Multimodal characterization of the collagen hydrogel structure and properties in response to physiologically relevant pH fluctuations.

pH fluctuations within the extracellular matrix (ECM) and its principal constituent collagen, particularly in solid tumors and chronic wounds, may influence its structure and function. Whereas previous research examined the impact of pH on collagen fibrillogenesis, this study focuses on determining how pH fluctuations affect collagen hydrogels that mimic the physiological ECM. Utilizing a type I collagen hydrogel, we examined the influence of pH fluctuations on its structure, properties, and function while keeping the collagen hydrated. We show that collagen's secondary structure remains unaltered during pathologically relevant microenvironmental pH changes. By employing cryo scanning electron microscopy and artificial intelligence-assisted image analysis, we show that at physiological pH, collagen hydrogel presents densely packed, aligned, and elongated fibrils, which upon a decrease to pH 6.5, are transformed into shorter, sparser, and disoriented fibrils. The collagen possesses a higher storage modulus yet a lower permeability at pH 7 and 7.8 compared with pH 6.5 and 7.4. Exposing acidified collagen to a basic buffer reinstates its native structure and viscoelastic properties. Our study offers an innovative approach to analyze and characterize perturbations in hydrated collagen-based systems with potential implications for better understanding and combating disease progression. STATEMENT OF SIGNIFICANCE: As the main component of the extracellular matrix, collagen undergoes conformational changes associated with pH changes during disease. We analyze the impact of pH on pre-formed collagen fibers mimicking healthy tissues subjected to disease, and do not focus on the more studied fibrillogenesis process. Using cryogenic SEM, which allowed imaging close to the native state, we show that even minor fluctuations in the pH affect the collagen thickness, length, fiber alignment, and rheological properties. Following exposure to acidic pH, the collagen had short fibers, lacked orientation, and had low mechanical strength. This acidic collagen restored its original properties after returning to a neutral pH. These findings can help determine how pH changes can be modulated to restore healthy collagen properties.

Glucose-Triggered Gelation of Supramolecular Peptide Nanocoils with Glucose-Binding Motifs.

Peptide self-assembly is a powerful tool to prepare functional materials at the nanoscale. Often, the resulting materials have high aspect-ratio, with intermolecular ß-sheet formation underlying 1D fibrillar structures. Inspired by dynamic structures in nature, peptide self-assembly is increasingly moving toward stimuli-responsive designs wherein assembled structures are formed, altered, or dissipated in response to a specific cue. Here, a peptide bearing a prosthetic glucose-binding phenylboronic acid (PBA) is demonstrated to self-assemble into an uncommon nanocoil morphology. These nanocoils arise from antiparallel ß-sheets, with molecules aligned parallel to the long axis of the coil. The binding of glucose to the PBA motif stabilizes and elongates the nanocoil, driving entanglement and gelation at physiological glucose levels. The glucose-dependent gelation of these materials is then explored for the encapsulation and release of a therapeutic agent, glucagon, that corrects low blood glucose levels. Accordingly, the release of glucagon from the nanocoil hydrogels is inversely related to glucose level. When evaluated in a mouse model of severe acute hypoglycemia, glucagon delivered from glucose-stabilized nanocoil hydrogels demonstrates increased protection compared to delivery of the agent alone or within a control nanocoil hydrogel that is not stabilized by glucose.

Effect of the ammonium salt anion on the structure of doxorubicin complex and PEGylated liposomal doxorubicin nanodrugs.

BACKGROUND: In Doxil®, PEGylated nanoliposomes are created by hydration of the lipids in ammonium sulfate, and are remotely loaded with doxorubicin by a transmembrane ammonium gradient. The ammonium sulfate is then removed from the external aqueous phase, surrounding the liposomes, and replaced by an isoosmotic sucrose solution in 10 mM histidine buffer at pH 6.5. METHODS: We prepared PEGylated liposomal doxorubicin (PLD) with a series of ammonium monovalent salts that after remote loading became the intraliposome doxorubicin counteranions. We analyzed the liposomes by solution X-ray scattering, differential scanning calorimetry, and electron micropscopy. RESULTS: PLDs prepared with sulfonic acid derivatives as counteranion exhibited chemical and physical stabilities. We determined the effect of these ammonium salt counteranions on the structure, morphology, and thermotropic behavior of the PEGylated nanoliposomes, formed before and after doxorubicin loading, and the bulk properties of the doxorubicin-counteranion complexes. By comparing the structure of the doxorubicin complexes in the bulk and inside the nanoliposomes, we revealed the effect of confinement on the structure and doxorubicin release rate for each of the derivatives of the ammonium sulfonic acid counteranions. CONCLUSIONS: We found that the extent and direction of the doxorubicin confinement effect and its release rate were strongly dependent on the type of counteranion. The counteranions, however, neither affected the structure and thermotropic behavior of the liposome membrane, nor the thickness and density of the liposome PEG layers. In an additional study, it was demonstrated that PLD made with ammonium-methane sulfonate exhibit a much lower Hand and Foot syndrome. GENERAL SIGNIFICANCE: The structure, physical state, and pharmacokinetics of doxorubicin in PEGylated nanoliposomes, prepared by transmembrane remote loading using gradients of ammonium salts, strongly depend on the counteranions.

