What Is Tissue Biomechanics?
Biomechanics (biomechanics) Biomechanics is a branch of biophysics that applies the principles and methods of mechanics to the quantitative study of mechanical problems in organisms. His research ranges from the whole organism to the system and organs (including blood, body fluids, organs, bones, etc.), from bird flight, fish swimming, flagella and cilia movement to the transport of plant body fluids. The basis of biomechanics is the three laws of conservation of energy, momentum, and mass, plus a constitutive equation describing physical properties. Biomechanical research focuses on mechanical issues related to physiology and medicine. According to the research object, it can be divided into biological fluid mechanics, biological solid mechanics and sports biomechanics.
- Chinese name
- biology
- Foreign name
- biomechanics
- Attribution
- Branch of biophysics
- area of research
- From the whole organism to the system and organs
- Biomechanics (biomechanics) Biomechanics is a branch of biophysics that applies the principles and methods of mechanics to the quantitative study of mechanical problems in organisms. His research ranges from the whole organism to the system and organs (including blood, body fluids, organs, bones, etc.), from bird flight, fish swimming, flagella and cilia movement to the transport of plant body fluids. The basis of biomechanics is the three laws of conservation of energy, momentum, and mass, plus a constitutive equation describing physical properties. Biomechanical research focuses on mechanical issues related to physiology and medicine. According to the research object, it can be divided into biological fluid mechanics, biological solid mechanics and sports biomechanics.
Biomechanical origins
- Although the term biomechanics only appeared in the 1960s, some of its contents are ancient topics. For example, Galileo calculated the quantitative relationship between the pendulum length and the period around 1582, and used the pendulum to determine the pulse rate of a person. In 1616, British physiologist W. Harvey demonstrated the existence of blood circulation theoretically based on the principle of continuity in fluid mechanics. By 1661, When Malpicki dissected the frog, he saw the existence of microcirculation in the lungs of the frog, confirming Gulvey's conclusion. G. A. Borelli discusses the movements of the flying, fish and heart and intestines in his book "On the Movement of Animals". L. Euler wrote a paper on wave propagation in arteries in 1775. H. Lamb's prediction of high-frequency waves in arteries in 1898 has been confirmed. British physiologist S. Hales measured arterial blood pressure in horses and sought a relationship between blood pressure and blood loss. He explained how the heart-pumped synaptic flow turned into a continuous flow in the blood vessels. He introduced the concept of peripheral resistance to blood flow and correctly pointed out that the main site of this resistance is in the small blood vessels. J.-L.-M. Poiseuille established the relationship between pressure drop, flow, and resistance during blood flow. O. Frank explained the mechanics of the heart. E. H. Starling proposed the law of mass transfer through membranes and explained the problem of water balance in the human body. A. Kroger won the Nobel Prize in 1920 for his contribution to microcirculation mechanics, AV. Hill won the Nobel Prize in 1922 for his muscle mechanics work, which laid the foundation for the systematic study of biomechanics that began in the 1960s.
Biomechanical development
- In the development of science, biology and mechanics promote and develop each other. Harvey in 1615 logically inferred the existence of blood circulation according to the continuity principle in fluid mechanics, and was confirmed by Marpi based on the discovery of frog lung microvessels in 1661; the famous Young's modulus in material mechanics is Yang Wei Proposed by establishing the elastic mechanics theory of vocal cord pronunciation; Poisson's theorem describing the laminar flow of a straight tube in fluid mechanics, whose experimental basis is the dog aorta
Research Status of Biomechanics
- In the early 1960s, a group of engineering scientists collaborated with physiologists to conduct in-depth research on issues related to biology, physiology, and medicine, using engineering perspectives and methods. The research on some of these topics has gradually developed into a branch of biomechanics, such as biorheology, which mainly studies the mechanical properties of biological materials. It generally divides biological materials into body fluids, hard tissues and soft tissues, and muscles belong to a more special category. The main focus of research is blood in body fluids. It mainly studies the viscosity of blood and the factors that affect viscosity (such as tube diameter, formed components, and red blood cells), and the specific distribution of red blood cells in the branches of the system. The mechanical properties of red blood cells themselves , The interaction between red blood cells, the role of red blood cells and the tube wall. For soft tissue, it is mainly to study its rheological properties and establish constitutive relations, because constitutive relations are not only the basis for further analysis of its mechanical problems, but also have clinical significance. For hard tissues, in addition to studying its rheological properties, a lot of research has been done on the relationship between bone growth and changes and stress.
- The dynamics of various systems, especially the circulatory and respiratory systems, have been the object of long-term research. Circulatory system dynamics mainly studies the blood flow in the heart, arteries, microvascular beds, veins, and the mechanical problems of the heart and heart valves. On the one hand, it studies the flow in its piping system, and on the other hand, it focuses on the analysis of local flow patterns, such as those at the bends, forks, and stagnation points. This is because the formation and deterioration of atherosclerosis are considered to be related to Local flow regime. Respiratory system dynamics mainly studies the gas flow in the airway during breathing, the blood flow in the pulmonary circulation, and the gas exchange between gas and blood.
