An In Vitro Assessment of a Cell-Containing Collagenous Extracellular Matrix-like Scaffold for Bone Tissue Engineering

Extracellular matrix (ECM) consists of a complex mixture of macromolecules such as collagens, proteoglycans, glycoproteins, and elastic fibers. ECM is essential to preserving tissue architecture, signaling to cells, and regulating calcification in mineralized tissues. Osteoblasts in culture secrete and assemble an extensive ECM rich in type I collagen, and other noncollagenous proteins that can be mineralized. Three-dimensional matrix models can be used in vitro to most appropriately resemble the geometry and biochemistry of natural ECMs. In the present study, MC3T3-E1 mouse calvarial preosteoblasts were cultured within a dense three-dimensional collagenous ECM-like scaffold produced through the method of plastic compression. Plastic compression rapidly produces scaffolds of collagen density approaching native tissue levels with enhanced biomechanical properties while maintaining the viability of resident cells. The proliferation, morphology, and gene expression of seeded MC3T3s, as well as collagen production and matrix mineralization, were investigated for up to 7 weeks in culture. Soluble collagen secretion ranged in concentration from 5 to 30 mu g/mL over a 24-h period, concomitant with a steady rate of collagen mRNA expression. Expression of osteogenic markers such as tissue-nonspecific alkaline phosphatase (Alpl), bone sialoprotein (Bsp), and osteopontin (Opn) examined by biochemical assay and reverse transcription-polymerase chain reaction demonstrated cell differentiation. Pericellular voids of ECM around cells, together with evidence of MMP13 mRNA expression, suggested matrix remodeling. Ultrastructural analyses, X-ray micro-analysis, micro-computed tomography, as well as Fourier-transform infrared and imaging all confirmed the formation of a calcium-phosphate mineral phase within the fibrillar collagen matrix. In conclusion, preosteoblastic MC3T3 cells seeded within an ECM-like dense collagen scaffold secrete matrix proteins and induce scaffold mineralization in a manner potentially appropriate for bone tissue engineering uses.