Biomedical subjects

M W King

Publications and source records attributed to M W King.

At least 19 recordsLinked to original sources

PubMed2001

Human truncated Smad 6 (Smad 6s) inhibits the BMP pathway in Xenopus laevis.

A previously identified truncated form of the human Smad 6 gene containing a unique 12 amino acid motif at its N-terminus was studied. We have named this truncated form of the gene Smad 6s, for 'short-form', to distinguish it from the full-length form (Smad 6fl). Reverse transcription-polymerase chain reaction and immunohistochemistry revealed that Smad 6s has a unique pattern of expression in human coronary tissue and is upregulated in diseased heart tissue. We used the expression of human Smad 6s in Xenopus laevis as a model system to assess Smad 6s function. Injection of Smad 6fl RNA (4-cell embryos, 2 x ventral) produced tadpoles with partial secondary axes. In contrast, Smad 6s RNA injected in a similar manner produced tadpoles with a severe 'head-only' phenotype with no morphological appearance of a secondary axis. Mutant Smad 6s RNA lacking the unique 12 amino acids at the N-terminus of the Smad 6s isoform produced no embryonic phenotype, suggesting that this region is important in conferring biological activity. Ectodermal explant assays show that Smad 6s has activity consistent with being a BMP antagonist and can synergize with and enhance the activities of the activin and fibroblast growth factor pathways, all of which are novel findings in this study.

Animals↗

PubMed2000

Analysis of retrieved polymer fiber based replacements for the ACL.

The present retrospective analysis of 117 surgically excised anterior cruciate ligament (ACL) prostheses was designed to elucidate the etiology and mechanisms of failure of synthetic ligamentous prostheses. They were harvested from young and active patients (26 +/- 7 yrs) at various orthopaedic centers in France between 1983 and 1993. The average duration of implantation of augmentation and replacement prostheses were 21.5 +/- 12.6 and 33.2 +/- 25.3 months, respectively. The principal causes for their excision were ruptures and synovitis. Each ACL prosthesis was examined macroscopically, histologically, and, after tissue removal, by scanning electron microscopy (SEM) to determine the model, manufacturer, surgical technique used at implantation, the extent of healing, the site of rupture, and the morphology of the damaged fibers. Fourteen types of ACL prostheses were analysed, each fabricated using a different combination of polymers, fibers and textile constructions. Consequently, they generated a variety of healing characteristics and mechanical responses in vivo. SEM observations revealed that abrasion of the textile fibers as a result of yarn-on-yarn and/or yarn-on-bone contact was a common phenomenon to almost all models, and was the primary cause of prosthetic failure. Healing inside the synthetic ACL was poorly organized, incomplete and unpredictable as the extent of collagenous infiltration into the textile structure did not increase with the duration of implantation. In fact, the collagenous infiltration into certain models appeared to be more detrimental than beneficial since it caused deterioration and fraying of the textile structure rather than serving as a reinforcing matrix around the prosthesis. In conclusion, the present study shows that three mechanisms may be involved in the failure of ACL prostheses: (1) inadequate fiber abrasion resistance against osseous surfaces; (2) flexural and rotational fatigue of the fibers, and (3) loss of integrity of the textile structure due to unpredictable tissue infiltration during healing.

Adult↗

PubMed2000

Selection of a polyurethane membrane for the manufacture of ventricles for a totally implantable artificial heart: blood compatibility and biocompatibility studies.

Membranes made from 4 commercial poly(carbonate urethanes): Carbothane (CB), Chronoflex (CF), Corethane 80A (CT80), and Corethane 55D (CT55), and from 2 poly(ether urethanes): Tecoflex (TF) and Tecothane (TT) were prepared by solution casting and sterilized by either ethylene oxide (EO) or gamma radiation. Their biocompatibility was evaluated in vitro in terms of proliferation, cell viability, and adhesion characteristics of human umbilical veins (HUVEC), monocytes (THP-1), and skin fibroblasts, and by measuring complement activation through the generation of the C3a complex. Their hemocompatibility was determined by measuring the level of radiolabeled platelet, neutrophil, and fibrin adhesion in an ex vivo arteriovenous circuit study in piglets as well as via an in vitro hemolysis test. The results of this study showed no endothelial cell proliferation on any of the materials. The cell viability study revealed that the CB, CF, and TF membranes sterilized by EO maintained the highest percentage of monocyte viability after 72 h of incubation (>70%) while none of the gamma-sterilized membranes displayed any cell viability. The fibroblast adhesion and C3a generation assays revealed that none of the materials supported any cell adhesion or activated complement, regardless of the sterilization method. The hemolysis test also confirmed that the 4 poly(carbonate urethanes) were hemolytic while none of the poly(ether urethanes) were. Finally, the ex vivo study revealed that significantly more platelets adhered to the CB and CT55 membranes while the levels of neutrophil and fibrin deposition were observed to be similar for all 6 materials. In conclusion, the study identified the CF and TF membranes as having superior biocompatibility and hemocompatibility compared to the other polyurethanes.

