A comparative study of tissue-engineered constructs from Acropora and Porites coral in a large animal bone defect model

Abstract

Objectives: To compare the therapeutic potential of tissue-engineered constructs (TECs) combining mesenchymal stem cells (MSCs) and coral granules from either Acropora or Porites to repair large bone defects.

Materials and methods: Bone marrow-derived, autologous MSCs were seeded on Acropora or Porites coral granules in a perfusion bioreactor. Acropora-TECs (n = 7), Porites-TECs (n = 6) and bone autografts (n = 2) were then implanted into 25 mm long metatarsal diaphyseal defects in sheep. Bimonthly radiographic follow-up was completed until killing four months post-operatively. Explants were subsequently processed for microCT and histology to assess bone formation and coral bioresorption. Statistical analyses comprised Mann-Whitney, t-test and Kruskal-Wallis tests. Data were expressed as mean and standard deviation.

Results: A two-fold increaseof newly formed bone volume was observed for Acropora-TECs when compared with Porites-TECs (14 sd 1089 mm³versus 782 sd 507 mm³; p = 0.09). Bone union was consistent with autograft (1960 sd 518 mm³). The kinetics of bioresorption and bioresorption rates at four months were different for Acropora-TECs and Porites-TECs (81% sd 5% versus 94% sd 6%; p = 0.04). In comparing the defects that healed with those that did not, we observed that, when major bioresorption of coral at two months occurs and a scaffold material bioresorption rate superior to 90% at four months is achieved, bone nonunion consistently occurred using coral-based TECs.

Discussion: Bone regeneration in critical-size defects could be obtained with full bioresorption of the scaffold using coral-based TECs in a large animal model. The superior performance of Acropora-TECs brings us closer to a clinical application, probably because of more suitable bioresorption kinetics. However, nonunion still occurred in nearly half of the bone defects.Cite this article: A. Decambron, M. Manassero, M. Bensidhoum, B. Lecuelle, D. Logeart-Avramoglou, H. Petite, V. Viateau. A comparative study of tissue-engineered constructs from Acropora and Porites coral in a large animal bone defect model. Bone Joint Res 2017;6:208-215. DOI: 10.1302/2046-3758.64.BJR-2016-0236.R1.

Keywords: Atrophic nonunion of the long bones; Bone marrow-derived mesenchymal stem cells; Coral scaffold.

Display of a) Acropora and b) Porites scaffolds accessed by microCT: Acropora exhibited larger and more irregular pore size; Porites had a more homogeneous structure with smaller pores. The porosity of Acropora was lower than that of Porites.

Fig. 2

Radiographs after surgery and at two months, CT reconstructions, and histological slides at four months of the metatarsal bone defects of animals implanted with Acropora-tissue-engineered constructs (TEC) a), Porites-TEC b) and autograft c). At two months post-operatively, on radiographs, newly-formed bone could not be distinguished from the remaining scaffold material in case of Acropora-TEC (a), but partial to full bioresorption was observed with Porites-TEC (b). At 4 months, full bone regeneration was observed in some animals (a and b top), resembling that observed in autografted animals (c). Recorticalisation was observed in the Acropora-TEC filled defect (a top). In the other animals, new bone formation was limited (a and b bottom). There were still Acropora-TEC present in the defect (a), whereas almost no Porites-TEC remained (b), four months post-operatively. Stains: Stevenel blue and von Gieson picrofuschin. Bone, cells, and coral stained red, blue, and brown, respectively.

Graphs showing quantitative analysis of new bone formation and scaffold material bioresorption in defects filled with Acropora-tissue-engineered constructs (Acropora-TEC), Porites-TEC and autograft, four months post-operatively. a) The amount of newly formed bone was not statistically different in defects filled with either Acropora- or Porites-TECs (p = 0.09). High variability and scattering of the pertinent values were observed in the Acropora-TEC group. Two of the defects filled with Acropora-TECs showed the greatest amount of newly formed bone and full bone regeneration, (red triangles), these values were higher than those observed with the Porites-TECs (squares) and autograft cases (circles). b) The bioresorption rates of the scaffold material were lower in Acropora-TEC than in Porites-TEC (p = 0.04). c) New bone formation in Acropora- and Porites-TECs was similar based on the area of the defect, except in the proximal third (p = 0.01). The two Acropora-TEC (blue triangles) and the four Porites-TEC (black squares) which exhibited the highest scaffold material bioresorption (more than 90%; grey line) had the least bone formation.

Representative histology of newly formed bone in the tested defects. New bone tissue was present above and inside the remaining coral scaffolds (a and b). Both mature and immature bone tissue was observed, with, respectively, well-orientated, small and dark cells (osteocytes in lacunae) forming a lamellar tissue (c and e) and disorganised, large-nucleated cells forming a non-lamellar tissue (b and f). Abundant osteoid (yellow arrow heads) encircled by bone-lining cells (black arrow heads) was present surrounding the bone tissue, revealing active bone formation (c, e and f). When bone tissue was absent, fibrous tissue was filing the defect (d). The images were obtain from two sheep of the Acropora-TEC group. Stains: Stevenel Blue and von Gieson picrofuschin. Bone, cells, and coral stained red, blue, and brown, respectively.