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Mechanical environment plays an important role in the growth of cells, tissues and organs, in the study of mechanobiology and tissue engineering, and loading bioreactor acts as the basic platform. We developed a combined multi-functional bioreactor based on linear motor, and studied on the loading performance of different modules and loading methods. In the rolling / sliding loading module, in the effective distance for 50mm case, the bioreactor frequency is 0.01Hz to 0.3Hz. Under tensile and compressive loading module, the minimum amplitude of the bioreactor can reached 0.01mm while the frequency can reach 10Hz. Under the impact test module, in the effective distance for 50mm case, acceleration a=54.16m/s2 can be realized. In the high acceleration cyclic loading module, acceleration 8Gcan be realized. The combined multi-functional bioreactor provides conditions for the study related mechanobiology and tissue engineering.

Craniotomy, as a part of neurosurgery, implies a safe opening of the skull with mechanical equipment. Grinding is a traditional machining method that can accurately and efficiently remove bone tissue. Aiming at low-damage and high-efficiency bone grinding, this study analyzed the kinematic law of a single abrasive grain during the grinding process. The theoretical model of grinding force was established based on the calculation of specific energy and friction force. The grinding test platform was set up, and the full factorial experimental design was performed to link the grinding force evolution with different processing parameters. The experimental results obtained on porcine femurs validated the model predictions where the grinding force grew with feed speed and grinding depth; it exhibited a decreasing trend with rotation speed, followed by increasing one. [ABSTRACT FROM AUTHOR]

The periodontal ligament (PDL) exhibits different material mechanical properties along the long axis of the teeth. To explore the creep and the relaxation effects of dissimilar layers of PDL, this paper took the central incisors of porcine mandibular as experimental subjects and divided them perpendicular to the teeth axis into five layers. Creep experiments and relaxation experiments on five layers were conducted to obtain the creep compliance and relaxation modulus at different layers. Linear elastic model, generalized Kelvin model, and generalized Maxwell model were used to describe the major characteristics of the PDL: Instantaneous elasticity, creep and relaxation. Fitting accuracy of three-parameter, five-parameter, and seven-parameter of the model was compared, and the constitutive equations of different layers were established by the least square method. The results presented that the creep strain and the relaxation stress of PDL were exponentially correlated with time under different loading conditions. Different layers showed a significant effect on the creep strain and relaxation stress of PDL. Along the long axis of the teeth, the changing rule of the creep compliance and relaxation modulus of each layer showed quite the contrary, and the instantaneous elastic modulus first decreased to the minimum, then increased to the maximum. Higher instantaneous elastic modulus led to lower creep compliance and higher relaxation modulus. The generalized Kelvin model and the generalized Maxwell model well characterized the creep and relaxation properties of PDL. Fitting accuracy increased with the number of model parameters. The relaxation time of PDL was about one order of magnitude shorter than the creep retardation time, which indicated that the relaxation effect lasted shorter than the creep effect. [ABSTRACT FROM AUTHOR]

Objective To research the mechanical properties of magnesium alloy degradation affected by mechanical environment. Methods: After being divided into 4 groups randomly such as No.1, 2, 3 and 4,12 AZ31 magnesium alloy screws need suspending in the vessels containing 35ml simulated body fluid. No.1 was control group. Group 1 was under no load condition, experimental group 2, 3, and 4 were discontinuously applied fixed axial compression load of 30N, 60N, 90N respectively on time. The weight loss of magnesium alloy screws and the amount of gas generated were measured regularly. Results: From the cumulative amount of hydrogen production, group 1 and group 4 were relatively large, whereas group 2 and group 3 were relatively small. From the weight loss of magnesium alloy screws, group 3 > group 4 > group 2 > group 1. Conclusions: The general trend is the greater the load, the faster the degradation.

