Probing peptide amphiphile self-assembly in blood serum

Navigating the Expansive Landscapes of Soft Materials: A User Guide for High-Throughput Workflows

Synthetic polymers are highly customizable with tailored structures and functionality, yet this versatility generates challenges in the design of advanced materials due to the size and complexity of the design space. Thus, exploration and optimization of polymer properties using combinatorial libraries has become increasingly common, which requires careful selection of synthetic strategies, characterization techniques, and rapid processing workflows to obtain fundamental principles from these large data sets. Herein, we provide guidelines for strategic design of macromolecule libraries and workflows to efficiently navigate these high-dimensional design spaces. We describe synthetic methods for multiple library sizes and structures as well as characterization methods to rapidly generate data sets, including tools that can be adapted from biological workflows. We further highlight relevant insights from statistics and machine learning to aid in data featurization, representation, and analysis. This Perspective acts as a "user guide" for researchers interested in leveraging high-throughput screening toward the design of multifunctional polymers and predictive modeling of structure-property relationships in soft materials.

Dual functionalized hyaluronic acid micelles loading paclitaxel for the therapy of breast cancer

Although many carriers for the delivery of chemotherapeutic drugs have been investigated, the disadvantages of passive targeting and uncontrolled drug release limit their utility. Herein, hyaluronic acid (HA) was hydrophobically modified to serve as a carrier for binding to cluster determinant 44 (CD44) overexpressed on tumor cell surfaces. Specifically, after deacetylation, HA was grafted to dodecylamine or tetradecylamine to afford amphiphilic zwitterionic polymer micelles, designated dHAD and dHAT, respectively, for the delivery of paclitaxel (PTX). The micelles were negatively charged at pH 7.4 and positively charged at pH 5.6, and this pH sensitivity facilitated PTX release under acidic conditions. The cell uptake efficiencies of the dHAD-PTX and dHAT-PTX micelles by MCF-7 cells after 4 h of incubation were 96.9% and 95.4%, respectively, and their affinities for CD44 were twice that of HA. Furthermore, the micelles markedly inhibited tumor growth both in vitro and in vivo, with IC50 values of 1.943 μg/mL for dHAD-PTX and 1.874 μg/mL for dHAT-PTX for MCF-7 cells; the tumor inhibition rate of dHAD-PTX (92.96%) was higher than that of dHAT-PTX (78.65%). Importantly, dHAD and dHAT micelles showed negligible systemic toxicity. Our findings suggest that these micelles are promising delivery vehicles for antitumor drugs.

Control of Peptide Amphiphile Supramolecular Nanostructures by Isosteric Replacements

Supramolecular nanostructures with tunable properties can have applications in medicine, pharmacy, and biotechnology. In this work, we show that the self-assembly behavior of peptide amphiphiles (PAs) can be effectively tuned by replacing the carboxylic acids exposed to the aqueous media with isosteres, functionalities that share key physical or chemical properties with another chemical group. Transmission electron microscopy, atomic force microscopy, and small-angle X-ray scattering studies indicated that the nanostructure's morphologies are responsive to the ionization states of the side chains, which are related to their pK_a values. Circular dichroism studies revealed the effect of the isosteres on the internal arrangement of the nanostructures. The interactions between diverse surfaces and the nanostructures and the effect of salt concentration and temperature were assessed to further understand the properties of these self-assembled systems. These results indicate that isosteric replacements allow the pH control of supramolecular morphology by manipulating the pK_a of the charged groups located on the nanostructure's surface. Theoretical studies were performed to understand the morphological transitions that the nanostructures underwent in response to pH changes, suggesting that the transitions result from alterations in the Coulomb forces between PA molecules. This work provides a strategy for designing biomaterials that can maintain or change behaviors based on the pH differences found within cells and tissues.

Potential sealing and repair of human FM defects after trauma with peptide amphiphiles and Cx43 antisense

OBJECTIVE

We examined whether peptide amphiphiles functionalised with adhesive, migratory or regenerative sequences could be combined with amniotic fluid (AF) to form plugs that repair fetal membrane (FM) defects after trauma and co-culture with connexin 43 (Cx43) antisense.

