Heterobifunctional Poly(Ethylene Glycol)–Tethered Bone Morphogenetic Protein-2–Stimulated Bone Marrow Mesenchymal Stromal Cell Differentiation and Osteogenesis

Abstract

We describe a biomimetic mode of insoluble signaling stimulation to provide target delivery of bone morphogenetic protein-2 (BMP-2), with the aim of prolonging the retention of BMP-2 use in bone tissue engineering and to enable its localized release in response to cellular activity. In our novel localization process, we used heterobifunctional acrylate-N-hydroxysuccinimide poly(ethylene glycol) (PEG) as a spacer to tether BMP-2 onto a poly(lactide-co-glycolide) scaffold. Use of PEG-tethered BMP-2 was feasible because BMP-2 retained its activity after covalent conjugation. The PEG-tethered BMP-2 conjugate sustained stimulation and retained its mitogenic activity, notably affecting pluripotent stem cell proliferation and differentiation. We seeded the scaffolds with bone marrow-derived mesenchymal stromal cells as progenitor cells to evaluate their morphology and phenotypic expression. We also created bilateral, full-thickness cranial defects in rabbits to investigate the osteogenic effect of cultured mesenchymal stromal cells on bone regeneration in vivo. Histomorphometry and histology demonstrated that the PEG-tethered BMP-2 conjugate enhanced de novo bone formation after surgery. Our work revealed the potential for biomimetic surface engineering by entrapping signaling growth factor to stimulate osteogenesis. Our technique may provide a new platform for bone-engineered stem cell therapies.

Chemically-Conjugated Bone Morphogenetic Protein-2 on Three-Dimensional Polycaprolactone Scaffolds Stimulates Osteogenic Activity in Bone Marrow Stromal Cells

“…Interestingly, previous studies and our current study have shown the distinctive release pattern of the conjugated BMPs from the biomaterial surface with different conjugation strategies and biomaterials. [13][14][15] The different release patterns in different studies may indicate that the conjugation strategy as well as the material itself also affect the release pattern.…”

“…The possibility of substrate bound growth factors influencing cell behavior has been confirmed by several studies. Studies conjugating BMPs on biomaterials such as PLGA, 12,14,15 titanium, 25 and chitosan 16 have demonstrated that the conjugated BMPs maintain their bioactivity, stimulating increased cell proliferation and differentiation. More importantly, in vivo studies using conjugated BMP-2 on PLGA scaffolds induced bone formation in a rabbit femoral defect 12 and in a hind limb defect.…”

“…12 Subsequently, several studies have shown that after covalent conjugation a variety of growth factors, including insulin, epidermal growth factors, BMP-2, and BMP-4, onto a range of biomaterial surfaces, the conjugated growth factors remained stable and demonstrated prolonged bioactivity with reduced burst release. [13][14][15][16] In addition, in vivo studies with conjugated growth factors have demonstrated improved bone formation. 12,14,15 This delivery approach may be a way to reduce the initial BMP-2 loading amount, while retaining and extending the growth factor's activity in facilitating the cell-material interactions and subsequent bone regeneration.…”

“…[13][14][15][16] In addition, in vivo studies with conjugated growth factors have demonstrated improved bone formation. 12,14,15 This delivery approach may be a way to reduce the initial BMP-2 loading amount, while retaining and extending the growth factor's activity in facilitating the cell-material interactions and subsequent bone regeneration.…”

Growth Factor Delivery Through Self-assembling Peptide Scaffolds

“…Growth factors, including TGF-b1, have been covalently immobilized or tethered onto other polymer scaffolds or hydrogels with other cell types [2,8,20,21,29,34], sometimes with altered signaling as a result [10,35,42]. The density of tethered growth factors can also affect bioactivity [45]; however, both IGF-1 and TGF-b receptors exist as functional complexes on cell surfaces, and binding of one ligand can initiate signaling [9,43].…”