A Japanese research team has developed a solid ultrasound gel pad made from tamarind seed gum that matches conventional liquid gel for diagnostic image quality while significantly improving patient comfort. The feasibility study, published in Scientific Reports on 12 January 2026, points to a potential shift in how acoustic coupling media are designed, stored, and used across a wide range of clinical settings.
increased procedural costs. Recently, researchers from Japan have developed a reusable, solid
ultrasound gel pad composed of tamarind seed gum. This gel pad demonstrated improved patient
satisfaction compared to conventional gel and the imaging quality is comparable to conventional
liquid gel. This gel pad can contribute to more accessible, patient-friendly, and sustainable
ultrasound diagnostics in the coming years.
© Professor Hajime Monzen, Kindai University, Japan
Ultrasound gel is, in many ways, the unsung consumable of diagnostic imaging. Without it, the air gap between the transducer probe and the skin surface causes acoustic impedance mismatches that degrade image resolution and confound anatomical interpretation. Yet despite its central importance, conventional commercial liquid gel has remained largely unchanged for decades – cold, messy, prone to drying out, variably applied, and consistently a source of patient dissatisfaction.
Now, researchers from Kindai University and Watanabe Kosei Clinic in Japan have reported the first clinical evaluation of a novel solid gel pad incorporating tamarind seed gum, a natural polysaccharide extracted from the endosperm of the tamarind seed (Tamarindus indica). The results of this early-stage feasibility study suggest that the material can perform comparably to the conventional liquid standard across multiple probe types and anatomical sites – while substantially outscoring it on patient satisfaction.
From a perceived drawback to a clinical asset
The innovation arose from an unexpected observation. “Initially, I encountered a gel made only from water and tamarind,” recounted Professor Hajime Monzen of the Department of Medical Physics at Kindai University, the study’s corresponding author. “The developer explained that the continuous release of moisture was considered a drawback. However, I realised that this property could help prevent drying during ultrasound examinations, reduce the formation of air gaps between the probe and the skin, and thereby maintain stable image quality.”
That property – known as syneresis, the controlled weeping of fluid from a gel matrix – forms the functional core of the new product. As described in the paper, the solid gel pad is composed of tamarind seed gum (0.1–5.0 wt%), polyhydric alcohol (25.0–70.0 wt%), and water (30.0–70.0 wt%), with preservatives included to inhibit microbial growth. Each pad is moulded to a standardised 50×50×5 mm format. The tamarind seed gum itself, a high-molecular-weight polysaccharide (50,000–1,000,000 Da) with a glucose backbone and ß
-1,4 linkages, provides the structural matrix; glycerine and ancillary polyols constitute the primary polyhydric alcohol components.
Physical characterisation: Flexibility, stability, and self-recovery
Dynamic viscoelastic measurements across the range of 10°C to 50°C confirmed that the gel’s storage modulus (G’) consistently exceeded its loss modulus (G”) at all frequencies tested – behaviour indicative of a stable, cohesive gel structure. This thermal stability is clinically relevant: it ensures consistent acoustic transmission properties regardless of
ambient or body temperature variation.
The gel’s compressive elastic modulus was measured at 0.0062 ± 0.0008 MPa at 25% compression, substantially lower than both commercially available comparator gel pads tested in the study. This softer mechanical profile facilitates conformity to irregular skin contours, particularly in areas with surface topology challenges such as the intercostal spaces used for cardiac imaging.
The syneresis rate of approximately 25% fluid release over one hour ensures a self-sustaining film of glycerine-containing fluid at the probe–skin interface. Critically, upon resealing the gel pad after surface desiccation, continued syneresis re-moistened the surface within 24 hours – a self-recovery capability not demonstrated by either of the two comparator commercial solid gel pads evaluated. The investigators also confirmed that accelerated stability testing at room temperature over three months produced no significant changes in rheological properties, syneresis behaviour, or acoustic coupling performance.
Image quality and patient satisfaction: the clinical trial
The feasibility study enrolled four healthy male volunteers, each undergoing paired imaging with the new solid gel and the conventional liquid gel (Aquasonic 100, Parker Laboratories). Three anatomical sites were evaluated using three different probe configurations: the common carotid artery and thyroid gland with a high-frequency linear probe (8–13 MHz); the liver using a convex probe (3–5 MHz); and the parasternal four-chamber cardiac view using a sector probe (1.8–4.2 MHz). Image quality was assessed in real-time by one radiologist and two radiologic technologists using a 5-point Likert scale.
