The selective laser melting (SLM) of Ti–Ni mixed powder with atomic ratio of 1:1 was performed in the present work in order to elaborate shape memory alloy (SMA). The martensite phase of Ti–Ni alloy can be found by X-ray diffraction (XRD) analysis under temperature field, moreover, the Ti2Ni phase at a high scanning velocity. The crystalline phase images also show that the synthesized Ti–Ni alloy possessed a refined martensite microstructure. In order to evaluate the mechanical properties, the microhardness and porosity were measured. The microhardness is relatively high about 400HV0.2 with champ temperature. Besides, the porosity is quite low due to the excellent laser energy absorptivity and meltability of Ni element. The differential scanning calorimetry (DSC) analysis shows that the transformation temperature from austenite phase to martensite phase is relatively high and stable.

Microstructure and Transformation Behavior of in-situ Shape Memory Alloys by Selective Laser Melting Ti--Ni Mixed Powder

4D printing of shape memory polymer composites: A review on fabrication techniques, applications, and future perspectives

4D bioprinting is promising to build cell‐laden constructs (bioconstructs) with complex geometries and functions for tissue/organ regeneration applications. The development of hydrogel‐based 4D bioinks, especially those allowing living cell printing, with easy preparation, defined composition, and controlled physical properties is critically important for 4D bioprinting. Here, a single‐component jammed micro‐flake hydrogel (MFH) system with heterogeneous size distribution, which differs from the conventional granular microgel, has been developed as a new cell‐laden bioink for 4D bioprinting. This jammed cytocompatible MFH features scalable production and straightforward composition with shear‐thinning, shear‐yielding, and rapid self‐healing properties. As such, it can be smoothly printed into stable 3D bioconstructs, which can be further cross‐linked to form a gradient in cross‐linking density when a photoinitiator and a UV absorber are incorporated. After being subject to shape morphing, a variety of complex bioconstructs with well‐defined configurations and high cell viability are obtained. Based on this system, 4D cartilage‐like tissue formation is demonstrated as a proof‐of‐concept. The establishment of this versatile new 4D bioink system may open up a number of applications in tissue engineering.

Jammed Micro‐Flake Hydrogel for Four‐Dimensional Living Cell Bioprinting

Nature's material systems during evolution have developed the ability to respond and adapt to environmental stimuli through the generation of complex structures capable of varying their functions across direction, distances and time. 3D printing technologies can recapitulate structural motifs present in natural materials, and efforts are currently being made on the technological side to improve printing resolution, shape fidelity, and printing speed. However, an intrinsic limitation of this technology is that printed objects are static and thus inadequate to dynamically reshape when subjected to external stimuli. In recent years, this issue has been addressed with the design and precise deployment of smart materials that can undergo a programmed morphing in response to a stimulus. The term 4D printing was coined to indicate the combined use of additive manufacturing, smart materials, and careful design of appropriate geometries. In this review, we report the recent progress in the design and development of smart materials that are actuated by different stimuli and their exploitation within additive manufacturing to produce biomimetic structures with important repercussions in different but interrelated biomedical areas.

4D printing in biomedical applications: emerging trends and technologies

A review on four-dimensional bioprinting in pursuit of advanced tissue engineering applications

https://iopscience.iop.org/article/10.1088/1361-665X/abcc0a/pdf

Yang Yang

Papers

4D printing and collaborative design of highly flexible shape memory alloy structures: a case study for a metallic robot prototype