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High‐yield Synthesis of Block Copolymer‐mediated ..
In the search for smart biomaterials, three block copolymers comprised of elastin (E) and cartilage oligomeric matrix protein (COMP) coiled-coil domains have been prepared . The blocks were fused in two orientations (EC and CE) and an additional E block was appended to the final construct. Although nearly identical in composition, the EC and CE diblock copolymers exhibit differences in secondary structure and behaved differently when subjected to changes in temperature. The EC, a random coil-like structure was observed at low temperatures, which then transformed to a predominantly helical and β-conformation at higher temperatures. The CE diblock revealed an overall random and β-structure at low temperatures and exhibited a transition to a predominantly β-conformation as a function temperature. The ECE triblock showed similar behavior as the EC diblock copolymer at low and high temperatures . This study further demonstrates that block orientation plays a significant role in protein-based block copolymers, in contrast to synthetic block copolymers. presents examples of elastin-based block copolymers and their use in biomedical applications. The biomedical applications of elastin-based polymers are described in detail elsewhere .
Peptide-polymer conjugates inspired by coiled-coil domains of human fibrin have been prepared using the sequence: IDFISTYITKIDKKIQSIEDIIHQIENKISEIKQLIK) . A triblock copolymer composed of a central PEG block flanked by two coiled-coil forming sequences (γKI-PEG-γKI) self-assembled into viscoelastic hydrogels. Analytical ultracentrifugation revealed the presence of dimeric and tetrameric bundles ().
In Situ Synthesis of Block Copolymer Nanoassemblies …
As an alternative to the synthesis of hybrid block copolymers, the de novo design of a peptide sequence, (VSSLESK)6, was used to genetically engineer α-helical coiled coil structures , . The hybrid hydrogels formed by cross-linking with water-soluble N-(2-hydroxypropyl) methacrylamide and N-(N',N'-dicarboxymethylaminopropyl)-methacrylamide (poly(HPMA-co-DAMA)) containing a metal chelating group iminodiacetic acid (IDA) in the presence of Ni2+, through IDA-Ni2+-His complexation , . demonstrates this hybrid hydrogel assembly from synthetic polymer and coiled coil protein blocks. The hydrogels were biocompatible and responsive to strong metal-chelating ligands such as imidazole . However, in both examples the hybrid block copolymers did not demonstrate higher-order assembly.
Fibrin-inspired coiled coil biomaterials demonstrated no cytotoxicity to primary human endothelial cells . In terms of mechanical properties, the triblocks exhibited moduli similar to fibrin gels, although fibrin gels can attain the same stiffness values at significantly lower concentrations. The attractive mechanical properties, absence of cytotoxicity, and ease of synthesis make γKI-PEG-γKI triblock copolymers promising candidates for biomedical technologies, such as for scaffolds for regenerative medicine . summarizes the hybrid-block copolymer systems with coiled-coil forming sequences.
Nanocomposites: synthesis, structure, properties and …
The synthesis and self-assembly of hybrid block copolymers based on the peptide sequence, GEAK(LAEIAK)2LAEIYA, derived from the α-helical coiled-coil motif, has been described . This amino acid sequence was derived from a de novo designed coiled-coil . The conjugation of a peptide block with a synthetic block (PEG) did not disrupt the self-organization of the peptide sequence and led to the formation of discrete nano-objects that were formed into thin films. These features coarsened and eventually disappeared upon decreasing the PEG molecular weight and removing the PEG chains.
High molecular weight multiblock copolymers comprising PEG and coiled-coil peptide segments were prepared via NHS-activated amide bond formation . Two coiled-coil forming peptides (glutamic acid-rich and arginine-rich peptides) and homobifunctional polyethylene glycol N-hydroxysuccinimide esters were utilized in the synthesis of (AB)m-type peptide-PEG polymers with m>15, through the f-position of the peptides and termini of the PEG. These block copolymers formed heterooligomeric assemblies in the form of hydrogels, as well as homooligomeric micellar structures, suggesting that the peptides retained their coiled-coil capacity . The architectures (micelles and hydrogels) can be utilized as drug delivery reservoirs and controlled release systems, as well as chemically and thermally responsive hydrogels.
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Journal of Drug Targeting - Taylor & Francis
The driving force for fiber formation was the self-assembly of the antiparallel-sheet peptides, whereas PFS prevented uncontrolled lateral aggregation of fibers . Introduction of inorganic metals to the peptide-based block copolymers offers access to novel biomaterials with new structures and functions. Moreover, conjugation of β-sheet forming peptides to synthetic polymers provides a useful strategy to enhance nanostructure formation and blend the properties of the biological polymers with those of the synthetic polymers. More examples of the block copolymers containing β-sheet forming sequences are listed in . For more information on β-sheet-forming peptides and their analogues possessing the self-organizing features, readers are referred to a prior review .
Click Chemistry Publications - Scripps Research Institute
A similar approach was used to study the effect of polyisoprene in spider silk-like block copolymers. The synthesis and characterization of segmented multiblock copolymers was accomplished in which the poly(alanine) blocks were preserved and the glycine-rich blocks were replaced with polyisoprene blocks to improve solubility . Fourier transform infrared spectroscopy, wide angle X-ray diffraction (WAXD), and nuclear magnetic resonance (NMR) spectroscopy supported the presence of β-sheets in the poly(alanine) block. After casting the polymer in solvents such as chloroform and 2-chloroethanol, micellar-like aggregation was observed by TEM . The authors observed that only the block copolymers with shorter isoprene blocks formed micellar-like aggregates and concluded that by varying the length of a soft block it is possible to direct the assembly in silk-like block copolymers.
PDF Downloads : Oriental Journal of Chemistry
Protein-based block copolymers are emerging as a new class of biomaterials due to their unique physical, chemical, and biological properties. Protein-based polymers have many advantages over conventional synthetic polymers because they are able to assemble hierarchically into stable, ordered conformations , . This ability depends on the structures of protein chains as well as the microenvironment. Protein-based block copolymers have the ability to form varied nanostructures in aqueous solution that provides potential benefits for biomedical applications, such as therapeutic delivery, tissue engineering, and medical imaging . Some prototypical examples of engineered protein-based block copolymers are silk-like , , resilin-like and elastin-like polymers -, coiled-coil and leucine zipper domains , , and various peptide amphiphiles .
Copolymer series | Products | Ashland Inc.
Inspired by the structure of spider silk of Nephila clavipes, multiblock copolymers were prepared by replacement of the amorphous peptide domains of a spider silk with PEG . The PEG-poly(alanine) block copolymers retained the antiparallel β-sheet structure that was confirmed by FTIR and X-ray diffraction studies . AFM studies revealed phase-separated architectures with the poly(alanine) domains in the range of 100-200 nm ().
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