Fabrication of calcium phosphate-loaded carboxymethyl cellulose non-woven sheets for bone regeneration

Calcium phosphate-loaded carboxymethyl cellulose non-woven sheets (CMC/CaP sheet) were fabricated and their potential to induce in vitro osteoblast differentiation and in vivo bone regeneration were investigated. The CMC/CaP sheets were prepared by alternately soaking protonated-CMC non-woven sheets in CaCl₂ and Na₂HPO₄ aqueous solutions. Because of its slow water uptake rate, the protonated-CMC was successfully loaded with a mixed phase of brushite and hydroxyapatite. In vitro, the CMC/CaP sheet induced osteoblast differentiation of human mesenchymal stromal cells (hMSCs), as shown by calcification and the upregulation of osteoblast marker genes. In absence of CaP, hMSCs on the CMC sheet had enhanced expression of alkaline phosphatase (ALP) only, indicative of early osteoblast differentiation. Finally, bone regeneration by the CMC/CaP sheet was demonstrated in a mouse calvarial defect model, based on micro-computed tomography (micro-CT), Masson's trichrome staining, and immunostaining for osteoblast markers. Cells expressing the transcription factor Sp7/Osterix, which is essential for osteoblast differentiation, were detected around the new bone. The combined effect of CMC and CaP enhanced osteoblast differentiation and the CMC/CaP non-woven sheet was found to be an easy-to-handle and flexible scaffold for bone regeneration.