Tissue engineering rib with the incorporation of biodegradable polymer cage and BMSCs/decalcified bone: an experimental study in a canine model

Abstract

Background: The reconstruction of large bone defects, including rib defects, remains a challenge for surgeons. In this study, we used biodegradable polydioxanone (PDO) cages to tissue engineer ribs for the reconstruction of 4cm-long costal defects.

Methods: PDO sutures were used to weave 6cm long and 1cm diameter cages. Demineralized bone matrix (DBM) which is a xenograft was molded into cuboids and seeded with second passage bone marrow mesenchymal stem cells (BMSCs) that had been osteogenically induced. Two DBM cuboids seeded with BMSCs were put into the PDO cage and used to reconstruct the costal defects. Radiographic examination including 3D reconstruction, histologic examination and mechanical test was performed after 24 postoperative weeks.

Results: All the experimental subjects survived. In all groups, the PDO cage had completely degraded after 24 weeks and been replaced by fibrous tissue. Better shape and radian were achieved in PDO cages filled with DBM and BMSCs than in the other two groups (cages alone, or cages filled with acellular DBM cuboids). When the repaired ribs were subjected to an outer force, the ribs in the PDO cage/DBMs/BMSCs group kept their original shape while ribs in the other two groups deformed. In the PDO cage/DBMs/BMSCs groups, we also observed bony union at all the construct interfaces while there was no bony union observed in the other two groups. This result was also confirmed by radiographic and histologic examination.

Conclusions: This study demonstrates that biodegradable PDO cage in combination with two short BMSCs/DBM cuboids can repair large rib defects. The satisfactory repair rate suggests that this might be a feasible approach for large bone repair.

Figure 1

The structure of DBM. (A) shows the gross view of the DBM which was characterized by electron scanning microscope (B) (×80) and micro-CT (C). DBM has an interconnected porosity. (D)(×250) the microstructure of DBM/BMSCs. BMSCs are seen attaching on the wall of the DBM.

Figure 2

Gross view and microstructure of the PDO cage. The cage was 6cm in length and 1.2cm in diameter as shown in (A) and (B). Microstructure of the PDO cage (C) showed that has pores of size 250um × 250um which potentially allow the penetration of nutrients.

Figure 3

The surgical procedure. (A) the 4 cm long rib together with periosteum defect was created. (B) the preparation of DBMs/BMSCs and PDO cage. (C) The DBMs/BMSCs were put into the PDO cage. (D) The 6cm-long PDO cage containing two 2cm-long BMSCs/DBMs was then fit into the defect with the ends of the cage overlapping the cortex at both ends of the rib by 10 mm.

Figure 4

The result of the experiment. (A) and (B) show the situation of the wound 24 weeks after surgery; the wound healed well. (C) shows the gross view of reconstructed rib. (I) the flank group whose rib defect receives no material; (II) the control group whose rib defect received PDO cage/DBM; (III) the experimental group whose rib defect received PDO cage/DBM/BMSCs; (IV) the normal rib. The arrow shows the junction of the normal rib and scaffold.

Figure 5

3-D reconstruction of the thoracic cage. We could see that there was no bone regeneration in the flank group, which is shown by the red arrow. In the PDO cage/DBMs group there was no new bone regeneration not only in the junction of two scaffolds but also in the junction between the rib and scaffold, which is shown as the green arrow. The radian of the reconstructed rib, however, was similar to the primary rib. In the PDO cage/DBMS/BMSCs, there was bone union in both the junctions which are shown with the blue arrow.

Figure 6

H&E staining of the junction of primary rib (red triangular arrow) and scaffold (green triangular arrow). (A) (×10) The primary rib and scaffold of the PDO/DBM/BMSCS group. No clear borderline was observed in the junction of the primary rib and scaffold. (B) (×40) At the junction of primary rib and scaffold of PDO/DBM/BMSCS group, marrow (black arrow) and new bone were observed; (C) (×10) In the primary rib and scaffold of the PDO/DBM group, a clear borderline was observed at the junction. (D) (×40) In the junction of the primary rib and scaffold of PDO/DBM group, fibrous tissue (blue arrow) was found both in the junction and in the scaffold.

Figure 7

H&E staining of the junction of scaffold and scaffold. (A) (×10) the junction of two scaffolds of the PDO/DBM/BMSCS group. There was bone connection in the junction, and marrow was observed as is shown in Figure B (×100); (C) (×10) the junction of the two scaffolds of the PDO/DBM group. No bone connection was observed, and fibrous tissue (blue arrow) was seen in the junction and scaffold as is shown in figure (D) (×100).

Figure 8

H&E staining of the tissue around the reconstructed rib (×100). The PDO degraded almost completely. Some pieces of PDO can be observed in the tissue and are shown by the black arrow. New blood vessels can be also seen in the tissue and are shown by the yellow arrow.