Stem cell differentiation
How an uncommitted cell chooses a fate — under chemical, mechanical, and spatial instruction.
Differentiation is the process by which an uncommitted cell narrows into a specific identity, driven by transcription factor networks that activate lineage programmes and silence alternatives. In bone, RUNX2 is the master regulator: drive it and a mesenchymal stem cell commits toward the osteoblast lineage.
Instructions come from more than chemistry. Soluble factors — BMPs, TGF-β, Wnt — are the classic inputs, and osteogenic differentiation is exactly what BMP-2 induces. But matrix stiffness alone can bias fate, and cell shape and density modulate it further. The instruction is the sum of the environment, which is why scaffold and hydrogel properties are biologically active choices, not just structural ones.
In culture this is directed with defined media; in a construct it must be achieved in a far less controlled setting, which is a recurring reason in vitro success does not carry into in vivo results. See The extracellular matrix.
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