Merging a Thrombectomy and Atherectomy Device For More Efficient Removal of Vascular Occlusions

Hello!

My name is Shyam Ganesh Babu. I am currently a senior in the Discovery Research Magnet Program at Spring Valley High School in Columbia, South Carolina. Out of school, I enjoy getting involved in sports such as tennis and cross country. I also play the clarinet in the Spring Valley Symphonic band. I am interested in biomedical engineering, biology, anatomy, and cardiology. I aspire to be a cardiologist, interventional radiologist, or pediatrician.

My research journey...

“It’s simple. A balloon travels up the artery, expands, and disrupts plaque.” This was my first thought after watching a balloon angioplasty animation. Despite the seemingly straightforward nature of the endovascular procedure, I was amazed at how the balloon, only the size of the tip of a pencil, could prevent life-threatening conditions like heart attack and stroke. This experience sparked my intellectual curiosity and marked the start of a two-year journey where I learned about the complexities of endovascular technologies through clinical experiences and research.

After watching the animation, I contacted a cardiac electrophysiologist at Prisma Health to explore the applications of endovascular technology, and a cardiovascular disease specialist at the Medical University of South Carolina to get insight into how these devices function. My interest in endovascular technology grew as the specialists explained their limitless applications to cure vascular diseases and the variety in types of devices. My curiosity and dedication towards this topic allowed me to explore it through different contexts.

Wanting to observe the technology in the real world, I interned at the Lexington Medical Center. In interventional radiology, I watched a thrombectomy catheter travel up a patient’s femoral artery to carefully remove thrombi. This experience taught me to appreciate the synergy of modern technology and medicine in healthcare.

Wanting to delve deeper into this topic, I conducted research on endovascular devices. The goal of my research was to design, construct, and test a more efficacious device. Rather than developing an entirely new medical instrument, I combined a rotational atherectomy, aspiration thrombectomy, and balloon valvuloplasty device into one instrument with improved safety and function. Using the knowledge from the internship and medical specialists, the prototype I designed theoretically seems to perform better than existing devices.

I wrote a research paper about my journey exploring how to merge an aspiration thrombectomy and rotational atherectomy device for efficacious removal of vascular occlusions and submitted it to the South Carolina Junior Academy of Science. I did well in their research paper and oral presentation competition and got the opportunity to become an AJAS Fellow!

Slide 2: Animation of each component of my prototype coming together.

Slide 3: Video of how the prototype works.

Slide 4: Complete Paper

Slide 5: Complete Scientific Poster

Slide 6: Additional Pictures

Title: Merging a Thrombectomy and Atherectomy Device for Removal of Vascular Occlusions

Author Name: Shyam Ganesh Babu

School: Spring Valley High School

City, State: Columbia, South Carolina

Teacher name: Mrs. Michelle Spigner and Mr. Scott Price

Rationale/Introduction

I was inspired to pursue this project after being amazed by a balloon angioplasty animation. I was amazed at how the balloon, only the size of the tip of a pencil, could prevent life-threatening conditions like heart attack and stroke. Following this experience, I contacted a cardiac electrophysiologist at Prisma Health and cardiovascular disease specialist at the Medical University of South Carolina to learn more about endovascular devices. An internship in interventional radiology triggered the start of this project.

Slide 2 - Issues this project addresses:

Endovascular occlusive diseases, such as thrombosis and atherosclerosis, are among the leading causes of death. Thrombosis is the formation of blood clots. It is responsible for 1 in 4 people dying worldwide. Atherosclerosis is the buildup of cholesterol, fats, and calcium on artery walls. It is the underlying cause of about 50% of deaths in westernized society. According to Bhat et al., there is no device that has evolved as the default gold standard to treat thrombosis and atherosclerosis due to there being a variety of different designs with different approaches, success rates, and safety features.

Slide 3 - Experimental Design:

Goal:

The research goal of this project was to combine an aspiration thrombectomy device with a rotational atherectomy device for efficacious individual or joint removal of thrombi and plaque. The joint device should be able to clear a majority of the occlusions quickly because it combines two clinically successful devices for clearing vascular occlusions.

Benefit:

Patients suffering from thrombosis, atherosclerosis, or both conditions simultaneously could benefit from this project. This project attempts to design a more safe, efficient, and efficacious instrument to remove blood clots and plaque.

Measures of success:

The joint device should be able to increase the blood vessel lumen diameter by clearing the vascular debris. The time taken for the device to remove the occlusions was measured in seconds using a stopwatch. The occlusions removed were measured in grams using an electronic scale and the percentage removed from the model blood vessel was calculated as follows.

