We met for a conversation with Professor Jeremy Goldman, a visiting scientist at the Technion who is involved in the development of such a support.
Clean wires of iron (A) and magnesium (F) undergo weathering after being implanted in the wall of an artery. The iron rusts and condenses after a few months (BC), while the magnesium decays (GH).
A stent, or stent, is a cylindrical, springy metal mesh inserted through a catheter into blocked arteries to widen them and prevent future narrowing. Implantation of stents has revolutionized the treatment of cardiovascular diseases and greatly reduced the number of open heart surgeries. Today, stents are implanted in more than 90% of the therapeutic catheters. However, the support is covered with cellular tissue that may accumulate sclerotic material or create scar tissue and these will return and block the blood vessels. One of the research directions to solve the problem is the development of a biodegradable support, which will disappear from the blood vessels after about nine months.
We met to talk with Professor Jeremy Goldman, a visiting scientist at the Technion who is involved in the development of such a support.
How did you come to the topic, and what were the first steps in the research?
I am a biomedical engineer by training, and I am interested in the circulatory system. I am particularly interested in physical effects, such as mechanical pressure and blood flow, on blood vessels and the development of diseases. A few years ago, the Boston Scientific company, which deals among other things in the development of stents, approached me to participate in the characterization and testing of new stents in an arterial environment.
After examining the subject, I discovered that the research in the field suffers from oversimplification. Some of the studies done in the laboratory, outside the body, were too simple and it was not possible to draw valid conclusions from them. Whereas the animal studies were too complex and expensive: the researchers would produce whole supports and implant them in large animals, such as pigs. This is a cumbersome process, from which it is difficult to draw general conclusions because it is greatly influenced by the geometry of the support, and it is difficult to isolate the basic variables related to the material itself, such as mechanical strength and the speed of fusion (corrosion).
Therefore, the first thing we did was to develop a new and controlled experimental system that would be simple and cheap enough to quickly test many substances, without difficult experiments on animals, but would also provide enough general information that would be relevant to conditions in the body.
We therefore use thin metal wires, of uniform thickness and geometry, which can be tested in the laboratory or easily implanted in small animals, such as rats, inside the arteries or on the walls of the arteries. This is a quick procedure that does not severely harm the animal. After a few days, weeks or months, the small implant can be taken out to be examined in the laboratory: to check its strength, its mechanical structure and the chemical reactions it has undergone.
This is an initial screening process. Then experimental stents can only be made from the most promising materials.
Why didn't they do it before?
The supports used today are non-degradable, therefore they are made of well-known and durable materials, such as stainless steel. Sometimes the stent is coated with a polymer containing drugs that are slowly released into the artery and delay its re-narrowing. In such a system the structure of the support is important and not the material from which it is made, so it was logical to test it in large animals only.
What consumables may be used for supports?
Degradable polymer-plastic materials are often used in medicine. However, we do not have a biodegradable polymer with the desired mechanical properties. Such supports simply do not withstand the physical pressure prevailing in the arteries. Therefore, the new approach, and this is a really new concept, is the use of a perishable metal. This is a new requirement also in the world of metallurgy (metal research), where they usually look for metals that are resistant to fusion, whereas I look for the opposite.
Another requirement is that the metal be friendly to the body. We are deliberately looking for a metal that will react with its environment in the arteries and disintegrate. Therefore, it is important to make sure that the products of this fusion are not toxic and are easily removed from the body. The logical metals are therefore metals that the body needs, and even supplements are taken, especially iron and magnesium.
The first candidate was Barzel. But it turned out that iron supports weather too slowly. Moreover, rust, a product of iron wear and tear, is not quickly removed from the body and accumulates on the support, increasing its volume and harming the artery.
Attention was therefore directed to magnesium, a more active metal whose weathering products are not problematic. However, pure magnesium is not strong enough and wears out too quickly. Now they are looking for a magnesium alloy that will be stronger and wear out more slowly.
Is that why you came to Israel?
Yes, Israel has some of the best metallurgists in the world, such as Nobel laureate Professor Dan Shechtman. At the Technion, I work in Menachem Bamberger's lab in collaboration with Eli Egion from Ben Gurion University. In Israel we are looking for a new alloy, because here is the knowledge to plan the microscopic and nanometric structure of the material in an intelligent way and according to the goals. I will take the most promising alloys with me to the USA and test them in the system I developed. If we find a suitable alloy, we will make supports from it, and if not we will return to the laboratory table for a round of improvements.
The development of alloys is a field where trial and error abound, but the experts can predict desirable properties and reduce the scope for error. This is what the researchers in Israel excel at, and that's why I came here.
on the maneroin
Professor Jeremy Goldman He is an arterial engineer in the biomedical department of the School of Engineering at Michigan Technological University. He completed his BS in Chemical Engineering at Cornell University and his PhD in Biomedical Engineering at Northwestern University.
Professor Goldman was in Israel as part of the Fulbright program for the exchange of lecturers and students (www.fulbright.org.il) to promote the scientific ties between Israel and the USA. Israel's participation in this program is managed by the US-Israel Education Foundation.
