Abstract
The self-assembly of nanometric structures from molecular building blocks is an effective way to make new functional materials for biological and technological applications. In this work, four symmetrical bolaamphiphiles based on dehydrodipeptides (phenylalanyldehydrophenylalanine and tyrosyldehydrophenylalanine) linked through phenyl or naphthyl linkers (terephthalic acid and 2,6-naphthalenedicarboxylic acid) were prepared, and their self-assembly properties were studied. The results showed that all compounds, with the exception of the bolaamphiphile of tyrosyldehydrophenylalanine and 2,6-naphthalene dicarboxylic acid, gave self-standing hydrogels with critical gelation concentrations of 0.3 wt % and 0.4 wt %, using a pH trigger. The self-assembly of these hydrogelators was investigated using STEM microscopy, which revealed a network of entangled fibers. According to rheology, the dehydrodipeptide bolaamphiphilic hydrogelators are viscoelastic materials with an elastic modulus G′ that falls in the range of native tissue (0.37 kPa brain–4.5 kPa cartilage). In viability and proliferation studies, it was found that these compounds were non-toxic toward the human keratinocyte cell line, HaCaT. In sustained release assays, we studied the effects of the charge present on model drug compounds on the rate of cargo release from the hydrogel networks. Methylene blue (MB), methyl orange (MO), and ciprofloxacin were chosen as cationic, anionic, and overall neutral cargo, respectively. These studies have shown that the hydrogels provide a sustained release of methyl orange and ciprofloxacin, while methylene blue is retained by the hydrogel network.
Highlights
Supramolecular hydrogels have attracted considerable attention due to their potential applications as promising biomaterials for many biotechnological and biomedical applications, such as drug delivery [1,2], cell culture [3], tissue engineering [4], wound healing [5,6], and many others
We describe the synthesis, characterization, and gelation properties of four new bis-dehydropeptide bolaamphiphiles 1–4, containing a phenylalanine or tyrosine residue connected to a dehydroamino acid residue at the C-terminus
The rheology properties of hydrogels prepared were studied by oscillatory rheology, and the results showed a storage modulus (G0 ) significantly higher that their loss modulus (G”), which confirmed that they exhibit a viscoelastic behavior, which is characteristic of supramolecular hydrogels
Summary
Supramolecular hydrogels have attracted considerable attention due to their potential applications as promising biomaterials for many biotechnological and biomedical applications, such as drug delivery [1,2], cell culture [3], tissue engineering [4], wound healing [5,6], and many others. Bolaamphiphilic gelators are composed of two polar heads at both ends of a central hydrophobic chain, which effectively doubles the amount of supramolecular interactions contained within the gel structure whilst maintaining essentially the same overall polarity of the corresponding monomer These hydrogelators have shown interesting properties compared with their monomeric counterparts [18,19]. We were keen to adapt our previous dehydrodipeptide hydrogelators into bolaamphiphilic versions in order to improve the physical properties (Figure 1D) Combining these two structures (bolaamphiphiles and dehydropeptides) into a single molecule would increase the number of interactions in the gel structure whilst increasing the stability to proteolytic degradation and reducing the molecular flexibility of the molecules.
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