Journal of Mechanics in Medicine and Biology

The objective of this study was to establish an ovine model for CH-VAD (CH Biomedical Inc., JiangSu, China) implantable ventricular assist device (IVAD) to evaluate experimental protocols, including anesthesia management, surgical process, autopsy criteria and a validated anticoagulation procedure. Method: IVAD was implanted into the chest of sheep without stopping the beating heart through a left thoracotomy, and the inflow cannula was connected to the left ventricular apex and the outflow cannula was anastomosed to the descending aorta. Results: Totally 23 cases were established: 6 died of an anaesthetic or surgical reasons, one died of lung infection, the other 16 cases survived for more than 15 days, among which four cases were terminated because of decrease of pump flow and the other 12 cases survived for more than 30 days. Conclusions: Sheep models suitable for implantation of CH-VAD implantable LVAD were successfully established and the appropriate safety evaluation indicators of this model were validated in the course of the animal experiments, and the survival rate of the experiments were improved gradually over time.

Knee joints play an indispensable role in the activities of daily living. In particular, the knee joints of the elderly and the physically challenged require continuous care in order to ensure a healthy daily life. This study proposes a health monitoring system for knee joints, which is able to classify lower extremity movements using the angle and acceleration components of these joints. The proposed monitoring system consists of a wearable frame placed on the knee joint, consisting of a sensor part for monitoring the knee joint angle and acceleration and a wireless communication part for transferring bio signals to a smart device. Knee joint angles and accelerations are measured using potentiometers installed at the hinges of the upper and lower parts of the wearable frame and an inertial sensor (IMU) attached to the thigh. Data thus measured are transferred via Bluetooth to an application on a smart device. The proposed system incorporates a classification algorithm for lower extremity movements, which can distinguish users’ actions such as sitting, lying, and standing by using real-time measurements of knee joint angles and accelerations. This study shows that the proposed monitoring system detects postures that negatively affect knee joints and informs a user when these postures are adopted, thereby helping to maintain healthy knee joints.

According to the mechanical conditions of fracture fixation and the oxygen levels in the tissues, a simulation model of fracture healing process was built to describe the relationship among mechanical stability, oxygen levels in tissues and tissue differentiation during the second fracture healing. Different from the previous simulation model, in this paper, we took the three-dimensional model as the research object, solved the mechanical stimulation by finite element method, established the partial differential equation to solve the spatial and temporal variation of the oxygen in tissues. The process of tissue differentiation was described by fuzzy control method. The initial stage of fracture healing, intramembranous ossification, chondrogenesis, cartilage calcification and endochondral ossification during the fracture healing process were simulated, and the properties of tissue materials were continuously updated to complete the iterative process. The simulation program of fracture healing process was independently developed in Eclipse environment, and the simulation results were compared with experimental data and those of other fracture healing simulation models to verify the simulation program in this paper. Finally, the processes of transverse fracture healing in rats with different axial stability under normoxic, hypoxic and hyperoxic conditions was simulated, and the effects of different tissue oxygen levels and interosseous stabilities on fracture healing were analyzed. It is concluded by simulation that the delayed healing or non-union of bone will occur when in state of tissue hypoxia or interosseous instability, normal healing will occur when in state of tissue normoxia, and the healing will be accelerated when in state of tissue hyperoxia.

Objective: To optimize the minimum detectable difference (MDD) of a cardiac X-ray imaging system using the Taguchi L₈(2⁷) analysis and a precise line pair (LP) gauge. Methods: The optimal combination of the four critical factors of the cardiac X-ray imaging system, namely X-ray focus, kilovoltage (kVp), milliamper-seconds (mAs) and source image distance (SID), providing the MDD was calculated via the Taguchi analysis and experimentally verified. Two (low and high) levels were assigned for each factor, and eight combinations of four factors were used to acquire instant X-ray images using an NDT commercial LP gauge (with a gauge length of 64mm and a width of $3.5$mm). The latter had five lines and was split gradually from top to bottom for the inspection of X-ray images, whose quality was ranked by three well-trained radiologists according to the double-blind criterion. The ranking grade was given by sharp contrast, low noise and precision to distinguish the LP. Accordingly, the MDD was derived to represent the spatial resolution of instant X-ray images by the revised Student’s $t$-test analysis. The optimal combination of factors was experimentally identified and clinically verified in the follow-up inspections. Results: For the conventional setting, Group No. 7 (which obtained the highest grade among eight groups) and the optimal setting, the obtained MDD values were $0.183$, $0.167$ and $0.157$mm, respectively, while the LP (line pair/mm) interpolated from the gauge scale amounted to $2.7$, $3.1$ and $3.2$LP/mm, respectively. Conclusion: The Taguchi L₈ analysis was proved to be instrumental in optimizing the cardiac X-ray imaging system MDD and is recommended to be used jointly with the revised Student’s $t$-test analysis for improving the spatial resolution of instant X-ray images.

