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Biomedical subjects

R Guidoin

Publications and source records attributed to R Guidoin.

At least 127 records · Page 7Linked to original sources
PubMed1988

Characteristics of polyester arterial grafts coated with albumin: the role and importance of the cross-linking chemicals.

Preclotting is mandatory prior to implanting a knitted polyester arterial graft, unless the structure is made impermeable to blood by coating with a bioerodible material. Before achieving wide-spread clinical acceptance, the technique of impregnating with cross-linked albumin must be optimized in order to develop a graft that is immediately implantable, easy to handle and suture and has improved healing characteristics. The choice of the chemical to cross-link the albumin is of paramount importance. In this study two alternative candidates have been evaluated by using a series of tests to measure the physical properties, the morphology and the cytocompatibility of albumin-coated grafts. A carbodiimide cross-linking agent appears more promising than glutaraldehyde, since it is equally effective in producing a blood impermeable prosthesis, yet presents improved biocompatibility and provokes a less intense inflammatory response from the host.

Aldehydes↗
PubMed1988

In vivo evaluation of polyester arterial grafts coated with albumin: the role and importance of cross-linking agents.

Previous in vitro studies have predicted that the type of chemical used to cross-link albumin-coated polyester arterial prostheses may influence the rate of bioerosion of the albumin layer in vivo. This study has confirmed that the healing process of this type of compound prosthesis does indeed depend on the nature and concentration of the cross-linking agent used. Four series of implantations in the thoracic aorta of dogs for scheduled periods for 4 h up to 6 months were conducted using 1.6% glutaraldehyde, 2.5% glutaraldehyde and 0.2 M carbodiimide as the alternative cross-linking agents plus a nonalbuminated preclotted polyester prosthesis which served as the control. The pathology of the explanted grafts revealed that in the short and medium term the rate of healing and the extent of tissue ingrowth was dependent initially on the presence of and later on the rate of bioerosion of the albumin layer. After 3 months in situ, the prostheses coated with albumin cross-linked with 1.6% glutaraldehyde and carbodiimide had healed more rapidly and were invaded by more extensive tissue ingrowth than the one cross-linked with 2.5% glutaraldehyde or the preclotted control. Moreover, the migration of cells over the carbodiimide-treated surface was the most fully developed and most regularly organized of all four series. Immunostaining revealed that the presence of glutaraldehyde induced an inflammatory response which failed to support the growth of normal luminal cells with the endothelial phenotype.

Aldehydes↗
PubMed1988

Fate of polyester arterial prostheses implanted as thoraco-abdominal by-passes in dogs: haematology, pathology, and biochemistry.

This study was designed to evaluate the haematological, pathological and biochemical characteristics of the flow surface in polyester arterial prostheses. Their implantations as thoraco-abdominal by-passes in dogs were scheduled to remain in place for periods ranging from four hours to six months. The haematologic parameters of the hosts were evaluated before implanting the prostheses and before harvesting the graft. To quantify the thrombogenicity of the flow surface, the platelet deposition and fibrinogen uptake were measured by means of an isotopic technique involving Indium-III labelled platelets and iodine-125 labelled fibrinogen. Synthesis of prostacyclin (PGI2) and thromboxane (TXA2) by the internal capsulae was determined by radioimmunoassay. The pathology was assessed according to previously described protocols. The haematologic parameters of the hosts did not alter substantially in the presence of the prostheses. The observed changes, though slight, were not pathologically significant 48 hours after implantation. Platelet and fibrin deposition was highest on the luminal surface of the prostheses 24 hours post-implantation. These decreased and became negligible after one month when the flow surface became smooth and glistening. The PGI2/TXA2 ratio of the luminal surface was much lower than that observed in native aortic tissue. These results show that the large calibre Dacron vascular prosthesis has a flow surface with a low degree of blood compatibility. The concentration of PGI2 on the newly-formed luminal surface remained low. This characteristic and the incomplete endothelialization of the luminal surface might be among the main factors that determine the high failure rate of synthetic prostheses when used as small diameter blood conduits.

6-Ketoprostaglandin F1 alpha↗
PubMed1987

Textile arterial prostheses: is water permeability equivalent to porosity?

