07.28.10
The Fabric of Healing
Biomedical textile structures are impacting the way orthopedic implants advance joint repair.
Secant Medical, LLC
Orthobiologics has become an intensely competitive growth market, and, in response, a greater number of medical device manufacturers are augmenting their traditional portfolios with a suite of biologically based products designed to enhance the repair of musculoskeletal defects.
From bone grafting and fusion to cartilage repair and ligament and tendon tears, myriad biomaterials have been developed to treat a broad range of orthopedic conditions. An evolving trend within the patient population points to a continuing prevalence of the orthopedic conditions that these and the advanced orthopedic products of the future will treat—a younger patient population engaged in a more active lifestyle and demanding access to the technologies that can allow them to minimize the effects of treatment.
One such technology that is poised to take a leading role in the orthobiologic market is the biomedical textile structure. Textiles that are implanted inside the human body are not uncommon and, in fact, have been used for decades in applications including synthetic vascular grafting and hernia repair.What is novel today is the engineering of implantable fabric structures that possess a certain set of mechanical and biologic properties and are designed to serve as load-sharing scaffolds, minimally invasive containment vessels, and as resorbables to facilitate osteoconductive healing.
There is a significant amount of design flexibility that can be engineered into textile structures that are woven, knitted or braided. Textiles are inherently compressible and can be made very dense, which allows them to be used in minimally invasive delivery applications for the localized containment of an injectable fluid. Fabrics can contain sections of varying porosity that are designed to elicit tissue in-growth in certain areas while serving as a tissue barrier in others. Perhaps most notable is the range of biomaterials from which these structures can be formed. Polymers, metals and even biologic materials such as collagen filaments can be formed into an ordered structure using traditional textile forming methods. It is this diverse range of capabilities and biologic properties that device designers are leveraging in orthobiologic applications currently under development.
Orthopedic Trends and Textiles
In recent years, developments in orthopedic treatment modalities have evolved to meet changing demographics in the patient population. First, there is a large effort centered on earlier patient intervention with devices targeting a younger patient population that maintains a more active lifestyle than the traditional orthopedic patient. Today’s patients fall into an“actively aging” group that increasingly is aware of their treatment choices and more apt to consult with their surgeons about the various options that meet their respective needs. These shifting demographics have resulted in minimally invasive devices designed to return a patient quickly to health with minimal recovery time than those of larger-scale surgical procedures. A second area of focus—motion preservation—is most notable in the spinal segment. Even traditional spinal devices are being reengineered to minimize the loss of patients’ natural movement as evidenced by an increase of device options in this field.
Orthopedic textiles deliver a variety of unique material characteristics and performance properties.
Because biomedical fabric structures are compressible for easy delivery via a cannula and undergo shape transformation at the delivery site (to give just a few examples), an orthopedic application niche is being established that few other technologies can offer. Woven and braided tubes and tether-based structures have become excellent candidates for both their inherent ability to be delivered via minimally invasive techniques and their ability to change aspect ratio and shape once they are positioned by the surgeon. Procedures such as the internal stabilization of a long bone fracture, annular repair and the dynamic stabilization of the spine are just a few examples in which biomedical textiles are used to meet the current wave of innovation and design in the orthopedic market.1
Another major focus of orthopedic device design follows the explosive growth of the orthobiologic segment. Technologies such as scaffolds, bone morphogenic proteins (BMP), demineralized bone matrices (DBM), stem cells, and gene therapy are among the cutting edge in treatment options for leveraging tissue engineering to address musculoskeletal repairs.2These implantable biomaterials are applicable in the treatment of joint and cartilage degeneration, tendon and ligament repair and bone grafting, to name a few. These technologies offer surgeons additional options beyond the traditional rigid products of plates and screws to more biologically based repairs.
Of course, there are limits to these new technologies. Delivery of these materials to the specific site of implantation and engineering a specific biologic response from the body are among the challenges. Containment and localization of BMP, DBM and other biologics have been noted as issues and have given rise to opportunities to develop materials that work in concert with these orthobiologic materials as a “composite” of sorts.By their very nature, fibrous textile materials are an excellent design option for bridging this gap.
Osteoconductive Composites
Implantable biomaterial textile structures can be formed via four major technologies: weaving, knitting, braiding and non-wovens. Each of these fabric-forming pro-cesses produces geometries with unique properties that a design engineer can leverage in order to facilitate a certain set of physical and mechanical properties when used in an application within the body. However, there is another layer of complexity that is innate to engineered fabrics. All textile materials are formed from an interweaving or “controlled entanglement” of fibers that work in unison to achieve a composite of properties of the individual filaments comprising the structure.
