Bone regeneration in strong porous bioactive glass (13-93) scaffolds with an oriented microstructure implanted in rat calvarial defects

Abstract

There is a need for synthetic bone graft substitutes to repair large bone defects resulting from trauma, malignancy and congenital diseases. Bioactive glass has attractive properties as a scaffold material but factors that influence its ability to regenerate bone in vivo are not well understood. In the present work, the ability of strong porous scaffolds of 13-93 bioactive glass with an oriented microstructure to regenerate bone was evaluated in vivo using a rat calvarial defect model. Scaffolds with an oriented microstructure of columnar pores (porosity=50%; pore diameter=50-150 μm) showed mostly osteoconductive bone regeneration, and new bone formation, normalized to the available pore area (volume) of the scaffolds, increased from 37% at 12 weeks to 55% at 24 weeks. Scaffolds of the same glass with a trabecular microstructure (porosity=80%; pore width=100-500 μm), used as the positive control, showed bone regeneration in the pores of 25% and 46% at 12 and 24 weeks, respectively. The brittle mechanical response of the as-fabricated scaffolds changed markedly to an elastoplastic response in vivo at both implantation times. These results indicate that both groups of 13-93 bioactive glass scaffolds could potentially be used to repair large bone defects, but scaffolds with the oriented microstructure could also be considered for the repair of loaded bone.

Fig. 1

Optical images of disc-shaped bioactive glass (13–93) scaffolds with (a) an oriented microstructure and (b) a trabecular microstructure (positive control). SEM images of cross sections of the oriented and trabecular scaffolds are shown in (c) and (d), respectively. The cross section in (c) is perpendicular to the pore orientation direction.

Fig. 2

Synchrotron micro-computerized X-ray tomography (SR microCT) images of oriented scaffold after implantation for 12 weeks (a) and 24 weeks (b), and trabecular scaffold after implantation for 12 weeks (c) and 24 weeks (d). The distribution of old bone (O), new bone formation (B) and the bioactive glass scaffold (S) is shown.

Fig. 3

H&E stained sections of rat calvarial defects implanted with oriented scaffolds at 12 weeks (a, c) and 24 weeks (b, d); defects implanted with trabecular scaffolds at 12 weeks (e) and 24 weeks (f), and untreated defects at 12 weeks (g) and 24 weeks (h). Stained sections at higher magnification (c, d) show new bone (B) in the pores of the oriented scaffolds (S) at 12 weeks and 24 weeks. Arrows indicate the edges of the old bone. Scale bar = 1 mm for (a,b and e–h), and 200 µm for (c, d).

Fig. 4

Histomophometric analysis of H&E stained sections showing total bone regeneration in rat calvarial defects implanted with oriented and trabecular scaffolds at 12 and 24 weeks: (a) normalized to the total defect area; (b) normalized to the available pore area of the scaffolds (*significant difference between scaffolds: p<0.05).

Fig. 4

Histomophometric analysis of H&E stained sections showing total bone regeneration in rat calvarial defects implanted with oriented and trabecular scaffolds at 12 and 24 weeks: (a) normalized to the total defect area; (b) normalized to the available pore area of the scaffolds (*significant difference between scaffolds: p<0.05).

Fig. 5

SEM backscattered electron images and X-ray maps for Ca (K), P(K) and Si(K) for oriented bioactive glass scaffolds after implantation for 12 weeks (a–d) and 24 weeks (e–h) in rat calvarial defects. Mineralized tissue (B) was formed adjacent to the hydroxyapatite (HA)-like layer (H) formed on the surface of the glass. G denotes the unconverted glass, and S the SiO₂-rich layer or SiO₂-rich core.

Fig. 6

Von Kossa stained sections of rat calvarial defects implanted with oriented scaffolds at 12 weeks (a) and 24 weeks (b), defects implanted with trabecular scaffolds at 12 weeks (c) and 24 weeks (d), and empty defects at 12 weeks (e) and 24 weeks (f). Arrows indicate the edges of the old bone.

Fig. 7

Histomophometric analysis of von Kossa positive area (total mineralized area of new bone and HA-like layer of scaffold) in rat calvarial defects implanted with oriented and trabecular scaffolds 12 weeks and 24 weeks postimplantation (*significant difference between scaffolds: p<0.05).

Fig. 8

Force vs. displacement response for oriented scaffolds as fabricated, after immersion in SBF for 12 and 24 weeks, and after implantation in rat calvarial defects for 12 and 24 weeks. The response of trabecular scaffolds (positive control) after implantation for 24 weeks is also shown. (The curves were arbitrarily shifted along the x-axis to maintain clarity.)

Fig. 9

SEM backscattered images showing the cross-sections of (a) oriented scaffolds and (b) trabecular scaffolds after implantation in rat calvarial defects for 24 weeks and testing in the diametral compression test. (S: converted bioactive glass scaffold; B: mineralized tissue)