength after 3 months of implantation of 34.3 +/- 6.5 MPa and 26.8 +/- 3.9 MPa, respectively, while alpha-TCP and blanco titanium lead to an interface strength of 10.0 +/- 3.5 MPa and 9.7 +/- 1.3 MPa, respectively. Histological examinations revealed that hydroxylapatite and tetracalciumphosphate give rise to an excellent bone formation, while alpha-TCP and blanco titanium evoked remodeling and less bone contact.

Alloys↗
PubMed1991

Histologic evaluation of the osseous adaptation to titanium and hydroxyapatite-coated titanium implants.

The aim of this study was to obtain more information about the bone reaction to titanium and hydroxyapatite (HA)-coated titanium implants during the first 3 months after implantation. Therefore, uncoated and coated implants were inserted into the tibia of rabbits for various implantation periods. The histological results demonstrated that although there were no marked differences in bony reaction at the cortical level to the different implant materials, HA-coating appeared to induce more bone formation in the medullary cavity. It was also noted, that 3 months after insertion loss of coating thickness had occurred.

Animals↗
PubMed1991

A mechanical investigation of fluorapatite, magnesiumwhitlockite, and hydroxylapatite plasma-sprayed coatings in goats.

Ceramic coatings of fluorapatite (FA), magnesiumwhitlockite (MW), and hydroxylapatite (HA), and noncoated Ti-6Al-4V alloy (Ti) implants were evaluated before and after implantation in an animal study. Cylindrical plugs were coated by plasma-spraying with FA, MW, and HA. X-ray-diffraction patterns showed for FA and HA a crystalline and for MW an amorphous-crystalline coating structure. The plugs were implanted into the right femora and left humeri of 16 adult goats. Follow-up periods were 12 and 25 weeks. The in vivo results were evaluated using push-out tests and scanning electron microscopy. There were significant differences in push-out strengths between femur and humerus. The FA and HA implants showed significantly higher push-out strengths than the MW and Ti alloy implants, especially for the 12 week follow-up period. Furthermore, at 12 weeks, MW showed significantly lower push-out strengths than Ti alloy. SEM-investigation of the interfaces revealed that FA did not degrade while both MW and HA showed extensive degradation at 12 and 25 weeks. In addition, the interface after push-out testing showed for the MW, HA, and Ti alloy implants to be fractured at the implant-tissue interface and for the FA to be fractured at the coating-titanium interface.

Animals↗
PubMed1991

Development of a new percutaneous access device for implantation in soft tissues.

The objective of this study was to evaluate a new type of percutaneous device (PD) designed to be implanted in soft tissues. The new PD consisted out of: (1) a flange-shaped subcutaneous component, made from sintered titanium fiber-web, and (2) a percutaneous component, made from dense sintered hydroxyapatite. The PDs were inserted in the back of 15 rabbits. The surgical procedure was performed in two steps. In the first session the subcutaneous component was placed. In the second session, after 3-4 months the percutaneous component was fixed in the subcutaneous component. The implants were left in situ for 1 and 4 months after the second implantation session. Clinical and histological investigations were performed. It is found, that there was only a limited epidermal down-growth in the percutaneous area. No inflammatory reaction was observed in the dermal connective tissue. Histological analysis also demonstrated that titanium fiber mesh evokes minor adverse effects of the surrounding tissues. In conclusion, these experiments have shown that stabilization of the PD in the hypodermal area by using a sintered titanium fiber-web structure favors the longevity of PDs implanted in soft tissues.

Animals↗
PubMed1991

Fibroblast and epithelial cell interactions with surface-treated implant materials.

The basic mechanisms underlying skin-implant interactions were investigated by means of in vitro experiments with fibroblast and epithelial cell cultures. Cells were cultured on various implant materials treated with radio frequency glow discharge. The possible influence of this treatment on the morphological mode of cell attachment, as well as cell behaviour in attachment and growth rate were investigated. The results demonstrate that there are significant behavioural differences between fibroblasts and epithelial cells.

