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Biomedical subjects

K de Groot

Publications and source records attributed to K de Groot.

At least 19 recordsLinked to original sources
PubMed1992

Tensile strength of the interface between hydroxyapatite and bone.

Tensile strength of the interface between hydroxyapatite (HA) and bone was tested. Scanning electron microscopy was used to observe the tensile failure mode and the morphological change of hydroxyapatite ceramic surface in bone. The porosity of hydroxyapatite is 14% and pore size less than 2 microns. After 2 weeks of implantation, the tensile strength of the interface is 0.72 MPa. After 4, 8, and 16 weeks, the average tensile strength stayed at 1.5 MPa. SEM showed that tensile failure occurred at the HA-bone interface at the second week, but after 4 weeks, the failure occurred between HA particles within the bulk, and not at the HA-bone interface. Calcified tissue was directly deposited on the HA ceramic surface and exits also in the micropores. Near the interface, sintered necks among HA ceramic particles were subjected to biodegradation.

Animals↗
PubMed1992

A finite element analysis of the push-out test: influence of test conditions.

The commonly used method for quantitative evaluation of the strength of a bone-implant interface is the push-out test. In order to give an impulse to standardization and to gain more insight in the biomechanics of the push-out test, a finite element analysis of this test was performed. This study focused on the influence of test conditions on the push-out results. The influence of the following four parameters on the interface stress distribution was tested: (a) clearance of the hole in the support jig, (b) Young's modulus of the implant; (c) cortical thickness; and (d) implant diameter. The distance between the implant and the support jig turned out to be very critical for the occurrence of peak stresses in the interface. Variations of the Young's modulus of the implants resulted in a wide range of interface shear stresses. Variation of the cortical thickness showed a reciprocal relationship between cortical thickness and interface shear stress. However, the interface stress distribution remained uniform under the specific test circumstances. These findings also hold for variations in implant diameter. The present investigation shows that the clearance of the hole in the support jig, and the Young's modulus of the implant are parameters which most strongly influence the interface stress distribution. The clearance of the hole in the support jig is the most critical parameter, but also the parameter that can be controlled most easily. Lack of standardization with regard to these parameters can lead to uninterpretable test results. It is recommended that the clearance of the hole in the support jig is at least 0.7 mm and that push-out results are only compared with each other when materials with similar Young's modulus are concerned.

Animals↗
PubMed1992

Preparation of dense hydroxylapatite or rhenanite containing bioactive glass composites.

The effect of time at 600 degrees C and of small additions of Al2O3 and B2O3 on the sintering of two composite materials of (1) hydroxylapatite (Ca10(PO4)6(OH)2) and bioactive glass (SiO2-CaO-P2O5-Na2O) or (2) rhenanite (CaNaPO4) and bioactive glass were studied. Scanning microscopy, quantitative EDX, x-ray diffraction, helium gas density measurements, and diametral measurements were performed on the resulting composites. No reactions were observed with the SEM or XRD between the hydroxylapatite particles and the glass matrix within sufficient sintering times to achieve maximum density. The rheunanite-containing composites were observed to form Na2O2CaO3SiO2 crystals by x-ray diffraction, probably as a result of dissolution of the rhenanite particle surfaces into the glass phase, the crystals formed in the glass or at the interface of the glass, and the ceramic particles. However, within the short sintering times needed to achieve maximum density the rhenanite particles remained mostly intact. The rhenanite-containing materials gave better results than the hydroxylapatite-containing materials. The glass composition had a great effect on the densification process.

Biocompatible Materials↗
PubMed1992

Evaluation of hydroxylapatite/poly(L-lactide) composites: mechanical behavior.

By mixing hydroxylapatite (HA) into L(-)-dilactide monomer, prior to polymerization to poly(L-lactide) (PLLA), hydroxylapatite filled poly(L-lactide) composites were obtained. This study reports about the mechanical properties of these composites compared with unfilled PLLA. It was concluded that a 30 wt% HA/PLLA composite has better compressive and tensile strengths, higher stiffness and Vickers hardness number than unfilled PLLA (Mv: 125-150,000). Gas sterilization (ethylene oxide) affects molecular weight and flexural strength significantly. Implantation studies revealed loss of 50% of initial flexural strength within 3 weeks, and a faster decline of flexural strength was observed in phosphate buffered saline than in the subcutis of goats. From a mechanical point of view storage at -20 degrees C proved to be a safe method. In its current state HA/PLLA composites can not be used as implant materials that have to resist major forces. However, such composites might be useful in non-loadbearing applications in orthopedic or maxillofacial surgery.

