William “Bill” Cook started Cook Medical out of a spare bedroom in his Bloomington, IN, apartment in 1963. It was where he and his wife, Gayle, made guide wires, guiding catheters, and other small devices used in diagnostic radiology.

Later that same year, Cook set out on one of his first major sales endeavors at the Radiological Society of North America (RSNA) in Chicago. From his exhibitor booth, he showcased his devices to attending physicians. One of those physicians, Charles Dotter, a radiologist from Portland, OR, proved to be very important. Dotter, affectionately named “Crazy Charlie” by some of his skeptical colleagues, had an idea to use Cook’s diagnostic catheters to treat blocked arteries in the legs using a minimally invasive approach. He termed the technique “angioplasty”.

On January 16, 1964, merely two months after this historic meeting at RSNA, Dotter performed the first percutaneous transluminal angioplasty (PTA) procedure on a blocked artery in the leg of an 82-year-old woman. What ensued was nothing short of a revolution in the field of interventional radiology.

In the late 1960s, Dr. Andreas Gruentzig, a German-born cardiologist, heard about Dotter’s work while attending a lecture in Frankfurt. Gruentzig soon set out to blaze his own trail by designing a balloon on the catheter. In Zurich during 1977, he performed the first percutaneous transluminal coronary angioplasty (PTCA).

Dotter and Gruentzig’s accomplishments would lay the foundation for what is now upon us in the world of minimally invasive medical devices and procedural-based innovation. Today, we see coronary and peripheral stents and stent grafts, inferior vena cava (IVC) filters, septal occluders, artificial heart valves, and many more devices being routinely delivered via percutaneous catheterbased approaches. However, it permeates far beyond interventional radiology, which provides evidence that Dotter and Gruentzig’s influence is far reaching into many other applications.

The world’s first wearable cardiac pacemaker was invented by Medtronic co-founder Earl E. Bakken in the winter of 1957-58. The Medtronic 5800, as it was marketed, was a transistorized battery-powered pacemaker. It liberated patients from burdensome, tethered power cords. In October 2013, St. Jude Medical announced its acquisition of Nanostim and their fully implantable, percutaneously deliverable, leadless pacemaker.

Not too many years ago, if you suffered from chronic sinusitis and were unresponsive to drug therapy, your only treatment option may have been sinus surgery. These procedures involved instrumentation that drilled holes through the jaw, cut through tissue, and removed pieces of bone to allow sinus drainage. It was a painful surgery that can cause excessive bleeding, bruising, and even scarring in some cases. Today, you can walk into almost any otolaryngology (ENT) office and undergo a simple balloon sinuplasty procedure. This essentially involves nothing more than a guide wire and balloon catheter being inserted through the nasal cavity.

Polymer Science Makes the Difference

Medical device technology and procedural-based innovation have come a very long way in a relatively short period of time. The field of medicine will forever be indebted to the pioneers who made it their life’s work to pursue innovative technologies and therapies. But who might be the unsung hero?

Aside from the game-changing clinical pioneers and the medical device companies that provide the necessary tools, what has allowed these advancements to be brought to life? The answer, plainly and simply, is tubing.

Advancements in polymer science and extrusion technology can be directly correlated to the evolution from surgical-based intervention to minimally invasive approaches and associated medical device design. The desire to reduce procedure time, hospitalization, and patient trauma, while improving outcomes has created a dependency on polymer science and extrusion to keep pace with clinical demands. This article will examine some of the milestones in polymer extrusion technology that have afforded such innovation. It will also look forward to newer advancements that will continue to facilitate a culture of constant innovation with novel techniques and devices.

Extruded polymer tubing has been used in cutting-edge medical devices and applications for more than 50 years. However, it wasn’t really until the 1980s when some of the more commonly used polymers began to surface as critical componentry in device technology. Minimally invasive techniques like angioplasty drove the need for tubing with small diameters, thin walls, tight tolerances, lubricity, flexibility, biocompatibility, high tensile strength, and a number of other characteristics. Extrusion of fluoropolymers like polytetrafluoroethylene (PTFE) and fluorinated ethylene propylene, as well as nylon polymers, commonly used in guiding catheters became a very precise science. Continued advancement in extrusion techniques played a vital role in keeping pace with the device innovation curve.

