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Biomedical subjects

A Hernando

Publications and source records attributed to A Hernando.

At least 37 records · Page 2Linked to original sources
PubMed1996

Similarity in behavior of polytetrafluoroethylene (ePTFE) prostheses implanted into different interfaces.

The biomaterial ePTFE is widely used in the clinical environment for vascular replacement or bypass, as well as in the repair of tissue defects, especially those involving the abdominal wall. The objective of this study was to evaluate the healing response to ePTFE prostheses implanted into a circulatory interface and a tissue interface, each in a different animal species. For vascular implants, the Sprague-Dawley rat (n = 60) was used, while the New Zealand white rabbit (n = 20) was used in the tissue replacement model. In the former, a vascular microprosthesis measuring 5 mm in length and 1 mm in internal diameter, having a porosity of 30 microns, was implanted into the common iliac artery. In the rabbit, a 7 x 5-cm fragment of ePTFE (Soft-Tissue Patch) was implanted into a defect in anterior abdominal wall that involved all the tissue layers. In this case, the prosthesis was left touching the intestinal loops. The implants were studied between 14 and 90 days of postimplantation by means of light microscopy, scanning electron microscopy, and immunohistochemistry. The latter involved the use of anti-rat (MAC-341) and anti-rabbit (RAM-11) macrophage-specific monoclonal antibodies. The behavior of the ePTFE in the different interfaces (vascular and abdominal wall) was similar with respect to the following aspects: the prosthesis presented a process of encapsulation which was more intense on the outer surface; colonization of the implant was limited to the outermost two thirds, with minimal invasion of the middle portion; colonization was absent on the edges of the prosthesis; collagenization of the interstice of the mesh occurred late; the foreign body reaction taking place on the outer surface was similar in both interfaces, with formation of a barrier consisting of macrophages and giant cells that did not penetrate the prosthesis; and, finally, in neither of the two models was vascular colonization of the PTFE prosthesis observed; rather, the angiogenic process was limited to the periprosthetic zones. The integration of the implant made of ePTFE is similar despite the differences in interfaces and the use of different animal species. The macrophage response does not determine the success or failure of the implant.

Abdominal Muscles↗
PubMed1996

Improvement of the tissue integration of a new modified polytetrafluoroethylene prosthesis: Mycro Mesh.

We studied the behaviour of the different tissue interfaces formed on a new type of prosthesis used for the repair of abdominal wall defects, Mycro Mesh (W. L. Gore and Ass., Flagstaff, AZ, USA), which consists of perforated layers of polytetrafluoroethylene (PTFE). In 20 New Zealand white rabbits, a full-thickness (except skin) 7 cm x 5 cm defect was created in the anterior abdominal wall. The defects were repaired with a prosthetic implant (Mycro Mesh) that was placed in direct contact with abdominal viscera and subcutaneous tissue. At 14, 30, 60 and 90 d post-implantation, samples were obtained from the tissue interfaces formed between the prosthesis and subcutaneous tissue, visceral peritoneum and receptor tissue, respectively. Samples were studied by optical microscopy and scanning electron microscopy. The immunohistological study was made with RAM-11, a monoclonal antibody specific for rabbit macrophages. Tensile strength was measured with an Instron tensiometer using 2 cm wide strips obtained parallel to the shorter axis of the implant. Strips included the prosthesis and two anchor zones on the receptor tissue. Macroscopically, the prosthesis induced little adhesion formation on the visceral peritoneum interface. Microscopically, an organized neoperitoneum and abundant tissue formed on the subcutaneous interface. In the prosthesis perforations, bridges of tissue linked the peritoneal and subcutaneous sides. The macrophage response decreased significantly in intensity between day 14 and day 90 (Student-Newman-Keuls test, P = 0.01). Tensile strength increased significantly (Wilcoxon test, P < 0.05) at every study period. To conclude: the Mycro Mesh prosthesis proved suitable for implantation in sites where it comes in contact with abdominal viscera and it provided good support for the formation of an organized neoperitoneum; the perforations in the prosthetic material improved implant integration; the macrophage response was not altered by the biomaterial and the tensile strength of the prosthesis increased as scar tissue formation and tissular integration of the prosthesis progressed.