Tailored self-assembled nanocolloidal Huygens scatterers in the visible.

Existing nanocolloidal optical resonators exhibiting strong magnetic resonances often suffer from multi-step low yield synthesis methods as well as a limited tunability, particularly in terms of spectral superposition of electric and magnetic resonances, which is the cornerstone for achieving Huygens scatterers. To overcome these drawbacks, we have synthesized clusters of gold nanoparticles using an emulsion-based formulation approach. This fabrication technique involved emulsification of an aqueous suspension of gold nanoparticles in an oil phase, followed by controlled ripening of the emulsion. The structural control of the as synthesized clusters, of mean radius 120 nm and produced in large numbers, is demonstrated with microscopy and X-ray scattering techniques. Using a polarization-resolved multi-angle light scattering setup, we conduct a comprehensive angular and spectroscopic determination of their optical resonant scattering in the visible wavelength range. We thus report on the clear experimental evidence of strong optical magnetic resonances and directional forward scattering patterns. The clusters behave as strong Huygens sources. Our findings crucially show that the electric and magnetic resonances as well as the scattering patterns can be tuned by adjusting the inner cluster structure, modifying a simple parameter of the fabrication method. This experimental approach allows for the large scale production of nanoresonators with potential uses for Huygens metasurfaces.

Cardinal Role of Intraliposome Doxorubicin-Sulfate Nanorod Crystal in Doxil Properties and Performance.

The uniqueness of Doxil can be attributed, to a large extent, to its intraliposomal doxorubicin-sulfate nanorod crystal. We re-examine these nanocrystal features and their mechanism of the formation by studying pegylated liposomal doxorubicins (PLDs) of the same lipid composition, size distribution, and extraliposome medium that were prepared at different ammonium sulfate (AS) concentrations. This study includes a comparison of the thermotropic behavior, morphology, and in vitro ammonia-induced doxorubicin release (relevant to Doxil's in vivo performance) of these PLDs. In this study, we confirm that a transmembrane ammonium gradient is critical for doxorubicin remote loading, and we demonstrate that the intraliposomal concentration of sulfate counteranions and ammonium ions determine to a large extent the physical state and stability of the PLDs' remote loaded doxorubicin. "Fully-developed" intraliposome doxorubicin-sulfate nanorod crystals (as defined by cryogenic transmission electron microscopy imaging) develop only when the ammonium sulfate (AS) concentration used for PLD preparation is ≥150 mM. Less than 10% of PLDs prepared with 100 mM AS show fully developed nanorod crystals. Intraliposomal AS concentration ≥200 mM is required to support the stable nanocrystallization in PLDs. The presence of nanocrystals and their melting enthalpy and phase transition co-operativity strongly affect the ammonia-induced doxorubicin release of PLDs. A quick, biphasic release occurs for PLDs that lack the nanorod crystals or have crystals of poor crystallinity, whereas PLDs prepared with ≥200 mM AS show a monophasic, zero-order slow release. This study also demonstrates that after remote loading, residual intraliposomal ammonium concentration and the transmembrane pH gradient related to it also play an important role in doxorubicin-sulfate intraliposomal crystallization and ammonia-induced doxorubicin release.

Practical aspects in size and morphology characterization of drug-loaded nano-liposomes.

Size and morphology distributions are critical to the performance of nano-drug systems, as they determine drug pharmacokinetics and biodistribution. Therefore, comprehensive and reliable analyses of these properties are required by both the US Food and Drug Administration (FDA) and European Medicines Agency (EMA). In this study, we compare two most commonly used approaches for assessing the size distribution and morphology of liposomal nano-drug systems, namely, dynamic light scattering (DLS) and cryogenic-transmission electron microscopy (cryo-TEM); an automated quantitative analysis method was developed for the latter method. We demonstrate the advantages and disadvantages of each of these two approaches for a commercial formulation of the anti-cancer drug doxorubicin - Doxil®, in which the drug is encapsulated, mostly in the form of nano-rod crystals. With increasing drug concentration, these nano-rods change the shape of the liposomes from spherical, before drug loading, to prolate (oval), post drug loading. Cryo-TEM analysis provides a detailed size distribution of both the liposomes (minor and major axes) and the nano-rod drug. Both these values are relevant to the drug performance. In this study, we show that at elevated drug concentration (2.75 mg/ml) the drug grows mainly along the major axis and that this high concentration can result, in some cases, in liposome rupture. We show that the combination of cryo-TEM and DLS constitutes a reliable tool for demonstrating the stability of the formulation in human plasma at body temperature, a characteristic that is crucial for achieving therapeutic efficacy.

Nematic ordering of SWNT in meso-structured thin liquid films of polystyrenesulfonate.

