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Biomedical subjects

K de Groot

Publications and source records attributed to K de Groot.

At least 163 records · Page 9Linked to original sources
PubMed1989

Epithelial reaction to percutaneous implant materials: in vitro and in vivo experiments.

The major fact in determining percutaneous implant success is the formation of a stable skin-implant junction. However, the characteristics an implant material must meet to secure a durable percutaneous seal are still unknown. The objective of this study, therefore, is to gain more insight into the mechanisms underlying implant-skin reactions by means of in vitro cell culture and in vivo animal experiments. For the in vitro experiments rat palatal epithelial cells were cultured on various implant materials and the possible influence of the initial surface free energy and state of cleanliness of these materials on the growth rate of cells was studied. The results of these experiments demonstrate no significant relation between these parameters and cellular growth. In the in vivo experiments, plasma-sprayed and dense hydroxylapatite percutaneous implants were inserted into the tibia and dorsum of guinea pigs and into the tibia and onto the cranium of rabbits. The implants were left in situ for 3 weeks to 8 months. Clinical and histological investigations were performed. The results show, that stabilization of a percutaneous implant by bony skeletal tissue is effective in the maintenance of a permanent percutaneous passage.

Animals↗
PubMed1988

Guinea pig and rabbit model for the histological evaluation of permanent percutaneous implants.

The object of this study was to develop a small experimental animal model for a systematic study of the interfacial phenomena between percutaneous implants and skin. Plasma-sprayed and dense hydroxyapatite test implants were inserted into the tibia and dorsum of guinea pigs and into the tibia and on the cranium of rabbits. At preselected periods, the animals were killed and the implants with their surrounding tissues were processed histologically. The results revealed that the tibia and cranial implants had healed uneventfully. The epidermis showed no tendency to grow down into the dermis, but appeared to form a stable junction with the implant surface. Around the dorsal implants, the epidermis migrated downwards and most of these implants were lost 6 weeks after insertion. It was concluded that the guinea pig and the rabbit were a suitable model for studying the pathophysiology of percutaneous wound healing and that the implant location is an important factor for percutaneous implant success.

Animals↗
PubMed1988

Bonding of bone to apatite-coated implants.

Implants of solid sintered hydroxyapatite form very tight bonds with living bone, but are susceptible to fatigue failure. This problem can be overcome by using plasma-sprayed apatite coatings on titanium implants. A very strong bond is formed between bone and this composite material; this was studied in canine bone with plug implants, avoiding any mechanical retention. Mechanical testing showed an interface shear strength at six weeks of 49 MPa with a maximum of 64 MPa after six months. There was histological evidence of direct bonding between the apatite coating and living bone while uncoated control plugs were easily extracted. The results indicate that apatite-coated implants can form a chemical fixation with a strength comparable to that of cortical bone itself. This fixation is far stronger than that provided by current cemented or uncemented fixation techniques.

Adhesiveness↗
PubMed1988

A simple method for preparing thin (10 microM) histological sections of undecalcified plastic embedded bone with implants.

A simple method for preparing undecalcified thin sections of bone with implants has been developed. After exposing a surface of bone and implant in a plastic block by sawing thick sections, the surface is stained prior to making a thin section. A glass coverslip is affixed with a thin layer of cement to the stained surface to stabilize the tissue and implant during sectioning. A mixture of glycerine and water is used as a coolant and lubricant. The orientation in situ is preserved allowing demonstration of bone architecture and cells, and the tissue-implant interface.

Animals↗
PubMed1987

Plasma sprayed coatings of hydroxylapatite.

The technique of plasma spraying has been applied to deposit a thin, dense layer of hydroxylapatite onto a titanium substrate. Bond strength of such apatite coatings with the substrate have been measured, as well as the (absence of) influence of the coating process on fatigue properties of the substrate. Animal studies showed similar histological reactions to apatite coatings as to (well documented) apatite bulk materials.

Animals↗
PubMed1987

Gap junction ultrastructure in rat liver parenchymal cells after in vivo ischemia.

The ultrastructure of gap junctions between rat liver parenchymal cells has been studied after in vivo ischemia, with and without subsequent blood reflow. Freeze fracture replicas were analysed by electron microscopic observation, optical diffraction and morphometric analysis. In control specimens gap junction connexons were widely dispersed and arranged in nearly random fashion over nearly the whole junctional area, with only minute spots of hexagonal connexon arrangement. An ischemic period of 30 min, from which the vast majority of cells are capable of recovery after restoration of the blood supply, usually entails only a slight enlargement of the areas of hexagonally arranged connexons. After 120 min of ischemia without reflow, which results in necrosis of most parenchymal cells, all gap junctions showed a completely hexagonal arrangement of connexons. The numerical density of connexons after 30 and 120 min of ischemia without reflow was significantly higher than in controls, whereas after 30 min of ischemia followed by 2 h of reflow the numerical density had returned to control levels. A fully hexagonal arrangement of gap junction connexons, as occurs after longer periods of ischemia, seems to be related to irreversible cell damage and presumably to metabolic uncoupling of cells. This was preceded by an increase in the numerical density of connexons, which is probably a reversible phenomenon.

Animals↗
PubMed1987

Comparison of calcium phosphate glass ceramics with apatite ceramics implanted in bone. An interface study--II.