Percentage of occlusion removed = (mass of occlusion removed by device / initial mass of occlusion) x 100%

Because this engineering project was proof of the joint atherectomy and thrombectomy device concept, the device was considered successful if, on average, the lumen diameter increases.

Process:

Everything was modeled. The prototype was constructed using motors, tubes, and burrs that model the function of the actual surgical instruments. I used models to conduct in-vitro testing as well. The blood vessel was modeled using a tube. Styrofoam was used to model plaque. And a jello and cotton ball mixture was used to model blood clots.

Methods

To explore how to combine a rotational atherectomy device and an aspiration thrombectomy device, the standard engineering process was followed: a prototype was designed, constructed, and tested.

Joint Atherectomy and Thrombectomy Device

The joint atherectomy and thrombectomy device combines an aspiration thrombectomy device with a rotational atherectomy device. Of the many types of thrombectomy and atherectomy devices available, these types were chosen because Reisman et al. (1997) and Przybylowski et al. (2014) found that rotational atherectomy devices and aspiration thrombectomy devices are effective at clearing vascular occlusions and are easy to modify, respectively. An aspiration thrombectomy device utilizes a vacuum to collect vascular debris. The vacuum should be able to suction wet blood clots and plaque. To construct the vacuum, a 120 volt (V) motor fan with a switch and a 14-gauge non-metallic cable, which could be plugged into a wall outlet, were used. To allow the vacuum to suction wet and dry material, a plastic container and vacuum filter were arranged as shown in Figure 1.

Figure 1. Aspiration Thrombectomy Vacuum System

The model above is a 3D rendering of the aspiration thrombectomy vacuum system. The 120 V motor fan is shown in gray. The dry vacuum filter is the black conical shape inside the clear plastic container. The vacuum generates negative pressure in the black plastic tube on the far left. Electrical wiring is not displayed.

The plastic tubing was securely attached to the plastic container and motor. The suctioned plaque would stay inside the plastic container due to the dry vacuum filter and the blood clot would settle at the bottom of the container due to gravity and low suction power. The vacuum generated negative pressure in the black plastic tube, which was connected to the joint device later.

To construct the model rotational atherectomy device, a stainless steel shaft with an outer diameter (OD) of 6-millimeter (mm) and a length of 25-centimeter (cm) was used. The shaft would be spun at high speeds with a plaque-grinding burr attached to one end. A gear train, composed of two same-sized vertical gears to increase rotation torque, was used to spin the shaft. As shown in Figure 2, the gear train was secured using 3D-printed housing.

Figure 2. Gear Train and 3D Printed Gear Train Housing

The model above is a 3D rendering of the gear train and the 3D printed gear train housing. The housing secured a stainless steel hollow shaft that had an outer diameter of 5.94 mm. The material used for printing was polylactic acid (PLA) filament. The red circles on the left and right sides are ball bearings that supported the steel shaft when it spun at high speeds. The components in white were 3D printed. The two brown columns are wooden dowel rods. The 6 volt DC motor is shown in light gray. This figure shows the rotational atherectomy component of the joint device. Electrical wiring is not displayed.

The gear train was driven by a 6-volt motor. The stainless steel shaft was further supported by ball bearings. The thrombectomy and atherectomy systems were base components of the joint device and were constructed using available materials to only model the real devices. The burr, shown in Figure 3, was a 3D printed cone with sheet metal blades attached to the surface.

Figure 3. Rotational Atherectomy 3D-Printed Burr with Sheet Metal Blades

This is a 3D rendering of the rotational atherectomy 3D-printed burr with sheet metal blades. The blades 1 mm thick blades were sharper and thinner than what is shown. The cone had a base diameter of 5 cm. The hollow opening in the center of the cone had a diameter of 6.1 mm and allowed the shaft to securely fit through it. To construct the blades, a 2 cm x 0.5 cm strip of sheet metal was cut and bent by hand to a 45° angle. The blades were secured to the cone using hot glue.

