A novel gradient and multilayered sheet with a silk fibroin/polyvinyl alcohol core-shell structure for bioabsorbable arterial grafts.

Bioabsorbable arterial grafts can potentially improve patency and neovessel formation; however, their application in clinical settings has not been realized. In this study, we developed bioabsorbable gradient sheets based on silk fibroin (SF) and polyvinyl alcohol (PVA) with a core-shell nanofibrous structure. This gradient sheet was expected to promote vascular remodeling while we maintained its physical properties and a gradual degrading process from the luminal surface. ESP was conducted at various flow rates for SF and PVA to achieve the multilayer gradient structure. Furthermore, the elasticity of the gradient sheet could be increased by increasing the PVA flow rate; however, this reduced the tensile strength of the core-shell fibers. Notably, the physical properties of the gradient sheet did not degrade even after 7 days of immersion in a phosphate buffer saline solution, which indicates that the structure could maintain its structural integrity while resisting arterial pressure. In vitro experiments revealed that the number of endothelial cells attached to the SF/PVA sheet was notably higher than that on the cell-culture dish. The gradient sheets were implanted in rat abdominal aortas and explanted after 14 days to confirm acute-phase patency and vascular remodeling. The gradient sheets constructed with SF composed of polyurethane and PVA improved the ease of handling of the material, and these sheets resulted in a favorable vascular remodeling outcome. Our results strongly suggest that the SF/PVA-based gradient sheets described in this study can serve as a novel design for bioabsorbable arterial grafts upon further modifications.

Effect of Loading Changes on the Intraventricular Pressure Measured by Color M-Mode Echocardiography in Rats.

Evaluation of diastolic function is a pivotal challenge due to limitations of the conventional echocardiography, especially when the heart rate is rapid as in rats. Currently, by using color M-mode echocardiography (CMME), intraventricular pressure difference (IVPD) and intraventricular pressure gradient (IVPG) in early diastole can be generated and are available as echocardiographic indices. These indices are expected to be useful for the early diagnosis of heart failure (HF), especially diastolic dysfunction. There have not been any studies demonstrating changes in IVPD and IVPG in response to changes in loading conditions in rats. Therefore, the present study aims to evaluate CMME-derived IVPD and IVPG changes in rats under various loading conditions. Twenty rats were included, divided into two groups for two different experiments, and underwent jugular vein catheterization under inhalational anesthetics. Conventional echocardiography, CMME, and 2D speckle tracking echocardiography were measured at the baseline (BL), after intravenous infusion of milrinone (MIL, n = 10), and after the infusion of hydroxyethyl starch (HES, n = 10). Left ventricular IVPD and IVPG were calculated from color M-mode images and categorized into total, basal, mid-to-apical, mid, and apical parts, and the percentage of the corresponding part was calculated. In comparison to the BL, the ejection fraction, mid-to-apical IVPG, mid IVPG, and apical IVPD were significantly increased after MIL administration (p < 0.05); meanwhile, the end-diastolic volume, E-wave velocity, total IVPD, and basal IVPD were significantly increased with the administration of HES (p < 0.05). The increase in mid-to-apical IVPD, mid IVPD, and apical IVPD indicated increased relaxation. A significant increase in basal IVPD reflected volume overloading by HES. CMME-derived IVPD and IVPG are useful tools for the evaluation of various loading conditions in rats. The approach used in this study provides a model for continuous data acquisition in chronic cardiac disease models without drug testing.

Silk fibroin/polyurethane patch implantation in hyperglycemic rat model.

PURPOSE: To understand the complication and histopathological characteristics between the Silk Fibroin/Polyurethanes (SF/PU) and the host response, and to unveil the compatibility of the patch in diabetes individuals. METHODS: Rats were divided into DM and control (CT) groups, and the DM group was induced with streptozotocin. All groups underwent the SF/PU patch implantation in the abdominal aorta, and the implanted patches were evaluated at one, two, three, and four weeks after implantation. RESULTS: DM group had more fibrosis formation and a delayed endothelialization compared to the CT group. There was no evidence of chronic inflammation in both DM and CT groups. CONCLUSIONS: Fibrosis in hyperglycemic individuals could promote the formation of new vascular structures in the implanted patch such as endothelial and vascular smooth muscle cells. In summary, the SF/PU patch was no serious complications when implanted under hyperglycemia, and the patch was suitable to implant in diabetes mellitus.

Effects of Individual and Coexisting Diabetes and Cardiomyopathy on Diastolic Function in Rats (Rattus norvegicus domestica).

The goal of this study was to evaluate diastolic intraventricular pressure gradients (IVPG) and 2-dimensional tissue tracking (2DTT) patterns during diabetes and cardiomyopathy. Rats (n = 60) were induced to become diabetic (DM group, n = 15) by using streptozotocin, to become cardiomyopathic (CM group, n = 15) by using isoproterenol, and to become both diabetic and cardiomyopathic (DMCM group, n = 15); control rats (CT group, n = 15) were injected with saline. Two months after induction, all rats underwent conventional echocardiography, IVPG, and 2DTT and then were euthanized for microscopic examination of cardiac fibrosis. Compared with the controls, all 3 treated groups showed diastolic dysfunction and delayed cardiac relaxation. DMCM rats showed the most pronounced cardiac abnormalities. In addition, CM and DMCM groups had showed decreased middle IVPG, whereas DMCM rats had decreased midapical IVPG. Although the overall IVPG of the CM group was normal, the middle segment was significantly decreased. 2DTT results showed that the DMCM group had a delay in relaxation compared with other groups. IVPG and 2DTT can be used to overcome the limitation of conventional echocardiographic methods and reveal diastolic dysfunction. DM worsened diastolic function during cardiac disease.