Smart materials have been attracting much attention because of their stimuli responsive nature. We have synthesized biocompatible thermoresponsive crosslinked poly(ethylene glycol) methyl ether methacrylate (PEGMA)-co-vinyl pyrrolidone nanoparticles (PEGMA NPs) using disulfide-based crosslinker by surfactant-free emulsion polymerization method. Particle characterization studies were carried out by dynamic light scattering, and scanning electron microscopy. Polymerization kinetics, effect of crosslinker and initiator concentrations on both average hydrodynamic diameter and polydispersity index were investigated. Hydrodynamic diameters of thermoresponsive PEGMA NPs were decreased from 210 nm to 90 nm upon heating over the lowest critical solution temperature (LCST). Disulfide crosslinked PEGMA NPs were demonstrated as a dual delivery system. Rhodamine B, a model of small-sized drug molecule, and poly(ethylene glycol) (PEG)-alizarin yellow, a model of large drug molecule, were loaded into PEGMA NPs where LCST of these NPs was tuned to 37°C, the body temperature. The rhodamine B was released from PEGMA NPs upon heating to 39°C. Then, PEG-alizarin content was released by subsequent degradation of nanoparticles using dithiothreitol (DTT), which reduces disulfide bonds to thiols. Furthermore, cytotoxicity studies of PEGMA NPs were carried out in 3T3 cells, which resulted in no toxic effect on the cells.
Since the discovery of dipeptide self-assembly, diphenylalanine (Phe-Phe)-based dipeptides have been widely investigated in a variety of fields. Although various supramolecular Phe-Phe-based structures including tubes, vesicles, fibrils, sheets, necklaces, flakes, ribbons, and wires have been demonstrated by manipulating the external physical or chemical conditions applied, studies of the morphological diversity of dipeptides other than Phe-Phe are still required to understand both how these small molecules respond to external conditions such as the type of solvent and how the peptide sequence affects self-assembly and the corresponding molecular structures. In this work, we investigated the self-assembly of valine-alanine (Val-Ala) and alanine-valine (Ala-Val) dipeptides by varying the solvent medium. It was observed that Val-Ala dipeptide molecules may generate unique self-assembly-based morphologies in response to the solvent medium used. Interestingly, when Ala-Val dipeptides were utilized as a peptide source instead of Val-Ala, we observed distinct differences in the final dipeptide structures. We believe that such manipulation may not only provide us with a better understanding of the fundamentals of the dipeptide self-assembly process but also may enable us to generate novel peptide-based materials for various applications.
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