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Implantation Model (implantation + model)

Distribution by Scientific Domains

Medical Sciences	50%

Selected Abstracts

Time-related Histopathologic Changes in Fresh Frozen Carotid Xenografts in a Pig-to-Goat Implantation Model

ARTIFICIAL ORGANS, Issue 10 2009
Ji M. Chang
Abstract We performed an animal experiment with an emphasis on time-related histopathologic changes to evaluate the clinical feasibility of immunologically nontreated xenogenic vascular grafts. Bilateral porcine carotid arteries were harvested, and then, after short-term freezing at ,70°C, interposed into goats' carotid arteries. An antiplatelet agent was administered orally for 3 months postoperatively. The goats were randomly assigned to five periods of observation (1 week, and 1, 3, 6, and 12 months after implantation); two animals were observed at each of these times. Doppler ultrasonography was performed periodically during the observation period. At predetermined times, grafts were explanted and examined using hematoxylin and eosin, and Masson's trichrome stains. Immunohistochemical evaluations were conducted with T-lymphocyte indicator and von Willebrand factor. Two goats died prematurely, one from respiratory problems related to anesthesia and the other from pneumonia. A total of 16 grafts from the remaining eight animals were evaluated. Grafts were all patent except one at 3 months after transplantation. Histologically, xenogenic arterial grafts showed early endothelial cell loss at 1 week. This was followed by a progressive spread of recipient endothelial cells from the anastomotic site, and re-endothelialization was complete at 1 month. The degree of neointimal and medial thickening increased until 3 months, and then decreased. At 12 months, no additional growth of the intimal or medial layers was observed. Adventitial inflammation became severe at 3 months, but was reduced at 6,12 months. The proportions of CD3-positive T-lymphocytes among inflammatory cell infiltrations were very low. Fresh frozen xenogenic arterial grafts showed acceptable patency throughout the 12-month period and showed no evidence of being unduly influenced by rejection reactions. [source]

Porous Structures: In situ Porous Structures: A Unique Polymer Erosion Mechanism in Biodegradable Dipeptide-Based Polyphosphazene and Polyester Blends Producing Matrices for Regenerative Engineering (Adv. Funct.

ADVANCED FUNCTIONAL MATERIALS, Issue 17 2010
Mater.
Abstract Synthetic biodegradable polymers serve as temporary substrates that accommodate cell infiltration and tissue in-growth in regenerative medicine. To allow tissue in-growth and nutrient transport, traditional three-dimensional (3D) scaffolds must be prefabricated with an interconnected porous structure. Here we demonstrated for the first time a unique polymer erosion process through which polymer matrices evolve from a solid coherent film to an assemblage of microspheres with an interconnected 3D porous structure. This polymer system was developed on the highly versatile platform of polyphosphazene-polyester blends. Co-substituting a polyphosphazene backbone with both hydrophilic glycylglycine dipeptide and hydrophobic 4-phenylphenoxy group generated a polymer with strong hydrogen bonding capacity. Rapid hydrolysis of the polyester component permitted the formation of 3D void space filled with self-assembled polyphosphazene spheres. Characterization of such self-assembled porous structures revealed macropores (10,100 ,m) between spheres as well as micro- and nanopores on the sphere surface. A similar degradation pattern was confirmed in vivo using a rat subcutaneous implantation model. 12 weeks of implantation resulted in an interconnected porous structure with 82,87% porosity. Cell infiltration and collagen tissue in-growth between microspheres observed by histology confirmed the formation of an in situ 3D interconnected porous structure. It was determined that the in situ porous structure resulted from unique hydrogen bonding in the blend promoting a three-stage degradation mechanism. The robust tissue in-growth of this dynamic pore forming scaffold attests to the utility of this system as a new strategy in regenerative medicine for developing solid matrices that balance degradation with tissue formation. [source]

In situ Porous Structures: A Unique Polymer Erosion Mechanism in Biodegradable Dipeptide-Based Polyphosphazene and Polyester Blends Producing Matrices for Regenerative Engineering

