Previous studies found that the peripheral cutting edge and end cutting edge in micro end milling had different cutting phenomena considering the size effect in micro cutting processes. This paper is a further study on this point considering different workpiece materials and cutting edge radii. Finite element simulations have been conducted to determine the minimum undeformed chip thickness (MUCT) by the chip morphology and the results are verified by micromilling experiments. Both the simulations and experiments show that the MUCT of the peripheral cutting edge and the end cutting edge are different even if the cutting edge radii remain unchanged. The MUCT is directly proportional to the cutting edge radius. Material properties also have some effects on the MUCT of the peripheral cutting edge. But it has limited effects on that of the end cutting edge. The results indicate that the feed engagement other than the axial depth of cut should be carefully selected in micro end milling when considering different workpiece materials.

Studying the vibration behavior of the entire spine can guide the design of seat comfort and vibration safety. However, due to simplification of traditional biomechanical models, very few studies have analyzed in detail the vibration behavior characteristics of the entire spine inside a seated human body. Therefore, this study aimed to provide guidance and reference for spinal modeling and biomechanical research in ergonomics. A developed finite element model of three-dimensional seated human body was validated and adjusted based on anatomical data of human spine in detail. Static analysis, modal analysis and random response analysis (under vertical excitation between 0 and 20 Hz at 1 m/s² r.m.s.) were conducted. The range of motion, modal frequencies and the tri-axial transmissibility of the developed models matched well with experimental results. In the vertical resonance mode, the entire spine contained both vertical deformation (60% of the total) and vertical displacement (40%), in addition, the cervical spine, especially the lumbar spine, also contained bending deformation which could alleviate the impact, but led to complex alternating stresses, increasing the risks of the spinal injuries under vertical whole-body vibration. From the bottom to the top of the spine, the frequency distribution of vertical transmissibility became steeper, the peak value increased, and the number of peaks decreased. This study provided new insights into the vibration behavior and frequency response of the entire spine inside a seated human body for improving seat comfort and vibration safety.

Cardiovascular disease is the leading cause of death worldwide. Traditional autologous transplantation has become a severe issue due to insufficient donors. Artificial blood vessel is an effective method for the treatment of major vascular diseases, such as heart and peripheral blood vessel diseases. However, the traditional single-material printing technology has been unable to meet the users’ demand for product functional complexity, which is not only reflected in the field of industrial manufacturing, but also in the field of functional vessel-like structure regeneration. In order to achieve the printing and forming of multi-layer vessel-like structures, this paper carries out theoretical and experimental research on the printing and forming of a multi-layer vessel-like structure based on multi-material 3D bioprinting technology. Firstly, theoretical analysis has been explored to research the relationship among the different parameters in the process of vessel forming, and further confirm the synchronous relationship among the extrusion rate of material, the tangential speed of the rotating rod, and the movement speed of the platform. Secondly, sodium alginate and gelatin have been used as the experimental materials to manufacture the vessel-like structure, and the corrected parameter of the theoretical analysis is further verified. Finally, the cell-loaded materials have been printed and analyzed, and cell viability is more than 90%, which provides support for the research of multi-layer vessel-like structure printing.

Vascular replacement is one of the most effective tools to solve cardiovascular diseases, but due to the limitations of autologous transplantation, size mismatch, etc., the blood vessels for replacement are often in short supply. The emergence of artificial blood vessels with 3D bioprinting has been expected to solve this problem. Blood vessel prosthesis plays an important role in the field of cardiovascular medical materials. However, a small-diameter blood vessel prosthesis (diameter < 6 mm) is still unable to achieve wide clinical application. In this paper, a response surface analysis was firstly utilized to obtain the relationship between the contact angle and the gelatin/sodium alginate mixed hydrogel solution at different temperatures and mass percentages. Then, the self-developed 3D bioprinter was used to obtain the optimal printing spacing under different conditions through row spacing, printing, and verifying the relationship between the contact angle and the printing thickness. Finally, the relationship between the blood vessel wall thickness and the contact angle was obtained by biofabrication with 3D bioprinting, which can also confirm the controllability of the vascular membrane thickness molding. It lays a foundation for the following study of the small caliber blood vessel printing molding experiment.