Magnetically Guided Recellularization of Decellularized Stented Porcine Pericardium-Derived Aortic Valve for TAVI

Decellularization in Tissue Engineering and Regenerative Medicine: Evaluation, Modification, and Application Methods

Reproduction of different tissues using scaffolds and materials is a major element in regenerative medicine. The regeneration of whole organs with decellularized extracellular matrix (dECM) has remained a goal despite the use of these materials for different purposes. Recently, decellularization techniques have been widely used in producing scaffolds that are appropriate for regenerating damaged organs and may be able to overcome the shortage of donor organs. Decellularized ECM offers several advantages over synthetic compounds, including the preserved natural microenvironment features. Different decellularization methods have been developed, each of which is appropriate for removing cells from specific tissues under certain conditions. A variety of methods have been advanced for evaluating the decellularization process in terms of cell removal efficiency, tissue ultrastructure preservation, toxicity, biocompatibility, biodegradability, and mechanical resistance in order to enhance the efficacy of decellularization methods. Modification techniques improve the characteristics of decellularized scaffolds, making them available for the regeneration of damaged tissues. Moreover, modification of scaffolds makes them appropriate options for drug delivery, disease modeling, and improving stem cells growth and proliferation. However, considering different challenges in the way of decellularization methods and application of decellularized scaffolds, this field is constantly developing and progressively moving forward. This review has outlined recent decellularization and sterilization strategies, evaluation tests for efficient decellularization, materials processing, application, and challenges and future outlooks of decellularization in regenerative medicine and tissue engineering.

Bioengineered percutaneous heart valves for transcatheter aortic valve replacement: a comparative evaluation of decellularised bovine and porcine pericardia

Glutaraldehyde-treated, surgical bioprosthetic heart valves undergo structural degeneration within 10-15 years of implantation. Analogous preliminary results were disclosed for percutaneous heart valves (PHVs) realized with similarly-treated tissues. To improve long-term performance, decellularised scaffolds can be proposed as alternative fabricating biomaterials. The aim of this study was to evaluate whether bovine and porcine decellularised pericardia could be utilised to manufacture bioengineered percutaneous heart valves (bioPHVs) with adequate hydrodynamic performance and leaflet resistance to crimping damage. BioPHVs were fabricated by mounting acellular pericardia onto commercial stents. Independently from the pericardial species used for valve fabrication, bioPHVs satisfied the minimum hydrodynamic performance criteria set by ISO 5840-3 standards and were able to withstand a large spectrum of cardiac output conditions, also during extreme backpressure, without severe regurgitation, especially in the case of the porcine group. No macroscopic or microscopic leaflet damage was detected following bioPHV crimping. Bovine and porcine decellularized pericardia are both suitable alternatives to glutaraldehyde-treated tissues. Between the two types of pericardial species tested, the porcine tissue scaffold might be preferable to fabricate advanced PHV replacements for long-term performance. CONDENSED ABSTRACT: Current percutaneous heart valve replacements are formulated with glutaraldehyde-treated animal tissues, prone to structural degeneration. In order to improve long-term performance, bovine and porcine decellularised pericardia were utilised to manufacture bioengineered replacements, which demonstrated adequate hydrodynamic behaviour and resistance to crimping without leaflet architectural alteration.

Ectopic mineralization in heart valves: new insights from in vivo and in vitro procalcific models and promising perspectives on noncalcifiable bioengineered valves

Ectopic calcification of native and bioprosthetic heart valves represents a major public health problem causing severe morbidity and mortality worldwide. Valve procalcific degeneration is known to be caused mainly by calcium salt precipitation onto membranes of suffering non-scavenged cells and dead-cell-derived products acting as major hydroxyapatite nucleators. Although etiopathogenesis of calcification in native valves is still far from being exhaustively elucidated, it is well known that bioprosthesis mineralization may be primed by glutaraldehyde-mediated toxicity for xenografts, cryopreservation-related damage for allografts and graft immune rejection for both. Instead, mechanical valves, which are free from calcification, are extremely thrombogenic, requiring chronic anticoagulation therapies for transplanted patients. Since surgical substitution of failed valves is still the leading therapeutic option, progressive improvements in tissue engineering techniques are crucial to attain readily available valve implants with good biocompatibility, proper functionality and long-term durability in order to meet the considerable clinical demand for valve substitutes. Bioengineered valves obtained from acellular non-valvular scaffolds or decellularized native valves are proving to be a compelling alternative to mechanical and bioprosthetic valve implants, as they appear to permit repopulation by the host's own cells with associated tissue remodelling, growth and repair, besides showing less propensity to calcification and adequate hemodynamic performances. In this review, insights into valve calcification onset as revealed by in vivo and in vitro procalcific models are updated as well as advances in the field of valve bioengineering.

Single-session double valve replacement: TAVI+tricuspid valve-in-valve procedures

We describe a 70-year-old lady with rheumatic heart disease and a history of the mitral valve and tricuspid valve replacement, who underwent transcatheter aortic valve implantation and the tricuspid valve-in-valve procedure in a single session.

