Biomedical subjects

K de Groot

Publications and source records attributed to K de Groot.

At least 109 records · Page 6Linked to original sources

PubMed1995

A model for the evaluation of mandibular bone response to implant materials.

An in vivo animal (goat) mandibular bone model has been evaluated for the cortical and trabecular bone response to biomaterials with different elastic modulus and/or different surfaces. The effect of the elastic modulus on the bone formation was also studied. The difficulties encountered in orientation of the implants probably could have been surmounted if pre-operative radiographs had been available. It was also established that there is a large variance in the amount of trabecular and cortical bone in the mandible of the goat 'bone model'.

Aluminum Oxide↗

PubMed1994

The role of hydrated silica, titania, and alumina in inducing apatite on implants.

Pure soluble silica prepared by a sol-gel method induced bone-like hydroxyapatite formation onto its surface when the silica was immersed in a simulated body fluid (SBF), whereas silica glass and quartz did not. This finding directly supports the hypothesis that hydrated silica plays an important role in biologically active hydroxyapatite formation on the surfaces of bioactive glasses and glass-ceramics, which leads to bone-bonding. Gel-derived titania is also a hydroxyapatite inducer because of its abundant TiOH groups. These results provide further insight into the unique osseointegration of titanium and its alloys. It is suspected that gel-derived titania develops an apatite layer by taking calcium and phosphate from the body fluid, thus producing bone-bonding. Although sufficient AlOH groups may remain in the alumina gel, they do not serve to initiate apatite generation when immersed in SBF. This phenomenon explains the fact that an intermediate fibrous tissue is usually found to separate the alumina implant from bone. One may infer that both abundant OH groups and negatively charged surfaces of gel-derived silica and titania are important for hydroxyapatite induction. material which possesses and/or develops both a negatively charged surface and abundant OH groups in a physiologically-related fluid is most likely to be an efficient apatite inducer. Such materials are suitable candidates to serve as bone-bonding biomaterials.

Aluminum Oxide↗

PubMed1994

In vivo tensile testing of fluorapatite and hydroxylapatite plasma-sprayed coatings.

A tensile test has been developed to test bioactive coating materials. Hydroxylapatite (HA) and fluorapatite (FA) coatings with various roughnesses were tested using sandblasted titanium (Ti) as a control material. Twelve goats received 7 implants each for 6 (2 goats), 12 (5), and 24 (4) week implantation periods. After 12 weeks the mean tensile strength values were highest for polished hydroxylapatite (HAP) followed by HA > FAP (polished fluorapatite) > FA > Ti, and hydroxylapatite type coatings were found to exhibit significantly higher values than fluorapatite type coatings or titanium implants. After 24 weeks no statistically significant differences could be found between any of the implant types. The order of the mean strength values was now HAP > HA > FA > FAP > Ti. Fracture always occurred between the coating and titanium if bone contact had been established. In conclusion, it is suggested that results from different types of test methods cannot be used to compare different types of bioactive coatings.

Animals↗

PubMed1994

Calcium phosphate plasma-sprayed coatings and their stability: an in vivo study.

Several factors playing a possible role in determining coating stability and bone tissue response were studied in in vivo experiments. These factors involving the plasmaspray coating procedure were as follows: 1) plasmaspray powder port 2 or 6; 2) particle size distribution; 3) hydroxylapatite versus fluorapatite coatings; and 4) the effect of post-heat treatment. Coating stability and bone tissue response were examined by measuring coating thickness, coating length, and bone apposition against the coatings. The result was that heat treatment influenced coating stability significantly. Also, bone formation was more intense. Fluorapatite proved to be more stable than hydroxylapatite, which was in agreement with our previous reports.

Alloys↗

PubMed1994

Features of calcium phosphate plasma-sprayed coatings: an in vitro study.

