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As concerns over the possible effects of metal-on-metal implants continue to percolate and the pressure for fewer revisions intensifies, orthopaedic device manufacturers are taking a longer look at alternative materials. From emerging biomaterials to tried-and-true fabrics, fiber-based structures have the potential to satisfy the functional capabilities that device applications require by delivering more biomimetic performance than ever before. A long and steady evolution of more natural structures made from fiber has now extended to pieces as integral as ligaments and tendons.
Biomedical textile structures better mimic the natural makeup of tissue, and thus offer more lifelike movement and overall performance than metals, alloys, ceramics and other traditional materials. Among biomaterials specifically, biomedical textiles are unique due to their ability to be at once lightweight, porous, conformable and strong. And because these attributes enable better mobility and flexibility, they also significantly increase the possibility of an improved—and quicker—patient healing process.
Absorbability Enables Real Tissue Growth
For several years, the orthopaedic industry has been steadily increasing its use of Ultra High Molecular Weight Polyethylene (UHMWPE) due to its high strength and ability to meet durability requirements after implantation. What OEMs need now, however, are longer-term absorbable options that can provide the same level of strength for support while offering dual regrowth capabilities for natural cells. Enabling absorbability without sacrificing strength is a best-case scenario for many applications, but has only recently been explored as a viable alternative to the traditionally strong but permanent implants in many parts of the body.
Many orthopaedic devices aid in support and reconstruction at the same time, so absorbable fibers must be able to induce the regrowth of natural tissue as they perform repair functions. The lifelike properties of textile structures allow for post-operative mobility while enabling cellular regeneration, but only under precise mechanical specifications and a carefully engineered degradation profile. For absorbable structures, implantation as repair allows the textile to act in place of the damaged tissue even as it encourages cell growth. As new cells multiply, the textile steadily degrades and is replaced by completely natural tissue, but its load-bearing capabilities are critical to both early mobility post-implant and natural healing before this tissue growth is complete.
Until now, the most common understanding of absorbable textiles was an acknowledgement of their value in tissue engineering applications in areas outside orthopaedic construction where strength is often less important.
Textile structures intended to bear a load while still functioning dynamically now include braided textiles and tapered weaves, both two- and three-dimensional. Composed of long-term absorbable fibers such as PGA, PLLA, PDO or other biomaterials, they have unique properties according to their processing.
What does this Mean for Orthopaedics?
Orthopaedic applications often require initial strength, meaning that biomedical textiles specially designed for such devices will usually employ a fiber with a longer absorption profile. In these cases, the textile itself lasts a longer time in the body and can provide strength to the affected area or application by replicating damaged tissue. These kinds of applications, such as artificial tendons or ligaments, generally rely on woven structures. For tendon repair, for example, a woven absorbable fabric can be inserted to act as a synthetic tendon and imitate the strength and flexibility of the damaged tissue, while at the same time acting as a platform that will allow the tendon to heal dynamically. As it provides the performance of real tissue with limited stretch and control of tempered movement, it also assists the body’s natural healing process by inducing the re-growth of new tendon tissue that will eventually take its place when it completely disintegrates. The result is a surgical repair site that has healed and is free of any residual textile materials.
The total cost of tendon and ligament injury has been estimated at $30 billion per year,1 and this number is expected to increase as the population ages. Synthetic replacements currently available are still limited, however, and building a functional shape that mirrors natural geometries has been a challenge. Shaping bio-absorbable fibers to resemble the human anatomy of tendons via tapering and other sophisticated processing techniques is proving to be a solution to this problem, and allows for precise dimensions and loadbearing performance characteristics to be built right into the design. The result is a new level of implant performance that not only delivers repair, but also helps generate regrowth in the same device.
Engineered to be Exact
Manufacturing of textiles must be a sophisticated and highly controlled process, because most absorbable fibers rely on hydrolysis to initiate the degradation of their crystalline structure. In order to ensure that the finished biomedical structure retains the most initial strength possible to meet device performance requirements, all processing must limit them fabric’s exposure to ambient humidity levels. In other words, manufacturing processes must be tightly sequenced, efficiently executed and quickly completed within a specific process plan. OEMs seeking to take advantage of regenerative options for orthopaedic repair need to ensure that they have a fully trained and experienced partner in place for fiber processing and textile development.
Summary
Slowly and steadily, biomedical textiles are garnering increasing attention from OEMs across all therapeutic sectors, especially orthopaedics. As the range of biomaterials proven for implant performance widens, developers are taking advantage of new ways to build implants that function like never before by inducing regrowth of native cells to help rebuild damaged tissue from the inside out. For applications like artificial tendons and ligaments, the possibilities are only beginning to emerge, and OEMs can work to leverage absorbable options now for next-generation devices.
REFERNCES
1 Jimin Chen, Jiake Zu, Allan Wang, Minghao Zheng. “Scaffolds for tendon and ligament repair: review of the efficacy of commercial products.” Expert Review of Medical Devices 6(1), 61-73 (2009).
Todd Blair, Director of Sales & Marketing at Biomedical Structures (BMS), has 17 years of experience in business development, commercial, technical and program management, 11 of which have been in life sciences. At BMS, he has led new business development across all technology platforms for surgical and implantable fabrics. He may be reached at tblair@bmsri.com.
Biomedical Structures
www.bmsri.com