As balloon angioplasty evolved to include stenting in the late ’80s, physicians needed delivery systems with larger inner diameters while maintaining the same outer diameter or profile, effectively reducing wall thickness in some tubing components to as low as .0005". With the advent of the drug-eluting stent revolution, clinicians and medical device engineers were pushing the envelope even further. They developed highly sophisticated delivery systems that challenged polymer science and extrusion technology to keep pace again. Today, innovative extrusion of fluoropolymers and nylons continues to be a crucial component to medical device innovation. However, what’s on the horizon for innovation in polymer science and extrusion could dwarf what has been seen thus far.

The first bare metal stent was approved by the FDA in the early ’90s. The bare metal stent was intended to prevent restenosis (reclosing) of arteries treated with balloon angioplasty by “propping” the artery open following the PTCA procedure. However, early stent thrombosis (clotting) due to inflammatory responses to the metal stent quickly became a concern. The solution for stent thrombosis was to add an anti-inflammatory drug coating to the metal stent to stave off the body’s natural immune response. This was put into practice at the turn of the millennium with the advent of drug-eluting stents. However, once again a challenge presented itself. After the drug coating completely eluted and was no longer present, the issue of thrombosis (late stent thrombosis) arose.

So how could these issues be resolved? What was the ideal scenario? Ideally, following angioplasty, a stent would be placed that would ward off an inflammatory response, hold the artery open long enough for the body’s natural self-healing processes to occur, and then would no longer be needed. But how would a physician remove the stent? The idea of explantation simply wasn’t feasible.

Enter bioabsorbable polymers. These polymers, namely poly(lactic acid) or PLA, and poly(glycolic acid) or PGA, have a longstanding history as safe and effective implantable polymers. They can perform a certain function for a given period of time and essentially disappear. The polymers make a strong argument for their candidacy by having predicate use in orthopedic pins, plates, screws, sutures, and other proven devices. If there were a way to make a fully absorbable stent (or scaffold) that would hold an artery open, elute an anti-inflammatory drug, and then disappear after the artery remodeled (healed), that would potentially be the “Holy Grail”.

As it turns out, this scenario is entirely possible. It starts with extrusion. A number of fully absorbable coronary scaffolds are either being sold or are in development today. These scaffolds start out as tubing—very precisely extruded tubing with finely tuned chemistry and exacting dimensional and mechanical properties. The tubing is then laser cut and, after a few other downstream processes, becomes an implantable scaffold. The very same technology that allowed interventionalists to create complex stent delivery systems is now being used to produce the stent itself.

The bioabsorbable revolution is upon us and it permeates beyond coronary scaffolding. Devices utilizing this technology are being developed and evaluated across the board for virtually every medical application imaginable. Aside from vascular applications, ENT, brachytherapy, gastrointestinal/endoscopy, tissue engineering, targeted drug delivery, and wound care/closure are just a few of the areas that could benefit from bioabsorbable polymer science and extrusion. Essentially any device or implant that only needs to perform a function for a given period of time and then, ideally, go away could be a viable candidate for this technology.

Whether it’s a PTFE thin wall tube used as a liner for a guiding catheter or a bioabsorbable poly-L-lactide tube laser cut into a coronary scaffold, extrusion technology has played an undeniably instrumental role in medical device innovation and the evolution of minimally invasive surgery.

Pioneers will undoubtedly continue to follow the likes of Dotter and Gruentzig, pushing the innovation envelope to improve patient care, procedures, and outcomes. If history is any indicator, tubing will be there to help guide their way.

This article was written by Josh Ridley, Business Development Manager for Biomaterials, Zeus, Inc., Orangeburg, SC. For more information, Click Here.

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