Modified granular impact force laws for the OSIRIS-REx touchdown on the surface of asteroid (101955) Bennu

The OSIRIS-REx mission collected a sample from the surface of the asteroid (101955) Bennu in October 2020. Here we study the impact of the OSIRIS-REx Touch-and-Go Sampling Acquisition Mechanism (TAGSAM) interacting with the surface of an asteroid in the framework of granular physics. Traditional approaches to estimating the penetration depth of a projectile into a granular medium include force laws and scaling relationships formulated from laboratory experiments in terrestrial-gravity conditions. However, it is unclear that these formulations extend to the OSIRIS-REx scenario of a 1300-kg spacecraft interacting with regolith in a microgravity environment. We studied the TAGSAM interaction with Bennu through numerical simulations using two collisional codes, pkdgrav and GDC-i. We validated their accuracy by reproducing the results of laboratory impact experiments in terrestrial gravity. We then performed TAGSAM penetration simulations varying the following geotechnical properties of the regolith: packing fraction (P), bulk density, inter-particle cohesion (σc), and angle of friction (ϕ). We find that the outcome of a spacecraft-regolith impact has a non-linear dependence on packing fraction. Closely packed regolith (P≳0.6) can effectively resist the penetration of TAGSAM if ϕ≳28° and/or σc≳50 Pa. For loosely packed regolith (P≲0.5), the penetration depth is governed by a drag force that scales with impact velocity to the 4/3 power, consistent with energy conservation. We discuss the importance of low-speed impact studies for predicting and interpreting spacecraft-surface interactions. We show that these low-energy events also provide a framework for interpreting the burial depths of large boulders in asteroidal regolith

Acute deterioration of idiopathic portal hypertension requiring living donor liver transplantation: a case report.

Case reports of severe idiopathic portal hypertension (IPH) requiring liver transplantation are very rare. We report the case of a 65-year-old woman who was diagnosed as having IPH. At the age of 60 years, her initial symptom was hematemesis, due to ruptured esophageal varices. Computed tomography of the abdomen showed splenomegaly and a small amount of ascites, without liver cirrhosis. She was diagnosed as having IPH and followed-up as an outpatient. Five years later, she developed symptoms of a common cold and rapidly progressive abdominal distension. She was found to have severe liver atrophy, liver dysfunction, and massive ascites. Living donor liver transplantation was then performed, and her postoperative course was uneventful. Histopathological findings of the explanted liver showed collapse and stenosis of the peripheral portal vein. The areas of liver parenchyma were narrow, while the portal tracts and central veins were approximate one another, leading to a diagnosis of IPH. There was no liver cirrhosis. The natural history of refractory IPH could be observed in this case. Patients with end-stage liver failure due to severe IPH can be treated by liver transplantation

Human Fibroblast Sheet Promotes Human Pancreatic Islet Survival and Function In Vitro

In previous work, we engineered functional cell sheets using bone marrow-derived mesenchymal stem cells (BM-MSCs) to promote islet graft survival. In the present study, we hypothesized that a cell sheet using dermal fibroblasts could be an alternative to MSCs, and then we aimed to evaluate the effects of this cell sheet on the functional viability of human islets. Fibroblast sheets were fabricated using temperature-responsive culture dishes. Human islets were seeded onto fibroblast sheets. The efficacy of the fibroblast sheets was evaluated by dividing islets into three groups: the islets-alone group, the coculture with fibroblasts group, and the islet culture on fibroblast sheet group. The ultrastructure of the islets cultured on each fibroblast sheet was examined by electron microscopy. The fibroblast sheet expression of fibronectin (as a component of the extracellular matrix) was quantified by Western blotting. After 3 days of culture, islet viabilities were 70.2 ± 9.8%, 87.4 ± 5.8%, and 88.6 ± 4.5%, and survival rates were 60.3 ± 6.8%, 65.3 ± 3.0%, and 75.8 ± 5.6%, respectively. Insulin secretions in response to high-glucose stimulation were 5.1 ± 1.6, 9.4 ± 3.8, and 23.5 ± 12.4 μIU/islet, and interleukin-6 (IL-6) secretions were 3.0 ± 0.7, 5.1 ± 1.2, and 7.3 ± 1.0 ng/day, respectively. Islets were found to incorporate into the fibroblast sheets while maintaining a three-dimensional structure and well-preserved extracellular matrix. The fibroblast sheets exhibited a higher expression of fibronectin compared to fibroblasts alone. In conclusion, human dermal fibroblast sheets fabricated by tissue-engineering techniques could provide an optimal substrate for human islets, as a source of cytokines and extracellular matrix

Development of a novel rat model with pancreatic fistula and the prevention of this complication using tissue-engineered myoblast sheets

Background: Pancreatic fistula (PF) is one of the most important complications of pancreatic surgery. The aims of this study were to establish a PF model in rats and to investigate the efficacy of our new method for preventing PF, which utilizes myoblast sheets made using tissue engineering techniques. Methods: To establish a PF model, the rats underwent transection of each of four pancreatic ducts: the gastric, duodenal, common, and splenic ducts, respectively. Their ascitic amylase and lipase levels were then measured. To investigate the efficacy of myoblast sheets at preventing PF, a myoblast sheet was attached to the pancreatic stump in the PF models. The levels of amylase and lipase in both serum and ascites were then measured, and surgical specimens were investigated pathologically. Results: The new PF model established by transecting the splenic duct in rats may prove very useful. There were no significant differences in serum amylase and lipase levels between the myoblast sheet (+) group and the sheet (-) group. However, there were significant differences in ascitic amylase and lipase levels between the two groups (p < 0.05). Among the pathological findings, the number of inflammatory cells in the myoblast sheet group was smaller than that in the control group. In addition, the presence of the myoblast sheets on the surface of the pancreatic stump was confirmed by immunofluorescence staining. Conclusion: Our data demonstrate the efficacy of the new rat model of PF presented herein, and that it might be possible to prevent PF using myoblast sheets