Making informed choices between high-density, low-density and 3D braiding offers greater design flexibility for implantable textile components that are fit-for-purpose.
Maddy Moncla, Michelle Lishner and Zachary Robbins, Cortland Biomedical
Biomedical textiles have the potential to enable lower-profile medical devices, less invasive surgical procedures and greater overall flexibility and biocompatibility across a variety of medical applications. But unlocking the full potential that textiles can offer starts at the earliest stages of the product design and development process. The right decisions must be made on how to create an implantable textile component that’s optimally fit-for-purpose.
Braiding raw material (i.e., fiber) is one of the most prevalent methods of creating biomedical textiles structures, but within this category, there are still technology decisions that must be made. Medical device OEMs — guided by their textile engineering partner — should assess whether high-density braiding, low-density braiding or 3D braiding is the best option for the product they aim to create.
The braiding process involves yarn prep, twisting and plying. After yarn preparation, it’s possible to make braids by winding bobbins, braiding and rewinding. These bobbins are loaded into the braider and will all contribute to creating a braid. Half of the bobbins will travel clockwise, and the other counterclockwise, interlacing in and out between each other.
An effective tensioning system can handle anything from fine, delicate materials to heavier yarns and wires. Using individual tension controls, axial braid ends can be highly customized (for example, loose or tight). It’s possible to apply different tensions to different braid ends to create a textured surface, which is well-suited for promoting tissue ingrowth.
Creating custom geometries with high-density braiding
High-density braids are ideal in scenarios that necessitate design flexibility and custom geometries. These braids can either be bulky or very thin and hollow. Overlaps of the material create a hollow, tubular braid. This braid can either be formed over a mandrel, or independent of any structural aid, depending on the application. Each machine can offer continuous or discrete units. By customizing a variety of bobbins for high-density braiders, the individual braid can be of different materials, colors and sizes. The formation of the braid can be over almost any item or shape, and one can design the braid wall to be thick or thin.
For more complex solutions, a two-part braid structure may be required. Working with what is essentially a braider inside of a braider, the outer and inner ring can run together at the same time, forming one unique braid on top of the other (a core and jacket). Having an outer ring/jacket can allow the incorporation of qualities that may be totally opposite from the core braid. This is a useful capability for applications where the product needs to hit a certain strength target with distinctive outer surface qualities. Programmable picks per inch (PPI), referring to the braid density, can be adjusted to influence the mechanical properties and surface texture of any part of the braid.
High-density braiding might be the best choice if an OEM is looking for a delivery component or sleeve for other device components with a determined diameter. These braids can combine high coverage with flexibility. To achieve a fixed diameter, they can be braided over a rigid object with an established diameter and then heat set. High-density braids are also a good choice for an open, continuous structure, and can even be manufactured exceptionally “open” to promote cell growth.
Is low-density braiding right for your surgical application?
Low-density braiding is a good choice for tethers, cords or pull wires, which are frequently used in delivery systems for minimally invasive surgeries, transcatheter procedures and robotics. If a more advanced braid is needed, textile engineers could incorporate suture tipping and/or fabrication into the process.
Low-density braiding is also ideal for creating custom sutures and soft tissue assemblies, as these braids can fit around small radii and tight bends, whereas metal and wire might fatigue. Low-density braids don’t transfer torque, so one end can be twisted while the other remains stable.
When to choose 3D braiding
3D braiding is a good choice if an OEM is looking for a braid that can be tied around a member and then anchored to a point such as an artificial ligament.
Like normal braiding, 3D and branch braiding using a variation braider involves bobbins on a carrier going around a designated path, and strands coming together in a helical pattern. The ability of the carrier path to change allows this machine to create custom braid structures that can bifurcate, trifurcate, continuing up to octfurcate.
When designing one of these custom-built structures, the first step is to use software to model the actual braid path which will output the product that the OEM is looking for. This allows for an unlimited number of design options and possibilities. 3D braiding allows for considerable customization and furcation to suit the OEM’s needs and make a structure that is completely unique to them.
Maddy Moncla is a sales engineer at Cortland Biomedical with a Bachelor of Science in textile sciences and engineering from North Carolina State University. She is a subject matter expert in medical textile product engineering and development.
Michelle Lishner is a lead development engineer at Cortland Biomedical with a Bachelor of Science in textile technology focused on medical textiles from North Carolina State University. She has industry and academic experience in tissue engineering and material-based medical devices with awards in leadership, project management, innovation and product design.
Zachary Robbins is a textile process engineer at Cortland Biomedical with a Bachelor of Science in materials engineering from Georgia Institute of Technology. His technical experience in research and engineering combine to form a deep understanding of fibers and textiles to affect both manufacturing and innovative material performance.
The opinions expressed in this post are the author’s only and do not necessarily reflect those of MedicalDesignandOutsourcing.com or its employees.