The purpose of this study was to compare the ankle joint moments in different foot strike patterns during stair descent and to find a better strategy. Methods: Twenty young subjects participated in this study. Subjects performed two trials of descending stairs in rearfoot strike (RFS) and forefoot strike (FFS) strategies. Kinematic and kinetic data were measured by a motion capture system and force plates. Ankle joint moments, ground reaction forces, and moment arms in three planes of motion were calculated from the measured data. The root-mean-squared means of ankle joint moments, ground reaction forces, and moment arms were compared between different foot strike patterns for each phase of stair descent (weight acceptance, forward continuance, and controlled lowering). Results: In the weight acceptance phase, FFS showed greater ankle joint moments than RFS in all three (dorsi/plantar-flexion, inversion/eversion, and internal/external rotation) directions ($p<0.01$). In the forward continuance phase, FFS showed greater dorsi/plantar moments than RFS ($p<0.05$). In controlled lowering phase, FFS showed smaller dorsi/plantar moments than RFS ($p<0.01$). Discussion: The greater ankle joint moments of FFS in the weight acceptance phase were influenced by both the greater GRF magnitudes and greater moment arms. The greater dorsi/plantar moments of FFS in the forward continuance phase and the smaller dorsi/plantar moment of FFS in the controlled lowering phase were dominated by the greater moment arm and the smaller ground reaction force, respectively. RFS strategy resulted in smaller ankle joint moments in the majority of stair descent phases (weight acceptance and forward continuance), therefore, RFS would be a better strategy than FFS for stair descent in terms of ankle joint load.

Material mechanical behavior plays an important role in pelvic complex simulation under lateral impact. Aiming to investigate effects of material model selection on the responses of lateral impact simulations, a seating pelvic complex model was constructed. The model was subjected to a series of impacts at velocity of 3–10m/s, and two material models were, respectively, assigned to the pelvic bone to evaluate the accuracy of the simulation. The results showed that the pelvic response and fracture pattern with plastic–elastic material model agreed well with the literature, while linear elastic material model was dissatisfied factory, especially the pelvic response at low velocity deviated from most cadaveric test data. In addition, drastic change of arterial pressure was responsible for hemorrhages associated with pelvic fracture. Ligament loading sequence verified that the posterior pelvic ring bore the greatest amount of load during the impact. Based on the above findings, we concluded that a plastic–elastic with strain rate effect material model can improve the simulation accuracy of pelvic complex under lateral impact, and pelvic fracture pattern may help to estimate the parameters’ selection in impact simulation.

Patients with scans without evidence of dopaminergic deficits (SWEDDs) show symptoms (e.g., tremors) similar to those of Parkinson’s disease (PD) patients, so they are often misdiagnosed. Sensory electrical stimulation (SES) was reported to suppress essential tremor in patients, but SES was never applied to patients with PD and SWEDDs. As the pathophysiological mechanisms of PD and SWEDDs are likely to be different, we hypothesized that the effect of SES would also be different in the two patient groups. This study aimed to test that hypothesis. Fourteen patients with PD and nine with SWEDDs participated in this study. Three wrist muscles were stimulated for 15s using SES with a stimulation intensity lower than the motor threshold. Angular motion of the index finger was measured via a triaxial gyrosensor before, during, and after stimulation. Outcome measures included the amplitude and peak frequency of the angular motion of the index finger. Tremor amplitude decreased during and after SES in patients with PD ($p<0.05$). However, tremor amplitudes during and after SES were not different from the base level in SWEDDs patients. The peak frequency of tremors temporarily decreased during stimulation in PD patients, but not in SWEDDs patients. SES suppressed tremors in patients with PD, but not with SWEDDs. The results could help understand the pathophysiological differences of tremors between PD and SWEDDs.

Three kinds of collision reaction strategies for increasing safety during human and robot interactions without relying on torque sensors are proposed in this paper. In the proposed algorithms, motor torque is estimated by driver current. The generalized momentum observer is used for collision detection, which does not need joints acceleration information and calculates the inverse of the inertia matrix. Three different collision reaction strategies, going away, dragging by hands and mechanical impedance developed in this paper, aim to enhance safety to humans during physical interaction with robots. For verifying the efficiency of the proposed algorithms, experiments are tested between a 1-DOF manipulator system and a human being. At last, the experiments’ results show that the proposed collision reaction algorithms are effective.

