The effect of a gelatin β-tricalcium phosphate sponge loaded with mesenchymal stem cells (MSC), bone morphogenic protein-2, and platelet-rich plasma (PRP) on equine articular cartilage defect

Abstract

We evaluated the curative efficacy of a gelatin β-tricalcium phosphate (β-TCP) sponge loaded with mesenchymal stem cells (MSC), bone morphogenic protein-2 (BMP-2), and platelet-rich plasma (PRP) by insertion into an experimentally induced osteochondral defect. A hole of 10 mm diameter and depth was drilled in the bilateral medial femoral condyles of 7 thoroughbred horses, and into each either a loaded sponge (treatment) or a saline-infused β-TCP sponge (control) was inserted. After 16 weeks, defects were examined by computed tomography, macroscopic analyses, and histological analyses. The median subchondral bone density and macroscopic subscores for joint healing were significantly higher in the treatment legs (P < 0.05). Although there was no significant difference in total histological scores between groups, hyaline cartilaginous tissue was observed across a wider area in the treatment group. Equine joint healing can be enhanced by inserting a BMP-2-, MSC-, and PRP-impregnated β-TCP sponge at the lesion site.

Figure 1

The β-TCP sponge impregnated with bone morphogenetic protein-2 (BMP-2), mesenchymal stem cells (MSCs), and platelet-rich plasma incorporated onto gel microspheres (PRP/GM). The appearance (a) and structure (b) of the impregnated sponge are shown. The impregnated sponge was designed as a bilayer by maintaining the PRP/GM within the upper layer so that growth factors in PRP were released only from the upper layer, whereas BMP-2 was released from the entire sponge. Scale bar = 10 mm.

Figure 2

Total macroscopic scores and subscores (surface texture, void filled, tissue integration) for joint defects treated with the impregnated sponge (treatment, T) and the saline-infused sponge (control, C). Macroscopic scores were significantly higher in the treatment group. The numbers beside data points denote the number of specimens with that particular score. *P < 0.05 (Wilcoxon signed-rank test)

Figure 3

Macroscopic appearance of the treated and control joints of horse No. 5. On the treatment side (left), the subchondral bone in the drill hole was covered by white, smooth tissue (macroscopic subscores: surface texture = 4, filled = 3, tissue integration = 3, total = 10). On the control side (right), the drill hole was covered with red, rough tissue (macroscopic subscores: surface texture = 2, filled = 3, tissue integration = 2, total = 7). Scale bar = 5 mm.

Figure 4

Total histological scores and subscores for the treated and control joints. There were no significant differences in histological scores between the treatment and control groups. Numbers beside each data point denote the number of specimens with that particular score. T — treatment group; C — control group; DF — depth of defect filled; CP — chondrocyte predominance; CO — chondrocyte organization; TP — tidemark presence; CC — perilesional chondrocyte cloning; IC — integration with adjacent perimeter cartilage; IS — integration with subchondral bone; SA — surface architecture (fibrillation); Saf — Safranin-O staining relative to adjacent cartilage; Col — collagen type 2 predominance.

Figure 5

Histological appearance of the cartilage in horse No. 4. The broken line indicates the drill-hole region. The arrowhead indicates that the tissue is positive for safranin-O staining and immunopositive for type 2 collagen. In the treatment group, safranin-O staining and tissue immunopositive for type 2 collagen covered a wider area than observed in the control group. Subchondral bone regeneration was observed over a wider area in the treatment group compared with the control group. The treatment side had a subchondral bone density score of 3, and the control side had a subchondral density score of 0. Upper panel: treatment group, lower panel: control group, Scale bar = 5 mm.