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4D printing is an emerging additive manufacturing technology that combines the precision of 3D printing with the versatility of smart materials. 4D printed objects can change their shape over time with the application of a stimulus (i.e., heat, light, moisture). Light driven smart materials are attractive because light is wireless, remote, and can induce a rapid shape change. Herein, we present a method for fabricating polymeric bilayer actuators via 3D printing which reversibly change their shape upon exposure to light. The photoactive layer consists of a poly(siloxane) containing pendant azobenzene groups. Two different photoactive polymers were synthesized, and the photomechanical effect displayed by the bilayers was evaluated. These bilayers exhibit rapid actuation with full cycles completed within seconds, and photo generated stresses ranging from 1.03 to 1.70 MPa.

The purpose of this paper is to review the mechanisms of electrohydrodynamic (EHD) phenomenon. From this review, researchers and students can learn principles and development history of EHD. Significant progress has been identified in research and development of EHD high-resolution deposition as a direct additive manufacturing method, and more effort will be driven to this direction soon. An introduction is given about current trend of additive manufacturing and advantages of EHD inkjet printing. Both theoretical models and experiment approaches about the formation of cone, development of cone-jet transition and stability of jet are presented. The formation of a stable cone-jet is the key factor for precision EHD printing which will be discussed. Different scaling laws can be used to predict the diameter of jet and emitted current in different parametrical ranges. The information available in this review builds a bridge between EHD phenomenon and three-dimensional high-resolution inkjet printing.

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High pressure optical measurements are useful for understanding structure and function of biological molecules. Commonly used high-pressure optical cells can only observe a single sample under elevated pressure. If researchers wish to observe the interaction between different biological samples, they must mix the samples at atmospheric pressure, place the mixture within the pressure chamber, and wait until the desired pressure is reached. In many cases, researchers want to observe the initial reaction between two separate biological samples; however, the sample mixing and the assembly of the high pressure optical cell coupled with a spectrometer at desired pressures can take several minutes or longer. Our current design uses a shape memory alloy (SMA) spring actuator to seal a dual chamber cuvette for separation of two different biological samples. Once the desired pressure is reached, power is applied to the system that activates the SMA to unplug and mix the two samples using a micro dc-motor. During the mixing efficiency tests, deionized water was placed in the top chamber of the cuvette and an aqueous solution of carboxyfluorescein (a fluorescent dye) placed in the bottom chamber. Based on this design, we were able to achieve a total unplugging and mixing time within a few seconds (at atmospheric pressure). Quicker mixing means researchers will have more reliable data for analyzing the initial reactions between two different biological samples. Future tests on this new actuator will be conducted at elevated pressures.

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