Branched peptides integrate into self-assembled nanostructures and enhance biomechanics of peptidic hydrogels

Self-assembling peptides (SAP) have drawn an increasing interest in the tissue engineering community. They display unquestionable biomimetic properties, tailorability and promising biocompatibility. However their use has been hampered by poor mechanical properties making them fragile soft scaffolds. To increase SAP hydrogel stiffness we introduced a novel strategy based on multiple ramifications of (LDLK)(3), a well-known linear SAP, connected with one or multiple "lysine knots". Differently branched SAPs were tested by increasing the number of (LDLK)(3)-like branches and by adding the neuroregenerative functional motif BMHP1 as a single branch. While pure branched peptides did not have appealing self-assembling propensity, when mixed with the corresponding linear SAP they increased the stiffness of the overall hydrogel of multiple times. Notably, optimal results (or peak) were obtained 1) at similar molar ratio (between linear and branched peptides) for all tested sequences and 2) for the branched SAPs featuring the highest number of branches made of (LDLK)(3). The functional motif BMHP1, as expected, seemed not to contribute to the increase of the storage modulus as efficiently as (LDLK)(3). Interestingly, branched SAPs improved the beta-sheet self-arrangement of (LDLK)(3) and allowed for the formation of assembled nanofibers. Indeed in coarse-grained molecular dynamics we showed they readily integrate in the assembled aggregates providing "molecular connections" among otherwise weakly paired beta-structures. Lastly, branched SAPs did not affect the usual response of human neural stem cells cultured on (LDLK)(3)-like scaffolds in vitro. Hence, branched SAPs may be a valuable new tool to enhance mechanical properties of self-assembling peptide biomaterials harmlessly; as neither chemical nor enzymatic cross-linking reactions are involved. As a consequence, branched SAPs may enlarge the field of application of SAPs in tissue engineering and beyond. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.