Animals↗

PubMed2000

Biostability, inflammatory response, and healing characteristics of a fluoropassivated polyester-knit mesh in the repair of experimental abdominal hernias.

The present study was undertaken to validate the benefits of a fluoropolymer treatment on the biostability, inflammatory response, and healing characteristics of a polyester mesh used for hernia repair, the Fluoromesh, as compared to a commercial monofilament-knit polypropylene mesh, Marlex, used as the control. Both were implanted for the repair of surgically induced abdominal hernias in piglets for prescheduled durations of implantation of 4, 15, and 60 days. The mesh and surrounding tissue were harvested at the sacrifice for the bursting strength and inflammatory response measurements in terms of alkaline and acid phosphatase secretion in the tissue, and for histological observations of the healing sequence and tissue thickness measurements by histomorphometric techniques. After cleaning to remove adherent tissue, the presence of the fluoropolymer at the surface of the mesh was detected using SEM and ESCA. The results demonstrated greater mechanical reinforcement and tissue development for the Fluoromesh than for the polypropylene mesh. The healing performance of the Fluoromesh was attributed to a more intense chronic inflammatory reaction early after implantation that stimulated significantly greater tissue ingrowth and integration. The concentration of fluoropolymer at the surface of the mesh was masked as a result of biological species adsorption. Textile analysis revealed that the Fluoromesh was dimensionally more stable in vivo than the polypropylene control mesh, which demonstrated stretching in the weft direction and shrinking in the warp direction during implantation.

Acid Phosphatase↗

PubMed2000

Polymerization and surface analysis of electrically-conductive polypyrrole on surface-activated polyester fabrics for biomedical applications.

A new synthetic route is reported for the synthesis and covalent bonding of electrically conductive polypyrrole to a poly(ethylene terephthalate) fabric. It involves a three-step process including surface phosphorylation and graft polymerization from the gaseous phase. In the first step, the fibre surfaces are activated using phosphorus trichloride. Then, 1-(3-hydroxypropyl) pyrrole is introduced and grafted to the phosphorus chloride to create an ester bond between the fibres and the pyrrole. Finally, the pyrrole-grafted fibres are dipped in an aqueous FeCl3 catalyst and exposed to pyrrole monomer vapor for the final polymerization. This last step creates an electrically conductive polypyrrole layer covalently linked to the poly(ethylene terephthalate) fibres. ESCA analysis indicates a high degree of phosphorylation and grafting of the anchor molecules. Scanning electron microscopy reveals an overall smooth and uniform surface coating of polypyrrole on the polyester fibres. The use of ATR-FTIR spectroscopy is not able to distinguish between polypyrrole-coated and non-coated fabrics because of the extremely thin polypyrrole layer. Measurements of dynamic surface wetting indicated that the polypyrrole-coated fabric is more hydrophilic than the untreated control. With values for surface resistivity in the range 10(4)-10(5) ohmz/square, such polypyrrole-coated fabrics are considered attractive candidates for biomedical applications.

Biocompatible Materials↗

PubMed2000

Endovascular repair of thoracic aortic aneurysm in dogs: evaluation of a nitinol-polyester self-expanding stent-graft.

