<jats:title>Abstract</jats:title><jats:p>Synthetic hydrogels provide controllable 3D environments, which can be used to study fundamental biological phenomena. The growing body of evidence that cell behavior depends upon hydrogel stress relaxation creates a high demand for hydrogels with tissue‐like viscoelastic properties. Here, we have created a unique platform of synthetic PEG hydrogels in which star‐shaped PEG molecules were conjugated with alendronate and/or RGD peptides, attaining modifiable degradability as well as flexible cell adhesion. We identified novel reversible ionic interactions between alendronate and calcium phosphate nanoparticles, leading to versatile viscoelastic properties with varying initial elastic modulus and stress relaxation time. This new crosslinking mechanism provides shear‐thinning properties resulting in differential cellular responses between cancer cells and stem cells. The novel hydrogel system is an improved design to the other ionic crosslink platforms and opens new avenues for the development of pathologically relevant cancer models, as well as minimally‐invasive approaches for cell delivery for potential regenerative therapies.</jats:p><jats:p>This article is protected by copyright. All rights reserved</jats:p>