Lin_Pister_cardiac_cell_mechanics - 996 IEEE TRANSACTIONS...

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996 IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING, VOL. 48, NO. 9, SEPTEMBER 2001 Miniature Heart Cell Force Transducer System Implemented in MEMS Technology Gisela Lin*, Roy E. Palmer, Kristofer S. J. Pister, and Kenneth P. Roos Abstract— A fully submersible force transducer system for use with isolated heart cells has been implemented using microelec- tromechanical systems (MEMS) technology. By using integrated circuit fabrication techniques to make mechanical as well as elec- trical components, the entire low-mass transducer is only a few cubic millimeters in size and is of higher fidelity ( 100 nN and 13.3 kHz in solution) than previously available. When chemically acti- vated, demembranated single cells attached to the device contract and slightly deform a strain gauge whose signal is converted to an amplified electrical output. When integrated with a video micro- scope, the system is capable of optical determination of contrac- tile protein striation periodicity and simultaneous measurement of heart cell forces in the 100-nN to 50- N range. The average measured maximal force was max aS UU P QV N. Nor- malizing for the cell’s cross-sectional area, max /area was 14.7 7.7 mN/mm 2 . Oscillatory stiffness data at frequencies up to 1 kHz has also been recorded from relaxed and contracted cells. This novel MEMS force transducer system permits higher fidelity mea- surements from cardiac myocytes than available from standard macro-sized transducers. Index Terms— CMOS, force transducer, heart cell, MEMS, mi- cromachining, micromechanical. I. INTRODUCTION T HE MEASUREMENT of contractile force in the N range from isolated ventricular heart cells (cardiac my- ocytes) is crucial to the fundamental understanding of function in normal and diseased heart. The complicated organization of the heart precludes all but the simplest measures of cardiac function. Isolated cardiac myocytes provide a simplified model that can more directly be related to the molecular structures responsible for contraction and its regulation. However, current transducer technology has limited mechanical measurements from cardiac myocytes [1]–[10]. Commercially available force transducers are relatively large and must be placed outside the cell’s saline bath. Cell attachment can only be achieved with relatively complex massive structures (e.g.: pipettes, needles, fibers, troughs, plates, or paddles), which are subject to surface Manuscript receivedJune 29, 2000; revised June 2, 2001. This work was sup- ported by a Grant-in-Aid from the American Heart Association, Greater Los Angeles Affiliate, under Grants 1059 GI-1, 2, 3 (KSJP). This work was also sup- ported in part by the National Institutes of Health (NIH) under Grant HL-47065 (KPR). Asterisk indicates corresponding author . *G. Lin is with Standard MEMS Incorporated, 7155 Crest Road, Rancho
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This note was uploaded on 12/21/2011 for the course ME 270 taught by Professor Murphy during the Fall '08 term at Purdue University.

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Lin_Pister_cardiac_cell_mechanics - 996 IEEE TRANSACTIONS...

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