PURPOSE: To validate the ease of deployment and in vivo healing performance of a nitinol-polyester self-expanding stent-graft using a canine thoracic aortic aneurysm model. METHODS: Arterial aneurysms were surgically created in 8 dogs by sewing a polyester patch onto the anterior side of the thoracic aorta. The nitinol-polyester self-expandable stent-grafts (Cragg EndoPro System 1) were implanted transluminally via the femoral route and deployed at the site of the thoracic aneurysm. Aneurysm exclusion and endograft patency were assessed by angiography after implantation and before animal sacrifice at scheduled periods ranging from 1 week to 3 months. The explanted specimens were examined with magnetic resonance imaging (MRI) to study the position of the stent-graft with respect to the aneurysmal sac. Histological analysis using light microscopy and scanning electron microscopy was performed to examine the inflammatory response and healing characteristics of the device. RESULTS: Seven of 8 stent-grafts were implanted successfully; a bend occurred within the aneurysmal sac in 1 dog, which led to continued perfusion of side branches. This endoleak sealed spontaneously within 1 week, and complete exclusion of the aneurysms in all 8 animals continued throughout implantation. At the time of explantation, all devices were structurally intact and well positioned in the aneurysmal sac. At 1 week, the luminal surface displayed a thin layer of thrombotic matrix, which was gradually replaced by a collagenous internal capsule with endothelial-like cell coverage along both ends of the stent-grafts at 2 and 3 months. No exacerbated inflammatory reaction due to either the nitinol wires or the polyester sleeve was observed after 3 months of implantation. CONCLUSIONS: This short-term in vivo study of a nitinol-polyester self-expanding endograft demonstrated the effective exclusion of thoracic aneurysms with a satisfactory healing response and no excessive tissue or inflammatory reactions.

Alloys↗

PubMed2000

First-generation aortic endografts: analysis of explanted Stentor devices from the EUROSTAR Registry.

PURPOSE: To examine the structure and healing characteristics of chronically implanted Stentor endografts that were explanted due to migration, endoleak, thrombosis, or aneurysm expansion. METHODS: The devices were harvested following reoperation (n = 5) or autopsy (n = 1) with implantation times ranging from 13 to 53 months. Structural modifications to the metal components were examined using radiography, endoscopy, and magnetic resonance imaging (MRI). Specimens taken from components of the modular stent-grafts were examined histologically and with scanning electron microscopy (SEM) to assess healing behavior. Physical and chemical stability of the nitinol wires and woven polyester graft material was evaluated using SEM and electron spectroscopy for chemical analysis. RESULTS: Although the endografts were retrieved for a variety of reasons, they exhibited similar healing and structural modifications. The woven polyester sleeve showed evidence of yarn shifting and distortion, yarn damage, and filament breakage leading to the formation of openings in the fabric. The luminal surface endografts showed incomplete healing characterized by a poorly organized, nonadherent thrombotic matrix of variable thickness. Radiographic and endoscopic observations indicated that structural failure of the grafts, particularly in the main aortic component, was related to severe compaction and dislocation of the metallic frame due to suture breaks. Corrosion marks were observed on some nitinol wires in all devices. Chemical analysis and ion bombardment of the nitinol wires revealed that the surface concentrations of titanium and nickel were not homogenous. The first layer was composed of carbon or organic elements, followed by a stratum of highly oxidized titanium with a low nickel concentration; the titanium-nickel alloy lay beneath these layers. CONCLUSIONS: Although the materials selected for construction of endovascular grafts appears judicious, the assembly of these biomaterials into various interrelated structures within the device requires further improvement.

Aged↗

PubMed1999

Totally implantable artificial hearts and left ventricular assist devices: selecting impermeable polycarbonate urethane to manufacture ventricles.