ADVANCED FUNCTIONAL MATERIALS, Issue 17 2010
Meng Deng
Abstract Synthetic biodegradable polymers serve as temporary substrates that accommodate cell infiltration and tissue in-growth in regenerative medicine. To allow tissue in-growth and nutrient transport, traditional three-dimensional (3D) scaffolds must be prefabricated with an interconnected porous structure. Here a unique polymer erosion process through which polymer matrices evolve from a solid coherent film to an assemblage of microspheres with an interconnected 3D porous structure is demonstrated for the first time. This polymer system is developed on the highly versatile platform of polyphosphazene-polyester blends. Co-substituting a polyphosphazene backbone with both hydrophilic glycylglycine dipeptide and hydrophobic 4-phenylphenoxy group generates a polymer with strong hydrogen bonding capacity. Rapid hydrolysis of the polyester component permits the formation of 3D void space filled with self-assembled polyphosphazene spheres. Characterization of such self-assembled porous structures reveals macropores (10,100 ,m) between spheres as well as micro- and nanopores on the sphere surface. A similar degradation pattern is confirmed In vivo using a rat subcutaneous implantation model. 12 weeks of implantation results in an interconnected porous structure with 82,87% porosity. Cell infiltration and collagen tissue in-growth between microspheres observed by histology confirms the formation of an in situ 3D interconnected porous structure. It is determined that the in situ porous structure results from unique hydrogen bonding in the blend promoting a three-stage degradation mechanism. The robust tissue in-growth of this dynamic pore forming scaffold attests to the utility of this system as a new strategy in regenerative medicine for developing solid matrices that balance degradation with tissue formation. [source]

Mifepristone (Ru486) Antagonizes Monocyte Chemotactic Protein-3 Down-Regulation at Early Mouse Pregnancy Revealing Immunomodulatory Events in Ru486 Induced Abortion

AMERICAN JOURNAL OF REPRODUCTIVE IMMUNOLOGY, Issue 1 2004
Jaya Nautiyal
Problem:, The survival of an embryo bearing the paternal antigens within the immunocompetent environment of the maternal uterus renders ,pregnancy' to be a state of immunological paradox. The ratio of Th1/Th2 responses is crucial for pregnancy maintenance. Monocyte Chemotactic Protein-3 (MCP3) is a pro-inflammatory, CC chemokine and a Th1 effector which is capable of eliciting significant anti-tumoral immune responses. Method of study:, MCP3 expression was investigated in the murine uterine tissue at different days of initial pregnancy and the effect of RU 486 in immature and delayed implantation model studied using Western blotting and Immunocytochemical techniques. Results and conclusion:, Our results show very high uterine MCP3 expression during pre-implantation followed by a significant MCP3 down-regulation at peri-implantation and low levels of MCP3 during post-implantation period. At the peri-implantation stage, embryos exhibited lowered MCP3 expression when compared with the pre-implantation stage. Ru486, a progesterone antagonist when given in a competitive mode with progesterone resulted in a massive surge in MCP3 expression in both immature mice and delayed implantation models. We hypothesize that it is imperative for MCP3 expression to be down-regulated for the success of pregnancy. The cross-talk between Ru486 and amplified MCP3 expression may be one of the mechanisms by way of which RU486 performs its abortificient and anti tumor role. [source]

Changes in histone modification upon activation of dormant mouse blastocysts

ANIMAL SCIENCE JOURNAL, Issue 6 2007
Tamako MATSUHASHI
ABSTRACT Gene expression in the implanting blastocyst is altered by stimulation with estrogen secreted from maternal ovaries. In the present study, to understand the mechanism regulating the changes in gene expression, diverse histone modifications in blastocysts were studied using a delayed implantation model, in which embryos were kept in a dormant state in the uterus by maternal ovariectomy and progesterone treatment, and then activated by injection with estrogen. Total transcriptional activity increased markedly in activated embryos, and immunocytochemistry with antibodies recognizing specific histone modifications revealed differential modification of several histones in the trophectoderm (TE) and inner cell mass (ICM) of dormant and activated embryos. High levels of histone H3 lysine 9 (H3K9) dimethylation, which suppresses gene expression, were observed in the ICM, but not in the TE, of dormant embryos, and the levels decreased when the embryos were activated, consistent with changes in transcriptional activity. Substitution of histone H3.3, a variant of H3, for dominant H3.1 increased in activated embryos, suggesting that histone substitution is involved in inducing gene expression associated with activation. In the nucleus, H3.3 was mainly localized in the nucleoli of activated embryos but not in those of dormant ones. In contrast, there were no obvious differences in the trimethylation of histone H3K9 or the acetylation of histones H3K9, H3K18 and H4K12 between dormant and activated embryos. These results suggest that a decrease in H3K9 dimethylation contributes to the acquisition of implantation competence by releasing genes from suppression. In addition, histone H3.3 substitution seems to be involved in global gene activation and facilitates the prompt recovery of dormant blastocysts to the active state by inducing rRNA synthesis, resulting in an increase in translational activity. [source]

