Deformation Responses of a Physically Cross-Linked High Molecular Weight Elastin-Like Protein Polymer (original) (raw)
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Biomacromolecules, 2005
Physically cross-linked protein-based materials possess a number of advantages over their chemically crosslinked counterparts, including ease of processing and the ability to avoid the addition or removal of chemical reagents or unreacted intermediates. The investigations reported herein sought to examine the nature of physical cross-links within two-phase elastin-mimetic protein triblock copolymer networks through an analysis of macroscopic viscoelastic properties. Given the capacity of solution processing conditions, including solvent type and temperature to modulate the microstructure of two-phase protein polymer networks, viscoelastic properties were examined under conditions in which interphase block mixing had been either accentuated or diminished during network formation. Protein networks exhibited strikingly different properties in terms of elastic modulus, hysteresis, residual deformability, and viscosity in response to interdomain mixing. Thus, two-phase protein polymer networks exhibit tunable responses that extend the range of application of these materials to a variety of tissue engineering applications.
Elastin-mimetic protein polymers capable of physical and chemical crosslinking
Biomaterials, 2009
We report the synthesis of a new class of recombinant elastin-mimetic triblock copolymer capable of both physical and chemical crosslinking. These investigations were motivated by a desire to capture features unique to both physical and chemical crosslinking schemes so as to exert optimal control over a wide range of potential properties afforded by protein-based mutiblock materials. We postulated that by chemically locking a multiblock protein assembly in place, functional responses that are linked to specific domain structures and morphologies may be preserved over a broader range of loading conditions that would otherwise disrupt microphase structure solely stabilized by physical crosslinking. Specifically, elastic modulus was enhanced and creep strain reduced through the addition of chemical crosslinking sites. Additionally, we have demonstrated excellent in vivo biocompatibility of glutaraldehyde treated multiblock systems.
Viscoelastic and mechanical behavior of recombinant protein elastomers
Biomaterials, 2005
Recombinant DNA synthesis was employed to produce elastin–mimetic protein triblock copolymers containing chemically distinct midblocks. These materials displayed a broad range of mechanical and viscoelastic responses ranging from plastic to elastic when examined as hydrated gels and films. These properties could be related in a predictable fashion to polymer block size and structure. While these materials could be easily processed into films and gels, electrospinning proved a feasible strategy for creating protein fibers. All told, the range of properties exhibited by this new class of protein triblock copolymer in combination with their easy processability suggests potential utility in a variety of soft prosthetic and tissue engineering applications.
Protein-Based Thermoplastic Elastomers
Macromolecules, 2005
Investigations of high molecular weight recombinant protein triblock copolymers demonstrate unique opportunities to systematically modify material microstructure on both nano-and mesolength scales in a manner not been previously demonstrated for protein polymer systems. Significantly, through the biosynthesis of BAB-type copolymers containing flanking, plastic-like end blocks and an elastomeric midblock, virtually cross-linked protein-based materials were generated that exhibit tunable properties in a manner completely analogous to synthetic thermoplastic elastomers. Through the rational choice of processing conditions that control meso-and nanoscale structure, changes of greater than 3 orders of magnitude in Young's modulus (0.03-35 MPa) and 5-fold in elongation to break (250-1300%) were observed. Extensibility of this range or magnitude has not been previously reported for virtually cross-linked copolymers that have been produced by either chemical or biosynthetic approaches. We anticipate that these versatile protein-based thermoplastic elastomers will find applications as novel scaffolds for tissue engineering and as new biomaterials for controlled drug release and cell encapsulation.
Artificial Protein Block Copolymers Blocks Comprising Two Distinct Self-Assembling Domains
Chembiochem, 2009
Synthetic block copolymers comprising two or more compositionally distinct chains have attracted significant attention due to their ability to self-assemble into ordered microstructures. Although tremendous progress has been made in the chemical synthesis of polymers, the unsurpassed degree of control and diversity of monomers combined with advances in recombinant DNA technology permits the synthesis of unique artificial protein-derived block polymers. These include silk-elastin, [3] elastin-elastin hybrids of varying elastin blocks, [4] and helix-random coil-helix triblock combinations. [5] These polymers consist of nearly similar self-assembling chains, as in the case of silk-elastin and elastin-elastin hybrids, or one self-assembling motif fused to a disordered random motif. Herein, we describe three block copolymers comprising two distinct self-assembling chains-elastin (E) and cartilage oligomeric matrix protein coiled-coil (COMPcc; C)-fused in two orientations (EC and CE) and a final construct in which an additional E block is appended (ECE; A-C). Remarkably, the polymer structures as well as temperature and small-moleculedependent assembly rely on the block orientation and the number of blocks.