In the development of a new generation of totally implantable artificial hearts and left ventricular assist devices (VADs) for long-term use, the selection of an acceptable material for the fabrication of the ventricles probably represents one of the greatest challenges. Segmented polyether urethanes used to be the material of choice due to their superior flexural performance, acceptable blood compatibility, and ease of processing. However, because they are known to degrade and to be readily permeable to water, they cannot meet the rigorous requirements needed for a new generation of implantable artificial hearts and VADs. Therefore, the objective of the present study was to identify alternative polymeric materials that would be satisfactory for fabricating the ventricles, and in particular, to determine the water permeability through membranes made from four commercial polycarbonate urethanes (Carbothane PC3570A, Chronoflex AR, Corethane 80A, and Corethane 55D) in comparison to those made from two traditional polyether urethanes (Tecoflex EG80A and Tecothane TT-1074A). In addition to determining the rate of water transmission through the six membranes by exposing them to deionized water, saline, and albumin-Krebs solution under pressure and measuring the displacement of liquid by means of a recently developed capillary method, the inherent surface and chemical properties of the six membranes were characterized by SEM, contact angle measurements, FTIR, DSC, and GPC techniques. The results of the study demonstrated that the rate of water transmission through the four polycarbonate urethane membranes was significantly lower than through the two polyether urethanes. In fact the lowest values were recorded with the two Corethane membranes, and the harder type 55D polymer had a lower value (2.7 x 10(-7) g/s cm2) than the softer 80A version (3.3 x 10(-7) g/s cm2). This level of water vapor permeability, which appears to be controlled primarily by a Fickian diffusion mechanism, is between 2 and 4 times lower than that obtained with traditional polyether urethane membranes of equivalent thickness. The superior performance of the polycarbonate urethanes is likely due to the inherently lower chain mobility of the carbonate structure in the soft segment phase. In addition, the study shows that additional impermeability to water vapor can be achieved by selecting a polyurethane polymer with a high hard segment content, an aromatic rather than aliphatic diisocyanate comonomer, and a more hydrophobic surface. The use of a higher molecular weight polyurethane is not necessarily efficacious if the above requirements are not met. As expected by Raoult's Law, the study found that the use of physiological media instead of deionized water further decreases the rate of water vapor transmission. Because none of today's commercial polyurethanes are totally impervious to water vapor transmission, additional work is needed to develop permeable polymers or to apply additional treatments to existing candidates to achieve an acceptable impermeable ventricle material.

Biocompatible Materials↗

PubMed1999

A new generation of polyurethane vascular prostheses: rara avis or ignis fatuus?

Three polyurethane (PU) vascular grafts with novel designs were investigated and compared in terms of the microporous structure, reinforcement technology, polymer chemistry, microphase separation, and mechanical properties. The Corvita graft, composed of a poly(carbonate urethane) polymer, displayed a helically wound filament structure with communicating inter-fiber spaces. The reinforced model contained an external PET mesh impregnated with a protein sealant, and displayed good microphase separation, the highest Young's modulus in the longitudinal direction, and the second highest in the radial direction. The Thoratec graft was made of a polyetherurethaneurea with an average micropore size of 15 microns. Silicone was observed on both surfaces of the graft. The Thoratec device displayed a low degree of hydrogen-bonding among the urethane groups and had no well-organized hard-segment domains. Its mechanical strength was superior to that of the Pulse-Tec graft. A solid PU layer underneath the luminal surface precluded any communication between the luminal and adventitial sides. The Pulse-Tec prosthesis was composed of polyetherurethane, with an average micropore size of 28 microns. It offered the highest radial compliance, a high degree of hydrogen-bonding, a narrow molecular weight distribution, and a certain degree of microphase separation. Its tensile strength and hysteresis loss were inferior to those of the other two grafts.

Animals↗

PubMed1999

Assessing the resistance to calcification of polyurethane membranes used in the manufacture of ventricles for a totally implantable artificial heart.

Ventricles made from segmented polyurethane membranes and used in the fabrication of a totally implantable artificial heart are known to undergo biomaterial-associated calcification. As there is no effective method currently available to prevent such biomaterials from calcifying, a practical solution is to use only materials with a relatively high resistance to calcification, to extend ventricular durability and ensure a longer functional life for the manufactured device. In the present study, an in vitro calcification protocol was used to determine the relative resistance to calcification of six different polyurethanes, namely, Carbothane PC3570A, Chronoflex AR, Corethane 80A, Corethane 55D, Tecoflex EG80A, and Tecothane TT1074A. The results demonstrated that all six polyurethanes did become calcified during the 60-day incubation period in the calcification solution. The degree of calcification was found to be associated with the surface chemistry of the particular polyurethane, with the Tecothane TT1074A exhibiting the highest level. The Corethane 80A and 55D polymers showed a relatively low propensity to calcify. These two membranes can, therefore, be considered as the most appropriate materials for the fabrication of ventricles for a totally implantable artificial heart. In addition, since the calcification occurred primarily at the surface of the membranes, without affecting the bulk microphase structure, the issue of modifying the surface chemistry to reduce the incidence of calcification is discussed.

