Abstract
To prevent the reported side effects of rhBMP-2, an important cytokine with bone forming capacity, the sustained release of rhBMP-2 is highly important. Synthetic copolymer polylactic acid-polyethylene glycol (PLA-PEG) is already shown to be a good carrier for rhBMP-2. The nano-sized hydroxyapatite (nHAp) is mentioned to be superior to conventional hydroxyapatite due to its decreased particle size which increases the surface area, so protein-cell adhesion and mechanical properties concomitantly. In the literature no study is reported with PLA-PEG / rhBMP-2/ nHAp for bone regeneration. In this study, we assessed the controlled release profile of rhBMP-2 from the novel biomaterial of PLA-PEG / rhBMP-2 / nHAp in vitro and evaluated the bone forming capacity of the composite in rat posterolateral spinal fusion (PSF) model in vivo.
Composites were prepared via addition of rhBMP-2 (0µg, 3µg or 10µg) and nHAp (12.5mg) into PLA-PEG (5mg) + acetone solution and shaping. The release kinetics of the cytokine from the composites with 5µg BMP-2 was investigated by ELISA. The effect of nHAp and nHAp with rhBMP-2 on cell differentiation (rat BMSC cells, passage 3) was tested with ALP staining. In vivo bone formation was investigated by PSF on L4-L5 in a total of 36 male SD rats and weekly µCT results and histology at 8th weeks post operation were used for assessment of the bone formation. All animal experiments was approved by the institutional review board confirming to the laws and regulations of Japan.
The composite showed an initial burst release in the first 24 hours (51.7% of the total released rhBMP-2), but the release was continued for the following 21 days. Thus, the sustained release of rhBMP-2 from the composite was verified. ALP staining results showed nHAp with rhBMP-2 contributed better on differentiation than nHAp itself. µCT and histology demonstrated that spinal fusion was achieved either one or both transverse processes in almost all BMP 3µg and BMP 10µg treated animals. On the contrary, only small or no bone formation was observed in the BMP0µg group (bilateral non-union / unilateral fusion/ bilateral fusion, BMP0µg group; 9/0/0, BMP3µg group; 1/0/11, BMP10µg group; 0/1/11).
We developed a new technology for bone regeneration with BMP-2/PLA-PEG/nHAp composite. With this composite, the required dose of BMP-2 for spinal fusion in rats (10µg) was decreased to 1/3 (3µg) which can be explained by the superior properties of nano-sized hydroxyapatite and by the achievement of sustainable release of rhBMP-2 from the composite.
This study is supported by Japanese Society of the Promotion of Science (JSPS) and Scientific and Technological Research Council of Turkey (TUBITAK). [Project No: 215S834]