Factors involved with the plasma-spray coating procedure, such as starting powder compound (fluorapatite, hydroxylapatite, magnesium-whitlockite, or tetra-calcium phosphate), powder particle distribution 1-45 or 1-125 microns), powder port gun (port 2 or 6), and post-heat treatment of 1 h at 600 degrees C, were examined for their effects on crystallinity and solubility/stability of the coating. From solubility tests, X-ray diffractometry, and scanning microscopy studies, the solubility and crystallinity were found to be dependent on Ca/P ratio, particle distribution, and post-heat treatment. The post-heat treatment influenced the degree of both crystallinity and solubility. The plasma-spray powder port factor for the hydroxylapatite coatings was not significant. Incubation in buffer of the coatings introduced precipitation at the surfaces of all non-heat-treated coatings except fluorapatite. No precipitation could be observed in any of the heat-treated coatings.

Calcium Phosphates↗

PubMed1994

In vivo reactions of Ca,P particle containing surface reactive glasses.

Four Ca,P particle containing surface reactive glass composites and two glasses (in the SiO2-CaO-P2O5-Na2O-Al2O3-B2O3 system) were implanted in the diaphyseal area of goat femora up to 24 weeks. Scanning electron microscopic, energy dispersive x-ray, and histological analysis were performed to evaluate the material-tissue interactions. A new type of integration mechanism was observed. Instead of the bone growing to the material surface, a gel-like silica formation appeared between the cortex bone and the material surface. In time the gel-like formation was replaced by a Ca,P layer. The results provided indirect evidence that pure silica gel formed in the tissues could also achieve an apatite layer formation and bone bonding on its surface.

Animals↗

PubMed1994

Study of the surface characteristics of magnetron-sputter calcium phosphate coatings.

Plasma-sprayed hydroxylapatite coatings on metals such as titanium have been investigated for many years and have shown a good biocompatibility when implanted in bony tissues. Radiofrequency magnetron sputtering was used as an alternative method to deposit thin films of hydroxylapatite on titanium substrates. X-ray diffraction demonstrated that the sputtered layer was crystalline with a preferred (001) crystallographic orientation with the C-axis perpendicular to the substrate surface. Scanning electron microscopy showed that the deposited films had a uniform and dense structure. The calcium phosphate ratio varied between 1.5 and 2.0, as determined by energy-dispersive X-ray analysis. The in vitro dissolution appeared to be determined by the degree of the coating's crystallinity.

Biocompatible Materials↗

PubMed1994

Formation of a bone apatite-like layer on the surface of porous hydroxyapatite ceramics.

Phosphoric acid solution was used to react with commercial hydroxyapatite (HA) powders to demonstrate the possibility of converting HA to non-stoichiometric apatite and thus to treat porous HA ceramics, to form a thin bone-apatite like layer on the HA ceramic surface. Such a carbonate-containing non-stoichiometric apatite "bioceramic" would be more efficient in bone bonding or bone formation, due to its analogy to natural bone apatite.

Bone and Bones↗

PubMed1994

Evaluation of polylactide monomers in an in vitro biocompatibility assay.

The effect of 0.1 and 0.5% L- and D-monomers on cultured fibroblasts was determined by studying the proliferation, morphology and cellular activity. The addition of 0.5% monomer reduced the metabolic activity of the cells by about 40%, but the proliferation and morphology were only negatively affected for the 0.5% monomer in combination with an increased osmolarity of the medium. The addition of sucrose, however, resulted in an increased proliferation and acid phosphatase activity, as well as an altered morphology. Therefore, it can be concluded from this study that the osmolarity, as well as the nature and concentration of the added material, can exert an influence on proliferation, morphology and/or cellular activity.

Cell Division↗

PubMed1994

Osseous substance formation induced in porous calcium phosphate ceramics in soft tissues.

Porous calcium phosphate ceramics prepared according to the methods of laboratories in Leiden were implanted subcutaneously in rats for 3, 6 and 12 w. No bone formation could be observed. Porous calcium phosphate ceramics prepared according to the methods of laboratories in Sichuan were implanted subcutaneously/intramuscularly in dogs for 1, 3, 5 and 7 months. In particular, ceramics containing alpha-tricalcium phosphate evoked bone formation in the pores of the ceramics. The amount of bone was similar at the different time periods.

