Identification of Autologous Tissue Sources and Optimization of a Treatment Method for Intraoperative Manufacturing of Heart Valve Constructs.

The study was aimed at assessing T cell subsets of peripheral blood from recipients of long-term functioning (more than 60 months) biological and mechanical heart valve prostheses. The absolute and relative number of CD4 and CD8 T cell subsets was analyzed: naïve (N, CD45RA+CD62L+), central memory (CM, CD45RA−CD62L+), effector memory (EM, CD45RA−CD62L−), and terminally differentiated CD45RA-positive effector memory (TEMRA, CD45RA+CD62L−) in 25 persons with biological and 7 with mechanical prosthesis compared with 48 apparently healthy volunteers. The relative and absolute number of central memory and naïve CD3+CD8+ in patients with biological prosthesis was decreased (p < 0.001). Meanwhile the number of CD45RA+CD62L−CD3+CD8+ and CD3+CD4+ was increased (p < 0.001). Patients with mechanical prosthesis had increased absolute and relative number of CD45RA+CD62L−CD3+CD8+ cells (p = 0.006). Also the relative number of CD3+CD4+ cells was reduced (p = 0.04). We assume that altered composition of T cell subsets points at development of xenograft rejection reaction against both mechanical and biological heart valve prostheses.

Inhibition of blood coagulation activation and oral anticoagulants in patients with mechanical heart valve prostheses

Aims: The physiological design, the selection of scaffold material and the fabrication technique play a crucial role in the development of tissue engineered heart valves. In our current experiment, we recreate the complex anatomic structure of a human heart valve using stereolithography and developed a new fabrication technique to shape regenerating human heart valve tissue.

On-demand heart valve manufacturing using focused rotary jet spinning

Nanofibrous bioengineered heart valve-Application in paediatric medicine.

Only mechanical and biological heart valve prostheses are currently commercially available. The former show longer durability but require anticoagulant therapy; the latter display better fluid dynamic behavior but do not have adequate durability. New Polymeric Heart Valves (PHVs) could potentially combine the hemodynamic properties of biological valves with the durability of mechanical valves. This work presents a hydrodynamic evaluation of 2 groups of newly developed supra-annular, trileaflet prosthetic heart valves made from styrenic block copolymers (SBC): Poli-Valves. 2 types of Poli-Valves made of SBC and differing in polystyrene fraction content were tested under continuous and pulsatile flow conditions as prescribed by ISO 5840 Standard. A pulse duplicator designed ad hoc allowed the valve prototypes to be tested at different flow rates and frequencies. Pressure and flow were recorded; pressure drops, effective orifice area (EOA), and regurgitant volume were computed to assess the behavior of the valve. Both types of Poli-Valves met the minimum requirements in terms of regurgitation and EOA as specified by the ISO 5840 Standard. Results were compared with 5 mechanical heart valves (MHVs) and 5 tissue heart valves (THVs), currently available on the market. Based on these results, PHVs based on styrenic block copolymers, as are Poli-Valves, can be considered a promising alternative for heart valve replacement in the near future.