Tissue response to titanium implantation in the rat maxilla, with special reference to the effects of surface conditions on bone formation

CLINICAL ORAL IMPLANTS RESEARCH, Issue 6 2003
Masaki Shirakura
Abstract: Tissue responses to titanium implantation with two different surface conditions in our established implantation model in rat maxillae were investigated by light and transmission electron microscopy and by histochemistry for tartrate-resistant acid phosphatase (TRAPase) activity. Here we used two types of implants with different surface qualities: titanium implants sandblasted with Al2O3 (SA-group) and implants coated with hydroxyapatite (HA-group). In both groups, bone formation had begun by 5 days postimplantation when the inflammatory reaction had almost disappeared in the prepared bone cavity. In the SA-group, however, the bone formation process in the bone cavity was almost identical to that shown in our previous report using smooth surfaced implants (Futami et al. 2000): new bone formation, which occurred from the pre-existing bone toward the implant, was preceded by active bone resorption in the lateral area with a narrow gap, but not so in the base area with a wide gap. In the HA-group, direct bone formation from the implant toward the pre-existing bone was recognizable in both lateral and base areas. Many TRAPase-reactive cells were found near the implant surface. On the pre-existing bone, new bone formation occurred with bone resorption by typical osteoclasts. Osseointegration around the implants was achieved by postoperative day 28 in both SA- and HA-groups except for the lateral area, where the implant had been installed close to the cavity margin. These findings indicate that ossification around the titanium implants progresses in different patterns, probably dependent on surface properties and quality. Résumé Les réponses tissulaires à l'implantation du titane avec deux conditions de surfaces différentes dans le maxillaire du rat ont étéétudiées par microscopie optique et électronique à transmission et par histochimie pour l'activité de l'acide phosphatase résistant au tartrate (TRAPase). Deux types d'implants avec différentes qualité de surface ont été utilisés : des implants en titane sablés par du AL2O3 (groupe SA) et des implants couverts par de l'hydroxyapatite (groupe HA). Dans les deux groupes la formation osseuse avait démarré cinq jours après l'implantation, lorsque la réaction inflammatoire avait presque disparue de la cavité osseuse préparée. Cependant, dans le groupe SA le processus de formation osseuse de la cavité osseuse était quasi identique à celle montrée dans un rapport précédent utilisant des implants à surface lisse (Futami et al., 2000) : la néoformation osseuse qui démarre de l'os préexistant vers l'implant, était précédée par une résorption osseuse active dans l'aire latérale avec une brèche étroite, mais pas dans l'aire de base avec un espace large. Dans le groupe HA, une formation osseuse directe de l'implant vers l'os préexistant était reconnaissable tant dans les aires latérales qu'au niveau de la base. Beaucoup de cellules réactives au TRAPase ont été trouvées près de la surface de l'implant. Sur l'os préexistant une néoformation osseuse est apparue avec une résorption osseuse par des ostéoclastes typiques. L'ostéoïntégration autour des implants a été achevée au jour 28 après l'opération tant dans le groupe SA que HA excepté pour l'aire latérale où l'implant avait été inséré près du rebord de la cavité. Ces découvertes indiquent que l'ossification autour des implants en titane progresse de manière différente dépendant probablement de la qualité et des propriétés de surface. Zusammenfassung Die Gewebsantwort auf implantiertes Titan in einem