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R Guidoin

Publications and source records attributed to R Guidoin.

229 records · Page 13Linked to original sources
PubMedDate not supplied

Endothelial cell behavior on vascular prosthetic grafts: effect of polymer chemistry, surface structure, and surface treatment.

When implanting any vascular prosthetic grafts, one important goal to ensure long-term patency is achieving complete endothelialization of the luminal surface, a process that has rarely been observed clinically in humans. Seeding vascular grafts with endothelial cells has been seen as an attractive approach but has not been clinically convincing. A determining factor may be the type of polymer and surface structure. Using organotypic culture assays, the present investigation studied the effect of different polymers, surface structures, and surface treatments on endothelial cell behavior. The materials tested were polyester (PET), polytetrafluoroethylene (PTFE), polyesterurethane (PESU), and polyetherurethane (PETU) grafts with different surface structures. The surface treatments on the PET grafts included impregnation with cross-linked albumin, collagen, and gelatin, and treatments with fluoropolymer and electrically conducting polypyrrole polymer. Low density polyethylene (LDPE) and polydimethylsiloxane (PDMS) sheets (smooth surface, plain wall) were used as controls. After incubation for 7 days at 37 degrees C, cell adhesion and migration on the different polymers and structures were as follows: woven and knitted PET (high porosity) > PTFE, PESU, PETU hydrophobic (low porosity) > PETU hydrophilic, LDPE, PDMS (no porosity). Cell density results showed no difference between polymers and porous structures and a higher cell density on smooth nonporous surfaces. Compared with the nonimpregnated PET structures, knitted PET treated with albumin, collagen, or gelatin showed slight decreases of cell adhesion. No differences in cell migration and density were reported between any of the PET grafts, except for one polyester graft with a different chemistry than Dacron, which exhibited greater cell migration and lower cell density. Polyester grafts with a fluoropolymer treatment showed lower cell adhesion and migration and higher cell density than the nontreated PET. Finally, the woven PET grafts treated with electrically conducting polypyrrole exhibited contrasting cell behavior depending on the conductivity involved.

Blood Vessel Prosthesis↗
PubMedDate not supplied

Fresh venous femoral autografts and allografts as carotid substitutes in matched dogs from the same litter.

Pathological and biochemical investigations were performed on femoral veins used as fresh autografts and allograft substitutes in the carotid arteries of dogs from the same litter and separated in two groups described as compatible and incompatible after a mixed leukocyte culture (MLC). After 5 months of implantation, all the arterial substitutes were patent. The analyses gave the following results: 1. The haematologic parameters were not affected by the grafts. 2. Light microscopy (LM) and scanning electron microscopy (SEM) indicate a thrombotic accumulation and the presence of inflammatory cells in the compatible and the incompatible allografts. The occurrence of pathological changes was more pronounced in the incompatible group. 3. Immunostaining of anti-factor VIII-related antigen reveals a better preservation of the endothelial cell wall on the autograft. 4. The 6-keto-PGF1 alpha/TXB2 ratios of the autografts and the compatible allografts were similar.

6-Ketoprostaglandin F1 alpha↗
PubMedDate not supplied

Chemically processed bovine heterografts of the second generation as arterial substitutes: a comparative evaluation of three commercial prostheses.

The use of chemically processed bovine heterografts is primarily confined to the construction of arterio-venous blood accesses in those patients requiring hemodialysis, plasmapheresis or chemotherapy. The grafts of the first generation i.e. Artegraft and Solcograft are now being supplanted by those of the second generation i.e. Reinforced Artegraft, Solco P and NCGT. We have investigated these three types of arterial prostheses as a biomaterial in terms of sterility, inflammatory response and cytocompatibility and as a blood conduit in dogs in terms of patency and healing. For each type of graft, two implantations were carried out for durations of 4 hours, 24 hours, 48 hours, one week, two weeks, one month, three months, and six months. Therefore a total of 48 grafts were implanted. All grafts but five were patent at sacrifice: thromboses were observed in two Reinforced Artegraft (after two weeks and after one month) and in three NCGT (after 24 hours, after 48 hours, and after one month). Therefore the following patencies were observed: Reinforced Artegraft 14/16, Solco P 16/16 and NCGT 13/16. In all the patent grafts, the healing was reduced to the formation of a pannus along both anastomoses; thrombotic accumulations were observed on the surface defects of the grafts, particularly the NCGT graft. The Reinforced Artegraft presents only minor advantages over the previous Artegraft; the Solco P, somewhat more acceptable is no longer commercially available since the manufacturer withdrew it after early clinical failures. The improvements noted in the bovine heterografts of the second generation appear to be marginal as compared to those of the first generation.

