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Improving the Osteogenicity of PCL Fiber Substrates by Surface-Immobilization of Bone Morphogenic Protein-2

Abstract

Polycaprolactone (PCL) fiber scaffolds are attractive, albeit inert, substrates for ligament regeneration, that may be improved by incorporating trophic factors to guide tissue remodeling in vivo. In particular, immobilization of bone morphogenic protein-2 (BMP-2) to the scaffold surface may facilitate rapid and robust integration of the scaffold with adjacent bone tissues. As a first step toward testing this, model PCL surfaces were modified by the addition of heparin (Hep) and BMP-2 to facilitate osteoblastic differentiation. Specifically, Hep was combined with PCL at 0, 0.5, and 1 wt% (denoted as PCL, PCL–0.5Hep, and PCL–1Hep), cast into films, and then BMP-2 was immobilized to surfaces by either adsorption and covalent conjugation. Here, BMP-2 concentration increased systematically with incorporation of Hep, and higher concentrations were achieved by covalent conjugation. Next, blends were electrospun to form thin meshes with fiber diameters of 0.92, 0.62, and 0.54 μm for PCL, PCL–0.5Hep, and PCL–1Hep, respectively. Mesenchymal stem cells (MSCs) had no difficulty attaching to and proliferating on all meshes. Lastly, PCL–1Hep meshes were prepared with adsorbed or covalently conjugated BMP-2 and cultured with MSCs in the absence of osteogenic factors. Under these conditions, alkaline phosphatase activity and deposition of bone sialoprotein, osteopontin, and calcium minerals—markers of osteoblastic differentiation—were significantly higher on surfaces with immobilized BMP-2. Together, these data indicate that covalent immobilization of trophic factors confers bioactivity to scaffolds, which may be applied in a spatially controlled manner for ligament regeneration and bone integration.

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Acknowledgments

The authors would like to thank Dr. William Ducker for the use of his contact angle goniometer, Dr. Rafael Davalos for the use of his spin coater, and Dr. Vincent Wang for the use of his mechanic testing frame. This work was supported by the Interdisciplinary Graduate Educational Program in Regenerative Medicine and the Department of Chemical Engineering at Virginia Tech.

Conflict of interest

The authors declare no competing financial interests.

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Correspondence to Aaron S. Goldstein.

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Gadalla, D., Goldstein, A.S. Improving the Osteogenicity of PCL Fiber Substrates by Surface-Immobilization of Bone Morphogenic Protein-2. Ann Biomed Eng 48, 1006–1015 (2020). https://doi.org/10.1007/s10439-019-02286-1

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Keywords

  • BMP-2
  • Electrospinning
  • Polycaprolactone
  • Mesenchymal stem cells
  • Osteoblastic differentiation