METHODS

We assessed interactions between peptide amphiphiles and AF and examined the plugs in FM defects after trauma and co-culture with the Cx43antisense.

RESULTS

Confocal microscopy confirmed directed self-assembly of peptide amphiphiles with AF to form a plug within minutes, with good mechanical properties. SEM of the plug revealed a multi-layered, nanofibrous network that sealed the FM defect after trauma. Co-culture of the FM defect with Cx43 antisense and plug increased collagen levels but reduced GAG. Culture of the FM defect with peptide amphiphiles incorporating regenerative sequences for 5 days, increased F-actin and nuclear cell contraction, migration and polarization of collagen fibers across the FM defect when compared to control specimens with minimal repair.

CONCLUSIONS

Whilst the nanoarchitecture revealed promising conditions to seal iatrogenic FM defects, the peptide amphiphiles need to be designed to maximize repair mechanisms and promote structural compliance with high mechanical tolerance that maintains tissue remodeling with Cx43 antisense for future treatment.

Polymorphic Self-Organization of Lauroyl Peptide in Response to pH and Concentration

Amphipathic peptides are attractive building blocks for the preparation of self-assembling, bio-inspired, and stimuli responsive nanomaterials with pharmaceutical interest. The bioavailability of these materials can be improved with the insertion of d amino acid residues to avoid fast proteolysis in vivo. With this knowledge, a new lauroyl peptide consisting of a sequence of glycine, glycine, d-serine, and d-lysine was designed. In spite of its simple sequence, this lipopeptide self-assembles into spherical micelles at acid pH, when the peptide moiety adopts disordered conformations. Self-aggregates reshape toward fibers at basic pH, following the conformational transition of the peptide region from random coil to β-sheet. Finally, hydrogels are achieved at basic pH and higher concentrations. The transition from random coil to β-sheet conformation of the peptide headgroup obtained by increasing pH was monitored by circular dichroism and vibrational spectroscopy. A structural analysis, performed by combining dynamic light scattering, small-angle X-ray scattering, transmission electron microscopy, and molecular dynamic simulations, demonstrated that the transition allows the self-assemblies to remodel from spherical micelles to rodlike shapes, to long fibers with rectangular cross-section and a head-tail-tail-head structure. The viscoelastic behavior of the hydrogels formed at the highest pH was investigated by rheology measurements.

Peptide-based building blocks as structural elements for supramolecular Gd-containing MRI contrast agents

Magnetic resonance imaging (MRI) is one of the most important clinic diagnostic tool used to obtain high-quality body images. The administration of low-molecular-weight Gd complex-based MRI contrast agents (CAs) permits to increase the ¹ H relaxation rate of nearby water molecules, thus modulating signal intensity and contrast enhancement. Even if highly accurate, MRI modality suffers from its low sensitivity. Moreover, low-molecular-weight CAs rapidly equilibrate between the intravascular and extravascular spaces after their administration. In order to improve their sensitivity and limit the extravasation phenomenon, several macromolecular and supramolecular multimeric gadolinium complexes (dendrimers, polymers, carbon nanostructures, micelles, and liposomes) have been designed until now. Because of their biocompatibility, low immunogenicity, low cost, and easy synthetic modification, peptides are attractive building blocks for the fabbrication of novel materials for biomedical applications. We report on the state of the art of supramolecular CAs obtained by self-assembly of three different classes of building blocks containing a peptide sequence, a gadolinium complex, and, if necessary, a third functional portion achieving the organization process.

