Dynamic Hydrogels: Translating a Protein Conformational Change into Macroscopic Motion (original) (raw)
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Protein Engineering in the Development of Functional Hydrogels
Annual Review of Biomedical Engineering, 2010
Proteins, which are natural heteropolymers, have evolved to exhibit a staggering array of functions and capabilities. As scientists and engineers strive to tackle important challenges in medicine, novel biomaterials continue to be devised, designed, and implemented to help to address critical needs. This review aims to cover the present advances in the use of protein engineering to create new protein and peptide domains that enable the formation of advanced functional hydrogels. Three types of domains are covered in this review: (a) the leucine zipper coiled-coil domains, (b) the EF-hand domains, and (c) the elastin-like polypeptides. In each case, the functionality of these domains is discussed as well as recent advancements in the use of these domains to create novel hydrogel-based biomaterials. As protein engineering is used to both create and improve protein domains, these advances will lead to exciting new biomaterials for use in a variety of applications.
Biomacromolecules, 2005
A series of poly(ethylene glycol)-protein hydrogels were synthesized with different proteins, and the resultant structures were characterized in terms of swelling behavior and mechanical, optical, and drug release properties. Irrespectively of the protein involved in polymerization with poly(ethylene glycol), all studied systems were found to be loosely cross-linked networks, where both polymer and protein are completely solvated, enabling as high as 96% water content. Changes in the apparent transparency of the hydrogels synthesized with different proteins were attributed to the ability of the protein component to self-associate via hydrophobic interactions. The polyelectrolyte nature of the protein component governs the pH responsiveness of the network, which manifested itself in a pH-dependent mechanism of swelling and drug release. It was demonstrated that there is great opportunity to modulate the final characteristics of the hydrogel system to fit the need of specific biomedical application.
Genetically engineered protein in hydrogels tailors stimuli-responsive characteristics
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.
Biomacromolecules, 2020
Responsive pure protein organogel sensors and catalysts are fabricated by replacing the aqueous mobile phase of protein hydrogels with pure ethylene glycol (EG). Exchanging water for EG causes irreversible volume phase transitions (VPT) in bovine serum albumin (BSA) polymers; however, BSA hydrogel and organogel sensors show similar volume responses to protein−ligand binding. This work elucidates the mechanisms involved in this enabling irreversible VPT by examining the protein secondary structure, hydration, and protein polymer morphology. Organogel proteins retain their native activity because their secondary structure and hydration shell are relatively unperturbed by the EG exchange. Conversely, the decreasing solvent quality initiates polymer phase separation to minimize the BSA polymer surface area exposed to EG, thus decreasing distances between BSA polymer strands. These protein polymer morphology changes promote interprotein interactions between BSA polymer strands, which increase the effective polymer cross-link density and prevent organogel swelling as the mobile phase is exchanged back to water. ■ INTRODUCTION Hydrogels and organogels are versatile materials with numerous applications as sensors, 1−5 catalysts, 6,7 drug delivery materials, 8,9 tissue engineering scaffolds, 10 wound dressings, 11 membranes, 12 and mechanical actuators. 13 These responsive materials consist of two primary components: a stationary phase made up of a 3-dimensional chemically or physically cross-linked polymer network and a liquid mobile phase that facilitates diffusion and mass transport within the polymer network. Hydrogels contain an aqueous mobile phase, whereas organogels contain an organic solvent mobile phase. Our group pioneered the development of photonic crystal-based colorimetric chemical sensors 14,15 that utilize the hydrogel volume phase transition (VPT) responses to external stimuli such as pH, light, and chemical analytes. 4,16−19 Hydrogels or organogels that have molecular recognition groups attached to the polymer network selectively undergo VPT in response to a specific analyte. 17,18,20,21 This analyte induced VPT shifts the embedded photonic crystal particle spacing, thus shifting the photonic crystal light diffraction. 14−16 These VPT involve distinct changes in the hydrogel/ organogel volume in response to small changes in the hydrogel/organogel chemical environment. 22 These volume changes are caused by osmotic pressures, Π, which derive from changes in the Gibbs free energy, ΔG total. 23,24 Osmotic pressures in the system induce mass transfer of the mobile phase: either partitioning the mobile phase into the polymer network to cause swelling, or expelling the mobile phase to cause shrinking. When the polymer and mobile phase are at equilibrium, Π total = ∂ΔG total /∂V = 0. In general, for hydrogel/ organogel chemical sensors, analyte recognition must induce a change in the Gibbs free energy to actuate a VPT. Recently, we developed several stimuli responsive pure protein hydrogels that sense pH, glucose, yeast cells, drugs, surfactants, and fatty acids. 3,5,25 These protein hydrogels have selective chemical responses because the constituent proteins show specific molecular recognition. There exists a large body of research developing functional pure protein hydrogels using a variety of fabrication methods, such as glutaraldehyde cross-linking, or enzyme catalyzed cross-linking of proteins, and self-assembly of engineered proteins. 6,7,9,26−28 There are very few studies of pure protein organogels, 29,30 despite the intense interests in utilizing protein chemistries in organic solvents for industrial applications such as enzymatic synthesis of pharmaceuticals and biofuels, 31,32 as well as for sensing and degrading toxic compounds important to the defense industry. 33,34 Organic solvents typically denature proteins and significantly decrease protein reactivity. 35 This has led to the development of several techniques to stabilize proteins against denaturation or deactivation by organic solvents. 36−38
