Hydrogels which morph between programmed shapes in response to aqueous stimuli are of significant interest for biosensors and artificial muscles, among other applications. However, programming hydrogel shape change at small size scales is a significant challenge. Here we use the inherent ordering capabilities of liquid crystals to create a mechanically anisotropic hydrogel; when coupled with responsive comonomers, the mechanical anisotropy in the network guides shape change in response to the desired aqueous condition. Our synthetic strategy hinges on the use of a methacrylic chromonic liquid crystal monomer which can be combined with a non-polymerizable chromonic of similar structure to vary the magnitude of shape change while retaining liquid crystalline order. This shape change is directional due to the mechanical anisotropy of the gel, which is up to 50% stiffer along the chromonic stack direction than perpendicular. Additionally, we show that the type of stimulus to which these anisotropic gels respond can be switched by incorporating responsive, hydrophilic comonomers without destroying the nematic phase or alignment. The utility of these properties is demonstrated in polymerized microstructures which exhibit Gaussian curvature in response to high pH due to emergent ordering in a micron-sized capillary.
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Cation-induced shape programming and morphing in protein-based hydrogels
Smart materials that are capable of memorizing a temporary shape, and morph in response to a stimulus, have the potential to revolutionize medicine and robotics. Here, we introduce an innovative method to program protein hydrogels and to induce shape changes in aqueous solutions at room temperature. We demonstrate our approach using hydrogels made from serum albumin, the most abundant protein in the blood plasma, which are synthesized in a cylindrical or flower shape. These gels are then programmed into a spring or a ring shape, respectively. The programming is performed through a marked change in stiffness (of up to 17-fold), induced by adsorption of Zn 2+ or Cu 2+ cations. We show that these programmed biomaterials can then morph back into their original shape, as the cations diffuse outside the hydrogel material. The approach demonstrated here represents an innovative strategy to program protein-based hydrogels to behave as actuators.
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- NSF-PAR ID:
- 10186604
- Date Published:
- Journal Name:
- Science Advances
- Volume:
- 6
- Issue:
- 18
- ISSN:
- 2375-2548
- Page Range / eLocation ID:
- eaba6112
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Programmable behavior combined with tailored stiffness and tunable biomechanical response are key requirements for developing successful materials. However, these properties are still an elusive goal for protein-based biomaterials. Here, we use protein-polymer interactions to manipulate the stiffness of protein-based hydrogels made from bovine serum albumin (BSA) by using polyelectrolytes such as polyethyleneimine (PEI) and poly-L-lysine (PLL) at various concentrations. This approach confers protein-hydrogels with tunable wide-range stiffness, from ~10–64 kPa, without affecting the protein mechanics and nanostructure. We use the 6-fold increase in stiffness induced by PEI to program BSA hydrogels in various shapes. By utilizing the characteristic protein unfolding we can induce reversible shape-memory behavior of these composite materials using chemical denaturing solutions. The approach demonstrated here, based on protein engineering and polymer reinforcing, may enable the development and investigation of smart biomaterials and extend protein hydrogel capabilities beyond their conventional applications.
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null (Ed.)New device architectures favorable for interaction with the soft and dynamic biological tissue are critical for the design of indwelling biosensors and neural interfaces. For the long-term use of such devices within the body, it is also critical that the component materials resist the physiological harsh mechanical and chemical conditions. Here, we describe the design and fabrication of mechanically and chemically robust 3D implantable electronics. This is achieved by using traditional photolithography to pattern electronics on liquid crystal elastomers (LCEs), a class of shape programmable materials. The chemical durability of LCE is evaluated under accelerated in vitro conditions simulating the physiological environment; for example, LCE exhibits less than 1% mass change under a hydrolytic medium simulating >1 year in vivo . By employing twisted nematic LCEs as dynamic substrates, we demonstrate electronics that are fabricated on planar substrates but upon release morph into programmed 3D shapes. These shapes are designed to enable intrinsically low failure strain materials to be extrinsically stretchable. For example, helical multichannel cables for electrode arrays withstand cyclic stretching and buckling over 10 000 cycles at 60% strain while being soaked in phosphate-buffered saline. We envision that these LCE-based electronics can be used for applications in implantable neural interfaces and biosensors.more » « less
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4D Printing of Multi‐Stimuli Responsive Protein‐Based Hydrogels for Autonomous Shape Transformationsmore » « less
Abstract Stimuli responsive hydrogels that can change shape in response to applied external stimuli are appealing for soft robotics, biomedical devices, drug delivery, and actuators. However, existing 3D printed shape morphing materials are non‐biodegradable, which limits their use in biomedical applications. Here, 3D printed protein‐based hydrogels are developed and applied for programmable structural changes under the action of temperature, pH, or an enzyme. Key to the success of this strategy is the use of methacrylated bovine serum albumin (MA–BSA) as a biodegradable building block to Pickering emulsion gels in the presence of
N ‐isopropylacrylamide or 2‐dimethylaminoethyl methacrylate. These shear‐thinning gels are ideal for direct ink write (DIW) 3D printing of multi‐layered stimuli‐responsive hydrogels. While poly(N ‐isopropylacrylamide) and poly(dimethylaminoethyl methacrylate) introduce temperature and pH‐responsive properties into the printed objects, a unique feature of this strategy is an enzyme‐triggered shape transformation based on the degradation of the bovine serum albumin network. To highlight this technique, protein‐based hydrogels that reversibly change shape based on environmental temperature and pH are fabricated, and irreversibly altered by enzymatic degradation, which demonstrates the complexity that can be introduced into 4D printed systems. -
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Abstract Across fields of science, researchers have increasingly focused on designing soft devices that can shape‐morph to achieve functionality. However, identifying a rest shape that leads to a target 3D shape upon actuation is a non‐trivial task that involves inverse design capabilities. In this study, a simple and efficient platform is presented to design pre‐programmed 3D shapes starting from 2D planar composite membranes. By training neural networks with a small set of finite element simulations, the authors are able to obtain both the optimal design for a pixelated 2D elastomeric membrane and the inflation pressure required for it to morph into a target shape. The proposed method has potential to be employed at multiple scales and for different applications. As an example, it is shown how these inversely designed membranes can be used for mechanotherapy applications, by stimulating certain areas while avoiding prescribed locations.
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1126/sciadv.aba6112
