Gravity Compensation of an Exoskeleton Joint Using Constant-Force Springs.

Stroke is one of the leading causes of impairment in the world. Many of those who have suffered a stroke experience long-term loss of upper-limb function as a result. BLUE SABINO is an exoskeleton device being developed at the University of Idaho to help assess these patients and aid in their rehabilitation. One of the central design challenges with exoskeletons is limiting the overall weight of the device. Motors used in actuation of these devices are often oversized to allow gravity balancing of the device and user and the creation of torques to facilitate patient movements. If the torques required for gravity balancing are achieved through elastic elements, the motor and other upstream components can be lighter, potentially greatly reducing the overall weight of the device. In this paper, constant-force springs may provide an effective method of generating a constant offsetting torque to compensate for gravity. In experimental testing of multiple mounting configurations of C-shaped constant-force springs (single, back-to-back, double-wrapped), the force output fluctuated less than 8.6% over 180° of wrapping, with friction values below 2.6%, validating the viability of constant-force springs for this application. The results suggest the back-to-back configuration provides a simpler implementation with better force consistency while the double-wrapped configuration adds less friction to the system.

Microfluidic sample preparation: cell lysis and nucleic acid purification.

Due to the lack of development in the area of sample preparation, few complete lab-on-a-chip systems have appeared in recent years that can deal with raw samples. Cell lysis and nucleic acid extraction systems are sufficiently complex even before adding the complexity of an analysis system. In this review, a variety of microfluidic sample preparation methods are discussed and evaluated. Microsystems for cell lysis are discussed by grouping them into categories based on their lysis mechanisms: mechanical, chemical, thermal or electrical. We classify the nucleic acid purification techniques according to the mechanism that links nucleic acids to substrates: silica-based surface affinity, electrostatic interaction, nanoporous membrane filtration, and functionalized microparticles. The techniques for microfluidic cell lysis and nucleic acid purification are compared based on the ease of microfabrication and integration, and sample flexibility. These assessments can help us determine the appropriate sample preparation technique for generating a true lab-on-a-chip.