An additional safety feature added to the joint atherectomy and thrombectomy device was an inflatable balloon on the distal end of the shaft, following the burr. During an atherectomy or thrombectomy, the endovascular device travels in the same direction of the blood flow (G. Morgan, personal communication, December 9, 2020). As a result, pieces of ground blood clots, plaque, and other vascular debris can flow downstream, leading to adverse events in small-diameter blood vessels. The inflatable balloon was designed to prevent the downstream flow of vascular debris by blocking the vessel during the procedure. According to Dr. Morgan, a blood vessel can be blocked for no more than 30-45 seconds at a time (G. Morgan, personal communication, December 9, 2020). To construct the inflatable balloon, a 9-volt mini air pump was connected to a 7mm OD surgical tubing. The air pump was placed behind the 3D printed gear train housing and the surgical tube was inserted through the hollow stainless steel shaft until 3 cm of the tube was protruding past the burr. A water balloon, modeling an angioplasty balloon, was attached to the other end of the surgical tube using an O-ring with an inner diameter and ring thickness of 2 mm. The balloons used during balloon angioplasty (a procedure used to open narrowed arteries using a balloon) have the tensile strength of steel to ensure safe and successful treatment of the patient (G. Morgan, personal communication, December 9, 2020; Steele et al., 1985).

To construct the joint rotational atherectomy and aspirational thrombectomy device, each of the components was assembled together, as shown in Figure 4.

Figure 4. Three-Dimensional Rendering of Joint Atherectomy and Thrombectomy Device

The diagram above is a 3D model of the joint atherectomy and thrombectomy device with all of the components connected. The aspiration component is shown in detail in Fig 1. The gear train is shown in detail in Fig 2. The high-speed rotating burr is shown in detail in Fig 3. The vacuum motor tube and rack and pinion gear system are discussed below. Electrical wiring is not displayed.

As shown in Figure 4, the vacuum component was connected to a PVC expandable repair coupling so that the negative pressure of the vacuum would be applied directly behind the rotating burr. The expandable coupling, referred to as the vacuum tubes in Figure 4, had two components. Neither of the components spun with the main shaft because they were connected to the shaft using ball bearings. The orange tube in Figure 4, had an inner diameter of 4.5 cm and was immobile. The pink vacuum tube in Figure 4 had an inner diameter of 6.35 cm and could move back and forth about 3 cm along the stainless steel shaft. The moving tube ensured that all vascular debris was suctioned by the vacuum, making the device more safe. It was an additional safety feature added to the base components of the joint device. The back and forth movement was accomplished using a rack and pinion gear system. In Figure 4, the rack is shown in yellow, attached to the pink pipe. The pinion was connected to a 1.5-volt motor that was glued to the 3D-printed gear train housing. Pictures of all the joint device components can be seen in Appendix B.

All the motors and pumps were wired with an ON/OFF switch after the device was constructed to ensure safe usage of the device. The switches were organized in a wooden switchboard. A circuit drawing of the wiring can be seen in Figure 5. Pictures of the wiring and switchboard can be seen in Appendix A.

Figure 5. Circuit Drawing for Powering the Joint Atherectomy and Thrombectomy Device

The diagram above is the circuit drawing for powering the joint atherectomy and thrombectomy device. The switchboard, not displayed in this diagram, included the double pole double throw (DPDT) switch, the single pole single throw switch (SPST), and the preset potentiometer. The 120V vacuum motor fan was powered by an electrical wall outlet. The gear train direct current motor was powered by a DC power supply set at 6 V. The 9V mini air pump was powered by 2 AA batteries, meaning it was supplied with 3V. The rack and pinion DC motor rotation speed was controlled by the preset potentiometer and powered by 1 AA battery. Instead of an SPST switch, it had a DPDT switch so that the polarity could be reversed and the large vacuum tube could move forward and backward. All of the wire work was completed using a soldering iron, lead-based solder, and 22 gauge silicone electrical wire.

Model Thrombi

Due to limited resources, model thrombi were used to test the joint atherectomy and thrombectomy device in-vitro. According to Tocantins, blood clots are gel-like and “made up of a meshwork of fibrin needles” with some bundles of fibers (Tocantins, 1935, p. 709; Chernysh et al., 2020, p. 1). Specifically, 43% of arterial thrombi volume and 35% of venous thrombi volume make up the fiber network (Chernysh et al., 2020, p. 2). So, blood clots were modeled using materials with similar properties. The primary component of the model blood clot was gelatin; this would represent the gel-like physical property. To make the gelatin, 340.194 grams of dry raspberry Jello powder was added to 473.176 mL of boiling water. This mixture was stirred until the Jello powder was completely dissolved in the water. Next, 473.176 mL of cold water was added to the mixture and stirred. The red color of the Jello made the model blood clot easy to observe during experimentation. To model the fibrin needles and bundles, torn pieces of cotton were placed evenly throughout the Jello solution. Forty-three percent and thirty-five percent were averaged to calculate the average volume of the fiber network in blood clots; so, 39% of the model blood clot volume was cotton balls. The equation shown in Figure 6 was used to determine the volume of cotton balls that were added to the gelatin mixture.

