Mesoscale, Cantilever-Based Indentation Device for Mechanical Characterization of Soft Matter and Biological Tissue

Abstract

Tissue engineering has been driving a growing interest in mesoscale tissue mechanics (10-4 - 10-2 m), requiring tools to compare modulus between irregularly shaped primary tissue explants and synthetic scaffolds. We have designed and built a simple cantilever-based mesoscale indentation device to record force-displacement data during spring-loading, stress-relaxation, and creep experiments. Its simple design enables quantification of a wide range of soft matter moduli, from ~500 Pa collagen hydrogels to ~2 MPa silicones, by its compatibility with cantilevers of different stiffnesses and indentation probes of different sizes. A piezo-electric stage is used to drive a cylindrical or spherical indentation tip into the sample, while custom programming in LabVIEW through a data acquisition card enables stage control and acquisition of cantilever deflection using a capacitive sensor. Cantilever stiffness, deflection, and piezoelectric stage positions, acquired at a rate of 10Hz, are used to calculate force and indentation depth throughout indentation cycles. Using xyz manual coarse stages, tissue properties can be mapped across the sample surface. We have also built in commands to tune initial tip location using the piezo-stage to more easily find the sample surface, which is critical for accurate application of contact models. Here, we provide detailed information on how to design, build, and code a system for mesoscale indentation.