This composite effect can be further enhanced by the mixing and matching of various fiber-based biomaterials. It is possible to mix polymeric materials typically used inside the body such as polyethylene, PEEK and polyester with metallic elements such as stainless steel, titanium and shape-memory nitinol. By mixing of the ratios of the various biomaterial fibers, design engineers can enhance the ability of the fabric structure to meet the specific biologic needs of the medical device. When coupled with variations in density, shape, layers, thickness and orientation in the fabric geometry, the design opportunities virtually are limitless.
Unique properties can be attained by leveraging this “composite nature” of the textile materials in combination with the advanced biologic materials that are available to today’s device designers. Most discussions surrounding tissue engineering and biologic materials generally refer to the scaffold as the preferred vehicle to promote tissue healing. Scaffolds define a general set of criteria that refers to a structure that has porosity and a certain amount of surface area that is intended to facilitate tissue growth into and through the structure. When used in orthopedic applications where bony soft tissue is the intended area of growth, these scaffolds are known as osteoconductive materials. Osteoconductive materials generally do not have the innate ability to induce new tissue formation; rather, they serve as a conduit for facilitating tissue response through their porous nature.
Many materials have been leveraged as scaffolds including foams, sponges and porous metals; however, biomedical textiles present an unmatched opportunity for cellular differentiation. By leveraging the ability to engineer a multi-level, multi-material and varied density structure, it is possible to design an osteoconductive scaffold that responds in a controlled and predictable manner.
This scaffold is useful in applications where it is desirable to provide the body a platform on which to rebuild tissue while offering some mechanical integrity during the process. The result is a composite of synthetic biomaterials, formed by a woven, knitted or braided fabric, and the newly formed tissue that has grown into the scaffold’s porous structure.
Another example of orthopedic textiles used as composites is the combination of synthetic fabric with xenogenic or allogenic materials. As with bony in-growth applications, tissue grafts applied over a fabric substrate is an excellent design option to establish a hybrid repair in soft tissue applications. These devices often have a soft-tissue replacement that is sewn on or otherwise fastened to or contained by the textile structure. Typically, the fabric scaffold is designed to bear load immediately after the implantation of the device while providing a porous region to facilitate growth in and through both the xenograft or allograft tissue and the textile over time. This hybrid method is viewed by many to strike a balance between reducing the amount of synthetic materials left behind in the body while facilitating an immediate surgical repair of the damaged tendon, ligament or meniscus.
Fabric Technologies
Another area of overlap for textile materials and orthobiologics is the combination of synthetic biomaterials with osteoinductive materials such as bone morphogenic proteins and demineralized bone matrices. Such materials have the innate ability to form new tissue using the body’s cellular response to biochemical signals.3 These technologies have been used in spinal fusion, long bone fracture and bone void applications. Fabric technologies offer an additional benefit with their level of control and containment not available with current carrier materials.
Novel textile structures today are being designed to work with BMP and DBM technologies as a delivery vehicle for getting these materials to the site of treatment and, most importantly, keeping them there to facilitate the biologic healing. Fabric structures that are formed into sealed tubes and vessels are excellent candidates for the containment of DBMs for a number of reasons. They have a structure that is porous and acts in some ways as a membrane, allowing biologic materials to pass from outside to inside and vice versa. However, the pores can be engineered to a specific size allowing for the selective passage of materials across the membrane. This enables the vessel to contain some materials in a localized treatment site while not adversely affecting the osteoinductive nature of the DBM.
Another novel use of fabric technology is as an alternative to porous sponges and other materials used as delivery vehicles or carriers for BMP technology. Because most existing carriers are resorbable synthetics or biologic in nature, they tend to be homogeneous and without differentiation. Engineered fabric structures can be formed from the same resorbable synthetics (polyglycolides and poly-L-lactic acid are among the most popular). The woven, knitted and braided textile forming processes gives these fabric structures a unique design feature that allows the resorption of the polymers within the structures to coincide with the healing rate of the biologic material. The result is control of the resorption kinetics of the fabric with a fully biologic
repair as the end point.
