Two-step self-assembly of liposome-multidomain peptide nanofiber hydrogel for time-controlled release

Abstract

Progress in self-assembly and supramolecular chemistry has been directed toward obtaining macromolecular assemblies with higher degrees of complexity, simulating the highly structured environment in natural systems. One approach to this type of complexity are multistep, multicomponent, self-assembling systems that allow approaches comparable to traditional multistep synthetic organic chemistry; however, only a few examples of this approach have appeared in the literature. Our previous work demonstrated nanofibrous mimics of the extracellular matrix. Here we demonstrate the ability to create a unique hydrogel, developed by stepwise self-assembly of multidomain peptide fibers and liposomes. The two-component system allows for controlled release of bioactive factors at multiple time points. The individual components of the self-assembled gel and the composite hydrogel were characterized by TEM, SEM, and rheometry, demonstrating that peptide nanofibers and lipid vesicles both retain their structural integrity in the composite gel. The rheological robustness of the hydrogel is shown to be largely unaffected by the presence of liposomes. Release studies from the composite gels loaded with different growth factors EGF, MCP-1, and PlGF-1 showed delay and prolongation of release by liposomes entrapped in the hydrogel compared to more rapid release from the hydrogel alone. This bimodal release system may have utility in systems where timed cascades of biological signals may be valuable, such as in tissue regeneration.

Figure 1

Schematic of the process of multidomain peptide self-assembly in to nanofibers. Multidomain peptide scaffolds with the sequence K(SL)₃RG(SL)₃KGRGDS form facial amphiphiles that self-assemble into β-sheet forming fibers. With the introduction of multivalent salts, terminal charge repulsion is shielded allowing for long-range fiber growth.

Figure 2

Stepwise orthogonal self-assembly combining liposomes, growth factors, and MDP fibers.

Figure 3

(a) Schematic diagram and (b) photograph of a transwell set up for EGF-FITC release studies.

Figure 4

(a) Negatively stained TEM of 1 wt % K(SL)3RG(SL)3KGRGDS peptide in 298 mM sucrose, (b) cryo-TEM of GF-encapsulated liposomes (indicated by red arrow) and drying artifacts (indicated by *), and dynamic light scattering showing (c) size plot of unloaded liposomes showing stability over 14 days and (d) size plot of EGF-FITC, MCP-1-CFDA, and PlGF-1-TAMRA loaded liposomes after purification.

Figure 5

(a, b) Negatively stained TEM images of composite gel. (c) SEM image and (d) Cryo-TEM image of composite gel.

Figure 6

Shear recovery of gel without liposomes (a) compared to the composite gel with liposomes (b).

Figure 7

Release profiles for (a) EGF-FITC, (b) MCP-1-CFDA, and (c) PlGF-1-TAMRA, showing release from gel matrix of control gels without liposomes (blue) and release from liposomes in composite gels (red), along with the respective curve fit (n = 3 for each sample). R² values are given in SI, Table S1.

Figure 8

Release profiles obtained from the bimodal release of EGF-FITC and PlGF-1-TAMRA. Blue indicates release from hydrogel alone while red is release from liposomes within the hydrogel. Dashed lines indicate burst release or sigmoidal release models. R² values are given in SI, Table S2 (n = 3 for each sample).