In the project's early phase, upon establishing the objective to fabricate artificial heart valves using titin, the hardware team opted to preliminarily investigate specific manufacturing processes.
Assuming successful protein purification, the necessary explorations in hardware are:
1. Utilizing wet spinning for the transformation of Titin into elongated fiber strands.
2. Employing plain weaving techniques to convert fibers into fabric.
3. Experimenting with the application of an elastic substance as a protective layer on both sides of the fabric.
4. Constructing a heart valve prototype to examine its efficacy in regulating blood flow direction.
1. Wet Spinning to Produce Titin Fiber Threads
Wet spinning is a yarn-making process capable of creating high-strength, high-toughness protein fiber threads. It involves three main steps:
First, mixing the protein as a solute with a solvent that can dissolve the protein. Here, we plan to use hexafluoroisopropanol as the solvent, extruding the solution through a fine needle to form threads.
Second, allowing the protein solution to enter a coagulation bath, which is a water solution with a specific pH value. This solution can quickly absorb the solvent molecules in the protein solution, enabling the protein molecules to rapidly polymerize into threads
Third, ensuring the swift collection of protein threads."
Figure 1. Wet Spinning explained, referenced from [1]
1.1 Electric Injector
To achieve protein fibers with consistent diameters, we developed an electric injector, comprising a stepper motor and ball screw, creating an electric slide table to uniformly drive the syringe plunger and extrude the protein solution into fibers.
Figure 2: The Electric injector is composed of a stepper motor slide table, a pusher, and a syringe.
The silver section at the lower part of the image is the ball screw slide table, propelled by a 42 stepper motor from behind, moving the black slide block (center-left in the image) forward in a manner akin to "turning a screw." Above the slide is the syringe push rod, tasked with operating the syringe plunger. The syringe is secured to a bracket on the slide table's right side, ensuring a constant ejection rate of the solution, thereby providing our protein threads with a uniform and steady diameter.
Figure 3: Team members design, 3D-print, and assemble the slider pusher.
We designed and 3D printed the hinges, push rods, and syringe bracket. We assembled a frame from purchased 2020 aluminum profiles to regulate the injection angle. The resulting injector is depicted below.
Figure 4: Design sketches and the final assembled device
Figure 5: Video - Electric Injector Test
1.2 Coagulation Bath and Fiber Spinning Test
Figure 6: Device testing, featuring the coagulation bath on the left and the electric injector on the right, topped by the injector's control panel and controller.
We also purchased a stepper motor controller and panel to control the motor's speed, ensuring the injector's precise operation. After thorough calibration, we determined the ideal motor speed, injection velocity, and temperature, leading to the initiation of wet spinning trials.
Figure 7: Video showcasing the fiber spinning test.
In this video, we used a syringe to inject a mixed solution into a cold-water coagulation bath, where it forms long filaments. The filaments are originally colorless, but for the sake of the video, we added a safe and economical blue pen ink to show the color. This is an example of wet spinning, a process of producing fibers from polymer solutions. The coagulation bath causes the polymer to precipitate in fiber form by removing the solvent. Wet spinning is also more environmentally friendly than dry spinning, as it does not emit volatile organic compounds into the air.
Figure 8. Testing wet spinning and injection conditions, such as temperature, solution viscosity, and injection diameter/speed.
Figure 9. We tested needles with various diameters.
1.3 Spinning Wheel
Our objective was to develop a consistently rotating spinning wheel to expedite the gathering of protein threads. We purchased a spinning wheel model from an online retailer for analysis. Nonetheless, time limitations prevented us from actualizing this spinning wheel's construction.
Figure 10. We purchased a spinning wheel device to study the design.
2. Transforming Fibers into Fabric via Plain Weaving
We started with engineering a toy-model plain weave mechanism, composed of a weaving frame, spindles, and a warp-lifting rod. Utilizing TPU elastic threads as stand-ins for titin protein fibers, we employed distinct colors to distinguish between warp and weft in the weaving process. Eventually we succeeded with the fabrication of cloth, affirming the practicality of our concept.
Figure 11: Simplified Spinning Device
Figure 12: Test of Fabric Weaving with TPU Elastic Threads
3. Elastic Coating for Fabric Protection
3.1 Coating Fabric on Both Sides with an Elastic Material for Protection
Studies suggest[2] that encasing plain-woven fibers in WPU material strengthens the fabric. We investigated this by fabricating a plain weave prototype. Post-3D modeling, we utilized red and green to denote warp and weft, respectively. The model was then set in a mold and enveloped with 2% agar, mirroring the methodology in literature[2]. This confirmed the viability of a comparable approach for encapsulating Titin-based fabric.
Figure 13: Assessing the Feasibility of WPU Coating Process Using a Model
Heart Valve Model and Blood Flow
Creating Heart Valve Models to Investigate Blood Flow Direction Control
To explore heart valve fabrication methods and understand their shape, we crafted an enlarged model and tested its role in regulating water flow direction. Initially, we 3D-printed valve scaffolds, then covered them with a silicone membrane, reinforced with rivets. Subsequently, we sealed the valve-to-scaffold connections with glue to prevent water seepage during experiments. Finally, we inserted the heart valve model into an acrylic tube, simulating its role in controlling blood flow direction within vessels.
Figure 14: Examining mechanical valve structure; on the left is our valve framework, in the center is our valve test model, and on the right is a schematic of a commercial heart valve.
During the experiment, we injected equal amounts of water from either end of the model and observed the flow rate through the model. The results indicated a significant difference in the speed of water passing through both sides of the heart valve.
Figure 15: Video: injecting water from the reverse flow side, observing the fluid's speed through the valve.
Figure 16: Video: injecting water from flow side, observing that the fluid passes through much faster.
References
[1] https://www.researchgate.net/figure/Wet-spinning-set-up-showing-the-as-synthesized-fibres-drawn-by-a-rotating-coagulation_fig2_333852798
[2] “Structural stability of novel composite heart valve prostheses - Fatigue and wear performance”, Biomedicine & Pharmacotherapy, 136 (2021) 111288, Han Zhou, Linzhi Wu, Qianqian Wu
