Sound-Activated Gels to Treat Back Pain
Veerle Brans – veerle.brans@eng.ox.ac.uk
Instagram: @itsdranddr
University of Oxford – Botnar Research Centre, Old Rd, Oxford, Oxfordshire, OX3 7LD, United Kingdom
Complete author list:
[Veerle A. Brans*], Anna P. Constantinou*, Matthew J. Kibble, Valeria Nele, Daniel Reumann, Luca Bau, Sebastien J. P. Callens, James P. K. Armstrong, Nicolas Newell, Constantin Coussios, Molly M. Stevens, Michael D. Gray
* These authors contributed equally to this work
Popular version of 2pBAa5 – Quantitative cavitation monitoring for automated ultrasound-controlled hydrogel formation in spinal disc repair
Presented at the 189th ASA Meeting
Read the abstract at https://eppro02.ativ.me//web/index.php?page=Session&project=ASAASJ25&id=3982886
–The research described in this Acoustics Lay Language Paper may not have yet been peer reviewed–
Back pain affects over 600 million people worldwide and is the leading cause of disability. Most back pain is linked to the breakdown of the intervertebral disc, which is the soft, elastic cushion between the bones of the spine that absorbs shocks and keeps us moving comfortably (Figure 1.a). When these discs wear down with age or injury, bones rub together, causing pain.
Figure 1: a) The main parts of a spinal disc: the tough outer ring (annulus fibrosus), the soft, jellylike centre (nucleus pulposus), and the thin cartilage endplates that separate each disc from the bones above and below. b) How our injectable material works: a liquid is injected into the damaged disc and, when exposed to focused ultrasound, it gently warms and solidifies into a soft gel that restores the disc’s function. Adapted from Brans et al. (2025). Advanced Healthcare Materials. [accepted].
Figure 1: a) The main parts of a spinal disc: the tough outer ring (annulus fibrosus), the soft, jellylike centre (nucleus pulposus), and the thin cartilage endplates that separate each disc from the bones above and below. b) How our injectable material works: a liquid is injected into the damaged disc and, when exposed to focused ultrasound, it gently warms and solidifies into a soft gel that restores the disc’s function. Adapted from Brans et al. (2025). Advanced Healthcare Materials. [accepted].Current treatments are limited: physiotherapy manages symptoms but rarely fixes the problem, while surgery is invasive, costly, and not always successful. Scientists are therefore exploring minimally invasive materials that can be injected as liquids and then solidify (‘gel’) inside the body, restoring cushioning to damaged discs. The challenge is how to control where and when this solidification happens.
For this, we propose to use ultrasound – sound waves beyond human hearing – not just for imaging but for therapy. Focused ultrasound can safely heat deep tissues, much like a magnifying glass focuses light to start a fire. Our team at the University of Oxford and Imperial College London developed an injectable liquid implant that solidifies into a gel when warmed to just over 41°C, a temperature reached locally and non-invasively using ultrasound (Figure 1.b). The material consists of three components: 1) a polysaccharide (sugar) solution, 2) glass spheres to accelerate heating of the material, and 3) lipid vesicles, tiny fluid-filled spheres that release calcium when heated. This released calcium links the sugar molecules into a network, turning the liquid into a gel (Figure 2.b).
To test this, we designed treatment algorithms that precisely control heating while also ‘listening’ to the behaviour of tiny bubbles inside the liquid (Figure 2.a). These bubbles form and move in response to the changing pressure of the ultrasound waves, a process known as cavitation. You can imagine it like opening a bottle of sparkling water: bubbles suddenly appear and grow as the pressure drops, and then collapse.
Figure 2: Testing ultrasound-triggered gel formation. (a) Custom setup for heating and ‘listening’ to the material with focused sound waves. (b) Heating curve and photo of the soft gel formed after ultrasound exposure. (c) Testing the approach in cow spinal segments held in a custom rig. (d) Treated discs regained some biomechanical function, with the gel well integrated into the damaged centre after testing. Adapted from Brans et al. (2025). Advanced Healthcare Materials. [accepted].
Figure 2: Testing ultrasound-triggered gel formation. (a) Custom setup for heating and ‘listening’ to the material with focused sound waves. (b) Heating curve and photo of the soft gel formed after ultrasound exposure. (c) Testing the approach in cow spinal segments held in a custom rig. (d) Treated discs regained some biomechanical function, with the gel well integrated into the damaged centre after testing. Adapted from Brans et al. (2025). Advanced Healthcare Materials. [accepted].In our material, this bubble activity generates sound that changes as the liquid turns into a gel: starting off loud then fading as the material stiffens and the bubbles can no longer move freely (compared to a liquid control, see audiofiles). By tracking these sound changes, we can monitor gelation and thus the treatment’s success in real time.
Audiofiles: ‘Control‘ and ‘Gel‘
In our most recent experiments using cow spines (which are anatomically similar to human), we successfully injected the liquid material into degenerated disc tissue and used focused ultrasound to trigger gelation at the correct location (Figure 2.c). Mechanical testing showed that the treatment partially restored the disc’s natural cushioning ability (Figure 2.d), and the material stayed in place without leaking and blended well with the surrounding tissue.
These early results show real promise for using sound-activated gels to repair worn spinal discs, with ongoing improvements in the material and ultrasound technique aiming to make the treatment even more effective in the future, helping millions stand tall again.
Want to find out more? Check out this TED-style talk (https://www.youtube.com/watch?v=_phNGuTyWCQ) by Dr Veerle Brans.