Bone Bricks: The Effect of Architecture and Material Composition on the Mechanical and Biological Performance of Bone Scaffolds

Abstract

Large bone loss injuries require high-performance scaffolds with an architecture and material composition resembling native bone. However, most bone scaffold studies focus on three-dimensional (3D) structures with simple rectangular or circular geometries and uniform pores, not able to recapitulate the geometric characteristics of the native tissue. This paper addresses this limitation by proposing novel anatomically designed scaffolds (bone bricks) with nonuniform pore dimensions (pore size gradients) designed based on new lay-dawn pattern strategies. The gradient design allows one to tailor the properties of the bricks and together with the incorporation of ceramic materials allows one to obtain structures with high mechanical properties (higher than reported in the literature for the same material composition) and improved biological characteristics.

Figure 1

Bone anatomy and the bone bricks concept investigated in this work.

Figure 2

Bone brick designs based on anthropometric and computer-aided design strategies (P stands for porosity).

Figure 3

Different regions for the water contact angle tests: (a) inner region, (b) middle region, and (c) outer region.

Figure 4

SEM images of (A) 15 wt % HA bone bricks (top view) corresponding to the architecture case 5 and (B) 15 wt % TCP bone bricks (top view) corresponding to the architecture case 6.

Figure 5

SEM images of bone bricks (top and cross-section views) (case 7) on (A, B) PCL bone brick, (C, D) HA 10 wt % bone brick, (E, F) HA 15 wt %, and (G, H) HA 20 wt % bone brick.

Figure 6

SEM images of bone bricks (top and cross-section views) (case 7) on (A, B) TCP 10 wt % bone brick, (C, D) TCP 15 wt % bone brick, (E, F) TCP 20 wt %, and (G, H) HA/TCP 10/10 wt % bone brick.

Figure 7

TGA curves of (a) TCP bone bricks and (b) HA bone bricks.

Figure 8

Water droplet on a PCL bone brick filament at 0 s (A) and 20 s (B).

Figure 9

FTIR spectra of pure PCL and composite printed bone bricks.

Figure 10

SEM and EDX spectra of PCL bone brick (A, B), PCL/TCP (80/20 wt %) (C, D), PCL/HA (80/20 wt %) (E, F), and PCL/HA/TCP (80/10/10 wt %) (G, H).

Figure 11

High-resolution XRD patterns for (a) PCL, PCL/HA, and PCL/TCP bone bricks; (b) PCL bone bricks; (c) PCL/HA bone bricks; and (d) PCL/TCP bone bricks in the range of 2θ = 20–24°.

Figure 12

Compressive modulus as a function of bone brick architecture and material composition. *Statistical evidence (p < 0.05) analyzed by one-way ANOVA and Tukey’s post-test. * indicates statistical evidence (p < 0.05); **, *** illustrate the differences between the compression results.

Figure 13

Average fluorescence intensity as a function of bone brick architecture and material composition for different days after cell seeding. *Statistical evidence (p < 0.05) analyzed by one-way ANOVA and Tukey’s post-test. * indicates statistical evidence (p < 0.05); **, *** illustrate the differences between the compression results.

Figure 14

Top and cross-section SEM images showing cell spreading on bone bricks (case 7) with different material compositions for (A, B) PCL, (C, D) 10 wt % HA, (E, F) 15 wt % HA, and (G, H) 20 wt % HA.

Figure 15

SEM images showing cell spreading on bone bricks (case 7) (top and cross section) for (A, B) 10 wt % TCP, (C, D) 15 wt % TCP, (E, F) 20 wt % TCP, and (G, H) 10/10 wt % HA/TCP.

Figure 16

SEM images of cells attached and spreading on bone bricks (case 7) as a function of material composition for (A) PCL bone brick, (B) 10 wt % HA bone brick, (C) 15 wt % HA bone brick, (D) 20 wt % HA bone brick, (E) 10 wt % TCP bone brick, (F) 15 wt % TCP bone brick, (G) 15 wt % TCP bone brick, and (H) 10/10 wt % HA/TCP bone brick.

Figure 17

Number of cells at different regions on the bone bricks (case 7). For clarity, statistical analysis was conducted considering only the total number of cells for the different material compositions.

Figure 18

Confocal images of cells attached and spreading on day 1 (A, C, E, G) and day 14 (B, D, F, H) (case 7) on (A, B) PCL bone brick, (C, D) 10 wt % HA bone brick, (E, F) 15 wt % HA bone brick, and (G, H) 20 wt % HA bone brick.

Figure 19

Confocal images of cells attached and spreading on day 1 (A, C, E, G) and day 14 (B, D, F, H) on bone bricks (case 7) presenting different material compositions. (A, B) Correspond to 10/10 wt % HA/TCP bone bricks; (C, D) correspond to 10 wt % TCP bone bricks; (E, F) correspond to 15 wt % TCP bone bricks; and (G, H) correspond to 20 wt % TCP bone bricks.