Open Source, In-Situ , Intermediate Strain-Rate Tensile Impact Device for Soft Materials and Cell Culture Systems

Background Intermediate-strain-rate mechanical testing of soft and biological materials is important when designing, measuring, predicting, or manipulating an object or system’s response to common impact scenarios. Open source micro-mechanical test instruments that provide high spatial and temporal resolution volumetric strain field measurements, non-destructive testing and gripping of soft materials with low elastic moduli, programmable strain rates spanning from 10^-6 s ^-1 to 10^2 s ^-1 , and biocompatibility for living cell cultures and tissues in one instrument are lacking in the current literature. Methods We introduce a micro-tensile testing device developed to meet all these criteria while being straightforwardly accessible to the end user. This device sits atop an inverted microscope stage, granting the researcher access to 3D spatial resolutions as low as 100 nm and frame rates only limited by the camera speed and availability of recordable photons. The micro-tensile specimen is attached to the test device by a specially designed fixture. This enables a material to be cast into the mold assembly and tested without being manually manipulated before or after testing. The tensile deformation is controlled by two voice-coil linear actuators synchronized to pull a specimen in opposing directions. A field of view focused centrally on the specimen experiences a highly-controllable uniform tensile strain with minimal rigid body motion. Results We validate the resulting in-plane strain fields on a 2D poly-dimethylsiloxane (PDMS) substrate and a heterogeneous polyurethane foam using Digital Image Correlation (DIC) and volumetrically on 3D polyacrylamide (PA) hydrogels using Digital Volume Correlation (DVC). High-Rate Volumetric Particle Tracking Microscopy (HR-VPTM) is used to quantify and validate the 3D volumetric strain fields at impact-relevant rates. The device can apply up to 200