Objective: To observe the release pattern of the microcysts and the effect of ectopic osteogenesis of combined micromorselized bone by optimized preparation of microcysts.
Methods: Optimized poly-DL-lactide-coglycolide (PLGA) microcysts manufacturing method was performed with the orthogonal design, and the accumulated release amount of microcysts was calculated at 2 h, 4 h, 8 h, 12 h, 24 h, 36 h, 48 h, 60 h, 72 h, 84 h, 96 h, 120 h, 144 h, 168 h, 192 h, 216 h, 240 h and 264 h. Twenty-four Wistar rats were divided into 4 groups (n=6) and 1 cm length incision was cut in their bilateral thighs skin, forming 48 gluteus maximus muscle sack models. In group A, collagen was implanted to bilateral muscle sacks respectively. In group B, collagen and autologous morselized bone were implanted to bilateral muscle sacks. In group C, collagen and rhBMP-2/PLGA delayed release microcysts were implanted to bilateral muscle sacks respectively. In group D, collagen and morselized bone/rhBMP-2/PLGA delayed release microcysts were implanted to bilateral muscle sacks. Gross and histologic observations were made at 3, 4 and 5 weeks postoperatively.
Results: Every optimized variance had an effect on particle diameter of microcyst and its encapsulating rate. The microcyst's surface was smooth and had a fine spheroplast, which released slowly within 11 days in vitro. In the third week postoperatively, the graft in group A could not be touched, while the graft in all other 3 groups was still found. After 3 weeks, collagen was absorbed completely in group A, the residual collagen could be seen in groups B, C and D. After 4 weeks, collagen could be seen in group A; micromorselized bone continued to be absorbed and became smaller in group B; microsphere became smaller, osteoblasts increased in group C; micromorselized bone and microsphere continued to be absorbed, oteoblasts and chondroblasts increased. After 5 weeks, implants became small, microsphere was absorbed, osteoblasts and chondroblasts became more in groups B, C and D. Microcysts presented with white granulo-shape and were packaged in tissue pieces. Histologic observation showed that the PLGA microcysts in 3 weeks and 4 weeks could be absorbed gradually as the time in vivo, if combining with morselized bone they could produce abundant induced osteoblasts and chondroblasts.
Conclusion: Optimizing the preparation technology of microcysts has delayed their release during a long period in vitro. Autologous micromorselized bone can be ectopicly induced to produce large amount of osteoblasts in gluteus maximus muscle sack, where PLGA microcysts can combine organically and bring about the bone formation with less amount of growth factors.