Previously, we reported the implantation of a single tissue engineered leaflet in the posterior position of the pulmonary valve in a lamb model. The major problems with this leaflet replacement were the scaffold's inherent stiffness, thickness, and nonpliability. We have now created a scaffold for a trileaflet heart valve using a thermoplastic polyester. In this experiment, we show the suitability of this material in the production of a biodegradable, biocompatible scaffold for tissue engineered heart valves. A heart valve scaffold was constructed from a thermoplastic elastomer. The elastomer belongs to a class of biodegradable, biocompatible polyesters known as polyhydroxyalkanoates (PHAs) and is produced by fermentation (Metabolix Inc., Cambridge, MA). It was modified by a salt leaching technique to create a porous, three-dimensional structure, suitable for tissue engineering. The trileaflet heart valve scaffold consisted of a cylindrical stent (1 mm X 15 mm X 20 mm I.D.) containing three valve leaflets. The leaflets were formed from a single piece of PHA (0.3 mm thick), and were attached to the outside of the stent by thermal processing techniques, which required no suturing. After fabrication, the heart valve construct was allowed to crystallize (4 degrees C for 24 h), and salt particles were leached into doubly distilled water over a period of 5 days to yield pore sizes ranging from 80 to 200 microns. Ten heart valve scaffolds were fabricated and seeded with vascular cells from an ovine carotid artery. After 4 days of incubation, the constructs were examined by scanning electron microscopy. The heart valve scaffold was tested in a pulsatile flow bioreactor and it was noted that the leaflets opened and closed. Cells attached to the polymer and formed a confluent layer after incubation. One advantage of this material is the ability to mold a complete trileaflet heart valve scaffold without the need for suturing leaflets to the conduit. Second advantage is the use of only one polymer material (PHA) as opposed to hybridized polymer scaffolds. Furthermore, the mechanical properties of PHA, such as elasticity and mechanical strength, exceed those of the previously utilized material. This experiment shows that PHAs can be used to fabricate a three-dimensional, biodegradable heart valve scaffold.

The approval of a heart valve for the European market takes place in accordance with European and international standards. A new version of the EN Standards was published in June 2006, which responded to different technical innovations in the area of heart valve technology. This work outlines the differences between the new EN ISO 5840 (2005) and the old EN 12006-1 (1999). We compared the 'new' EN ISO 5840 (2005) and the 'old' EN 12006-1 (1999). The following aspects have been updated in the new EN ISO 5840: Size designation of biological and mechanical heart valve prostheses in accordance with the patient annulus. Differentiation of the annular implantation position (intra-annular, intra-supra-annular, supra-annular). Table for the description of the components of a heart valve prosthesis. Use of compliance chambers for the hydrodynamic testing of prostheses without scaffold. Determination of the minimum requirement for heart valve prostheses in hydrodynamic tests and specification of reference values with regard to prosthesis-related complications in clinical studies. Definition of the requirements for clinical long-term studies (patient number, length). Introduction of an obligatory post-observation timeframe of 5 years for mechanical heart valves and of 10 years for biological heart valves. The update in the new EN ISO 5840 gives consideration to the technologic evolution of heart valve development. Several changes in the new standard will improve safety for the patient and ensure high quality in the field of heart valve technology.

A crucial factor in tissue engineering of heart valves is the functional and physiologic scaffold design. In our current experiment, we describe a new fabrication technique for heart valve scaffolds, derived from x-ray computed tomography data linked to the rapid prototyping technique of stereolithography. To recreate the complex anatomic structure of a human pulmonary and aortic homograft, we have used stereolithographic models derived from x-ray computed tomography and specific software (CP, Aachen, Germany). These stereolithographic models were used to generate biocompatible and biodegradable heart valve scaffolds by a thermal processing technique. The scaffold forming polymer was a thermoplastic elastomer, a poly-4-hydroxybutyrate (P4HB) and a polyhydroxyoctanoate (PHOH) (Tepha, Inc., Cambridge, MA). We fabricated one human aortic root scaffold and one pulmonary heart valve scaffold. Analysis of the heart valve included functional testing in a pulsatile bioreactor under subphysiological and supraphysiological flow and pressure conditions. Using stereolithography, we were able to fabricate plastic models with accurate anatomy of a human valvular homograft. Moreover, we fabricated heart valve scaffolds with a physiologic valve design, which included the sinus of Valsalva, and that resembled our reconstructed aortic root and pulmonary valve. One advantage of P4HB and PHOH was the ability to mold a complete trileaflet heart valve scaffold from a stereolithographic model without the need for suturing. The heart valves were tested in a pulsatile bioreactor, and it was noted that the leaflets opened and closed synchronously under subphysiological and supraphysiological flow conditions. Our preliminary results suggest that the reproduction of complex anatomic structures by rapid prototyping techniques may be useful to fabricate custom made polymeric scaffolds for the tissue engineering of heart valves.

