Access devices (10) and related methods are disclosed that generally involve flexible or adjustable cannulas (14) that have a substantially cylindrical insertion configuration and a substantially conical expanded configuration. Various methods and features are provided for transitioning the cannula from the insertion configuration to the expanded configuration while the access device is inserted through tissue to form a conical opening through the tissue. Examples include cables (15), biasing elements (120), retaining elements (122), bimodal rings (152), and coil springs (219). The devices and methods disclosed herein can allow for improved retention of the access device, improved angulation of instruments passed through the access device, and can increase the integrity of a seal formed between the access device and surrounding tissue.