Structure-Stability-Function Mechanistic Links in the Anti-Measles Virus Action of Tocopherol-Derivatized Peptide Nanoparticles

Measles remains one of the leading causes of child mortality worldwide and is re-emerging in some countries due to poor vaccine coverage, concomitant with importation of measles virus (MV) from endemic areas. The lack of specific chemotherapy contributes to negative outcomes, especially in infants or immunodeficient individuals. Fusion inhibitor peptides derived from the MV Fusion protein C-terminal Heptad Repeat (HRC) targeting MV envelope fusion glycoproteins block infection at the stage of entry into host cells, thus preventing viral multiplication. To improve efficacy of such entry inhibitors, we have modified a HRC peptide inhibitor by introducing properties of self-assembly into nanoparticles (NP) and higher affinity for both viral and cell membranes. Modification of the peptide consisted of covalent grafting with tocopherol to increase amphipathicity and lipophilicity (HRC5). One additional peptide inhibitor consisting of a peptide dimer grafted to tocopherol was also used (HRC6). Spectroscopic, imaging, and simulation techniques were used to characterize the NP and explore the molecular basis for their antiviral efficacy. HRC5 forms micellar stable NP while HRC6 aggregates into amorphous, loose, unstable NP. Interpeptide cluster bridging governs NP assembly into dynamic metastable states. The results are consistent with the conclusion that the improved efficacy of HRC6 relative to HRC5 can be attributed to NP instability, which leads to more extensive partition to target membranes and binding to viral target proteins.

"Chemistry-on-the-complex": functional RuII polypyridyl-type sensitizers as divergent building blocks

Ruthenium polypyridyl type complexes are potent photoactive compounds, and have found - among others - a broad range of important applications in the fields of biomedical diagnosis and phototherapy, energy conversion schemes such as dye-sensitized solar cells (DSSCs) and molecular assemblies for tailored photo-initiated processes. In this regard, the linkage of RuII polypyridyl-type complexes with specific functional moieties is highly desirable to enhance their inherent photophysical properties, e.g., with a targeting function to achieve cell selectivity, or with a dye or redox-active subunits for energy- and electron-transfer. However, the classical approach of performing ligand syntheses first and the formation of Ru complexes in the last steps imposes synthetic limitations with regard to tolerating functional groups or moieties as well as requiring lengthy convergent routes. Alternatively, the diversification of Ru complexes after coordination (termed "chemistry-on-the-complex") provides an elegant complementary approach. In addition to the Click chemistry concept, the rapidly developing synthesis and purification methodologies permit the preparation of Ru conjugates via amidation, alkylation and cross-coupling reactions. In this regard, recent developments in chromatography shifted the limits of purification, e.g., by using new commercialized surface-modified silica gels and automated instrumentation. This review provides detailed insights into applying the "chemistry-on-the-complex" concept, which is believed to stimulate the modular preparation of unpreceded molecular assemblies as well as functional materials based on Ru-based building blocks, including combinatorial approaches.

Importance of Evaluating Dynamic Encapsulation Stability of Amphiphilic Assemblies in Serum

In targeted drug delivery systems, it is desirable that the delivery of hydrophobic drugs to a cell or tissue is achieved with little to no side effects. To ensure that the drugs do not leak during circulation, encapsulation stability of the drug carrier in serum is critical. In this paper, we report on a modified FRET-based method to evaluate encapsulation stability of amphiphilic assemblies and cross-linked polymer assemblies in serum. Our results show that serum components can act as reservoirs for hydrophobic molecules. We also show that serum albumin is likely to be the primary determinant of this property. This work highlights the importance of assessing encapsulation stability in terms of dynamics of guest molecules, as it provides the critical distinction between hydrophobic molecules bound inside amphiphilic assemblies and the molecules that are bound to the hydrophobic pockets of serum albumin.

Micellar Stability in Biological Media Dictates Internalization in Living Cells

The dynamic nature of polymeric assemblies makes their stability in biological media a crucial parameter for their potential use as drug delivery systems in vivo. Therefore, it is essential to study and understand the behavior of self-assembled nanocarriers under conditions that will be encountered in vivo such as extreme dilutions and interactions with blood proteins and cells. Herein, using a combination of fluorescence spectroscopy and microscopy, we studied four amphiphilic PEG-dendron hybrids and their self-assembled micelles in order to determine their structure-stability relations. The high molecular precision of the dendritic block enabled us to systematically tune the hydrophobicity and stability of the assembled micelles. Using micelles that change their fluorescent properties upon disassembly, we observed that serum proteins bind to and interact with the polymeric amphiphiles in both their assembled and monomeric states. These interactions strongly affected the stability and enzymatic degradation of the micelles. Finally, using spectrally resolved confocal imaging, we determined the relations between the stability of the polymeric assemblies in biological media and their cell entry. Our results highlight the important interplay between molecular structure, micellar stability, and cell internalization pathways, pinpointing the high sensitivity of stability-activity relations to minor structural changes and the crucial role that these relations play in designing effective polymeric nanostructures for biomedical applications.

