Three-dimensional (3D) printing is a novel promising technology based on 3D imaging and layer-by-layer additive fabrication. It has a profound influence on all aspects of our lives and is playing an increasing important role in many areas including engineering, manufacturing, art, education and medicine. “3D bioprinting” has been put forward with the technical progress in 3D printing and might be a possible way to solve the serious problem of human organ shortage in tissue engineering and regenerative medicine. Many research groups flung them into this area and have already made some gratifying achievements. However, it is a long way to fabricate a live organ. Many elements lead to the limitation of 3D bioprinting. This review introduces the background and development history of 3D bioprinting, compares different approaches of 3D bioprinting and illustrates the key factors of the printing process. Meanwhile, this review also points out existing challenges of 3D bioprinting and has a great prospect. Some points proposed in this review might be served as reference for the research of this field.

Conventional industrial robots are unable to guarantee the inherent safety when working together with humans due to the use of rigid components and the lack of force sensation. To enhance the safety of human-robot collaboration (HRC), the new collaborative robot skin (CoboSkin) with the features of softness, variable stiffness and sensitivity is designed and studied in this paper. The CoboSkin is composed of an array of inflatable units and sensing units. The sensing units made of soft porous materials are capable of measuring distributed contact force in a real-time manner. By leveraging the foaming process, the sensing units are interconnected with inflatable units fabricated by the elastomer of which the deformation is limited by the textile wrapped around it. Variation of stiffness is enabled by adjusting the internal air pressure supplied to inflatable units, thereby changing the sensitivity of the sensing units and reducing the peak impact force. Soft porous materials endowed the CoboSkin with increased sensitivity, minimal hysteresis, excellent cycling stability, and response time in the millisecond range, which enabled sensing feedback for controlling a robot arm at different levels of stiffness. Finally, the validation of the CoboSkin for safer HRC was conducted with a robot arm to detect an unintended collision, illustrating its potential application in robotics.

High-speed on / off valve (HSV) has been widely concerned in the field of hydraulic engineering, mainly focusing on improving its dynamic characteristic. However, relatively little attention is paid to the adjustment of HSV switching characteristic, which limits the applications of HSVs in some specific systems. Therefore, an advanced pulsewidth modulation (PWM) control algorithm is proposed in this article to change the dynamic behaviors of the experimental HSV and makes it adjustable in a wider scope to adapt to more applications. Applying the voltages of opening preduty ratio and holding duty ratio, the opening initial current and closing initial current can be generated, respectively. Combining with the voltages of opening duty ratio and closing duty ratio, the opening and closing dynamic behaviors can be fully controlled and adjusted in a wide range. The effectiveness of the proposed algorithm is proved by numerical analysis and experimental studies. Results show that the opening delay time can be controlled in a range of 0.2–18.3 ms and the closing delay time can be adjusted in a range of 0.1–6.8 ms, while the opening moving time can be adjusted from 1.9 to 14.1 ms and the closing moving time can be adjusted from 1.8 to 6.1 ms. Consequently, the total opening time and total closing time can be controlled in the ranges of 2.1–32.1 ms and 1.9–12.9 ms, respectively. Compared with the conventional single voltage control strategy, the advance PWM control algorithm is verified to be a promising method to improve or even adjust the dynamic behaviors of HSVs and adapt to more complex working conditions.

A hyper-redundant manipulator(HRM) can flexibly accomplish tasks in narrow spaces. However, its excessive degrees of freedom pose challenges for path planning. In this letter, an ellipsoid-shape rapidly-exporing random tree (E-RRT*) method is proposed for path planning of HRMs in workspace, particularly those with angle limits. This method replaces line segments with ellipsoids to connect adjacent nodes. Firstly, an analysis of angle constraints of the HRM is conducted, providing restrictions on node selection during path planning. Secondly, a slow-speed informed guiding approach is introduced to optimize the sampling process. Finally, the obtained path is enhanced by adding control points and applying cubic polynomial interpolation to achieve path smoothing. Simulations demonstrate that the proposed E-RRT* method effectively solves the path planning problem for HRMs. Especially in narrow environments, appropriate informed guiding speeds enable E-RRT* to outperform other methods.