Enzyme-Triggered Folding of Hydrogels: Toward a Mimic of the Venus Flytrap (original) (raw)
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The Journal of Physical Chemistry B, 2005
This letter describes the fabrication of three-dimensional particulate-like hydrogel microstructures using a combination of soft lithography and volume expansion induced self-folding. Bilayer structures are produced by solvent casting and photocuring of liquid resins. They curl into three-dimensional (3D) structures upon contacting with water due to differential swelling of the two layers. The curvature can be controlled by adjusting the polymer composition of the primary swelling layer. A simple semiempirical mathematical model is used to predict this self-folding behavior. By designing the two-dimensional (2D) shapes of the bilayers, this technique can lead to complicated 3D microstructures.
Dynamic Hydrogels: Translating a Protein Conformational Change into Macroscopic Motion
Angewandte Chemie-international Edition, 2007
The development of materials that undergo shape changes occupies a central theme in materials science and has proven important in several applications. Several classes of hydrogels, which are cross-linked water-soluble polymers, can change their properties (such as, volume, cross-link density) in response to temperature, pH value, or ionic strength. These dynamic hydrogels can also be modified with biochemical moieties to give materials that change their properties in response to proteins and ligands. For example, hydrogels that undergo volume changes because of antigen-antibody and lectin-carbohydrate interactions have been used as biosensors. The underlying principle of operation of dynamic hydrogel materials relates to a change in their physical or chemical cross-linking density in response to environmental cues. An unexplored alternative to these approaches relies on the use of a natural protein that undergoes a conformational change as a mechanism to alter the characteristics of a material. The functional importance of protein motions in biological systems, together with the wide range of protein motions that can be harnessed, offers a flexible approach to the preparation of dynamic materials.
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Nature Materials, 2005
C ertain proteins undergo a substantial conformational change in response to a given stimulus. Th is conformational change can manifest in diff erent manners and result in an actuation, that is, catalytic or signalling event, movement, interaction with other proteins, and so on 1-6 . In all cases, the sensing-actuation process of proteins is initiated by a recognition event that translates into a mechanical action. Th us, proteins are ideal components for designing new nanomaterials that are intelligent and can perform desired mechanical actions in response to target stimuli. A number of approaches have been undertaken to mimic nature's sensing-actuating process 1-5 . We now report a new hybrid material that integrates genetically engineered proteins within hydrogels capable of producing a stimulus-responsive action mechanism. Th e mechanical eff ect is a result of an induced conformational change and binding affi nities of the protein in response to a stimulus. Th e stimuli-responsive hydrogel exhibits three specifi c swelling stages in response to various ligands off ering additional fi ne-tuned control over a conventional two-stage swelling hydrogel. Th e newly prepared material was used in the sensing, and subsequent gating and transport of biomolecules across a polymer network, demonstrating its potential application in microfl uidics and miniaturized drug-delivery systems.
We highlight recent developments in hydrogel materials with biological responsiveness built in. These 'smart' biomaterials change properties in response to selective biological recognition events. When exposed to a biological target (nutrient, growth factor, receptor, antibody, enzyme, or whole cell), molecular recognition events trigger changes in molecular interactions that translate into macroscopic responses, such as swelling/collapse or solution-to-gel transitions. The hydrogel transitions may be used directly as optical readouts for biosensing, linked to the release of actives for drug delivery, or instigate biochemical signaling events that control or direct cellular behavior. Accordingly, bioresponsive hydrogels have gained significant interest for application in diagnostics, drug delivery, and tissue regeneration/wound healing. https://doi.org/10.1016/S1369-7021(07)70049-4
Photolithographically patterned smart hydrogel based bilayer actuators
Polymer, 2010
We describe the fabrication of photopatterned actuators, composed of stimuli-responsive hydrogel bilayers made from N-isopropyl-acrylamide (NIPAm), acrylic acid (AAc), and poly-ethylene oxide diacrylate (PEODA). The hydrogels were deposited by spin coating and casting and were patterned by noncontact photolithography. We investigated the swelling behavior of the individual photopatterned hydrogels in aqueous solutions of varying pH and ionic strength (IS). By combining materials with optimal swelling responses, bilayer structures were triggered via changes in pH and IS to actuate into three dimensional (3D) structures. We also used these hydrogel bilayers as hinges to actuate integrated structures composed of rigid polymeric SU-8 panels, patterned to resemble the shape of a Venus Flytrap. This system provides a straightforward way to design and fabricate actuator hinges composed entirely of polymers.
Tunable Pentapeptide Self-Assembled β-Sheet Hydrogels
Angewandte Chemie (International ed. in English), 2018
Oligopeptide-based supramolecular hydrogels hold promise in a range of applications. The gelation of these systems is hard to control, with minor alterations in the peptide sequence significantly influencing the self-assembly process. We explored three pentapeptide sequences with different charge distributions and discovered that they formed robust, pH-responsive hydrogels. By altering the concentration and charge distribution of the peptide sequence, the stiffness of the hydrogels could be tuned across two orders of magnitude (2-200 kPa). Also, through reassembly of the β-sheet interactions the hydrogels could self-heal and they demonstrated shear-thin behavior. Using spectroscopic and cryo-imaging techniques, we investigated the relationship between peptide sequence and molecular structure, and how these influence the mechanical properties of the hydrogel. These pentapeptide hydrogels with tunable morphology and mechanical properties have promise in tissue engineering, injectable ...
Ultrasoft, highly deformable microgels
Microgels are colloidally stable, hydrogel microparticles that have previously been used in a range of (soft) material applications due to their tunable mechanical and chemical properties. Most commonly, thermo and pH-responsive poly(N-isopropylacrylamide) (pNIPAm) microgels can be fabricated by precipitation polymerization in the presence of the co-monomer acrylic acid (AAc). Traditionally pNIPAm microgels are synthesized in the presence of a crosslinking agent, such as N,N0-methylenebisacrylamide (BIS), however, microgels can also be synthesized under ‘crosslinker free’ conditions. The resulting particles have extremely low (<0.5%), core-localized crosslinking resulting from rare chain transfer reactions. AFM nanoindentation of these ultralow crosslinked (ULC) particles indicate that they are soft relative to crosslinked microgels, with a Young's modulus of 10 kPa. Furthermore, ULC microgels are highly deformable as indicated by a high degree of spreading on glass surfaces and the ability to translocate through nanopores significantly smaller than the hydrodynamic diameter of the particles. The size and charge of ULCs can be easily modulated by altering reaction conditions, such as temperature, monomer, surfactant and initiator concentrations, and through the addition of co-monomers. Microgels based on the widely utilized, biocompatible polymer polyethylene glycol (PEG) can also be synthesized under crosslinker free conditions. Due to their softness and deformability, ULC microgels are a unique base material for a wide variety of biomedical applications including biomaterials for drug delivery and regenerative medicine.