Construction Of Microporous Pipe Network And Study On Internal Flow Field Of Biomimetic Compact Bone Scaffold

Certain destructive factors and sudden accidents may cause tissue and organ failure or even loss of function,and millions of operations are required annually to repair or replace damaged tissues and organs.For bone injury,repair is generally completed by autologous bone transplantation,allogeneic bone transplantation and artificial replacement based on bone tissue engineering.Autologous bone grafts will cause secondary damage to the patient’s body.There are two problems in allogeneic bone transplantation: large rejection and difficulty in obtaining appropriate allogeneic bone.The study of bone tissue engineering provides a new path.Bone tissue engineering scaffolds are substitutes for damaged human bones.It is implanted into the patient after in vitro culture,and finally the damaged bone is restored to health after degradation.Therefore,if the bone tissue engineering scaffold has a pore structure closer to the human bone,it will better ensure that the nutrient solution is transported to all positions of bone injury.In this paper,in view of the problems of non-growth and non-union of bone after the implantation of tissue engineered bone in some patients in the process of bone transplantation,it is proposed from the engineering point of view that the uneven flow of nutrients in the pipeline of implanted bone scaffold has a great impact on bone regeneration.Nutrient liquid velocity,pressure gradient is too high,all kinds of nutrients can not stay and adhere to the micro-channel wall.When the nutrient fluid flows,the fluid shear stress is too high,the osteoblasts will die in large numbers.When the velocity and pressure gradient of nutrient solution were too low,nutrients could not be transported to all positions of the microchannel,and osteoblasts and growth factors needed for bone repair were not introduced into the damaged parts.These will cause the failure of bone regeneration process.In view of the above problems,this paper takes human humerus as the research object,studies the internal characteristics of human bone,focuses on the internal structure of dense bone,and combines bionics to design bionic bone scaffold which focuses on the internal flow of dense bone.The velocity distribution nephogram,pressure distribution nephogram and shear stress distribution nephogram of each scaffold under different perfusion velocities were obtained by numerical simulation.A micro-channel testdevice for bone scaffold was designed.PIV testand numerical simulation were used to further analyze the influence of the internal structure of the scaffold and the change of perfusion velocity on the internal flow field and shear stress of the bone scaffold.Many PIV tests were carried out,and the velocity vector curves of seven kinds of scaffolds were obtained.Its main research contents include the following aspects :(1)The classification and modeling methods of micro-scale channels are analyzed,and their applicable occasions are discussed.The important parameters of bionic bone tissue engineering scaffold were studied,the relationship between pore and pore surface area of bone scaffold was studied,the porosity of bone scaffold was studied,and the pore surface area formula and porosity formula of bionic scaffold were established.(2)Combined with the characteristics of traditional bone tissue engineering scaffolds and human bone structure,a bone tissue engineering scaffolds with emphasis on the flow of dense bone was proposed,and the microporous pipe network structure of bone scaffolds was designed.The structure of the microporous pipe network focuses on the internal flow state and shear stress change of the nutrient solution.Therefore,the bone scaffold has 90 °,60 °,45 ° and 30 ° connection angles between the bone center pipeline and the Harvard pipeline,and the transition fillet is set at the connection to prevent sudden changes in speed and pressure at the intersection of various micro-channels.(3)Fluent was used to simulate and analyze the bionic bone scaffold model,and the velocity nephogram and pressure nephogram of each bone scaffold were obtained.The velocity nephogram and pressure nephogram were compared and analyzed.Combined with the mass flow histogram,it was concluded that the flow field distribution in I–90°bone scaffold was the most uniform,and the useful flow was the largest.I–90° was the optimal bone scaffold.The average shear stress in the scaffold was studied.According to the optimal shear stress range,the most suitable perfusion speed of I,II and III bionic bone scaffolds was determined.(4)Based on the similarity theory,the designed bionic bone scaffold model was prepared after proportional amplification,and the PIV test bench was built.PIV technology was used to collect the flow field vector curves of I–90°,I–60°,I–30°,II–90°,II–60°,and II–30° models.After comparing the flow field vector curves with the vector curves obtained by numerical simulation,it was found that the motion traces of the two were generally similar,and the velocity variation also conforms to the requirements of the similarity theory.It shows that when the test is difficult and expensive,it is feasible to use numerical simulation software to analyze the research of bionic bone scaffold,and the numerical method can correctly reveal the flow field state in the microporous pipe network of bionic dense bone scaffold.