In vitro endothelialization of commercially available heart valve bioprostheses with cultured adult human cells

The path to a hemocompatible cardiovascular implant: Advances and challenges of current endothelialization strategies

Cardiovascular (CV) implants are still associated with thrombogenicity due to insufficient hemocompatibility. Endothelialization of their luminal surface is a promising strategy to increase their hemocompatibility. In this review, we provide a collection of research studies and review articles aiming to summarize the recent efforts on surface modifications of CV implants, including stents, grafts, valves, and ventricular assist devises. We focus in particular on the implementation of micrometer or nanoscale surface modifications, physical characteristics of known biomaterials (such as wetness and stiffness), and surface morphological features (such as gratings, fibers, pores, and pits). We also review how biomechanical signals originating from the endothelial cell for surface interaction can be directed by topography engineering approaches toward the survival of the endothelium and its long-term adaptation. Finally, we summarize the regulatory and economic challenges that may prevent clinical implementation of endothelialized CV implants.

An In Vitro Model to Study Endothelialization of Cardiac Graft Tissues Under Flow

Pulmonary valve replacement is performed with excellent resultant hemodynamics in patients that have underlying congenital or acquired heart valve defects. Despite recent advancements in right ventricular outflow tract reconstruction, an increased risk of developing infective endocarditis remains, which has a more common occurrence for conduits of bovine jugular vein (BJV) origin compared with cryopreserved homografts. The reason for this is unclear although it is hypothesized to be associated with an aberrant phenotypic state of cells that reendothelialize the graft tissue postimplantation. The aim of this study was to develop an in vitro model that enables the analysis of endothelial cell (EC) attachment to cardiac graft tissues under flow. In the experiments, EC attachment was optimized on bovine pericardium (BP) patch using human umbilical vein ECs. Different biological coatings, namely gelatin, fibronectin, plasma, or a combination of fibronectin and plasma were tested. After cell adaptation, graft tissues were exposed to laminar flow in a parallel-plate flow chamber. Cell retention to the tissue was analyzed after nuclear staining with YO-PRO-1 and a membranous localization of VE-cadherin. Experiments showed that combined coating with fibronectin and blood plasma together with a two-phased shear pattern resulted in a relevant cell monolayer on BP patch and cryopreserved homograft. For BJV tissue, no adherent cells under both static and shear conditions were initially observed. In conclusion, having established the new flow chamber system we could obtain EC layers on the surface of BP patch and cryopreserved pulmonary homograft tissues. The presented in vitro system can serve as a competent model to study cell phenotypes on cardiac grafts in the close-to-physiologic environment. Moreover, this approach allows broad applications and enables further development by testing more complex conditions.

Endothelialization of cardiovascular devices

Blood-contacting surfaces of cardiovascular devices are not biocompatible for creating an endothelial layer on them. Numerous research studies have mainly sought to modify these surfaces through physical, chemical and biological means to ease early endothelial cell (EC) adhesion, migration and proliferation, and eventually to build an endothelial layer on the surfaces. The first priority for surface modification is inhibition of protein adsorption that leads to inhibition of platelet adhesion to the device surfaces, which may favor EC adhesion. Surface modification through surface texturing, if applicable, can bring some hopeful outcomes in this regard. Surface modifications through chemical and/or biological means may play a significant role in easy endothelialization of cardiovascular devices and inhibit smooth muscle cell proliferation. Cellular engineering of cells relevant to endothelialization can boost the positive outcomes obtained through surface engineering. This review briefly summarizes recent developments and research in early endothelialization of cardiovascular devices. STATEMENT OF SIGNIFICANCE: Endothelialization of cardiovascular implants, including heart valves, vascular stents and vascular grafts is crucial to solve many problems in our health care system. Numerous research efforts have been made to improve endothelialization on the surfaces of cardiovascular implants, mainly through surface modifications in three ways - physically, chemically and biologically. This review is intended to highlight comprehensive research studies to date on surface modifications aiming for early endothelialization on the blood-contacting surfaces of cardiovascular implants. It also discusses future perspectives to help guide endothelialization strategies and inspire further innovations.

