Active Modulation of States of Prestress in Self-Assembled Short Peptide Gels.

Henry Cox,Jian R Lu,Thomas A Waigh,Meiwen Cao,Hai Xu

doi:10.1021/acs.biomac.9b00085

Henry Cox, Jian R Lu + Show 3 more

Open Access

https://doi.org/10.1021/acs.biomac.9b00085

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Abstract

Peptide hydrogels are excellent candidates for medical therapeutics due to their tuneable viscoelastic properties, however, in vivo they will be subject to various osmotic pressures, temperature changes, and biological co-solutes, which could alter their performance. Peptide hydrogels formed from the synthetic peptide I3K have a temperature-induced hardening of their shear modulus by a factor of 2. We show that the addition of uncross-linked poly(N-isopropylacrylamide) chains to the peptide gels increases the gels’ temperature sensitivity by 3 orders of magnitude through the control of osmotic swelling and cross-linking. Using machine learning combined with single-molecule fluorescence microscopy, we measured the modulation of states of prestress in the gels on the level of single peptide fibers. A new self-consistent mixture model was developed to simultaneously quantify the energy and the length distributions of the states of prestress. Switching the temperature from 20 to 40 °C causes 6-fold increases in the number of states of prestress. At the higher temperature, many of the fibers experience constrained buckling with characteristic small wavelength oscillations in their curvature.

Highlights

Gels are complex materials, expressing a range of designer viscoelastic properties, which a solid or liquid alone cannot deliver
We used a combination of bulk rheology and image analysis of the dynamics of individual peptide fibrils through singlemolecule fluorescence microscopy to demonstrate active modulation of peptide gel mechanics through the control of osmotic pressures
The addition of the pNIPAM to the I3K gel at low temperatures resulted in a lowering of the elastic modulus and an increase in the scaling between elastic modulus and frequency, suggesting that the system was acting as a solution of semiflexible filaments and that a sol−gel transition has occurred

Summary

Introduction

Gels are complex materials, expressing a range of designer viscoelastic properties, which a solid or liquid alone cannot deliver. Peptide-based gels have gained significant interest commercially as they are formed from naturally occurring amino acids and are biodegradable and often biocompatible.[9] Synthetic peptides can be designed to harness the properties of different amino acids and self-assemble through thermodynamically driven processes into large ordered structures.[10] Some of the most popular peptides self-assemble into long, thin fibrils which cross-link and entangle, forming networks which trap water and provide mechanical strength.[10,11] The resulting macroscopic properties of these gels are determined by the physical interactions between the fibrils and, despite considerable research effort, there is not an accurate theory which describes such semiflexible polymeric gels.[7,12] The networks are complex, load-bearing structures, and researchers have demonstrated that changing a variety of environmental factors can yield large changes in their bulk properties.[13] These effects are commonly attributed to the modulation of cross-link strength between fibrils, such as changing the ion concentrations in the gel which alters the interfibre adhesive potentials. The load bearing structures lead to novel states of quenched disorder, such as states of prestress, which have important implications for the mechanical properties.[14−16]

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