Journal of Mechanics in Medicine and Biology

The biomechanical modeling and simulation of human tissue are the basic part of virtual surgery system. As an important human soft tissue, the biomechanical modeling and simulation method of subcutaneous adipose tissue are urgent problems to be solved in virtual surgery system. In this paper, biomechanical modeling and simulation of subcutaneous adipose tissue were completed based on linear elastic and hyperelastic finite element model. First, the deformation process of subcutaneous adipose tissue was divided into two stages: Initial loading stage and later loading stage. Furthermore, the linear elastic model at initial loading stage and the nonlinear elastic model at later loading stage were established, respectively. Then, the biomechanical model of subcutaneous adipose tissue was solved based on the finite element method. Finally, the linear finite element calculation was included in nonlinear finite element calculations, and finite element simulation program of the subcutaneous adipose tissue was compiled in Visual Studio environment. The accuracy of the model was verified by comparing the simulation results with the experimental results. The efficiency of finite element simulation program of the linear and nonlinear hybrid model is evaluated by comparing the simulation time with the single linear model and the hyperelastic model.

Monitoring human gait is essential to quantify gait issues associated with fall-prone individuals as well as other gait-related movement disorders. Being portable and cost-effective, ambulatory gait analysis using inertial sensors is considered a promising alternative to traditional laboratory-based approach. The current study aimed to provide a method for predicting the spatio-temporal gait parameters using the wrist-worn inertial sensors. Eight young adults were involved in a laboratory study. Optical motion analysis system and force-plates were used for the assessment of baseline gait parameters. Spatio-temporal features of an Inertial Measurement Unit (IMU) on the wrist were analyzed. Multi-variate correlation analyses were performed to develop gait parameter prediction models. The results indicated that gait stride time was strongly correlated with peak-to-peak duration of wrist gyroscope signal in the anterio-posterior direction. Meanwhile, gait stride length was successfully predicted using a combination model of peak resultant wrist acceleration and peak sagittal wrist angle. In conclusion, current study provided the evidence that the wrist-worn inertial sensors are capable of estimating spatio-temporal gait parameters. This finding paves the foundation for developing a wrist-worn gait monitor with high user compliance.

In this research, thermoelastic effect was investigated for biostimulation without damage on the biological medium using laser. Thermoelastic effect was generated and mechanical stress was induced by laser irradiation on the collagen, the main protein in the human body, under various conditions with short pulsed laser. The threshold laser energy to induce stress wave in each medium thickness was examined with a piezo sensor. Based on the test, the stimulation strength can be controlled through the adjustment of medium thickness, laser energy and beam diameter. The result implies that precise stimulation with various strengths of stress waves can be generated at the target depth without direct contact with the biological medium. This research can be used valuably in various fields such as contactless biostimulation, low power laser treatment and laser haptic applications.

Human gait is influenced by changes in joints of the pelvis, hips, knees and ankles, which demonstrate three degrees of freedom. Thus, this study presents a mathematical model for the establishment of the hip rotation trajectory using measured data. We used multibody dynamics simulation software (LifeMOD) to establish a model of the human lower limb, whereby the three dimensional trajectory of the hip joint could be analyzed. We used advanced equipment to measure the trajectories of the internal rotation and external rotation of the hip joint in middle aged to elderly adults during walking. Curve fitting was used to obtain the average internal rotation and external rotation of the hip joint, and relationships between the amplitude, period, initial movement phase, subject height and walking speed were assessed. The observations from this study suggest that mathematical modeling of internal rotation and external rotation of hip joint can be performed using this approach. This modeling technique can be used to track the trajectory planning of rehabilitation robots and the external skeletons leading to improved human–computer interactions, and evaluation of response to rehabilitation.

A novel dynamic brace for the treatment of idiopathic scoliosis based on parallel-actuated robotic system is proposed in this paper. The new brace can apply corrective forces on patients’ spine actively to correct the abnormal spine. However, the gravity of the dynamic system results in some adverse impacts, such as reducing comfort degree of patients, accuracy loss of rehabilitation force control, big error in direction and value of force. To overcome this problem, a new active force control strategy, proportional-derivative (PD) control with desired-gravity-compensation (DGC), is proposed to improve the effectiveness of scoliosis rehabilitation. Considering the electrically driven system and the environment contacting with the brace, the dynamic model of the active brace system is derived using Kane method. Based on the above mentioned, the force controller with DGC is designed for the brace system to compensate the impact of system gravity. The brace experiment system is built and various experiment tests are performed to verify the proposed control strategy. Experiment results demonstrate that the proposed control strategy, PD control with DGC, can distinctly reduce the influence of the brace system gravity and has more efficient control effectiveness compared with the classical PID controller.

