Polymer 4D printing: Advanced shape‐change and beyond

Abstract

4D printing is an exciting branch of additive manufacturing. It relies on established 3D printing techniques to fabricate objects in much the same way. However, structures which fall into the 4D printed category have the ability to change with time, hence the “extra dimension.” The common perception of 4D printed objects is that of macroscopic single‐material structures limited to point‐to‐point shape change only, in response to either heat or water. However, in the area of polymer 4D printing, recent advancements challenge this understanding. A host of new polymeric materials have been designed which display a variety of wonderful effects brought about by unconventional stimuli, and advanced additive manufacturing techniques have been developed to accommodate them. As a result, the horizons of polymer 4D printing have been broadened beyond what was initially thought possible. In this review, we showcase the many studies which evolve the very definition of polymer 4D printing, and reveal emerging areas of research integral to its advancement.

3D and 4D Printing in the Fight against Breast Cancer

“…Currently, smart materials can be distinguished between polymers, ceramics, alloys, composites, and metals. Moreover, they can be classified according to the endowed properties, including self-repairing, shape-changing, self-sensing, or self-assembling [ 57 , 58 ]. Smart materials can undergo single or multiple changes, that can be programmed as one-way or two-way.…”

“…When removing the external force, the temporary shape is retained until heating again above the transition temperature, at which point the original shape will be spontaneously recovered. This programming process can be repeated, and different temporary shapes can be obtained ( Figure 4 ) [ 58 , 62 ]. In the biomedical field, thermo-responsive polymers are the most investigated materials.…”

“…This mechanism is commonly used to create self-folding devices. However, the deformation is not defined and the response requires time [ 49 , 58 ].…”

4D Printing Applications in the Development of Smart Cardiovascular Implants

“…Ions are the common stimulus to change the swelling ratio of hydrogels. Hydrogel networks can directly interact with ions or are affected by osmotic pressure gradients due to ion concentration imbalance ( Imrie and Jin, 2022 ). Biodegradable hollow tubes applicable as vascular grafts were 4D printed from methacrylated alginate and hyaluronic acid hydrogels.…”

Novel Copper Complexes as Visible Light Photoinitiators for the Synthesis of Interpenetrating Polymer Networks (IPNs)

“…The elaboration of polymers by photochemical means, such as free radical photopolymerization (FRP) and cationic photopolymerization (CP), have been mainly based on the use of metal-free organic dyes and photoinitiators at the industrial and academic levels [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 ], and these synthetic processes (FRP and CP) are widely used in different fields, e.g., dentistry [ 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 ], adhesives [ 24 , 25 , 26 , 27 , 28 ], coatings [ 29 , 30 , 31 , 32 , 33 ], composites [ 34 ], medicine [ 35 , 36 , 37 , 38 , 39 , 40 ], direct laser write, 3D and 4D printing [ 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 ], etc. On the other hand, organometallic compounds are not really used in industry; in other words, manufac...…”