Bob Donohue, Natvar, a Tekni-Plex company, explains how the new generation of microextrusion medical tubing opens doors to new procedures.
Medical Tubing
Because of new technological developments, the definition of what constitutes microextrusion medical tubing has shifted. As a result, both medical device manufacturers and patients stand to greatly benefit.
Typically, extrusions were designed to assist with procedures from ‘the neck to the knee’. Tubing manufacturers could not extrude with tight enough tolerances to access the smallest arteries found in the head or below the knee. That meant certain life-sustaining, neurovascular interventional therapies and surgical procedures were often difficult.
What was once called a microextrusion—typically a .015 inner diameter (ID) x .055 outer diameter (OD)—is now considered a standard extrusion. What used to be outlier dimensions are now considered common. In the past, these micro tubes were produced out of glass or, in the case of fluoropolymers, involved a secondary stretching operation to achieve the desired ID and OD.
However, advances in plastic extrusion technology have changed the game. With minimally-invasive surgery becoming the wave of the future, microextrusion is allowing device manufacturers to provide products that otherwise would be difficult to achieve or expensive. The latest microextrusion tubing can now help OEMs develop complex devices that can provide therapies and treatments not previously possible for hard-to-access extremities.
Unrealistic requests become reality
As is typically the case, development of new technology is driven by need. Medical device manufacturers pushed the envelope by asking suppliers to develop tubing with tighter tolerances that were significantly outside the norm.
The need to miniaturise, enable implantable devices and make possible procedures that were previously thought to be impossible, were the drivers. What was initially considered an unrealistic expectation for the plastic extrusion process eventually turned into a reality as technological inroads on the processing side were made.
Today’s new microextrusion definition is an ID size in the 35 microns (or .0014 inch) range, with very thin walls and extremely tight tolerances to meet the needs of newer invasive applications.
Now that extrusion technology (both process and equipment) has caught up with the needs of the medical device industry, the latest microextrusion tubing can now be made in a one-step process from less expensive materials. The latest die designs, pressure transducers and high-end, inline, closed-loop controls, are a few of the many breakthroughs that have contributed to the development of thermoplastic microextrusion tubing.
Consistently achieved tight tolerances are now allowing manufacturers to deliver performance attributes that were previously out of reach.
It is also important to point out that multilayer microextrusions in catheter applications is another main driver behind these developments. Being able to use microextrusion technology in combination with coextrusion technology adds many new options for OEMs. This can allow for a highly lubricious inner surface (for device insertion), along with steerable characteristics, by modifying the outer shell of the catheter. This technology allows for the use of radio opaque indicators to be incorporated into the design without affecting performance.
New possibilities
Natvar has made a considerable investment in a manufacturing facility to produce the latest microextrusion tubing. Available are monolayer, coextruded (up to four layers), multi-lumen tubing or profiles in a variety of thermoplastic (PVC, urethanes, TPEs) materials at CPK values above 2.0. (The CPK value indicates how close a process is running to its specification limits, relative to the natural variability of the process. The higher the index, the less likely it is that any item will be outside the specifications. As a frame of reference, a CPK of 1.33 or better is what medical device companies typically require.)
Natvar’s new microextrusion tubing comes in wall thicknesses ranging from .003 to .005 inches.
Cost profile
The ability to create microextrusion tubing from thermoplastics means that medical device companies can realise desired performance attributes at a fraction of the cost associated with fluoropolymers and glass.
Multi-channel (or multi-lumen microcatheters) can aid in reducing cost by incorporating more than one device in a single structure. As microextrusions are being developed and enhanced, so are the devices that are used in conjunction with these structures. Fibre optics, guide wires, sensors and stents are a few examples that up until now were limited by size. This was due to the lack of extrusion capability needed to make these types of devices possible.
Psychological aspects of patient care
It is also important not to overlook the psychological aspects of patient care. Advances in medical devices and therapies supported by microextruded tubing can go a long way in potentially enhancing the patient’s comfort level and recovery time. Discomfort and recovery can be minimised if procedures are less invasive and more therapeutic.
Precision provides significant performance, production impact
The ability to consistently manufacture microextrusion tubing in tight tolerances impacts both device production, as well as patient satisfaction. Catheters, for example, are typically tip-formed and punched. When there are wide tolerance variances, the consumer experience will not be consistent each time he or she needs to catheterise themselves. One catheter tip may be painful upon insertion, while the next one might not be. Lack of consistency can result in consumer discomfort and stress in not knowing what the next usage experience will bring. When microextrusions are able to hold tight tolerances, then catheters are consistent and so is the consumer experience.
There are other applications, such as those where precise delivery is required, where tight tolerances also can have a positive impact. A good example to look at is a tube used for wound therapy. In this application, medication needs to be precisely administered to the wound area. Traditionally, liquid has been pushed through the tube to see how much volume was coming out. The tube would then be cut to get to the approximate correct volume. This less-than-precise way of delivering medication was the workaround used to compensate for an ID that was not in tight tolerance. Conversely, when the tube consistently delivers tight tolerances throughout its production run, then you are able to eliminate the delivery guesswork. It also benefits the device manufacturer by enabling higher throughput.
Speed-to-market
In order to help OEMs meet their commercialisation objectives, it’s important to partner with a supplier that can assist in getting validations correct on the first try. For many years, medical device manufacturers have had to modify their manufacturing process to accommodate out of spec tubing. This resulted in a less-than-efficient process which frequently had a negative impact on speed-to-market objectives. It’s important both for device functionality and production efficiency to work with tubing that consistently delivers tight tolerances.
Global supply capability
With a significant number of medical device companies marketing their products across the globe, an international supply pipeline can be critical. Not only should OEMs consider the supplier’s capabilities, but they should take a good look at their global manufacturing footprint. Medical device manufacturers want access to exactly the same components and materials regardless of where in the world their manufacturing facility is located.
Potential applications
Potential applications for the latest microextrusion tubing are extensive and include both implantable devices and minimally-invasive procedures. Possibilities include:
Heart leads. Connecting a pacemaker to the heart muscles.
Neurological. Treatments for stroke patients where micro stents need to be inserted into the vascular system to open capillaries to eliminate blockage.
Vascular. Below the knee procedures such as arterial drills to assist in blood flow below the knee that has been compromised by diabetes.
Catheters. Traditionally, heart catheterisation procedures use the femoral artery in the leg to access the body. Microextrusions would enable smaller devices to enter the brachial artery and aid in expanding smaller vessels that have potential blockage. With the capability to get into the smaller veins, as well as the larger ones, more of the heart is accessible.
In vitro fertilization. The new microextrusion technology can assist with a critical step of the in vitro fertilization process that enables the nucleus of the egg to be harvested more precisely.
Infant/paediatric care. The effectiveness of miniature devices, such as microcatheters that are engineered for the youngest among us, can also benefit from microextrusion tubing.
Additional opportunities exist for treatments in the following areas: chemotherapy, auditory, ophthalmic, wound care, spinal therapies and others where smaller diameters and tight tolerances are necessary to achieve product objectives.