This effort is a collaboration between the Engineering Research Center for Revolutionizing Metallic Biomaterials (RMB) at the North Carolina A&T State University, its partner institutions (the University of Pittsburgh, the University of Cincinnati, Hannover Medical School, industrial, innovator, and state and local government partners) and NC-based ERC small business innovation partner OrthoKinetic Technologies LLC and Southeast TechInventures, Inc., a technology accelerator also located in NC. The ERC was started in 2008. This proposal, specifically addresses the degradable Mg system developed at the ERC-RMB as a possible material for intervertebral spinal fusion application.
Intellectual Merit
The purpose of this effort is to transform current medical and surgical treatments by creating "smart" implants for craniofacial, dental, orthopedic, cardiovascular, thoracic and neural interventions. The ERC will develop biodegradable systems that combine novel bioengineered materials based on magnesium with miniature sensor devices that can control the integrity of implants. The ERC will develop biodegradable systems that combine novel bioengineered materials based on magnesium with miniature sensor devices that can control the integrity of implants. Biodegradable systems offer significant therapeutic advantages over implants used today. Such systems will be able to grow and adapt to the human body and eventually dissolve when no longer needed. The first phase of this research is to synthesize magnesium alloys that are biomechanically stable for possible use as a spinal fusion cage. The effort explores the use of alloying elements to increase corrosion resistance, increase toughness, and promote osteointegration. The second phase of this study will provide a comprehensive mechanical assessment of a spinal fusion cage for the lumbar spine using magnesium and its alloys as the bioresorbable materials. The third phase will be corrosion assessment or resorption process analysis.
Broader Impact
Spinal surgery is often a final alternative to spinal stabilization and relief of pain. Bone graft fusion with accompanying spinal instrumentation systems is a conventional surgical technique used to stabilize the spine. The eventual goal of this bone graft and spinal instrumentation construct is to create a balanced environment where the spinal instrumentation is used to initially function as the load bearing element that immobilizes the fusion segment during the early unstable stages of bone grafting and healing. The U.S. market for spinal implants is estimated to exceed $8 billion by 2016, while the minimally invasive surgical (MIS) spinal implant market is estimated to reach over $3 billion. The education and outreach plans are achieved through the ongoing ERC programs through broad-based outreach programs targeted at elementary and secondary school students, community college students and their teachers, counselors, parents and administrators. These include informal education, parent information sessions. This effort addresses the need for a novel biocompatible biomaterial capable of resorbing and allowing creep substitution by bone during resorption, while maintaining mechanical structural integrity, as an ideal alternative to spinal fusion.
Spinal surgery is often the final option for stabilization of the spine and pain relief in treating degenerative spine disease. Bone graft fusion, with accompanying spinal instrumentation, is the conventional surgical route for stabilizing the spine. This conventional approach is highly invasive, and there is a critical need for less invasive techniques necessitating innovative research. The spinal implant sector is the highest growth orthopedics area, with 13% annual growth. More than 3 million spine procedures were performed in 2008. The U.S. market for spinal implants is estimated to exceed $8 billion by 2016, while the minimally-invasive surgical (MIS) spinal implant market is estimated to reach over $3 billion. The eventual goal of a minimally-invasive bone graft and spinal instrumentation construct is to create a balanced environment where the spinal instrumentation initially functions as the load bearing element that immobilizes the fusion segment during the early stages of bone grafting and healing when the segment is still unstable. However, numerous challenges exist with these innovative spinal implants. Traditional metals and polymers lack the ability to allow for their gradual replacement (creep substitution) by regenerating bone, as these materials are either not capable of resorption, or are not optimized to the surrounding biological environment, as is the case with some polymeric components (polylactic acid, for example). Therefore, there is a need for a novel biocompatible biomaterial capable of being resorbed and allowing creep substitution by bone during resorption, while maintaining mechanical structural integrity. Such a material would be an ideal alternative for use in spinal fusion. The holy grail is a biodegradable, biocompatible, load-bearing material with greater mechanical stability for spine fusion. The most important requirement is that the implant should have controlled biodegradability, which means that it should gradually and safely resorb and be replaced with bone. This SBIR proposal directly deals with some of the requirements that need to be satisfied by innovative materials in order to address such a complex issue. Activities included: Development of new magnesium alloys for intervertebral spinal fusion Mechanical property evaluation of these newly-developed alloys Corrosion characterization to assess their biodegradability behavior Deeper understanding through assessment of their biological and biomechanical behavior The research explored the use of alloying elements to increase corrosion resistance, wear resistance, and toughness in Mg-based biodegradable materials systems. Mechanical assessment was performed by OrthoKinetic Technologies, LLC, the small business partner in this project, to determine the structural integrity of magnesium intervertebral fusion cages for aggressive loading in multiple planes and to evaluate their mechanical integrity with respect to cortical and cancellous bone in the spine. During the project, a series of novel alloy formulations were mechanically evaluated to determine the ideal alloys that will provide ample support to the spinal segment where it bears loads during early healing and shares the load during as the body regenerates bone. Corrosion assessment, or resorption process analysis, was studied at NCAT using an electrochemical station and 3D nano-computed tomography. Stress corrosion cracking (SCC) testing and evaluation of degradable alloys through the use of bioreactors generated critical insights into the dynamics of their mechanical behavior in a human body. Detailed studies on the materials by testing under compression fatigue loading revealed that extrusion processing of our new as-cast rare-earth Mg alloys can provide the mechanical integrity ideal for spinal fusion and fixation. The knowledge gained through this project is helping the investigators to actively participate towards the development of testing standards for evaluation of the biocompatibility and biodegradation of metallic implant materials with national and global standards organizations (ASTM and ISO).