It is clear that the use of biologic textile materials that can generate tissue is on the rise and they will continue to play a central role in the development of future medical device technologies. Novel biomaterial textiles offer a unique level of design variability to become a valuable asset to design and development engineers providing them choice and flexibility in their device designs.
Emerging Technologies
With the future of orthobiologics focused on fully biologic repairs and regenerative techniques using advanced biomaterials, what can textile structures offer that alternative technologies cannot? Technologies such as mesenchymal stem cells, collagen materials and gene therapy are at the forefront of device innovation and fabric-based biomaterials have some benefits unmatched by other materials.
Mesenchymal stem cells have an enormous amount of potential due to the unique ability to differentiate into a multitude of different tissue types including cartilage, tendon, bone and even skin. The use of an ordered yet differentiated carrier such as a multi-layer, woven fabric structure comprised of multiple materials at multiple densities in a 3-D geometry holds promise as an enabling technology that allows the stem cells to generate the correct amount and type of tissue for the applicable repair. Textile structures can be used in a similar manner for regional gene therapy where scaffolds are the preferred delivery vehicle.
Perhaps the most interesting future application of biomedical textile technology is the use of collagen materials as the fibers and filaments used to form the weave, knit or braid geometry. This technology goes beyond scaffold and hybrid materials in that the very nature of the fabric is biologic. Relying on similar forming techniques for polymeric and metallic fibers, collagen fibers that are generated in sufficient lengths can be interwoven to result in similar composite material properties that were discussed earlier. The benefits of having a fully biologic textile that uses collagen materials as opposed to waiting for collagen infiltration over a fixed healing time are many with the focus on patient recovery time and the effectiveness of the repair at the forefront.
Challenges and Opportunity
Biomedical textiles designed for use inside the body continue to build on a broad application history where few alternative technologies deliver results. And those textile-engineering teams that have helped to forge that history are working closely with device designers in the orthopedic industry to repeat that success with a new generation of biologic biomaterials.
There is no shortage of challenges for device designers and manufacturers today with pending healthcare reform and the push toward comparative effectiveness research. One certainty is that those who are at the leading edge of innovation will continue to spur on both technological and market growth while confronting these challenges. Biomedical textiles are an exciting option with a multitude of variables that can enable device designers to advance orthobiologic innovation.
Jeffrey M. Koslosky is director of technology and product development for Secant Medical LLC in Perkasie, Pa., a developer and manufacturer of custom-engineered biomedical textile structures for medical devices.
References:
1. S. O’Reilly. “The Hot Trend in Spine: Motion Preservation Mania” Medtech Insight, Vol 9. No. 6, (2007).
2. Windhover Information, Inc.; Tissue Engineering and Cell Transplantation: Technologies, Opportunities, and Evolving Markets in the U.S., 2007.
3. Steven M. Kurtz and Avram Allan Edidin. Spine Technology Handbook, Elsevier Academic Press, pp 241-243.
Biomedical textile structures are impacting the way orthopedic implants advance joint repair.
Secant Medical, LLC
A multi-layered osteoconductive scaffold structure for engineered tissue response. Photos courtesy of Secant Medical. |
From bone grafting and fusion to cartilage repair and ligament and tendon tears, myriad biomaterials have been developed to treat a broad range of orthopedic conditions. An evolving trend within the patient population points to a continuing prevalence of the orthopedic conditions that these and the advanced orthopedic products of the future will treat—a younger patient population engaged in a more active lifestyle and demanding access to the technologies that can allow them to minimize the effects of treatment.
One such technology that is poised to take a leading role in the orthobiologic market is the biomedical textile structure. Textiles that are implanted inside the human body are not uncommon and, in fact, have been used for decades in applications including synthetic vascular grafting and hernia repair.What is novel today is the engineering of implantable fabric structures that possess a certain set of mechanical and biologic properties and are designed to serve as load-sharing scaffolds, minimally invasive containment vessels, and as resorbables to facilitate osteoconductive healing.
There is a significant amount of design flexibility that can be engineered into textile structures that are woven, knitted or braided. Textiles are inherently compressible and can be made very dense, which allows them to be used in minimally invasive delivery applications for the localized containment of an injectable fluid. Fabrics can contain sections of varying porosity that are designed to elicit tissue in-growth in certain areas while serving as a tissue barrier in others. Perhaps most notable is the range of biomaterials from which these structures can be formed. Polymers, metals and even biologic materials such as collagen filaments can be formed into an ordered structure using traditional textile forming methods. It is this diverse range of capabilities and biologic properties that device designers are leveraging in orthobiologic applications currently under development.