Porosity and water permeability are two distinct terms that describe different characteristics of vascular prostheses. The porosity is a measure of the void fraction within the prosthesis wall and is believed to give a rough prediction of the capacity of the graft to anchor newly formed surrounding tissue after implantation, whereas the water permeability indicates the rate at which water can flow through the prosthesis wall and, when measured under physiological pressure conditions, provides the surgeon with information about the need for preclotting prior to implantation. The literature has not always clearly distinguished between these two terms, and some authors in fact have suggested that they both refer to the same property of a prosthesis. In an attempt to clarify the issue, porosity and water permeability measurements were made on 34 commercial vascular prostheses having different textile constructions. Linear regression analysis demonstrated that these two characteristics are only weakly related (r = 0.59). It is therefore recommended that the current draft standards for such devices reference both properties: porosity and water permeability.

Blood Vessel Prosthesis↗
PubMed1987

Physicochemical characterization of a hydrophilic microporous polyurethane vascular graft.

There is still a need for a viable small-diameter synthetic vascular graft. The expanded PTFE device appears to be the best presently available, but is still inferior to the autologous saphenous vein. Recently, a novel microporous, small-diameter vascular graft fabricated from Mitrathane, a polyether urethane urea (PEUU), has been developed. In this article, we report the findings of an in vitro evaluation of the morphological, mechanical, and chemical properties of this new device. The results are compared with those of established vascular prostheses made from alternative materials including expanded PTFE and bovine heterograft, and with natural blood vessels. The PEUU graft displays good mechanical properties in spite of the presence of some structural defects or anomalies. In particular it compares favorably to the expanded PTFE device by providing both superior radial compliance and improved suture tearing strength.

Animals↗
PubMed1987

Blood hemolysis by PTFE and polyurethane vascular prostheses in an in vitro circuit.

In order to improve understanding of the appearance of bright yellow stains in vivo (consecutive to the absorption of bilirubin) on a novel microporous, hydrophilic polyetherurethaneurea vascular prosthesis, the in vitro hemolytic activity of the material was compared with expanded polytetrafluoroethylene and silicone rubber. The results show that the tendency of the polyetherurethaneurea to produce free hemoglobin is low, so that the yellow staining observed is likely to be a result of the contact between the polymer and thrombi: Bilirubin is produced because of hemoglobin degradation in the thrombi rather than an active hemolysis on the surface of the prosthesis itself.

Biocompatible Materials↗
PubMed1987

Microporous hydrophilic polyurethane vascular grafts as substitutes in the abdominal aorta of dogs.

Polyurethanes are emerging as promising biomaterials. A microporous vascular graft fabricated from Mitrathane, a new polyetherurethane urea, appeared to be particularly interesting according to in vitro evaluation and was tested in vivo as an infrarenal aortic substitute (i.d. 5 mm) in 24 dogs. After implantation for scheduled periods ranging from 4 h to 6 mnth, morphology evaluation and healing analysis of the grafts were performed. At harvesting, 18 grafts were patent and 6 were thrombosed. The thrombosed grafts had been implanted for 4 h (1 graft), 1 mnth (2 grafts) and 6 mnth (3 grafts). No macroscopic deposits other than red mural thrombi were observed. At 1 mnth complete external encapsulation was observed in 2 grafts. The capsule then contracted and became thinner; over the long term it shrank, became translucent and incomplete at 6 mnth. Yellow and brown stains appeared on many of the grafts. Characterization of the brown stains showed them to be iron (Fe3+) and the yellow stains were associated with the deposition of a bile pigment (bilirubin).

Animals↗
PubMed1987

In vitro and in vivo characterization of an impervious polyester arterial prosthesis: the Gelseal Triaxial graft.

Over the years, textile polyester arterial prostheses have acquired an excellent reputation for easy handling and good healing characteristics. Until recently, the main drawback in using them was the need for preclotting. This, however, is no longer true. Nonporous polyester grafts which have been coated with an impervious bioerodible layer during manufacture are now commercially available. The Gelseal Triaxial prosthesis is one of this new generation of grafts. It is manufactured by impregnating a Triaxial prosthesis with a gelatin coating. An in vivo and in vitro evaluation of this new device has found that its water permeability is almost zero. It has good handling and conformability characteristics, and its bursting strength is slightly greater than that of the uncoated prosthesis due, no doubt, to the presence of the gel. The rates of degradation of the gelatin coating have proven to be rapid under both in vitro and in vivo conditions. In fact, only a few traces of the gel were found remaining on the graft after 2 wk in the canine thoracic aorta. In addition, this study has demonstrated that the use of a bioerodible gelatin coating, with its ability to promote cellular regeneration, is a feasible approach with which to achieve earlier and more complete biological healing.

