Planar Biaxial Testing for Soft Materials Research

Equipped with MTESTQuattro, an environmental bath, and the ADMET video extensometer for soft fibrous tissue (e.g. skeletal muscle, tendons, meniscus), ADMET’s eXpert 8000 Planar Biaxial testing system is utilized by Bucknell University’s mechanical and chemical engineering departments to engineer soft materials research. The development and design of biological soft tissue replacements is the main goal of this research to better the structure-function mechanisms in biological soft tissues, predominantly orthopedic tissues.

Planar Biaxial Testing


The Principal Investigator of Bucknell University Mechanics and Modeling of Orthopedic Tissues Laboratory, Benjamin Wheatley, Ph.D., collaborated with ADMET to discover a testing solution for himself and his colleague Kenny Mineart, Ph.D., searching for an instrument capable of:

  1. Stretching samples to high strain (more than 1000% uniaxial strain, certain polymeric gels remain elastic)
  2. Measuring a large variety of loads – from low (<1 N) to mid (~1 kN) while applying biaxial loading.

Fiber-reinforced and saturated with fluids, complex and soft orthopedic tissues, and their characterization, simulation and mechanical function, are the focus of Dr. Wheatley’s investigations, whereby mechanical analyses and modeling approaches offer a better understanding of how the tissues function, how diseases and impairment are related, and how clinical treatments can be established.

Skeletal muscle and its macro-to-micro level deformation is the laboratory’s focus, their addressed queries including the following: When skeletal muscle is deformed or stretched, how do the components of the tissue do so? How is the content and organization of the skeletal linked to muscle stiffness, predominantly in impaired tissues? How does fluid flow in the tissue? This evidence can help form comprehensive engineering and clinical approaches.

Dr. Mineart’s lab aims to advance structure-function relationships in novel polymer gels, specifically physically crosslinked polymeric gels, which are highly tunable in their mechanical response. This includes modulus and viscoelasticity and thus are exceptional candidates for an extensive range of uses, comprising orthopedic tissue replacement.

The necessary data for more applicable and complex deformations enabling Dr. Mineart and his group to better understand their mechanical function and design gels for desired applications is provided by the biaxial loading of the laboratory’s polymeric gels.

These teams were able to test a gel specimen that can stretch to 200+% of equibiaxial strain, then very soft tissues such as skeletal muscle, and finally stiffer tissues like the tendon in one day. The ADMET system was able to provide robustness, which is what investigators valued the most.

Dr. Wheatley commented further:

“The ability to do all of the above is important to us. We strongly value having a range of load and displacement capabilities, along with a state-of-the-art digital image correlation system.

Here are some specific ways in which we use the data that we collect with the instrument:

  • Correlate tissue structure to mechanics in orthopedic tissues
  • Develop and validate computational models of orthopedic tissues
  • Explore how polymeric gel formulation, and correspondingly nanostructure, affects gel mechanics.”


The Bucknell University planar biaxial testing system, an eXpert 8000 equipped with the MTESTQuattro controller and software, was supplied with several load cell capacities, allowing a variety of loads. Individual load cells are standardized per ASTM E4 for +/-1% accuracy down to 0.5% of capacity.

An environmental bath with nickel-plated stainless steel grips, a heater, recirculating assembly, ADMET’s video extensometer and digital image correlation system (integrated with MTESTQuattro) for post-processing analyses such as minimum/maximum, mean and standard deviation, time-slice extraction, stress-strain curve generation, data extraction along lines and so on, are included in the test frame.

The operator can measure sole points or set multiple virtual extensometers and non-contacting video-based strain data has adjustable gauge lengths and extension ranges. The video extensometer specifies real-time load vs. strain data with live output to MTESTQuattro for servo control and is also able to record live data in the axial and transverse axis to provide data to calculate Poisson’s ratio.

To provide full-field displacement and strain data for mechanical testing on planar samples, the package contains algorithms that can be used for material testing comprising fracture mechanics, biaxial tension testing, and FEA validation such as strain localization around cracks and notches.

All requiring cables and adapters, the video extensometer and DIC system include a high-resolution monochrome digital camera, lens, lighting and mounts.

This information has been sourced, reviewed and adapted from materials provided by Admet, Inc. - Materials Testing Equipment.

For more information on this source, please visit Admet, Inc. - Materials Testing Equipment.


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