Hybrid solid mesh structure for electron beam melting customized implant to treat bone cancer

Abstract

15Bone replacement implants manufactured by electron beam melting have been widely studied for use in bone tumor treatment. In this application, a hybrid structure implant with a combination of solid and lattice structures guarantees strong adhesion between bone and soft tissues. This hybrid implant must exhibit adequate mechanical performance so as to satisfy the safety criteria considering repeated weight loading during the patient's lifetime. With a low volume of a clinical case, various shape and volume combinations, including both solid and lattice structures, should be evaluated to provide guidelines for implant design. This study examined the mechanical performance of the hybrid lattice by investigating two shapes of the hybrid implant and volume fractions of the solid and lattice structures, along with microstructural, mechanical, and computational analyses. These results demonstrate how hybrid implants may be designed to improve clinical outcomes by using patient-specific orthopedic implants with optimized volume fraction of the lattice structure, allowing for effective enhancement of mechanical performance as well as optimized design for bone cell ingrowth.

Keywords: 3D printing; Bone cancer; Electron beam melting; Fracture analysis; Titanium alloy implant.

Figure 1.

Ti-6AI-4V hybrid implant post-surgery. (a) Plain radiography (X-ray) of shell-type (S-type) and (b) computed tomography image of pizza-type (P-type). CAD images of (a-1) S-type and (b-1) P-type. Laboratory image of (a-2) S-type and (b-2) P-type. CAD images of (a-3) S-type region and (b-3) P-type region.

Figure 2.

Schematic of lattice structure specimen. (a) Orientation; (b) unit cell size; (c) unit cell rotation.

Figure 3.

Boundary conditions for FEA results of hybrid structure with volume fraction 10%. (a) Mesh generation. (b) Fixed support and load conditions.

Figure 4.

FEA results for the lattice structure with different sizes and unit cell rotation. (a) 2 mm with 0° (1525 MPa); (b) 3 mm with 0° (1611 MPa); (c) 2 mm with 45° (1456 MPa).

Figure 5.

Illustration of hybrid structures for the volume fraction of lattice structure. (a) P-type; (b) S-type.

Figure 6.

FEA direct analysis results for P-type hybrid structures with different fractions. (a) 20%; (b) 40%; (c) 60%; (d) 80%; (e) 100%.

Figure 7.

FEA direct analysis results for S-type hybrid structures with different fractions. (a) 10%; (b) 20%; (c) 30%; (d) 40%; (e) 50%.

Figure 8.

Maximum von Mises stress with 500 N for P-type and S-type specimens.

Figure 9.

Experimental tensile test results of hybrid structures. (a) Engineering stress-strain curve of each structure specimen tensile-tested at room temperature (strain rate of 1 × 10⁻³/s). (b) Tensile strength with different mesh volume fractions for each type.

Figure 10.

Fractography of hybrid structures after tensile test. Low-magnification fractography of (a) P-type and (b) S-type specimens.

Figure 11.

Fractography of (a) P-type and (b) S-type specimens of mesh volume fraction of 40%. High-magnification image of (a-1, -2, -3) P-type and (b-1, -2) S-type specimens.

Figure 12.

Cross-sectional EBSD analysis of tensile test fractured (a) P-type 40% and (b) S-type 40% specimens. Inverse pole figure map and texture analysis results of (a-1) solid and (a-2) mesh region in P-type specimen. Inverse pole figure map and texture analysis results of (b-1) solid and (b-2) mesh region in S-type specimen. Texture analysis of (c) P-type 40% and (d) S-type 40% specimens.