The formation of nematic-like islands of single-walled carbon nanotubes (SWNT) in polystyrenesulfonate (PSS) dispersions confined into nanometrically thin films is reported. The SWNT are observed to assemble into orientationally ordered phases, where the intertube distance, as measured via transmission electron microscopy at cryogenic temperatures, matches the polyelectrolyte's bulk correlation length deduced from X-ray scattering. The micrometers-long islands of orientationally ordered carbon nanotubes are observed in both SWNT and double-walled carbon nanotubes (DWNT) but not in specimens prepared from similar dispersions of multiwalled carbon nanotubes (MWNT). These observations, together with relaxation and rheological experiments, suggest that the orientational ordering may result from coupling between confinement of the polymer-wrapped SWNT and DWNT and the microstructure of the solvated polyelectrolyte.

Effect of solubilizing agents on mupirocin loading into and release from PEGylated nanoliposomes.

Mupirocin was identified by quantitative structure property relationship models as a good candidate for remote liposomal loading. Mupirocin is an antibiotic that is currently restricted to topical administration because of rapid hydrolysis in vivo to its inactive metabolite. Formulating mupirocin in PEGylated nanoliposomes may potentially expand its use to parenteral administration by protecting it from degradation in the circulation and target it (by the enhanced permeability effect) to the infected tissue. Mupirocin is slightly soluble in aqueous medium and its solubility can be increased using solubilizing agents. The effect of the solubilizing agents on mupirocin remote loading was studied when the solubilizing agents were added to the drug loading solution. Propylene glycol was found to increase mupirocin loading, whereas polyethylene glycol 400 showed no effect. Hydroxypropyl-ß-cyclodextrin (HPCD) showed a concentration-dependent effect on mupirocin loading; using the optimal HPCD concentration increased loading, but higher concentrations inhibited it. The inclusion of HPCD in the liposome aqueous phase while forming the liposomes resulted in increased drug loading and substantially inhibited drug release in serum.

Phase behavior and shear alignment in SWNT-surfactant dispersions.

The effect of single-walled carbon nanotubes (SWNT) on the phase behavior of the cationic surfactant cetyltrimethylammonium bromide (CTAB) in aqueous solutions is investigated at room temperature. Small-angle X-ray scattering (SAXS) and cryogenic transmission electron microscopy (cryo-TEM) are used for characterization of bulk dispersions and nanometrically thin films. Additional carbonaceous additives (fullerenes, multi-walled carbon nanotubes, and carbon black) serve as reference systems. It is found that dispersions of carbonaceous additive (excluding fullerenes) at intermediate surfactant concentrations (below the liquid-crystalline region of the native surfactant) induce demixing and macroscopic phase separation in otherwise homogeneous solutions of CTAB. Two coexisting liquid phases of similar CTAB concentrations are observed, with the carbonaceous species residing within the lower phase. At high CTAB concentrations (liquid-crystal region) the SWNTs are found to incorporate into the ordered lyotropic liquid-crystalline phase while preserving the native d-spacing. Investigation of nanometrically thin films at intermediate surfactant concentrations under external shear reveals shear-induced structure (SIS) in the presence of minute amounts of SWNTs. The effect is found to be exclusive to SWNT and does not occur in dispersions of other carbonaceous additives.

Shear-induced ordering of micellar arrays in the presence of single-walled carbon nanotubes.

Single-walled carbon nanotubes were found to induce elongation and alignment of surfactant micelles in thin films under the action of shear, leading to the formation of ordered arrays over micron lengths.

Selective dispersion of single-walled carbon nanotubes in the presence of polymers: the role of molecular and colloidal length scales.

Dimensionality is known to play a key role in the solution behavior of nano- and mesoparticles. In particular, the shape and the range of the attractive van der Waals interparticle potential are determined by the number of microscopic versus mesoscopic dimensions. For single-walled nanotubes (SWNTs), where two of the dimensions are nanoscopic and one is mesoscopic, the intertube attraction is relatively short ranged, albeit very steep. The very large attraction (compared to the thermal energy, K(b)T) among long SWNTs leads to aggregation at different levels and constitutes a major barrier for manipulation and utilization of SWNTs. This study demonstrates that it is possible to shape the intertube potential by decorating SWNTs with end-tethered polymers. In good solvent conditions for the polymers, entropic repulsion among the tethered chains generates a free energy barrier that prevents SWNTs from approaching the attractive part of the intertube potential. Consequentially, stable dispersions of individual, well separated SWNTs can be prepared. Investigation of different chain lengths and tethering densities of the polymers as well as the interparticle potentials for nanometric versus mesoscopic particles suggests that polymer-induced steric stabilization provides a generic method for separation of SWNTs from mixtures of colloidal species, as demonstrated experimentally.

Generic approach for dispersing single-walled carbon nanotubes: the strength of a weak interaction.

A generic noncovalent approach for dispersing high concentrations of individual single-walled carbon nanotubes (SWNT) in organic as well as aqueous solutions of synthetic block copolymers is presented. It is suggested that a weak, long-ranged entropic repulsion among polymer-decorated tubes acts as a barrier that prevents the tubes from approaching the attractive part of the intertube potential. The method opens a new route for utilization of block copolymers as compatibilizers for SWNT, improving the incorporation of de-agglomerated SWNT into target polymeric matrixes.