Endothelialization of Cardiac Valve Bioprostheses

The main disadvantage of implanted xenograft valves used in cardiac surgery is their poor clinical long-term result, due to early tissue degeneration. In order to improve the performance of such glutaraldehyde fixed bioprostheses, a biological coating with viable endothelial cells was suggested. Therefore, glutaraldehyde preserved bovine pericard patches, as well as commercially available xenograft valves, were lined using human venous endothelial cells or microvascular cells from the subcutaneous fat tissue. Before cells were transplanted into their new environment, grafts were treated with an amino acid solution in order to neutralize the cytotoxic effect of free aldehydes, and precoated with fibronectinheparin and basic fibroblast growth factor (bFGF) or endothelial cell growth supplement (ECGS) in order to enhance cell proliferation. Coated specimens were kept in culture conditions for a further seven days. Proliferation of transplanted cells was verified by an increase of activation following 3H-thymidine incorporation, while the maintained metabolic cell activity was demonstrated via Prostacycline (PGI2) measurement. Morphology was evaluated by means of scanning electron microscopy (SEM). As evaluated by the β-Counter, 7 ng/ml bFGF (288,727 ± 39,668 counts on day 4) substantially enhanced cell proliferation after seeding, opposed to the stimulation with 30,000 ng/ml ECGS (91,924 ± 1129 counts on day 4), (p<0.001). The PGI2 release of transplanted cells was stimulated with 25 μM Na arachidonic acid by the factor 2.6 ± 0.3 and inhibited with 5 mM acetylsalecylic acid by the factor 0.7 + 0.2 on day 4 when compared with the basic level. After seven days of cultivation, SEM observation revealed that specimens stimulated with bFGF showed areas of confluent coated leaflets with an even distribution of cell layer. We therefore conclude that proliferation of transplanted cells is most favorable when stimulated with bFGF and that a special treatment of GA preserved cardiac valve bioprostheses allows a vital biological coating with human endothelial cells.

In vitro properties and performance of glutaraldehyde-crosslinked bovine pericardial bioprostheses treated with glutamic acid

Calcification is one of the major causes of failure of heart valve bioprostheses (HVBs) derived from glutaraldehyde (GA)-processed bovine pericardium (BP) or porcine aortic valves. New crosslinking reagent procedures are still far from giving satisfactory results, and this is the main reason why GA is still the reagent of choice for the fixation of native tissue intended for HVB manufacture. Nevertheless, two new findings with respect to GA processing may significantly improve HVB performance postimplantation: the finding that increasing concentrations of GA result in a decrease in calcification; the blocking of free aldehyde usually by nucleophyles or the treatment of processed material at low pH. This work investigates the in vitro properties of BP fixed with GA followed by the treatment with glutamic acid under alkaline conditions in order to prepare BP materials with lower calcification potential postimplantation. In comparison to conventional processing, except for the tensile strength that was slightly lower, elongation and toughness were higher than the accepted values. No significant differences were observed in the performance indexes (mean pressure gradient, mean effective area, regurgitant fraction, performance and efficiency indexes) with wear resistance over 150 × 10⁶ cycles. These results indicate that the processing of BP described in this work may be of potential use in the manufacture of HVBs.

RETRACTED: Poly(lactic-co-glycolic acid): carbon nanofiber composites for myocardial tissue engineering applications

This article has been retracted: please see Elsevier Policy on Article Withdrawal (https://www.elsevier.com/about/our-business/policies/article-withdrawal). This article has been retracted at the request of the Coordinating Editor and the Editor-in-Chief. An author-provided and previously published corrigendum updated Figures 9A and C and 10A and B. The authors had also provided a justification and an explanation for concerns raised in regards to Figure 3A. It was determined at that time that the conclusions of the publication remained the same. However, it has since been identified that parts of Figures 3, 9 and 10 are falsified and/or fabricated. The original data reported in this manuscript were not retained by the authors and the reliability of the reported results could not be confirmed. The editors regret any negative consequences that may have arisen from this matter within the scientific community.

Detoxification and Endothelialization of Glutaraldehyde-Fixed Bovine Pericardium With Titanium Coating

Background— Endothelial cell seeding of glutardialdehyde-fixed biological heart valves is hypothesized to improve biocompatibility and durability; however, the toxicity of glutardialdehyde prevents its use as a biological coating. Therefore, different detoxification strategies are applied, including surface coating with titanium, before in vitro endothelialization of glutaraldehyde-fixed bovine pericardium as the base material for prosthetic heart valves.