Orthopedic Trends and Textiles
Woven fabric substrate to be used with xenograft for joint repair. |
Orthopedic textiles deliver a variety of unique material characteristics and performance properties.
Because biomedical fabric structures are compressible for easy delivery via a cannula and undergo shape transformation at the delivery site (to give just a few examples), an orthopedic application niche is being established that few other technologies can offer. Woven and braided tubes and tether-based structures have become excellent candidates for both their inherent ability to be delivered via minimally invasive techniques and their ability to change aspect ratio and shape once they are positioned by the surgeon. Procedures such as the internal stabilization of a long bone fracture, annular repair and the dynamic stabilization of the spine are just a few examples in which biomedical textiles are used to meet the current wave of innovation and design in the orthopedic market.1
Another major focus of orthopedic device design follows the explosive growth of the orthobiologic segment. Technologies such as scaffolds, bone morphogenic proteins (BMP), demineralized bone matrices (DBM), stem cells, and gene therapy are among the cutting edge in treatment options for leveraging tissue engineering to address musculoskeletal repairs.2These implantable biomaterials are applicable in the treatment of joint and cartilage degeneration, tendon and ligament repair and bone grafting, to name a few. These technologies offer surgeons additional options beyond the traditional rigid products of plates and screws to more biologically based repairs.
Of course, there are limits to these new technologies. Delivery of these materials to the specific site of implantation and engineering a specific biologic response from the body are among the challenges. Containment and localization of BMP, DBM and other biologics have been noted as issues and have given rise to opportunities to develop materials that work in concert with these orthobiologic materials as a “composite” of sorts.By their very nature, fibrous textile materials are an excellent design option for bridging this gap.
Osteoconductive Composites
Implantable biomaterial textile structures can be formed via four major technologies: weaving, knitting, braiding and non-wovens. Each of these fabric-forming pro-cesses produces geometries with unique properties that a design engineer can leverage in order to facilitate a certain set of physical and mechanical properties when used in an application within the body. However, there is another layer of complexity that is innate to engineered fabrics. All textile materials are formed from an interweaving or “controlled entanglement” of fibers that work in unison to achieve a composite of properties of the individual filaments comprising the structure.
This composite effect can be further enhanced by the mixing and matching of various fiber-based biomaterials. It is possible to mix polymeric materials typically used inside the body such as polyethylene, PEEK and polyester with metallic elements such as stainless steel, titanium and shape-memory nitinol. By mixing of the ratios of the various biomaterial fibers, design engineers can enhance the ability of the fabric structure to meet the specific biologic needs of the medical device. When coupled with variations in density, shape, layers, thickness and orientation in the fabric geometry, the design opportunities virtually are limitless.
Unique properties can be attained by leveraging this “composite nature” of the textile materials in combination with the advanced biologic materials that are available to today’s device designers. Most discussions surrounding tissue engineering and biologic materials generally refer to the scaffold as the preferred vehicle to promote tissue healing. Scaffolds define a general set of criteria that refers to a structure that has porosity and a certain amount of surface area that is intended to facilitate tissue growth into and through the structure. When used in orthopedic applications where bony soft tissue is the intended area of growth, these scaffolds are known as osteoconductive materials. Osteoconductive materials generally do not have the innate ability to induce new tissue formation; rather, they serve as a conduit for facilitating tissue response through their porous nature.
Containment vessel for site-specific delivery of orthobiologic materials. |
This scaffold is useful in applications where it is desirable to provide the body a platform on which to rebuild tissue while offering some mechanical integrity during the process. The result is a composite of synthetic biomaterials, formed by a woven, knitted or braided fabric, and the newly formed tissue that has grown into the scaffold’s porous structure.
Another example of orthopedic textiles used as composites is the combination of synthetic fabric with xenogenic or allogenic materials. As with bony in-growth applications, tissue grafts applied over a fabric substrate is an excellent design option to establish a hybrid repair in soft tissue applications. These devices often have a soft-tissue replacement that is sewn on or otherwise fastened to or contained by the textile structure. Typically, the fabric scaffold is designed to bear load immediately after the implantation of the device while providing a porous region to facilitate growth in and through both the xenograft or allograft tissue and the textile over time. This hybrid method is viewed by many to strike a balance between reducing the amount of synthetic materials left behind in the body while facilitating an immediate surgical repair of the damaged tendon, ligament or meniscus.
