Necking process for the improved parisons
Author: Natalie Jensen | Major: Biomedical Engineering
My name is Natalie Smith, and I am a senior Biomedical Engineering major in the College of Engineering working under Dr. Morten Jensen in the Cardiovascular Biomechanics Lab. My research project focuses on the development of a customizable angioplasty balloon forming machine for the treatment of heart disease in coronary artery bifurcations. This past summer I took our prototype machine which produced balloons approximately seven times larger than the average size used for coronary arteries and resized the molds to form smaller balloons. In doing so, I explored how the reduction in size affected the balloon forming process and how certain variables such as pressure, heat time, and temperature influenced balloon formation.
Coronary artery disease, a type of heart disease, is the leading cause of death in the U.S. Angioplasty balloons are a common method of treatment and work by placing a stent at the lesion site to widen the blood vessel. A particularly difficult type of lesion to treat is a bifurcation lesion, due to its complex geometry which varies among patients. To address the issues which hinder the use of standard shaped balloons in bifurcations, our research group developed a balloon forming machine with customizable molds that would allow clinicians to produce angioplasty balloons adapted for each individual patient. The first prototype machine manufactured balloons that were approximately seven times larger than the balloons typically used in coronary arteries to allow for easier preliminary testing. As the initial prototype testing concluded, I looked to take this project to the next step and adjust the machine to produce appropriately sized angioplasty balloons for coronary arteries, which was my focus over this past summer.
To examine how a reduction in mold size affected the balloon formation process, I first reduced the size of the mold by approximately half. As I began conducting preliminary pressure, temperature, and heat time testing, I noticed that several process details which had a fairly insignificant impact on the larger prototype had greater effects upon the smaller prototype. Most of these issues revolved around the balloon preform, also known as a parison, which is made up of a tube attached to a luer lock. The smaller tubing which I selected for the resized prototype did not properly fill out the mold. During testing, the parison either would not fill the inside of the mold entirely or would inflate both inside and outside the back end of the mold. To find a solution to this issue, a graduate student in the research laboratory and I conducted extensive research into industry practices for the formation of the parison. By incorporating components from industry methods, our solution was to take larger tubing and neck down the ends by heating and stretching. Although I am continuing to perfect this process, these parisons have shown considerably more promise than the previous parisons. I have been working with Dr. Jensen to examine all factors which influence this problem as it has been the most persistent and most significant one.
Another issue which arose from the parison was the connection between the luer lock and the tubing. Cyanoacrylate glue is used to attach the luer lock and tubing together, which were initially laid flat on a surface to dry. However, this resulted in the tube setting at an angle in the luer lock, which inhibited the easy insertion of the parison into the smaller machine mold. So, I designed a setting rack which would hold the tubing in a centered position inside the luer lock as it dried, and the resulting parisons performed much better.
As I continue into the fall semester, I will perfect the process adjustments which I have made. In addition to Dr. Jensen and the graduate student working on this project, I have also been working with another undergraduate in the research laboratory. Additional pressure, temperature, and heat time testing will need to be conducted to identify the ideal ranges for balloon formation. Then, the next step will be to reduce the size of the balloon mold by half again, which will place the balloon size within the average range of clinically used angioplasty balloons. Ideally the process adjustments which I have already enacted will minimize the adjustments needed once I reduce the mold size again.