Anastomosis, Surgical↗
PubMedDate not supplied

New frontiers of vascular grafting.

Vascular grafting can be a very rewarding surgical technique: following surgery, most patients will maintain their autonomy and, in many cases, will be able to return to work. Should small diameter calibre substitutes be required, the autologous saphenous vein is the gold standard. If not available, the expanded PTFE is probably the best choice. For medium and large diameters, the polyesters (Dacron) are recommended provided they have a structure adapted to the needs of patients. However, progress in the last few years is not related to improvements in the grafts themselves. The only breakthrough has come with the success of graft seeding. This is the reason why other approaches have been proposed to restore or improve blood flow in atherosclerotic arteries: medication, sympathectomy, dilatation, laser endarterectomy, stent and spinal cord stimulation. All those approaches have more and more precise indications: they can supplement vascular grafting.

Arterial Occlusive Diseases↗
PubMedDate not supplied

[Experimental staphylococcal colonization of a Dacron arterial prosthesis (author's transl)].

Infection is certainly the most dramatic complication of reconstructive vascular surgery, even after long periods following the operation. A hematogenous mechanism is often implicated in late infections ; colonization of an arterial graft appears to depend on the material used and cicatrization processes. Animal studies have the disadvantage of requiring repeated operations. We have developed an in vitro infusion system in order to reproduce the bacteremic phenomenon, and to study the conditions necessary for colonization by a staphylococcus of a textile prosthesis (Dacron) in velvet, placed in the "Ex vivo" circulation of a dog for 2 hours. The prosthetic material is colonized very much more easily than a fragment of aorta used a control. The bacterial deposit (y) is a linear function of the inoculum (x) and, by approximation, y = 10(4) x (p 0.01). Colonization is independent of the infusion rate when this varies between 5 and 20 cm/sec. The reproducibility of the results, their quantification, and the ease with which these tests can be employed suggest that such models could be used to assess resistance to bacterial colonization of various materials used for arterial substitution.

Animals↗
PubMedDate not supplied

[On preclotting of woven Dacron vascular prostheses (author's transl)].

The role and the clinical value of common protocols of preclotting for a woven Dacron vascular prosthesis have been investigated. A comparative study of blood loss was carried out for Standard Woven De Bakey protheses inserted in a specially constructed extracorporeal blood circuit with canine models. The system detected transport of blood across the wall of the prostheses. These measurements were supplemented by gravimetric assessment of blood clot density and scanning electronmicroscopy examination of the internal surfaces of the prostheses. The pre-operative protocols investigated included : absence of pre-treatment, precoagulation with anticoagulant-free blood and various techniques using heparinized blood subsequent to an initial blood contact (modified method of Sauvage). The effect of using heparinized animals was also investigated. Leakages in unclotted prostheses could be reduced almost five fold by any precoagulation technique. Heparinization did not cause a significant increase in leakage and considerably improved the quality of the newly deposited blood product lining on the prostheses which consisted almost entirely of fibrin and eliminated any embolization.

Animals↗
PubMedDate not supplied

[Glutaraldehyde - fixed human umbilical cord vein as a small diameter arterial substitute. Experimentation on the monkey].