Animals↗
PubMed1987

Albumin-coated polyester arterial prostheses: is xenogenic albumin safe?

This paper adds a new dimension to the series of studies concerned with the development of an albumin-coated polyester vascular prosthesis by addressing the question of the origin of the albumin. Previous experiments in dogs have used canine albumin-coated polyester arterial grafts. This study evaluated the biocompatibility of xenogenic material by implanting in dogs prostheses coated with bovine albumin and cross-linked with glutaraldehyde. Two series of albuminated grafts, one gamma radiation sterilized, the other ethylene oxide sterilized, as well as a preclotted control series were undertaken. The origin of the albumin did not appear to be significant. In fact, the healing pattern of the xenogenic albumin coated grafts was identical to that found previously with isogenic albumin. Nor did the method of sterilization produce significantly different pathological results. However, a slower rate of healing with the coated grafts compared to the preclotted controls did appear to be related to the slow rate of albumin erosion and the potentially cytotoxic effect of the glutaraldehyde cross-linking agent.

Albumins↗
PubMed1987

Per-operative uncontrollable bleeding at polyester (Dacron) arterial prosthesis implantation.

An aortobifemoral knitted polyester graft was placed in a 58-year-old woman with aorto-iliac occlusive disease. Although the prosthesis was preclotted in the usual manner, it never became impervious to blood under normal intra-arterial pressure. Examination of the graft showed lipid infiltration not ordinarily seen. We recommend that when a knitted prosthesis fails to preclot a woven graft should be used instead.

Blood Coagulation↗
PubMed1987

Experimental colonization of an expanded polytetrafluoroethylene vascular graft with Staphylococcus aureus: a quantitative and morphologic study.

We developed an animal model to reproduce hematogenous seeding of vascular grafts with Staphylococcus aureus. Expanded polytetrafluoroethylene (ePTFE) grafts were implanted in 41 dogs as thoracoabdominal aortic bypasses for six durations of implantation between 2 hours and 6 months. The inoculum containing an average of 10(8) viable bacteria/ml was then injected intravenously in 1 minute. Normal dog aortas were used as controls. They entrapped very few bacteria (0.7 +/- 1.7 colony-forming unit [CFU]/cm2). Colonization of ePTFE grafts was maximal after 2 hours of implantation (589 +/- 733 CFU/cm2). Bacterial entrapment decreased after 2 days (225 +/- 315 CFU/cm2, p less than 0.001) and 8 days (70 +/- 115 CFU/cm2, p less than 0.001) of implantation, but it was similar after 8 days, 1 month (83 +/- 90 CFU/cm2), or 6 months (93 +/- 143 CFU/cm2) of implantation. Colonization of ePTFE measured after 2 months of implantation (371 +/- 591 CFU/cm2) was significantly higher (p less than 0.001) than after 1 or 6 months of implantation. More than 500 CFU/cm2 were seen in 37% of the prosthetic fragments tested after 2 hours of exposure to blood; 99% of the fragments tested after 6 months of implantation trapped less than 500 CFU/cm2. Scanning electron microscopy showed that staphylococci were mostly seen on native fibrin deposits, particularly after 2 hours and 2 months of implantation. That persistent susceptibility of a flow surface devoid of endothelium to hematogenous bacterial colonization has to be taken into account to prevent delayed graft infections. Furthermore, it would be important to compare the ePTFE with other types of grafts whose healing phenomena are different.

Animals↗
PubMed1987

[Progressive complications associated with polyester arterial prostheses. Study of 61 specimens following surgical excision].

Reports of individual surgical cases tend to be anecdotal because of the unique circumstances surrounding the patient, the surgeon, the intervention and, where applicable, the prosthetic device. To overcome this limitation the authors have taken a wider collaborative approach and report the analysis of 61 explanted polyester arterial prostheses associated with delayed complications on 53 patients reoperated upon in six different French hospitals. One advantage of such an independent and centralized retrieval programme is that the impact of centre specific factors, such as patient selection and surgical techniques, is minimized. Consequently, by following a standardized protocol for the evaluation of the morphologic, pathologic and mineralogic characteristics of the tissue surrounding the excised grafts, as well as the textile structure of the prostheses themselves, it has been possible to distinguish between iatrogenic and disease related complications and to demonstrate a number of general findings associated with the clinical performance of polyester arterial prostheses. Complications such as thromboses, infections and false aneurysms appear to occur randomly after different lengths of implantation, thicker fibrous tissue capsules are associated with velour grafts with highly textured yarns, the incidence of mineralized tissue and of endothelialized luminal surfaces is rare, weft knitted textile prostheses appear less mechanically stable and more sensitive to iatrogenic trauma than warp knitted, and the incidences of lipid and cholesterol adsorption, bacterial colonization and sterile fluid loss need further investigation. These observations lead to the recommendation that for patients with longer life expectancies surgeons should consider selecting low porosity, woven or warped knitted prostheses which contain yarns that have not been highly textured.

