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Peptide amphiphile nanofibers with conjugated polydiacetylene backbones in their core.

ABSTRACT: The coupling of electronic and biological functionality through self-assembly is an interesting target in supramolecular chemistry. We report here on a set of diacetylene-derivatized peptide amphiphiles (PAs) that react to form conjugated polydiacetylene backbones following self-assembly into cylindrical nanofibers. The polymerization reaction yields highly conjugated backbones when the peptidic segment of the PAs has a linear, as opposed to a branched, architecture. Given the topotactic nature of the polymerization, these results suggest that a high degree of internal order exists in the supramolecular nanofibers formed by the linear PA. On the basis of microscopy, the formation of a polydiacetylene backbone to covalently connect the beta-sheets that help form the fibers does not disrupt the fiber shape. Interestingly, we observe the appearance of a polydiacetylene (PDA) circular dichroism band at 547 nm in linear PA nanofibers suggesting the conjugated backbone in the core of the nanostructures is twisted. We believe this CD signal is due to chiral induction by the beta-sheets, which are normally twisted in helical fashion. Heating and cooling shows simultaneous changes in beta-sheet and conjugated backbone structure, indicating they are both correlated. At the same time, poor polymerization in nanofibers formed by branched PAs indicates that less internal order exists in these nanostructures and, as expected, then a circular dichroism signal is not observed for the conjugated backbone. The general variety of materials investigated here has the obvious potential to couple electronic properties and in vitro bioactivity. Furthermore, the polymerization of monomers in peptide amphiphile assemblies by a rigid conjugated backbone also leads to mechanical robustness and insolubility, two properties that may be important for the patterning of these materials at the cellular scale.

SUBMITTER: Hsu L

PROVIDER: S-EPMC2547985 | biostudies-literature | 2008 Mar

REPOSITORIES: biostudies-literature

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Peptide amphiphile nanofibers with conjugated polydiacetylene backbones in their core.

Hsu Lorraine L Cvetanovich Gregory L GL Stupp Samuel I SI

Journal of the American Chemical Society 20080304 12

The coupling of electronic and biological functionality through self-assembly is an interesting target in supramolecular chemistry. We report here on a set of diacetylene-derivatized peptide amphiphiles (PAs) that react to form conjugated polydiacetylene backbones following self-assembly into cylindrical nanofibers. The polymerization reaction yields highly conjugated backbones when the peptidic segment of the PAs has a linear, as opposed to a branched, architecture. Given the topotactic nature ...[more]

PMID: 18314978

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Project description:Peripheral nerve injuries can result in lifelong disability. Primary coaptation is the treatment of choice when the gap between transected nerve ends is short. Long nerve gaps seen in more complex injuries often require autologous nerve grafts or nerve conduits implemented into the repair. Nerve grafts, however, cause morbidity and functional loss at donor sites, which are limited in number. Nerve conduits, in turn, lack an internal scaffold to support and guide axonal regeneration, resulting in decreased efficacy over longer nerve gap lengths. By comparison, peptide amphiphiles (PAs) are molecules that can self-assemble into nanofibers, which can be aligned to mimic the native architecture of peripheral nerve. As such, they represent a potential substrate for use in a bioengineered nerve graft substitute. To examine this, we cultured Schwann cells with bioactive PAs (RGDS-PA, IKVAV-PA) to determine their ability to attach to and proliferate within the biomaterial. Next, we devised a PA construct for use in a peripheral nerve critical sized defect model. Rat sciatic nerve defects were created and reconstructed with autologous nerve, PLGA conduits filled with various forms of aligned PAs, or left unrepaired. Motor and sensory recovery were determined and compared among groups. Our results demonstrate that Schwann cells are able to adhere to and proliferate in aligned PA gels, with greater efficacy in bioactive PAs compared to the backbone-PA alone. In vivo testing revealed recovery of motor and sensory function in animals treated with conduit/PA constructs comparable to animals treated with autologous nerve grafts. Functional recovery in conduit/PA and autologous graft groups was significantly faster than in animals treated with empty PLGA conduits. Histological examinations also demonstrated increased axonal and Schwann cell regeneration within the reconstructed nerve gap in animals treated with conduit/PA constructs. These results indicate that PA nanofibers may represent a promising biomaterial for use in bioengineered peripheral nerve repair.

Project description:H2S is a gasotransmitter with several physiological roles, but its reactivity and short half-life in biological media make its controlled delivery difficult. For biological applications of the gas, hydrogels have the potential to deliver H2S with several advantages over other donor systems, including localized delivery, controlled release rates, biodegradation, and variable mechanical properties. In this study, we designed and evaluated peptide-based H2S-releasing hydrogels with controllable H2S delivery. The hydrogels were prepared from short, self-assembling aromatic peptide amphiphiles (APAs), functionalized on their N-terminus with S-aroylthiooximes (SATOs), which release H2S in response to a thiol trigger. The APAs were studied both in solution and in gel forms, with gelation initiated by addition of CaCl2. Various substituents were included on the SATO component of the APAs in order to evaluate their effects on self-assembled morphology and H2S release rate in both the solution and gel phases. Transmission electron microscopy (TEM) images confirmed that all H2S-releasing APAs self-assembled into nanofibers above a critical aggregation concentration (CAC) of ∼0.5 mg/mL. Below the CAC, substituents on the SATO group affected H2S release rates predictably in line with electronic effects (Hammett σ values) according to a linear free energy relationship. Above the CAC, circular dichroism, infrared, and fluorescence spectroscopies demonstrated that substituents influenced the self-assembled structures by affecting hydrogen bonding (β-sheet formation) and π-π stacking. At these concentrations, electronic control over release rates diminished, both in solution and in the gel form. Rather, the release rate depended primarily on the degree of organization in the β-sheets and the amount of π-π stacking. This supramolecular control over release rate may enable the evaluation of H2S-releasing hydrogels with different release rates in biological applications.

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Peptide amphiphile nanofibers with conjugated polydiacetylene backbones in their core.

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Peptide amphiphile nanofibers with conjugated polydiacetylene backbones in their core.

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