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Wang, et al.
yield stress of PEEK made by FDM, reported to be 60 – size and shape of the implant vary from person to person.
84 MPa . Therefore, these processing techniques are incapable of
[40]
The whole sternum reconstruction was the most manufacturing individualized PEEK implants. Machining
extreme case in the sternum-rib hybrid reconstruction, is also a commonly used PEEK processing method. In
consisting of the sternum, rib, and junction parts general, it is necessary to combine surface treatment
connecting with the residual ribs. The sternum part was technology to anneal the PEEK finished product before
designed based on CT data of the thoracic cage, where and after machining to eliminate the influence of residual
unnecessary geometric features were ignored and the stress on the finished production. It is worth noting that
surface of the sternum was smoothed greatly to reduce when machining implants with hollow structures or
the manufacturing difficulty while maintaining the curved surfaces (such as sphenoid bones or skulls) using
appearance of the thorax . The design method of the rib machining methods, the amount of cutting occupies
[42]
part and junction part was similar to that of the in-suit a large proportion of the raw materials, and the waste
rib prosthesis. Protecting the internal organs is the major situation of materials is more serious.
mechanical function of the whole sternum prosthesis, FEA In response to the limitations of traditional
was employed to predict the safety of the prosthesis under processing technology, 3D printing technology, as one
loading of 500 N, the maximum von Mises of the sternum of the most intelligent manufacturing technologies, plays
prosthesis was 16 MPa which indicated the safety of the a more and more prominent role [61,62] . PEEK material is
prosthesis. As for the segment sternum reconstruction, also fully suitable for processing and manufacturing by
countersunk holes for the screwing fastening were 3D printing technology. 3D printing technology is also
introduced for the fixation with the natural sternum. known as solid freeform fabrication, rapid prototyping,
The costal cartilages connect the sternum and ribs layered manufacturing, and additive manufacturing.
and play an important role during the breath, and they This manufacturing technology is direct manufacturing,
are prolonged when inhaled and expand the thoracic and a digital control mechanism centralizes its internal
cage . Post-operative respiratory function after the control through production by stacking layer by
[59]
reconstruction surgery was limited because of the much layer . In addition, the inherent characteristics of 3D
[63]
higher stiffness of PEEK compared to the costal cartilages, printing technology can also realize the preparation
thus decreasing the structural elastic modulus of the PEEK of controllable porous products . This structure can
[64]
rib prosthesis was the solution to the problem. A bionic increase the attachment of biological tissue cells, which
design methodology through a wavy elastic structure was is conducive to tissue growth . 3D printed porous PEEK
[65]
established by Zhang et al. , as shown in Figure 3. By parts also have great potential in load-bearing and non-
[38]
changing the design parameters of the wavy structure, the load-bearing applications . It can be used as an implant
[66]
local stiffness of the prosthesis could be adjusted. Both for load-bearing bones (such as femur and tibia) and
FEA (Figure 3C) and mechanical testing (Figure 3D non-load-bearing bones (such as sternum and ribs). At
and 3E) of stiffness of the wavy elastic structure with present, FDMs are one of the most suitable 3DP methods
different design parameters (Figure 3A right) are shown. for processing PEEK materials (Figure 4A and 4C).
The results showed that the stiffness was adjusted in the
range of 0.5 – 17.3 MPa (Figure 3F), which covered the 3.1. Process mechanism
elastic modulus of the costal cartilage . The long-term This technology is also called FDM . This fabrication
[60]
[67]
mechanical safety of the wavy structure should be paid method mainly uses continuous filaments processed into
special attention to because it would experience tension- corresponding diameters (Figure 4A). Moreover, after
compression deformation for a long time. The endurance heating to a temperature close to the melting point in a
properties of the wavy structure should be further studied liquefier, the PEEK filaments are extruded and deposited
by mechanical testing and animal experiment before on an unfixed platform [68,69] . The extrusion head and
clinical application. platform of the liquefier are controlled by the digital
3. FDM process for 3DP PEEK implants control device of the printer, and the corresponding
graphics are produced according to the preset path. For
PEEK is a polymer material with thermoplastic complex graphics, the printer will additionally print
properties, and its processing methods are diversified. supporting materials to support the overhanging part
Traditional PEEK processing methods include injection of the product . After the material is extruded, the
[70]
molding, compression molding, extrusion molding, subsequent cooling process will make the semi-molten
and machining. The traditional method of processing extruded filament return to a solid state. At this stage,
and molding requires the manufacture of molds first. the high thermal gradient will cause residual stress in the
There are considerable advantages to the standardized printed product . The optimal printing temperature to
[66]
manufacturing process in large quantities. However, the print PEEK filaments is from 360°C to 430°C according
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