Biomedical textiles include textiles with designed geometries in the form of knitted, woven, braided or nonwoven structures that are often used as components of implantable medical devices such as scaffolds, stent grafts, orthopedic tethers, etc.
The intertwining of three or more yarns to make a fabric. The medical fabric is formed by interfacing the yarns diagonally to the production axis of the material. The major variables in braided products are the numbers of elements (yarns, wires, combinations of both), the braid angle, and the number of crossings per inch (density) An infinite variability of process parameters creates braids with widely differing physical and mechanical properties. Among these are porosity, flexibility and radial strength.
The mass in grams of 9,000 meters of a yarn. Denier attempts to describe the linear density of fibrous polymeric materials. It is a direct method and larger numbers translate to larger diameter yarns. A typical size range for yarns used to fabricate biomedical textiles can be from 10 denier for the ultra thin, minimally invasive structures, to 500 denier for ultra strong, tension bearing orthopedic structures.
Elongation is defined similarly to other engineering materials and is typically expressed as a percent in terms of extension or strain. One important characteristic of textiles is that overall elongation of the structure can be affected by two components, the raw material and the geometry. It is typical to utilize specific raw material properties or to manipulate the geometry (or do both) to achieve the final device properties.
Refers to the number of yarn/ fiber/ wire elements oriented in the warp (machine) direction on a weaving, knitting or braiding machine. These elements are typically expressed as a number per unit area (typically inches). Quantifying the "ends per inch" is critical in defining a fabric structure.
The density of the ends/wales and picks/courses in a given unit area. This measure speaks to the overall density of the fabric structure and most of the physical and mechanical properties of the fabric are result of the fabric count.
See also "Picks." Filling yarn is the weaving term used to describe the yarn system that is placed perpendicular to the warp ends in a fabric structure. It is typical to utilize either the same raw material as the warp ends, a different size or a different material altogether giving a large range of design flexibility with a woven fabric structure.
Used to relieve the stresses in the polymeric yarn or metallic wire as the product was being made, ensuring consistent and predictable mechanical properties. Many biomedical textiles can be augmented by heat-setting in a post-process to deliver a three dimensional shape. This process is used in many devices where a minimal delivery profile is required.
Implantable biomaterials are a family of materials that are biocompatible with and suitable for placement inside of the human body. These materials can elicit a wide variety of responses once implanted. These responses depend on the type, geometry, surface characteristics, amount of the biomaterial, and where the biomaterial is implanted inside the body. Textile structures can use a wide array of implantable biomaterials that are drawn into fine filaments.
Also known as implantable biomaterials.
Any structure formed by traditional textile means and comprised of known materials suitable for long-term implant in the body. In addition, an implantable textile must undergo post-processing that renders it clean enough to meet biocompatibility standards. Contrary to popular belief, there are no implantable raw materials such as Polyester. Rather, the raw material needs to undergo a post-process cleaning step that enables the structure to meet ISO 10993 testing requirements.
Knitted biomedical textiles are constructed by interlocking a series of loops of one or more yarns. Two major classes of medical textile knitting are warp knitting and weft knitting that speaks to the orientation of the yarns that are forming the stitches. There are numerous variants available from a design standpoint when knitting fabrics. Most typically, knitted biomedical textiles are used for soft tissue support and applications where conformability and controlled elongation and pore size are essential.
Medical Device Components
Structures designed and developed by skilled application specialists in conjunction with medical device engineers to create more efficient and effective medical devices to promote faster recovery times, decreased revision and failure rates.
Comprised of a family of forming methods that do not fit into the general way a textile structure is formed. Popular non-woven structures in biomedical textiles include the following: • Carded/ needle-punched fabrics (felt) • Spunbonded • Meltblown Non-woven fabrics are not formed from yarns but from fibers or filaments only. These structures often have excellent surface area and permeability characteristics making them good candidates for tissue engineering and wound care. However, the mechanical properties can be lower than alternative methods of fabric formation.
Biomedical textile structures that are implanted inside the human body designed to support bone, muscle, and tendon repair, replacement or regrowth. These structures are critical components in high-strength, load-supporting applications such as anchoring devices and orthopedic tethers in a variety of areas such as general orthopedics, spine, trauma, and extremities.
Refers to the number of yarn/ fiber/ wire elements oriented in the weft (machine) direction on a weaving, knitting or braiding machine. These elements are typically expressed as a number per unit area (typically inches). Quantifying the "picks per inch" is critical in defining a fabric structure.
A variety of value-added processing that can include: heat-setting (annealing), coating, forming, packaging, sterilization, slitting/cutting, and other processes.
Used to describe resistance to compressive forces in the radial direction. This is a critical requirement in many biomedical textile applications where tubular fabrics are required to maintain a lumen for containment or fluid transfer. Radial strength can be increased through the addition of yarn/wire elements in the radial or helical direction of a structure.
The process used to clean a textile structure and remove any process aids or manufacturing lubricant present on the raw material yarns or wires. Scouring is typically conducted in either USP purified water or solvents such as Isopropanol. Scouring for biomedical textiles uses no physical contact, rather the solvent is moved through the fabric structure using mild agitation or ultrasonics under tightly controlled temperature and flow conditions.
Refers to the strength of a material in the long/axial direction of a biomedical textile. It can be used to quantify the yarn, fabric or device and is often a metric on the product specification.
Used to bundle multifilament yarns more tightly together during the forming process. Twisting has a two-fold benefit in that it can reduce the cross-sectional area of the yarn while minimizing the amount of broken filaments in the yarn bundle.
Biomedical textile structures that are implanted inside the human body designed to come in direct contact with blood and interact with the vascular system in specific ways. These include minimally invasive vascular grafts, heart valves, and embolic protection systems.
Indicates the long or continuous direction of the raw materials in a textile structure. Warp is used interchangeably with the machine direction in the weaving and knitting processes.
Type of knitting in which the yarns are oriented in the warp or lengthwise direction on the knitting machine. The yarns are prepared as warps on beams with one or more yarns for each needle. Examples of this type of knitting are tricot, raschel and double needle bed knitting. There are many different types of patterns that can be achieved in warp knitting making it an excellent design choice for soft-tissue applications.
Woven medical textiles are achieved through the process of interlacing two yarns or wires so that they cross each other at right angles to one another. The warp yarns, or ends, run lengthwise on the machine, and the filling threads (weft/picks), run transverse or perpendicular to the warp ends. Many biomedical textile structures are made on looms that utilize a shuttle to transport the filling yarn across the fabric. This has an added advantage in that the resultant fabric has a woven edge. This enables seamless tubes to be formed that can be tapered along the length to produce near net-shape geometries. Woven fabrics generally have the most design flexibility of all the biomedical textile forming techniques.
Indicates the transverse or non-continuous direction of the raw materials in a textile structure. Weft is used interchangeably with the cross-machine direction in the weaving and knitting processes.
Type of knitting in which yarns are oriented in the weft (course) or crosswise direction on the knitting machine. One example is circular weft knitting used to create a tubular fabric, typically small in diameter, with a repeatable and controlled pore size. These fabric structures are used in many cardiovascular applications due to their surface area and in-growth characteristics.
Yarn / Fabric Testing
A series of tests designed to determine the physical and/or mechanical properties of a textile. Yarn and fabric testing is typically conducted to determine the product's ability to meet the material specification.