Kunhao Yu, Zhangzhengrong Feng, Haixu Du, An Xin, Kyung Hoon Lee, Ketian Li, Yipin Su, Qiming Wang, Nicholas X. Fang, and Chiara Daraio

PNAS January 19, 2021 118 (3) e2016524118

Significance

Living creatures are continuous sources of inspiration for designing engineering materials and structures. However, synthetic engineering materials are typically different from living creatures, because the latter consist of living cells to support their metabolisms, such as remodeling, growth, and reproduction. How to harness living cells to metabolize synthetic engineering materials remains largely elusive. Here, we report an attempt to exploit living chloroplasts to metabolize three-dimensional-printed polymers. With living chloroplasts and synthetic polymers, the system leads to a class of hybrid synthetic-living materials whose microstructures and properties can be remodeled on-demand by the photosynthesis of chloroplasts.

Abstract

The mechanical properties of engineering structures continuously weaken during service life because of material fatigue or degradation. By contrast, living organisms are able to strengthen their mechanical properties by regenerating parts of their structures. For example, plants strengthen their cell structures by transforming photosynthesis-produced glucose into stiff polysaccharides. In this work, we realize hybrid materials that use photosynthesis of embedded chloroplasts to remodel their microstructures. These materials can be used to three-dimensionally (3D)-print functional structures, which are endowed with matrix-strengthening and crack healing when exposed to white light. The mechanism relies on a 3D-printable polymer that allows for an additional cross-linking reaction with photosynthesis-produced glucose in the material bulk or on the interface. The remodeling behavior can be suspended by freezing chloroplasts, regulated by mechanical preloads, and reversed by environmental cues. This work opens the door for the design of hybrid synthetic-living materials, for applications such as smart composites, lightweight structures, and soft robotics.

See: https://www.pnas.org/content/118/3/e2016524118

Figure 1: Concept of the photosynthesis-assisted remodeling of 3D-printed structures. (A) Schematics to illustrate photosynthesis-assisted remodeling of plants. The photosynthesis-produced glucose undergoes a condensation reaction to form stiff polysaccharide (e.g., cellulose). (B) Schematics to illustrate photosynthesis-assisted remodeling of a synthetic polymer. The photosynthesis-produced glucose undergoes a reaction with isocyanate (NCO) side groups to form additional cross-links. (C) Image sequence of a 3D-printed treelike structure with various light illumination periods (white light intensity 69.3 W/m2W/m2) of the photosynthesis process. (D) Unstrengthened and strengthened 3D-printed treelike structures loaded by the same weight (1 g). (E) Image sequence of a 3D-printed Popeye-like structure with various light illumination periods of the photosynthesis process. (F) Unstrengthened and strengthened 3D-printed Popeye-like structures loaded by the same weight (200 g). The red dashed boxes denote glass slides. The unstrengthened Popeye’s height reduces by 34.7%, but the strengthened Popeye only by 7% (SI Appendix, Fig. S7).