# Nano-Fibrous Networks from Co-Assembly of Amphiphilic Peptide and Polyelectrolyte
## 3 Results and Discussion  
C\({}_{16}\)-V\({}_{3}\)A\({}_{3}\)K\({}_{3}\)G-NH\({}_{2}\) lipidated PA (Figure 1) has been synthesized using standard 9-fluoreylmethylethoxycarbonyl-based solid phase procedure. It integrates three values and three alanines as structuring part, which impart a polarity gradient between the hydrophobic part C\({}_{16}\) and the hydrophilic part K\({}_{3}\)G-NH\({}_{2}\), known to help alignment of PA thus leading to robust cylindrical micelles containing \(\beta\)-sheet secondary structure in the V\({}_{3}\)A\({}_{3}\) peptide domain [9]. PA self-assemble into fibrils as shown in AFM (Figure 2) with a size and global shape depending on the initial PA concentration going from 0.05 to 20 mg.mL\({}^{-1}\). Solutions were spin-coated onto a silicon wafer in sort that a water evaporation along with solution spreading lead to a progressive--although quick--PA concentration driving the PA assembly from almost individualized PA cylindrical micelles (Figure 2C) at low concentration (0.05 mg.mL\({}^{-1}\)) towards larger aggregates, such as ribbon-like fibrils at higher concentration (20 mg.mL\({}^{-1}\)) (Figure 2A). Figure 1: Schematic representation of a nanofibrous membrane from peptide amphiphile C\({}_{16}\)V\({}_{3}\)A\({}_{3}\)K\({}_{3}\)G-NH\({}_{2}\) and poly(sodium 4-styrenesulfonate) (PSSNa) co-assembly. The signature of \(\beta\)-sheet formation of the C\({}_{16}\)V\({}_{3}\)A\({}_{3}\)K\({}_{3}\)G-NH\({}_{2}\) in aqueous solution is confirmed in Circular dichroism (CD) spectroscopy (Figure 3). In addition, the importance of the length of the alkyl chain is also underlined as shown by the signal, shifted to random coil, observed with the same PA except with regard to its hydrophobic part, reduced from a C16 to a C2. PA cylindrical micelles could be disturbed by the presence of other amphiphilic molecules, such as surfactant. As an illustration, CD spectrum of the PA in presence of Triton X-100 surfactant shows a decrease in CD intensity at 206 nm which is a marker of \(\beta\)-sheet content. PA cylinders were then used as structuring agent for the membrane formation and electrostatic interactions with PSSNa were promoted to yield membranes able to sustain water pressure (Figure 1). PSSNa is a polyanion able to interact with the K\({}_{3}\) sequence of the lipidated PA as demonstrated in literature [24]. In doing so, PSSNa should be able to amplify the cylindrical structure of the PA micelle to another scale allowing the formation of gels or functional materials. Concretely, the polymer will line the external surface of the PA micelles via electrostatic interactions. Therefore, the balance between the number of charges brought by the PA and the number of charges brought by the polymer is an important parameter. Depending on the ratio PA (+) charges /polymer (-) charges (R\({}_{+/-}\)) used, the appearance of a gel was visually observed with the highest rigidity when R\({}_{+/-}\) is equal to 1, that is to say for a total compensation of electrostatic charges (Figure 4D-F). However, it is advisable to be very careful with this indicator, which should only be considered as a relative reference. Indeed, R\({}_{+/-}\) assumes that all charges are accessible which cannot be the case with the use of polymer due to the steric hindrance and chain folding. In addition, when the two aqueous solutions are put into contact, an almost instantaneous structuring of the  
Figure 2: AFM of C\({}_{16}\)V\({}_{3}\)A\({}_{3}\)K\({}_{3}\)G-NH\({}_{2}\) self-assemblies from different PA concentrations: [PA\({}_{\rm A}\)] = 20 mg\(\cdot\)mL\({}^{-1}\); [PA\({}_{\rm B}\)] = 5 mg\(\cdot\)mL\({}^{-1}\); [PA\({}_{\rm C}\)] = 0.05 mg\(\cdot\)mL\({}^{-1}\). interface occurs, then limiting the inter-diffusion of the solutions [17]. Therefore, the charge balance is in fact distorted by a partial segregation of the solutions components. AFM images show a similar material organization for R\({}_{+/-}>1\) with a polymer homogeneously distributed within the nanostructure (Figure 4C).