- All these work, including the study of the rheological properties and dynamics of biological materials, not only help to understand the physiological titration process of the human body, but also provide scientific basis for the design and manufacture of artificial organs. Biomechanics also studies the transport of plant body fluids (see Flow in Plants).
- The influence of environment on physiology is also a research content of biomechanics. As we all know, oxygen has a great impact on the development of organisms. Under the conditions of hypoxia, organisms develop slowly, and in the environment rich in oxygen, they develop faster. Even in the short term, the environmental impact is clear. Experiments have shown that young rats in an environment containing 10% oxygen and a pressure of 1 atmosphere (1 atmosphere = 101 325 Pa), even if they only live for 24 hours, under the wall of the pulmonary arterioles with a diameter of 15 to 30 microns, There will be a large number of fibroblasts. If it lasts 4 to 7 days, the fibrocytes will transition into typical smooth muscle cells, which will undoubtedly affect the blood flow in the pulmonary circulation. Another example is a person in a high acceleration state, the inertia of their blood will change significantly, and the overhanging organ will deviate from its original position, thereby changing the blood flow state in the body.
- When designing tools for navigation in the water, it is often necessary to consider the best shape. Best propulsion and best maneuvering. Due to natural selection, immortal organisms with these advantages are easier to survive. Therefore, studying the movement of certain aquatic organisms can get some worthy knowledge. For example, a dolphin is a higher-level animal. It has an efficient propulsion mechanism and a good shape, especially its skin, which is divided into two layers, filled with elastic fibers and adipose tissue, and has special drag reduction properties. It can maintain the laminar boundary layer state during high-speed swimming. This is because its skin is very sensitive to changes in pressure gradient in the boundary layer, and it can make appropriate elastic deformation to reduce the reverse pressure gradient. Therefore, during high-speed swimming, the epidermis Can produce wavy motion to suppress the occurrence of turbulence. Another example is that the movement of ciliates is achieved through the special movement of cilia. The low-level biological movement is also maintained in the human respiratory tract, that is, the use of cilia to exclude certain foreign objects in the respiratory tract. In short, the significance of studying biological movements in nature is obvious.
Biomechanical characteristics
- The most important difference between biomechanics and other branches of mechanics is that the object of study is organisms. Therefore, when studying the problems of biomechanics, the environment of the subject is very important. As experimental objects, there are generally in vivo and in vitro distinctions, and the results of the experiments also differ accordingly. Biological materials in a living state, that is, biological materials in a natural state, are generally in a stressed state. But after being released, being in the so-called free state is different from being in the body. For example, the length of the blood vessel will be shortened as soon as the blood vessel is separated from the body, and the lung will shrink after being separated from the body. In-vivo experiments are divided into anesthesia and non-anaesthesia. As for the in vitro experiment, after the subject is released, the experiment can be carried out in the overall upright position according to requirements, or it can be further processed into a test piece for experiment. Different experimental and processing conditions have a great impact on experimental results. This is exactly the characteristic of biomechanical research.
Biomechanical classification
Biomechanics
- Biosolid mechanics is the study of the mechanical problems related to biological tissues and organs by using the basic theories and methods of material mechanics, elastoplastic theory, and fracture mechanics. In approximate analysis, the strength theory of compression, tension, and fracture of human and animal bones and their state parameters can be applied to the standard formulas of material mechanics. However, bones are anisotropic in both morphological and mechanical properties.
- Since the 1970s, there have been many theoretical and practical researches on the mechanical properties of bones, such as combined rod hypothesis, two-phase hypothesis, and other detection techniques such as finite element method, fracture mechanics, stress sleeve method, and pretest elastic force method have been applied. For bone mechanics research. Bone is a composite material, and its strength is not only related to the structure of the bone, but also to the material itself. Bone is a combination of collagen fibers and inorganic crystals. The bone plate is composed of longitudinal fibers and circumferential fibers. The inorganic crystals in the bone greatly increase the bone strength. It reflects the functional adaptability of bone to bear the maximum external force with the least structural material.
- Wood and insect cuticles are composite materials composed of fibers embedded in other materials, which have similar mechanical properties to glass fiber reinforced plastic composed of very fine glass fibers embedded in synthetic resin. Animals and plants are polymers composed of polysaccharides, protein lipids, etc. The mechanical properties of proteins and polysaccharides can be derived from the polymer theory of rubber and plastics. Knowledge of viscoelasticity, elastic deformation, and elastic modulus can be used not only for proteins composed of amino acids, but also for analyzing the mechanical properties of cells. Such as the force of microfilaments during cell division, the working mode and working principle of myofilaments, and the mechanical properties of cell membranes.
- The study of bone in biosolid mechanics can be traced back to the 19th century. A large number of researchers studied bone tissue. Until the end of the 19th century, Wollf proposed the famous Wollf's Law. He believed that bone tissue is a self-optimizing organization Its structure will gradually change with the change of the external load, so as to reach the optimal state. In the future, researchers have done a lot of research, and based on this law, put forward many theoretical and mathematical models. Among the more famous professors are SC Cowin, D. R Carter, Husikes. In China, Professor Zhu Xinghua of Jilin University has also done a lot of work.
