![]() ![]() However, while shape-memory materials seem to have been widely researched within material science, their conjunction with 3D printing is a relatively recent venture. Current smart materials deemed suitable include shape memory polymers (SMPs), hydrogel composites, shape memory alloys (SMAs), and shape memory composites (SMCs). The most suitable method will vary depending on the printing materials used and the desired structural response. An active area for research into the SME is incorporating the thermo-mechanic programming within the 3D printing process. The shape-morphing capability is usually achieved by either (1) printing a combination of active and rigid materials in different regions of the structure to create areas of differential strain or (2) by programming the temporary shape into the thermo-mechanics of the structure after printing. The structural response is dependent on both the materials and techniques used in the printing process. Research developments have been successful in developing the SME to produce hierarchical self-morphing structures that can adopt multiple spatial configurations in response to a varying stimulus. This is called the two-way shape memory effect (SME) and has been exploited by material scientists to produce objects that can be actuated after printing. A desirable characteristic of smart materials is their ability to deform into a temporary configuration and recover to their original form by varying the applied stimulus. This technology has the potential to supplement, or even replace, devices used in various surgical procedures, including skin grafts or organ donations. Fabricating 4D structures for use in tissue engineering and drug delivery systems provides a promising prospective technology for future generations, and hence this review will focus on biomedical applications. The characteristic differences between 3D and 4D printing are given in Table 1 and Figure 1.Īdds dynamic element to all 3D printing applicationsįirst introduced in 2013, 4D printing has since received great interest within material science showing potential for application within the fields of soft robotics, defence, and manufacturing, among others. This review focuses on dynamic structures with shape-changing abilities. The shape-changing characteristics of these structures derive from the use of stimuli-responsive smart materials during the printing process, which give the structure the ability to change its function, shape, or physical properties such as Young’s modulus to form selective structures and configurations. These three-dimensional structures are dynamic and have the ability to self-transform in response to a predetermined environmental stimulus, such as electricity, light, temperature, or moisture, hence creating a fourth dimension of time. Printing methods using smart materials to produce four-dimensional architectures and metamaterials. At the core of this research is the development of additive manufacturing. This property had not, however, yet been achieved in manufactured objects until recently. Systems that respond autonomously to a change in their environment are commonly found in nature, for example, the nastic movement of leaves and flowers can be triggered by humidity, light, or touch. With this technique, a wide range of active programmable materials can be produced which have the capability to self-transform from one shape to another. It offers a streamlined path from idea to reality with performance-driven functionality built directly into the materials. This process demonstrates a radical shift in additive manufacturing. ĤD printing is the fabrication process of 3D objects that can change their shape over time or in response to an environmental stimulus. ![]() The drive to incorporate active materials into the 3D printing process to overcome these limitations has led to the development of four-dimensional (4D) printing technologies to create dynamic structures. Nevertheless, an inherent shortfall of these structures is their static and rigid nature retaining the shape in which they were originally printed and generally only performing one function. Developments since the introduction of 3D printing in 1984 have been improved fabrication accuracy, speed, multiple materials, and costs. It is an attractive alternative to traditional fabrication processes (e.g., moulding and machining) due to the reduction in both difficulty and cost of producing detailed customizable architectures. ![]() Additive manufacturing (AM), commonly known as three-dimensional (3D) printing, is a popular fabrication technique due to its ability to create complex, customizable structures from a 3D computer-aided design (CAD) file. ![]()
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