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Shape memory polymers are gaining significant interest as one of the major constituent materials for the emerging field of 4D printing. While 3D-printed metamaterials with shape memory polymers show unique thermomechanical behaviors, their thermal transport properties have received relatively little attention. Here, we show that thermal transport in 3D-printed shape memory polymers strongly depends on the shape, solid volume fraction, and temperature and that thermal radiation plays a critical role. Our infrared thermography measurements reveal thermal transport mechanisms of shape memory polymers in varying shapes from bulk to octet-truss and Kelvin-foam microlattices with volume fractions of 4%–7% and over a temperature range of 30–130 °C. The thermal conductivity of bulk shape memory polymers increases from 0.24 to 0.31 W m−1 K−1 around the glass transition temperature, in which the primary mechanism is the phase-dependent change in thermal conduction. On the contrary, thermal radiation dominates heat transfer in microlattices and its contribution to the Kelvin-foam structure ranges from 68% to 83% and to the octet-truss structure ranges from 59% to 76% over the same temperature range. We attribute this significant role of thermal radiation to the unique combination of a high infrared emissivity and a high surface-to-volume ratio in the shape memory polymer microlattices. Our work also presents an effective medium approach to explain the experimental results and model thermal transport properties with varying shapes, volume fractions, and temperatures. These findings provide new insights into understanding thermal transport mechanisms in 4D-printed shape memory polymers and exploring the design space of thermomechanical metamaterials. 

Abstract 3D cell cultures are rapidly emerging as a promising tool to model various human physiologies and pathologies by closely recapitulating key characteristics and functions of in vivo microenvironment. While high‐throughput 3D culture is readily available using multi‐well plates, assessing the internal microstructure of 3D cell cultures still remains extremely slow because of the manual, laborious, and time‐consuming histological procedures. Here, a 4D‐printed transformable tube array (TTA) using a shape‐memory polymer that enables massively parallel histological analysis of 3D cultures is presented. The interconnected TTA can be programmed to be expanded by 3.6 times of its printed dimension to match the size of a multi‐well plate, with the ability to restore its original dimension for transferring all cultures to a histology cassette in order. Being compatible with microtome sectioning, the TTA allows for parallel histology processing for the entire samples cultured in a multi‐well plate. The test result with human neural progenitor cell spheroids suggests a remarkable reduction in histology processing time by an order of magnitude. High‐throughput analysis of 3D cultures enabled by this TTA has great potential to further accelerate innovations in various 3D culture applications such as high‐throughput/content screening, drug discovery, disease modeling, and personalized medicine.