To investigate whether patients with heart valve prostheses and similar International Normalized Ratios (INR) have the same level of protection against thromboembolic events, that is, whether the anticoagulation intensity is related to the intensity of hypercoagulability suppression. INR and plasma levels of prothrombin fragment 1+2 (F1+2) were assessed in blood samples of 27 patients (7 with mechanical heart valves and 20 with biological heart valves) and 27 blood samples from healthy donors that were not taking any medication. Increased levels of F1+2 were observed in blood samples of 5 patients with heart valve prostheses taking warfarin. These findings reinforce the idea that even though patients may have INRs, within the therapeutic spectrum, they are not free from new thromboembolic events. Determination of the hypercoagulability marker F1+2 might result in greater efficacy and safety for the use of oral anticoagulants, resulting in improved quality of life for patients.

Background —Tissue engineering is a new approach in which techniques are being developed to transplant autologous cells onto biodegradable scaffolds to ultimately form new functional autologous tissue. Workers at our laboratory have focused on tissue engineering of heart valves. The present study was designed to evaluate the implantation of a whole trileaflet tissue-engineered heart valve in the pulmonary position in a lamb model. Methods and Results —We constructed a biodegradable and biocompatible trileaflet heart valve scaffold that was fabricated from a porous polyhydroxyalkanoate (pore size 180 to 240 μm; Tepha Inc). Vascular cells were harvested from ovine carotid arteries, expanded in vitro, and seeded onto our heart valve scaffold. With the use of cardiopulmonary bypass, the native pulmonary leaflets were resected, and 2-cm segments of pulmonary artery were replaced by autologous cell–seeded heart valve constructs (n=4). One animal received an acellular valved conduit. No animal received any anticoagulation therapy. Animals were killed at 1, 5, 13, and 17 weeks. Explanted valves were examined histologically with scanning electron microscopy, biochemically, and biomechanically. All animals survived the procedure. The valves showed minimal regurgitation, and valve gradients were &lt;20 mm Hg on echocardiography. The maximum gradient was 10 mm Hg with direct pressures. Macroscopically, the tissue-engineered constructs were covered with tissue, and there was no thrombus formation on any of the specimens. Scanning electron microscopy showed smooth flow surfaces during the follow-up period. Histological examination demonstrated laminated fibrous tissue with predominant glycosaminoglycans as extracellular matrix. 4-Hydroxyproline assays demonstrated an increase in collagen content as a percentage of native pulmonary artery (1 week 45.8%, 17 weeks 116%). DNA assays showed a comparable number of cells in all explanted samples. There was no tissue formation in the acellular control. Conclusions —Tissue-engineered heart valve scaffolds fabricated from polyhydroxyalkanoates can be used for implantation in the pulmonary position with an appropriate function for 120 days in lambs.

Tissue engineering is a new approach in which techniques are being developed to transplant autologous cells onto biodegradable scaffolds to ultimately form new functional autologous tissue. Workers at our laboratory have focused on tissue engineering of heart valves. The present study was designed to evaluate the implantation of a whole trileaflet tissue-engineered heart valve in the pulmonary position in a lamb model. We constructed a biodegradable and biocompatible trileaflet heart valve scaffold that was fabricated from a porous polyhydroxyalkanoate (pore size 180 to 240 microm; Tepha Inc). Vascular cells were harvested from ovine carotid arteries, expanded in vitro, and seeded onto our heart valve scaffold. With the use of cardiopulmonary bypass, the native pulmonary leaflets were resected, and 2-cm segments of pulmonary artery were replaced by autologous cell-seeded heart valve constructs (n=4). One animal received an acellular valved conduit. No animal received any anticoagulation therapy. Animals were killed at 1, 5, 13, and 17 weeks. Explanted valves were examined histologically with scanning electron microscopy, biochemically, and biomechanically. All animals survived the procedure. The valves showed minimal regurgitation, and valve gradients were <20 mm Hg on echocardiography. The maximum gradient was 10 mm Hg with direct pressures. Macroscopically, the tissue-engineered constructs were covered with tissue, and there was no thrombus formation on any of the specimens. Scanning electron microscopy showed smooth flow surfaces during the follow-up period. Histological examination demonstrated laminated fibrous tissue with predominant glycosaminoglycans as extracellular matrix. 4-Hydroxyproline assays demonstrated an increase in collagen content as a percentage of native pulmonary artery (1 week 45.8%, 17 weeks 116%). DNA assays showed a comparable number of cells in all explanted samples. There was no tissue formation in the acellular control. Tissue-engineered heart valve scaffolds fabricated from polyhydroxyalkanoates can be used for implantation in the pulmonary position with an appropriate function for 120 days in lambs.

