## 4 Additive Manufacturing--3D Printing and 3D Printers  
Additive manufacturing (AM), commonly known as 3D printing (3 DP), is a process that creates a customized, three-dimensional (3D) object layer-by-layer from digital data created using Computer-Aided Design (CAD) Software [68]. This transformative technology has received significant attention across diverse industries due to its flexibility, speed, and ability to produce complex geometries that were previously challenging or impossible with the traditional manufacturing methods [50]. AM offers numerous advantages compared to the traditional subtractive manufacturing. The layer-by-layer process not only yields environmental and lean manufacturing benefits by minimizing material waste, but also allows for design freedom, enabling the production of complicated geometries and customization that would be considered 'unmanufacturable' using the conventional methods. Additionally, AM boasts rapid prototyping capabilities and material versatility and reduces the use of costly equipment such as molds [2]. Over the last decade, significant advancements in material diversity, design flexibility, printing techniques, speed, and cost within the realm of 3 DP have played a catalyzing role in propelling Industry 4.0 and personalized medicine forward [69]. This transformative progress has revolutionized the healthcare sector by transitioning pharmaceutical manufacturing from mass production to an on-demand, personalized model [70]. AM encompasses various types of 3D-printing technology, each employing unique techniques to create 3D objects. Stereolithography (SLA), developed by [PERSON] in 1986, was one of the first methods and marked the beginning of modern 3D printing. SLA utilizes ultraviolet (UV) light to cure liquid photopolymer resin layer-by-layer into solid objects [71]. Since then, numerous advancements have been made, resulting in technologies tailored for diverse applications [72]. Inkjet printing uses print heads to deposit binder or material droplets onto a powder bed or directly into the layers, enabling high-speed production and multi-material capabilities. Selective Laser Sintering (SLS) employs a laser to fuse powdered materials like polymers or metals layer-by-layer, producing durable and intricate components widely used in aerospace and automotive industries. Fused Deposition Modelling (FDM), also known as Fused Filament Fabrication (FFF), is one of the most cost-effective methods, involving the extrusion of thermoplastic filament through a heated nozzle to build objects layer-by-layer [73,74]. Digital Light Processing (DLP), similar to SLA, uses a digital light projector to cure entire layers of resin at once, offering faster print speeds. Binder Jetting, involves selectively depositing a liquid binding agent onto a thin layer of powdered material, such as metal or ceramic, to produce components with complex geometries that are later sintered or post-processed. Figure 2 provides a schematic \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Properties** & **PEKK** & **PEEK** & **Ti** & **Reference** \\ \hline Tensile strength (MPa) & 115 & 100.69 & 240-890 & [30,60,66] \\ Elastic modulus (GPa) & 5.1 & 3.5 & 103–114 & [30,60,66,67] \\ Compressive strength (MPa) & 246 & 118–169 & 130–170 & [30,60,66] \\ Melting temperature (\({}^{\circ}\)C) & 363–386 & 334–350 & 1650–1670 & [30,60,66] \\ Flexural strength (MPa) & 200 & 164 & 65 & [30,60,66] \\ Density (g/cm\({}^{3}\)) & FEFF1.3 & 1.3 & 4.4–4.5 & [30,60,66] \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Mechanical properties comparing PEEK, PEKK, and titanium [30,60,66]. representation of these diverse 3D-printing technologies, each contributing to the ongoing evolution of additive manufacturing and its expanding range of applications [75]. FFF is one of the most cost-effective methods of 3D printing worldwide. This process involves the use of materials which are heated and extruded layer-by-layer to create a 3D object [76; 77].