Adult↗
PubMed1987

[Fibrous hyperplasia in femoro-popliteal bypasses using treated human umbilical veins].

The authors report two clinical cases of the failure due to fibrous hyperplasia of processed human umbilical vein (HUV) grafts employed as femoro-popliteal bypasses. Failure occurred after 19 months implantation at the proximal anastomosis for one graft and after 10 months at the distal anastomosis for the other. Fibrous hyperplasia was the principal cause of reoperation. The lightly vascularized, more or less compacted fibrin involved, adhering loosely to the HUV, remains thrombogenic at the blood-contacting surface. Superposed onto this phenomenon which is widespread in laboratory animals but uncommon in humans, are the usual causes of failure: delamination of the HUV wall, lipid uptake and bacterial colonization.

Blood Vessel Prosthesis↗
PubMed1986

The initial blood retention properties of arterial prostheses.

The initial contact between blood and vascular grafts may be a determinant of the fate of the implants. They behave in different ways depending upon their nature: the processed human umbilical vein and the bovine heterograft just lead to minimal thrombotic retention; the expanded PTFE is even more antithrombogenic; the porous polyesters which are porous textiles, should be totally impregnated with a thrombotic matrix to make the wall impervious. These observations were clearly determined by exposing the grafts to blood, incorporating either labeled platelets or labeled fibrinogen, and they were correlated by SEM examination.

Arteries↗
PubMed1986

Anastomotic false aneurysms with aortic Dacron graft after twenty-five years.

One of the early diamond crimped knitted polyester (Dacron) grafts was surgically excised after implantation for 25 years in the aorto-biiliac position because of false aneurysm formation at the three anastomotic sites. The sutures were no longer visible. While the areas around the false aneurysm were poorly incorporated, the graft limbs were well encapsulated with some endothelial-like cells on the luminal surface. The integrity of the graft was well preserved despite mild fraying and the disruption of one stitch.

Adult↗
PubMed1986

Degradability of crosslinked albumin as an arterial polyester prosthesis coating in in vitro and in vivo rat studies.

In order to avoid the preclotting procedure in knitted polyester arterial prostheses and in woven models, compound polyester grafts have been proposed, containing preadsorbed collagen or albumin. Since we are currently investigating grafts impregnated with crosslinked albumin, it was decided to establish the degradation rate of this coating after stabilization with either glutaraldehyde (GA) or carbodiimide (CDI). Tests were performed in vitro by incubation in either PBS, plasma or pancreatin and in vivo by implantation in the abdominal cavity of rats. In PBS or plasma in vitro, the coatings were very stable (2% degradation after 144 h incubation), however, in pancreatin the CDI crosslinked albumin degraded much faster than the GA crosslinked albumin (more than 50% degradation in 12 h compared to less than 30% in 48 h). In vivo the degradation rates of the two types of crosslinked albumin were similar (almost all of the albumin having been lost after 4 weeks) but the cellular response was very different: a mild tissue reaction was observed with the CDI crosslinked coating whereas many foreign body giant cells were present on the GA crosslinked material.

Albumins↗
PubMed1986

Chemically fixed human umbilical cord vein grafts as arterial substitutes: potential and limits.

In spite of reported successes, synthetic fabric grafts and microporous and plain synthetic conduits have proven unsuitable for aorto-coronary bypasses and showed weaknesses below the knee. Readily available and uniform diameter vascular substitutes with biological and mechanical properties comparable to human vessels would be of paramount interest. Following reported successes with chemically fixed human umbilical veins (HUV), we have attempted to develop smaller diameter blood conduits and have improved the currently prevalent techniques of fixation, preparation and storage to generate more convenient surgical products. In vitro assessment of the processed HUV demonstrated that the HUV can be easily processed to make an arterial substitute that can be preserved either in a liquid medium or as a dry product. However, the in vivo implantations in dogs led to disappointing results for liquid-preserved or albuminated veins. Critical-point dried grafts gave better results, unfortunately they do not heal and they can only degrade after implantation.

Animals↗