3D-Printed Planar Biaxial Testing Setup for Imaging

Hi, we are 2022 Senior Design Team 16 and we were tasked by Dr. Valdez Jasso and Becky Hardie from the DVJ lab to create a planar biaxial device that would be able to stretch rat myocardium samples. This website serves as a summary of our work on this project. Below is a brief video summarizing our project. The rest of the website goes into more detail about what we did.

Introduction

To better describe the remodeling process undergone by the right ventricle in pulmonary arterial hypertension (PAH), we need to integrate tissue structure to mechanics. Current approaches involve planar biaxial testing mimicking in vivo conditions (Fig 1) and imaging in an unloaded state to quantify the structure (Fig 2).

Here we propose to develop a 3D printed device that will be used to mechanically test rat myocardium samples in a displacement-controlled planar biaxial tension setup. The device was designed such that a tissue can be fixed in a stretched configuration, so it can later be imaged under a multiphoton microscope (MPM). This will allow researchers in the DVJ lab to integrate structure to function and build structurally-motivated constitutive equations of right ventricular myocardium.

Figure 1: Rat RV tissue in Planar Biaxial device. Sample is hooked to loading arms.

Figure 2: MPM image of Collagen Fibers

Problem

There is currently a knowledge gap in knowing how diameter, orientation, and tortuosity of collagen fibers of the RV free wall affect the response to biaxial tension loading due in part to a lack of device that allows for both loading and imaging of a tissue sample using a microscope.

Goals

1. Design a 3D printable device to apply biaxial load to biological tissue

2. Ensure uniform applied displacement of 10% of the initial dimension

3. Design a locking mechanism to apply displacement for 48 hours

4. Device must allow for imaging with multiphoton microscope

5. Ensure sample can be submerged in a solution bath without leaking

6. Optimize tissue attachment method to prevent damage

More About Goals

(click on this section)

The most significant goal of this project is to produce a device that will allow the tissue samples to be biaxially stretched to displacement values representative of physiological conditions. This can be accomplished by designing a device where all the sides are simultaneously able to displace between 8% to 12% of the sample dimensions. It is important that the device applies load planar biaxially, so the conditions are similar to when the sample is in vitro.

In order to perform planar biaxial testing, the applied displacement must be applied in all directions simultaneously and to the same extent. In order to ensure consistent applied displacement in all directions, once the tissue is attached to the device, it must be “zeroed”. This means that the sutures must be pulled taut, but without applying significant force to the tissue. To account for differences in sample geometry, this will be performed separately for all 4 sides of the tissue.

Once the tissue sample is stretched to the needed amount, the device must be able to maintain this configuration for 48 hours. To do this, a locking mechanism must be created that is compatible with the displacement component of the device to keep the samples stretched.

In addition to loading the samples properly, a significant aspect of the project is to image the samples in their stretched state. To do so, the device must be able to fix the tissue in the stretch configuration. Fixing the tissue will allow it to be sandwiched between glass slides to be imaged with the MPM laser so it can pass completely through the tissue.

To preserve tissue structure, and thus function, the attachment method should prevent torsion. Ensuring even load distribution at each edge of the sample is also important to prevent one area from enduring more stress than another.

Finally, the samples will need to be submerged in a solution bath during the fixation process. Formalin is used to fix the tissue in the stretched configuration. It is highly volatile, so it is important that it can be contained. Also, the tissue must be fully submerged so that the environment stays consistent, and the tissue is able to be completely fixed.

Our Bioengineering Day Poster

16Poster.pdf

Created by: Delaney K. Donnelly, Ahmad Zaferi

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