Additive manufacturing (AM) or 3D printing is a digital manufacturing process and offers virtually limitless opportunities to develop structures/objects by tailoring material composition, processing conditions, and geometry technically at every point in an object. In this review, we present three different early adopted, however, widely used, polymer-based 3D printing processes; fused deposition modelling (FDM), selective laser sintering (SLS), and stereolithography (SLA) to create polymeric parts. The main aim of this review is to offer a comparative overview by correlating polymer material-process-properties for three different 3D printing techniques. Moreover, the advanced material-process requirements towards 4D printing via these print methods taking an example of magneto-active polymers is covered. Overall, this review highlights different aspects of these printing methods and serves as a guide to select a suitable print material and 3D print technique for the targeted polymeric material-based applications and also discusses the implementation practices towards 4D printing of polymer-based systems with a current state-of-the-art approach.

Magnetorheological elastomers (MREs) are one of the categories of smart materials, whose modulus increases considerably in the presence of a magnetic field. These elastomers are prepared by dispersing magnetic micro-sized particles into a soft solid carrier medium. The main feature of these elastomers is that they change their elastic and damping properties quickly in the presence of a magnetic field. The change in properties, also known as the magnetorheological (MR) effect of MREs are dependent on various parameters such as type of matrix material, distribution of magnetic particles, additives, working mode, and strength of the applied magnetic field. Various studies have been conducted to improve the MR effect and seek the possibility to implement the MREs in different applications including but not limited to vibration absorbers, isolators, soft actuators, and sensors. The focus of this review is to present the recent progress of MREs including materials used, fabrication strategies, MR effect, and potential applications.