Bone surgery is a complex process involving sustainable and healthy human recuperation, but poor surface quality and loose implant fixtures can affect the recovery time of orthopedic patients. However, it has been demonstrated that the application of ultrasonic vibration during drilling procedures can improve the success of bone remediation procedures. The focus of the present paper was on the investigation of surface quality and pullout strength of drilled holes. After analyzing the special kinematic characteristics of the ultrasonically-assisted drilling (UAD), UAD testing using fresh cortical bone was carried out and compared with the results obtained after conventional drilling (CD) procedures. Surface roughness measurements and microscope examination were used to evaluate surface quality, and an electro-mechanical tensile machine was used to measure pullout resistance. The test findings indicated that surface roughness was reduced by 17–68.7% when using UAD; the axial pullout strength of screws inserted into UAD holes was significantly increased by 4.28–30.1% compared to that of CD. It was found also that low spindle speeds and high feed rates reduced surface quality and the stability of the inserted cortical screws. The findings demonstrated that UAD produced better surface quality and higher pullout strengths, which could provide greater stability for implants and improved post-operative recovery. [ABSTRACT FROM AUTHOR]

BACKGROUND: Domestic and foreign scholars have done a lot of researches on the stress of articular cartilage under different mechanical environments and cyclic compressive loads, but they mainly studied the effect of cartilage under the cyclic compressive load. Studies on the effects of age factor on the mechanical properties of cartilage and studies regarding the properties of cartilage in complex stress environments are not exhaustive. OBJECTIVE: To investigate the effects of different rolling load conditions on the ratcheting behavior of adult and juvenile articular cartilage. METHODS: Adult cartilage and juvenile cartilage were used as experimental objects, and the load was applied by a rolling load device under different experimental conditions (compression: 10%, 20%, 30%; rolling rate: 1.66, 3.44, 6.68 mm/s; defect width: 1, 2, 4 mm). At the same time, non-contact digital technology was used to collect the sample during the loading process, and the cyclical pressure was studied by analyzing and processing the image. The ratcheting behavior of adult and juvenile articular cartilage was studied under rolling load. RESULTS AND CONCLUSION: Under rolling load, the ratcheting strain of adult cartilage and juvenile cartilage showed a rapid increase followed by a slow increase tendency with the rolling load. With the increase of compression, the ratcheting strain of adult cartilage and juvenile cartilage increased. At the same amount of compression, the ratcheting strain of juvenile cartilage was greater than that of adult cartilage, and their ratcheting strain gradually decreased from the surface layer to the deep layer along the depth of cartilage. As the rolling rate increased, the ratcheting strain of adult cartilage and juvenile cartilage decreased. The ratcheting strain values and trends of 1 mm microdefect articular cartilage were similar to those of intact articular cartilage. Under the condition of 2, 4 mm defect, the ratcheting strain value of the defected cartilage was higher than that of the intact cartilage. [ABSTRACT FROM AUTHOR]

BACKGROUND: Once the articular cartilage has a crack defect, its mechanical properties will change. In previous studies, the investigation of damaged articular cartilage mostly focused on compression, and there were few studies on tensile properties. OBJECTIVE: To measure the uniaxial quasi-static tensile properties by preparing crack defects on the cartilage layer samples. METHODS: The articular cartilage of the fresh adult pig knee joint was selected to prepare a cartilage specimen containing a crack defect. The tensile properties were tested at different stress rates (0.001, 0.01 and 0.1 MPa/s) and the creep properties were tested under different constant stresses (1, 2 and 3 MPa). RESULTS AND CONCLUSION: (1) In the tensile test at different stress rates, as the stress rate increases, the stress required to reach the same strain increased gradually, and the Young's modulus of the test piece increases with the increase of the stress rate. (2) The tensile stress-strain curves of the articular cartilage with cracks at different stress rates did not coincide, indicating that the tensile properties of the articular cartilage with crack defects are rate-dependent. (3) In the creep experiment under different constant tensile stress levels, the creep strain increased with the increase of the tensile stress level, the creep compliance decreased with the increase of the tensile stress level, and with the creep time. The creep strain increased rapidly and then increased slowly. (4) To conclude, different stress rates and different constant stresses have great influence on the tensile mechanical properties of articular cartilage with crack defects. The experimental results provide a mechanical reference for the repair of defective articular cartilage. [ABSTRACT FROM AUTHOR]