Novel Dissipative Total Disc Replacement for Restoration of Natural Motion for Treatment of Degenerative Disc Disease

Project Summary Degenerative disc disease is a condition of loss of integrity of the intervertebral disc, and is thought to occur in nearly every person over 60 years old. In many cases, low back pain is associated with the characteristic collapse of disc height as nerves become constricted and biomechanics of the spine change. When the disease progresses to cause significant pain, patients and doctors may choose surgical intervention – most commonly spinal fusion where a plastic or metal spacer (i.e. cage) is implanted between the affected vertebrae to restore proper disc height. Bone can then grow between the vertebrae in order to permanently immobilize that section of the spine. There are a myriad of challenges associated with the spinal fusion, including altered biomechanics, subsidence and migration of the fusion cage. To overcome these challenges, surgeons have been turning to a new type of implant: a total disc replacement (TDR). Instead of a rigid cage, a device which retains some range of motion in the disc space is used, however, current solutions fail to fully replicate natural motion and have proven to have significant challenge addressing DDD in the lumbar spine. The proposed solution will restore the functionality of native disc by incorporating the unique dissipative properties of liquid crystal elastomers (LCEs) in the core of the device while porous 3D printed titanium endplates interface the inferior and superior vertebrae to facilitate boney ingrowth. We hypothesize that the cooperative functionality of an osteoconductive 3D printed titanium lattice and dissipative LCE in a single-component TDR can restore native functionality of the intervertebral disc. Liquid crystal elastomers are a unique class of materials which, similar to natural cartilage, combine long range molecular order with network elasticity and can restore biomechanics while providing excellent shock absorption. These materials have been investigated for decades, yet only recently has a suitable synthetic technique been discovered to enable bulk manufacturing and commercialization. This technique involves a thiol/acrylate click reaction, which has previously been applied in other biomaterials such as dental adhesives. However, the adhesive properties of LCEs to 3D printed titanium has not been well studied. As such, the first aim of this study is to investigate the adhesive properties of LCEs to porous 3D printed titanium, with the goal to meet FDA recommendations for adhesive strength. The second aim of this study is to create a prototype device with clinical collaborators and test to ASTM 2346, Standard Test Methods for Static and Dynamic Characterization of Spinal Artificial Discs. The proposed device improves on current TDR technology by using advanced materials and manufacturing to restore permanent, natural motion to the spine. The team will consist of Ross Volpe (PI), who brings experience in biomedical device fabrication and characterization using both LCEs and 3D printed titanium; Nathan Evans, who has led the development and commercialization of a variety of 3D printed titanium implants at Restor3d Inc.; Amir Torbati, Principal Scientist at Impressio with almost a decade of experience optimizing LCEs for biomedical devices; and Dr. Vikas Patel MD and Dr. Philip Horne MD who are experienced and accomplished spine surgeons with expertise in treating DDD.PROJECT NARRATIVE This project investigates the uniquely dissipative liquid crystal elastomer synthesized around porous titanium for use in a total disc replacement device in order to restore natural motion to patients with degenerative disc disease, a condition which effects almost every American over 60 years old. The application of a soft damper into which bone can grow may have applicability in other areas of the body. Here we evaluate the adhesion of the liquid crystal elastomer to titanium as well as the performance of a prototype device in dynamic conditions.