Mikayla McWilliams, “Nano-Indentation Based Analysis of Healing Murine Callus”
Mentor: Priyatha Premnath, Biomedical Engineering
Poster #103

During the reparative phase of bone healing, a thick mass of callus forms around the bone ends, stemming from the fractured hematoma. The callus begins soft, composed of fibrous tissue and cartilage, and develops over time to become a hard callus. We have developed a novel method to differentiate the mechanical properties of soft tissue (including cartilage) and bone at different points during the healing cascade in the tibia of mice. The fractured tibia was attached to discs through bone cement. The fractured tibia is adjusted till the flattest part of the healing callus is at the highest point. Next, the sample is placed in the Agilent Nano Indenter G200, and the focus is adjusted to the flattest part of the callus. The Nano Indenter is run at night so no outside vibrations can impact the results. Following tests displacement into the surface, load on the sample, time on the sample, harmonic contact stiffness, hardness, and modulus were retrieved. We applied the Oliver-Pharr method to calculate the average hardness, average modulus, and elastic modulus for each indentation [1]. Through the elastic modulus results, we were able to determine where based on the indentation pattern, and at what week of the healing process the objects’ resistivity to elastic deformation is greater on the callus thus determining the parts of the callus are bone compared to cartilage.

References:

[1] Oliver-Pharr method: E_r=1/β  (S√π)/(2√A)