Growth factor-free synthetic matrices reveal intrinsic skeletal progenitor competence

Clinical translation of human skeletal progenitor cells has been limited by the inability to reliably predict their regenerative performance, as current characterization methods rely on phenotypic markers or instructive differentiation assays that obscure intrinsic cell function. Here we demonstrate that human skeletal progenitor competence can only be revealed within a precisely defined and growth factor-free synthetic microenvironment. By independently tuning matrix mechanics, degradability, adhesion, and cell density within a fully synthetic poly(ethylene glycol) hydrogel, we create a permissive niche that enables human bone marrow stromal cells (hBMSCs) to undergo spontaneous bone formation in vivo without osteoinductive supplementation. These exogenous growth factor-free conditions expose donor-specific differences in bone forming capacity that are otherwise masked. Strikingly, supplementation with even low concentrations of BMP-2 abolished inter-donor variability, directly demonstrating that osteoinductive factors override intrinsic progenitor competence. Single-cell transcriptomics, proteomic profiling, and longitudinal in vivo analyses converge to show that high performing donors are defined by chondrocyte-primed transcriptional states and coordinated extracellular matrix (ECM) remodeling programs that establish a pro-osteochondral niche and drive bone formation via endochondral ossification. In contrast, low performing donors fail to initiate this cascade despite comparable phenotypic profiles and proliferation rates. Together, these findings implicate matrix context as a critical regulator of stem cell competence. Within this permissive synthetic niche, intrinsic ECM remodeling capacity emerges as a defining feature of donor-specific osteogenic potential, one that remains invisible to conventional assays. These matrices thus provide a functional platform for prospective stratification of skeletal progenitor cells, with direct implications for donor selection in regenerative medicine.