Biocompatible Materials↗

PubMed1999

Tissue reactions to polypyrrole-coated polyesters: A magnetic resonance relaxometry study.

The electrically conductive properties of polypyrrole (PPy) as a coating on polyester material are very attractive for the manufacture of small diameter blood conduits. However, before these PPy-coated materials can be investigated for their capacity to generate endothelialized luminal surfaces, they must first be studied for their innocuousness in a living environment. The specific goal of the present study was to investigate the in vivo interactions of PPy-coated and noncoated woven polyester materials implanted subcutaneously in rats for prescheduled periods of 2, 5, 10, 20, and 30 days. The in vivo magnetic resonance (MR) relaxation times were computed for a small area of muscle tissue adjacent to the implants. A correlation was concurrently attempted with blood monocyte activation studies as well as histological observations of the tissue-material interface. The progressive pattern of the slower transversal relaxation time (T2s) values revealed a more persistent tissue reaction for the most conductive PPy-coated materials and a shorter acute tissue response as the surface resistivity increased. Similarly, the blood monocyte activation studies indicated that the thickness of the PPy coating, which correlated with the conductivity, was directly related to tissue response. Furthermore, both the MR and biological studies showed that the PPy-coated material with a high surface resistivity displayed the lowest tissue reaction over the entire period of implantation. The results obtained from the blood monocyte activation studies and histological observations correlate well with the noninvasive MR measurements of the body's healing process. The conductive materials with high surface resistivities must be further investigated. Finally, the noninvasive nature of MR relaxometry reveals its outstanding potential for future in vivo investigations of the body's tissue interactions with polymers and nonferromagnetic biomaterials.

Animals↗

PubMed1998

In vitro cellular response to polypyrrole-coated woven polyester fabrics: potential benefits of electrical conductivity.

Electrically conducting polypyrrole-treated films have recently been shown to influence the morphology and function of mammalian cells in vitro. This type of polymer represents a possible alternative biomaterial for use in vascular implantation. The present study compared the in vitro biocompatibility of the five different polyester woven fabrics having increasing levels of electrical conductivity ranging from 4.5 x 10(4) to 123 omega/square with that of low density polyethylene and polydimethylsiloxane primary reference materials. Biocompatibility was measured in terms of four different types of in vitro cellular response, including (a) an indirect and (b) a direct control organotypic culture assay using endothelial cells, (c) a polymorphonuclear (PMN) cell activation study using flow-cytometric measurements of CD11/CD18 integrin molecule expression, and (d) a semiquantification of interleukin (IL)-6 mRNA expression on monocytes/macrophages using reverse-transcriptase polymerase chain reaction. The organotypic culture study revealed that the fabrics with high levels of conductivity exhibited lower cell migration, proliferation, and viability. The PMN activation study of blood from 10 healthy adult donors demonstrated that the two most conductive fabrics were able to identify the more reactive donors. The levels of IL-6 mRNA expression by monocytes/macrophages decreased as the conductivity level of the fabrics increased. The results of the present study therefore indicate that high levels of conductivity (< 200 omega/square) on polyester fabrics are detrimental to the growth, migration, and viability of endothelial cells; induce elevated PMN activation; and affect the intracellular metabolism of monocytes. They also point to a specific range of conductivity (10(3) < 10(4) omega/square) which is associated with an optimum in vitro cellular response.

Adult↗

PubMed1998

Anterior structural defects by misexpression of Xgbx-2 in early Xenopus embryos are associated with altered expression of cell adhesion molecules.

The RNA of the noncluster homeobox gene, Xgbx-2, is localized during neurulation to a narrow band of tissue at the midbrain hindbrain boundary (anterior hindbrain). The localized expression of Xgbx-2 within the nervous system prompted us to assess its function during early development by injection of synthetic Xgbx-2 RNA into the animal pole region of both dorsal blastomeres at the four-cell stage. Injection of Xgbx-2 RNA leads to dose-dependent alterations in anterior dorsal structures. These defects include abnormal eye development including reduced and missing eyes, reduced or missing cement glands, and abnormal brain development. Additionally, coinjection with lineage label (either beta-galactosidase or green fluorescent protein) shows there is a dose-dependent misplacement of cells. These misplaced cells can be found in such locations as the blastocoele, gastrocoele, or ventricles in the brain. In some spawnings, misplaced cells are expelled from the embryo into the periviteline space. In general, the phenotype of Xgbx-2 RNA-injected embryos is strikingly similar to the phenotypes observed when dominant-negative RNA constructs of Ca2+-dependent cell-adhesion molecules are injected into similar regions of early embryos. Xgbx-2 misexpression enhanced the dissociation of animal hemisphere cells, and inhibited Ca2+-dependent cell adhesion in dissociated animal hemisphere cells in vitro. Additionally, when the expression of various calcium-dependent cadherins was tested, it was shown that misexpression of Xgbx-2 prevents N-cadherin expression during early neurulation. These observations suggest that the transcription factor, Xgbx-2, functions normally in the regionalization of the neural tube (specifically the anterior hindbrain) by regulating differential cell adhesion and subsequently cell identity.

