Mechanical Model for Evaluating Curative Effect of Laser on Hypertrophic Scar / 医用生物力学

:Objective To establish a mechanical model with times of laser treatment as the independent variable in treatment process of rabbit ear hypertrophic scar (HPS) by combining experimental research and numerical simulation, so as to evaluate the curative effect of HPS. Methods Firstly, the HPS model of rabbit ear was established by CO2 laser instrument, and then the HPS was treated for continuous three times by pulsed dye laser (PDL) combined with CO2 lattice laser. After each treatment, the uniaxial compressive mechanical properties of HPS were tested to fit Ogden hyperelastic model to obtain mechanical parameters of HPS during the treatment. The functional relationship between mechanical parameters of HPS and times of laser treatment was established by LM optimization algorithm. Results Mechanical parameters of HPS increased with the increase of laser treatment times, and gradually became a constant, namely, mechanical parameters of normal skin. With the increase of laser treatment times, the growth ratio of HPS mechanical parameters gradually decreased. The initial growth ratio was 60% and decreased to 4.09% after three times of treatment. Conclusions The initial curative effect of laser therapy is the most obvious, and with the relief of symptoms, the effect of single laser therapy is no longer significant.

Calculation Model for Insertion Torque of Medical Bone Screws Based on ASTM F543-17 / 医用生物力学

Objective To study numerical model for calculating the insertion torque of bone screw. Methods The three stages of screw insertion process for the self-tapping screw were analyzed, so as to make mechanical modeling and simulation calculation on torque and torque angle at screw forming stage. Meanwhile, the insertion experiments of screws with specification of φ2.9×12 from three manufactures on polyurethane test blocks with different grades were performed according to ASTM F543-17(YY/T 1506-2016), and the experimental results were compared with the calculated ones. Results The deviations between the predicted insertion torque by the model and the measured torque in the experiments were 5 mN·m and 12 mN·m within the acceptable error range, which were 10% smaller than the average measured torque in the experiments. Conclusions The developed mechanical calculation model can be used to simulate and predict the insertion torque of medical bone screws in research and development or clinical use, and its combination with in vitro mechanical experiments provides an effective way of developing and designing bone screws.

Evaluation on Mechanical Comprehensive Performance of Flexible Neural Electrodes Modified by Coatings / 医用生物力学

Objective To evaluate mechanical comprehensive performance of the flexible neural electrode with coating modification, so as to provide references for optimal design of the electrode and coating parameters. Methods Simplified mechanical models were established for the contact phase, implantation phase and micromotion phase. The electrode material was polyimide, the coating material was PEG, and PDMS mold injection method was selected as the coating method. The coating thickness gradients were set as 40, 80, 120, 160 and 200 μm, respectively, and the three factors (the critical load, the maximum total deformation and the maximum strain of brain tissues) were comprehensively evaluated. Results As the thickness increased, the critical load increased, the maximum total deformation and the maximum strain of brain tissues decreased, but meanwhile, the strain area of brain tissues increased. For consideration of equilibrium for three factors, 200 μm was chosen as optimal thickness of the coating. At this thickness, the critical load was 17.9 mN, the maximum total deformation was 10.1 μm, and the maximum strain of brain tissues was 0.011 4. Conclusions The coating thickness had a great influence on mechanical properties of the neural electrode. The optimal parameters could be selected by setting influencing factors from the mechanical performance factors under specific case. The optimal parameter selection of coating can improve the electrode performance, which is of great significance for clinical application of the neural electrode.

Biomechanical and Dynamic Characteristics of Human Body during Exercise on Elliptical Cross Trainer / 医用生物力学

Objective To analyzes the biomechanical and dynamic characteristics of human body during exercise on elliptical cross trainer. Methods An elliptical cross trainer model and a human skeletal muscle model were built by three-dimensional (3D) modeling software and AnyBody software, respectively, which were then coupled and simulated. Results During exercise on elliptical cross trainer, the lumbar spine L5 was subjected to the maximum force 1023 kN, and the maximum activation of external oblique and internal oblique muscles were 80% and 40%, respectively. The maximum muscle activation in lower limb muscle groups did not exceed 40%, and the maximum plantar ground reaction force was 600 N. Conclusions The use of elliptical cross trainer can alleviate the pain of patients with chronic low back pain, and help to improve the trunk control and balance function of patients with stroke and hemiplegia. Compared with running exercise, exercise on elliptical cross trainer can protect the human knee joint.

