## 4 Additive Manufacturing--3D Printing and 3D Printers
PAEK and HA powders are carefully blended to ensure the uniform distribution of particles, resulting in a composite material with enhanced mechanical and thermal properties. This mixture is then processed into a continuous filament, which serves as the raw material for the 3D printing process. During printing, the filament is fed into the extruder of the 3D printer, where it is heated to its melting point. The molten composite material is then pushed through a precision nozzle and deposited onto the build platform layer-by-layer, following the predetermined path defined by the CAD model. As each layer is deposited, the material cools and solidifies, gradually forming the desired 3D structure [78]. This method is particularly advantageous for fabricating PAEK composites due to its ability to produce complex geometries with high precision and minimal material wastage [77]. Figure 3 below provides a schematic representation of the FFF process for PAEK composites, illustrating the key steps involved in transforming the composite filament into the final printed object. Several factors and parameters must be carefully considered when 3D printing to ensure a successful outcome. Each parameter, such as the print speed and the nozzle temperature, plays a critical role in determining the final quality of the print, the printing time, and the overall cost [79]. These parameters need to be configured accurately to achieve a high-quality, functional 3D-printed object. The key considerations include layer height, which affects resolution and surface smoothness, with smaller heights offering finer details but increasing printing time. The print speed influences both quality and production time, as slower speeds improve precision, while higher speeds can compromise detail [80]. The nozzle temperature must be set appropriately for the material being used to ensure smooth extrusion and prevent clogging or under-extrusion [81]. The bed temperature is equally important for maintaining proper adhesion of the first layer, especially for materials like  
Figure 2: Schematic diagram of different 3D printers. PAEK, which are prone to warping [82]. Support structures are necessary for overhangs or complex geometries to prevent failure during printing, while adhesion to the bed can be improved using a heated bed, adhesive materials, or techniques like adding a raft or a brim [83]. Additionally, the flow rate must be finely tuned to avoid over-extrusion, which leads to blobs and rough surfaces, or under-extrusion, which results in weak and incomplete prints [80,84]. By carefully calibrating these factors based on the material, printer model, and design requirements, you can optimize the process and produce a high-quality, 3D-printed object. As detailed by in the literature and Table 6, orthopedic implants made through AM using PAEK exhibit notable advantages, including exceptional biocompatibility and properties such as density and mechanics comparable to those of natural bone [50]. The extrusion process utilizes a heated nozzle to melt thermoplastic filaments, which are then precisely deposited according to a programmed design. This technique allows for fabricating intricate and customized objects with relative ease and cost-effectiveness. [PERSON] et al. have explored the potential of open source 3 DP with extrusion-based systems, emphasizing accessibility and affordability [4,85]. Additionally, the work of [PERSON] and [PERSON] sheds light on the material considerations and process parameters involved in extrusion-based AM [73]. Extrusion-based techniques play a pivotal role in the democratization of manufacturing, making it accessible to a wider audience, while contributing to the ever-expanding applications of AM technologies.