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Biomaterials

Biomaterials - Poster Session C

Poster C10 - Long-Term Mechanical Study of an Injectable Hydrogel Treatment for Degenerative Disc Disease

Friday, October 25, 2024
10:00 AM - 11:00 AM EST
Location: Exhibit Hall E, F & G

Introduction:  Lower back pain is commonly caused by the degeneration of intervertebral discs. Treatments vary from ineffective therapies to highly invasive surgical procedures, which require long-term recoveries and limit post-operative mobility. An injectable gel treatment represents an attractive alternative to these invasive surgical techniques, as they are a minimally invasive implantation method with quick outpatient recovery. HYDRAFIL, a thermo-setting injectable hydrogel formulated by ReGelTec, has been tested for its mechanical properties and biocompatibility, and clinically in vivo. Although short-term mechanical characterization of such gels is common in literature, the safety and efficacy of such products depend on the continued performance of these gels over the patient's intended lifetime. Progress in the regulatory approval process requires further support for the gel’s feasibility as a treatment. Rheological studies allow for mechanical property analysis tailored to the viscoelasticity of a hydrogel. Although the mechanical properties of HYDRAFIL have been analyzed under compressive and rheological forces in short-term conditions, studies have not yet shown the longevity of these properties representative of spinal disc implant conditions.

Materials and

Methods:  Using a long-term mechanical assessment, HYDRAFIL samples were tested on a rheometer at 1% strain and a 50.2N axial force for over 1 million dynamic cycles, representing over a decade of human spinal disc activity. To replicate an in vivo environment, samples were tested while submerged in a saline solution at 37°C that was osmotically balanced to conditions of the intervertebral disc. Load-soak controls were also tested under equivalent axial loading conditions and time periods while omitting the dynamic shear loading. After testing, samples were visually assessed for their integrity, and analyzed for their complex modulus, change in gap height, mass, and volume before and after testing. A two-way ANOVA was performed on modulus, gap height, and volume across the treatment and control samples, with Šídák post hoc tests used for multiple comparison analysis.

Results, Conclusions, and Discussions: All samples survived the duration of a long-term test equivalent to over 10 years of use with no visible deformation. The effects of long-term loading on the mechanical performance of the hydrogel, equivalent to over a decade of human spinal motions, were insignificant compared to the axially loaded controls (p=0.0976). Cyclic shear caused no notable alteration in the gel’s mechanics. These results demonstrate that despite long-term dynamic loading, the hydrogel maintained stiffness viable for intervertebral implantation. Across all samples, axial loading did have an impact on the complex shear modulus of the gel, increasing their average moduli by 18.2% over the duration of the test compared to baseline values (p < 0.0001). However, these moduli remained within the acceptable range of intervertebral disc tissue. Axial loading further impacted the height of tested samples, with the height of all samples decreasing by an average of 5.6% (p=0.0025), though the difference between dynamically cycled and load-soak controls was negligible (p=0.9876). While HYDRAFIL’s long-term mechanical and rheological properties show support for further regulatory progress, dynamic mechanical analysis (DMA) may be conducted to promote further promise for longevity in human spinal disc implantation.

Acknowledgements (Optional):