Graft durability and fatigue after in situ fenestration of endovascular stent grafts using radiofrequency puncture and balloon dilatation.

OBJECTIVES: In situ fenestration of endovascular stent grafts is a technique that is becoming more common, as it has the advantages of decreased cost, increased availability, and more anatomic configuration than other methods of branch revascularization. However, a significant concern is the short- and long-term durability of the stent graft fabric during and after fenestration. METHODS: This study utilizes the textiles analysis techniques of macro- and microscopic imaging, tear strength testing, burst strength testing, and accelerated cyclic fatigue testing on the fabrics of the Cook Zenith, Medtronic Talent, and Medtronic Endurant stent grafts (three polyester grafts), as well as two different expanded polytetrafluoroethylene (ePTFE) membranes. Specimens were punctured using radiofrequency, and serially dilated with angioplasty balloons (3, 5, and 7 mm). For each type of fabric, three groups were analyzed: control, radiofrequency (RF) puncture only, and balloon dilated. RESULTS: A total of 110 specimens were analyzed, with 80 of them having been fenestrated. The Zenith fabric had the greatest strength after fenestration, but was limited by the inability to fully dilate the fenestration with the conventional balloons, which only achieved 26-29% of their nominal balloon diameter. While the Talent and Endurant grafts could be dilated with balloons, the orifices were markedly elliptical not circular. After accelerated fatigue testing, there was an increase in the size of fenestrations of the Talent fabric. There was no increase in fenestration size for the Endurant fabric, Zenith fabric, or the ePTFE fabrics, after fatigue testing. CONCLUSIONS: While the Zenith fabric was the strongest both before and after fenestration, it requires further study with cutting balloons to achieve full-sized fenestrations. All fenestrations remained stable during fatigue testing except for the Talent fabric. This study serves as the baseline for future studies that will include stent grafts, branch stents, and cutting balloons.

Rearing regimen producing piglet diarrhea (rotavirus) and its relevance to acute infantile diarrhea.

Piglets were weaned when 1 day old and thus were denied further access to the antibodies supplied by their dam's milk. They were placed in a nursery in which contamination by the ubiquitous rotavirus steadily increased with continuous use causing a progressive increase in the incidence of vomiting, diarrhea, and death among the piglets. A similar syndrome involving an antigenically related rotavirus and analogous management practices occurs in human infants.

Expression of the high mobility group A family member p8 is essential to maintaining tumorigenic potential by promoting cell cycle dysregulation in LbetaT2 cells.

The mechanism by which the HMGA protein p8 facilitates tumorigenesis may be cell cycle dysregulation. Control- (C) LbetaT2 cells, which express p8, form tumors at a rate five-times faster than p8-knockdown (p8-KD)-LbetaT2 cells. In association with this heightened tumorigenic potential, p8-expressing C-LbetaT2 cells avoid G(0)/G(1) arrest and become genetically unstable while p8-KD-LbetaT2 cells arrest in G(0)/G(1), become senescent upon overgrowth, and maintain a diploid population. These phenotypic changes correspond to altered cell cycle regulation at the G(1)-to-S transition that may be due to p8-mediated changes in expression of the Cip/Kip family members of cell cycle inhibitors, p21, p27, and p57.

Expression of the c-myc proto-oncogene during development of Xenopus laevis.

We isolated and characterized Xenopus laevis c-myc cDNAs from an oocyte-specific library. These cDNA clones encompass 2.35 kilobases of the X. laevis c-myc RNA and contain the entire coding domain of 1,257 nucleotides of the 419-amino acid-long X. laevis c-myc protein. The 2.7-kilobase X. laevis c-myc mRNA is expressed in the oocyte, maintained in the egg, and is present throughout the early cleavage stages of embryogenesis. At the time of transcriptional activation in the embryo the c-myc RNA levels show a significant decline and then reaccumulate continuously throughout the remainder of premorphogenic development. At the early neurula stage of embryogenesis the pattern of c-myc RNA expression is elevated in the mesoderm with respect to the endoderm and ectoderm. In the adult X. laevis the c-myc mRNA is expressed in some (e.g., skin, muscle) but not all differentiated tissues. The X. laevis c-myc protein migrates as a doublet of 61,000- and 64,000-dalton species. Both species are phosphorylated in oocytes and somatic cells, exhibit extremely short half-lives of less than 30 min, and are localized to the nuclear fraction of somatic cells. By contrast, the oocyte protein shows both cytoplasmic and germinal vesicle distribution and appears to be stable.

