Please contact Maria at sinzigeorgescu@gmail.com to coordinate your mechanical testing…

Anthony Simonetti

John Biswakarma

Hetian Wu

Sambit Acharya

Karmen Chong

1. Set up rubber gasket with runways in between two glass slides, clamp with binder clips. For sterile situations, alcohol everything, vacuum everything, to be safe there's no alcohol left, you can wash with PBS. Note: in order to get a construct with a chondral region of similar size to 2.3 mm, use a thicker rubber for the gaskets.
2. Use a 5mL pipette (small tip) to insert gel, moving pipette back and forth during casting to get air out of the loops
3. Place velcro sheet with gel regions on a bed of very thin rubber (in a large dish)
4. Punch a piece of regular rubber (2.3 mm thick) with a biopsy punch. Use a metal rod to push this rubber into the punch, like loading a revolutionary musket.
5. Punch gel until you hear/feel the underlying thin rubber pop. The underlying thin rubber gives an extra push, aiding the punching. Note: You will go through a ton of punches as the velcro REALLY wears down the punch.
6. Using the metal rod from the back, push on the rubber inside the punch slowly, so that the construct comes out. This distributes the force so that it doesn't stab the construct.
7. Reload the rubber, and repeat.

Notes: It's much, much easier to do this with higher percent gels. As the punch dulls and you are adding more force, it becomes easier for your construct to squish under the stress of the punching process, especially if 2%. We use alcohol to sterilize all of the rubber. Depending on drying time and presence of cells, we do a pbs wash to remove alcohol residue.

Schedule

A: Anthony Simonetti J: John Biswakarma H: Hetian Wu S: Sambit Acharya K: Karmen Chong

Determining the Agarose Young’s modulus and modeling a decrease in the modulus due to an added Layer of Velcro® Sambit Acharya John Biswakarma Karmen Chong Anthony Simonetti Hetian Wu

Instructors and Special Contributors: Eric Lima Maria Gorgesecu Diane … David Tan

Abstract:

Goal: The goal of this paper is to determine the young’s modulus of 2%, 4% and 6% agarose with and without Velcro® through creep loading and stress relaxation method using a mechanical tester. The agarose without the Velcro was the control group.This paper will attempt to show the reduction factor involved in adding a Velcro with shaved loops on the modulus of the agrose gels pellets.

Procedure: (change of format needs to be done properly and writing to be consistent with a scientific paper; this format is just to be clear of what was being done) The experiment was conducted in a sterile environment because agarose is an organic material that decays within 3 days. The samples were tested within a span of two days after being made. On each day atleast 1 group had to be completed i.e. 1 of each ctrl 2%,4%,6% and 1 of each Velcro bed added 2%,4%,6% agarose percent gels. Making of the agarose: Agarose 2%,4%,6% were made by creating a 6% agarose and diluting it to the respective required percentages. The 6% agarose gel was made by using 6% (by weight) agarose and adding it to a phosphate buffer solution (Pbs) and heated to a temperature of 300 celcius (not sure must check) for 15 minutes. The agarose was cooled until a stable viscous fluid could be mixed with a solution of phosphate buffer solution to make the respective dilutions via a pipet in the sterilized vent hood. Making of the Agarose pellets: The rubber frame, microscopic slides and clamps were kept under 70% alcohol solution to make them sterile. The sterile solution had been prepared before the agarose was made and kept inside the sterilized vent hood while waiting for the agarose to become viscous. With 2%,4% and 6% agarose content were kept into an assembly of rubber frame and microscopic slides. This was allowed to set in the assembly. After casting the agarose in the assembly the agarose was punched into small pellets with a 3.5mm sterile hole puncher(?). These pellets were transferred into a Pbs in petri dishes. These petri dishes were kept in the freezer and only parts that were being tested were taken out and kept in a different dish where the agarose gel was tested. Testing of agarose gel pellets w/o velcro: The required agarose gel were taken out from the freezer and allowed to thaw for 10 minutes. While the agarose was thawing, each agarose gel’s thickness was measured along with its diameter using a veneer caliper. The setup of the mechanical tester was done and the parts were tested. The testing was done on a phosphate buffer solution in a petridish to avoid drying the agarose gel during testing. Each test takes more than 35 minutes i.e. 5 minutes creep loading, 30 minutes stress relaxation testing and a minute and a half for dynamic testing for 0.5,1 and 1.5 dynamic modulus. Adding pictures of the mechanical tester to give a thorough understanding of what tests occurred.

Analysis: We observe that the compression testing due to the mechanical tester causes displacement ΔL. We have tried to model a solid works part of the pellets. However, due to the limits of solid works analysis programs i.e. the anisotropy of solid works is linear whereas the organic materials do not have such linear relations in real life. The solid works model was to help visualize the forces acting on a uniform grain organic material to understand stress/strain spikes using a mesh over the surface of the volume. Analysis of the experimental data: For each agarose pellet there were sets of data associated with it i.e. manual obtained measurements such as diameter and thickness via the Vernier caliper. Along with these manual measurements, there were automated measurements done by the mechanical tester*(this data is obtained through SRL tests, not creep) , which includes the stress applied in grams measured by the load cell, and displacement of the step motor using a dvdt voltage rectifier(?). These two data can be used in the following way. σ= ε_y δ where sigma is the stress, Ey is the young’s modulus and delta is the compression σ= F/A= (Force in grams applied by mech tester)/(contact surface of the pellet (circle Area)) δ=(length intial)/(change in length from dvdt voltage) Combining these known scientific relations we can obtain the young’s modulus by ignoring the noise collected from the mechanical tester. For negative young’s modulus, we can effectively change the reference point of the initial length at a compressed state which would give a reduced force. Accounting for the creep created before the stress relaxation technique, we can get the new initial length reference point. We need help with this part. From all the modulus equations, we will have enough experimental data to find the factors in determining the reduction factor.

Results:

Conclusion:

Citations: Fundamentals of Material Science, Calister The science and Engineering of Materials, Askeland

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