Animals↗

PubMed1994

Histological observations of coated and prestressed dental implants under flexible or rigid loading conditions.

Hydroxyapatite-coated and hydroxyapatite-prestressed titanium implants were implanted under load-free, flexible-loaded and rigid-loaded conditions in dog mandibula in vivo. The bone response, bone contact and the quality of the coating were evaluated histologically and histometrically. Hydroxyapatite coating on titanium implants enhanced the bone apposition. The bone contact can still be present while the coating is resorbed. Gingiva contact with the coating led to a faster degradation of the coating. There was no significant difference in bone contact between hydroxyapatite-coated and -prestressed implants with regard to the loading systems: rigid, flexible and load-free. All three implants showed the highest amount of bone contact apically. Only at the mesial side of the implant did the flexible element show rather high amounts of bone contact compared to the rigid and load-free implants. The hydroxyapatite coating more or less degraded during the implantation period. The degree of degradation varied in the implant itself, between the implants and between the animals.

Analysis of Variance↗

PubMed1994

Microstructure and crystallinity in hydroxyapatite coatings.

Plasma spraying was used to produce hydroxyapatite (HA) coatings on metal. The microstructure of these coatings, sprayed with two powder particle size distributions, was examined by scanning electron microscopy (SEM) and showed scattered HA particles with completely melted and unmelted or partially melted cores. Röntgen diffraction shows that the crystallinity increases after a vacuum heat treatment at 600 degrees C. SEM reveals that the amorphous phase recrystallized and new crystalline grains were formed at the surface of the crystalline cores.

Biomechanical Phenomena↗

PubMed1994

Better histology and biochemistry for osteoblasts cultured on titanium-doped bioactive glass: bioglass 45S5 compared with iron-, titanium-, fluorine- and boron-containing bioactive glasses.

In the present study we used an established cell culture model to compare Bioglass 45S5 with four other bioactive glasses. Small substitutions or additions of certain ions like iron, titanium, fluorine or boron modified the basic 45S5 glass network. We used several histological and biochemical parameters to interpret the results found in terms of the used model. Regarding 45S5 as a reference, we found that osteoblasts cultured on iron-doped bioactive glass showed a more flattened morphology, and both lower proliferation rate and osteoblast expression. Osteoblasts cultured on titanium-doped glasses also showed a flattened morphology, but higher proliferation and remarkably higher osteoblast expression. On fluorine- and boron-containing glasses the osteoblasts showed a rather compact morphology, a normal proliferation but only moderate osteoblast expression. With microprobe analysis it was shown that the formation of calcium and phosphorus on titanium-doped glass was relatively lower and the release of sodium slower when compared with 45S5. Osteoblasts cultured on titanium-doped bioactive glasses demonstrated superior histological and biochemical parameters when compared with the other glass types. Further research into the physico-chemical properties and the in vivo behaviour of doped bioactive glasses is recommended.

Alkaline Phosphatase↗

PubMed1994

Long-term in vivo study of plasma-sprayed coatings on titanium alloys of tetracalcium phosphate, hydroxyapatite and alpha-tricalcium phosphate.

In order to study the interaction of calcium phosphate coatings with bone tissue, coated titanium plugs of standard size were implanted in dog femora. The bone bonding and bone formation of hydroxyapatite, alpha-tricalcium phosphate (alpha-TCP) and tetracalcium phosphate plasma-sprayed coatings were evaluated by mechanical push-out tests and histological observations after 3, 5, 15 and 28 months of implantation. During this time all coating types degraded. alpha-TCP showed the most significant degradation after 3 months of implantation. Hydroxyapatite and tetracalcium phosphate showed significant signs of degradation after about 5 months of implantation. All coatings showed a small increase in bone bonding after 5 months of implantation. In general, all types of implants showed similar bone response, some bone contact and several remodelling lacunae along the surfaces after long-term implantation.