In the current prostate biopsy procedure, it is necessary for the doctor to hold the ultrasonic probe during the entire process. This increases the fatigue degree of the doctor, and the motion of the ultrasonic probe is more likely to cause damage to the anus of the patient. A medical device that can assist doctors in prostate scans and biopsy puncture devices was developed. We focused on the passive interlocking transrectal ultrasonic probe posture adjustment mechanism. Based on the posture adjustment mechanism, a passive interlocking transrectal ultrasound probe position and posture adjustment mechanism capable of assisting the doctor in prostate scanning and puncture intervention was designed. The passive interlocking posture adjustment mechanism with a seven-degree-of-freedom (DOF) interlocking mechanism was designed and can meet the requirements of doctors. The physical prototype of the passive interlocking transrectal ultrasonic probe posture adjustment mechanism was developed and commissioned. The locking torque and braking torque of the mechanism were measured. The results showed that the ultrasonic probe can achieve reliable locking and effectively meet the operation requirements.

Reduced muscle strength is an important fall risk factor. The fall occurs more in elderly women than in elderly men. The aim of this study is to investigate muscle strength and the ability to generate rapid torque for knee joint in elderly men and women. Twenty healthy elderly participants (10 men and 10 women) performed maximal voluntary knee extension and flexion during concentric, isometric and eccentric conditions. The peak torque and rate of torque development (RTD) was normalized by each subject’s body mass. Independent $t$-tests were employed in the comparison of elderly women with elderly men. Elderly women exhibited weaker isometric flexion and eccentric extension strength compared to elderly men ($p<0.05$). Although there was no significant gender difference in isometric extension peak torque, RTD of elderly women was slower than it of elderly men ($p<0.05$). In contrast, no significant gender differences were observed in concentric contraction condition ($p>0.05$). These results indicate that the deteriorated RTD as well as muscle strength per body mass may be associated with a higher frequency of falls in elderly women than in elderly men. This study suggests that training of specific-contraction type should be considered for fall prevention in elderly women.

The trajectory linearization control (TLC) was applied to design an autonomous nonlinear trajectory tracking controller for a novel rehabilitation exoskeleton shoulder joint in this paper. TLC is a relatively new control method which was applied in aircraft and mobile robot, which had good performance on real-time trajectory tracking, anti-jamming and universality. As a new application in the exoskeleton shoulder joint controller design, the controller in this research contained two loops that separately based on the inverse kinematics and pseudo-inverse dynamics models of the exoskeleton shoulder. Two PI controllers as the error regulator can reduce the tracking error. The position and angular velocity error feedback were employed to constitute the closed-loops. Since the controller was based on model and linearization, it can adapt to both linear and nonlinear control processes. The simulation of three different trajectories for single degree of freedom movement of shoulder joint (shoulder flexion and extension, abduction and extension), and the movement of both the two degrees were given. The simulation results showed that the TLC controller can follow the exoskeleton shoulder trajectory steadily and accurately.

A post-and-core crown is widely used in prosthetic dentistry; however, in clinical treatment, it easily causes root fracture and tooth penetration. To address these problems, this study aimed to present a customized post-and-core design for the posterior tooth implant. First, a residual tooth and its root canal were reconstructed. Then, the root canal surface was extracted, the surface curvature and length parameters were defined, and the customized post-and-core design was developed. Finally, the tooth, root canal, and post-and-core with different implant lengths in five masticatory directions were analyzed using finite element analysis to evaluate the stress distribution. The results showed that, with the similar shape of the post-and-core structure and the root canal, the tooth stress trend was uniform. When the length of the post-and-core structure $L$ was 0mm, that is, it was two thirds of the root canal length, the root canal stress was minimum. Therefore, the customized design of the post-and-core structure could well adapt to any kind of root canal, and the length of the post-and-core structure $L$ provided guidance for the post-and-core crown prosthesis in clinic.

Lower-limb exoskeletons are an effective means to provide paraplegic and hemiplegic individuals with the ability to walk upright. A lot of studies about lower-limb exoskeletons have been developed to assist the impaired populations. However, the existing devices are still too technically complex and expensive for practicality. In this paper, a compact lower-limb exoskeleton for walking assistance is developed, in which a steel-cable actuator is specially designed. In order to accomplish the different tasks presented to gait generation, a control method with multiple stages is employed. In this approach, four basic states and seven intended motions are designed for the finite-state machine. In addition, the reference trajectories of these intended motions are presented and fitted by a modified first-order polynomial-fitting method. Preliminary motion tests of the exoskeleton with three healthy subjects are performed. The results verify the effectiveness of the system design and the gait-generation approach proposed in this paper. The overall exoskeleton system is compact and the corresponding operations are convenient and reliable.