Abdominal Muscles↗
PubMed1996

Inhibitor of angiotensin-converting enzyme modifies myointimal origin in an arterial autograft model.

Pharmacologic modulation by an inhibitor of angiotensin-converting enzyme (IACE: cilazapril) of vascular proliferative response to a full-thickness arterial injury (autograft) was studied in rats. An arterial autograft 5 mm long was made in the right common iliac artery of 50 female Sprague-Dawley rats (weight 250-300 g) by microsurgical techniques. The animals were divided into two study groups: group I (controls), 20 animals that underwent arterial autograft but received no other treatment; and group II (cilazapril-treated), 20 rats that underwent arterial autograft and received cilazapril (Roche), 10 mg/day orally (p.o.) in an excipient of 2% arabic gum, for 4 days before operation. Animals were killed on postoperative days 7, 14, 21, 30, and 50, and grafts were studied by light microscopy, scanning and transmission electron microscopy, and morphometry. In the control group, the hyperplasic response had begun by postoperative day 14 and was established by postoperative day 50. In the medial layer, the muscle cells changed in phenotype from contractile to secretory cells. The adventitia had a highly proliferative appearance. In the cilazapril-treated group, fibrin deposits and platelets formed a layer on the internal elastic lamina. This layer appeared to evolve toward an intimal hyperplasia that became quantifiable by postoperative day 21. The medial layer was clearly thinned and showed intense accumulation of lipid microvacuoles, elastic degeneration, and vacuolized cells. Our results suggest that the use of an inhibitor of ACE modified the origin of the intimal hyperplasia in the arterial autograft model. Enhancement of the thrombogenicity of the luminal surface favors myointimal development by thrombus reorganization.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1996

Cyclosporin A delays the presentation of intimal hyperplasia in an experimental model of arterial autograft.

A study was made of the effect of cyclosporin A on intimal hyperplasia in an experimental model of arterial autograft. Fifty female Sprague-Dawley rats weighing 250-300 g were employed. Using a microsurgical technique, an arterial autograft measuring approximately 5 mm in length was implanted in right common iliac artery. Two groups were established: group I (control), consisting of 25 animals subjected only to arterial autograft, and group II (preoperative cyclosporin A), also consisting of 25 animals, which received a daily subcutaneous dose of 5 mg/kg cyclosporin A (Sandimmun, Sandoz) for 4 days before the surgical procedure. The animals were sacrificed on postoperative days 7, 14, 21, 30 or 50. Specimens were studied by optical microscopy, transmission and scanning electron microscopy, autoradiography, and morphometry. Endothelialization of the graft zone was slow in the cyclosporin-treated group. Hyperplasia was delayed notably, but at 30 days the hyperplastic process had improved and at 50 days it was similar to that of the control group. In the cyclosporin-treated group, thymidine was not taken up by the medial layer; the absence of medial thymidine uptake correlated with ultrastructural evidence of medial degeneration with lipid vacuolization of the smooth muscle cells and the presence of macrophages. These results suggest that cyclosporin A does not inhibit intimal hyperplasia but instead delays its occurrence, probably because of the drug's toxicity for smooth muscle cells.

Animals↗
PubMed1995

Atherogenic effects of cyclosporine in an experimental model of arterial autograft.

