Multidimensional narrow fabrics offer new ways to develop structures in medical and biomedical applications.
A narrow fabric is loosely defined as being any non-elastic woven textile having a width of 12 inches or less and a woven selvage on each side. Narrow fabrics found use early on as hat bands, in corsets and lingerie, and have found more recent use as pack webbing, rifle slings, in parachutes, belt loops, collars and leashes. The more technical applications for narrow fabrics include composite applications for aircraft frames and in medical applications.
Narrow fabrics used in medical devices include stents, endovascular and vascular prosthetic devices, orthopedic applications, artificial limbs, bandages and splints, blood and bone marrow filtration, tissue culture scrim, as dental prostheses, ligature tapes and tendons, spinal implants, suture material, heart valves, structures for hip replacement and for correcting anatomical deformities. More applications for technical narrow fabrics are found almost daily.
3-D structures offer high-fiber volume that translates into a fabric having high strength, able to provide great support versus its weight. They provide an opportunity to develop near-net shapes that translate into anatomically correct replacements and/or structures. 3-D structures also offer high surface area that functions to provide extensive protein binding.
3-D medical devices
An aortic abdominal aneurysm (AAA) is a catastrophic and life-threatening condition where the walls of an artery weaken and can burst. A woven AAA device can be threaded into position from the femoral artery to reduce the aneurysm, providing support to the affected artery. Over time, this prosthesis becomes a part of the repaired vessel. Similar applications can be treated with straight tubular grafts that function to keep the vessel open, supported and functional.
Medtronic (CoreValve), Edwards Life Sciences (Sapien) and Direct Flow Medical (Salus) have recently introduced devices that provide for the replacement of heart valves due to damage or severe aortic stenosis. Here, the damaged heart valve is replaced by a fabric and metal direct-flow, medical-fabric valve supported by a polymer frame structure and threaded into place via a procedure called transcatheter aortic valve replacement (TAVR). This procedure is much less invasive when compared with open heart surgery to repair or replace a diseased or damaged heart valve.
Still, this method is susceptible to throwing off material separated from the diseased vessel due to surgery. This is where a woven tubular narrow fabric device tapered at both ends, and threaded into place via the transcatheter method outside of the replacement valve, can be useful to gather this displaced material, preventing surgical debris from entering the circulating blood flow, possibly lodging and blocking a narrow vessel elsewhere.
When valve replacement is completed, this device is compressed and withdrawn along with the catheter used to deliver the replacement valve. Monofilament (single filament) and scrim fabrics (lightweight open weave) can be woven flat or into tubular devices to filter and separate blood or bone marrow replacement media. These devices also may be woven tapered to meet the application, or designed as near net shapes for anatomically correct, conforming devices.
Shuttle and jacquard shuttle looms are modified and used to construct 3-D fabrics. Weave patterns are controlled by either a manually punched pattern card installed in a dobby head, or automated jacquard head on either a shuttle or needle (shuttleless) loom.
A new and welcomed addition to weaving technology is the quad-axial loom allowing for the insertion of yarns in four directions. Typical weaving occurs in the 0 (length/warp) and 90 (width/weft) directions. The radical and inventive quad-axial loom allows Bally Ribbon Mills to weave in the 0 and – 45 bias or diagonal directions, all in a single plane.
The benefit is that, rather than having to weave materials in layers and then join these layers top to bottom with “Z” fibers, creating a thicker, layered structure in several plys that can fall apart, materials woven quad axially in one plane make for a thinner, stronger fabric better able to address the application.
Typically, medical devices are quite small, having a thinner profile (better able to be compressed to fit into a catheter) allowing the device to be delivered less invasively. Quad-axial woven materials should move the dynamic to where small materials can be produced with very high strength.
Three-dimensional narrow fabrics offer the user high strength and a substantial reduction in weight. They also provide higher surface volume for either protein binding or drug delivery. Constructing these 3-D fabrics with absorbable fibers will broaden their applications and reduce the risk of a permanent implant.
Medical devices require long product development cycles to complete the approval process. Quad-axial, or weaving in four axes, is now possible, offering the device industry new ways to develop structures that better life.
Louis C. Franconi is director of new business development for Bally Ribbon Mills, Bally, Pa.