Methods and compositions are provided that load and encapsulate an agent, such as a protein, in a porous self-healing polymer. A delivery system includes a porous self-healing polymer, an ionic affinity trap within the pores of the self-healing polymer, and an agent associated with the ionic affinity trap. Methods of encapsulating an agent in a polymer include providing a porous self-healing polymer comprising an ionic affinity trap within the pores. The polymer is incubated with an agent having an affinity for the ionic affinity trap. At least a portion of the pores in the polymer are then healed. Active encapsulation of macromolecules at low concentrations may be achieved due to affinity of the agent for the ionic affinity trap within the pores.