Glaucoma is considered a group of neurodegenerative diseases that damage the optic disc and result in a reduction of the field of vision. High intraocular pressure-induced deformation of optic nerve head (ONH) may compress the optic nerve and affect axonal transport. This study aims to show experimental observations: the activated astrocytes under high intraocular pressure play an important role in compression of optic nerve and block of axonal transport. Four-week duration of ocular hypertension (more than 20mm Hg) rats induced by cauterizing of three episcleral vessels and administering a fluorouracil subconjunctival injection in the right eye were enrolled and the left eyes of all the rats were used as a self-control. The axonal transport of the optic nerve was examined by a confocal laser scanning microscope after intravitreally injecting rhodamine-$\beta$-isothiocyanate. The morphology of the optic nerve head was examined by hematoxylin–eosin (HE) staining, immunofluorescence staining and transmission electron microscopy (TEM). The results showed transport of rhodamine-$\beta$-isothiocyanate was blocked in the experimental group, and fluorescent dye accumulated around the ONH. The nucleus counts of the coronal section kidney-shaped area showed that the number of cell nucleus in experimental eye was more than that of the control according to the results of HE staining. The increased collagen fibers in ONH were observed. The density of the glial fibrillary acidic protein in experimental eyes was a little bit higher than that in the control group by quantify analysis of the expression. The obvious changes of microstructure of the ONH also were found according to the images of TEM. It can be concluded that the activated astrocytes might squeeze the optic nerve, likely leading to optic nerve distortion and axonal flow blockage.

Hearing loss is becoming increasingly common due to the aging of society and the development of multimedia devices. Hearing loss is classified by hearing level, and patients require early diagnosis and rehabilitation. To overcome hearing loss, hearing aids are used, but conventional hearing aids have disadvantages that reduce the efficiency of speech transmission. In this paper, we proposed a subminiature ultrasonic transducer with a miniaturized parametric speaker. The transducer generates sound waves with high directionality. These sound waves are focused on the umbo located the center of the tympanic membrane and connected to ossicles of the middle ear. To generate sound waves, various parameters are considered, such as target distance, radiation area, and primary frequency. We tested the directionality of the proposed transducer using extracted parameters at audible frequencies. As a result, we confirmed high directionality and audible sound generated by the proposed transducer. The method can be expected to be applied to high-efficiency hearing rehabilitation devices and various multimedia devices.

Biokinetic model of Tc-99m MIBI for eight patients undergone myocardial perfusion examination was studied using gamma camera and MATLAB program. A six-compartment model was adopted to interpret the metabolic mechanism of each patient. Within the model framework, the respective set of simultaneous differential equations was solved by a self-developed program run in MATLAB. The experimental results exhibited a good fit with the theoretical predictions via the model. The average biological half-lives of body fluid, heart, thyroid, liver, GI Tract and remainder were assessed as $3.3\pm 1.1$, $0.6\pm 0.3$, $0.2\pm 0.2$, $11.7\pm 0.0$, $0.4\pm 0.2$, and $18.3\pm 1.1$h, respectively. A dimensionless AT index of disagreement between the experimental data and MATLAB optimal solution was proposed of validating the applied acquisition system and analytical method feasibility. An AT of zero implies a perfect agreement between the theoretical and empirical results, while averages of the derived AT were fluctuated from 3 $\pm$ 2 to $25\pm 18$ for five compartments. The proposed refined equation estimated the internal dose from gamma-ray as $3.38\pm 2.58$mSv for eight patients according to a fast screening method, which defined human body as a spherical ball to simplify the calculation in reality. The proposed MATLAB-based fitting of in-vivo data with the theoretical results was instrumental for assessing the radiation dose received by the Tc-99m MIBI scan participants.

The purpose of this study was to find a foot strike strategy that can reduce the ankle joint load during stair ascent by comparing the ankle joint load in two strategies of initial contact during stair ascent. Twenty young subjects performed ascending stairs with two strategies, i.e., rearfoot strike (RFS) and forefoot strike (FFS). Kinematic data was measured from 12 cameras and the ground reaction force was measured by a force plate inserted in the second step of four-step stairs. Stance phase was divided into three phase, i.e., weight acceptance, pull up, and forward continuance. Four ankle related kinetic variables were derived from the measured data, i.e., joint reaction force, moment, and the magnitude and moment arm of ground reaction force. Root-mean-square (RMS) was used as the representative value of the variables during each phase was compared between strategies. In the weight acceptance phase, FFS resulted in greater values of all four kinetic variables than RFS. For the pull-up and forward continuance phases, joint reaction force and ground reaction force were not different between strategies but joint moment and moment arm was greater for FFS than RFS. In weight acceptance phase, greater ground reaction forces and longer moment arm of FFS may have resulted from faster weight transfer to the ipsilateral foot and the more anterior location of center of pressure, respectively. Both have contributed greater joint moment of FFS. In pull-up and forward continuance phases, greater ankle moment of FFS was affected mainly by longer moment arms, which may reflect the persistent farther location of center of pressure from the ankle joint. The results suggest that RFS would be more advantageous than FFS in terms of ankle joint load.

