Design, Development, Testing at ISO standards and in-vivo feasibility study of a novel Polymeric Heart Valve Prosthesis

Clinically available prosthetic heart valves are life-saving, but imperfect: mechanical valves requiring anticoagulation therapy, whilst bioprosthetic valves have limited durability. Polymer valves offer the prospect of good durability without the need for anticoagulation. We report the design and development of a polymeric heart valve, its bench-testing at ISO standards, and preliminary extravivo and in-vivo short-term feasibility. Prototypes were manufactured by injection moulding of styrenic block copolymers to achieve anisotropic mechanical properties. Design was by finite element stress-strain modelling, which has been reported previously, combined with feedback from bench and surgery-based testing using various combinations of materials, valve geometry and processing conditions. Bench testing was according to ISO 5840:2015 standards using an in-vitro cardiovascular hydrodynamic testing system and an accelerated fatigue tester. Bench comparisons were made with a best-in-class bio-prosthesis. Preliminary clinical feasibility evaluations included extra-vivo and short-term (1-24 hours) in-vivo testing in a sheep model. The optimised final prototype met the requirements of ISO standards with hydrodynamic performance equivalent to the best-in-class bioprosthesis. Bench durability of greater than 1.2 billion cycles (30 years equivalent) was achieved (still ongoing). Extra-vivo sequential testing (n=8) allowed refinement of external diameter, 3D shape, a low profile, flexibility, suturability, and testing of compatibility to magnetic resonance imaging and clinical sterilisation. In vivo short-term (1-24 hours) feasibility (n=3) confirmed good suturability, no mechanical failure, no trans-valvular regurgitation, competitive trans-valvular gradients, and good biocompatibility at histopathology. We have developed and tested at ISO standards a novel prosthetic heart valve featuring competitive bench-based hydrodynamics and durability, well beyond the ISO requirements and comparable to a best-in-class bioprosthesis. In-vivo short-term feasibility testing confirmed preliminary safety, functionality and biocompatibility, supporting progression to a long-term efficacy trial.King's College, Cambridg

Fatigue life prediction and performance index evaluation of SEPS block-copolymers and advanced TPU for the design of a trileaflet Prosthetic Heart Valve

Analisi a fatica di materiali polimerici e definizione di Indice di Performance relativi all' applicazione di tali materiali a una protesi di valvola cardiaca

Fatigue life modelling of anisotropic styrenic block copolymers for a prosthetic heart valve application

This thesis describes a fatigue lifetime prediction model for anisotropic styrenic block copolymers. A shortlist of cylinder forming block copolymers has been tested for a flexible leaflet aortic prosthetic heart valve, designed to mimic the native structure of the aortic leaflet. Polymeric valves have the potential to overcome the limit of current available prosthesis, however no such valve is available clinically at present. Durability and calcification are among the main issues with polymeric valves designed and tested previously. The solution to these problems resides in the correct choice of material. In this study, a fatigue model was validated for anisotropic styrenic block copolymers to assist in the selection of the most durable material. The prediction is based on a unified approach of crack growth and nucleation tests. The model correctly predicted the lifetime of the material with same microstructure orientation, thickness and geometry. Material comparison based on the fatigue results highlighted the most durable material, a poly(styrene-b-butadiene-b-styrene) with 20% weight of styrene. The material was manufactured into a valve, which comfortably exceeded ISO standards for in vitro durability and hydrodynamic perfomance. Calcification and its effect on durability were tested. The calcification test was conducted in a simulated body fluid solution. Calcium levels on the styrenic block copolymers were significantly lower than on bovine pericardium, which is one of the materials used in clinical prosthesis. Durability of the calcified valve was not affected, indicating that the selected materials have great potential for biomedical applications. Finally, the effect of heparin coating was measured for both durability and calcification. The coating increased the level of calcification but did not affect durability in either unitensile specimens or valve prototypes

Changes in surgicaL behaviOrs dUring the CoviD-19 pandemic. The SICE CLOUD19 Study

BACKGROUND: The spread of the SARS-CoV2 virus, which causes COVID-19 disease, profoundly impacted the surgical community. Recommendations have been published to manage patients needing surgery during the COVID-19 pandemic. This survey, under the aegis of the Italian Society of Endoscopic Surgery, aims to analyze how Italian surgeons have changed their practice during the pandemic.METHODS: The authors designed an online survey that was circulated for completion to the Italian departments of general surgery registered in the Italian Ministry of Health database in December 2020. Questions were divided into three sections: hospital organization, screening policies, and safety profile of the surgical operation. The investigation periods were divided into the Italian pandemic phases I (March-May 2020), II (June-September 2020), and III (October-December 2020).RESULTS: Of 447 invited departments, 226 answered the survey. Most hospitals were treating both COVID-19-positive and -negative patients. The reduction in effective beds dedicated to surgical activity was significant, affecting 59% of the responding units. 12.4% of the respondents in phase I, 2.6% in phase II, and 7.7% in phase III reported that their surgical unit had been closed. 51.4%, 23.5%, and 47.8% of the respondents had at least one colleague reassigned to non-surgical COVID-19 activities during the three phases. There has been a reduction in elective (>200 procedures: 2.1%, 20.6% and 9.9% in the three phases, respectively) and emergency (<20 procedures: 43.3%, 27.1%, 36.5% in the three phases, respectively) surgical activity. The use of laparoscopy also had a setback in phase I (25.8% performed less than 20% of elective procedures through laparoscopy). 60.6% of the respondents used a smoke evacuation device during laparoscopy in phase I, 61.6% in phase II, and 64.2% in phase III. Almost all responders (82.8% vs. 93.2% vs. 92.7%) in each analyzed period did not modify or reduce the use of high-energy devices.CONCLUSION: This survey offers three faithful snapshots of how the surgical community has reacted to the COVID-19 pandemic during its three phases. The significant reduction in surgical activity indicates that better health policies and more evidence-based guidelines are needed to make up for lost time and surgery not performed during the pandemic