Fig. 1. Electron beam melting process features. (a) EBM system schematic showing process details: (1) Electron gun, (2) Magnetic lens and beam scanning, (3) Cassettes containing powder as illustrated in Fig. 1(b), (4) Layer raking of gravity fed powder, (5) Build product; VAC indicates vacuum. (Adopted from Murr [15]). (b) SEM image of Ti-6Al-4V powder. (c) Optical micrograph showing EBM fabricated, bulk Ti-6Al-4V characterized by lenticular alpha platelets surrounded by dark beta phase. (d) Optical micrograph showing fine alpha-prime platelets in rapidly cooled Ti-6Al-4V mesh strut section. (e) Optical micrograph showing Co-base superalloy mesh containing fine columns of chromium carbide (Cr23 C6) precipitates unique to the EBM process.

Fig. 2. Examples of open-cellular build elements and EBM fabricated mesh (a) and foam (b) samples of Ti-6Al-4V. Inserts in (a) and (b) show build elements. Functiona1 CAD models of fabricated foams are shown in (c) and (d). (c) shows an 83%/56% inside/outside foam porosity. (d) Shows a section view of (c). (Adapted from Murr [15]).

Fig. 3. Experimental bases for biomechanical compatibility design strategies for porous (open-cellular) implants fabricated by EBM. (a) Average open-cellular pore size versus relative density (ρ/ρs) for EBM fabricated Ti-6Al-4V (Adapted from Murr [15] and experimental data of Horn et al. [32]). (b) Relative stiffness (E/Es) versus relative density (ρ/ρs) for EBM fabricated Ti-6Al-4V and Co-26Cr-6Mo-0.22C superalloy mesh and foam samples (as in Fig. 2(a) and (b)) with corresponding porosities and stiffnesses for Fig. 2(c) and (d) functional foams. (Adapted from Murr [15]). (c) Fatigue and compressive strengths versus stiffness (Young’s modulus, E) for EBM fabricated Ti-6Al-4V mesh from data of Zhao et al. [35]. C and T (cortical (hard) and trabecular (soft) bone regimes) with E = 10 and 1 GPa; corresponding to (b). (Adapted from Murr [15]). Open circles correspond to compressive strength while solid circles correspond to fatigue strength.

Fig. 4. Illustrations of femur bone (a) and structure ((b) and (c)). (a) Upper femur bone. (b) Section view corresponding to arrows in (a) showing femur bone structure indicating the central trabecular (T) or soft bone regime and surrounding and outer cortical (C) or hard bone regime. (c) Shows a rendering of the vascularization of the femur bone shown in (a) and (b). (b) and (c) adapted from Murr [15].

Fig. 5. X-ray image for total hip replacement implant showing EBM-fabricated, partially porous Ti-6Al-4V acetabular cup (AC). The inserts at left show the EBM fabricated AC appliance. The porous regime is only ～4 mm thick allowing only limited bone cell ingrowth to anchor the implant. The implant femoral/stem is solid Ti-6Al-4V and displaces essentially the entire trabecular (intramedular) regime (or marrow and soft bone) shown in Fig. 4(b) and (c).

Fig. 6. X-ray image showing an intramedullary rod extending through a femur fracture (arrow) secured by a metal screw at top. Like the hip stem in Fig. 5, this solid Ti-6Al-4V rod displaces the entire trabecular (soft) bone regime containing marrow and extensive vascularization. Inserts to left and right show prospects for utilizing functional, foam rod of EBM fabricated Ti-6Al-4V using the foam CAD design shown in Fig. 2(c) and (d) (from left-to-right, respectively).

Fig. 7. Features of a living metal or alloy porous implant. (a) and (b) illustrate the concept of impregnating a functional, foam or open-cellular metal implant with speciated cells and molecular components in a collagen-hydrogel matrix to induce bone cell formation and bone cell ingrowth, as well as vasculature induction inside and at the bone implant interface. Alternatively, bone marrow concentrate extracted from the patient’s bone prior to implant insertion is infused into the porous regime in (b). (c) shows osteoblast connections and migration in a porous metal foam. (d) shows primary endothelial cells. (e) shows collagen strands with attached hydroxyapatite crystals. (d) and (e) are adapted from Google images.