The result of collision detection is closely related to the further deformation or cutting action of soft tissue. In order to further improve the efficiency and stability of collision detection, in this paper, a collision detection algorithm of bounding volume hierarchy based on virtual sphere was proposed. The proposed algorithm was validated and the results show that the detection efficiency of the bounding volume hierarchy algorithm based on virtual sphere is higher than that of the serial hybrid bounding volume hierarchy algorithm and the parallel hybrid bounding volume hierarchy algorithm. Different collision detection algorithms were tested and the results show that the collision detection algorithm based on virtual sphere has high detection efficiency and good stability. As the number of triangular patches increased, the advantage was more and more obvious. Finally, the proposed algorithm was applied to two large and medium-sized virtual scenes to implement the collision detection between the vastus lateralis muscle, thigh and surgical instrument. Based on the virtual sphere, the collision detection algorithm of bounding volume hierarchy can implement efficient and stable collision detection in a virtual surgery system. Meanwhile, the algorithm can be combined with other acceleration algorithms (such as the multithread acceleration algorithm) to further improve detection efficiency.

Electric wheelchairs developed so far have difficulties for elderly people to use, because of their bulkiness and heavy weight. To address this problem, this study presents a design for the construction of an electric wheelchair with an application of light duty materials at frame and a foldable structure that can be easily loaded in a narrow space. A structural analysis was performed to evaluate the structural safety of the foldable wheelchair. For the purpose of analysis, a carbon composite was used as the material for the frame; Structure Mechanics Module of COMSOL Multiphysics was used as the analysis software; and for the boundary condition, the lower part of the body frame was fixed, and a load of 150kg was applied to the upper part of the wheelchair. According to the results of the structural analysis, a maximum displacement of 2.869mm occurred at the handle where the carbon composite was applied, and tensile and compressive stress of 103MPa and 107.3MPa, respectively, were measured at the seat part of the wheelchair where the load was applied. The safety factors were 7.5 and 5.5 for tensile stress and compressive stress, respectively. A maximum variation of 0.0872mm occurred at the aluminum wheel shaft, and a maximum variation of 0.2046mm occurred at the joint. The maximum stress was 116.3MPa that corresponded to a safety factor of 2.66; this indicates that the wheelchair can be considered to be structurally safe as the safety factor exceeds the initial target of 2.

Single crouch walking gait (SCWG) is one of the main walking gaits when one of the legs is injured. However, the research on movement biomechanical characteristics (MBC) of lower extremity in SCWG has not been reported. So, the aim of this study is to analyze kinematics and main muscle fatigue damages of lower extremity in SCWG. Gaits data were collected with functional assessment biomechanics (FAB) system which applies the real-time wireless gait phase detection system, the movement function relations of joints of lower extremity were obtained by fitting the collected data in normal walking gait (NWG) and SCWG with Fourier series, the fitted movement functions were input to 3D human musculoskeletal model as driving functions for human movement to analyze the differences of MBC between SCWG and NWG. Finally, the muscle contractions were used to evaluate muscle fatigue damage. Compared with NWG, the result shows that the movement range of the joint angles of lower extremity are reduced in SCWG, the change law of hip internal/external rotation angle (IERA) has a significant difference, and the change laws of other joint angles are similarly between SCWG and NWG. The muscle contractions of Gluteus maximum (GMAX) 2, Gluteus meddle (GMED) 1, GMED2, Iliacus (ILI), Rectus femoris (RFEM), Soleus (SOL), Gastrocnemius (GAS) and Vastus lateralis (VLAT) are significantly larger in SCWG than in NWG (except GlutMed2 which is about 20–40% and VLAT which is about 63.8–76.1% of gait cycle), namely, these muscles easily cause muscle damages in SCWG. The contraction change of Adductor magnus (AMAG) is dispersed, so AMAG is prone to muscle fatigue in SCWG. The study results will fill in the gaps in the MBC of lower extremity in SCWG and provide data for Rehabilitation Medical Technology (RMT) and development of rehabilitation equipment of lower extremity.