Ultra-short self-assembled beta-peptide hydrogels as matrices for neural tissue engineering

摘要

Hydrogels have physical features of soft tissue and have been explored for their use in nerve regeneration and drug delivery. Hydrogels based on peplide self-assembly are extremely promising candidates to provide a suitable microenvironment for cells due to their facile synthesis, simple building blocks, inherent biocompatibility and the ability to control the structural and functional properties of the end product . However, applying the peptide hydrogel matrices in brain tissue engineering is faced with a number of key challenges. Peptide-based biomaterials that are used in neural tissue engineering have been based on α-amino acid peptides which can undergo rapid proteolysis and are unable to provide long term structural support. In cases where the matrix must fill and provide structural support in a large brain lesion, it may be preferable to use a non-degrading or permanent peptide matrix . Herein we introduce for the first time hydrogels consisting of peptide matrix composed of only β~3-amino acids as an efficient alternative for neural tissue engineering and to utilise their inherent proteolySc stability in vivo . To provide the required conditions for self-assembly the N-terminus of β-tripeptide (AzKA) was capped with an acetyl group which produced a total of six axially oriented hydrogen bonding interactions . A hydrophobic alkyl chain was added laterally to the peptide backbone to ensure the formation of stable hydrogel. Peptide self-assembled spontaneously to form a hydrogel upon dissolving in PBS buffer (pH 7.4) under physiological conditions at a concentration of 10mg/mL The morphology of the formed nanofibers was further investigated by AFM and TEM which revealed a network of nanofibers with consistent diameter. The mechanical properties of the peptide hydrogel were tested via rheological studies. The hydrogel showed viscoelastic properties with storage modulus in the range of 1 kPa. A balance between hydrophilic and hydrophobic domain in the peptide, allowed the hydrogel to flow under applied shear strain and to recover completely within seconds upon relaxation. To check the feasibility of the hydrogel for neural tissue engineering, the viability of SN4741, substantia nigra dopaminergic neuronal progenitor cell line, cultured on the hydrogel were assayed. The hydrogel proved to be highly biocompatible and even though it did not possess any bioactive motif, by pre-depositing protein from serum, it provided an environment for cells to adhere and proliferate with 80% cell viability in comparison to the positive control (cultured on TCPS). The facile design and synthesis of a β-peptide hydrogel can thus allow formation of controlled and variable biomaterials for different types of tissue engineering applications.