Active matter is a paradigm of soft materials made of a large number of interacting agents, ranging from colonies of bacteria to assemblies of biomimetic micro-swimmers, where individual self-propulsion leads to dynamics and structures without any equilibrium equivalent. The dissipation at the basis of activity offers the opportunity to design smart materials, for instance to extract work with unprecedented protocols, for which generic guiding principles are still lacking. Moreover, controlling dissipation allows one to select which order emerges at large scale by promoting dynamical phase transitions, whose properties are yet to be studied.

First, I will present design strategies for active engines which exploit specifically nonequilibrium effects, such as the autonomous motion of asymmetric obstacles and the lack of an equation of state in active fluids. I will discuss how to optimize their efficiency in terms of the protocol details and, when possible, compare their performances with thermal engines. Second, I will examine the emergence of spontaneous order when changing dissipation. Using large deviation techniques, I will describe unexpected phase transitions, for instance towards a collective motion despite the lack of aligning interactions, and rationalize the microscopic mechanisms triggering such collective effects.