**6. Conclusion**

Additive manufacturing was invented in the 1940s and it has developed a lot with innovative inventions since then. The different additive manufacturing process techniques have specific peculiarities and the disadvantage of one technique can lead to the innovation of a new technique. The development of different types of printers has enabled the AM to use different types of materials which include plastics, metals, and ceramics. New improvements in AM techniques allow the high filler loading in thermoplastic composites.

### *New Industrial Sustainable Growth: 3D and 4D Printing DOI: http://dx.doi.org/10.5772/intechopen.104728*

3D printing has diverse applications include for instance food, fashion, biomedical, health, aerospace, and cultural heritage preservation. 3D printing helps the consumer to customize the product as per their requirements. There are a few challenges that need to be addressed, such as emission of volatile organic compounds, creation of voids, high cost of thermoplastic polymers, and weak mechanical strength, of printed structures. To overcome these challenges composites with fillers have been fabricated such as carbon nanotube/polylactic acid composites, nanosilica/polyamide composites, and carbon black/polyamide composites which have increased the mechanical, electrical, and thermal properties of the composites.

Despite highly diverse applications of 3D printing and new advancements in 3D printing, there are still a few challenges that restrict the usage of 3D printing on a commercial scale. These include the resistance and adaptability of 3D-printed material's properties and structures against the change in environmental factors, such as temperature, electric energy, and pH.

4D printing is basically the combination of a 3D printer, smart material, and well-designed programming that allows the 3D-printed object to change its shape, properties, and functionality with time. 4D-printed objects change or modify against environmental conditions. These materials can be responsive to heat, water, pH, electric energy, and magnetic field. 4D printing has increased the number of application areas for additive manufacturing and thus expanded to include aviation, selfsustaining material, sensors, active materials, and bioprinting.

There has been a tremendous amount of technological advancement and research on 3D and 4D printing, and its applications. New advancements have been, however, the commercialization and implementation at a larger stage are still in progress and therefore more research and development are needed. Importantly more sustainable materials need to be explored due to the environmental risks associated with some of the materials and techniques used. The potential to create solutions to some of the most challenging product development needs in various industries using 3D- and 4D-printing technologies remain high. These developments are many times related to niche products that cannot be manufactured otherwise.
