PFI-TT: Total Intervertebral Disc Replacement Device using Novel Energy Absorbing Materials.

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The broader impact/commercial potential of this PFI project is to develop a prototype device aimed at improving the current standard of care for total disc replacement (TDR) procedures. Each year approximately $500,000 Americans will undergo surgery involving intervertebral disc replacement, resulting in a device market well over $1 billion. These procedures, which are most often interbody fusions or TDRs, are associated with a high rate of complications. Approximately one-third of patients will ultimately require a follow-up procedure. Although the underlying causes are unclear, the biomedical devices most often used are significantly stiffer than the original intervertebral disc, and no cushioning or force dissipation occurs across the disc space; this is likely a significant factor for complications such as subsidence and adjacent level disease. This study will be the first cyclic loading investigation into the use of novel liquid crystalline elastomers (LCEs) for potential use in spinal devices. If successful, the proposed research will develop LCEs for stable long-term mechanical dissipative properties with a hierarchical structure to mimic the natural organization of the intervertebral disc. Other potential applications involving the use this ultra-dissipative material are for protective equipment used in sports or military, such as helmets to better prevent concussions. The proposed project will investigate main-chain LCEs, which have vastly superior energy dissipation properties relative to traditional rubber-like materials such as silicone or hydrogels. Liquid crystal mesogen reorientation under mechanical stress provides a temperature and frequency insensitive mechanism for dissipating energy, more robust than typical viscoelasticity. This proposed research will be the first to investigate cyclic mechanical properties of main-chain LCEs. The proposed research will result in an LCE proof-of-concept device that exhibits mechanical properties seen in biological soft tissues (i.e., anisotropy, dampening, and low modulus). The LCE will be synthesized a spatially tailored device to match the mechanical properties and structure of a natural disc. The unique liquid-crystal structure within these materials makes cyclic behavior difficult to estimate a priori, and therefore direct characterization as a function of material structure, strain rate, and displacement magnitude must be investigated. High-cycle loading of LCEs will be investigated. Fundamental knowledge gained through this analysis will show the feasibility of LCEs for TDR and demonstrate broad applicability of LCEs for dampening applications. This project builds directly from fundamental research discovery supported by the NSF.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.