The materials available for the Right Ventricular Outflow Tract (RVOT) reconstruction in patients with Tetralogy of Fallot (TOF)/pulmonary atresia come with the severe limitation of long-term degeneration and lack of growth potential, causing right ventricular dysfunction, aneurysm formation and arrhythmias, thus necessitating several high-risk reoperations throughout patients' life.In this study, we evaluated the capacity of Mesenchymal Stem Cells (MSCs) derived from the Wharton's Jelly (WJ-MSCs), the gelatinous inner portion of the umbilical cord, to grow and recellularize an extracellular matrix (ECM) graft in our optimised xeno-free, good manufacturing practice-compliant culture system. WJ-MSCs were phenotypically and functionally characterised by flow cytometry and multi-lineage differentiation capacity, respectively. The typical MSCs immunophenotype and functional characteristics were retained in our xeno-free culture system, as well as the capacity to grow and engraft onto a naturally occurring scaffold. Wharton's Jelly MSCs, from both human and swine source, showed excellent capacity to recellularize ECM graft producing a living cell-seeded construct.In addition, we have provided an in vivo proof of concept of feasibility of the cellularised conduit, engineered with swine Wharton's Jelly MSCs, to be used in a novel porcine model of main pulmonary artery reconstruction, where it showed good integration within the host tissue.Our study indicates that the addition of WJ-MSCs to the ECM scaffold can upgrade the material, converting it into a living tissue, with the potential to grow, repair and remodel the RVOT. These results could potentially represent a paradigm shift in paediatric cardiac intervention towards new modalities for effective and personalised surgical restoration of pulmonary artery and RVOT function in TOF/pulmonary atresia patients.

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Congenital heart disease (CHD) is the most predominant birth defect and can require several invasive surgeries throughout childhood. The absence of materials with growth and remodelling potential is a limitation of currently used prosthetics in cardiovascular surgery, as well as their susceptibility to calcification. The field of tissue engineering has emerged as a regenerative medicine approach aiming to develop durable scaffolds possessing the ability to grow and remodel upon implantation into the defective hearts of babies and children with CHD. Though tissue engineering has produced several synthetic scaffolds, most of them failed to be successfully translated in this life-endangering clinical scenario, and currently, biological scaffolds are the most extensively used. This review aims to thoroughly summarise the existing biological scaffolds for the treatment of paediatric CHD, categorised as homografts and xenografts, and present the preclinical and clinical studies. Fixation as well as techniques of decellularisation will be reported, highlighting the importance of these approaches for the successful implantation of biological scaffolds that avoid prosthetic rejection. Additionally, cardiac scaffolds for paediatric CHD can be implanted as acellular prostheses, or recellularised before implantation, and cellularisation techniques will be extensively discussed.