Mesoporous bioactive glass/ɛ-polycaprolactone scaffolds promote bone regeneration in osteoporotic sheep

Abstract

Macroporous scaffolds made of a SiO₂-CaO-P₂O₅ mesoporous bioactive glass (MBG) and ɛ-polycaprolactone (PCL) have been prepared by robocasting. These scaffolds showed an excellent in vitro biocompatibility in contact with osteoblast like cells (Saos 2) and osteoclasts derived from RAW 264.7 macrophages. In vivo studies were carried out by implantation into cavitary defects drilled in osteoporotic sheep. The scaffolds evidenced excellent bone regeneration properties, promoting new bone formation at both the peripheral and the inner parts of the scaffolds, thick trabeculae, high vascularization and high presence of osteoblasts and osteoclasts. In order to evaluate the effects of the local release of an antiosteoporotic drug, 1% (%wt) of zoledronic acid was incorporated to the scaffolds. The scaffolds loaded with zoledronic acid induced apoptosis in Saos 2 cells, impeded osteoclast differentiation in a time dependent manner and inhibited bone healing, promoting an intense inflammatory response in osteoporotic sheep. STATEMENT OF SIGNIFICANCE: In addition to an increase in bone fragility and susceptibility to fracture, osteoporosis also hinders the clinical success of endosseous implants and grafting materials for the treatment of bone defects. For the first time, macroporous scaffolds made of mesoporous bioactive glass and ε-caprolactone have been evaluated in a sheep model that mimics the osteoporosis conditions in humans. These implants fostered bone regeneration, promoting new bone formation at both the peripheral and the inner parts of the scaffolds, showing thick trabeculae and a high vascularization degree. Our results indicate that macroporous structures containing highly bioactive mesoporous glasses could be excellent candidates for the regenerative treatment of bone defects in osteoporotic patients.

Keywords: Bone regeneration; Mesoporous bioactive glass; Osteoporosis; Scaffolds; Zoledronic acid.

Figure 1

Scanning electron micrographs of MBG-PCL-zol scaffolds. (a) magnification x 7 and (b) magnification x 20.

Figure 2

Zoledronic acid release from MBG-PCL-zol as a function of soaking time.

Figure 3

Scanning electron micrographs of MBG-PCL-zol scaffolds before (a) and after 21 days (b) and 30 days (c) of drug release test. Nitrogen adsorption/desorption isotherms of MBG-PCL-zol scaffolds before and after 30 days soaked in PBS (d).

Figure 4

Effects of MBG-PCL (grey) and MBG-PCL-zol (black) scaffolds on cell cycle phases of human Saos-2 osteoblasts after 7 days of culture. Controls in the absence of scaffolds (white) were carried out in parallel. Statistical significance: *** p < 0.005.

Figure 5

Effects of MBG-PCL and MBG-PCL-zol scaffolds on the morphology of osteoclast-like cells observed by confocal microscopy after 7 days of differentiation. (a) Controls in the absence of scaffolds; (b) MBG-PCL scaffolds immersed in the medium of osteoclast cultures from the first day; (c) MBG-PCL scaffolds immersed in the medium of osteoclast cultures from the sixth day; (d) MBG-PCL-zol scaffolds immersed in the medium of osteoclast cultures from the first day; (e) MBG-PCL-zol scaffolds immersed in the medium of osteoclast cultures from the sixth day. Actin was stained with rhodamine-phalloidin (red) and cell nuclei with DAPI (blue).

Figure 6

Histological examination after 12 weeks of implantation of MBG-PCL (a and b) and MBG-PCL-zol (c and d). The inset in figure 6.b shows osteoblast border (1), blood vessel (2) and osteoclast cells (3). (*) indicates inflammatory component.

Figure 7

Histomorphometrical studies of bones of osteoporotic sheep. (a) Ossification volume, (b) trabeculae thickness. Statistical significance * p < 0.005

Figure 8

Results of histological scoring. Scores for (a) the presence of osteoblasts at the scaffolds porosity, (b) the presence of osteoclasts at the scaffolds porosity, (c) the amount of inflammatory component and (d) the extent of vascularization degree. Statistical significance * p < 0.005.