Adaptation Of The Biodent For Spherical Microindentation To Determine Elastic Modulus In Small Rodent Bones

<p>Mechanical and material properties of bone are essential for understanding both normal skeletal function and the progression of bone-related diseases. Microindentation has become a widely used method for evaluating tissue mechanical properties of bone, as it samples the contributions of microarchitecture and composition. Microindentation using a standard pointed tip inherently introduces both elastic and plastic deformation into the material. In contrast, indentation with a spherical tip can be operated entirely in the elastic range, providing for a non-damaging test that has significant advantages over sharp indentation techniques. Moreover, a key advantage of using spherical indentation lies in its operation under Hertzian contact in a non-destructive manner, which opens its potential for future viscoelastic and dynamic studies.</p> <p>In the current study, we tested whether a BioDent^TM, Reference Point Indentation (RPI) device, could be reconfigured and repurposed for use as a spherical microindentation system for testing small rodent bones. Originally, the BioDent is a small, benchtop loading device containing an actuator, load cell and a high-resolution displacement transducer. To operate as a conventional microindenter, we had to: 1) Reconfigure the system software, 2) Remove the reference probe assembly and replace with a custom-designed spherical indenter, and 3) Create and calibrate new testing procedures for the remade BioDent. We designed two spherical microindenter test probes with tip radii of 425µm and 500µm, respectively. The Oliver-Pharr method of determining reduced elastic modulus (<em>E_r</em>) from indentations requires compliance calibration. For the small test frame and low force load cell of the BioDent, this necessitated development of a novel compliance determination method —our numerical threshold-based approach. After initial validation on a PMMA (polymethyl methacrylate) calibration standard, the method was tested on mid-diaphyseal humerus cross-sections from rabbits. Indentation tests were performed on PBS-hydrated samples which were then dried and tested on again to assess expected stiffening effects. Finally, adult rat mid-diaphyseal tibia sections were prepared and indented to test whether our method would work on smaller bones with narrow cortices (< 300 µm).</p> <p>We found that the elastic modulus (<em>E_r</em>) measured for PMMA, 2.79 ± 0.16 GPa, was effectively identical to the reference value of the standard (2.8 GPa). <em>E_r</em> for the hydrated rabbit cortical bone was 9.84 ± 1.65 GPa and 19.54 ± 8.48 GPa for the dehydrated sample. For rat cortical bone, modulus for hydrated bone samples was 12.64 ± 0. 05 GPa and increased to 15.73 ± 0.06 GPa after drying. These values fall within the published range for mature rat cortical bone and are consistent with the known stiffening effect of water loss on bone.</p> <p>This study conclusively shows that the BioDent could successfully be adapted into a spherical microindentation device and demonstrated a high degree of precision and repeatability in rodent bone tests. This modified system shows promise for reliable measurements of bone mechanical and material properties and lends itself as a highly suitable device for in vivo testing in small animals.</p>

Name thesis:degree_name

Master of Science (M.S.)

Level thesis:degree_level

Thesis

Discipline thesis:degree_discipline

Biomedical Engineering

Year dc:date.available

2025

Author dc:creator

• Jerome, Mixame E

Contributors dc:contributor

• Mitchell B. Schaffler

• spherical indentation
• microindentation
• compliance calibration
• BioDent
• rodent bone
• Biomedical Devices and Instrumentation

Repository record dc:identifier

https://academicworks.cuny.edu/cc_etds_theses/1242

OAI identifier oai:identifier

oai:academicworks.cuny.edu:cc_etds_theses-2393