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Accurate measurement of oxygen diffusion distances (ODDs) is important but difficult in the production of polyacrylonitrile (PAN)-based carbon fibers. Traditionally, the ODDs were deemed to be homogeneous in a single fiber and paid no attention. Herein, the skin widths of carbon fibers with the skin-core structure were proposed to assess the ODDs, and the ODDs were investigated by transmission electron microscopy. The ODDs were first found to be homogeneous for the commercially noncircular carbon fibers, while they were uniform in every direction for the circular single carbon fibers. The inhomogeneity of the ODDs was unrelated to the surface and cross-sectional morphologies of carbon fibers, and it was considered to result from the density difference at the edge of a single PAN precursor fiber. These findings not only deepen the understanding of the effect of the PAN precursor fiber shapes on the oxygen diffusion during stabilization, but also provide an opportunity for optimizing the stabilization conditions according to the density difference at the edges of single PAN precursor fibers.

Conventional robots have shown good positioning accuracy and reliability in multiple environments. However, the robots’ lack of flexibility makes them unsuitable for application in certain areas. Thus, a soft robotic system should be considered due to its adaptivity and flexibility. This paper proposes a novel shape memory alloy (SMA)-actuated multiple degrees of freedom (DOF) soft robot, which theoretically supports a maximum of nine-DOF movement and good positioning accuracy. A motion test and positioning evaluation are conducted for the proposed multi-DOF soft robot. The structural design, control method, and analysis of the kinematics and the coordinate system are also given.

4D printing is an emerging fabrication technology that enables 3D printed structures to change configuration over "time" in response to an environmental stimulus. Compared with other soft active materials used for 4D printing, shape-memory polymers (SMPs) have higher stiffness, and are compatible with various 3D printing technologies. Among them, ultraviolet (UV)-curable SMPs are compatible with Digital Light Processing (DLP)-based 3D printing to fabricate SMP-based structures with complex geometry and high-resolution. However, UV-curable SMPs have limitations in terms of mechanical performance, which significantly constrains their application ranges. Here, a mechanically robust and UV-curable SMP system is reported, which is highly deformable, fatigue resistant, and compatible with DLP-based 3D printing, to fabricate high-resolution (up to 2 µm), highly complex 3D structures that exhibit large shape change (up to 1240%) upon heating. More importantly, the developed SMP system exhibits excellent fatigue resistance and can be repeatedly loaded more than 10 000 times. The development of the mechanically robust and UV-curable SMPs significantly improves the mechanical performance of the SMP-based 4D printing structures, which allows them to be applied to engineering applications such as aerospace, smart furniture, and soft robots.