Rattenoberkiefer. Spezielles Augenmerk auf die Einflüsse der Oberflächenbeschaffenheit auf die Knochenbildung. An unserem etablierten Implantationsmodell am Rattenoberkiefer wurde die Gewebsantwort nach der Titanimplantation von zwei Prüfkörpern mit verschiedener Oberfläche mit Hilfe der Licht- und Transmissionselektronenmikroskopie, sowie mittels Histochemie zum Aktivitätsnachweis der tartratresitenten sauren Phosphatase (TRAPase) untersucht. Wir benutzten hier zwei Implantattypen mit verschiedenen Oberflächen: Mit Al2O3 sandgestrahlte Titanimplantate (SA-Gruppe) und mit Hydroxylapatit beschichtete Implantate (HA-Gruppe). Bei beiden Gruppen begann die Knochenbildung 5 Tage nach der Implantation, sobald die Entzündungsreaktion im präparierten Knochenbett am verschwinden war. In der SA-Gruppe aber, zeigte sich im präparierten Implantatbett ein beinahe gleicher Knochenbildungsvorgang, wie in unseren früheren Berichten für glatte Implantatoberflächen beschrieben (Futami et al., 2000): Die vom bereits vorhandenen Knochen ausgehende Knochenneubildung gegen das Implantat hin erfolgte erst nach einer aktiven Knochenresorption im lateralen Bereich. Es entstand eine minime Spalte zwischen Knochen und Implantat, währenddem im apicalen Bereich eine breitere Spalte entstand. In der HA-Gruppe konnte man sowohl im lateralen, wie auch im apicalen Bereich eine direkt vom Implantat ausgehende Knochenbildung in Richtung des vorhandenen Knochens feststellen. In der Nähe der Implantatoberfläche fand man viele TRAPase-reaktive Zellen. Beim vorhandenen Knochen erfolgte die Knochenneubildung gleichzeitig mit der Knochenresorption durch typische Osteoklasten. Die Osseointegration rund um die Implantate herum erreichte man, ausser im lateralen Bereich gegen den Rand des Implantatbettes hin, in der SA-und der HA-Gruppe am 28igsten postoperativen Tag. Diese Ergebnisse zeigen, dass die Ossifikation um Titanimplantate in verschiedenen Mustern abläuft, wahrscheindlich in Abhängigkeit von der Oberflächeneigenschaft und -qualität. Resumen Se investigó las respuestas tisulares a la implantación con titanio con dos condiciones diferentes de superficie en nuestro modelo establecido de implantación en el maxilar de la rata por medio de microscopía óptica y electrónica de transmisión y por medio de histoquímica para la actividad de fosfatasa alcalina tartrato resistente (TRAPase). Hemos usado aquí dos tipos de implantes con diferentes calidades de superficies: Implantes de titanio pulverizados con Al2O3 (grupo-SA), e implantes cubiertos con hidroxiapatita (grupo-HA). En ambos grupos la formación de hueso comenzó a los 5 días de la implantación cuando la reacción inflamatoria hubo casi desaparecido en la cavidad ósea preparada. De todos modos, en el grupo SA, el proceso de formación de hueso en la cavidad ósea fue casi idéntico a aquel mostrado en nuestro informe previo usando implantes de superficies lisas (Futami et al., 2000): neoformación de hueso, que tuvo lugar desde el hueso preexistente hacia el implante, siendo precedida por reabsorción ósea activa en el área lateral con un espacio estrecho, pero no así en el área basal con espacio ancho. Se encontraron muchas células TRAPase reactivas cerca de la superficie del implante. En el hueso preexistente, la neoformación ósea tuvo lugar con reabsorción ósea con osteoclastos típicos. La osteointegración alrededor de los implantes se logró al día 28 tras la operación en ambos grupos SA y HA excepto para el área lateral, donde el implante se instaló cerca del margen de la cavidad. Estos hallazgos indican que la osificación alrededor de los implantes de titanio progresa con patrones diferentes, probablemente dependiendo de las propiedades y las calidades de la superficie. [source]