For all four anatomical sites, there were no statistically significant differences in image quality scores between the new solid gel and the conventional liquid gel (all p > 0.05). The carotid artery and thyroid gland achieved ceiling scores (5.0 ± 0) with both gel types; liver scores were 4.8 ± 0.3 versus 4.7 ± 0.5; and the parasternal four-chamber view, arguably the most technically demanding site, scored 3.7 ± 0.3 with the solid gel compared to 3.5 ± 0.3 with the liquid gel.
The patient satisfaction picture was starkly different. Across all four sites, mean satisfaction scores were significantly higher with the solid gel (p = 0.02 for all comparisons). For the carotid artery and thyroid gland, the solid gel achieved a maximal score of 5.0 ± 0 compared with a mean of just 1.9 ± 0.8 for the conventional liquid gel; the parasternal view recorded 4.7 ± 0.5 versus 1.2 ± 0.5. The authors attributed this difference in large part to the gel’s non-adherence to body hair and its ease of removal – a noted practical limitation of conventional liquid gel, particularly in chest imaging.
Longitudinal imaging in one volunteer over 60 minutes showed no deterioration in image quality or evidence of surface drying, suggesting extended usability beyond the 15-minute lifespan of unassisted conventional gel.
A natural polymer with sustainability potential
The authors highlight the broader materials-science significance of tamarind seed gum as the novel functional ingredient. As they note in their Discussion, the new gel’s key innovative component is “tamarind seed gum, a natural polysaccharide extracted from tamarind seeds,” which “provides the unique self-moisturising function” and “may be less expensive and easier to obtain than synthetic alternatives.” The polysaccharide is both biocompatible and biodegradable, and tamarind-derived materials have established applications in pharmaceutical controlled-release formulations.
From a cost perspective, the paper provides a preliminary economic assessment suggesting the solid gel pad can be manufactured and marketed at approximately 1,000 yen (roughly US$7) per single-use 50×50×5 mm pad. Whilst higher than the direct per-use cost of conventional liquid gel – estimated at 200 mL for approximately 300 yen – the authors note that total procedural costs for liquid gel include pre-warming, post-examination cleaning, and variable usage volumes, factors not captured in simple unit-cost comparisons. The gel’s room-temperature storage stability and self-moisturising properties would also eliminate refrigeration requirements that apply to some existing solid gel alternatives.
Limitations and the road ahead
The investigators are candid about the study’s limitations. The sample size of four participants fundamentally constrains statistical power and generalisability, and all subjects were male volunteers within a healthy body mass index range. The study lacked objective quantitative image quality metrics – contrast resolution, signal-to-noise ratio, lateral resolution, and penetration depth – and no phantom-based acoustic impedance characterisation was performed. Inter-rater reliability was not formally assessed, and the absence of blinded image evaluation creates potential for observer bias.
Further limitations include the absence of data on repeat use after disinfection, inapplicability to specialised procedures such as extracorporeal shockwave lithotripsy or high-intensity focused ultrasound, and no assessment in paediatric, obstetric, or other specialist imaging contexts.
Looking ahead, the authors advocate for “further research with a larger sample size” to build on this preliminary evidence, specifically calling for “standardised phantoms and quantitative analysis software” and “formal inter-rater reliability analyses and randomised crossover design with blinded image evaluation.” Prof. Monzen concludes with a broader vision: “From an academic perspective, this study helps clarify how the properties of tamarind seed gum relate to the way ultrasound waves travel. It presents a new approach to designing materials used in ultrasound examinations. In the future, this work may support ultrasound diagnostics that are easier to use, more patient-friendly, and more sustainable.”
Comprehensive shelf-life validation studies are ongoing in accordance with International Council for Harmonisation Q1A(R2) stability testing guidelines, and the research team notes that biocompatibility profiling under ISO 10993 endpoints will be required before any pathway to clinical market adoption.
Reference:
Uehara, T., Monzen, H., Ujifuku, M., et al. (2026). Feasibility study of a newly developed solid gel pad containing tamarind seed gum for diagnostic ultrasonography in human subjects. Scientific Reports, 16, 104. https://doi.org/10.1038/s41598-025-33208-y
