Glass microneedles for force measurements: a finite-element analysis model

Abstract

Changes in developed force (0.1-3.0 μN) observed during contraction of single myofibrils in response to rapidly changing calcium concentrations can be measured using glass microneedles. These microneedles are calibrated for stiffness and deflect on response to developed myofibril force. The precision and accuracy of kinetic measurements are highly dependent on the structural and mechanical characteristics of the microneedles, which are generally assumed to have a linear forcedeflection relationship. We present a finite-element analysis (FEA) model used to simulate the effects of measurable geometry on stiffness as a function of applied force and validate our model with actual measured needle properties. In addition, we developed a simple heuristic constitutive equation that best describes the stiffness of our range of microneedles used and define limits of geometry parameters within which our predictions hold true. Our model also maps a relation between the geometry parameters and natural frequencies in air, enabling optimum parametric combinations for microneedle fabrication that would reflect more reliable force measurement in fluids and physiological environments. We propose a use for this model to aid in the design of microneedles to improve calibration time, reproducibility, and precision for measuring myofibrillar, cellular, and supramolecular kinetic forces.

Protein kinase A changes calcium sensitivity but not crossbridge kinetics in human cardiac myofibrils

“…The force probe had a tip diameter of ϳ10 m that tapered little along a 1-mm length (2). The force probes were calibrated by measuring the deflection of the probe with a nano-machined cantilever of known stiffness (a generous gift from Gerald Pollack; Ref.…”

Force produced after stretch in sarcomeres and half-sarcomeres isolated from skeletal muscles

“…The diameters of the circular cross-sectional area of the portion of the cone inside the myofibril are normally bellow ~0.5–0.7 μm, while its tip is under 0.2 μm. The calibration of the micro-needles also followed a protocol established earlier in our laboratory7 and of others25. The needles were pierced externally adjacent to Z-lines in the case of sarcomeres (Figure 4D and Movie 1 suppl.…”

History-dependent properties of skeletal muscle myofibrils contracting along the ascending limb of the force–length relationship

“…Calibration of the microneedle was performed by the cross-bending method (Ayittey et al 2009), using pairs of cantilevers of stiffness varying between 22 and 348 nm mm 21 , similar to those used previously in our laboratory for force measurements (Rassier 2008). The cantilevers were produced with nanofabrication techniques and were pre-calibrated before use (Fauver et al 1998).…”