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With the wide application of the Internet of Things (IoT), storing large amounts of IoT data and protecting data privacy has become a meaningful issue. In general, the access control mechanism is used to prevent illegal users from accessing private data. However, traditional data access control schemes face some non-ignorable problems, such as only supporting coarse-grained access control, the risk of centralization, and high trust issues. In this paper, an attribute-based data access control scheme using blockchain technology is proposed. To address these problems, attribute-based encryption (ABE) has become a promising solution for encrypted data access control. Firstly, we utilize blockchain technology to construct a decentralized access control scheme, which can grant data access with transparency and traceability. Furthermore, our scheme also guarantees the privacy of policies and attributes on the blockchain network. Secondly, we optimize an ABE scheme, which makes the size of system parameters smaller and improves the efficiency of algorithms. These optimizations enable our proposed scheme supports large attribute universe requirements in IoT environments. Thirdly, to prohibit attribute impersonation and attribute replay attacks, we design a challenge-response mechanism to verify the ownership of attributes. Finally, we evaluate the security and performance of the scheme. And comparisons with other related schemes show the advantages of our proposed scheme. Compared to existing schemes, our scheme has more comprehensive advantages, such as supporting a large universe, full security, expressive policy, and policy hiding.

Thermoset shape memory polyimides (TPIs) are widely used in the fields of high-temperature smart devices. However, the recent molding of polyimides limits most of potentials in the form of two-dimensional film. In this work, we synthesized a novel shape memory polyimide (SMPI) ink that could be used for both Digital Light Process and extrusion molding 3D printing. Through UV-induced free radical polymerization, 3D custom polyimides ink can be cured rapidly. Remarkably, the 3D printed PI exhibits excellent shape memory performance, with Rf of 99.8%, Rr of 98.3%, therefore the 4D printing PI was successfully prepared. The 3D printed airplane, ultrasonic motor and pagoda can actively recover the film folding, expanding combined compressing, and vertical distorting to their permanent shape, which presents the outstanding 4D printing properties. Moreover, SMPI can be used in extrusion molding to print films, the residual stress induced the self-folding and then a vector model was applied to characterize transformation of extruded plates. In order to develop the application diversity of extruded 4D polyimide, self-folding box and stimuli-response gripper are designed, the gripper is able to pull up steel ball 15 times heavier than itself. Thus, SMPI will be benefit to expand the applied scope of SMPI.