Researchers at the University of Leeds and University of Edinburgh have created synthetic soft surfaces with tongue-like textures for the first time using 3-D printing, opening new possibilities for testing the oral processing properties of food, nutritional technologies, pharmeceuticals, and dry mouth therapies.
The printed silicone structure mimics the topology, elasticity, and wettability of the tongue’s surface, the researchers said. These factors are instrumental in how food and saliva interact with the tongue, which in turn can affect mouthfeel, swallowing, speech, nutritional intake, and quality of life.
Since the onset of the COVID-19 pandemic, the researchers added, social distancing has posed significant challenges in carrying out such sensory trials and consumer tests. The biomimetic tongue then will be immensely helpful in increasing development productivity and reducing manufacturers’ reliance on human trials in early stages, according to the researchers.
“Harnessing expertise from multiple STEM disciplines, we’ve demonstrated the unprecedented capability of a 3-D printed silicone surface to mimic the mechanical performance of the human tongue,” said Anwesha Sarkar, PhD, MS, professor of colloids and surfaces at the University of Leeds School of Food Science and Nutrition.
The complex nature of the tongue’s biological surface has posed challenges in artificial replication, adding major obstacles to the development and screening of effective long-lasting treatments or therapies for dry mouth syndrome, experienced by about 10% of the general population and 30% of older adults, the researchers 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,” said lead author Efren Andablo-Reyes, PhD, who conducted the research while he was a postdoctoral fellow at the School of Food Science and Nutrition at Leeds.
“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,” Andablo-Reyes said.
“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,” he said.
The study brought together unique expertise in food colloid science, soft matter physics, dentistry, mechanical engineering, and computer science, the researchers said.
“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 Michael Bryant, PhD, of the Leeds School of Mechanical Engineering.
The researchers took silicone impressions of tongue surfaces from 15 adults. The impressions were 3-D optically scanned to map papillae dimensions, density, and the average roughness of the tongues. The texture of a human tongue was found to resemble a random layout.
Next, the researchers used computer simulations and mathematical modelling to create a 3-D printed artificial surface to function as a mold including wells with the shape and dimensions of the different papillae randomly distributed across the surface with right the density. This was replica-molded against elastomers of optimized softness and wettability.
“The randomness in distribution of papillae appears to play an important sensory role for the tongue,” said coauthor Rik Sarkar, PhD, MTech, of the University of Edinburgh School of Informatics.
“We defined a new concept called collision probability to measure mechanosensing that will have a large impact in this area. In the future, we will use a combination of machine learning and computational topology to create tongue models of diverse healthy and diseased individuals to address various oral conditions,” said Sarkar.
The artificial surface then was 3-D printed using digital light processing technology based in the School of Mechanical Engineering at Leeds. The researchers ran experiments using different complex fluids to ensure that the printed surface’s wettability, or how a liquid keeps contact and spreads across a surface, and the lubrication performance was the same as the human tongue impressions.
“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,” said Bryant.
“Accurately mapping and replicating the tongue’s surface and combining that with a material that approximates the elasticity of the human tongue was no small task,” said Sarkar.
“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 a quantitative understanding of how fluids interact within the oral cavity,” Sarkar said
“This biomimetic tongue surface could also serve as a unique mechanical tool to help detect counterfeits in food and high-valued beverages based on textural attributes, which is a global concern and can help to ensure food safety,” Sarkar said.
“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,” Sarkar said.
The study, “3D Biomemetic Tongue-Emulating Surfaces for Tribological Applications,” was published by ACS Applied Materials & Interfaces.
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