This paper aims to investigate the effect of continuous sensory electrical stimulation (SES) on the suppression of a Parkinsonian rest tremor. Fourteen patients with Parkinson’s disease participated in this study. Three wrist muscles were electrically stimulated on sensory level under motor threshold. Intensity of stimulation was determined for each muscle of each patient as the maximum tolerable current amplitude that does not induce muscle contraction. Tri-axial gyro sensors were attached to three upper limb segments. The angular velocity of each segment was measured for each of the three sessions, i.e., PRE-, ON- and POST- stimulations. Outcome measures were the tremor amplitude and main frequency of each axis in the power spectrum. Decrease in tremor amplitude was significant at ON and POST sessions in finger and at POST session in hand and forearm. Decrease in main frequency was significant mainly at ON session. About one-third of patients showed reduction in tremor power at ON-stimulation and at POST-stimulation. Subjects with suppression of tremor showed greater initial tremor amplitude than those without suppression. Continuous SES suppressed the Parkinsonian rest tremor. The results suggest that the properties of tremor-generating loop may be altered by continuous SES and the effect lasts temporarily.

Physiological loads are non-axisymmetric and can lead to interstitial bone fluid flow, particularly in osteon. According to research, interstitial bone fluid flow plays a key role in bone mechanotransduction. To evaluate the poroelastic responses of a non-axisymmetric loaded osteon, this paper presents a finite element osteon model that is bulit by using the Comsol Multiphysics software. Obtained results show that under the same loading amplitude, the generated pressure and velocity amplitudes in the axial compression loading case are the largest, followed by that in the compressive bending loading, and smallest in the bending case. Moreover, the induced pressure and velocity amplitudes in axial compression loading exhibit an axial symmetrical distribution and axial centrosymmetric distribution in the compressive bending. In the bend loading case, the pressure amplitude presents an antisymmetric distribution, but the velocity amplitude is axially symmetrically distributed. Therefore, the distributions of pressure and velocity are definitely affected by load types, which lead to different bone fluid stimuli in mechanotransduction.

This study compared the differences in the putter trajectory and psychophysiological variables of winners and losers in a competitive putting game that targeted professional and amateur golfers under stress. Eight professional golfers (handicap: $\le 5$) and eight amateur golfers (handicap: $\le 25$) participated. To maximize the tension of the competition, the putting game was held in a single-elimination one-on-one knockout tournament with a single 2.1m putting competition for each group. In the case of a hole-in or a failure by both golfers, the game resumed until the winner was determined. To compare the golfers during the game, the maximum speed, moving length, and amplitude of the putter head during the back-swing and the follow-through were set as the motion variables; and psychological variables (heart rate, heart rate variability (HRV), and Competitive State Anxiety Inventory-2 (CSAI-2)) were analyzed. The results showed significant differences between the putter trajectory variables (maximum velocity and amplitude of the putter head during follow-through) of the groups, but no differences in the psychophysiological variables. In comparing winners and losers within each group, however, the professional group showed a difference in only the psychophysiological variables (HRV and self-confidence of CSAI-2), whereas the amateur group showed a difference in only one putter trajectory variable (follow-through length). It was quantitatively confirmed that factors that determine the outcome of the game differed at a technical level.

It is important to assess lateral balance because falls to the side frequently occur and lead to hip fracture in elderly adults. The aim of this study was to investigate lateral balance in response to lateral tilting perturbation in young and elderly adults. Fifty healthy subjects (28 young and 22 elderly) participated in this study. They were instructed to maintain postural balance against right-down and left-down perturbations. As outcome measures, the mean distance, mean velocity and peak frequency were derived from the center of pressure (COP) data in the frontal plane (medio-lateral). Independent $t$-tests were performed to compare the elderly with the young. The elderly group exhibited a greater COP mean distance and faster mean velocity compared to the young group in right-down perturbation ($p<0.05$). The COP peak frequency of the elderly was higher than that of the young in both right- and left-down perturbations ($p<0.05$). These results suggest that the elderly have a dynamic lateral balance strategy with greater and faster body sway and with more frequent adjustments of the COP in response to lateral perturbation. This study will contribute to the understanding of lateral balance strategy in the elderly for the prevention and intervention of falls.

