Ultrasound‐Triggered Gelation for Restoring Biomechanical Properties of Degenerated Functional Spinal Units

TL;DR

This paper introduces a new method using ultrasound to create a gel implant in degenerated spinal discs, which could help treat lower back pain.

Contribution

The study introduces a novel ultrasound-triggered gelation method for in situ implant formation in degenerated spinal discs.

Findings

Ultrasound-mediated heating triggers liposomal release and hydrogel formation in situ.

Proof-of-concept experiments showed partial restoration of biomechanical function in degenerated bovine discs.

The implant integrated well into disc tissue without herniation.

Abstract

Lower back pain is closely associated with intervertebral disc (IVD) degeneration and is a leading cause of global disability. Existing treatment options are unable to provide suitable long‐term outcomes, and emerging strategies employing injectable biomaterials are hindered by factors including limited native tissue integration and depth‐ or time‐constrained gelation mechanisms. To overcome these issues, the present research evaluates a new concept employing ultrasound to remotely trigger in situ implant formation. The concept centers around an implant precursor biomaterial consisting of an anionic polysaccharide solution containing thermally sensitive liposomes loaded with ionic crosslinkers. Ultrasound‐mediated heating to 4–5 °C above normal body temperature triggers liposomal release of the crosslinking species, thereby initiating hydrogel formation. Optimization studies define the implant precursor material (1.5% wt/v sodium alginate seeded with calcium‐loaded liposomes (10–15 mm calcium chloride) and 6% wt/v glass microspheres) and the ultrasound parameters (0.95 MHz, 1.6 MPa amplitude, 87% duty cycle). Proof‐of‐concept experiments in degenerated ex vivo bovine IVDs indicate partial restoration of biomechanical function, with the implanted biomaterial well‐integrated into the disc tissue and without material herniation. These results offer promise for treating intervertebral disc degeneration, with continued refinement of biomaterials and protocols being essential for achieving robust in‐disc efficacy.

This study introduces an innovative approach to treating intervertebral disc degeneration using ultrasound‐triggered in situ hydrogel formation. Proof‐of‐concept experiments using optimized biomaterial and ultrasound parameters demonstrate partial restoration of biomechanical function and successful integration into degenerated disc tissue, offering a promising avenue for advanced, minimally invasive therapies for lower back pain. Created in BioRender. Kaesbauer, S. (2025) https://BioRender.com/f99g314.

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