Aortic valve cell seeding into decellularized animal pericardium by perfusion-assisted bioreactor

Animal-derived pericardium is the elective tissue employed in manufacturing heart valve prostheses. The preparation of this tissue for biological valve production consists of fixation with aldehydes, which reduces, but not eliminates, the xenoantigens and the donor cellular material. As a consequence, especially in patients below 65-70 years of age, the employment of valve substitutes contaning pericardium is not indicated due to progressive calcification that causes tissue degeneration and recurrence of valve insufficiency. Decellularization with ionic or nonionic detergents has been proposed as an alternative procedure to prepare aldehyde- or xenoantigen-free pericardium for biological valve manufacturing. In the present contribution, we optimized a decellularization procedure that is permissive for seeding and culturing valve competent cells able to colonize and reconstitute a valve-like tissue. A high-efficiency cellularization was achieved by forcing cell penetration inside the pericardium matrix using a perfusion bioreactor. Because the decellularization procedure was found not to alter the collagen composition of the pericardial matrix and cells seeded in the tissue constructs consistently grew and acquired the phenotype of "quiescent" valve interstitial cells, our investigation sets a novel standard in pericardium application for tissue engineering of "living" valve implants.

The future of transcatheter aortic valve implantation

Since the introduction of transcatheter aortic valve implantation (TAVI) into clinical practice, the treatment of aortic stenosis has changed dramatically. In the past, medical therapy with or without balloon aortic valvuloplasty was the only option for inoperable patients. More recently, TAVI has become the treatment of choice for these patients and the preferred alternative for high-risk operable patients. Surgical aortic valve replacement (SAVR) currently remains the gold standard for patients at low or intermediate operative risk. As randomized trials have demonstrated comparable results between TAVI and SAVR in the high-risk population, there is now a clear trend towards performing TAVI even in intermediate-risk patients while awaiting the results of randomized trials in that population. Nevertheless, there are still questions regarding TAVI involving paravalvular leak (PVL), stroke, pacemaker requirements, and durability that remain to be more definitively answered before TAVI can routinely be performed in a broader, lower risk population. Improvements in patient selection, imaging, and second and third generation devices have decreased the incidence of PVLs and vascular complications that followed the earliest TAVI procedures, but the rates of perioperative stroke and permanent pacemaker implantation must still be addressed. Furthermore, the long-term durability of TAVI devices and a role for post-procedure antithrombotic management remain unanswered. Until these questions are more clearly answered, it is the Heart Team's task to determine the optimal treatment for each patient based on risk scores, frailty metrics, comorbidities, patient preference, and potential for improvement in quality of life.

CD133 antibody conjugation to decellularized human heart valves intended for circulating cell capture

The long term efficacy of tissue based heart valve grafts may be limited by progressive degeneration characterized by immune mediated inflammation and calcification. To avoid this degeneration, decellularized heart valves with functionalized surfaces capable of rapid in vivo endothelialization have been developed. The aim of this study is to examine the capacity of CD133 antibody-conjugated valve tissue to capture circulating endothelial progenitor cells (EPCs). Decellularized human pulmonary valve tissue was conjugated with CD133 antibody at varying concentrations and exposed to CD133 expressing NTERA-2 cl.D1 (NT2) cells in a microflow chamber. The amount of CD133 antibody conjugated on the valve tissue surface and the number of NT2 cells captured in the presence of shear stress was measured. Both the amount of CD133 antibody conjugated to the valve leaflet surface and the number of adherent NT2 cells increased as the concentration of CD133 antibody present in the surface immobilization procedure increased. The data presented in this study support the hypothesis that the rate of CD133(+) cell adhesion in the presence of shear stress to decellularized heart valve tissue functionalized by CD133 antibody conjugation increases as the quantity of CD133 antibody conjugated to the tissue surface increases.

Recellularization of organs: what is the future for solid organ transplantation?

PURPOSE OF REVIEW

Allogeneic organ transplantation is burdened by donor shortage, graft rejection and adverse effects of lifelong immune suppression. Engineering bioartificial organs from acellular organ scaffolds and patient-derived cells are a new approach to potentially overcome these limitations.

RECENT FINDINGS

Decellularized organs yield a scaffold of extracellular matrix on which cells can adhere, integrate and ultimately form functional tissue. Various cell sources are currently used to repopulate acellular scaffolds, however, all have limitations. Patient-derived pluripotent stem cells hold great promise for tissue and organ engineering, when robust and mature cells can be directed in a reliable and safe manner. Finally, to produce mature organotypic tissue from a nonfunctional seeded scaffold, cellular scaffolds are cultured under biomimetic conditions in vitro. Alternatively, organs may be implanted at an immature stage to harness the recipient's body's regenerative capacity. In proof of principle experiments to date, bioengineered small animal organs have shown rudimentary function and maintained patency for limited time when transplanted in vivo.

SUMMARY

Recent advances in bioengineering organs raise the hope that we can overcome organ donor shortage and eliminate the need for livelong immunosuppression. However, significant challenges remain in generating mature large-scale donor-like bioartificial organs.

Heart Regeneration with Embryonic Cardiac Progenitor Cells and Cardiac Tissue Engineering

Myocardial infarction (MI) is the leading cause of death worldwide. Recent advances in stem cell research hold great potential for heart tissue regeneration through stem cell-based therapy. While multiple cell types have been transplanted into MI heart in preclinical studies or clinical trials, reduction of scar tissue and restoration of cardiac function have been modest. Several challenges hamper the development and application of stem cell-based therapy for heart regeneration. Application of cardiac progenitor cells (CPCs) and cardiac tissue engineering for cell therapy has shown great promise to repair damaged heart tissue. This review presents an overview of the current applications of embryonic CPCs and the development of cardiac tissue engineering in regeneration of functional cardiac tissue and reduction of side effects for heart regeneration. We aim to highlight the benefits of the cell therapy by application of CPCs and cardiac tissue engineering during heart regeneration.