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PubMedDate not supplied

[Distensibility changes in the thoracic aorta after stent-graft implantation. Experimental study in healthy and atheromatous animals].

UNLABELLED: The implantation into the arterial lumen of a stent-graft has repercussions in the metabolism of the different layers of the arterial wall. The authors conducted an experimental study with the purpose of evaluating the mechanical repercussions of an endoprosthesis into the arterial wall in normal and atheromatous animals. METHODS: The main group of animals was divided in two subgroups, the first with atheromatous induction and the second without treatment. Each subgroup was subdivided in two groups, a group with a simulated operation and the other with an endoprosthesis placed into the thoracic aorta. One half of the animals was evaluated at one month and the remaining at three months, with removal of the thoracic aorta. The animals were analyzed with electronics methods to assess the elasticity of the thoracic aorta. RESULTS: The study found that ePTFE endoprosthetic grafts placed in atherosclerotic animals increased the intimal hyperplasia and wall alterations compared with the control group and the group with implantation in normal animals but this group showed less alterations of atherosclerosis than the group without endoprosthetic grafts. DISCUSSION: Different factors may cause reactive changes in the arterial wall leading to atheromatosis in arteries with endoprosthesis implantation, but the lipid factor in induction of atheromatosis increases the possibility of alteration of the different layers of the arterial wall. The endoprosthesis implantation is an important factor for the development of the mechanical changes in the arterial wall.

Animals↗
PubMed2003

On the effects of cyclic transversal forces on osseointegrated dental implants: experimental and finite element shakedown analyses.

This paper is concerned with the mechanical strength of fixed osseointegrated dental implants subjected to cyclic external loads, applied mainly in a direction orthogonal to their axis. Such a loading condition, seen as a basic design action for the implant, has been given little attention so far. Experimental results and numerical simulations, performed on two- and three-dimensional Finite Element models, are discussed. The shakedown theory is used to show that a common implant design (threaded fixture-abutment-connection screw) is susceptible of low-cycle fatigue failure under loading conditions well within the working range, even if the same design is able to withstand loading of the same type, but applied monotonically, much in excess of the working values. The shakedown analyses give an indication of several possible failure modalities: the low-cycle fatigue either of the implant or of the connection screw, or the loosening of the connection screw itself. Experimental and numerical results are in good qualitative agreement, and both suggest that the issue of transversal cyclic loading on fixed dental implants should be carefully reconsidered in the design phase.

Bone Screws↗
PubMed1996

Studies on pulmonary tissue after administration of mutein VI-HREC TNF-alpha into implantable experimental Morris hepatoma.

Experiments were carried out on Buffalo rats with implantable Morris hepatoma 5123 growing in the skeletal muscles of the limbs. Mutein VI (a protein which differs from the native TNF-alpha molecule in its N-terminal amino acid composition) was administered at a dose of 10 micrograms per rat once a day in a cycle of 8 days. Control animals were given saline (PBS). Ultrastructural changes within the pulmonary tissue were evaluated with an electron transmission microscope (TEM), with special attention paid to endothelial cells and alveolar epithelial cells. Quantitative analysis of neoplastic metastases to the lungs was carried out. The animals given mutein VI compared to those injected with PBS demonstrated a decrease in the number of metastases. TEM pictures showed accumulations of eosinophilic granulocytes and monocytes in the lumen of the blood vessels. Enhanced activity of endothelial cells was observed. In pulmonary alveoli conglomerates of fibrin, and fragments of damaged cells were found, with erythrocytes, granulocytes and macrophages in their vicinity. The epithelium of pulmonary alveoli showed signs of considerable damage, including necrosis. The mutein VI-hrec TNF-alpha was found to block the neoplastic process, illustrated by a reduction in the volume of lung parenchyma occupied by neoplastic metastases. Also, the ultrastructural changes observed in the pulmonary tissue indicate the possibility of peripheral action of mutein VI after its administration to rats carrying the Morris hepatoma.

Animals↗
PubMed1998

Bone remodelling in the pores and around load bearing transchondral isoelastic porous-coated glassy carbon implants: experimental study in rabbits.

Cylinders of porous-coated glassy carbon were implanted into drill holes made through the articular surface of the medial condyle of both tibiae of ten rabbits for six and 12 weeks. Bone ingrowth and remodelling was examined by radiographic, histologic, oxytetracycline-fluorescence and microradiographic methods. Bone ingrowth into pores and load bearing implants was seen by all examination methods. Bone ingrowth occurred earlier when the pores were facing cancellous bone than cortical bone. Appositional bone formation occurred on the trabeculae a few millimetres from the interface during the early phase of remodelling at six weeks. At 12 weeks resorptive remodelling had occurred both in the surroundings and in those pores that face cancellous bone, whereas the amount of bone still increased in the pores facing cortical bone. In its porous-coated form glassy carbon functions well as a frame for ingrowing bone and it shows good osteoconductivity. Its mechanical properties are suitable for functioning as a structural bone substitute in places where the loads are mainly compressive. The difference between findings at six and 12 weeks indicated physiologic stress distribution and the adverse effects of stiff materials on bone remodelling were avoided by using this isoelastic material.