Alloys↗

PubMed1993

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

Plasma-sprayed ceramic coatings of fluorapatite (FA), magnesiumwhitlockite (MW), and hydroxylapatite (HA), and noncoated Ti-6Al-4V alloy (Ti) implants were evaluated histologically and histomorphometrically in a goat animal study. Cylindrical Ti-6Al-4V plugs were plasma-spray-coated with FA, MW, and HA. Noncoated, grit-blasted Ti plugs served as controls. The plugs were implanted into the right femur and left humerus of 20 adult goats. The results were evaluated using descriptive histology and histomorphometry. The histomorphometry consisted of measurements of bone apposition and coating thickness. The results demonstrated that FA showed a high amount of bone apposition without signs of degradation or dissolution. MW showed considerable reduction in thickness and at 12 weeks an adverse tissue reaction. However, at 25 weeks the amount of bone apposition was significantly increased compared with the 12-week implants. HA revealed considerable and progressive reduction in thickness and at 25 weeks a lower amount of bone apposition than FA and MW. At 12 weeks the Ti implants did reveal bone apposition, although frequently localized fibrous tissue was visible. At 25 weeks the Ti implants did not differ in bone apposition from the HA implants. Further studies are necessary on the effect of degradation or dissolution of HA on the compatibility with bone.

Alloys↗

PubMed1993

Hydroxylapatite/poly(L-lactide) composites: an animal study on push-out strengths and interface histology.

In the development of new materials for resorbable systems for bone fixation and replacement, composites of hydroxylapatite and poly (L-lactide) (HA/PLLA) were tested. In a transcortical implantation model in goats the interactions at the bone-implant interface were studied with post-operative intervals up to 1 year. Push-out testing of the implants indicated that PLLA reinforced with 50 wt% hydroxylapatite or PLLA plasma-sprayed with a hydroxylapatite coating of 50 microns thickness increases interfacial shear strength at 3 months of implantation when compared to unfilled poly(L-lactide) (P < .01). Scanning electron microscopy showed that the failure mode was predominantly at the coating-implant interface. Implantation periods longer than 3 months did not result in a significant increase in push-out strength because of the resorbing PLLA matrix. In support of the above findings there was histological evidence, on a light microscopical level, of increased bone contact at the interface for the composites, HA incorporated in or coated on PLLA, compared to unfilled poly(L-lactide).

Animals↗

PubMed1993

Histological and biochemical evaluation of osteoblasts cultured on bioactive glass, hydroxylapatite, titanium alloy, and stainless steel.

We investigated the behavior of fetal rat osteoblasts cultured on four bone replacing materials: bioactive glass, hydroxylapatite, a titanium alloy, and stainless steel. The cultures were histologically examined for individual cell morphology and osteoblast expression after several periods of time using scanning electron, fluorescence, and normal light microscopy. Other cultures were used for biochemical determinations of alkaline phosphatase activity (APA) and DNA content. Osteoblasts cultured on bioactive glass showed a better osteoblast-like morphology and a higher proliferation rate, leading to confluent cultures with higher cell density and a generally better expression of the osteoblast phenotype in comparison with the other substrates. The confluent bioactive glass cultures also showed significantly higher DNA content and APA as well as the calculated APA/DNA ratio. Based on the evaluation of histological and biochemical parameters we conclude that osteoblasts cultured on bioactive glass show a generally better osteoblast character than on the other materials.

Actins↗

PubMed1993

In vitro study on the integrity of a hydroxylapatite coating when challenged with staphylococci.

An in vitro study was performed to evaluate the effect of Staphylococcus aureus and Staphylococcus epidermidis on the integrity of a hydroxylapatite coating. The coating plasma-sprayed on poly(L-lactide), showed dissolution during a 24 h incubation period. This was indicated by an increase in pH and calcium release in the buffer solution. After 4 h of incubation, calcium levels decreased due to the precipitation of calcium phosphate complexes on the coating. The bacteria digested or dissolved the coating, creating irregularly shaped holes. Although the integrity of the hydroxylapatite coating was focally damaged within 2-4 h of incubation with staphylococci, the extent of the damage was only marginal. Due to the formation of a layer of CaP precipitates though, bacteria could not be counted accurately after 4-8 h of incubation. This model could reveal part of the failure mechanism of infected hydroxylapatite coated implants.

Calcium↗