Methods and Results— Bovine pericardium was fixed with 0.25% glutardialdehyde. Detoxification was performed with citric acid, aldehyde dehydrogenase, and plasma deposition with titanium at low temperatures of 30°C to 35°C. Toxic glutaraldehyde ligands were quantified photometrically, and the vitality of seeded cells was tested to validate detoxification methods. Detoxification agents and titanium coating were applied before seeding with human endothelial cells. Endothelial cells were visualized by electron microscopic surface scanning. To evaluate cell adhesion, shear stress was applied by a flow of 5 L/min over 24 hours. Compared with untreated glutaraldehyde-fixed samples, treatment with the different agents reduced free aldehyde groups gradually (citric acid 5% < citric acid 10% < titanium < aldehyde dehydrogenase). A combination of citric acid 10%, aldehyde dehydrogenase, and titanium coating resulted in a reduction of free aldehyde ligands to 17.3±4.6% ( P ≤0.05) and demonstrated a vitality of seeded cells of 94±6.7% ( P ≤0.05). This procedure yielded a completely confluent layer of regular human endothelial cells (n=5). After application of shear stress for 24 hours on these endothelial layers, cell vitality was 81%.

Conclusions— Titanium coating combined with chemical procedures yielded significant detoxification and complete endothelialization of conventional glutaraldehyde-fixed pericardium. This new technique might improve glutardialdehyde-fixed cardiovascular bioimplants for better biocompatibility and longer durability.

Successful Endothelialization of Porcine Glutaraldehyde-Fixed Aortic Valves in a Heterotopic Sheep Model

PURPOSE

The purpose of our study was to evaluate the stability of an artificially seeded endothelial cell layer on porcine aortic prostheses under in vivo conditions in the arterial system.

DESCRIPTION

Ten female sheep were divided into two groups. Animals of the study group (n = 7) had dissection of their right external jugular vein for cell harvesting. Myofibroblasts and endothelial cells were labelled with PKH-26, seeded onto pretreated (10% citric acid) porcine glutaraldehyde-fixed aortic valves (Freestyle, Medtronic Inc, Duesseldorf, Germany), and the valves were implanted into the descending aorta. Controls (n = 3) received pretreated but unseeded valves. A shunt between the aortic arch and the left atrial appendage ensured systolic or diastolic leaflet motions, or both, that were documented by sonography. After 3 months the valves were explanted. Specimens for scanning electron microscopy and immunohistochemical staining were taken prior to implantation and after explantation.

EVALUATION

A neointimal proliferation was detected in the control group. No endothelial cells were found on the leaflets and the sinuses, but erythrocytes and thrombocytes were seen entrapped within the collagen fibers. Thrombus formation was documented macroscopically and histologically on the leaflets and the sinuses. In the study group a confluent endothelial cell layer was documented on the walls and leaflets. Neither neointimal proliferation nor any clots were seen. Some cells were still labelled positively indicating their origin from the initial cell seeding. No dilatation of any prosthesis was observed, but all valves showed slight thickening of the leaflets.

CONCLUSIONS

The artificially seeded endothelial cell layers remained stable under in vivo conditions in the arterial system. Biocompatibility of the prostheses seemed to be improved by reduction of thrombogenicity.

Comparative study of the L-hydro process and glutaraldehyde preservation

Commercial bioprosthetic heart valves are commonly preserved in glutaraldehyde and are cytotoxic to host cells, preventing spontaneous endothelialization. The aim of this study was to demonstrate the potential for in vivo endothelialization of bioprostheses treated by the L-Hydro process which consists of mild extraction of antigenic substances and incorporation of antiinflammatory and antithrombotic agents. Seven stented porcine heart valves treated by the L-Hydro process and 3 glutaraldehyde-fixed porcine heart valves were implanted in the mitral position in juvenile sheep. The valves were evaluated by echocardiography, angiography, histology, and histochemistry. No hemodynamic differences were observed, but scanning and transmission electron microscopy showed nearly complete coverage by endothelial cells of all leaflets in the L-Hydro-treated valves after 5 months of implantation. The endothelial cells were in direct contact with the underlying collagen and expressed von Willebrand-related antigens. The surfaces of the glutaraldehyde-treated valves were covered by fibrin, macrophages, calcium, and thrombotic material; only sparse endothelial cells were observed and contact with the underlying tissue was incomplete. These data indicate that L-Hydro-treated porcine valves are capable of inducing spontaneous endothelialization.

Seeding of Human Endothelial Cells on Valve Containing Aortic Mini-Roots: Development of a Seeding Device and Procedure

PURPOSE

Complete covering of an artificial valvular scaffold with endothelial cells may prevent thromboembolic complications and lead to an excellent biocompatibility. For this purpose, we developed a seeding device for reproducible cell seeding on valve containing aortic roots.