Arterial stiffness is a major contributor to cardiovascular diseases. The aim of this study is to explore the physiological significance of the brachial mechanical parameters, which could be estimated from oscillometric blood pressure (BP) measurement, and investigate on the potential of these arterial parameters as an index of arterial stiffness. The mechanical characteristics of brachial artery were modeled based on the collapsible tube theory, which includes two important parameters to describe the compliance of brachial artery. After the model validation, the arterial parameters were estimated from the measured oscillometric envelope of 56 subjects by solving an inverse problem. The physiological significance of these parameters was explored by analyzing their association with pulse wave velocity (PWV) as well as with the BP. Arterial compliance parameters were successfully estimated from the envelope of the oscillometric pulse wave in the BP measurement. The parameters were found to be linearly associated with age, PWV, and BP. These results suggest that our method may provide a potential approach to assess arterial compliance based on oscillometric measurement of BP.

This study aims to investigate the interaction effect between the beam diameter and energy density, which are perceived as laser-induced tactile perception by humans, by diversely varying the laser parameters, beam diameter, and energy. Eight healthy male college students of 23.5$\pm$1.7 years participated in the study. The range of the beam diameter of the displayed laser stimulation was between 0.03mm and 8mm, and a total of 21 sizes were displayed. The laser energy was sequentially displayed from the minimum energy that can be displayed by one beam diameter to the maximum energy range that does not exceed the maximum permissible exposure (MPE) level since the energy varies according to the beam diameter. The laser energy was controlled by an optical density ($\mathrm{\text{OD}}=0.4$) filter and was measured by an optical power meter (energy meter). Furthermore, the beam diameter was adjusted by moving the lens, which was confirmed with the beam profiler. The experimental test consists of the control phase (19s), stimulus phase (7s), and response phase (4s); the total duration of the test was 30s. The stimulus phase is the period in which stimulation was displayed on the skin through laser irradiation, and the stimulation was displayed by changing the beam diameter and the energy from the laser. The total number of beam diameter and energy pairs displayed to the subjects was 113 and 5 trials of irradiation were conducted for each pair. Stimulation perception response was recorded by pressing the response buttons during the response phase, and the responses were predefined as “no feeling,” “tactile sensation”, and “pain.” Through the extracted response data from the response phase, the beam diameter and energy density pair in which more than 50% of the subjects responded as having perceived tactile sensation were selected from the possible laser energy that could be displayed from one beam diameter. The simulation results showed that increasing the beam diameter increased the penetration depth, indicating an effective energy transfer to the skin. Therefore, increasing the beam diameter results in increased scattering, and hence increased penetration depth, and ultimately a more effective energy transfer. Therefore, increased beam diameter results in higher energy transfer efficiency, indicating that the required energy density by more than 50% of the subjects to perceive tactile sensation decreased.

Efficient simulation of heating processes in thermal ablation is of great importance for surgical simulation of thermal ablation procedures. This paper presents a Graphics Processing Unit (GPU) assisted finite element methodology for modeling and analysis of bio-heat transfer processes in the treatment of thermal ablation. The proposed methodology employs finite element method for discretization of the bio-heat equation, and the finite element modeling is implemented using the High-Level Shader Language of the Microsoft Direct3D 11. Simulations and comparison analyses are conducted, demonstrating computational performance improvement of up to 55.3 times using the proposed methodology.

The objective of this study is to explore the feasibility of a compression test for measuring mechanical properties of intact eye lenses using novel parallel plate compression equipment to compare the accuracy of implementing a classical Hertzian model and a newly proposed adjusted Hertzian model to calculate Young’s modulus from compression test results using finite element (FE) analysis. Parallel-plate compression tests were performed on porcine lenses. An axisymmetric FE model was developed to simulate the experimental process to evaluate the accuracy of using the classical Hertzian theory of contact mechanics as well as a newly proposed adjusted Hertzian theory model for calculating the equivalent Young’s modulus. By fitting the force-displacement relation obtained from FE simulations to both the classical and adjusted Hertzian theory model and comparing the calculated modulus to the input modulus of the FE model, the results demonstrated that the classical Hertzian theory model overestimated the Young’s modulus with a proportional error of over 10%. The adjusted Hertzian theory model produced results that are closer to original input values with error ratios all lower than 1.29%. Measurements of three porcine lenses from the parallel plate compression experiments were analyzed with resulting values of Young’s modulus of between 3.2kPa and 4.3kPa calculated. This study demonstrates that the adjusted Hertzian theory of contact mechanics can be applied in conjunction with the parallel-plate compression system to investigate the overall mechanical behavior of intact lenses.