Biophysical Journal, 2012
Peptide-based hydrogels are attractive biological materials. Study of their self-assembly pathways from their monomer structures is important not only for undertaking the rational design of peptide-based materials, but also for understanding their biological functions and the mechanism of many human diseases relative to protein aggregation. In this work, we have monitored the conformation, morphological, and mechanical properties of a hydrogel-forming peptide during hydrogelation in different dimethylsulfoxide (DMSO)/H 2 O solutions. The peptide shows nanofiber morphologies in DMSO/H 2 O solution with a ratio lower than 4:1. Increased water percentage in the solution enhanced the hydrogelation rate and gel strength. Onedimensional and two-dimensional proton NMR and electron microscopy studies performed on the peptide in DMSO/H 2 O solution with different ratios indicate that the peptide monomer tends to adopt a more helical structure during the hydrogelation as the DMSO/H 2 O ratio is reduced. Interestingly, at the same DMSO/H 2 O ratio, adding Ca 2þ not only promotes peptide hydrogelation and gel strength, but also leads to special shear-thinning and recovery properties of the hydrogel. Without changing the peptide conformation, Ca 2þ binds to the charged Asp residues and induces the change of interfiber interactions that play an important role in hydrogel properties. 979-988 FIGURE 4 Mechanical and monomeric structural properties of h9e peptide in 70% DMSO solution with/without Ca 2þ . (A) G 0 of h9e hydrogel in 70% DMSO solution with 0, 3, and 30 mM Ca 2þ . (B) Shear-thinning and recovery properties of h9e hydrogel in 70% DMSO solution with 0, 3, and 30 mM Ca 2þ . (C) Chemical Shift Index of h9e peptide in 70% DMSO solution with 0, 3, and 6 mM Ca 2þ . Biophysical Journal 103(5) 979-988 Structural Study of a Peptide Hydrogel
Hydrogels in Biology and Medicine: From Molecular Principles to Bionanotechnology
Hydrophilic polymers are the center of research emphasis in nanotechnology because of their perceived "intelligence". They can be used as thin films, scaffolds, or nanoparticles in a wide range of biomedical and biological applications. Here we highlight recent developments in engineering uncrosslinked and crosslinked hydrophilic polymers for these applications. Natural, biohybrid, and synthetic hydrophilic polymers and hydrogels are analyzed and their thermodynamic responses are discussed. In addition, examples of the use of hydrogels for various therapeutic applications are given. We show how such systems' intelligent behavior can be used in sensors, microarrays, and imaging. Finally, we outline challenges for the future in integrating hydrogels into biomedical applications. -[*] Prof. N. A. Peppas Biomaterials, Drug Delivery, Bionanotechnology and Molecular Recognition Laboratories
2011
The terms gels and hydrogels are used interchangeably by food and biomaterials scientists to describe polymeric cross-linked network structures. Gels are defined as a substantially dilute cross-linked system, and are categorised principally as weak or strong depending on their flow behaviour in steady-state (Ferry, 1980). Edible gels are used widely in the food industry and mainly refer to gelling polysaccharides (i.e. hydrocolloids) (Phillips & Williams, 2000). The term hydrogel describes three-dimensional network structures obtained from a class of synthetic and/or natural polymers which can absorb and retain significant amount of water (Rosiak & Yoshii, 1999). The hydrogel structure is created by the hydrophilic groups or domains present in a polymeric network upon the hydration in an aqueous environment. This chapter reviews the preparation methods of hydrogels from hydrophilic polymers of synthetic and natural origin with emphasis on water soluble natural biopolymers (hydrocolloids). Recent advances in radiation cross-linking methods for the preparation of hydrogel are particularly addressed. Additionally, methods to characterise these hydrogels and their proposed applications are also reviewed. 1.1 Mechanism of network formation Gelation refers to the linking of macromolecular chains together which initially leads to progressively larger branched yet soluble polymers depending on the structure and conformation of the starting material. The mixture of such polydisperse soluble branched polymer is called 'sol'. Continuation of the linking process results in increasing the size of the branched polymer with decreasing solubility. This 'infinite polymer' is called the 'gel' or 'network' and is permeated with finite branched polymers. The transition from a system with finite branched polymer to infinite molecules is called 'sol-gel transition' (or 'gelation') and the critical point where gel first appears is called the 'gel point' (Rubinstein & Colby, 2003). Different types of gelation mechanism are summarised in Figure 1. Gelation can take place either by physical linking (physical gelation) or by chemical linking (chemical gelation). Physical gels can be sub categorised as strong physical gels and weak gels. Strong physical gel has strong physical bonds between polymer chains and is effectively permanent