DESCRIPTION

Human endothelial cells and fibroblasts were obtained from saphenous vein pieces. Cryopreserved aortic roots (n = 25) were put into an especially developed tube, set on a rotator, and incubated with the cell suspension. The device rotated in two axes (sagittal and axial), ensuring slight movements of the leaflets. The rotation alternated with resting periods, allowing cell attachment to the surface. Different resting periods were tested (groups 1, 2, and 3 were 30, 45, and 60 min, respectively; n = 5 each). Total incubation time was 24 hours followed by further culturing for 6 days. In two further groups (groups 4 and 5; n = 5 each), a modified inlay was used to allow the cell suspension to flow around the entire graft. In group 4 the grafts were again incubated with human endothelial cells; however, in group 5 pre-seeding with autologous fibroblasts was done in addition. Immunohistochemical staining with antibodies against factor VIII, CD31, laminin, collagen IV, and CD90 were done, and scanning electron microscopy was done after initial seeding and after 6 days in culture.

EVALUATION

Seeding resulted in homogenous cell layers on the luminal surface of the free walls in all groups. With resting periods of 45 minutes, these results were also obtained on the leaflets, whereas the other resting times resulted in defects of the endothelial cell layer on the cusps. After 6 days under culture conditions, the endothelial cell layers were confluent and viable, with the exception of the leaflets in group 1. With the modified inlay (groups 4 and 5), confluent cell layers were also achieved on the outer surface. In group 5 pre-seeding with autologous fibroblasts resulted in enhanced synthesis of extracellular matrix proteins, as was demonstrated with immunohistochemical staining for collagen IV and laminin.

CONCLUSIONS

With this newly developed seeding device, confluent cell layers on valve containing aortic roots were reproducibly achieved. The technique enables further experimental research and even clinical application.

Preseeding with autologous fibroblasts improves endothelialization of glutaraldehyde-fixed porcine aortic valves

OBJECTIVE

This study represents the development of a treatment and seeding procedure to improve endothelial cellular adhesion on glutaraldehyde-fixed valves.

METHODS

Porcine aortic valves were fixed with 0.2% glutaraldehyde. Wall pieces of these valves had either no additional treatment (n = 4), incubation in M199 Earle (1x), with sodium carbonate at 2.2 g/L without l-glutamine for 24 hours (n = 4), or additional pretreatment with 5%, 10%, or 15% citric acid (three groups, n = 4 each). Thereafter the pieces were washed and buffered to a physiologic pH. This was followed by seeding of human endothelial cells (5 x 10(6) cells). On the basis of the results of these pilot tests, complete glutaraldehyde-fixed aortic roots treated with 10% citric acid were subjected to cell seeding. The valves were seeded with endothelial cells (4.3 x 10(6) cells) either alone (n = 4) or in combination with preseeding of autologous fibroblasts (2.4 x 10(7) cells, n = 4). After each seeding procedure specimens of the free wall of the grafts were taken. In addition, one leaflet was taken for histologic examination after endothelial cell seeding, after 7 days, and after 21 days. Finally, two commercially available stentless aortic valve prostheses (Freestyle; Medtronic, Inc, Minneapolis, Minn) were treated with 10% citric acid and seeded with human fibroblasts and endothelial cells. Specimen were taken according to the glutaraldehyde-fixed aortic roots. Specimen of all experiments were examined with scanning electron microscopy. Frozen sections were stained immunohistochemically for collagen IV, factor VIII, and CD31.

RESULTS

On untreated glutaraldehyde-fixed aortic wall pieces, only poor adhesion (24%) was seen. No viable cells were found after 1 week. Cellular adhesion was best on aortic wall pieces pretreated with 10% citric acid. After 7 days, the cells formed a confluent layer. Endothelial cell seeding on citric acid-treated complete aortic valves showed 45% adhesion, but no confluent layer was found after 1 week. Preseeding of these valves with autologous fibroblasts resulted in an endothelial cellular adhesion of 76% and a confluent endothelial cell layer after 7 days. The layer remained stable for at least 21 days. Results of staining for collagen IV, factor VIII, and CD31 were positive on the luminal side of these valves, indicating the synthesis of matrix proteins and viability of the cells. Pretreatment of commercially available porcine valves with 10% citric acid and preseeding with autologous fibroblasts followed by endothelial cell seeding resulted in an adhesion of 78%. The cells formed a confluent cell layer after 7 days.

CONCLUSIONS

Pretreatment of glutaraldehyde-fixed porcine aortic valves with citric acid established a surface more suitable for cellular attachment. Preseeding these valves with autologous fibroblasts resulted in a confluent endothelial cell layer on the luminal surface. Flow tests and animal experiments are necessary for further assessment of durability and shear stress resistance.