Journal Article↗
PubMed1997

Progressive focal neurological dysfunction following experimental implantation glioma.

One of the difficulties in understanding peritumoural brain dysfunction is the lack of defined clinical deficits in experimental glioma models. In this study progressive focal neurological dysfunction was measured using the staircase test in rodents subjected to striatal implantation of C6 glioma cells. After 22 days none of the animals, all of which had cortico-striatal tumours ranging in size from 93 to 140 mm3, showed any obvious gross behavioural abnormality. However, contralateral forelimb function was significantly worse than that before surgery by day 7 (p < 0.01) and worse than sham-implanted animals by day 12 (p < 0.01). Using this experimental paradigm the staircase test can be used to measure progressive focal neurological deterioration and evaluate both the mechanisms of, and therapies for peritumoural brain dysfunction.

Analysis of Variance↗
PubMed1998

Animal experimental implantation of an atrial septal defect occluder system.

OBJECTIVE: To establish the implantation technique for the atrial septal defect occluder system (ASDOS) device in an experimental animal model and to determine long term mechanical stability of the device and its in vivo properties in terms of biocompatibility and tissue reaction. MATERIALS AND METHODS: An atrial septal defect was created and the device implanted in 17 pigs (mean weight 30 kg). The implantation technique was refined and modified because of initial technical and anatomical complications during nine acute pilot studies. The technique proved to be feasible in eight subsequent survival studies. Four pigs were electively killed three months after implantation (group 1). The remaining four pigs were killed six months after implantation (group 2). RESULTS: Necropsy showed all devices were embedded in soft tissue three months after implantation. Microscopic examination of atrial septal tissue showed an acute granulomatous inflammatory reaction in group 1 and fibrosis in group 2. The intensity of the inflammatory reaction around the device was clearly milder in group 2, indicating a decline in the inflammatory response with time. Clinical and biochemical investigations indicated acceptable biocompatibility of the device. CONCLUSION: The implantation technique for the ASDOS device in a chronic pig model has been established. Biocompatibility of the device was acceptable.

Animals↗
PubMed1990

Experimental implantation of human umbilical vein grafts in dogs.

Locally produced human umbilical vein grafts (HUVG), using glutaraldehyde as a stabilizing agent, were implanted into 24 mongrel dogs. Different arterial bypass procedures, using HUVG, were carried out in three experimental groups. In Group I, 2 dogs underwent femorofemoral crossover bypass procedures and 6 dogs received aortoiliac bypass procedures. Thrombus formation was found in all HUVG implants of Group I. In Group II, 8 dogs received abdominal aorta HUVG interposition. In Group III, 8 dogs received abdominal aorta HUVG bypass procedures. Patent HUVG implants without thrombus formation, demonstrated by postoperative angiogram, were found in 6 dogs of Group II and 5 dogs of Group III. Morphological and histological studies of the patent HUVG implants retrieved after sacrifice showed on sign of rejection, biodegeneration, or aneurysmal formation. Our preliminary experience with this cost-effective locally produced human umbilical vein graft material was promising and may pave the way to further clinical applications.

Animals↗
PubMed1988

Experimental implantation of hydrogel into the bone.

The present study deals with the application and possibilities of insoluble hydrophilic gels (poly(2-hydroxyethyl methacrylate] as substitutes of bone tissue experimentally. Their biocompatibility is examined with regard to the porous qualities of the implant and to its chemical structure, and their behavior in the cancellous and compact bone is evaluated. It was found that the modifications of hydrogels used in the experiment are biocompatible, with the compatibility increasing in proportion to increasing porosity. The nonporous and microporous hydrogels are not compatible and are demarcated. The sintered macroporous gel is surrounded by a thin fibrin membrane. By adding methacrylic acid to the hydrogel surface, adhesion increases markedly. Marked destruction also appears in the polymer especially in the cancellous bone. By an active destruction of the polymer, no direct phagocytosis can be proved. Upon breakdown of the implant in the compact bone the activity of the macrophages is delayed. When the gel without methacrylic acid is used alone, destruction does not occur even after 193 days. When methacrylic acid is added to the polymer surface, destruction does occur and the implant is filled only by bone trabeculae.

Animals↗
PubMed1982

[Neuroradiological Evaluation of an experimentally implanted tumor into cerebral hemisphere of neonatal beagles (author's transl)].

