In aqueous solution, MAX 1 peptide [(VK)₄V^DPPT(KV)₄] is unfolded, freely soluble and does not self-assemble. However, the peptide intramolecularly folds into a beta-hairpin conformation when the electrostatic interactions between charged lysine residues are screened, through increasing the ionic strength at neutral pH. Beta-hairpin molecules intermolecularly assemble via hydrophobic collapse and hydrogen bonding into a 3-D hydrogel network, consisting of well-defined fibrils on the nanoscale. Self-assembly triggered in cell-culture medium leads to rigid and shear thinning hydrogels, while the stiffness of the network recovers quickly when the stress is removed. Moreover, the hydrogels are cytocompatible, showing future prospects for biological applications such as injectable 3-D cell encapsulants. By combining the results of circular dichroism spectroscopy, cryogenic transmission electron microscopy, dynamic light scattering, and oscillatory rheology, we observe that the self-assembly proceeds by nucleation of monodisperse beta-sheet fibrils, that elongate and branch to form clusters of fibrils. Assembly kinetics at this early stage indicates power law growth with assembly time, similar to diffusion-limited clustering of clusters. Eventually, clusters of fibrils fill up the sample volume, and interpenetrate to form a percolated network, as evidenced by the increasing network rigidity. The early stage assembly process will be discussed and compared to published gelation models. Ultimately, our goal is to correlate the structural growth mechanism with in vitro cell function and response.