Improving the clinical patency of prosthetic vascular and coronary bypass grafts: the role of seeding and tissue engineering

In patients requiring coronary or peripheral vascular bypass procedures, autogenous vein is currently the conduit of choice. If this is unavailable, then a prosthetic material is used. Prosthetic graft is liable to fail due to occlusion of the graft. To prevent graft occlusion, seeding of the graft lumen with endothelial cells is undertaken. Recent advances have also looked at developing a completely artificial biological graft engineered from the patient's cells with properties similar to autogenous vessels. This review encompasses the developments in the two principal technologies used in developing hybrid coronary and peripheral vascular bypass grafts, that is, seeding and tissue engineering.

The anticalcific effect of glutaraldehyde detoxification on bioprosthetic aortic wall tissue in the sheep model

BACKGROUND

Increasing concentrations of glutaraldehyde (GA) lead to a decreased rather than increased calcification of bioprosthetic aortic wall tissue. This study determined to what extent the benefit of better cross-linking is masked by the intrinsic propensity of GA towards calcification.

MATERIALS AND METHODS

Porcine aortic roots were immediately fixed at the abattoir at three different concentrations of GA (0.2%, 1.0%, and 3.0% for 1 week at 4 degrees C). Subsequently, roots underwent a GA extraction process using high volumes of Urazole solution (acetic acid buffer, pH 4.5, 37 degrees C, 1 week) followed by NaBH4 reduction (2 days, 37 degrees C). Roots were implanted in the distal aortic arch of young sheep for 6 weeks and 6 months. Calcium analysis was quantitatively done by atomic absorption spectrophotometry and qualitatively assessed by light microscopy on Von Kossa stains.

RESULTS

There was a distinct anticalcification effect of GA detoxification after 6 weeks (56.8% to 97.9%; 95% confidence interval [CI]), which stabilized on a more moderate level after 6 months of implantation (19.1% to 31.6%; 95% CI). The most pronounced effect of GA extraction was seen in 0.2% fixed tissue, where aortic wall calcification was mitigated by 97% and 32% after 6 weeks and 6 months, respectively. Mitigation of aortic wall calcification was 71% (6 weeks) and 21% (6 months) in the 3.0% GA group. The combined effect of higher cross-link density and detoxification achieved an 82% (6 weeks) and 48% (6 months) reduction of calcium levels in the 3.0% GA group. In long-term implants (6 months), detoxification alone on top of standard 0.2% GA fixation was as effective (from 174.1 +/- 11.9 microg/mg without detoxification to 119.3 +/- 19.3 microg/mg with detoxification) as 3.0% fixation (114.8 +/- 10.0 microg/mg without detoxification to 91.3 +/- 11.5 microg/mg with detoxification).

CONCLUSION

We were able to determine in the circulatory sheep model to what degree the intrinsic procalcific effect of GA counteracts the protective effect of higher cross-link density. Our study also established that the effect of detoxification is particularly pronounced in commercial low-grade fixation.

Mitigation of bioprosthetic heart valve degeneration through biocompatibility: in vitro versus spontaneous endothelialization

BACKGROUND

Glutaraldehyde-related cytotoxicity and transanastomotic ingrowth inhibition prevent the spontaneous endothelialization of bioprosthetic heart valves. In order to evaluate the ability of improved biocompatibility to reduce tissue degeneration, conventionally fixed aortic root prostheses were both glutaraldehyde-detoxified and in vitro endothelialized.

METHODS

Entire aortic roots were fixed in 0.2% glutaraldehyde (GA) (control group) and either detoxified in acetic acid-buffered urazole (0.1 M) or detoxified and in vitro lined with cultured, autologousjugular vein endothelial cells. The valved roots were inserted in the distal aortic arch of 15 juvenile Merino sheep for a period of 12 weeks. Upon explant, leaflets, sinuses and aortic wall of the prostheses were analysed by SEM to assess the surface endothelium, histologically regarding tissue inflammation, and by atomic absorption spectrophotometry to determine the content of tissue calcium.

RESULTS

There was no endothelium on control grafts, except for a short anastomotic pannus. The detoxified group showed an incomplete patchy endothelium on the aortic wall but hardly any on the leaflets, whereas, the in vitro lined group had aortic wall, sinuses and most of the leaflets confluently endothelialized. Tissue inflammation was prominent in the control group and least expressed in the endothelialized group (p < 0.05). Detoxification significantly reduced leaflet calcification. In the aortic wall, both detoxification and endothelial lining were required to significantly mitigate calcification.

