Correlations between structure, material properties and bioproperties in self-assembled β-hairpin peptide hydrogels

Abstract

A de novo designed beta-hairpin peptide (MAX8), capable of undergoing intramolecular folding and consequent intermolecular self-assembly into a cytocompatible hydrogel, has been studied. A combination of small angle neutron scattering (SANS) and cryogenic-transmission electron microscopy (cryo-TEM) have been used to quantitatively investigate the MAX8 nanofibrillar hydrogel network morphology. A change in the peptide concentration from 0.5 to 2 wt% resulted in a denser fibrillar network as revealed via SANS by a change in the high q (q = (4 pi/lambda) x sin (theta/2), where lambda = wavelength of incident neutrons and theta = scattering angle) mass fractal exponent from 2.5 to 3 and by a decrease in the measured correlation length from 23 to 16 A. A slope of -4 in the USANS regime indicates well-defined gel microporosity, an important characteristic for cellular substrate applications. These changes, both at the network as well as the individual fibril lengthscales, can be directly visualized in situ by cryo-TEM. Fibrillar nanostructures and network properties are directly related to bulk hydrogel stiffness via oscillatory rheology. Preliminary cell viability and anchorage studies at varying hydrogel stiffness confirm cell adhesion at early stages of cell culture within the window of stiffness investigated. Knowledge of the precise structure spanning length scales from the nanoscale up to the microscale can help in the formation of future, specific structure-bioproperty relationships when studying in vitro and in vivo behavior of these new peptide scaffolds.

Injectable Solid Peptide Hydrogel as a Cell Carrier: Effects of Shear Flow on Hydrogels and Cell Payload

“…β-hairpin peptide hydrogels display shear-thinning and immediate recovery properties 9,19,20,30,31 ; the solid peptide hydrogel preformed in a syringe can be injected as a solid through a needle and precisely delivered to a target site with instant recovery into a solid post-injection 9,19,20 . In addition, these β-hairpin peptide gel materials can be inherently antibacterial 36 , are biologically benign toward several model cell lines 19,20,39,40 and unable to provoke immune-responses in macrophages in vitro 41 . Moreover, the gel properties ( e.g.…”

“…However, intramolecular folding of MAX8 peptides can be triggered by a combination of adding salt to screen electrostatic repulsions between lysines, by elevating temperature to induce hydrophobic collapse or by deprotonation of the lysines at basic pH 8,19 . As a result of the intramolecular folding conformation change into a β-hairpin, the folded peptides self-assemble into a stiff hydrogel with a three-dimensional, nanofibrillar network structure stabilized by physical crosslinks 9,39 that allow the hydrogel to shear-thin and flow into a thin catheter 9,19,20 . Due to fast gelation kinetics under physiological condition, MAX8 is capable of encapsulating living mammalian cells homogeneously in three-dimensions during initial hydrogelation, which is exactly desired for injectable delivery of cells 19,20 .…”

Peptidic Hydrogels

“…Right a MAX1 after a single substitution difference for reduced overall charge is known as b MAX8. The reduced charge leads to faster kinetics and gelation time for MAX8, as evidenced by the effects of gravity on encapsulated MSCs [73] number of physical crosslinks of the gel, ultimately affecting the stiffness of the MAX hydrogel created [73,94,95]. The Schneider group has also looked at substituting all l-amino (left handed) acids for d-amino acids (right handed), thereby reversing the natural chirality of MAX1 [85].…”

Hierarchical Structure of the Fibrillar Hydrogel Network of a Self‐Assembled Synthetic Peptide Revealed by X‐ray Scattering and Atmospheric Scanning Electron Microscopy

“…Schneider and co-workers examined self-assembled b-hairpin peptide hydrogels using a combination of small angle neutron scattering and TEM. [21,22] The structure is validated by a combined analysis of spectroscopic, scattering, and microscopic in situ approaches. In situ X-ray scattering measurements were obtained for the self-assembled SPG-178 peptide hydrogel.…”

“…Schneider and co-workers investigated self-assembled b-hairpin peptide hydrogels using a combination of small angle neutron scattering and TEM. [21,22] This combination approach, which probed real and reciprocal space, provides a solid picture of complex and hierarchical structures. An inverted scanning electron microscope with a detachable and open-culture dish has been developed to directly observe subcellular structures in an open environment.…”