Animals↗
PubMed1991

Successful induction of allergic contact dermatitis to mercury and chromium in mice.

Availability of reproducible mouse models for allergic contact dermatitis (ACD) to the metal allergens nickel, mercury and chromium, would be of great value for pathogenetic and preventive studies. We explored epicutaneous sensitization to nickel, mercury and chromium in mice in which oral grooming of the sensitization site was prevented by a plaster cast around the abdomen and lower thorax. This procedure was based on earlier findings that oral ingestion of allergen could prevent contact sensitization. The present results show that BALB/c mice can be readily sensitized to mercury and chromium using this epicutaneous casting method, without the further use of adjuvants. With nickel, however, neither this method, nor conventional methods involving the use of Freund's complete adjuvant (FCA) were effective.

Animals↗
PubMed1990

Tissue response to percutaneous implants in rabbits.

This study reports on certain aspects of wound-healing around percutaneous implants. Plasma-sprayed and dense hydroxylapatite, titanium, and carbon test implants were inserted into the tibia and the cranium of 12 rabbits. Four and 8 months after insertion, the animals were sacrificed and the implants with their surrounding tissues were processed histologically. Light- and transmission electron microscopic investigations were performed. It is found that direct and indirect bone-anchoring favors the longevity of percutaneous implants. No differences in tissue reaction between the various implant materials were observed.

Animals↗
PubMed1990

The biocompatibility of hydroxyapatite ceramic: a study of retrieved human middle ear implants.

The biocompatibility of 11 hydroxyapatite auditory canal-wall prostheses and 4 hydroxyapatite incus prostheses implanted for 4 to 40 months was evaluated by light microscopy, scanning electron microscopy, transmission electron microscopy, and Röntgen microanalysis. These 15 prostheses representing 4% of 375 prostheses, has been removed because of unresolved chronic middle ear infection, residual cholesteatoma, or poor fit. The findings confirmed earlier reports on the biocompatibility of hydroxyapatite in vitro, in animals, and in man. An electron-dense layer was found at the interface with bone and fibrous tissue, and a firm bond between the ceramic and bone at the hydroxyapatite ceramic/bone interface developed. Macropores became filled with bone and fibrous tissue, and the tissue in the individual pores was interconnected. Furthermore the incus prostheses were covered with an epithelium similar to that found in the human middle ear. Findings diverging from those made in other studies were the relatively large amount of exudate in the pores, an apparent increase of degradation during infection, and the accumulation of trace elements in one of the canal-wall prostheses. In all likelihood these three phenomena may be attributed to the unfavorable conditions to which these prostheses were exposed during implantation.

Biocompatible Materials↗
PubMed1990

X-ray diffraction studies on plasma-sprayed calcium phosphate-coated implants.

Calcium phosphate coatings on steel, obtained by the plasma-spray technique, were examined by x-ray diffraction in order to get some information on their crystallographic structure and crystallinity. Surface roughness values were also determined. These coatings are of interest for hip-prosthesis materials in particular.

Biocompatible Materials↗
PubMed1990

Stress-absorbing elements in dental implants.

By means of finite element analysis, calculations, were made of the stress-distribution in bone around implants with and without stress-absorbing elements. A freestanding implant and an implant, it was concluded the variation in the E-modulus of the stress-absorbing element had no effect on the stresses in bone. Changing the shape of the stress-absorbing element had little effect on the stresses in cortical bone. For the implant connected with a natural tooth, it was concluded that a more uniform stress was obtained around the implant with a low E-modulus of the stress-absorbing element. It was also concluded that the bone surrounding the natural tooth showed a decrease in the height of the peak stresses.

Computer Simulation↗
PubMed1990

Studies of the solubility of different calcium phosphate ceramic particles in vitro.

