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In a Different Tongue: 3D Printed Tongue Offers New Methods for Studying Oral Treatments

Researchers at the University of Leeds, in collaboration with the University of Edinburgh, have developed the first ever 3D printed biomimetic tongue surface. The material features mechanically relevant and accurate characteristics for novel methods of testing in research dedicated to oral care, food products and therapeutic treatments, among others.

 “The application of bio-tribological principles, the study of friction and lubrication, in the creation of this tongue-like surface is a significant step forward in this field. The ability to produce accurate replicas of tongue surfaces with similar structure and mechanical properties will help streamline research and development for oral care, food products and therapeutic technologies.” said co-author Dr Michael Bryant from the School of Mechanical Engineering at Leeds.

3D model of the biomimetic tongue surface mimicking human oral tribology. Image courtesy of University of Leeds

The synthetic silicone tongue has been designed and made to mimic the topology, elasticity and wettability of the surface of a human tongue. The final digital model was arrived at after taking silicone impressions of fifteen adult tongues, with each human tongue optically 3D scanned to capture structural details, such as average roughness, density, and papillae (the little bumps on the tongue’s surface) dimensions.

Real adult tongue impressions were captured to develop the biomimetic tongue design. Image courtesy of University of Leeds

Interestingly, the researchers noted that the random distribution of papillae on the surface play an important sensory role for the tongue, and this distribution could be different for healthy or diseased individuals. The naturally occurring distribution is very similar to a random distribution, and is highly effective in helping us detect even the tiniest bit of food, as well as identify and manage chewing, swallowing or spitting out anything we may put in our mouth. Lead study author Dr. Efren Andablo-Reyes said: 

“Recreating the surface of an average human tongue comes with unique architectural challenges. Hundreds of small bud-like structures called papilla give the tongue its characteristic rough texture that in combination to the soft nature of the tissue create a complicated landscape from a mechanical perspective. We focused our attention on the anterior dorsal section of the tongue where some of these papillae contain taste receptors, while many of them lack such receptors. Both kinds of papillae play a critical role in providing the right mechanical friction to aid food processing in the mouth with the adequate amount of saliva, providing pleasurable mouthfeel perception and proper lubrication for swallowing. We aimed to replicate these mechanically relevant characteristics of the human tongue in a surface that is easy to use in the lab to replicate oral processing conditions.”

Previously, artificial tongues have been developed to mimic its sensing mechanisms and the five basic tastes using lipid/polymer membranes, stripped epithelium cells, enzymes, hydrogels or electronic receptors. Last year, researchers in Scotland developed an artificial tongue, based on glass and light-sensitive chemically coated metal sensors (gold and aluminium), to detect the composition of whiskeys, juices, poisons and even to monitor the composition of river water. In Canada, researchers at the University of Montreal developed an artificial tongue, using gold nanoparticles, to identify the various taste profiles of maple syrup (of which there are more than sixty).

Yet these attempts have been highly specific in focus, for a certain taste or chemical reaction, and have not entirely addressed the accurate design and replication of the complex, natural mechanical and chemical structure of the human tongue. In addition, the COVID-19 pandemic has posed significant challenges to in-person sensory trials and consumer tests, and renewed the emphasis on development of non-human trials or testing.

However, development of biomimetic designs using 3D printing is not new. We had also reported previously on how 3D printing was used to develop a biomimetic tongue based on that of a cat  by researchers at Georgia Tech – for applications in soft robotics and gripping tools. Additionally, we covered research into the development of a biomimetic forebrain for robots to enable an artificial sense of touch. Earlier this year, researchers from Canada and Germany used the pine cone needle as inspiration to develop multi-material 4D printed scale and flap systems that are versatile and self-sufficient.

3D printed negative mold – with multiple tiny wells for fungiform and filliform papillae found on the human tongue. Image courtesy of University of Leeds

With the method introduced by researchers at Leeds, such natural random distributions can be recreated to better study oral processing and to treat oral conditions. For dry mouth in particular, from which about 10% of the general population and 30% of the older population suffer, such a biomimetic tongue would enable the development of long-lasting treatments.

After developing a final design from the 3D scans, researchers then created an inverse mold for an artificial tongue by using computer simulations and modeling to develop the 3D-printable artificial surface with inverse shaped wells and the dimensions of different papillae randomly distributed across the surface in the right density. A replica was 3D printed using digital light processing (DLP) technology using elastomers optimized for wettability and softness.

The biomimetic tongue 3D printed in polymer using DLP. Image courtesy of University of Leeds

Professor of Colloids and Surfaces at University of Leeds and principle investigator, Anwesha Shankar, had found a way, using computational mathematical modeling, 3D scanning and printing, to recreate the surface of the human tongue, a feat with no small significance:

“Harnessing expertise from multiple STEM disciplines, we’ve demonstrated the unprecedented capability of a 3D printed silicone surface to mimic the mechanical performance of the human tongue. We believe that fabricating a synthetic surface with relevant properties that mimics the intricate architectural features, and more importantly the lubricating performance of the human tongue is paramount to gaining quantitative understanding of how fluids interact within the oral cavity.

This biomimetic tongue surface could also serve as a unique mechanical tool to help detect counterfeit in food and high-valued beverages based on textural attributes, which is a global concern and can help to ensure food safety. Ultimately, our hope is that the surface we have designed can be important in understanding how the biomechanics of the tongue underpin the fundamentals of human feeding and speech.”

The project, published as a paper ‘3D Biomimetic Tongue-Emulating Surfaces for Tribological Applications’ in the ACS Applied Materials & Interfaces, received funding from the European Research Council as part of the European Union’s Horizon 2020 Research and Innovation program. It brought together expertise from diverse areas to develop the biomimetic solution – including computer science, mechanical engineering, food colloid science, soft matter physics, and dentistry.

The development of such a tongue, that resembles so closely the natural mechanical and chemical properties of a human tongue, will be particularly relevant to identify and study basic oral mechanobiological questions about the functioning of the human tongue that were not possible to study till now. It would also provide a unique oral tribological surface similar to biological tissue for the development of nutritional, biomedical and clinical products and applications, perhaps even in soft robotics.

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