Mixing systems for producing a mixture to deliver to a treatment site. An illustrative system may comprise a needle hub, a multi-reservoir system, and a syringe. The multi-reservoir system may comprise a plunger assembly including a first tubular plunger and a second tubular plunger, a barrel portion including a housing defining a first reservoir in fluid communication with a first port and configured to contain a first constituent and a second annular reservoir configured to contain a second constituent and in fluid communication with a second port, and a third plunger. A third constituent may be injected from the syringe into the first reservoir to form a precursor. Actuating the plunger assembly relative to the barrel portion may cause the precursor and the second constituent to be delivered into the needle hub.