4D-printed programmable sample-/eluent-actuated solid-phase extraction device for trace metal analysis

To integrate valves, manifolds, and solid-phase extraction (SPE) columns into a compact device is technically difficult. Four-dimensional printing (4DP) technologies, employing stimuli-responsive materials in three-dimensional printing (3DP), are revolutionizing the fabrication, functionality, and applicability of stimuli-responsive analytical devices that can show time-dependent shape programming to enable more complex geometric designs and functions. However, 4D-printed stimuli-responsive actuators and valves utilized to control flowing streams in SPE applications remain rare. The tunable stimuli-responsive 4D-printed flow control actuators and valves with the capability of the programmable actuation can be used to manipulate flowing streams and simplify the automation of a conventional SPE scheme. We employed digital light processing three-dimensional printing (3DP), bisphenol A ethoxylate dimethacrylate-based photocurable resins, and 2-carboxyethyl acrylate (CEA)-incorporated flexible photocurable resins to fabricate an SPE column positioned between two [H+]-responsive flow-actuated needle valves. The two valves sequentially close after loading an alkaline sample (pH > pKa of CEA) due to swelling of the stem. Subsequently, they sequentially open upon loading an acidic eluent (pH