Living organisms use spatially controlled expansion and contraction of soft tissues to achieve complex three-dimensional (3D) morphologies and movements and thereby functions. However, replicating such features in man-made materials remains a challenge. Here we report an approach that encodes 2D hydrogels with spatially and temporally controlled growth (expansion and contraction) to create 3D structures with programmed morphologies and motions. This approach uses temperature-responsive hydrogels with locally programmable degrees and rates of swelling and shrinking. This method simultaneously prints multiple 3D structures with custom design from a single precursor in a one-step process within 60 s. We suggest simple yet versatile design rules for creating complex 3D structures and a theoretical model for predicting their motions. We reveal that the spatially nonuniform rates of swelling and shrinking of growth-induced 3D structures determine their dynamic shape changes. We demonstrate shape-morphing 3D structures with diverse morphologies, including bioinspired structures with programmed sequential motions.
Motion in biological organisms often relies on the functional arrangement of anisotropic tissues that linearly expand and contract in response to external signals. However, a general approach that can implement such anisotropic behavior into synthetic soft materials and thereby produce complex motions seen in biological organisms remains a challenge. Here, a bioinspired approach is presented that uses temperature‐responsive linear hydrogel actuators, analogous to biological linear contractile elements, as building blocks to create three‐dimensional (3D) structures with programmed motions. This approach relies on a generalizable 3D printing method for building 3D structures of hydrogels using a fugitive carrier with shear‐thinning properties. This study demonstrates that the metric incompatibility of an orthogonally growing bilayer structure induces a saddle‐like shape change, which can be further exploited to produce various bioinspired motions from bending to twisting. The orthogonally growing bilayer structure undergoes a transition from a stretching‐dominated motion to a bending‐dominated motion during its shape transformation. The modular nature of this approach, together with the flexibility of additive manufacturing, enables the fabrication of multimodular 3D structures with complex motions through the assembly of multiple functional components, which in turn consist of simple linear contractile elements.
TitleInjectable polyethylene glycol-laponite composite hydrogels as articular cartilage scaffolds with superior mechanical and rheological properties
ABSTRACTIn this study, injectable PEG-based hydrogels containing Laponite particles with mechanical and structural properties close to the natural articular cartilage are introduced. The nanocomposites are fabricated by imide ring opening reactions utilizing synthesized copolymers containing PEG blocks and nanoclay through a two-step thermal poly-(amic acid) process. Butane diamine is used as nucleophilic reagent and hydrogels with interconnected pores with sizes in the range of 100-250 µm are prepared. Improved viscoelastic properties compared with the conventional PEG hydrogels are shown. Evaluation of cell viability utilizing human mesenchymal stem cells determines cytocompatibility of the nanocomposite hydrogels.
GRAPHICAL ABSTRACT ARTICLE HISTORY
Two-dimensional (2D) growth-induced 3D shaping enables shape-morphing materials for diverse applications. However, quantitative design of 2D growth for arbitrary 3D shapes remains challenging. Here we show a 2D material programming approach for 3D shaping, which prints hydrogel sheets encoded with spatially controlled in-plane growth (contraction) and transforms them to programmed 3D structures. We design 2D growth for target 3D shapes via conformal flattening. We introduce the concept of cone singularities to increase the accessible space of 3D shapes. For active shape selection, we encode shape-guiding modules in growth that direct shape morphing toward target shapes among isometric configurations. Our flexible 2D printing process enables the formation of multimaterial 3D structures. We demonstrate the ability to create 3D structures with a variety of morphologies, including automobiles, batoid fish, and real human face.
Selective
modulation of near-infrared (NIR) fluorescence of single-walled
carbon nanotubes (SWNTs) is important for their applications as NIR
optical sensors and devices. Here, we study the target-molecule-mediated
NIR fluorescence modulation of refolded DNA aptamer-functionalized
SWNTs, using platelet-derived growth factor (PDGF) and a PDGF-binding
aptamer as a model system. The aptamer–SWNT complexes use SWNT
as nanoscale NIR optical emitters and DNA aptamers as molecular recognition
elements. The binding of target molecules, PDGFs in this study, to
PDGF-binding aptamers on the surface of SWNTs induces a conformation
change of the aptamers, which modulates the NIR fluorescence of SWNT
emitters. This study suggests that PDGF-binding aptamers noncovalently
assembled on the SWNT surface can undergo a temperature- and divalent-ion-induced
conformational change into a folded structure through multiple stages,
which renders aptamer-functionalized SWNTs optically responsive to
target molecules. In addition, our experimental and theoretical results
show that the aptamers have a nanotube-diameter-dependent affinity
for SWNTs. We demonstrate that refolded aptamer-functionalized SWNTs
reversibly modulate their NIR fluorescence in response to PDGF at
the nanomolar range 0.1–10 nM with apparent dissociation constants
of ∼0.71 nM (solution-phase complexes) and ∼3.1 nM (complexes
in hydrogels). This study could open new opportunities to design label-free,
reversible NIR optical sensors that can detect various target molecules
upon availability or selection of their cognate aptamers.
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