pH-Responsive Biocompatible Supramolecular Peptide Hydrogel

Abstract

Peptide-based hydrogels are highly promising for various biomedical applications owing to their precise selfassembly, biocompatibility, and sensitivity toward biologically relevant external stimuli. Herein, we report pH-responsive selfassembly and gelation of a highly biocompatible amphiphilic peptide PEP-1. This is an octa-peptide and double mutant of a naturally occurring β-strand peptide fragment of the protein Galectin-1, available in bovine spleen. PEP-1 was synthesized by using the Rink amide resin as the solid support in a homemade apparatus. At pH 7.4, it exhibits spontaneous gelation with very high yield stress of 88.0 Pa and gel-to-sol temperature of 84 °C at C = 2.0 wt %. Microscopy studies revealed entangled fibrillar morphology whereas circular dichroism, Fourier tranform IR, and Thioflavin T assay indicated formation of β-sheet rich secondary structure. The assembled state was found to be stable in neutral pH whereas either decrease or increase in the pH resulted in disassembly owing to the presence of the pH responsive Asp and Lys residues. The gel network showed ability to entrap water-soluble guest molecules such as Calcein which could be selectively released at acidic pH whereas under neutral condition the release was negligible. MTT assay revealed remarkable biocompatibility of the PEP-1 gel as almost 100% cells were alive after 48 h incubation in the presence of PEP-1 (2.0 mg/mL).

Maneuverability of Magnetic Nanomotors Inside Living Cells

“…In addition, under certain conditions, the motors can show precession dynamics that can depend on the local viscosity, strength, and frequency of magnetic drive, and geometry of the motors. While this has been used to estimate the local mechanical properties of heterogeneous environments made of Newtonian, shear thinning, and Boger fluid, it will be very interesting to extend this technique to more complicated milieu such as the cellular cytoplasm. In the Supporting Information (section III), we present a synopsis of how dynamics of helical nanomotors can be used to relate with the rheological parameters of the surrounding medium.…”

pH- and concentration-dependent supramolecular self-assembly of a naturally occurring octapeptide

“…Fmoc-protected Rink amide resin (0.45 g, 0.5 mmol) was swelled in 10 mL of DMF for two hours. After that, the swelled resin was loaded into the special apparatus [23], and the solvent was drained off. The swelled resin was washed with DMF (10 mL × 4).…”

“…After washing the resin with DMF, the deprotection procedure was repeated, and the resin was thoroughly washed with DMF. Subsequently, a Kaiser test [23] was performed to monitor the deprotection step. A few resin beads were placed in a small vial and washed with ethanol, and then, two drops of each of the three solutions were added and heated to 100 °C for 4-6 min.…”

“…For the ThT assay, we used a protocol similar to the one previously described [23]. A diluted solution of ThT at a concentration of 1.0 × 10 −3 M was prepared in PBS buffer (pH 7.4) from a concentrated stock solution (5.0 × 10 −3 M) and then filtered with a syringe filter.…”

“…Noncovalent interactions, such as hydrogen bonding, van der Waals interactions, hydrophobic interactions, electrostatic interactions, and π–π interactions [ 18 – 22 ] are common driving forces in peptide self-assembly. These noncovalent interactions can also be designed to be responsive to various external stimuli, such as heat, pH, light, enzymes, metal ions, and chemical triggers [ 23 – 39 ]. In this regard, a particularly relevant property of peptide assemblies is their ability to undergo significant changes in their morphologies and secondary structures in response to pH stimuli.…”