Recombinant Silk-Elastinlike Protein Polymer Displays Elasticity Comparable to Elastin
Biomacromolecules, 2009
We evaluated the mechanical properties of the genetically engineered, recombinant silk-elastinlike protein copolymer, SELP-47K. In tensile stress-strain analysis, methanol-treated non-cross-linked SELP-47K films exceeded the properties of native aortic elastin, attaining an ultimate tensile strength of 2.5 (0.4 MPa, an elastic modulus of 1.7 (0.4 MPa, an extensibility of 190 (60%, and a resilience of 86 (4% after 10 cycles of mechanical preconditioning. Stress-relaxation and creep analysis showed that films substantially maintained their elastic properties under sustained deformation. Chemical cross-linking of SELP-47K films doubled the elastic modulus and ultimate tensile strength and enhanced the extensibility and resilience. The underlying conformational and microstructural features of the films were examined. Raman spectroscopy revealed that the silklike blocks of SELP-47K existed in antiparallel-sheet crystals in the films, likely responsible for the robust physical crosslinks. Scanning electron microscopy (SEM) revealed that the various processing treatments and the mechanical deformation of the films induced changes in their surface microstructure consistent with the coagulation and alignment of polymer chains. These results demonstrate that films with excellent elasticity, comparable to native aortic elastin, are obtainable from SELP-47K, a protein copolymer combining both silk-and elastin-derived sequences in a single polymer chain.
Strain Stiffening in Synthetic and Biopolymer Networks
Biomacromolecules, 2010
Strain-stiffening behavior common to biopolymer networks is difficult to reproduce in synthetic networks. Physically associating synthetic polymer networks can be an exception to this rule and can demonstrate strain-stiffening behavior at relatively low values of strain. Here, the stiffening behavior of model elastic networks of physically associating triblock copolymers is characterized by shear rheometry. Experiments demonstrate a clear correlation between network structure and strain-stiffening behavior. Stiffening is accurately captured by a constitutive model with a single fitting parameter related to the midblock length. The same model is also effective for describing the stiffening of actin, collagen, and other biopolymer networks. Our synthetic polymer networks could be useful model systems for biological materials due to (1) the observed similarity in strain-stiffening behavior, which can be quantified and related to network structure, and (2) the tunable structure of the physically associating network, which can be manipulated to yield a desired response.
Journal of the American Chemical Society, 2007
Three-dimensional (3D) network polymers are an important family of materials. For many applications of 3D networks it is important to combine high modulus, high tensile strength, and high extensibility. 1 Rigid network materials tend to fail after only a short extension. While flexible elastomers are more extensible, they usually have low moduli and exhibit shallow stress-response. Although many engineering approaches and chemical modifications 2 have been developed to improve mechanical properties of network polymers, it remains a challenge to design ideal networks that have a combination of desired properties. Among chemical methods, interesting work has been reported on using interchain hydrogen bonding to improve polymer physical properties. 3 Given the importance of cross-linker structure on mechanical properties of network polymers, it is surprising that there is very limited investigation on designing molecularly engineered cross-linkers to enhance network properties. Herein we introduce a novel biomimetic design of a reversibly unfolding modular cross-linker that can increase elastomer stiffness without sacrificing extensibility leading to a dramatic tensile strength enhancement.
Swelling and mechanical behaviors of chemically cross-linked hydrogels of elastin-like polypeptides
Biomacromolecules, 2003
Genetically engineered elastin-like polypeptides consisting of Val-Pro-Gly-X-Gly repeats, where X was chosen to be Lys every 7 or 17 pentapeptides (otherwise X was Val), were synthesized and expressed in E. coli, purified, and chemically cross-linked using tris-succinimidyl aminotriacetate to produce hydrogels. Swelling experiments indicate hydrogel mass decreases by 80-90% gradually over an approximate 50°C temperature range. Gels ranged in stiffness from 0.24 to 3.7 kPa at 7°C and from 1.6 to 15 kPa at 37°C depending on protein concentration, lysine content, and molecular weight. Changes in gel stiffness and loss angle with cross-linking formulation suggest a low-temperature gel structure that is nearly completely elastic, where force is transmitted almost exclusively through fully extended polypeptide chains and chemical crosslinks, and a high-temperature gel structure, where ELP chains are contracted and force is transmitted through chemical cross-links as well as frictional contact between polypeptide chains.
Genetic engineering of structural protein polymers
Biotechnology Progress
Genetic and protein engineering are components of a new polymer chemistry that provide the tools for producing macromolecular polyamide copolymers of diversity and precision far beyond the current capabilities of synthetic polymer chemistry. The genetic machinery allows molecular control of chemical and physical chain properties. Nature utilizes this control to formulate protein polymers into materials with extraordinary mechanical properties, such as the strength and toughness of silk and the elasticity and resilience of mammalian elastin. The properties of these materials have been attributed to the presence of short repeating oligopeptide sequences contained in the proteins, fibroin, and elastin. We have produced homoblock protein polymers consisting exclusively of silk-like crystalline blocks and elastin-like flexible blocks. We have demonstrated that each homoblock polymer as produced by microbial fermentation exhibits measurable properties of crystallinity and elasticity. Additionally, we have produced alternating block copolymers of various amounts of silk-like and elastin-like blocks, ranging from a ratio of 1:4 to 2:1, respectively. The crystallinity of each copolymer varies with the amount of crystalline block interruptions. The production of fiber materials with custom-engineered mechanical properties is a potential outcome of this technology.