Twenty-five neonatal beagles were used for this study. Gliosarcoma was injected into the cerebral hemisphere of 7 neonatal beagles (Group I). These animals were then treated by boron neutron capture therapy. The response of the tumor to therapy was evaluated by serial CT scans and 3 times magnification of cerebral angiography. The animals were sacrificed at varying post-therapy periods for histological study. Fifteen neonatal beagles implanted gliosarcoma without therapy (Group II) and 3 normal controls without tumor (Group III) were subjected to the same follow-up studies. (Results) (1) Neonatal beagles with implanted tumor showed moderate degree of ventricular dilatation within a short period. The finding of communicating hydrocephalus was interpreted as initial growth of tumor. (2) Animals after therapy had variable cavitation in the hemisphere that had contained calcium deposit on CT. Moderate dilatation of the lateral ventricle was present without any significant midline shift and there was an area of porencephaly extending out from the right lateral ventricle on CT (Fig. 1, Case 2). Cerebral angiography demonstrated hydrocephalus with an avascular region in the right cerebral hemisphere, compatible with the previously described porencephalic cyst (Fig. 2, Case 2). (3) Three cases out of 7 showed neurological symptoms after tumor implantation (Cases 3, 5 and 6). Carotid angiography showed large temporal lobe tumor with some tumor stain and also some involvement of the right frontal lobe after therapy (Fig. 7, Case 3). In postmortem examination, there was tumor seen coating the right lateral ventricle as well as the left temporal horn. The right cerebral hemisphere was slightly smaller than the left. The left lateral ventricle was remarkably enlarged (Fig. 9). (4) Four out of 7 treated animals with injected gliosarcoma showed no evidence of tumor at postmortem examination. CT demonstrated moderate dilatation of the lateral ventricle without any significant midline shift, an area of porencephaly and definite decrease in size of the right cerebral hemisphere and calvarium (Fig. 4). (5) Fifteen neonatal beagles implanted gliosarcoma without therapy (Group II) developed symptomatic and died within two weeks. (6) Control animals showed no ventricular dilatation or other abnormalities. (7) Microscopic examinations showed no similarities between implanted gliosarcoma and human glioblastoma. (Conclusion) Serial CT scans and magnification cerebral angiography in this experimental model appear extremely helpful in following the effects of therapy and important tool for the evaluation of a tumor growth or regression.

Animals↗
PubMed2004

Capsulorhexis ovaling and capsular bag stretch after rigid and foldable intraocular lens implantation: experimental study in pediatric human eyes.

PURPOSE: To compare the amount of capsulorhexis ovaling and capsular bag stretch produced by various intraocular lenses (IOLs) implanted in pediatric human eyes obtained post-mortem. SETTING: David J. Apple, MD Laboratories for Ophthalmic Devices Research, John A. Moran Eye Center, Salt Lake City, Utah, USA. METHODS: In this nonrandomized comparative study, 16 pediatric human eyes obtained postmortem were divided into 2 groups: Eight eyes were obtained from children younger than 2 years (Group A), and 8 eyes were obtained from children older than 2 years (Group B). All eyes were prepared according to the Miyake-Apple posterior video technique. Six types of rigid and foldable posterior chamber IOLs manufactured from poly(methyl methacrylate) (single-piece), silicone (plate and loop haptics), and hydrophobic acrylic (single-piece and 3-piece AcrySof, Alcon Laboratories) biomaterials were implanted. The capsulorhexis opening and capsular bag diameters were measured before IOL implantation and after in-the-bag IOL fixation with the haptics (or the main axis) at the 3 to 9 o'clock meridian. The percentage of ovaling of the capsulorhexis opening was calculated by noting the difference in the opening's horizontal diameter before and after IOL implantation. The percentage of capsular bag stretch was also calculated by noting the difference in the horizontal capsular bag diameter before and after IOL implantation. RESULTS: All IOLs produced ovaling of the capsulorhexis opening and stretching of the capsular bag parallel to the IOL haptics. There were significant differences in capsulorhexis ovaling and capsular bag stretch (P<.001, analysis of variance) between the 6 IOL types in each group of eyes. The postimplantation difference was significant only between the single-piece hydrophobic acrylic IOL (AcrySof) and the other IOLs. The single-piece hydrophobic acrylic IOL was associated with significantly less capsulorhexis ovaling and capsular bag stretch in both groups (mean 12.06% +/- 0.59% [SD] and 7.6% +/- 1.47%, respectively). CONCLUSIONS: Modern rigid and foldable IOLs designed for the adult population implanted in the capsular bag of infants and children produced variable degrees of capsulorhexis ovaling and capsular bag stretch. The Miyake-Apple posterior video technique confirmed the well-maintained configuration of the capsular bag (with minimal ovaling) after implantation of a single-piece hydrophobic acrylic IOL because of its flexible haptic design.

Capsulorhexis↗
PubMed1990

Separation of non-collagenous proteins of bone formed in titanium implants: experimental study in the rabbit tibia, using a bone harvest chamber.

The non-collagenous proteins of mature cortical rabbit bone and 3 wk old bone specimens formed in titanium implant bone harvest chambers, were separated by means of fine pressure liquid chromatography. It was found that a sufficient amount of bone could be obtained from five bone harvest chambers in five rabbits during a period of 15 wk. A different protein chromatographic pattern was found in bone grown in bone harvest chambers as compared to normal cortical bone from the same region. This indicates a difference in bone quality and shows that this implant design can be used for biochemical analysis of bone formed adjacent to a biomaterial.

Animals↗