Formulations of Polyvinyl Alcohol Cryogel That Mimic the Biomechanical Properties of Soft Tissues in the Natural Lumbar Intervertebral Disc
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STUDY DESIGN: An original investigation that characterizes polyvinyl alcohol cryogel (PVA-C) in the context of the human lumbar intervertebral disc (IVD). OBJECTIVES: To evaluate the mechanical properties of PVA-C under physiological conditions; to assess PVA-C's suitability as a key component in a tissue-mimicking artificial lumbar intervertebral disc; and to identify suitable formulations that mimic the nucleus pulposus and anulus fibrosus. SUMMARY OF BACKGROUND DATA: Current lumbar intervertebral disc prostheses provide suboptimal symptom relief and do not restore natural load-cushioning. PVA-C is a promising material due to its high water content, excellent biocompatibility, and versatile mechanical properties. METHODS: PVA-C samples were prepared with different PVA concentrations and number of freeze-thaw cycles (FTC). Unconfined compression was conducted to characterize various PVA-C formulations. Compressive stress relaxation and creep were performed to assess the stability of PVA-C under loading. The results were compared to the mechanical properties of human lumbar intervertebral discs obtained from literature. RESULTS: PVA-C compressive elastic modulus increased with increasing PVA concentration and number of FTC's. The 3% 3FTC is the optimal formulation for mimicking the nucleus pulposus in compression. In general, compressive stress relaxation and creep decreased with increasing PVA concentration and number of FTC's. Compressive stress relaxation and creep were lower for PVA-C than human lumbar intervertebral discs, suggesting that PVA-C will likely exhibit stable and predictable mechanical response in vivo. All formulations provided good mimicry of the human IVD in stress relaxation and creep. PVA-C also provided good match to the anulus fibrosus matrix. CONCLUSION: Good unconfined compression, stress relaxation and creep behavior, combined with excellent biocompatibility, makes PVA-C a suitable choice as a major component of a tissue-mimicking artificial IVD. A potential artificial IVD design combining two or more different PVA-C formulations could provide excellent overall mimicry of the human IVD. Results of this investigation provide a solid foundation for future work in this area.
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