One of the methods of obtaining supramolecular gels consists of the possibility of self-assembly of low molecular weight gelators (LMWGs). However, LMWG-based gels are often difficult to handle, easy to destroy and have poor rheological performance. In order to improve the gels’ properties, the LMWGs molecules are co-assembled, which induces more cross-links with more stable structures. Starting from these aspects, the present study refers to the preparation of a bionic hydrogel stabilized with a physiologically occurring, bifunctional biomolecule, L-lysine, co-assembled with other amino acids or peptides (such as a modified amino acid (Fmoc-serine or Fmoc-glutamic acid) or a tripeptide (Fmoc-Gly-Gly-Gly)) with the potential to support the repair of injuries or the age-related impaired structures or functions of living tissues. The introduction of a copartner aims to improve hydrogel characteristics from a morphological, rheological and structural point of view. On the other hand, the process will allow the understanding of the phenomenon of specific self-association and molecular recognition. Various characterization techniques were used to assess the ability to co-assemble: DLS, FT-IR, SEM and fluorescence microscopy, rheology and thermal analysis. Studies have confirmed that the supramolecular structure occurs through the formation of inter- and intramolecular physical bonds that ensure the formation of fibrils organized into 3D networks. The rheological data, namely the G′ > G″ and tan δ approximately 0.1–0.2 gel-like behavior observed for all studied samples, demonstrate and sustain the appearance of the co-assembly processes and the ability of the samples to act as LMWG. From the studied systems, the Fmoc–Lys–Fmoc_ Fmoc–Glu sample presented the best rheological characteristics that are consistent with the observations that resulted from the dichroism, fluorescence and SEM investigations.
In the last years, physical hydrogels have been widely studied due to the characteristics of these structures, respectively the non-covalent interactions and the absence of other necessary components for the cross-linking processes. Low molecular weight gelators are a class of small molecules which form higher ordered structures through hydrogen bonding and π–π interactions. In this context it is known that the formation of hydrogels based on FMOC–amino acids is determined by the primary structures of amino acids and the secondary structure arrangement (alpha–helix or beta–sheet motifs). The present study aimed to obtain supramolecular gels through co-assembly phenomenon using FMOC–amino acids as low molecular weight gelators. The stability of the new structures was evaluated by the vial inversion test, while FTIR spectra put into evidence the interaction between the compounds. The gel-like structure is evidenced by viscoelastic parameters in oscillatory shear conditions. SEM microscopy was used to obtain the visual insight into the morphology of the physical hydrogel network while DLS measurements highlighted the sol-gel transition. The molecular arrangement of gels was determined by circular dichroism, fluorescence and UV-Vis spectroscopy.
Short aromatic peptide derivatives, i.e., peptides or amino acids modified with aromatic groups, such as 9-fluorenylmethoxycarbonyl (Fmoc), can self-assemble into extracellular matrix-like hydrogels due to their nanofibrillar architecture. Among different types of amino acids, lysine (Lys) and glycine (Gly) are involved in multiple physiological processes, being key factors in the proper growth of cells, carnitine production, and collagen formation. The authors have previously successfully presented the possibility of obtaining supramolecular gels based on Fmoc-Lys-Fmoc and short peptides such as Fmoc-Gly-Gly-Gly in order to use them as a substrate for cell cultures. This paper investigates how the introduction of a gelling polymer can influence the properties of the network as well as the compatibility of the resulting materials with different cell types. A series of hydrogel compositions consisting of combinations of Fmoc-Lys-Fmoc and Fmoc-Gly-Gly-Gly with Agarose and Phytagel are thus obtained. All compositions form structured gels as shown by rheological studies and scanning electron microscopy. Fourier transform infrared spectroscopy analysis evidences the formation of H-bonds between the polysaccharides and amino acids or short peptides. Moreover, all gels exhibit good cell viability on fibroblasts as demonstrated by a live-dead staining test and good in vivo biocompatibility, which highlights the great potential of these biomaterials for biomedical applications.
Double network (DN) hydrogels composed of self-assembling low-molecular-weight gelators and a hybrid polymer network are of particular interest for many emerging biomedical applications, such as tissue regeneration and drug delivery. The major benefits of these structures are their distinct mechanical properties as well as their ability to mimic the hierarchical features of the extracellular matrix. Herein, we describe a hybrid synthetic/natural polymer gel that acts as the initial network based on sodium alginate and a copolymer, namely poly(itaconic anhydride-co-3,9-divinyl-2,4,8,10-tetraoxaspiro (5,5) undecane). The addition of amino acids and peptide-derived hydrogelators, such as Fmoc-Lys-Fmoc-OH and Fmoc-Gly-Gly-Gly-OH, to the already-made network gives rise to DNs crosslinked via non-covalent interactions. Fourier transform infrared spectroscopy (FTIR) and thermal analysis confirmed the formation of the DN and highlighted the interactions between the two component networks. Swelling studies revealed that the materials have an excellent water absorption capacity and can be classified as superabsorbent gels. The rheological properties were systematically investigated in response to different variables and showed that the prepared materials present injectability and a self-healing ability. SEM analysis revealed a morphology consisting of a highly porous and interconnected fibrous network. Finally, the biocompatibility was evaluated using the MTT assay on dermal fibroblasts, and the results indicated that the new structures are non-toxic and potentially useful for biomedical applications.
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