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Fabricating Innovation With Advanced Material Options

Thu, 01/11/2007 - 7:19am
Custom fabrics are becoming available to medical device manufacturers for applications where they traditionally were not an option. New capabilities and technologies provide designers with choices that offer unique advantages. This article explores the impact of this emerging materials revolution.
By Jeffrey Koslosky


One of the most exciting areas in medicine today is the use of implantable fabrics in medical devices that form the cornerstone for the latest minimally invasive procedures. The array of design choices now available to medical device manufacturers is broader than ever, and thanks to the role of versatile medical fabrics, these options continue to expand.

Some fabrics can incorporate more than one type of material. This braided, tubular polyester and wire fabric provides an excellent example.
Technology enables the production of unique geometries, such as this tapered, woven polyester fabric.
Textile products have been used historically in a variety of medical device applications. Design engineers have long seen the benefits of leveraging flexible materials to facilitate repair or elicit a certain tissue response from the human body. Braided sutures, knitted cuffs on heart valves, and woven vascular prostheses are some of the traditional ways that fabrics have been used in medical devices.

Today, implantable fabrics are being designed and used in ways not previously imagined. These advanced materials have a unique ability to undergo shape transformation—that is, to be fitted, expanded, or actuated once placed inside a structure. This is a huge advantage in medical treatments where surgeons have a limited space in which to operate within the body. Thanks to today’s complex processing techniques, fabrics can be engineered for a specific purpose such as filtering emboli from the blood stream, to provide a scaffold for cellular in-growth or, conversely, as a barrier to prevent tissue from growing into or through the fabric material. Modern textile engineering is melding with innovative device design to offer unprecedented options in patient treatments.
Collaboration is Key
Since the manufacture of implantable fabric structures is a specialized area, requiring a fusion of textile manufacturing experience and medical science expertise, contract manufacturers of fabrics and their clients in the device market are achieving ever-increasing levels of collaboration. These fabrics are rarely “off the shelf” materials that are fit to a specific end use application. More often, engineers from different disciplines are required to understand the limits and possibilities of both device and textile technologies in order to successfully develop a novel device.

It is essential to begin this collaboration early in the design process where there is more latitude to incorporate the most desired properties of the device. Typically, the first step is an in-depth process of discovery and analysis regarding the desired purpose, functionality, and performance characteristics of the medical device in question. Once this initial process is complete, a decision can be made regarding which “forming technology” to employ for the fabric. This dialogue between engineers results in a decision tree that leads to a choice between woven, knitted, non-woven, or braided fabric geometry.

Each of these particular structures has its own physical and mechanical performance benefits that can be leveraged in the final device. There are literally dozens of variables specific to each structure that can be modified to drive the performance closer to the needs of the design engineer.

Fabrics can be made dense with very small pores to facilitate fluid movement through a tube or to separate dissimilar tissue planes inside the body. Alternatively, a fabric can be made highly porous, with a lattice structure of interconnected filaments that work in unison to provide structural reinforcement to weakened or ruptured tissue. Perhaps the most exciting and innovative use of textiles inside the body are those designs that facilitate delivery in a condensed state, yet when actuated by a physician, undergo a shape transformation to an expanded state.
Minimally Invasive Technologies
Textile structures have long been utilized for their inherent ability to be flexible, accommodate repeated loading, and recover after being compressed for extended periods of time—all factors that have long made textiles ideal for everyday apparel. Imagine, then, how those same properties apply to the delivery of a fabric inside a very small incision.

Braiding polyester on a 144-carrier braider takes place only after a very meticulous setup process to ensure high quality fabric is produced.
 
View of braider from opposite angle as above.
 
The nature of textile structures makes them excellent candidates for devices designed to be delivered with less trauma to a patient. Fabrics can be designed to have the ability to be compressed into a small catheter or cannula and then deployed by a surgeon during a procedure. The structure can even be imparted with a shape memory so that once deployed inside a space, it returns to its predetermined state and performs its function.

