In-vivo evaluation of silk fibroin small-diameter vascular grafts: state of art of preclinical studies and animal models.

Autologous vein and artery remains the first choice for vascular grafting procedures in small-diameter vessels such as coronary and lower limb districts. Unfortunately, these vessels are often found to be unsuitable in atherosclerotic patients due to the presence of calcifications or to insufficient size. Synthetic grafts composed of materials such as expanded polytetrafluoroethylene (ePTFE) are frequently employed as second choice, because of their widespread availability and success in the reconstruction of larger arteries. However, ePTFE grafts with small diameter are plagued by poor patency rates due to surface thrombogenicity and intimal hyperplasia, caused by the bioinertness of the synthetic material and aggravated by low flow conditions. Several bioresorbable and biodegradable polymers have been developed and tested to exploit such issues for their potential stimulation to endothelialization and cell infiltration. Among these, silk fibroin (SF) has shown promising pre-clinical results as material for small-diameter vascular grafts (SDVGs) because of its favorable mechanical and biological properties. A putative advantage in graft infection in comparison with synthetic materials is plausible, although it remains to be demonstrated. Our literature review will focus on the performance of SF-SDVGs in vivo, as evaluated by studies performing vascular anastomosis and interposition procedures, within small and large animal models and different arterial districts. Efficiency under conditions that more accurately mime the human body will provide encouraging evidence towards future clinical applications.

COVID-19 and aortic disease: a practical systematic review of the literature on management and outcomes.

INTRODUCTION: Since the outbreak of the 2019 coronavirus (COVID-19), vascular specialists have faced dramatic changes in clinical and surgical practice. Although COVID-19 pulmonary signs and symptoms were the most pertinent problems initially, in the long term, cardiovascular complications became the most fearsome, with poor outcomes in terms of morbidity and mortality. Algorithms and decision-making procedures have been modified, not only to treat new clinical findings in COVID-19 positive patients, but also to avoid complications related to pulmonary and systemic infections. Additionally, COVID-19-negative patients experienced challenging management, due to hospital crowding, the risk of nosocomial COVID-19 transmission, and pandemic emergencies. In this context, aortic interventions were subject to several difficulties. First, in COVID-19-positive patients, there was the onset of new pathological scenarios including thrombotic manifestations and the subsequent complications. Second, in both COVID-19-negative and positive patients, there was a need to deliver optimal treatment with acceptable perioperative risks, forcing a rethinking of decision-making especially in terms of indications for treatments. The aim of this systematic review is to present evidence published on COVID-19 and aortic-related issues, highlighting some challenging aspects regarding management, treatment and outcomes. EVIDENCE ACQUISITION: Data search was performed on PubMed, Scopus and Web of Science, using as time range "January 1st, 2000 - May 1st, 2021." Only articles in English language were included. Key words used for the query were "Aorta" AND "COVID-19" OR "SARS-CoV-2." Furthermore, the NCBI database of "SARS-CoV-2 Resources" was interrogated to find further relevant studies. EVIDENCE SYNTHESIS: The search retrieved 416 papers; among these, 46 studies were eligible and reviewed in depth. The published literature suggests the existence of a hypercoagulable state in patients with COVID-19 disease occurring via direct and indirect mechanisms. COVID-19 infection seems to promote a prothrombotic status that aggravates vascular disease. Regardless of clinical laboratory or status, active COVID-19 infection is considered a risk factor for poor vascular surgery outcomes. Specifically, it is associated with a fourfold increased risk of death and a threefold increased risk of major adverse events. Prognosis of patients hospitalized with COVID-19 disease is often determined by the extent of pulmonary disease, although vascular complications also greatly affect outcomes. Nevertheless, although COVID­19 is highly morbid, in high­risk operations good outcomes can still be achieved even in elderly patients with COVID­19. CONCLUSIONS: In the case of aortic disease during active COVID-19 infection, poor outcomes are associated with COVID-19 vascular and non-vascular complications, while for COVID-19-negative patients not much changed in terms of outcomes, despite the difficulties in management. Endovascular repair, when possible, minimized the impact of treatment, reducing the risk of COVID-related postoperative complications or acquired infection in negative patients.