Figure 6. Mathematical Equation Used to Determine Cotton Ball Volume in Model Blood Clot

x = volume of cotton balls added to the Jello solution

1286.546 mL = Total volume of jello solution (water + dry powder)

x / ( x + 1286.546 ) = 0.39 (0.39 = 39% average thrombi volume made of a fiber network)

x = 822.546

822.546 mL of cotton balls had to be added to the Jello solution so that the model fibers made up 39% of the model blood clot. To measure out this volume of cotton balls, a measuring cup was used.

Once the 822.546 mL of small cotton ball pieces were evenly placed throughout the Jello solution, the mixture was placed in the refrigerator for 5 hours so that it would become firm. Figure 7 shows the end result of the model blood clot.

Figure 7. Model Blood Clot Composed of Raspberry Jello Mix and Cotton Balls

The picture on the left shows the model blood clot right after it was taken out of the refrigerator. The picture on the right shows the model blood clot after it was placed in the model blood vessel, discussed later.

Because 5 trials had to be conducted, the mixture was split into 5 even groups and placed separately inside a model blood vessel, discussed later.

Model Plaque

Due to limited resources, model plaque was used to test the joint atherectomy and thrombectomy device in-vitro. According to Davaine et al., arterial calcification, also known as plaque-buildup, is a process that mimics bone formation (2016). Plaque is hard and similar to mammalian bone tissue on the outer surface and somewhat spongey on the inside (G. Morgan, personal communication, December 9, 2020). To model plaque, packaging styrofoam was cut and shaped so that it would fit tightly inside a model blood vessel. The hard, outer surface of plaque was not modeled because the constructed joint device lacked power and torque to cut through bone tissue-like material. In the center of the plaque, a small hole, with a diameter of 1.5 cm, was cut to relieve mechanical stress from the joint device during a simulation and to model minute blood flow present in the blood vessel. Figure 8 shows the model plaque.

Figure 8. Pictures of Styrofoam Model Plaque Before Experimentation

This figure shows the model plaque used to test the joint device. The diameter of the model plaque was based on the diameter of the model blood vessel. The width of the plaque was determined based on the maximum width the joint device could cut through due to the physical limitations of the design. The image on the right shows the model plaque placed inside of the model blood vessel, discussed below.

Model Blood Vessel

The model plaque and model blood clot were placed inside of a model blood vessel to test the joint atherectomy and thrombectomy device in-vitro. Blood vessels are tube-like structures that transport blood, so a plastic tube was used to model the blood vessel. A study by Gepstein et al. followed a similar method of using tubing to successfully and accurately test endovascular devices in-vitro (1997). The model blood vessel was a clear, plastic tube 31 cm long with a diameter of 7.5 cm. During experimentation, the model blood clots or model plaque were placed inside of the plastic tube to model vascular occlusions caused by atherosclerosis and thrombosis.

Data Collection and Data Analysis

During an atherectomy and thrombectomy, the catheter-based device would be manually inserted into a blood vessel to drain or remove the blood clot or plaque (Heunis, Sikorski, & Misra, 2018). So, the procedures of this experiment attempted to simplify and replicate the genuine procedures. The purpose of these methods was to test the joint device’s ability to remove plaque and blood clots in a mammalian blood vessel through in-vitro model testing. The procedure was timed to measure the general efficiency of the device to remove occlusions. This general method of testing a novel endovascular device in-vitro using models was influenced by a study by Chueh et al., which successfully and accurately tested numerous thrombectomy devices using occlusion and blood vessel models (2012).

In the proposed research, model thrombectomies were performed first. Prior to experimentation, the mass of the model blood clot placed inside the vessel was measured in grams using an electronic scale and written down in the corresponding row of the data table. The vacuum motor fan was then powered on and the blood clots were sucked from the blood vessel into the wet vacuum container. A back-and-forth motion was used to more accurately model a thrombectomy. The blood clots were not sucked through the PVC expandable repair coupling at the front of the device but directly by the plastic tubing that would connect the joint device and the plastic container. This had to be done to avoid clogging and damaging the ball bearings located inside the coupling. The experimenter attempted to get as much of the blood clot as possible and the time taken to do so was measured using a stopwatch. After the vacuum motor fan was powered off, the mass of the remaining blood clot present inside the blood vessel was measured in grams using an electronic scale. The model atherectomy was performed 5 times.