To investigate the hemodynamic effects of partial obstruction to the renal orifice caused by inappropriate stent-graft location. Pre-operative and deployment models of a stent graft with various degrees of obstruction to the renal orifice are constructed based on medical images of abdominal aortic aneurysm. Hemodynamics, including flow pattern, time-averaged wall shear stress (TAWSS), oscillatory shear index (OSI), as well as relative residence time (RRT) are analyzed using numerical simulations. Flow rate distributions are assessed and verified by in vitro experiments. Results show that partial blockage to the renal branch orifice leads to flow recirculation and vortices with low wall shear stress around the renal ostia, whereas OSI and RRT on the renal arteries increase with the degree of obstruction. While the in vitro experiment indicates a decreasing flow rate to the bilateral renal arteries as renal artery ostia are obstructed. In conclusion, obstruction to the renal arteries induced by an inappropriate stent graft location causes stenosis in the renal artery in the long term. This study reveals a possible pathological mechanism of renal complications due to the implantation of a stent graft.

The elevated intraocular pressure (IOP) is one of the important risk factors of glaucomatous optic nerve damage. The deformations of glaucomatous optic nerve head (ONH) due to the elevated IOP might lead to further damage to the optic nerve. The ONH deformations due to the elevated IOP depend on their geometry. Therefore, it is meaningful to investigate the relationship between geometrical parameters and the deformation of ONH. Firstly, the geometrical parameters of ONH were obtained by in vivo using spectral domain optical coherence tomography. Then, individual-specific three-dimensional (3D) models of ONH for glaucoma and normal subjects were established and the deformations of ONH were acquired by using finite element method. Furthermore, the thickness changes of retina and lamina cribrosa were calculated under different IOPs. Finally, correlations between geometrical parameters and the relative deformations of the human ONH were researched by using Spearman correlation. It was found that the relative thickness change of patient’s retina was larger than that of normal subjects under the same condition. The correlation of several parameters, including cup area, and lamina cribrosa depth, with relative deformations of ONH had statistical significance.

The objective of this study was to compare heart rate, blood pressure, and lactic acid level with different recovery methods after having maximal exercise to provide reliable data regarding efficient recovery methods. Heart rate, blood pressure, and lactic acid level were continuously recorded for 30min at 5-min intervals during a recovery period after performing a maximal exercise test based on the Bruce-protocol. Study subjects were 36 healthy men in the 20s. They were randomly assigned to a passive recovery group ($\mathrm{\text{PRG}}=12$ people), a sling exercise group ($\mathrm{\text{SRG}}=12$ people), and a sling exercise with whole-body vibration group ($\mathrm{\text{SWRG}}=12$ people). One-way ANOVA was conducted to compare the recovery effects by using SPSS 18.0 Korea. The statistical significance was accepted at $p<0.05$. Our results revealed that SWRG showed significantly faster heart rate recovery than SRG. Systolic and diastolic blood pressure tended to decrease more in the combined group than the PRG. Thirdly, the lactic acid level decreased to a lower level in the combined group than the PRG.

Flexible needle has been widely used in the therapy delivery because it can advance along the curved lines to avoid the obstacles like important organs and bones. However, most control algorithms for the flexible needle are still limited to address its motion along a set of arcs in the two-dimensional (2D) plane. To resolve this problem, this paper has proposed an improved duty-cycled spinning based three-dimensional (3D) motion control approach to ensure that the beveled-tip flexible needle can track a desired trajectory to reach the target within the tissue. Compared with the existing open-loop duty-cycled spinning method which is limited to tracking 2D trajectory comprised of few arcs, the proposed closed-loop control method can be used for tracking any 3D trajectory comprised of numerous arcs. Distinctively, the proposed method is independent of the tissue parameters and robust to such disturbances as tissue deformation. In the trajectory tracking simulation, the designed controller is tested on the helical trajectory, the trajectory generated by rapidly-exploring random tree (RRT) algorithm and the helical trajectory. The simulation results show that the mean tracking error and the target error are less than 0.02mm for the former two kinds of trajectories. In the case of tracking the helical trajectory, the mean tracking error target error is less than 0.5mm and 1.5mm, respectively. The simulation results prove the effectiveness of the proposed method.

