Research On Biomechanics During The Masticatory And Swallowing Process Based On Viscoelastic Theory

Masticatory and swallowing refers to the whole process of food from the oral intake to stomach.Such process is an important guarantee for organisms to obtain energy and nutrients,meanwhile,influence the development of other relevant industries,such as food-processing industry and medical device industry.In food industries,the sensory evaluation during masticatory and swallowing is an important index for the research and development of functional food.In clinic medicine,the mechanical analysis of masticatory and swallowing system contribute to the diagnosis and treatment of related diseases.In medical instrument domain,the analysis of biomechanical behavior can provide theoretical basis for the optimization of implant denture system and the design of gastrointestinal capsule-like robot.As the food materials which mixed with saliva and the biomaterials exhibit obvious viscoelastic properties,the theory of viscoelasticity were introduced for the research of mechanical behavior of biomaterials including oral cavity and esophagus during masticatory and swallowing process in the present study.And the study includes:(1)The agar gels samples were prepared as a typical viscoelastic material,then the influencing factors of mechanical properties and constitutive model were researched based on texture experiments.It was found that strain rate has great influence on the mechanical properties of agar gel,both the collapsing strength and elastic modulus increase with rasing strain rate.According to the results of stress relaxation test,the five elements general Maxwell viscoelastic model of agar gels was established,which have a good prediction accuracy for stress decay during relaxation process,providing a material constitutive for the food material and biomaterials such as oral and esophagus in later chapters.(2)The dynamic process of chewing was simulated using finite element method based on a single tooth system composed of teeth,periodontal ligament and alveolar bone.The result of simulation showed that the stress of bone interface increase with orthotropic material setting for alveolar bone compare with isotropic model,and the uniform stress distribution was observed,suggesting that orthotropic approximation is more close to biological feature.Periodontal ligament can absorbs part of energy and delay the crash with large deformation during the chewing process rely on the hyperelastic(high Poisson's ratio and low stiffness).And the existence of periodontal ligament make a smooth stress field in the bone interface,expand the range of stress distribution.Resulting in the decrease of stress concentration on osseointegration surface and the improvement of biological activity for bone tissue.(3)The mandibular system including mandible and masticatory muscles was further built to simulate the mandibular biomechanical behavior.The simulation indicated that masseter muscle has the maximum force during chewing.Also,stress concentration appeared at alveolar cavity and mandibular oblique line zone.Particularly,with same chewing force,the loading point just influences the distribution of muscle force on mandible,has no effect on the maximum value among the whole masticatory muscles.(4)The peristaltic motion was simplified as a sine wave transmitted at a certain speed,then hydrodynamic theory and theories lubrication approximation theory were introduced to establish a dynamic model of peristaltic on esophageal bolus transport for Newtonian fluid.Numerically solving was carried out with different parameters,finding that the pressure rises very sharply at the initial end,reaches the crest,then falls at a lower rate to front of bolus,leading pressure difference between the tail and head so as to transport the bolus.And it is further observed that the pressure increased at contractive regions with increase in magnitude of bolus viscosity.It may be therefore concluded that fluids with low viscosity are favorable to swallow in comparison to fluids with higher viscosity,cause it can improve efficiency of peristaltic transport and decrease pressure along the esophagus.However,the increase of amplitude of the peristaltic wave does not always conducive to the improvement of transport efficiency,even though it can increase the pressure difference,but also lead to violent trapping phenomenon.(5)The esophagus is simplified into a flexible pipe with constant inner diameter,taking the capsule micro robot as research object to build an interaction model between capsule and esophagus under motion state.The viscoelastic model was used as material constitution for esophageal tissue and the deformation of capsule was not considered.Stress distribution and frictional resistance of esophagus were analyzed based on this model with theoretical method and numerical simulation method.Results showed that higher stress and friction resistance were obtained when the velocity and diameter of capsule raising.The chamfering parameters of capsule had more influences on frictional resistance in comparison with stress.Also,the direction of gravity hardly had influence on biomechanics of esophagus,the main effects were the motion path of capsule.The mechanical behavior of biological tissue with various food texture under different chewing and swallowing situation was studied in this paper.Such researches provide a theoretical basis for the research and development of food,dental implant and medical device.