4D Multimaterial Printing of Soft Actuators with Spatial and Temporal Control.

Soft actuators (SAs) are devices which can interact with delicate objects in a manner not achievable with traditional robotics. While it is possible to design a SA whose actuation is triggered via an external stimulus, the use of a single stimulus creates challenges in the spatial and temporal control of the actuation. Herein, a 4D printed multimaterial soft actuator design (MMSA) whose actuation is only initiated by a combination of triggers (i.e., pH and temperature) is presented. Using 3D printing, a multilayered soft actuator with a hydrophilic pH-sensitive layer, and a hydrophobic magnetic and temperature-responsive shape-memory polymer layer, is designed. The hydrogel responds to environmental pH conditions by swelling or shrinking, while the shape-memory polymer can resist the shape deformation of the hydrogel until triggered by temperature or light. The combination of these stimuli-responsive layers allows for a high level of spatiotemporal control of the actuation. The utility of the 4D MMSA is demonstrated via a series of cargo capture and release experiments, validating its ability to demonstrate active spatiotemporal control. The MMSA concept provides a promising research direction to develop multifunctional soft devices with potential applications in biomedical engineering and environmental engineering.

Time-Resolved Activation of pH Sensing and Imaging in Vivo by a Remotely Controllable DNA Nanomachine.

Construction of probes or nanodevices capable of sensing pH with high spatial and temporal precision remains a challenge, despite their importance in monitoring of diverse physiological and pathological processes. Here we disclose the first remotely and noninvasively controlled DNA nanomachine that can monitor pH in live cells and animals in a temporally programmable manner. The nanomachine is designed by rational engineering of the DNA motif with a light-responsive element and further combination with an upconversion nanoparticle that works as a transducer to manipulate the nanomachine with the high precision of NIR light. The nanomachine not only allows for activated fluorescent imaging of intracellular pH, but it also can exert spatiotemporal control over its pH sensing activity in tumor-bearing mice by NIR light irradiation at a chosen time and place. This work illustrates the potential of combining DNA nanotechnology with upconversion tools to yield a precisely controlled nanomachine for temporally resolved pH sensing and imaging.