Functional analysis of the AUG- and CUG-initiated forms of the c-Myc protein.

Activation of the c-myc proto-oncogene by chromosomal translocation or proviral insertion frequently results in the separation of the c-myc coding region from its normal regulatory elements. Such rearrangements are often accompanied by loss or mutation of c-myc exon 1 sequences. These genetic alterations do not affect synthesis of the major c-myc protein, p64, which is initiated from the first AUG codon in exon 2. However they can result in mutation or loss of the CUG codon located in exon 1 that normally serves as an alternative translational initiation codon for synthesis of an N-terminally extended form of c-Myc (p67). It has been hypothesized that p67 is a functionally distinct form of c-Myc whose specific loss during c-myc rearrangements confers a selective growth advantage. Here we describe experiments designed to test the functional properties of the two c-Myc protein forms. We introduced mutations within the translational initiation codons of a normal human c-myc cDNA that alter the pattern of Myc protein synthesis (p64 vs. p67). The functions of each of these proteins were experimentally addressed using co-transformation and transcriptional activation assays. Both the p64 and p67 c-Myc proteins were independently able to collaborate with bcr-abl in the transformation of Rat-1 fibroblasts. In addition, both the exon 1- and exon 2-initiated forms of the c-Myc protein stimulated transcription of a Myc/Max-responsive reporter construct to a similar level. Given the apparent absence of functional differences between p64 and p67, we conclude that the basis for c-Myc oncogenic activation lies primarily in the overall deregulation of its expression and not in alterations in the protein. The existence of the CUG translational initiator may reflect a mechanism for the continued synthesis of c-Myc protein under conditions where AUG initiation is inhibited.

Characterization and expression of the Xenopus c-Myb homolog.

The c-Myb protein is a sequence specific DNA-binding transcriptional regulator that is critically involved in the regulation of hematopoietic differentiation. Its role in these processes suggests that the function of c-Myb may be important early in the establishment of the hematopoietic lineage. We have isolated cDNA and partial genomic clones representing the Xenopus c-Myb homolog (Xc-Myb) in order to examine the role this gene plays in early mesodermal patterning in the frog embryo. The establishment of these clones as c-Myb homologs, as opposed to Myb-related sequences, is based upon both predicted amino acid sequences and the location of the exon-intron boundaries within the Xc-Myb gene. Maternally derived Xc-Myb RNA is degraded following fertilization then, beginning at midblastula, re-accumulates throughout early development. Xc-Myb RNA is localized to the animal cap region of the early blastula. Following the onset of gastrulation expression predominates in the ventral half of the embryo. During neurulation expression of Xc-Myb is observed in both the anterior dorsal and ventral vegetal regions of the embryo. Expression of Xc-Myb occurs in several adult tissues, the highest levels of which are in the intestine, heart, liver, lung and ovary. Xc-Myb encodes a protein of 624 amino acids and exhibits a mobility in SDS-PAGE of approximately 75 kDa, identical with that of the murine c-Myb protein. Xc-Myb protein exhibits 70% identity with avian and 67% identity with mammalian c-Myb proteins.

POU-domain sequences from the flatworm Dugesia tigrina.

Redundant primers matching well-conserved sequences within vertebrate and invertebrate POU genes were used in the PRC (polymerase chain reaction) to detect three different POU-domain-containing genes within the genome of the flatworm, Dugesia tigrina. Two of these genes appear to be close homologues of class-III POU genes previously identified in Dugesia japonica, while the third represents a new class-III POU gene. Nucleotide sequences encoding highly related POU domains within the two species of planaria exhibited a surprisingly poor degree of shared identity. Since only class-III POU genes have been observed to date in flatworms, these genes may represent ancestral versions of the multiple classes of POU genes that exist in vertebrates, and may play important roles in the development of metazoan nervous tissue.

A rapid and efficient, nonradioactive method for screening recombinant DNA libraries.

In this report we present a rapid and inexpensive PCR-based method to screen recombinant DNA libraries. The efficiency of this method was demonstrated by the isolation of clones of interest from three different libraries using different vector systems. This method is nonradioactive and makes it easier to handle a large number of samples since there is no need for DNA extraction. The advantages and applications of the method are discussed.

Expression of calbindin-D28K mRNA as a function of altered serum calcium and phosphorus levels in vitamin D-replete chick intestine.