Autologous saphenous veins, the preferred substitute material for aorto-coronary, femoro-popliteal and femoro-tibial by-pass, are usable in only 70% of individuals in need of such procedures. The development of small diameter substitute arteries is therefore essential to broaden the pool of patients who could benefit from this class of cardiovascular surgery. Existing substitutes, however, present major difficulties and have had limited success. In this laboratory, an attempt has been made to develop a vessel of 3 millimetres or less in diameter derived from human umbilical cord processed in glutaraldehyde. This substitute can be stored in 45% ethanol or dessicated by critical point drying. This device had been implanted as a segment of abdominal aorta in eight primates (Macaca fascicularis). Preliminary results are disappointing. The indicate that retention of a patency for more than a year post-implantation is difficultly achievable and that connective tissue hyperplasia leading to occlusion at the anastomoses is a major problem. Similar but larger diameter by-passes in the order of 6-8 millimetres should be investigated in greater detail, in order to better establish the "in-vivo" behavior of this class of tissue prosthesis. This would address the more fundamental issues pertaining to the clinical usefulness of fixed biological tissue by-pass devices.

Animals↗
PubMedDate not supplied

Physical characterization of unimplanted gel filled breast implants. Should old standards be revisited?

Physical characterization of unimplanted gel filled mammary prostheses was undertaken using both destructive and non-destructive test methods. Physical properties measured included mass, volume, optical transmittance, coefficient of kinetic friction, mechanical stiffness, dynamic response to a stationary random vibration, bursting strength, elasticity of the envelopes, and nuclear magnetic resonance relaxation times. The data obtained from this study will provide reference points for quantifying the rate of degradation of prostheses in past and current clinical use. Some of the test methods are suitable for use as routine quality control procedures to improve the uniformity of the properties and performance of breast prostheses. This investigation also showed that some currently used prostheses do not comply with the relevant American Society for Testing and Materials standards, or even with the manufacturers' own stated claims or specifications.

Breast Implants↗
PubMedDate not supplied

Why make monofilament sutures out of polyvinylidene fluoride?

In recent years some clinical reports have associated suture failures with polypropylene monofilaments. Therefore there is interest in developing an alternative suture material that is less thrombogenic than polyester and similar in handling characteristics but less prone to mechanical failure than polypropylene. To this end, Peters Laboratoire Pharmaceutique has developed a new monofilament suture material from polyvinylidene fluoride (PVDF), which has been subjected to a special treatment to modify its crystalline form and level of crystallinity. The purpose of this study was to evaluate its mechanical, chemical, and biologic properties and to compare its performance, in a peripheral vascular application, to that of a polypropylene control. A series of in vitro tests were performed to study the morphology, tensile properties, creep, surface chemistry, thermal characteristics, and resistance to iatrogenic trauma. In addition, an in vivo trial was undertaken in which vascular prostheses anastomosed with either PVDF or polypropylene sutures were implanted as a thoracoabdominal bypass for 6 months in the dog. Histologic and degradation analyses were performed on the explants. The results from the mechanical tests on 4-0, 5-0, and 6-0 PVDF and polypropylene sutures demonstrated that although both materials have similar breaking strengths, the PVDF has a higher extension at break, has less delayed extension when under tensile creep testing, and suffers less trauma than the polypropylene when compressed by a standard needle holder. While chemical analyses found evidence of surface oxidation on both types of sutures, thermal analysis confirmed that the level of crystallinity of the PVDF polymer is higher than that of the polypropylene control. During the pilot study in animals, PVDF sutures were found to have good handling and frictional characteristics that facilitated the tying of knots. Histologic analysis of the explants found no inflammatory cells in the tissue surrounding either the PVDF or polypropylene sutures, and scanning electron microscopic examination of the cleaned suture surfaces found no evidence of degradation during 6 months in vivo. Though preliminary in nature, these findings indicate that monofilament sutures made from PVDF provide an attractive alternative to those made from polypropylene for use in cardiovascular surgery. In addition to providing acceptable in vivo behavior and being easy to manipulate and more resistant to iatrogenic injury, PVDF materials can be sterilized by beta or gamma radiation and so can reduce dependence upon ethylene oxide and chlorofluorohydrocarbons.

Animals↗
PubMedDate not supplied

Uptake of 3H-7-cholesterol along the arterial wall at an area of stenosis.

