Current Trends in Cardiac Transplantation

Klein, Deborah G.

doi:10.1016/j.ccell.2007.08.001

Cited by 6 publications

(1 citation statement)

References 46 publications

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“…Even the recently FDA approved AbioCor heart by Abiomed [287], an MIT based company, can only promise 6 months of extended waiting time for the patients. A solution for this problem is a transdermal energy transport mechanism by AC electromagnetic field, but so far has only limited success has been achieved [288]. All these facts emphasize the importance of a remotely controlled heart pump.…”

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Magnet-polymer composite transducers

Nguyễn¹

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Current actuation technologies do not provide a satisfactory solution to the requirement of having a muscle like motion, such motion will be very useful in robotics, MEMS and biomedical applications, etc. Hence a magnetically actuated material was studied as an "artificial muscle". The material is a composite of a soft polymer with magnetic material as the filler (Magpol). Magpol composites are a new class of bio-inspired smart soft transducers for morphing, damping, and artificial muscle applications. Magpol exhibits large changes in shape and physical properties in response to an external magnetic field. This shape changing behavior of Magpol in an external magnetic field was studied and actuation performance investigated. The large change in electrical resistivity driven by the shape change was also examined for sensing applications. This versatile combination of actuation and sensing behavior results in attractive transducers. Various actuation modes, including contraction, elongation and deflection were studied. These actuation modes can be combined to produce complex motions. A novel coiling mode was observed. Simply by changing boundary conditions, Magpol can exhibit a change in actuation mode from axial contraction to a novel coiling mechanism. The magnetic buckling which results in coiling was studied by computer simulation and analytical modeling. The analytically predicted magnetic fields for buckling agreed well with experimental values. The relationship between strain and magnetic field suggested that post buckling behavior is a stable symmetric bifurcation, which is useful for continuous actuation. The actuation metrics of Magpol were studied, maximum strains were 40% for contraction, 60% for coiling and 80% for elongation. Maximum stress of up to 164 kPa, 184 kPa and 216 kPa were measured in contraction, coiling and elongation modes, respectively. These metrics are equal or better than those in natural muscles and most competing artificial muscle technologies. This thesis also presents the first report of work-loop measurement for this class of smart material. The maximum measured work values were 141 kJ/m 3 for contraction and 164 kJ/m 3 for coiling. The maximum work density of Magpol was higher than the maximum work density of mammalian iii skeletal muscles. A proof-of-concept artificial muscle made from Magpol was demonstrated. Experiments on the dynamic properties showed that Magpol can achieve a strain rate of more than 1500 %.s-1 and respond to a driving frequency of up to 80 Hz. A strain-time model showed that the dynamic properties could be related to its unique "on-off" actuation behavior. Percolation principles can be used to make this type of actuator an intrinsic self-sensor. The electrical resistivity of a polymer matrix containing fillers of iron particles and graphite flakes at percolation concentration is a strong function of mechanical strain and thus can be used for automatic sensing. Large changes in resistivity of three to four orders of magnitude and sensitivity (i.e., the chan...

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confidence: 99%