Electrochemical reduction of carbon dioxide (CO2) into chemicals and fuels has recently attracted much interest, but normally suffers from a high overpotential and low selectivity. In this work, single P atoms were introduced into a N‐doped carbon supported single Fe atom catalyst (Fe‐SAC/NPC) mainly in the form of P−C bonds for CO2 electroreduction to CO in an aqueous solution. This catalyst exhibited a CO Faradaic efficiency of ≈97 % at a low overpotential of 320 mV, and a Tafel slope of only 59 mV dec−1, comparable to state‐of‐the‐art gold catalysts. Experimental analysis combined with DFT calculations suggested that single P atom in high coordination shells (n≥3), in particular the third coordination shell of Fe center enhanced the electronic localization of Fe, which improved the stabilization of the key *COOH intermediate on Fe, leading to superior CO2 electrochemical reduction performance at low overpotentials.

516Ventricular septal defect (VSD) is the most common congenital heart malformation and can be detected during the prenatal and postnatal period, in childhood, and in adulthood. Spontaneous closure of VSD can be determined through a variety of methods-echocardiography, Doppler color flow imaging, angiography, auscultation, and cardiac catheterization-and can be proven by pathological evidence at necropsy. There are two major types of VSD, membranous and muscular, as well as the perimembranous variety, which comprises variable portions of the adjacent muscular septum but lacks the membranous septum. VSD appears either as an isolated cardiac defect without other abnormalities or with several complex malformations. It has long been recognized that VSD can close spontaneously, but the incidence of spontaneous VSD closure is still uncertain. Since necropsy study of the hearts with VSD has rarely been reported, information on morphological features of spontaneous VSD closure remains limited. In addition, the mechanisms for spontaneous VSD closure are not fully understood. Herein, we present a brief review of the incidence of spontaneous VSD closure, morphological characteristics of the closure, and the main mechanisms responsible for the closure. INCIDENCE OF SPONTANEOUS VSD CLOSURETh e incidence of spontaneous ventricular septal defect (VSD) closure varies greatly, depending on the age and gender of subjects at spontaneous closure, the size and site of the defect, the types of defect, as well as the population studied, methods employed, and length of follow-up period. Table 1 presents available data on the incidence of spontaneous VSD closure.Age and gender. Age has been found to have a significant infl uence on the incidence of spontaneous VSD closure, whereas gender seems less likely to aff ect the incidence. Although spontaneous VSD closure can occur at any agegestation, infancy, childhood, adolescence, and adulthood (1)-it occurs most commonly during the fi rst 6 months of life (2), during the fi rst year (3, 4), or soon after the fi rst year of life (5). Afterward, the occurrence of closure declines progressively and occurs less commonly after the age of 10 (5). It has been documented that the incidence of the close increases with age, from 24% at 18 months of age to 50% at 48 months and 75% at 120 months (6). However, in older children, at 3.5 years old, the incidence declines sharply to 44% and then rises to 66% at 7 years and 75% at 10.5 years (6). A similar trend has been found in other reports, which showed 57% (109/190) of cases closed before 3 years of age, 89% (169/190) closed before 8 years of age (7), and 4% to 10% closed after the age of 17 (8, 9). During adulthood, the incidence of spontaneous VSD closure remarkably declines. One study showed that of 188 adults with VSD, 19 patients' (10%) VSD closed spontaneously between the age of 17 and 45 years, and the incidence of closure was greater in the 17-to 24-year age group than the 25-to 34-year group, the 35-to 44-year group, and the ≥45-year group (8)...

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Bone marrow mesenchymal stem cells (MSCs) have demonstrated their pluripotency to differentiate into different cell lineages and may be an alternative cell source for vascular tissue engineering. The objective of this study is to create small diameter vessels by seeding and culture of genetically modified MSCs onto a synthetic polymer scaffold produced by an electrospinning technique. A tubular scaffold (2 mm in diameter) with a microstructure of nonwoven fibers was produced by electrospinning of poly (propylene carbonate) (PPC). Rat MSCs obtained from bone marrow were expanded in culture and modified with vasculoprotective gene endothelial nitric oxide synthase (eNOS) or marker gene green fluorescent protein (GFP). These MSCs were seeded onto the electrospun fibrous grafts (internal diameter = 2 mm), and cultured in 5% CO(2) at 37 degrees C. The growth of MSCs in the scaffold was analyzed with scanning electron microscopy (SEM) and hematoxylin and eosin (H&E) staining. The gene transfer and transgenic gene expression were examined with fluorescence-activated cell sorting (FACS), immunochemical staining, reverse transcriptase-polymerase chain reaction (RT-PCR), and western blot. The production of nitric oxide (NO) by the engineered vessels was measured with an NO detection kit. Our data showed that the seeded cells integrated with the microfibers of the scaffold to form a three-dimensional cellular network, indicating a favorable interaction between this synthetic PPC scaffold with MSCs. High transduction efficiency was obtained with the use of concentrated retrovirus in the gene transfection of MSCs. The eNOS gene transcripts and protein were detected in the grafts seeded with eNOS-modified MSCs by RT-PCR and immunochemical staining. The amount of NO produced by grafts seeded with eNOS-modified MSCs was comparable to that produced by native blood vessels, and it was significantly higher than that in the grafts seeded with nonmodified MSCs. In summary, the vascular graft produced by culture of eNOS gene-modified MSCs onto the electrospun tubular scaffolds shows promising results in terms of function. The use of MSCs and therapeutic genes in tissue engineering of blood vessels could be helpful in improving vessel regeneration and patency.

Hydrogel bioprinting is a major area of focus in the field of tissue engineering. However, 3D printed hydrogel scaffolds often suffer from low printing accuracy and poor mechanical properties because of their soft nature and tendency to shrink. This makes it challenging to process them into structural materials. In this study, natural chitosan hydrogel scaffolds were, for the first time, reinforced with milled silk particles and fabricated by 3D printing. Compared with pure chitosan scaffolds, the addition of silk particles resulted in up to a 5-fold increase in compressive modulus as well as significantly better printing accuracy and improved scaffold stability. The chitosan/silk inks flowed well during printing; loading of up to 300% silk (w/w) resulted in only minor changes in the rheological properties of the ink. Particle loading also enabled tuning of the surface roughness of the scaffolds and improved scaffolds’ biodegradability. The printed composite hydrogel scaffolds showed no cytotoxicity and supported adherence and growth of human fibroblast cells.

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