Fabric Technologies
Another area of overlap for textile materials and orthobiologics is the combination of synthetic biomaterials with osteoinductive materials such as bone morphogenic proteins and demineralized bone matrices. Such materials have the innate ability to form new tissue using the body’s cellular response to biochemical signals.3 These technologies have been used in spinal fusion, long bone fracture and bone void applications. Fabric technologies offer an additional benefit with their level of control and containment not available with current carrier materials.
Novel textile structures today are being designed to work with BMP and DBM technologies as a delivery vehicle for getting these materials to the site of treatment and, most importantly, keeping them there to facilitate the biologic healing. Fabric structures that are formed into sealed tubes and vessels are excellent candidates for the containment of DBMs for a number of reasons. They have a structure that is porous and acts in some ways as a membrane, allowing biologic materials to pass from outside to inside and vice versa. However, the pores can be engineered to a specific size allowing for the selective passage of materials across the membrane. This enables the vessel to contain some materials in a localized treatment site while not adversely affecting the osteoinductive nature of the DBM.
Another novel use of fabric technology is as an alternative to porous sponges and other materials used as delivery vehicles or carriers for BMP technology. Because most existing carriers are resorbable synthetics or biologic in nature, they tend to be homogeneous and without differentiation. Engineered fabric structures can be formed from the same resorbable synthetics (polyglycolides and poly-L-lactic acid are among the most popular). The woven, knitted and braided textile forming processes gives these fabric structures a unique design feature that allows the resorption of the polymers within the structures to coincide with the healing rate of the biologic material. The result is control of the resorption kinetics of the fabric with a fully biologic
repair as the end point.
It is clear that the use of biologic textile materials that can generate tissue is on the rise and they will continue to play a central role in the development of future medical device technologies. Novel biomaterial textiles offer a unique level of design variability to become a valuable asset to design and development engineers providing them choice and flexibility in their device designs.
Emerging Technologies
With the future of orthobiologics focused on fully biologic repairs and regenerative techniques using advanced biomaterials, what can textile structures offer that alternative technologies cannot? Technologies such as mesenchymal stem cells, collagen materials and gene therapy are at the forefront of device innovation and fabric-based biomaterials have some benefits unmatched by other materials.
Mesenchymal stem cells have an enormous amount of potential due to the unique ability to differentiate into a multitude of different tissue types including cartilage, tendon, bone and even skin. The use of an ordered yet differentiated carrier such as a multi-layer, woven fabric structure comprised of multiple materials at multiple densities in a 3-D geometry holds promise as an enabling technology that allows the stem cells to generate the correct amount and type of tissue for the applicable repair. Textile structures can be used in a similar manner for regional gene therapy where scaffolds are the preferred delivery vehicle.
Perhaps the most interesting future application of biomedical textile technology is the use of collagen materials as the fibers and filaments used to form the weave, knit or braid geometry. This technology goes beyond scaffold and hybrid materials in that the very nature of the fabric is biologic. Relying on similar forming techniques for polymeric and metallic fibers, collagen fibers that are generated in sufficient lengths can be interwoven to result in similar composite material properties that were discussed earlier. The benefits of having a fully biologic textile that uses collagen materials as opposed to waiting for collagen infiltration over a fixed healing time are many with the focus on patient recovery time and the effectiveness of the repair at the forefront.
Challenges and Opportunity
Biomaterial textiles offer a unique level of design variability. |
There is no shortage of challenges for device designers and manufacturers today with pending healthcare reform and the push toward comparative effectiveness research. One certainty is that those who are at the leading edge of innovation will continue to spur on both technological and market growth while confronting these challenges. Biomedical textiles are an exciting option with a multitude of variables that can enable device designers to advance orthobiologic innovation.
Jeffrey M. Koslosky is director of technology and product development for Secant Medical LLC in Perkasie, Pa., a developer and manufacturer of custom-engineered biomedical textile structures for medical devices.
References:
1. S. O’Reilly. “The Hot Trend in Spine: Motion Preservation Mania” Medtech Insight, Vol 9. No. 6, (2007).
2. Windhover Information, Inc.; Tissue Engineering and Cell Transplantation: Technologies, Opportunities, and Evolving Markets in the U.S., 2007.
3. Steven M. Kurtz and Avram Allan Edidin. Spine Technology Handbook, Elsevier Academic Press, pp 241-243.