Animals↗

PubMed1997

In vitro and in vivo studies of a polyester arterial prosthesis with a warp-knitted sharkskin structure.

The present study was undertaken to assess the performance of a new knitted and gelatin-sealed polyester vascular graft that is believed to have greater dimensional stability than current commercial devices. Samples of the uncrimped, crimped, and sealed prosthesis were submitted to a series of in vitro and in vivo trials. Four commercial polyester knitted devices were included as controls for the in vitro tests, which included measurements of the textile and yarn structure and physical, chemical, and thermal properties of the graft, such as water permeability, dilatation, suture retention strength, melting point, and crystallinity index. The in vivo evaluation involved implanting the prototype device as a canine thoraco-abdominal bypass for periods ranging from 4 h to 1 year and assessing the biocompatibility, biofunctionality, and biostability of the explanted specimens. The warp-knitted structure of the prototype device has a unique sharkskin stitch that confers a superior dilatation resistance and suture retention strength to the prosthesis. The animal trial demonstrated that the gelatin ensures initial hemostasis without preclotting. The gelatin is bioresorbed during the first 2 weeks of implantation, which generates a temporary, moderate, acute inflammatory response. An external capsule of granulomatous tissue and an internal collagen capsule are formed between the first and third month. Analysis of the textile and physical properties of the explanted prostheses confirmed there was neither dilatation nor significant changes in structure or mechanical performance during implantation, thus confirming the biostability of this new prototype device and opening the way for clinical trials.

Anastomosis, Surgical↗

PubMed1997

Failure mechanisms of anterior cruciate ligament prostheses: in vitro wear study.

Previous retrieval studies analyzing the cause of failure of anterior cruciate ligament (ACL) prostheses identified a wear mechanism. However, the relative importance of yarn on bone compared to yarn on yarn wear has not been clearly understood. Therefore, the objective of this study was to elucidate which type of wear is the dominant cause of clinical failure. A variety of ACL prosthetic structures were exposed to two in vitro tests: one for yarn on yarn and the other for a novel yarn on bone wear test system. The latter included the use of both smooth (uncut) and rough (cut) bone surfaces to simulate the conditions around the condyle and at the exit of the tibial tunnel, respectively. The damaged textile structures were viewed by SEM. The various fiber fracture morphologies were identified and classified for the two types of wear tests; for the smooth and rough bone surfaces; for the braided, knitted, woven, and twisted textile structures; and for the three types of fibers that were included: polyethylene terephthalate, polypropylene, and ultrahigh molecular weight polyethylene. The results confirmed that yarn on bone and yarn on yarn wear phenomena are associated with significantly different failure mechanisms. While the more aggressive rough (or cut) bone causes more rapid and intense fiber damage and faster ACL failure than the smooth (uncut) osseous surface, both abradants cause the same type of abrasive wear phenomenon. Differences in failure mechanisms were identified between the different textile structures and the different fiber types. By interpreting the damaged fiber images from clinically failed and retrieved ACL prostheses, we are now able to confirm that the predominant cause of synthetic ACL failure is yarn on bone abrasion. Improvements in future ACL prosthesis designs will only be possible by eliminating or minimizing the effect of this type of abrasive wear.

Anterior Cruciate Ligament↗

PubMed1997

The Dialine II graft: a new collagen-impregnated warp-knitted polyester arterial prosthesis.