This property of fabrics has been leveraged before by many cardiovascular devices. However, there is now a strong push to utilize this technique in orthopedic devices to minimize the amount of surgical trauma a patient experiences during a procedure. When combined with the minimally invasive trends in orthopedic device design, fabric technologies are helping to shape the next generation of spinal and orthopedic devices.Fabrics are beginning to be used to augment or replace large metallic implants traditionally used in fracture, joint, or spinal repairs. A flexible structure can be delivered inside a patient through a small incision and deployed into the area of the repair. The fabric can be actuated to regain its intended size or filled with a fluid until the desired shape is achieved.

Fabrics may be integrated with other materials to make a rigid composite structure inside the body, providing the necessary mechanical strength to facilitate a permanent repair. These textile structures can be formed from a variety of materials well known to the medical device industry, making the transition from rigid, machined device components to flexible fabrics a more viable option.
Unprecedented Choice
Device engineering teams now have an incredible level of choice in the selection of fabric materials, forming technologies, and performance characteristics—interrelated factors that all contribute to the capabilities of the newest generation of medical devices.

Joining more traditional fabric materials, such as polyester and polypropylenes, are a wide selection of fabric structures—made from more exotic materials—coming out of the development facilities of some of the leading medical textile companies. One of the most obvious trends in this area is the expanding use of bioabsorbable polymers, such as polyglycolides and polylactides to name a few. Though not new, these novel polymers are gaining wider usage in applications where a non-permanent repair is desired. Fabrics constructed from absorbable and bio-active polymers, for example, are ideal for tissue engineering and orthobiologics applications requiring surface area for tissue growth or support while the body repairs itself.

The inherent purity, chemical inertness, and enhanced mechanical properties of advanced materials such as polyarylretherketones and high-performance polyethylenes are attracting more attention lately among the top innovators in medical textiles. As design engineers in device manufacturing firms become more familiar with the options now available to them, formerly exotic materials like these will gain additional ground.

Innovations are certainly not limited to thermoplastics, however. One very exciting development is the ability to produce high performing, flexible, and soft fabric structures out of metals like stainless steel, Nitinol, platinum, and titanium. Such fabrics often exhibit superior mechanical properties for certain applications, when compared with polymeric-based fabrics, while retaining shape transformation properties due to newly developed textile forming techniques. The ability of device manufacturers to leverage known materials provides not only a benefit to modeling the mechanical and biological performance of a device under development, but can offer a smoother regulatory approval path due to the history of a material’s use as an implant.

The key driver here is the interaction of the device designers working with the textile engineers to think outside the box, applying creative thinking in materials and implant science to fabric forming techniques with the goal of pushing forward innovations in device design and development.
Adding Value Behind the Scenes
Manufacturers of specialized implantable fabrics have worked hard over the years to tailor their capabilities, certifications, and other value-added features and processes to the requirements of the medical device industry.


The process for weaving endovascular grafts takes place on a very traditional-looking loom.
 
While the textile roots of the medical fabric industry are visible in some of the manufacturing and processing techniques used, other aspects of the field address the regulatory requirements of the medical industry; ISO 13485:2003 certification is one clear example. The same is true for process validation and risk analysis—two key services now provided by the most forward-thinking manufacturers of implantable medical fabrics.

This same level of commitment to medical device manufacturing is evident in how implantable fabric producers manage and improve their supply chains. Today, they work with approved suppliers and controlled raw materials—all with the goal of ensuring the level of quality required within the medical industry. The use of clean rooms and controlled environment manufacturing facilities is now commonplace, a further assurance to device manufacturers that medical fabric manufacturing has and will continue to evolve to meet the industry’s needs.
Conclusion
Today’s design engineers are fortunate. Never before have they had such a broad range of options and choices in the development of medical fabrics for their devices. In materials selection, forming techniques, and manufacturing processes, there is an almost limitless potential today to engineer effective solutions for a world of medical treatments, both existing and yet to come.

As textile engineers and their counterparts in the top medical device firms continue to collaborate on the development and deployment of more effective devices, the explosive growth in new therapies based on such devices will no doubt continue for many years to come.
ONLINE
For additional information on the technologies and products discussed in this article, visit Secant Medical LLC at www.secantmedical.com.

Jeffrey Koslosky is the director of research and development at Secant Medical LLC. He is responsible for designing and developing implantable medical fabrics. Koslosky can be reached at 215-257-8680 or jeff.koslosky@secantmedical.com.
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