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Functional Requirements
1. Suction mechanism required to pull the intestine upwards to hold it in place
2. Needle injection into the epithelium layer of the intestine after aspiration
3. Needle pulled out before the intestine is released to prevent damage
Design Improvements from the Inital Design
Decreased the air chamber angle from 30 to 10 degrees for a pencil-like feel making the new design more compact and easier to use.
Increased pore surface area for more suction and added side edges to prevent fluid escape.
CAD Bottom View of Aspiration Holes. (Left: Pore Area = 2.4 mm², Right: Pore Area = 7.4 mm²)
CAD view of needle entrance track
CAD side profile of entrance track
Before
After
Added a fillet around the needle entrance track that allows the needle to slide into the entrance track without damaging it.
Simulations and Analysis
FEA Analysis with 1ATM Constant Pressure Applied Across the Surface.
Outer Case FEA Simulation
Objective: to analyze how the shape of the device deforms with a pressure difference is created in the vacuum chamber. Also, to see if the VeroClear Material is strong enough so that it does not break.
Ansys Modeling:
Modulus of Elasticity 2,000 --- 3,000 MPa
Tensile Strength 50 --- 65 MPa
Poisson’s ratio of PMMA 0.35
Results:
Max Von-Mises stress: 6.9 MPa
Minimum FOS: 8.7
Device Suction Analysis (Initial Prototype)
Reliability of Procedure (Initial vs Final Prototype)
[1] Abramson et al, 2019 (A luminal unfolding microneedle injector for oral delivery of macromolecules)
[2] Yoshida et al, 2003 (Biological lubrication of hydrated surface layer in small intestine)
FEA Simulation of Intestine
The objective is to apply conditions corresponding to the suction and injection phases of the procedure and observe the behavior of an intestine model. The intestine was modeled as a long cylinder and simulated using conditions in the procedure on Altair Hypermesh. The boundary conditions and applied forces are shown to the left and the results on the right in the figure below.
Results: The crest of the intestine deflects 0.45 mm upwards in the desired shape of the cavity. Since the required deflection is ~100 microns, this suggests an effective factor of safety of ~4.5.
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