Expansion of muscle stem cells (MuSCs) ex vivo is an unmet goal of regenerative medicine approaches for the treatment of muscle wasting conditions like aging-associated sarcopenia and Duchenne muscular dystrophy. Here we aimed to engineer biomimetic two-dimensional poly(ethylene glycol) hydrogel models of the muscle stem cell microenvironment with independent control of biomolecular and mechanical stimuli to expand MuSCs without loss of their essential stem-cell phenotype as defined by molecular (Pax7 expression) and functional characterization (in vivo transplantation). Inspired by the role of acute inflammation on MuSC self-renewal, we developed in vitro models combining stimulation by inflammatory cytokines (IL-1α, IL-13, TNFα, IFNγ) and p38 mitogen-activated protein kinase pathway inhibition in conjunction with mechano-sensing imparted by a tunable modulus (rigidity) hydrogel substrate to stimulate MuSC expansion. We demonstrated that a muscle-like rigidity (~10 kPa elastic modulus) synergistically promoted long-term MuSC expansion with the cytokine and p38 inhibitor treatments. We observed that this system exhibits control of MuSC phenotypes for 4-5 weeks of culture in terms of proliferative expansion (~106–108-fold) and myogenic differentiation as indicated by MuSC immunostaining and RT-qPCR. Our findings suggest that reliably large pools of MuSCs can be maintained long-term, establishing a platform for the further optimization of in vitro personalized modeling and medicine.