Multi-Scale Modelling of Textile Reinforced Tissue Engineered Heart Valves
Transcatheter aortic valve implantation of fibrin-based tissue engineered heart valves with a tubular leaflet construct have been developed as an alternative to invasive traditional surgical heart valve implantation, but currently need reinforcement to withstand pressures found in the aortic position. To increase valve strength, a PET textile reinforcement has been introduced to the fibrin scaffold. However, care must be taken when using a textile reinforcement. Increasing reinforcement may increase the strength, but also increases stiffness which can interfere with the functionality of the valve, prohibiting full valve closure. In order to predict the behavior of the valve, improve design, and eventually optimize valve performance by tailoring the textile reinforcement, a 4-tiered hierarchical multi-scale modelling framework has been created. The model includes an individual fiber scale model, two textile-level models, and a full heart valve model. Geometry generation based on microscopic images of the composite will be discussed, along with application of boundary conditions and loading application. Fitting the various material models based on homogenization of the smaller scale will be demonstrated. Finally, experimental validation and characterization at various scales will be discussed.
Tissue bioengineering and artificial organs.
The scarcity of organs and tissues for transplant and the need of immunosuppressive drugs to avoid rejection constitute two reasons that justify organ and tissue production in the laboratory. Tissue engineering based tissues (TE) could allow to regenerate the whole organ from a fragment or even to produce several organs from an organ donor for grafting purposes. TE is based in: (1) the ex vivo expansion of cells, (2) the seeding of these expanded cells in tridimensional structures that mimic physiological conditions and, (3) grafting the prototype. In order to graft big structures it is necessary that the organ or tissue produced "ex vivo" bears a vascular tree to ensure the nutrition of its deep layers. At present, no technology has been developed to provide this vascular tree to TE derived products. Thus, these tissues must be thin enough to acquire nutrients during the first days by diffusion from surrounding tissues. This fact constitutes nowadays the greatest limitation of technologies for organ development in the laboratory.In this chapter, all these problems and their possible solutions are commented. Also, the present status of TE techniques in the regeneration of different organ systems is reviewed.
Limited Long-Term Durability of the Cryolife O’Brien Stentless Porcine Xenograft Valve
Background— Despite the fact that early and midterm hemodynamic and clinical results of the Cryolife O’Brien (CLOB) stentless valve have been reported to be favorable, the long-term durability and clinical results of this valve are largely unknown. Accordingly, we analyzed 10-year outcomes after aortic valve replacement with this valve. Methods and Results— From January 1994 to September 2004, 185 patients (67, 73, and 75 years, 25th, 50th, and 75th quartiles, respectively; 38% older than 75 years; 56% females) underwent aortic valve replacement with the CLOB valve. Sixty-eight percent of patients were in NYHA class 3 to 4. Standard EuroSCORE was 7.1±2.7. Pure aortic stenosis accounted for 42% (n=79), and pure insufficiency for 12% of cases (n=22). Concomitant surgery: 28% coronary artery bypass (n=51), 11% mitral valve replacement/annuloplasty (n=21), and 2% ascending aorta replacement (n=3). Sixty-one percent of patients received a 23-mm valve or smaller size. Follow-up was 100% completed, and cumulative follow-up was 65 months/patient. The 30-day mortality was 5.4% (none were valve related). Actuarial survival at 5 and 10 years were 68% and 40%, respectively. Actuarial freedom from structural valve deterioration was 91% at 5 years and dropped to 44% at 10 years. Actuarial freedom from reoperation was 94% at 5 years and declined to 57% at 10 years. Conclusions— In a population with a high prevalence of elderly females with small aortic root, the CLOB valve demonstrated satisfactory clinical results till 8-years. Afterward, a significant increase in hazard for structural valve deterioration and reoperation occurred in late follow-up.