Animals↗
PubMed1992

The ultrastructure of the bone-hydroxyapatite interface in vitro.

Rat bone marrow cells were cultured on plasma-sprayed hydroxyapatite (HA). The cells formed a mineralized extracellular matrix (ECM) that exhibited several characteristics of bone tissue. The interface between this mineralized ECM and the HA was studied at the ultrastructural level with scanning and transmission electron microscopy and x-ray microanalysis. Initially, the deposition of a globular, afibrillar matrix was observed on HA. This was followed by the integration of collagen fibers in this matrix and their subsequent mineralization. At the bone-HA interface two distinctly different interfacial structures were observed. An electron-dense layer with a thickness of 20-60 nm was regularly present, which contained both organic and inorganic material and was rich in glycosaminoglycans. The interfaces differed however, in the presence or absence of an amorphous zone which was free of collagen fibers and had an average thickness of 0.7-0.8 microns. It was frequently seen interposed between the electron-dense layer and the hydroxyapatite. Similar interfacial structures have also been described in the in vivo environment, where they were referred to as lamina limitans-like or cement linelike. From the results of this study, it can be concluded that the described in vitro system is a suitable model to study bone-biomaterial interactions.

Animals↗
PubMed1992

Behaviour of fetal rat osteoblasts cultured in vitro on bioactive glass and nonreactive glasses.

We examined the behaviour of fetal rat osteoblasts cultured upon bioactive glass and nonreactive glasses, and the supposed stimulatory effects of bioactive glass on osteoblasts. Nonreactive glass cultures showed flattened cells with almost no dorsal ruffles. Bioactive glass cultures showed compact cells with dorsal ruffles and filapodia resulting in the formation of a denser cell layer. For confluent nonreactive glass cultures the osteoblast expression was mainly concentrated in the clustered cells which were formed upon the monolayer, whereas for confluent bioactive glass cultures the osteoblast expression was more generally distributed. The production of type I collagen, osteocalcin and an osteoblast-specific antigen was shown by immunocytochemistry for all cultures, although differences in distribution were observed. The bioactive layer of bioactive glass is responsible for a better osteoblast-like morphology, a higher proliferation rate and generally a better osteoblast expression.

Alkaline Phosphatase↗
PubMed1992

Soft tissue response to different types of sintered metal fibre-web materials.

Recently, it has been demonstrated that the soft tissue response to polymeric filter implants was predominantly dependent on the implant surface topography and that variation in the implant material had little effect. The purpose of this study, therefore, was to compare histologically the soft tissue response to sintered fibre-web implants made from different materials and with varying web porosity. Three different fibre-web materials with two different weights and two different porosities were used. The implants were inserted subcutaneously in the dorsum of rabbits. The implants were left in situ for 4 and 12 wk. Histological and tissue compatibility evaluations were performed. It is found that all the tested fibre-web materials show a good biocompatible behaviour. In addition, the results appear to indicate a relation between flexibility of an implant material and tissue behaviour.

Adipose Tissue↗
PubMed1992

Cellular reaction on the intraperitoneal injection of four types of polylactide particulates.

Four types of polylactide particulates, P-L-LA 100, 250, 550 KD and a P-DL-LA 400 KD were injected into the peritoneal cavity of mice. The inflammatory reaction showed an increase in cell number (mainly neutrophilic granulocytes) up to 48 h after which the cell numbers decreased below the control (phosphate-buffered saline). All four polylactide particulates aggregated and intermingled with inflammatory cells. The aggregates remained throughout the investigation period of 6 months. Quantitative measurements showed that standardization of the particle form and size is essential. From this study and other experiments in which calcium phosphates and asbestos were injected intraperitoneally, it is concluded that the inflammatory response observed in the peritoneal cavity is related to the type of material injected and probably to form and size of the individual particles, but not to molecular weight.

Animals↗
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↗