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

The cardiotomy reservoir - a preliminary evaluation of a new cell source for cardiovascular tissue engineering

OBJECTIVES

Cell sources for cardiovascular tissue engineering (TE) are scant. However, the need for an ideal TE cardiovascular implant persists. We investigated the cardiotomy reservoir (CR) as a potential cell source that is more accessible and less ethically problematic.

METHODS

CR (n = 10) were removed from the bypass system after surgery. Isolation was performed using different isolation methods: blood samples were taken from the cardiopulmonary bypass and centrifuged at low density. The venous filter screen was cut out and placed into petri dishes for cultivation. The spongelike filter was removed, washed and treated in the same way as the blood samples. After cultivation, cell lines of fibroblasts (FB) and endothelial cells (EC) were obtained for analysis. The cells were seeded on polyurethane patches and analyzed via scanning electron microscopy (SEM), Life/Dead assay and immunohistochemistry.

RESULTS

No correlation between age, time of surgery and quality of cells was observed. The successful extraction of FB and was proven by positive staining results for TE-7, CD31 and vWF. Cell morphology, cytoskeleton staining and quantification of proliferation using WST-1 assay resembled the cells of the control group in all ways. The topography of a confluent and vital cell layer after cell seeding was displayed by SEM analysis, Life/Dead Assay and immunohistochemistry. The establishment of an extracellular matrix (ECM) was proven by positive staining for collagen IV, laminin, fibronectin and elastin.

CONCLUSIONS

Viable FB and EC cell lines were extracted from the CR after surgery. Easy access and high availability make this cell source destined for widespread application in cardiovascular tissue engineering.

Is Transcatheter Aortic Valve Implantation of Living Tissue-Engineered Valves Feasible? An In Vitro Evaluation Utilizing a Decellularized and Reseeded Biohybrid Valve

Transcatheter aortic valve implantation (TAVI) is a fast-growing, exciting field of invasive therapy. During the last years many innovations significantly improved this technique. However, the prostheses are still associated with drawbacks. The aim of this study was to create cell-seeded biohybrid aortic valves (BAVs) as an ideal implant by combination of assets of biological and artificial materials. Furthermore, the influence of TAVI procedure on tissue-engineered BAV was investigated. BAV (n=6) were designed with decellularized homograft cusps and polyurethane walls. They were seeded with fibroblasts and endothelial cells isolated from saphenous veins. Consecutively, BAV were conditioned under low pulsatile flow (500 mL/min) for 5 days in a specialized bioreactor. After conditioning, TAVI-simulation was performed. The procedure was concluded with re-perfusion of the BAV for 2 days at an increased pulsatile flow (1100 mL/min). Functionality was assessed by video-documentation. Samples were taken after each processing step and evaluated by scanning electron microscopy (SEM), immunohistochemical staining (IHC), and Live/Dead-assays. The designed BAV were fully functioning and displayed physiologic behavior. After cell seeding, static cultivation and first conditioning, confluent cell layers were observed in SEM. Additionally, IHC indicated the presence of endothelial cells and fibroblasts. A significant construction of extracellular matrix was detected after the conditioning phase. However, a large number of lethal cells were observed after crimping by Live/Dead staining. Analysis revealed that the cells while still being present directly after crimping were removed in subsequent perfusion. Extensive regions of damaged cell-layers were detected by SEM-analysis substantiating these findings. Furthermore, increased ICAM expression was detected after re-perfusion as manifestation of inflammatory reaction. The approach to generate biohybrid valves is promising. However, damages inflicted during the crimping process seem not to be immediately detectable. Due to severe impacts on seeded cells, the strategy of living TE valves for TAVI should be reconsidered.

Culture of ovine esophageal epithelial cells and in vitro esophagus tissue engineering

BACKGROUND

Esophagus replacement presents major surgical challenges both in the pediatric and in adult patients since the various surgical techniques presently employed are associated with complications and high morbidity.

AIM

The aim of this study was to establish protocols for isolation and culture of ovine esophageal epithelial cells (OEEC) and to investigate their viability on collagen scaffolds for in vitro tissue engineering.