Biomechanics
- Biohydrodynamics is the study of biological cardiovascular system, digestive and respiratory system, urinary system, endocrinology, swimming, flight and other mechanical issues related to hydrodynamics, aerodynamics, boundary layer theory and rheology.
- The flow of blood and plant fluids in humans and animals are similar to laminar, turbulent, seepage and two-phase flows in fluid mechanics. In the analysis of hemodynamic properties, blood can be regarded as a homogeneous fluid when it flows in large blood vessels. Because the diameter of the microvessels is equal to the diameter of the red blood cells, when analyzing the microcirculation, the blood can be regarded as a two-phase fluid. Of course, the thinner the blood vessels, the more prominent the non-Newtonian properties of the blood.
- Most of the blood flow in the human body is laminar, and turbulence is easy to occur in areas where blood flows quickly or the blood vessels are thick. In the aorta, blood moving at peak speeds is barely laminar, but in many cases turns into turbulence. Urinary flow in the urethra is often turbulent. And the material exchange through the capillary wall is a kind of seepage. For the internal flow such as blood flow, the pulsating blood flow of the heart is volatile, and because the blood vessels are elastic, the flow boundary is not fixed. Therefore, the state of blood flow in the body is more complicated.
- For outflow, knowledge of fluid mechanics is also used in the study of animal swimming. For example, the fish has a streamlined shape and is easy to flex. It can propel itself through Xingbo. Water hole experiments show that in the fluid boundary layer when the fish swims, the velocity gradient is large, so the power to overcome the fluid's viscous resistance is also large. The migration of small organisms and single cells is also a problem of outflow. Fluctuations of flagella and slapping of cilia push fluid on the cell surface, causing cells to move forward. Sperm swim with flagella, the inertia of water can be ignored, and its hydrodynamic force is proportional to the relative swimming speed of the sperm. Protozoa moving in liquid, the resistance can be obtained according to the formula for calculating the resistance of small particles in the flow field (Stokes' law).
- In addition, aerodynamic principles and methods are commonly used to study animal flight. Aircraft and flying animal flight power consists of two parts: zero lift power and induced power. The former is used to overcome the viscous resistance of air in the boundary layer; the latter is used to accelerate the air downward to provide a lift equal to the weight of an airplane or a flying animal. Birds can adjust the glide angle by flapping their wings back and forth in the air, which is the same as the glider flap adjustment. Wind tunnels have been used to study the flight characteristics of flying animals, such as vultures and bats, and their gliding performance is very similar to model gliders.
Biomechanics
- Sports biomechanics is a discipline that studies the movement of the human body with the basic principles of statics, kinematics, and dynamics combined with anatomy and physiology. The study of biology using the principles and methods of theoretical mechanics is a relatively early and in-depth field.
- In human sports, the basic principles and equations of layer kinematics and dynamics are used to analyze and calculate the extreme capabilities of athletes in running, jumping, throwing and other sports. The results are very similar to the records of the Olympic Games. In the aspect of wound biomechanics, the finite element method is applied from the viewpoint of dynamics to calculate the frequency response of head and neck when impacted and to establish a wound model, so as to improve the protection of head and neck and accelerate the treatment of wounds.
- Various organs and systems of the human body, especially the dynamics of the heart-circulatory system and the lung-respiratory system, the thermodynamic balance between biological systems and the environment, and the problems of specific functions are also hotspots in current research. The study of biomechanics not only involves medicine and sports, but also has in-depth aspects of traffic safety, aerospace, and military science.
Chinese Journal of Biomechanics
Combination of biomechanics and traditional Chinese medicine
- A considerable part of biomechanical research in China is integrated with traditional Chinese medicine. Therefore, it has formed its own characteristics in the research of bone mechanics, pulse wave, non-destructive testing, massage, qigong, biological soft tissue and other items.
- The research of biomechanics must first understand the geometric characteristics of biological materials, and then determine the mechanical properties of tissues or materials, determine the constitutive equations, derive the main differential equations and integral equations, determine the boundary conditions, and solve. The solution to the above boundary problem needs to be verified by physiological experiments. If necessary, a separate mathematical model is needed to solve the problem, in order to make the theory and experiment consistent.
- Secondly, the biological materials as experimental objects are divided into in vivo and in vitro. The biological material in the body is generally in a stressed state (such as blood vessels and muscles). Once it is free, it is in a free state, that is, a non-physiological state (such as blood vessels and muscles, once contracted, it becomes significantly shorter and shorter). The experimental results of the two state materials are quite different.
Biomechanical description
- The research of biomechanics should be carried out from the two aspects of mechanics and histology, physiology, and medicine, that is, to link the macromechanical properties with the microstructure. Therefore, it requires multidisciplinary joint research or researchers with multidisciplinary knowledge.
Major subdomains of biomechanics
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- Mechanics
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| Quantum mechanics |
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Biomechanical bibliography
- Feng Yuanzhang: Biomechanics, Science Press, Beijing, 1983.