**1. Introduction to 3D printing**

Gaining immense interest both in academic and industrial sector is the concept of three dimensional (3D) printing (3DP) technologies. Domains like aerospace, engineering, FMCG, architecture, military, fashion industry, chemical industry, and medical field are by no way untouched by this technology [1, 2]. 3DP has a wide range of applications like tissue design, printing of organ, diagnostics, manufacture of biomedical devices, and the design of drug and delivery systems in the medical field [3, 4]. From the data originated by various techniques like computed tomography (CT) scan and magnetic resonance imaging (MRI), complex anatomical and medical structures according to the need of patient can be fabricated [5, 6]. Replacing and repairing the defective organs like kidney, heart etc. or all together creating a new organ that mimics the same functions as that of original are some additional uses of this technology [7]. This technology is so widespread that its applications include things that are an integral part of human life like clothing, eyeglasses, jewelry, parts of cars, and drugs that can be printed in almost any geometry and shape as per the requirement of the user [8].

In this technology a concept is transformed into prototype by taking help from 3D computer-aided design (CAD) files, hence digitally controlled and customized product can be fabricated [9]. This technology utilizes a bottom-up approach in which layers of materials like living cells, wood, alloy, thermoplastic, metals etc. are placed on top of each other in order to make the required 3D object [10]. Therefore, 3D printing is also known by other terminologies such as layered manufacturing, additive manufacturing, computer automated manufacturing, rapid prototyping, or solid freeform technology (SFF) [9].

In subtractive methodology or conventional method, the product is designed from the bulk substance and due to non-advanced tools used non-standard geometries and objects made from many materials cannot be made with high quality [11, 12]. In contrast to the conventional method, 3DP technology is more automated, rapid and easy to use, customized and sophisticated and cost-effective [13–15].