The Dialine graft, a new prototype of knitted vascular prosthesis that uses a different brand of polyester fibers as an alternative to Dacron fibers, has been shown to offer excellent in vitro physical performance and in vivo healing. Although it still requires preclotting, the Dialine prosthesis was made impervious by impregnation of bovine type I collagen cross-linked with vapors of formalin. The purpose of the present investigation was to compare the in vitro physical characteristics of the Dialine II graft with those of the collagen-impregnated Hemashield graft. In addition, we studied the healing performance as a thoracoabdominal bypass in dogs for prescheduled periods of implantation ranging from 4 hours to 6 months. In vitro, the bursting strength, resistance to dilatation, and suture retention strength properties of the Dialine II prosthesis were all shown to exceed those of the Hemashield control graft. In the first weeks after implantation, the Dialine II grafts induced a discrete inflammatory response, as shown by the constant leukocyte counts observed both before implantation and when the animals were killed, as well as by the histologic observation of a few inflammatory cells in contact with the collagen. Consequently, the Dialine II grafts showed a slow rate of bioresorption of cross-linked collagen. At 1 month, a thin internal collagenous capsule was present at both anastomoses, laying over the original collagen coating. At 3 and 6 months, areas of thrombotic deposits and endothelialized areas were observed on the luminal surface. Because results of early clinical trials have been highly satisfactory, this prosthesis may be recommended for use without restriction as a medium- and large-diameter blood conduit.

Animals↗

PubMed1997

Vascugraft polyurethane arterial prosthesis as femoro-popliteal and femoro-peroneal bypasses in humans: pathological, structural and chemical analyses of four excised grafts.

Following positive results obtained in in vitro studies and in vivo implantations in animals, a clinical trial using the Vascugraft polyurethane arterial prosthesis as a below-knee substitute was undertaken in 15 patients. Eight grafts became occluded during the first year, and segments from four of them were explanted and made available for pathological, structural and chemical investigations. The implantation periods ranged from 21 to 358 days. Failures were associated with kinking (one case), possible anastomotic mismatch between the graft and the artery (one case), and poor run-off (two cases). No organized collagenous internal encapsulation was noted; however, endothelial-like cells were observed at the anastomotic site of one graft. No significant structural degradation of the prostheses was observed in those grafts implanted for 21, 38 and 46 days. Some deteriorations in the fibrous structure were observed on the external surface of the prosthesis implanted for 358 days. High-resolution carbon C1s analysis by ESCA demonstrated a 60 to 80% decrease in carbonate content on the surface of all explanted prostheses. Chemical analyses of each polyurethane graft by IR, SEC and DSC revealed no significant chemical changes. The clinical performance of the Vascugraft prosthesis for below-knee implantation proved to be no more impressive than that of expanded polytetrafluorethylene, the currently accepted reference. The decision by B. Braun Melsungen AG to end this program is therefore to be regarded as highly professional.

Aged↗

PubMed1997

Shelf-life of bioprosthetic heart valves: a structural and mechanical study.

This study was undertaken to evaluate the influence of storage conditions on the shelf-life of porcine bioprosthetic valves. Fifty-five unimplanted porcine bioprostheses have been evaluated. The valves were stored in 0.5% buffered glutaraldehyde solution for different periods of time (7, 23 and 32 months). Twenty-eight valves were refrigerated while the remaining valves were stored at room temperature. The pH of the glutaraldehyde solution at room temperature decreased with time of storage, while that kept in the refrigerator remained stable over the course of the study. Macroscopic observations showed that the valve tissues kept at room temperature, especially for the periods of 23 and 32 months, became darker and more yellow in colour, whereas the refrigerated specimens exhibited no such changes in appearance. Scanning electron microscopy analysis revealed no noticeable differences on the surfaces of the leaflets stored under different conditions. Mechanical tests, including stress-strain response, stress relaxation and fracture behaviour, were carried out. Analysis of variance showed that the storage temperature, but not the length of storage, had a significant effect on some mechanical properties. The stress relaxation at 1000 s (P = 0.05), the ultimate tensile strength (P = 0.01) and the strain at fracture (P = 0.04) were all higher after storage at room temperature compared to the results after refrigeration. No statistically significant changes in the denaturation temperature of the collagen were observed between the different storage conditions. In conclusion, the storage temperature appears to have some influence on the bioprosthetic tissue. The bioprostheses stored under ambient conditions experience changes which may influence their longterm in vivo performance.

Animals↗