**3. Trends, challenges and existing opportunities in the 3D printing domain**

There are different types of materials that are still very difficult to be printed, like PMMA, Hydroxyapatite, or chitosan if we are referring to the medical domain or different types of materials that are easier to be made by casting instead of 3D printing, such as different types of Irons, so, therefore, these methods are considered to be also very important in this field in close correlation with the 3D printing technologies [18]. Rapid Tooling methods are using 3D printed parts as master models for the realized molds and, therefore, it is one real challenge to produce master models made of different types of materials that are suited to the Rapid Tooling method that is used for producing the molds in the end [19]. New types of materials mixed with new types of 3D printing or rapid tooling methods that are more and more used in the last years are really encouraging, are very promising, and represent one strong proof that there is still one wide open room in this domain, as there are still lot of things to be investigated in this field, in order to provide one quick response to the medical or industrial sector needs [20].

Life cycle of the products became very short, developing and personalizing of products are highly demanding also, need for standardization in the field of 3D printing is also one very important challenge as new types of additive. Manufacturing (3D printing) methods are still under development and are launched every year on the market [21].

The use of subtractive technological methods (like CNC cutting) in combination with additive manufacturing technologies in so-called "Hybrid manufacturing" technologies represents one of the most important trends on the market and provides lot of research topics for the researchers all over the world [22]. Whether we are referring to metallic, ceramic, or plastic materials, in principle, the trends, challenges, or opportunities are the same in the field of Rapid Prototyping technologies. Using of robots integrated with these methods, integration of "in-line" quality control systems in the manufacturing chain jointly with 3D printing methods, application of different types of heat treatment or coating methods in the rapid development process of a new product, and use of "digitalization" or "optimization" procedures or software programs correlated with the new developed 3D printing methods are just few of the most important examples of the opportunities in this field, both, for industrial or medical sectors [23–26].

Topological optimization or bionic design methods are quite well correlated with the additive manufacturing technologies, being also quite well integrated with specific software programs that are usually used to optimize the shape and redesign some components in order to decrease their weight, this trend being highly seen in the industrial sector (aerospace or automotive), but also in the medical sector, when such methods are used to enhance the biocompatibility of different medical implants, by designing the models with specific lattice structures in which bioactive materials can be inserted or integrated [27, 28]. Biomimetic structures, which refer actually to structures that imitate nature or biomimetic materials that can be used on 3D printing equipment are on top interest in the medical domain as well [29]. Bioengineering,

*Introductory Chapter: Rapid Prototyping – Trends and Opportunities DOI: http://dx.doi.org/10.5772/intechopen.106036*

biomedical, or bio 3D printing are new domains in which progress that has been made in the last years is really impressive and remarkable. Vessels, tissues, personalized bone structures, or even organs can be now realized or produced using 3D printing or 4D printing methods [30, 31].

Last, but not least, possibility of using multi-materials in the process of 3D printing and the possibility of using composite materials that are suitable to be used by 3D printing have enlarged the domains of applicability of these methods even more, by providing access to different applications, such as building constructions, textile and fashion, and consumer goods industry, etc. [32–34].
