The attention towards an effective recycling of post-consumer plastics in different industrial sectors has grown considerably over the past two decades. The interest in plastic waste materials mainly originates from environmental reasons, due to the fact that post-consumer plastics are the most relevant wastes with a low rate of biodegradation, and in consideration of the severe environmental problems created by the disposal of such materials in land- fills, or their floating in the ocean. The indiscriminate abandonment of fishing nets on the seabed can cause a growing form of desertification of marine ecosystems.

Also the management of electronics and electrical equipment waste has became a priority worldwide, and researchers from different countries are nowadays developing new models for the collection and environmentally sound disposal of this waste. These discarded electronic products are one of the fastest growing waste streams and it has been estimated that these items already constitute ~10% of municipal waste in several industrialized countries. It has been demonstrated that the average life span of a computer in 1997 was four years which has reduced to two years in 2005, now even less.

4D printing is today’s most emerging manufacturing which is helpful in fabricating customized prototypes/functional parts which can act when their external environment is changed. Though various types of readymade materials are commercially available for such fabrications but very few materials are available for ferromagnetic properties. Further, the commercial materials are made of virgin sources such as polymers and their fillers and the consumption of such may lead to environmental hazards. Very interesting is the recycling of waste rare earth magnets for use along with waste polymers in the development of FDM feedstock filament for 4D printing applications.

It is also worth noting that the nascent field of mechanical and acoustic metamaterials, defined as engineered lattice materials that feature unconventional behaviors mainly derived by the geometry of their microstructure, rather than from their chemical composition, is growing rapidly and attracting increasing attention from many research areas - including acoustics, aerospace, civil and mechanical engineering, medical diagnosis and remote sensing, seismic engineering, sound and heat control. Today, there is an urgent need for advanced studies exploring the engineering potential of such materials, and practical methods for their fabrication.