Long term anticoagulant therapy is mandatory for patients with artificial heart valve prosthesis and is suggested for some patients with biological heart valve prosthesis. Oral anticoagulants reduce but not abolish thromboembolic complication in these patients. They act lowering the level of vitamin K-dependent coagulation factors and that in turn should result in a depression of "in vivo" thrombin formation. Fibrinopeptide A (FpA) is a good marker of thrombin formation and therefore we ascertained in several occasions the thrombin formation in 43 patients with artificial and 18 with biological heart valve prosthesis, all the patients being on oral anticoagulant treatment at least from 1 year. FpA was significantly higher in patients with artificial (determinations n = 138) with respect to biological (n=73) heart valve prosthesis (p 0.01). The FpA level in biological valves was close to that obtained in 22 not anticoagulated healthy subjects. When we divided FpA values in artificial heart valves according to the intensity of anticoagulation, we obtained a decreasing FpA mean levels with the increase of the degree of anticoagulation. In particular FpA values with an INR 4.5 were close to values obtained in healthy subjects. These data support the concept that patients with artificial heart valves are at higher risk of thromboembolism and therefore the intensity of anticoagulation should be different with respect to biological valves and probably a little higher than that recommended at the Leuven Consensus Conference.

Background: A crucial factor in tissue engineering of heart valves is the functional and physiological scaffold design. In our current experimental report we describe a new fabrication technique for heart valve scaffolds, derived from x-ray computed tomography data linked to the rapid prototype technique of stercolithography. Methods: In order to recreate the complex anatomical structure of a pulmonary and aortic homograft. we have used stereolithographic models derived from x-ray computed tomography and specific software (CP. Aachen, Germany). These stereolithogrphic models were used to generate biocompatible heart valve scaffolds by a thermal processing technique. The scaffold-forming polymer was a biodegradable and thermoplastic elastomer, a poly-4-hydroxybutyrate (P4HB) and polyhydroxyoctanoate (PHOH) (Tepha Inc. Cambridge. MA) Analysis of the heart valve scaffolds included biomechanical testing (MTS Systems Corporation Eden Prairie. MN), functional testing in a pulsatile biorcactor and direct measurements. Results: Using stereolithography, we were able to fabricate plastic models with the accurate anatomy of a human valvular homograft Moreover, we fabricated heart valve scaffolds with a physiological valve design, which included the smus of valsalva, and resembled our reconstructed homografts. One advantage of P4HB and PHO was the ability to mold a complete aortic root scaffold from a stereolithographic model without the need for suturing Biomechanical testing of the scaffold materials revealed physical properties appropriate for use in cardiovascular surgery. The heart valve scaffolds were tested in a bioreactor and it was noted that the leaflets opened and closed synchronously under sub- and supraphysiological flow conditions. Direct measurements of the homograft, the plastic models and the final heart valve scaffolds revealed only minor differences. Conclusion: Our preliminary results suggest that the reproduction of complex anatomical structures by stereolithography might be a useful technique to fabricate custom-made polymeric scaffolds for the tissue engineering of heart valves.

Mechanical heart valve prosthesis in pregnancy – multicenter retrospective observational study