CONCLUSION

In the 12 week circulatory sheep model, the calcium mitigating effect of detoxification was more pronounced than that of in vitro endothelialization. Nevertheless, there was a distinct overall benefit if detoxification was combined with endothelialization.

In vitro endothelialization of bioprosthetic heart valves provides a cell monolayer with proliferative capacities and resistance to pulsatile flow

OBJECTIVES

Degeneration of bioprosthetic heart valves has been suggested to be at least partly an immunogenic reaction toward the xenogeneic tissue. An autologous endothelial lining has been proposed to overcome this problem. We examined in vitro endothelialization of such tissue and retention of endothelial cells after exposure to flow resembling the in vivo situation.

METHODS

Cultured human saphenous vein endothelial cells were used to in vitro endothelialize photo-oxidized bioprosthetic heart valves. The endothelialized valves were mounted in a specially designed flow device, creating a pulsatile flow through the valve. Maintenance of a confluent cell layer and deposition of basement membrane markers were determined with immunohistochemical labeling.

RESULTS

Labeling of the main components of the basement membrane, laminin and collagen type IV, was verified within 6 hours after in vitro endothelialization. Under static conditions, 4-mm wide denudations were completely re-endothelialized in 4 days, which was similar to the growth rate on gelatin-coated cell culture plastic, which served as a control material. After exposure of endothelialized valves to pulsatile flows for 24 hours (80 beats/min, 3.4 L/min), there were minimal cell losses from the bioprostheses. The cell layer adapted to the pulsatile flow, as verified by rearrangement of morphology and intracellular stress fibers.

CONCLUSIONS

This study shows the feasibility of in vitro endothelialization of photo-oxidized bioprosthetic heart valves. The cells are able to withstand a pulsatile flow in vitro, to develop basement membrane-like structures, and to re-endothelialize denuded areas. This technology may be used to enhance the performance of bioprosthetic heart valve prostheses.

Cell adhesion and short-term patency in human endothelium preseeded 1.5-mm polytetrafluoroethylene vascular grafts: an experimental study

It has been shown that endothelialization improves short-term patency of 1.5-mm expanded polytetrafluoroethylene vascular grafts. A model for endothelialization of 1.5-mm expanded polytetrafluoroethylene vascular grafts with human endothelial cells is described. In this model, the adherence of endothelial cells was increased significantly in grafts coated with serum proteins and collagen. By means of this protocol, graft patency was tested after implantation in two animal models: the rat aorta and the rabbit common carotid artery. Anastomosis was performed with a 3M Precise Microvascular Anastomotic System. In both animal models, no significant loss of endothelial cells in the precoated grafts (rat, n = 8) were noted 1 hour after blood flow restoration. All uncoated grafts showed significant endothelial cell loss. In the rabbit model, all nonendothelialized grafts (n = 8) clotted 5 to 25 minutes after flow restoration. Seven (n = 8) endothelialized grafts showed no clotting during 1 hour's observation: one clotted immediately for a patency rate of 87.5 percent. These results indicate that endothelialization of 1.5-mm grafts is practical. Furthermore, adhesion of endothelial cells to the graft walls is not affected by short-term, pulsatile, high-pressure blood flow.

In vitro endothelialization of photooxidatively stabilized xenogeneic pericardium

The possibility of improving the performance of heart valve bioprostheses and vascular biografts by means of preendothelialization with cultured autologous cells has been suggested. Such culture techniques are available, but the glutaraldehyde-preserved heart valve prostheses used clinically appear cytotoxic. Recently, dye-mediated photooxidation has been reported to stabilize pericardial tissue, possibly through the cross-linking of collagen fibrils. We have seeded cultured adult human saphenous vein endothelial cells (HSVECs) onto photooxidatively stabilized tissue and investigated the morphologic characteristics 7 days later. A confluent lining of cultured HSVECs similar to native endothelium was demonstrated by scanning electron microscopy. The presence of von Willebrand's factor, an integrin located at the interendothelial cell contacts (PECAM/CD 31), and the basement membrane component collagen type IV was demonstrated using monoclonal antibodies. The results were similar for the HSVECs seeded onto both bovine and porcine pericardial tissues. The results clearly indicate that the dye-mediated photooxidation technique produces a tissue that is cell compatible. Provided the HSVECs remain attached and retain antithrombotic and antiinflammatory properties, this appears to be a feasible way of endothelializing bioprosthetic heart valves before implantation.