Next, model atherectomies were performed. Prior to experimentation, the mass of the model plaque was measured in grams using an electronic scale. To perform the model atherectomy, the burr portion of the joint device was powered with 7.5 volts and moved back-and-forth through the model plaque, until a 5 cm diameter hole was made. The wet vacuum and balloon were not used together to observe the device’s safety and ability to prevent the downstream flow of vascular debris. This was due to safety concerns caused by the powerful 120V vacuum motor fan. Because this was a proof of concept project, it was assumed that when negative pressure is applied to one end of the PVC pipe, the ground styrofoam pieces would be sucked into the vacuum container. The time taken to remove the plaque needed to create a 5 cm diameter hole was measured using a stopwatch. After the model atherectomy was completed, the mass of the remaining plaque was measured in grams using an electronic scale.

To make conclusions about the novel joint device, the average percentage of each type of occlusion removed and the average time taken to remove the occlusion were calculated using the data. For the model atherectomy, initial and post-procedure lumen diameter was also measured. The type of data collected was also influenced by the study by Chueh et al. (2012). While the study measured blood flow of the blood vessel before and after the endovascular procedure, the proposed research measured initial and post-procedure lumen diameter, which correlates with blood flow and does not require simulated blood flow in a model blood vessel. The joint device was considered successful if it increased the blood vessel lumen diameter. The purpose of this data was to prove that the joint atherectomy and thrombectomy device is capable of being inserted into a blood vessel to successfully remove plaque and blood clots.

Slide 4 - Results

The goal of this project was to combine 3 existing medical devices to increase success rate of the atherectomy and thrombectomy procedures. Success rate is improved by increasing the lumen diameter of a blood vessel.

Slide 4 shows before and after pictures of a thrombectomy in a model blood vessel. According to the line graph on Slide 5, all the trials had a 100% clearance of the blood vessel. Furthermore, the mass of the blood clot changes from around 200g to 0g in all trials.

Slide 4 shows before and after pictures of an atherectomy in a model blood vessel. As shown by the line graph of change in plaque lumen diameter in Slide 6, the lumen diameter increased significantly. On average, 70% of the blood vessel was cleared of occlusions.

Slide 7 - Discussion

Discussion: The engineering goal of this research project was reached, since the blood vessel lumen diameter significantly increased in all trials.

There was a 100% lumen clearance for the thrombectomy and a 346.67% lumen diameter increase for the atherectomy. The data could not be compared with other studies because the procedures were unique to my research.

Sources of Error: There may have been error or inaccuracies in measuring the mass of the before and after vascular occlusion models.

Limitations: I was not able to test both thrombectomy and atherectomy procedures together because the jello could not be suctioned by the device due to the ball-bearings used to build it. Furthermore, the models do not perfectly model vascular occlusions. As a result of these limitations, this project will be a proof of concept for a design. The constructed device can not be directly applied and a lot more research needs to be done.

Applicability: This device can be used to clear occlusions in large blood vessels; maybe small vessels if the design and tech permits in the future. Conceptually, it increases the success rate of both procedures and should save the patient and medical institution money.

Possible Benefits: Benefits for using a joint device: 1 intervention for patients with both occlusions leads to a shorter procedure time. The cost of training and equipment for the procedures will be reduced since medical professionals will need to be trained on one device rather than one. The success and safety rate of each procedure will be higher due to the combination of technology and added safety features in the join prototype.

Future Goals: In the future, I would like to test all the components at once and quantitatively measure its safety. By making the data collection methods more realistic, I may be able to compare the data with other studies. Finally, I would like to make the burr expandable, because it would have application benefits (increased safety and fewer moving parts).

Slide 8 - Acknowledgements:

I would like to thank Mr. Scott Price, Dr. Garrison Morgan, Dr. Sultan Siddique, Mrs. Michelle Spigner, Dr. Michelle Wyatt, my parents, and Spring Valley High School for their help and support throughout the research process.

Thanks to Mr. Price for helping me with power tools, 3D printing, and electronics. Thanks to Dr. Morgan and Dr. Siddique for sharing their experience and knowledge from the medical field. Thanks to Mrs. Spigner and Dr. Wyatt for helping me with the engineering process, paper writing, and presentation creating. Finally, thanks to my parents for their moral and financial support.

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