Abstract
With the increasing application of orthopedic scaffolds, a dramatically increasing number of requirements for scaffolds are precise. The porous structure has been a fundamental design in the bone tissue engineering or orthopedic clinics because of its low Young’s modulus, high compressive strength, and abundant cell accommodation space. The porous structure manufactured by additive manufacturing (AM) technology has controllable pore size, pore shape, and porosity. The single unit can be designed and arrayed with AM, which brings controllable pore characteristics and mechanical properties. This paper presents the current status of porous designs in AM technology. The porous structures are stated from the cellular structure and the whole structure. In the aspect of the cellular structure, non-parametric design and parametric design are discussed here according to whether the algorithm generates the structure or not. The non-parametric design comprises the diamond, the body-centered cubic, and the polyhedral structure, etc. The Voronoi, the Triply Periodic Minimal Surface, and other parametric designs are mainly discussed in parametric design. In the discussion of cellular structures, we emphasize the design, and the resulting biomechanical and biological effects caused by designs. In the aspect of the whole structure, the recent experimental researches are reviewed on uniform design, layered gradient design, and layered gradient design based on topological optimization, etc. These parts are summarized because of the development of technology and the demand for mechanics or bone growth. Finally, the challenges faced by the porous designs and prospects of porous structure in orthopedics are proposed in this paper.
Highlights
The bone structure consists of cortical and cancellous bone
The critical load of the Voronoi designed porous structures was increased by nearly 300%, which showed the ability for internal load-bearing implant structure. For another model built with algorithm, the results showed that the manufactured model exhibited a high load to weight ratio, which is a crucial parameter for the scaffold (Sharma et al, 2019)
The results showed that alkaline phosphatase (ALP) activity was higher in the high porosity of the same scaffold
Summary
The bone structure consists of cortical and cancellous bone. Bone is a non-uniform porous structure, the density of which gradually increases from the inner cancellous bone to the outer cortical bone. Adding vertical stiffeners through the center of the BCC/OC unit was a way to improve the original BCC/OC (shown in Figure 1a2) (Feng et al, 2016) All these reinforced BCC/OC scaffolds were better than the original BCC structures in compressive properties and Young’s modulus. As the orthopedic scaffold designs, BCC and its reinforced design had the advantages of the excellent mechanical properties and easy to manufacture characteristics It had some disadvantages, such as insufficient internal surface area and relatively low anisotropy. The mechanical properties of porous Ti6Al4V scaffolds in Diamond/FCC structure were evaluated, and similar conclusions were obtained that Young’s modulus was similar to natural bone (Li et al, 2016; Yanez et al, 2016). The Young’s modulus, which matched the height of bone, showed that the TABLE 1 | The mechanical properties of various cellular designs
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