METHODS

OEEC were sourced from adult Austrian mountain sheep. Briefly, the esophagus was dissected, treated with dispase to separate the epithelial layer, and further subjected to a modified explants technique to isolate OEEC. The OEEC were cultured in vitro and seeded on to unidirectional two-dimensional and three-dimensional collagen scaffolds.

RESULTS

Successful protocol was established for OEEC isolation and culture. OEEC exhibited organization and differentiation after 7 days in culture, which was complete after 18 days with the formation of a single layer sheet of differentiated cells exhibiting morphology of mature esophageal epithelium. OEEC seeded on two-dimensional collagen scaffolds demonstrated viability up to 6 weeks of in vitro culture with single layer epithelium formation after 3 weeks confirmed using pan-Cytokeratin markers. OEEC on three-dimensional scaffolds were viable for 6 weeks but did not form an epithelium sheet.

CONCLUSION

Protocols for OEEC isolation were developed and established from adult ovine esophageal tissue. The generation of sheets of esophageal epithelium in culture and the viability of OEEC on collagen scaffolds for 6 weeks in vitro was observed. The prerequisite for esophagus tissue engineering, which is the ability to form epithelium when seeded on collagen scaffolds, was demonstrated.

Esophagus tissue engineering: in situ generation of rudimentary tubular vascularized esophageal conduit using the ovine model

PURPOSE

Esophagus replacement using the present surgical techniques is associated with significant morbidity. Tissue engineering of the esophagus may provide the solution for esophageal loss. In our attempts to engineer the esophagus, this study aimed to investigate the feasibility of generating vascularized in situ esophageal conduits using the ovine model.

METHODS

Esophageal biopsies were obtained from lambs, and ovine esophageal epithelial cells (OEEC) were proliferated. The OEEC were seeded on to bovine collagen sheets preseeded with fibroblasts. After 2 weeks of maintaining the constructs in vitro, the constructs were tubularized on stents to create a tube resembling the esophagus and implanted into the omentum for in situ tissue engineering. The edges of the omentum were sutured using nonabsorbable suture material. The implanted constructs were retrieved after 8 and 12 weeks.

RESULTS

The omental wrap provided vascular growth within and around the constructs as they were integrated along the outer surface area of the scaffold. After removal of the stents, the engineered conduit revealed a structure similar to the esophagus. Histologic investigations demonstrated esophageal epithelium organization into patches on the luminal side and vascular ingrowths on the conduit's outer perimeter.

CONCLUSION

Our study demonstrated the seeding of OEEC on collagen scaffolds and formation of a rudimentary conduit resembling esophageal morphology after in situ omental implantation. Vascular coverage and ingrowth in the periphery of the construct could also be demonstrated. These findings hold future promise for the engineering of the esophagus with improved microarchitecture.

Impact of freezing/thawing procedures on the post-thaw viability of cryopreserved human saphenous vein conduits

BACKGROUND

Cryopreserved human blood vessels are important tools in reconstructive surgery. However, patency of frozen/thawed conduits depends largely on the freezing/thawing procedures employed.

METHODS

Changes in tone were recorded on rings from human saphenous vein (SV) and used to quantify the degree of cryoinjury after different periods of exposure at room temperature to the cryomedium (Krebs-Henseleit solution containing 1.8M dimethyl sulfoxide and 0.1M sucrose) and after different cooling speeds and thawing rates following storage at -196 degrees C.

RESULTS

Without freezing, exposure of SV to the cryomedium for up to 240 min did not modify contractile responses to noradrenaline (NA). Pre-freezing exposure to the cryomedium for 10-120 min attenuated significantly post-thaw maximal contractile responses to NA, endothelin-1 (ET-1) and potassium chloride (KCl) by 30-44%. Exposure for 240 min attenuated post-thaw contractile responses to all tested agents markedly by 62-67%. Optimal post-thaw contractile activity was obtained with SV frozen at about -1.2 degrees C/min and thawed slowly at about 15 degrees C/min. In these SV maximal contractile responses to NA, ET-1 and KCl amounted to 66%, 70% and 60% of that produced by unfrozen controls. Following cryostorage of veins for up to 10 years the responsiveness of vascular smooth muscle to NA was well maintained.

CONCLUSION

Cryopreservation allows long-term banking of viable human SV with only minor loss in contractility.