Design and manufacture of a low-cost 3D-printed laboratory device to measure the hyperelastic properties of polymeric films with small form factor suitable for medical devices.

Hyperelastic materials are extensively incorporated in medical implants and microelectromechanical systems due to their large, elastic, recoverable strains. However, their mechanical properties are sensitive to processing parameters that may lead to inconsistent characterization. Various test setups have been employed for characterizing hyperelastic materials; however, they are often costly. Recent advancements in additive manufacturing and open-source software/hardware suggest the possibility of simpler solutions in research settings for characterizing them; raising the question of whether one can characterize these materials with low-cost tools and tests that take advantage of soft and small form-factor samples. Here, the authors investigate the potential of an open-source, 3D-printed test system designed for characterizing such materials. This system is tailored for small form-factor samples (sub-mm thickness) and large elastic deformations, common in polymeric parts of minimally invasive implants. The authors developed parts using additive manufacturing for uniaxial and planar tension testing, with a low-cost image correlation method adapted for measuring large strains. Polydimethylsiloxane was chosen for demonstration of a two-parameter Mooney-Rivlin model, due to its documentation and use in biocompatible devices. The estimated Young's and shear moduli were repeatable and consistent with the literature. Curve-fitting was challenging and dependent on the optimization choices, when data points were limited, consistent with prior reports. However, with a large number of data points and ideal optimization error choice, and were found to be close to those reported previously. This work demonstrates a low-cost, 3D-printed, open-source test setup for characterizing hyperelastic materials using a two-parameter Mooney-Rivlin model with reasonable accuracy.