Design Considerations for Biomedical Textiles: Fiber vs. Yarn



When terms like “yarn”, “fiber”, and “filament” are used, you might, at first, think that these terms are synonymous. In this blog, we’re going to disentangle the definitions, comb through the types, and dispel the looming cloud of uncertainty, so that you may weave the terms into your sentences with expertise.

When it comes to textiles, there is some additional nuance in the terminology, of which you might not be aware. Fibers, are threadlike strands of material that are significantly longer than they are wide, with an aspect ratio of 100:1. Fibers come in both synthetic and natural forms, ranging from polyesters to silk to cellulose (cotton). Fibers can also be divided up into filament and staple fibers. Filaments are continuous long lengths of fibers (measured in yards or meters) and staple fibers are short lengths (measured in inches). Filament fibers can come in two different forms – monofilament and multifilament – and are produced by extruding polymer through a spinneret to form either a single-strand or multiple-strand filament, respectively.

Yarns are multi-filament meaning they are comprised of a plurality of individual filaments that form a bundle. Yarns are measured in the common textile vernacular of denier, which can be defined as linear density or (mass (g)/9,000 m). Fibers are singular filaments in nature, comprised of a lone solid filament. The choice between using a monofilament or multifilament depends on the target application. For example, a monofilament will have decreased surface area and will be more rigid, compared to a similarly-sized multifilament. Multifilament-based meshes have superior drapability, and a noticeably softer texture, over monofilament-based meshes. Furthermore, your application may need to alter the filament’s denier (linear density) or tenacity (tensile strength), which we can tailor using our variety of polymers or by varying process parameters.

For example, a test method validation (TMV) might show that using a scale with demarcations every nanometer is really only useful and consistent to measure to the closest millimeter if used with an unaided human eye. For some specifications, this might be perfectly adequate. For others, this measurement method would not suffice. By changing the how from the unaided human eye to a microscope, we can keep what is being measured and the measurement tool the same, while the precision of the measurement dramatically increases. Further assessment with a TMV would allow us to determine whether this method is now compatible with the product and whether the method is dependable across all operators or only possible with the expert who designed the method. This same process holds true with simple measurements such as dimensions, more complex measurements such as moisture content, and even qualitative attributes of the product. Only by properly performing TMVs for each specific product and specification can we ensure that our measurement system and methods are compatible with the device specifications.

If you are looking to use an extruded bioresorbable fiber or textile in your next medical product, contact us at sales@poly-med.com for more information.

James Turner, Ph.D.