In Vitro Real-Time Mechanical Fatigue Assessment of Novel Pulmonary Valve Root Replacements

Heart valve replacement procedures are increasing globally; however, current replacement options are not ideal for use in younger patients due to a lack of repair and regeneration. Low-concentration sodium dodecyl sulphate (SDS) decellularised porcine pulmonary valve roots (PVRs) capable of somatic growth have been developed to provide an off-the-shelf solution for right ventricular outflow tract (RVOT) reconstruction during the Ross procedure, particularly in younger patients. Before progressing to clinical use, evaluating the in vitro fatigue and durability of these decellularised valve roots is important to ensure their safety, biomechanical integrity and reliability. In vitro accelerated fatigue assessment has been widely used to pre-clinically estimate the fatigue resistance and overall durability of replacement valves. However, these decellularised PVRs also require evaluation under physiological loading conditions due to their inherent viscoelastic properties. Additionally, a significant challenge lies in identifying an appropriate terminal sterilisation method that minimally affects their biomechanical function and durability.
The primary aim of this research was to develop a novel method to assess the in vitro real-time mechanical fatigue of cellular porcine pulmonary valve roots under physiological pulmonary pressure conditions. The secondary aim was to apply this developed method to decellularised porcine PVRs and supercritical carbon dioxide (scCO2) sterilised decellularised porcine PVRs to determine the impact of decellularisation and terminal sterilisation processes on the in vitro mechanical fatigue of porcine pulmonary valve roots.
The in vitro real-time mechanical fatigue of cellular porcine PVRs, decellularised porcine PVRs and scCO2 sterilised decellularised porcine PVRs was assessed under normotensive pulmonary pressure (20±5 mmHg systolic /10±3 mmHg diastolic) at a median heart rate of 120 bpm for 3 million cycles (18 days) in the Real-Time Wear Tester (RWT). In both the cellular and decellularised PVRs, two of the six roots failed due to leaflet tears near the belly region while scCO2 sterilised decellularised PVRs showed no visible signs of macroscopic root damage following real-time fatigue assessment.
However, following physiological cyclic loading in RWT, all three groups (cellular PVRs, decellularised PVRs and scCO2 sterilised decellularised PVRs) showed increased regurgitation and leaflet thinning while sustaining their wall circumferential expansion, tensile material properties and histological characteristics compared to their respective non-fatigue control groups. Additionally, real-time cyclic loading caused thinning of the pulmonary artery in cellular PVRs and decellularised PVRs; however, scCO2-sterilised decellularised PVRs retained the root wall thickness.
Overall, this study has developed a novel in vitro method to assess the real-time mechanical fatigue of cellular, decellularised and sterilised decellularised porcine pulmonary valve roots under physiological loading conditions. In summary, the results indicated that neither decellularisation nor scCO2 sterilisation negatively impacted the in vitro durability of porcine pulmonary valve roots. The finding suggests that the scCO2 sterilisation process offers a promising and effective approach for the terminal sterilisation of decellularised porcine pulmonary valve roots. The methodology developed in this study is a significant advancement in in vitro tissue-engineered valve fatigue assessment and offers a robust platform for pre-clinical fatigue assessment in tissue-engineered replacement valve development.