The cannulation of blood vessels is one of the most basic and essential interventions in medical practice. A common adverse event of this procedure is miscannulation with infiltration of the second... Show moreThe cannulation of blood vessels is one of the most basic and essential interventions in medical practice. A common adverse event of this procedure is miscannulation with infiltration of the second part of the vessel wall, often resulting in a perivascular hematoma. In hemodialysis patients, surgically created arteriovenous conduits are cannulated 3-4 times per week to provide sufficient blood supply to the hemodialysis machine. However, the high blood flow and pressure in these vascular access sites increase the risk of complications upon miscannulation. A novel needle system that allows for rapid automatic retraction of the needle in response to contact with blood after positioning the cannula in the blood vessel was developed to reduce the risk of miscannulation. The device can easily be incorporated into existing needle designs. The mechanical functionality of the device was validated by testing prototypes in an ex vivo system. Optimization of the needle system was performed to enhance response time and piston shape. A final prototype design was manufactured and validated. The optimal membrane composition and piston shape were determined, which resulted in a needle response time of 40 ms upon contact with fluid at a pressure of 100 mmHg (arterial pressure). Here, we have successfully designed, mechanically validated, and tested a novel automated rapid needle retraction system that allows incorporation into existing needle systems. This device could notably decrease the difficulty of vessel cannulation and the prevalence of hematoma formation. Show less
Cells use membranes as their boundary, shielding their inside from the outside world, and to create internal structure. The different membranes in a cell have large variations in chemical... Show moreCells use membranes as their boundary, shielding their inside from the outside world, and to create internal structure. The different membranes in a cell have large variations in chemical composition, elasticity, shape and function. In contrast with the standard static picture often shown in cartoons, membranes are moreover one of the most dynamic components of the cell. Based on a detailed study of the structure and shape of various membranes we have developed techniques to measure the relevant physical parameters. Using these, we can directly couple the structure and shape to the function of the membrane. Combining these studies with studies of the membrane dynamics we find that membranes can spontaneously demix in different domains, which can interact with each other by forces mediated by the membrane itself. This interaction results in a sorting of the domains by size. Introducing an active element, molecular motors, into the system, we find that new structures are formed. An example of such a structure is a long membrane tube. These tubes also exhibit rich dynamics, and oscillating growth and shrink patters, which makes them suitable length and shape regulators in living cells. Show less
Membrane tubes are ubiquitous within cells. They have a diameter of approximately 50 nanometers, and are formed when a sufficiently large localized force is exerted on a membrane. Important... Show moreMembrane tubes are ubiquitous within cells. They have a diameter of approximately 50 nanometers, and are formed when a sufficiently large localized force is exerted on a membrane. Important generators of this force are the motor proteins that can move along cytoskeletal filaments. We studied membrane tube formation by motor proteins from giant vesicles in an in vitro reconstituted system, and showed that motor proteins can dynamically associate to form clusters that work together. In addition, the physical parameters that determine the force required to form tubes were examined, and it was found that the force barrier for tube formation increases with the area the pulling force is exerted on. Finally, some first results are presented on the competition between motor proteins of opposite directionality. Our findings suggest regulatory mechanisms that may be used for the intracellular spatial organization of membranes. Show less