In order to study bone tissue interaction on calcium phosphate glass ceramics and on apatite ceramics, cylinders of standard size were implanted in the tibiae of rabbits. The materials were evaluated by radiography, light microscopy and microradiography. Apatite ceramics gave rise to a very close contact with new bone. Glass with an apatite surface evoked bone growth similar to that for apatite ceramics but with a loose contact while glass without an apatite surface gave rise to porous remodelling of new bone without close contact to the implant.

Animals↗
PubMed1987

SDS-PAGE analysis of the protein layers adsorbing in vivo and in vitro to bone substituting materials.

The composition of the protein layer adsorbed to the bone substituting materials, hydroxyapatite, beta-whitlockite, titanium and aluminium, in vivo (intramuscularly in guinea pig) and in vitro, was investigated using SDS-gel electrophoresis (SDS-PAGE). After in vivo implantation for 1 d mainly proteins with molecular weights between 10,000 and 20,000 were adsorbed. After 3 months the biolayer of the implanted biomaterials also contained proteins with molecular weights 35,000, 45,000, 60,000 and 200,000. No large qualitative differences in protein composition of the biolayers on the various implanted materials were found. In vitro incubation with human serum resulted in binding of proteins with estimated molecular weights of 30,000, 60,000 (albumin), 200,000 and greater than 200,000. It is suggested that the differences between in vivo and in vitro protein adsorption are due to proteolysis occurring in vivo in the vicinity of the implanted material.

Adsorption↗
PubMed1987

Chemical implant fixation using hydroxyl-apatite coatings. The development of a human total hip prosthesis for chemical fixation to bone using hydroxyl-apatite coatings on titanium substrates.

Sintered hydroxyl-apatite implants form very tight bonds with living bone but are susceptible to fatigue failure. Plasma-sprayed apatite coatings on titanium substrates overcome the fatigue problem. The static tensile substrate bond strength of the apatite coating is in excess of 85 megapascals (MPa) (12,000 psi). In a plug implant study designed to discount mechanical retention, a bone bonding shear strength of 64 MPa (9280 psi) was achieved, comparable to the strength of cortical bone. Histologic sections confirm the close bonding between apatite coating and living bone. In a canine total hip arthroplasty study, the apatite-coated implants proved far superior to the uncoated controls. Uncoated prostheses were surrounded by fibrous tissue and were easily extracted from the femur at any postoperative time. The apatite-coated implants were rigidly fixed within three weeks with demonstrable bone formation up to the implant surface. Bony defects up to 2 mm in depth were filled with bone within six weeks. The hypothetical mechanism of bone bonding is chemical. Hydroxyl-apatite coatings permit an implant fixation far superior to current methods using either cemented or cementless techniques. The plan is to study a human total hip prosthesis with hydroxyl-apatite coating for chemical fixation to bone.

Animals↗
PubMed1986

The biological performance of calcium phosphate ceramics in an infected implantation site: I. Biological performance of hydroxyapatite during Staphylococcus aureus infection.

In the present study the biological performance of macroporous and dense hydroxyapatite after implantation in the rat middle ear was evaluated during an induced Staphylococcus aureus middle ear infection. The course of the infection was similar to that in the absence of an implant. Hydroxyapatite was frequently integrated with fibrous ingrowths in the middle ear lumen, originating solely from the infection. Good epithelial covering of the implant with all types of epithelial cells of importance for middle ear defence, was found. Increase of the exudate in the pores due to the infection was relatively small, and most of the exudate was restricted to pores on the implant surface. The bony tissue in the pores was not influenced significantly by the induced infection. Degradation of hydroxyapatite was consistent with earlier results obtained in the non-infected middle ear. The results obtained so far suggest that hydroxyapatite is highly suitable for middle ear implantation.

Animals↗
PubMed1986

Macropore tissue ingrowth: a quantitative and qualitative study on hydroxyapatite ceramic.

The aim of this study was to obtain more information about macropore tissue ingrowth into the pores of sintered hydroxyapatite implanted in the rat middle ear, for the assessment of the usefulness of this material in reconstructive middle-ear surgery. The exudate filing the pores during the early post-operative period was gradually replaced by equal amounts of fibrous tissue and bone. The percentage of the macropore area occupied by bone was directly correlated with the macropore size. Bone was deposited not only from the pore wall towards the pore centre, but also in the opposite direction. Bonding osteogenesis was demonstrated. At sites of mechanical irritation, the presence of multinucleated cells and proliferatively active mononuclear phagocytes persisted for as long as a year. Under appropriate conditions hydroxyapatite seems to be a promising material for bone substitution in reconstructive middle-ear surgery.

Animals↗
PubMed1986

A comparative study of different beta-whitlockite ceramics in rabbit cortical bone with regard to their biodegradation behaviour.

Different beta-whitlockite ceramic cylinders of standard size were implanted in the tibiae of rabbits to study the influence of micropores and chemistry on the biodegradation rate. The materials were evaluated by radiography and light microscopy. Surface chemistry was varied by the addition of impurities, while different applied pressures before sintering and different sintering temperatures gave rise to different micropores. Both factors influenced the biodegradation rate.

Animals↗
PubMed1985

Interaction of biodegradable beta-whitlockite ceramics with bone tissue: an in vivo study.

The biodegradation of different porous beta-whitlockite materials are studied by in vivo experiments, radiographic follow-ups and light microscopy observations. The materials were implanted in rabbit tibiae for 16 month. Micropores play an important role in the biodegradation rate. The resorbing materials evoke an inflammation with plasma cells. The resorption starts in the medulla, and the phagocytosed particles are removed to the lymph nodes. Normal bone function can be restored after all the implant material is resorbed.

Animals↗