Protein-Based Thermoplastic Elastomers (original) (raw)
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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.
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.
Biomacromolecules, 2008
Recombinant protein polymers were synthesized and examined under various loading conditions in order to assess the mechanical stability and deformation responses of physically crosslinked, hydrated, protein polymer networks designed as triblock copolymers with central elastomeric and flanking plastic-like blocks. Uniaxial stress-strain properties, creep and stress relaxation behavior, as well as the effect of various mechanical preconditioning protocols on these responses were characterized. Significantly, we demonstrate for the first time that ABA triblock copolymers when redesigned with substantially larger endblock segments can withstand significantly greater loads. Furthermore, the presence of three distinct phases of deformation behavior was revealed upon subjecting physically crosslinked protein networks to step and cyclic loading protocols in which the magnitude of the imposed stress was incrementally increased over time. We speculate that these phases correspond to the stretch of polypeptide bonds, the conformational changes of polypeptide chains, and the disruption of physical crosslinks. The capacity to select a genetically engineered protein polymer that is suitable for its intended application requires an appreciation of its viscoelastic characteristics and the capacity of both molecular structure and conditioning protocols to influence these properties.
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.
Journal of Nano Research, 2009
Genetic engineering was used to produce an elastin-like polymer (ELP) with precise amino acid composition, sequence and length, resulting in the absolute control of MW and stereochemistry. A synthetic monomer DNA sequence encoding for (VPAVG) 20 , was used to build a library of concatemer genes with precise control on sequence and size. The higher molecular weight polymer with 220 repeats of VPAVG was biologically produced in Escherichia coli and purified by hot and cold centrifugation cycles, based on the reversible inverse temperature transition property of ELPs. The use of low cost carbon sources like lactose and glycerol for bacteria cells culture media was explored using Central Composite Design approach allowing optimization of fermentation conditions. Due to its self-assembling behaviour near 33 ºC stable spherical microparticles with a size ~ 1µm were obtained, redissolving when a strong undercooling is achieved. The polymer produced showed hysteresis behaviour with thermal absorbing/releasing components depending on the salt concentration of the polymer solution.
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.
Biomacromolecules, 2012
We report herein the unexpected temperature triggered self-assembly of proteins fused to thermally responsive elastin-like polypeptides (ELPs) into spherical micelles. Six ELP block copolymers (ELP BC ) with different hydrophilic and hydrophobic block lengths were genetically fused to two single domain proteins, thioredoxin (Trx) and a fibronectin type III domain (Fn3) that binds the α v β 3 integrin. The self-assembly of these protein-ELP BC fusions as a function of temperature was investigated by UV spectroscopy, light scattering, and cryo-TEM. Self-assembly of the ELP BC was -unexpectedly-retained upon fusion to the two proteins, resulting in the formation of spherical micelles with a hydrodynamic radius that ranged from 24-37 nm, depending on the protein and ELP BC . Cryo-TEM images confirmed the formation of spherical particles with a size that was consistent with that measured by light scattering. The bioactivity of Fn3 was retained when presented by the ELP BC micelles as indicated by the enhanced uptake of the Fn3-decorated ELP BC micelles in comparison to the unimer by cells that overexpress the α v β 3 integrin. The fusion of single domain proteins to ELP BC s may provide a ubiquitous platform for the multivalent presentation of proteins.
Biotechnology and Applied Biochemistry, 2005
Rapid progress has been made in the design and synthesis of oligomers and polymers that emulate the properties of natural proteins. Molecular bioengineering offers the chance to design and produce artificial polymeric proteins with tailored polymeric properties. The elastin-like polypeptides are a well-defined family of polymers with noteworthy characteristic based on the VPGVG repeated motif of bovine elastin. In the human homologue, the most regular sequence is represented by the repetition of the VAPGVG hexapeptidic motif. On the basis of this sequence, a synthetic gene has been designed, cloned and expressed in Escherichia coli to obtain artificial protein polymers. The rapid one-step in-frame cloning of any biologically active sequence can be achieved directly in the expression vector, allowing further improvement of the potential of the resulting product.