Catheters of the present disclosure include a catheter shaft and an expandable tip, which can retrieve materials slightly larger than an inner diameter of the catheter shaft. The tip may be expandable such that it can easily transform from a first size and shape to a second size and shape to aid in the retrieval of the materials (i.e., the thrombus, embolus, or foreign body). Catheter tips may be expanded by inflation, removal of a constraining member, or an input such as heat, light, or electrical energy.