The availability of specific cDNA probes to the chick intestinal calbindin-D28K (CaBP) mRNA has allowed us to assess the regulation of this mRNA in response to 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) administration. It has previously been demonstrated that dietary calcium and phosphorus can effect alterations in the steady-state intestinal levels of chick CaBP. We have examined whether or not perturbations in dietary calcium and phosphorus have an effect on the expression of the intestinal mRNA coding for CaBP in the vitamin D-replete chick. We found altered protein levels of CaBP as expected; however there was surprisingly no difference in steady-state CaBP mRNA levels between the different dietary groups. These data suggest that calcium and phosphorus regulation of CaBP occurs at a post-transcriptional level. In addition, we have examined what effect dietary manipulations of calcium and phosphorus levels have on the response of the vitamin D-replete intestine to 1,25(OH)2D3 administration as assessed by CaBP mRNA changes. Administration of 1,25(OH)2D3 to vitamin D-replete chicks maintained on normal calcium and phosphorus levels resulted in a less than 2-fold increase in CaBP mRNA levels. Previous studies have demonstrated that receptor occupancy goes up 6-fold under these conditions; therefore there is apparently a very tight regulation of CaBP gene activity. 1,25(OH)2D3 administration to chicks raised on either low calcium, high calcium, or low phosphorus vitamin D-replete diets similarly showed only small changes in the intestinal CaBP mRNA levels; however there seemed to be qualitative differences in response attributable to the dietary alterations.

In vivo performance of the polyesterurethane Vascugraft prosthesis implanted as a thoraco-abdominal bypass in dogs: an exploratory study.

Among the various prototype vascular prostheses that have been developed over recent years as small vessel substitutes, the Vascugraft polyurethane device produced by Braun-Melsungen AG has a number of attractive features. As well as having high mechanical compliance similar to that of the arterial tree, it has been manufactured from a specially synthesized poly(ester urethane) with improved biostability and its microfibrous structure provides a highly porous wall with open communicating pores. With a view to evaluating the in vivo biofunctionality and biostability of this prosthesis in the dog, 10 mm diameter grafts were implanted as thoraco-abdominal bypasses for prescheduled periods of 1 months and 12 months, and their performance monitored in terms of gross morphology, histology and the measurement of the chemical and physical properties of the explanted and cleaned specimens. Both grafts were patent at retrieval. Each had a smooth and glistening flow surface without organized mural thrombi and showed the development of a thin collagenous internal capsule with the presence of endothelial-like cells. Both grafts were well encapsulated externally and revealed a small distal bend or kink which is frequently observed by any thoraco-abdominal bypass in dogs. The fresh explanted prostheses were cleaned by a new enzyme treatment which provided specimens for microscopic, mechanical and thermal analyses, as well as studies of the surface and bulk chemistry. By comparing the results from the explanted and cleaned material with those of the virgin prosthesis, we have observed some deterioration in the integrity of the microfibrous structure, some loss in mechanical performance, marginal changes in molecular weight, and an apparent microphase separation of the hard and soft segment domains at a depth of a few microns. While the biofunctionality of a 10 mm calibre device has been demonstrated, additional in vivo studies are recommended to assess the biofunctionality at different diameters and the biostability over longer periods of implantation.

Quantitative analysis of the surface morphology and textile structure of the polyurethane Vascugraft arterial prosthesis using image and statistical analyses.

The surface morphology and textile structure of the Vascugraft polyurethane arterial prosthesis were investigated. Novel methods of image analysis and the presentation of statistical data were used to obtain quantitative results of the surface morphology of the non-woven microfibrous structure of prostheses of three different sizes. These techniques have identified apparent differences in the distributions of thickness and orientation of the microfibres between the internal and external surfaces and between the three prostheses investigated.

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.

Carbodiimide cross-linked gelatin: a new coating for porous polyester arterial prostheses.

The performance of a polyester arterial prosthesis impregnated with gelatin and cross-linked with carbodiimide (Uni-graft) was compared with its porous parent graft (Protegraft) using a canine thoraco-abdominal bypass model. The grafts were investigated in terms of their handling characteristics, imperviousness at implantation, surface thrombogenicity and healing behaviour. Prostheses 30 cm in length were implanted for the following periods: 4, 24 and 48 h, 1, 2 and 4 weeks, 2, 3, 4, 5 and 6 months. Both types of graft had good handling characteristics. The ready-to-use impregnated graft provided satisfactory haemostasis at implantation with no blood permeating through the wall after flow was restored. Both grafts exhibited low surface thrombogenicity, as determined by the uptake of labelled fibrin and platelets, and the healing sequence of the impregnated graft after resorption of the gelatin was equivalent to that of the preclotted control. Biodegradation of the gelatin was complete within 1 month of implantation with the subsequent development of a collagenous internal capsule at both anastomoses. Endothelial cells were observed between 4 and 6 months, but were confined to small islets distributed along the luminal surface. The prostacyclin/thromboxane A2 (PGI2/TXA2) ratio, which gives an indication of the level of endothelial cell activity, was greater than 1.0 after 1 week of implantation for the control graft. For the impregnated graft it reached 1.0 only after 3 months of implantation, but remained above 1.0 for periods of up to 6 months.(ABSTRACT TRUNCATED AT 250 WORDS)

