These three technologies improve the manufacturing and functionality of microfluidic devices. The technologies enable fast, easy, and inexpensive construction of microfluidic devices that can perform complex functions, have innovative designs, and operate autonomously. Devices fabricated using these technologies offer self-regulating functions, better "constriction regions" for positioning objects within the device, and the ability to create a large liquid-air interface by means of "virtual walls" in the device's channels.