Analysis of behavior of forces in a pelvis-soft tissue mechanical model / Análisis del comportamiento de fuerzas en un modelo mecánico de pelvis-tejido blando

Pressure ulcers are tissue damage resulting from the constant pressure on the underlying soft tissue to bony prominences for long periods. Some of the most common ulcers are developed at the ischial tuberosities area (ITs). It has been found that stresses produced in the underlying tissue to the ITs may exceed 5 to 11 times the surface stresses, making it necessary to estimate the forces generated between the soft tissue and the ITs. However, it is not possible to determine these stresses in vivo in a patient, due to ethical reasons. This paper presents a mechanical model of the pelvis-soft tissue in order to study the behavior of contact forces. The model simulates the load on the ITs of a male subject of 70 kg weight and 1.70 m height, which were recorded for 8 min. The registered forces in the model were compared with the surface forces estimated from pressure records measured by the Force Sensing Array system in a patient with spinal cord injury. After 2 min, both forces measured in the model, and the ones estimated in the patient followed the trend described by Crawford during clinical measurements of pressures during sitting. It was also found in the model that measured forces below the ITs are higher than those measured below soft tissue, which suggests that the model may be valid for the study of the forces generated inside the tissue.

Las úlceras por presión son daños en el tejido, derivados de la presión constante por periodos prolongados sobre el tejido blando subyacente a una prominencia ósea, algunas de las úlceras más comunes se desarrollan en la zona de las tuberosidades isquiáticas (TI´s). Se ha detectado que esfuerzos generados en el tejido subyacente a las TI´s pueden exceder entre 5 a 11 veces a los esfuerzos superficiales, lo que hace necesario conocer las fuerzas que se generan entre el tejido blando y las TI´s, sin embargo medir estos esfuerzos in vivo en un sujeto, no es posible por razones éticas. Este trabajo presenta un modelo mecánico del sistema pelvis-tejido blando con la finalidad de estudiar el comportamiento de las fuerzas, el modelo simula la carga en las TI´s de un sujeto masculino de 70 kg y 1,70 m, en el cual se registraron por 8 min. Las fuerzas registradas en modelo fueron comparadas con las fuerzas superficiales estimadas a partir de los registros de presión medidas por el sistema Force Sensing Array, en un paciente con lesión medular. A partir de 2 min, tanto fuerzas medidas en el modelo, como estimadas en el paciente, siguen la tendencia descrita por Crawford para mediciones de presiones clínicas durante la sedestación, también se encontró en el modelo que las fuerzas medidas por debajo de las TI's son mayores a las medidas debajo del tejido blando; lo que sugiere que el modelo puede ser válido, para el estudio de las fuerzas que se generan al interior del tejido.

Recent advances in modeling of airway mechanical behaviors in association with airway constrictions in asthma / 医用生物力学

Although it is important to explore potential treatment of chronic obstructive airway diseases such as asthma, as well as to discover interesting biophysical phenomena in airway system, the research on biomechanical models of airway narrowing remains a both appealing and challenging field. However, there have been significant advances during recent years, with number of emerging new models and new approaches. This review article briefly introduces some of the most recent work published in the literature. In particular, those work that emphasize on asthmatic airway narrowing behavior, and strive to explain the corresponding in vivo airway behaviors. More specifically, models that discuss not only individual airway behaviors, but also interactions due to coupling between airways and their surrounding structures are focused on. This includes interesting phenomena involving the airways and the smooth muscle that surrounds the airways, as well as the emergent spatial ventilation patterns due to dynamic airway interaction.