Uniaxial test is easy to access and to obtain accuracy data, but it is difficult to acquire two-dimensional deformation information. We investigated the relationship between the two strain components of corneal strip in uniaxial tests, which is the basis for determining of anisotropic strain energy function of cornea via uniaxial tests. Nine rabbits were taken. The left and right corneas were cut along superior-inferior (SI) and nasal-temporal (NT) direction, respectively. For each strip the uniaxial test was carried out, and the tensile displacements, strip images and loads were recorded. Then the stretching strain, the transversal strains and stress were obtained. Optimization based inverse analysis was utilized to find the best among six fitting models that characterizes the relationship between two strain components in uniaxial tests. All models fitted well the experimental data gathered for corneal strips ($R^2>0.91$). According to the model selection index, the power model achieved the best performance index: 0.1268 for SI strips and 0.1063 for NT strips versus 0.151 (SI strips) and 0.107 (NT strips) found at most by other models. Thus, it is the most suitable one for describing the relationship between the two strain components of corneal strip during uniaxial stretching.

The biokinetic model of Ga-67 evolution was elaborated in this study for the case-control group of canine liver carcinoma via in-vivo gamma camera/8-slice CT technique. One liver carcinoma dog and two normal dogs were anesthetized with the further whole body scanning by a gamma camera to acquire the time-dependent Ga-67 concentration variations among eight compartments, namely: 1. body fluid, 2. liver, 3. GI Tract, 4. kidney, 5. heart, 6. remainder, 7. bladder, and 8. excretion. Each compartment was assumed to have a unique biological half-life and to be connected to other ones. The initial simplification of assigned compartments was performed based on the general-purpose biokinetic model recommended by the ICRP-30 report. Each object/dog underwent eight scans within 72h. The time-dependent empirical data were normalized to the maximal counts/pixel/sec and then integrated with the theoretical estimates, in order to optimize the correlations among compartments. A self-developed program run in MATLAB was used to reflect the actual performance acquired from the gamma camera scanning, while the dimensionless agreement (AT) was applied to assess the discrepancies between empirical and theoretical results. An AT of zero implies a perfect agreement between the theoretical and empirical results, while AT under 20 indicates an excellent consistency between the optimal computational and empirical data, whereas a wide fluctuation of the obtained ATs in the range of 7%–60% corresponded to a medium range of data disagreement in this study. The liver carcinoma dog has revealed a longer biological half-life than normal dogs in the limited range (40 versus 35 or 15h). However, the quantified data for other compartments and branching ratios among compartments provided a quite robust substantiation for constructing the biokinetic model of Ga-67 being administrated in the canine hepatic survey.

Functional mitral regurgitation (FMR) occurs following left ventricle (LV) dysfunction with normal mitral valve (MV) leaflet. The progress and severity of FMR are closely related to LV dilatation, which often results in displacement of the papillary muscles (PMs) and enlargement of the mitral annulus. We investigated the effect of PM displacement and annular dilation on FMR development to better understand the complex intercorrelation between these pathologic alterations leading to FMR. Virtual MV modeling was performed to create a normal human MV, and several different types of PM displacement, annular dilation, and the combination of PM displacement and annular dilation mimicking the pathology of FMR were modeled. Dynamic finite element evaluation of MV function was performed across the complete cardiac cycle for the normal and FMR MV models. PM displacement to both lateral and apical directions revealed markedly reduced leaflet coaptation and large stress distribution in the P2 scallop. Annular dilation greater than 2% demonstrated the occurrence of leaflet malcoaptation and increased stresses near the anterior saddle-horn region. The pathologic MV model with annular dilation combined with PM displacement provides physiologically realistic biomechanical characteristics as the MVs having FMR. Simulation-based biomechanical evaluation of MV pathology related to LV chamber dilatation provides an excellent tool to better understand the pathophysiologic mechanism of FMR.