Removing fresh tissue from explanted polyurethane prostheses: which approach facilitates physico-chemical analysis?

Chemical, physical and structural analyses of polymers from explanted vascular prostheses are frequently jeopardized because of incomplete removal of the encroaching host tissue. In this study, microporous polyurethane arterial prostheses implanted as a canine thoraco-abdominal bypass were explanted after 1 and 12 months and were cleaned without fixation using four different digesting enzyme treatments, including collagenase, pancreatin and trypsin alone and collagenase and pancreatin in series, followed by washing in a solution of Triton X-100 detergent. By following this approach all the fresh tissue attached to the external and internal walls of the prostheses was removed with minimal damage to the underlying synthetic polymer. The morphology of the explanted and cleaned polyurethane prostheses could be obtained readily by light and scanning electron microscopy. Surface microporous features and the presence of polyurethane microfibres that had experienced in vivo biodegradation could therefore be identified easily. The surface and bulk physico-chemical properties of the polyurethane polymer were determined by electron spectroscopy for chemical analysis, attenuated total reflectance-Fourier transform infrared spectroscopy and differential scanning calorimetry. It was found that the most successful approach for removing fresh tissue and exposing a clean and uncontaminated polyurethane surface was to incubate the explanted samples first in collagenase followed by digestion in pancreatin. This particular cleaning technique has proved valuable in enabling us to monitor small in vivo changes in the surface chemistry and in the bulk microphase segmented structure of polyurethane biomaterials.

Vascugraft microporous polyesterurethane arterial prosthesis as a thoraco-abdominal bypass in dogs.

In their progression towards clinical acceptance, any new synthetic vascular grafts under development must undisputedly prove that the chemistry and structure used in the construction of the prostheses is safe and that their biocompatibility and performance as arterial substitutes are satisfactory without degradation or weakening of the device. This study was conducted to evaluate the safety of the microporous polyesterurethane Vascugraft by investigating its biocompatibility in terms of cellular proliferation, morphology and adhesion of human fibroblasts on virgin and blood-soaked Vascugraft prostheses, and its performance in vivo as a large calibre graft in a canine thoraco-abdominal bypass model for periods of implantation ranging from 4 h to 6 months. After 3 d incubation, better cell proliferation and adhesion were observed on blood-soaked Vascugraft than on a non-porous polyurethane graft, Mitrathane, and two other polytetrafluorethylene prostheses, Impra and Goretex. Furthermore, no leachable cytotoxic contaminants were released from the prostheses. In vivo, the Vascugraft has demonstrated a good performance with the development of an endothelialised internal capsule at both anastomoses 2 weeks after implantation, reaching the medial portion of the graft at 4 months. During this period, the prostacyclin I2/thromboxane A2 ratio increased and was higher than 1.0 at 2 months. In addition, the Vascugraft exhibited low surface thrombogenicity in terms of radiolabelled platelets and fibrin deposited. Chemically, as revealed by ESCA and FTIR analyses, a slight decrease in carbonate content was observed on the external surface of the Vascugraft during the early post-implantation periods. Breaks in the microfibrous structure were also observed at 4 and 6 months, occurring mainly in the anastomotic regions and believed to be stress-related. This study shows that the polymer used in the Vascugraft is biocompatible in terms of fibroblast proliferation and promotes fair healing characteristics. However, the chemical and structural surface modifications noted in this study are disturbing and question the total inocuity of the Vascugraft. Consequently, the decision by B. Braun Melsungen AG to end this project is both highly conscientious and professional.

Chemical and morphological analysis of explanted polyurethane vascular prostheses: the challenge of removing fixed adhering tissue.