Numerical simulation of streaming potential distribution in cancellous bone / 医用生物力学

Objective To analyze the pressure-driven streaming potential in a cancellous bone meso-mechanical model with numerical simulation, so as to understand characteristics of streaming potential distributions in cancellous bone. Methods Based on the control equations of electric field and fluid, the finite element method was used to calculate the streaming potential in the cancellous bone model when subjected to pressure. Results The streaming potential near the solid surface of the model was relatively large (about 43.4 μV), while the streaming potential away from the solid surface was smaller (about 19.7 μV). Pressure and Zeta potential had a significant impact on the streaming potential of the model, presenting a linear relationship with the streaming potential. The streaming potential was greatly affected when the ion concentration was low, whereas the effect on the streaming potential was small when the ion concentration was high. Conclusions This research finding provides a theoretical reference for prevention and treatment by stimulation methods of electric current and electromagnetic fields in clinical fractures, senile osteoporosis and other bone diseases.

Shear modulus measurement of biological tissues based on Zener model / 医用生物力学

Objective To measure the shear modulus of biological tissues by using Zener model so as to overcome the limitation of Voigt model-based ultrasound vibrometry, and to provide effective approaches of tissue characterization. Methods The mechanical constitutive relation-based shear wave propagation velocity formula was utilized to estimate the shear modulus in terms of the velocities at multiple frequencies via mathematical methods. To obtain shear wave velocities in different objects, experiments were conducted by using different consistencies-based gelatin models and thermally damaged porcine livers as subjects, in which shear waves were induced by ultrasound radio forces. Results Voigt and Zener models were utilized to fit the velocities respectively. The Zener model exhibited higher fitting accuracy than the Voigt model, and the shear modulus could well distinguish gelatin models with different consistencies or porcine livers of different damage degrees. Conclusions The method in this paper provides a potential means of measuring the shear modulus of biological tissues non invasively, which is very promising for tissue characterization and disease diagnosis in medicine.

3-D center of gravity mapping:a new method for assessment of FES-assisted paraplegic walking efficiency / 中华物理医学与康复杂志

Objective To explore a new method for assessing the walking efficiency of the paraplegic patients assisted by functional electrical stimulation (FES). Methods The measurement system based on a standard walker was developed. During FES assisted walking of the paraplegic, the real time of the upper limb support were obtained and transformed into a 3 D center of gravity (CG) motion map with a paraplegic upper body mechanical model to describe the CG motion locus. Then the FES efficiency indicated by walking balance condition was assessed objectively and quantitatively. Results In this design, the pilot study of a paraplegic patient undergoing walking training with FES showed that the force accuracy was better than 1.01%, nonlinearity was less than 0.8%, and crosstalk was less than 3.2%. Conclusion The results showed that this system may be used as 1) an evaluation index of FES assisted paraplegic walking efficiency, 2) a balance control indicator during FES assisted paraplegic walking training and 3) a feed back signal to choose an efficient FES pattern and sequence.

Mechanical Analysis of the Excimer Laser Photorefractive Keratectomy

This study proposed a mechanical model of the excimer laser photorefractive keratectomy(PRK) for myopia patients utilizing finite element method, which is a simulation technique widely used in engineering fields. The outcomes of the surgery depends on many factors, which are also dependent on each other. In this study, some mechanical factors are selected and the effects of the selected factors on the surgical results were analyzed. One of the important factors in the finite element analysis is the mechanical properties of the object. The representative characteristic of the human cornea is that it shows highly nonlinear property in the stress-strain relationship like most soft tissues in the human body. Therefore, the nonliear property was adopted in this study. Other important mechanical properties which affect the outcomes of the surgery are: a preoperative thickness, intraocular pressure, diameter of ablation zone and the depth of ablation. With various changes of the those mechanical factors, the outcomes of the surgery were predicted using the finite element method. The results show the qualitative agreement with clinical outcomes also promising agreement quantitatively. Therefore, this study shows a potential of the finite element method in clinical application of excimer laser PRK.