In vitro solubility tests of hydroxyapatite, tetracalcium phosphate or tricalcium phosphate particles were performed in lactate, citrate, Gomoris or Michaelis buffer with pH 6.2 or 7.2 and in aqua destillata. The results showed that in general the solubility decreased in the order tetracalcium phosphate greater than tricalcium phosphate greater than hydroxyapatite, except for lactate or citrate buffer where the solubility order was tetracalcium phosphate = tricalcium phosphate greater than hydroxyapatite. The influence of the specific buffer used is much larger than either pH or specific calcium phosphate salt tested. The pH stability of lactate buffer and aqua destillata is very low, the other buffer solvents had a rather stable pH value.

Biocompatible Materials↗
PubMed1990

Oral induction of immunological tolerance to chromium in the guinea pig.

Metal alloys used in dentistry may elicit adverse side-effects. Contact allergic reactions to metals released from such alloys are among the most frequently encountered problems. In an earlier study, we observed that oral contacts with nickel or chromium salts did not sensitize, but rather decreased the risk of subsequent sensitization to these metals. In the present study, we focused on chromium allergy and extended our earlier observations by further dose-response studies. In addition, we compared different chromium valencies as to their potential oral tolerogenic effects. Development of immunological tolerance in chromium-fed guinea pigs was demonstrated by their inability to develop chromium hypersensitivity after a subsequent immunization attempt. For these studies, the techniques of immunization and skin testing were first improved. One feeding with a high dose of K2Cr2O7 (containing hexavalent chromium) was effective in full tolerance induction. In contrast, trivalent chromium (CrCl3) induced a distinctly lower degree of tolerance, whereas metallic chromium powder was not detectably tolerogenic after a limited number of feedings. Dose-frequency-response studies with K2Cr2O7 showed that full tolerance could also be induced by an increase in the number of feedings with sub-optimal tolerogenic doses. The present results therefore support our hypothesis that long-lasting oral contact with chromium-releasing metal alloys may ultimately result in strong immune tolerance to this metal in subjects without previous skin contact with it. This view is further supported by recent insights into the unique tolerogenicity of oral, as compared with gastro-intestinal, allergenic contacts.

Administration, Oral↗
PubMed1990

Histological evaluation of biocompatible orthopaedic polymer.

The biocompatibility of biocompatible orthopaedic polymer implant materials was studied in subcutaneous and bony tissue of rats and rabbits. The tissue response was evaluated by histological techniques. No bone induction capacity of biocompatible orthopaedic polymer could be observed. In rabbits, the presence of plasma cells was significantly higher than in rats. The biomaterial showed some signs of biodegradation and was not very biocompatible.

Animals↗
PubMed1989

Patent literature as a source of information for research and development: an investigation on calcium phosphate-containing biomaterials, Part I.

The usefulness of patent literature for research and development is mostly unknown. Therefore a specific patent retrieval has been carried out concerning calcium phosphate-containing biomaterials. This research field includes chemical, medical, and engineering problems and is of importance to the development of bioactive materials for bone replacement. The preliminary work includes information on the characteristics and the availability of patent literature as well as about patent classification systems according to which the documents are filed in patent collections. By reading the non-patent literature searching questions can be formulated. The proper patent retrieval starts with the study of secondary literature especially that in Chemical Abstracts, which report on patents since 1907. The structure of Chemical Abstracts, their indexes and sections help to find relevant patents of chemical or chemical engineering contents fast and inspire to read patents of bordering areas. This retrieval from Chemical Abstracts led to 171 patents disclosed 1975-1985 and to 95 patents disclosed in 1986; the latter are listed in a table. The contents of the abstracts inform on the research activity and help to reduce time and effort for a continuation of the retrieval in a patent collections or database.

Bibliographies as Topic↗
PubMed1989

Effect of surface treatments on attachment and growth of epithelial cells.

The objective of this study was to enlarge the understanding of the basic mechanisms underlying epithelial tissue implant reaction by means of in vitro experiments with epithelial cell cultures. For the experiments, rat palatal epithelial cells were cultured on various implant materials. The implant surfaces were treated by different procedures. The possible influence of these treatments on the attachment percentage and growth rate of the cells was studied. The results of the experiments demonstrate no significant relation between surface treatment and the behaviour of rat palatal epithelial cells cultured on the various kinds of substrates relevant for implants.

Animals↗