During in vivo experiments to evaluate the biocompatibility and biostability of alternative biomaterials, the ideal protocol for the handling and preservation of the explanted material is often compromised in order to meet the needs of both the pathologist and the materials scientist. Explants surrounded by tissue are often fixed in formalin or glutaraldehyde to facilitate later pathological and histological analysis, but the subsequent removal of such fixed tissue from thermally sensitive and less chemically stable polymers, such as polyurethanes, poses major problems for the materials scientist, who does not wish to modify the chemical, physical or morphological characteristics of the underlying biomaterial. The present study has attempted to find a solution to this problem by exposing virgin specimens of the microporous polyurethane Vascugraft vascular prosthesis to six different cleaning conditions, all known to be effective in removing fixed tissue. These conditions included the use of 20% aqueous potassium hydroxide solution for 48 h at room temperature, 5% sodium bicarbonate solution for 5 min at the boil, and 9, 10, 11 and 12N hydrochloric acid for 48 h at room temperature. The appearance and chemical properties of the virgin and treated specimens were compared using electron spectroscopy for chemical analysis, Fourier transform infrared spectroscopy, gel permeation chromatography for molecular weight and differential scanning calorimetry techniques. The use of temperatures close to the boil resulted in the formation of a translucent, rubbery material with gross changes in the microporous and microfibrous structure. The strongly acidic and alkaline conditions caused a loss in the surface carbonate group content. In addition, 12N hydrochloric acid reduced the molecular weight and urethane content. Consequently, 9N hydrochloric acid is recommended as the cleaning agent of choice for removing fixed tissue from this type of microporous polyurethane. Control experiments on virgin material should also be included in any cleaning protocol.

Histopathological and immunological investigations of synthetic fibres and structures used in three prosthetic anterior cruciate ligaments: in vivo study in the rat.

Three types of prosthetic anterior cruciate ligaments were investigated by enzymatic and histological analysis of the tissue surrounding each implant and immunologically by a cytofluorometric analysis of T-cell populations in the peripheral blood of rats. Two of the prostheses had a braided construction, one made from polyester and the other from high performance polyethylene fibres. The third type also contained high performance polyethylene fibres, but had been manufactured in a knitted construction (Raschel high performance polyethylene). Five specimens from each prosthesis were implanted intraperitoneally in rats by a trocar for different periods of time up to 4 wk. A control group of rats underwent the surgery, but not the implant. No modification in peripheral T-cell populations was induced by the presence of any implant. Whilst the levels of acid phosphatase and esterase activity appeared to have increased slightly following implantation of any of the prostheses, such increases were not highly significant. Histologically, all three materials induced an intense acute inflammatory reaction at 3 d which gave way to a typical chronic response after 4 wk. The only major difference between the prostheses was that after 4 wk the polyester fibres exhibited less inflammation, and the surrounding tissue was more mature, more vascularized and more densely infiltrated with collagen than with the two high performance polyethylene implants. In conclusion, all three devices provided satisfactory biocompatibility in terms of cellular and healing response.

An albumin-coated polyester arterial graft: in vivo assessment of biocompatibility and healing characteristics.

The albumin-coated vascular graft (ACG) and its uncoated polyester substrate, the Vascular II (V-II), were evaluated in terms of biocompatibility and biofunctionality using two in vivo animal studies. Biocompatibility and immunoreactivity were assessed by implanting intraperitoneally in the rat small segments of the ACG and the V-II graft and harvesting them with their surrounding tissue 3d, 1, 2 and 4 weeks later. Cytofluorometric determination of total T cells (CD3), the ratio of CD4/CD8 subsets and the percentage of IL-2 receptor-positive T cells in the peripheral blood has revealed that no significant difference in any of the T cell populations was found between the ACG and the V-II graft. The cellular reactivity of the ACG in terms of acid phosphatase activity at the implant side was significantly greater at 3 d but not at longer periods. Biofunctionality was evaluated by implanting both grafts as a thoracoabdominal vascular bypass in dogs for 11 different periods ranging from 4 h to 6 months. The rate of albumin resorption was such that traces were still present at 1 month, but no longer observable at 2 months. Tissue incorporation into the graft wall was earlier for the V-II (2 weeks) than for the ACG (4 weeks), which showed complete encapsulation, tissue incorporation and endothelialization after 2 months in vivo. Only small differences were observed between both grafts in terms of platelet and fibrin uptake on the luminal surface. The prostacyclin/thromboxane A2 ratio increased to a level higher that 1.0 aorta within 1 month for the V-II and 4 months for the ACG. In conclusion, the Bard ACG has demonstrated excellent biocompatibility in terms of blood T cell behaviour and acid phosphatase activity at the implant site. Finally, its healing response is equivalent to that of the uncoated Dacron prosthesis once the albumin coating has been resorbed.

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.

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.