Oppositely Charged Polyurethane Microspheres with Tunable Zeta Potentials as an Injectable Dual-Loaded System for Bone Repair

To effectively repair irregular shaped bone defects by a minimally invasive procedure, the exploration of an injectable gel to fill the defect is desirable. Herein, positively and negatively charged polyurethane microspheres (PU-A and PU-B) with adjustable zeta potentials as well as the hydroxyapatite-loaded PU microsphere (PU-A/HA) and the dexamethasone-loaded PU microsphere (PU-B/Dex) were successfully prepared, and the oppositely charged microspheres could self-assemble into injectable gels with 3D structures by a mutually electrostatic attraction. The self-assembly PU-A/HA+PU-B/Dex gel exhibited a much higher elastic modulus (about 0.20 MPa) and excellent shear-thinning and self-recovery behaviors, which would allow the gel to be injected through a fine syringe to fill the irregular defect. The in vitro and in vivo experiments demonstrated that the coexistence of HA and Dex in PU-A/HA+PU-B/Dex gel had a synergistic effect on cell differentiation and accelerating new bone formation, displaying a good prospect as an injectable gel for bone repair in minimally invasive surgery.

Balancing the intermolecular forces in peptide amphiphiles for controlling self-assembly transitions

While the influence of alkyl chain length and headgroup size on self-assembly behaviour has been well-established for simple surfactants, the rational control over the pH- and concentration-dependent self-assembly behaviour in stimuli responsive peptides remains an elusive goal. Here, we show that different amphiphilic peptides can have similar self-assembly phase diagrams, providing the relative strengths of the attractive and repulsive forces are balanced. Using palmitoyl-YYAAEEEEK(DO3A:Gd)-NH2 and palmitoyl-YAAEEEEK(DO3A:Gd)-NH2 as controls, we show that reducing hydrophobic attractive forces through fewer methylene groups in the alkyl chain will lead to a similar self-assembly phase diagram as increasing the electrostatic repulsive forces via the addition of a glutamic acid residue. These changes allow creation of self-assembled MRI vehicles with slightly different micelle and nanofiber diameters but with minimal changes in the spin-lattice T1 relaxivity. These findings reveal a powerful strategy to design self-assembled vehicles with different sizes but with similar self-assembly profiles.

One-Component Supramolecular Filament Hydrogels as Theranostic Label-Free Magnetic Resonance Imaging Agents

Gadolinium (Gd)-based compounds and materials are the most commonly used magnetic resonance imaging (MRI) contrast agents in the clinic; however, safety concerns associated with their toxicities in the free ionic form have promoted the development of new generations of metal-free contrast agents. Here we report a supramolecular strategy to convert an FDA-approved anticancer drug, Pemetrexed (Pem), to a molecular hydrogelator with inherent chemical exchange saturation transfer (CEST) MRI signals. The rationally designed drug-peptide conjugate can spontaneously associate into filamentous assemblies under physiological conditions and consequently form theranostic supramolecular hydrogels for injectable delivery. We demonstrated that the local delivery and distribution of Pem-peptide nanofiber hydrogels can be directly assessed using CEST MRI in a mouse glioma model. Our work lays out the foundation for the development of drug-constructed theranostic supramolecular materials with an inherent CEST MRI signal that enables noninvasive monitoring of their in vivo distribution and drug release.

Probing the self-assembly and stability of oligohistidine based rod-like micelles by aggregation induced luminescence

The synthesis and self-assembly of a new C₂-symmetric oligohistidine amphiphile equipped with an aggregation induced emission luminophore is reported.