One of the effects attributed to CsA is a possible acceleration of atherogenic processes, which contributes to the failure of transplanted organs. This study was undertaken to evaluate the effect of CsA and two vehicles, cremophor and ethanol, in an experimental model of arterial autograft in the rat. Female Sprague-Dawley rats were distributed into 3 study groups: Group 1 (control) had an arterial autograft in the common iliac artery without pretreatment; group 2 (CsA-cremophor) animals were pretreated with a daily dose of CsA (5 mg/kg, Sandimmun) for 4 days before the autograft was made; and group 3 (CsA-ethanol + Tween) animals were pretreated for 4 days before implantation of the autograft with CsA in a vehicle of ethanol + Tween at the same dose as used in group 2 (5 mg/kg). The study periods were 7, 14, 21, 30, and 50 postoperative days. Studies were made by optical microscopy, transmission electron microscopy, scanning electron microscopy, and autoradiography. Evaluation of the results showed that in the control group the postoperative repair process lead to formation of an intimal neolayer throughout the entire surgical zone, with scant participation of white cells. Group 2 (CsA-cremophor) had a marked increase in luminal thrombogenicity, important adhesion and infiltration of white cells, loss of smooth muscle cells in the medial layer, and atherogenic degeneration of the medial layer. The generation of the neointimal layer is delayed by 2 weeks with respect to the control group. However, once the neointimal begins to form, its thickness increases rapidly, reaching values similar to those seen in the control group at 50 days. The myointima also shows atherogenic characteristics, such as monocyte-macrophage infiltration and dystrophic calcification. In group 3 (CsA-ethanol+Tween, that is, CsA in a nonoleaginous vehicle), the effects were similar to those seen in group 2 (CsA-cremophor), with a reduction in the presence of lipid-laden cells in the medial layer. Based on these observations, we conclude that CsA per se induced atherogenic changes in the repair process of the arterial lesion that were independent of the vehicle of administration. CsA delayed, but did not inhibit, formation of a myointima and the myointima formed exhibited atherogenic characteristics. The most important effects were noted in the medial layer, which experienced intense degeneration.

Animals↗
PubMed1995

Behavior of cryopreserved endothelial cells in different phases: their application in the seeding of vascular prostheses.

Various methods of cryopreservation of human endothelial cells (EC) were studied to determine their viability and behavior when seeded onto vascular prostheses made of polytetrafluoroethylene (PTFE). Three different protocols were used: (1) cyropreservation of whole umbilical vein, (2) cyropreservation of freshly extracted umbilical EC in suspension, and (3) cryopreservation of EC derived from a first subculture. Fresh EC and EC from a first subculture were used as controls. The viability and growth of these cells in culture media were studied, and basal prostacyclin levels were determined. The cells were assessed morphologically after they were seeded onto PTFE discs. Our results showed that the cryopreservation method that maintained the greatest viability was that in which previously cultured EC were used. Basal prostacyclin levels were significantly different following cyropreservation. However, when these cells were seeded onto PTFE discs their behavior was similar to that of fresh EC.

Blood Vessel Prosthesis↗
PubMed1995

Integration of biomaterials implanted into abdominal wall: process of scar formation and macrophage response.

The behaviour of two biomaterials polytetrafluoroethylene (PTFE) and polypropylene (PL) has been studied, focussing especially on the macrophage response to the implant, as well as on certain aspects of the process of scar formation. A total of 24 animals (white New Zealand rabbits) received prostheses implanted into the anterior abdominal wall in such a way as to involve every layer over an area of 7 cm x 5 cm. The interfaces formed with the visceral peritoneum, subcutaneous tissue layer and the recipient muscle-aponeurotic tissue were assessed. The techniques employed were light microscopy, scanning electron microscopy and immunohistochemical methods, the latter using a monoclonal antibody specific for rabbit macrophages (RAM-11). From the results obtained, it can be seen that: (a) the structure of PL allows its total integration with the reparative tissue, while PTFE becomes encapsulated, on both the subcutaneous and the peritoneal aspects, by orderly connective tissue; (b) the macrophage response, determined on the basis of the presence of labelled macrophages, shows a similar pattern in both biomaterials; and (c) angiogenesis is very intense in the PL mesh, whereas the PTFE prosthesis undergoes almost no vascular colonization.

Abdominal Muscles↗
PubMed1995

Adhesion and stability of fibronectin on PTFE before and after seeding with normal and synchronized endothelial cells: in vitro study.

The possible influence of the cell cycle on the efficacy of endothelial cell (EC) seeding onto the surface of polytetrafluoroethylene (PTFE) prostheses was studied. Likewise the ideal fibronectin concentration and optimal incubation time to guarantee the binding of this protein to the prosthetic surface have been calculated. Synchronized ECs, previously labeled with 3H-thymidine, were used, and the loss of radioactivity was determined at several times throughout the study. The results showed a progressive loss of cells on the prosthetic surface similar to that occurring with the seeding of unsynchronized ECs. The optimal concentration of fibronectin was 20 micrograms/ml, and the optimal incubation time was 1 h.

Adsorption↗