Abnormal uptake of atherogenic substances and lipid infiltration have been believed to contribute to the localized genesis and development of atherosclerosis, as well as to late failures of synthetic arterial prostheses. To verify the theoretical prediction that accumulation of lipoproteins on the luminal surface of arterial walls occurs in the regions of disturbed flow, we have carried out an in vitro mass transfer experiment to test the effect of a pseudo steady recirculation flow on the uptake of 3H-7-cholesterol by the arterial wall at a surgically created stenosis. It was found that, as predicted by the theory, in the flow field of the stenosis the uptake of labeled cholesterol reached a maximum around the reattachment point of the vortex distal to the stenosis, where the wall shear stress was lowest (zero). This value of the highest uptake rate was almost twice the average, whereas the uptake level was at a minimum at the stenosis itself where the wall shear stress was highest. The lowest uptake was only 60% of the average. These results provide strong support to our hypothesis, based upon the theory that, in addition to the flow induced changes to the biologic function of endothelial cells, the disturbed flow with slow recirculation itself favors the accumulation of atherogenic lipoproteins at the blood-endothelium boundary, therefore playing an important role in the localized pathogenesis and development of atherosclerosis.

Animals↗
PubMedDate not supplied

Localization of atherosclerosis in arterial junctions. Modeling the release rate of low density lipoprotein and its breakdown products accumulated in blood vessel walls.

Arterial bifurcations and surgically created junctions at anastomoses are places where blood flow may be disturbed and slow recirculation may occur. To address the hypothesis that such disturbances in flow may result in atherogenesis, the transfer of atherogenic substances from vessel wall to flowing blood was studied theoretically using a two dimensional T-junction model. Calculations showed that the transfer of atherogenic substances from vessel wall into flowing blood was suppressed in the two regions of disturbed flow, one in the main vessel, the other in the subsidiary vessel. The lowest release rates were at the points of flow separation and were found to be much lower than those in the undisturbed flow regions. Therefore, our mathematical model predicts that locally disturbed blood flows at arterial bifurcations and surgically created junctions are responsible for two distinct phenomena. First, they provide favorable conditions for the accumulation of LDL at the luminal surface, thus increasing the potential for lipid infiltration into the vessel wall, and second, they impair the transfer into blood of atherogenic substances accumulated in the vessel wall. Such mass transfer abnormalities may account for atherogenesis and late failures of arterial grafts at these sites.

Anastomosis, Surgical↗
PubMedDate not supplied

Magnetic resonance study of virgin and explanted silicone breast prostheses. Can proton relaxation times be used to monitor their biostability?

The development of sensitive and non invasive magnetic resonance (MR) techniques for monitoring the fate of silicones in breast prostheses in vivo requires detailed knowledge of the MR properties of these silicones. To characterize changes in the proton dynamics, relaxation time measurements (T1 and T2) were obtained on virgin and explanted breast prostheses using both spectroscopic and imaging techniques in a magnetic field of 1.5 Tesla. Averaged transverse relaxation times (T2) were observed to depend neither on the measurement technique employed (virgin silicone, T2 = 160 +/- 5 msec with imaging and 154 +/- 9 msec spectroscopically) nor on the effect of being implanted in the body for various periods of time ranging from 4 months to 17 years (explanted silicone, T2 = 164 +/- 16 msec with imaging and 159 +/- 25 msec spectroscopically). Average longitudinal relaxation times (T1) were also found to be similar for virgin and explanted prostheses (virgin silicone T1 = 899 +/- 32 msec, explanted silicone T1 = 879 +/- 75 msec, measured with imaging), but appeared to depend on the measurement technique employed (virgin silicone T1 = 764 +/- 17 msec, explanted silicone T1 = 765 +/- 23 msec, measured spectroscopically). Although the measured relaxation times did not reveal any differences between virgin and explanted prostheses, marginal differences were detected between the relaxation times of explanted prostheses from different manufacturers. More reference data on standard silicone products may be required before changes in implanted silicone can be assessed using proton magnetic relaxation times.

Biocompatible Materials↗