Deciphering the Lipid-Random Copolymer Interactions and Encoding Their Properties to Design a Hybrid System.

Lipid/copolymer colloidal systems are deemed hybrid materials with unique properties and functionalities. Their hybrid nature leads to complex interfacial phenomena, which have not been fully encoded yet, navigating their properties. Moving toward in-depth knowledge of such systems, a comprehensive investigation of them is imperative. In the present study, hybrid lipid/copolymer structures were fabricated and examined by a gamut of techniques, including dynamic light scattering, fluorescence spectroscopy, cryogenic transmission electron microscopy, microcalorimetry, and high-resolution ultrasound spectroscopy. The biomaterials that were mixed for this purpose at different ratios were 1,2-dioctadecanoyl-sn-glycero-3-phosphocholine and four different linear, statistical (random) amphiphilic copolymers, consisting of oligo(ethylene glycol) methyl ether methacrylate as the hydrophilic comonomer and lauryl methacrylate as the hydrophobic one. The colloidal dispersions were studied for lipid/copolymer interactions regarding their physicochemical, morphological, and biophysical behavior. Their membrane properties and interactions with serum proteins were also studied. The aforementioned techniques confirmed the hybrid nature of the systems and the location of the copolymer in the structure. More importantly, the random architecture of the copolymers, the hydrophobic-to-hydrophilic balance of the nanoplatforms, and the lipid-to-polymer ratio are highlighted as the main design-influencing factors. Elucidating the lipid/copolymer interactions would contribute to the translation of hybrid nanoparticle performance and, thus, their rational design for multiple applications, including drug delivery.

Formation of complexes in aqueous solutions of amphiphilic triblock polyelectrolytes of different topologies and an oppositely charged protein.

The complexation of lysozyme with aggregates from two triblock amphiphilic polyelectrolytes of the same blocks but different topologies and block molar masses, namely PS-b-SCPI-b-PEO and SCPI-b-PS-b-PEO, is investigated by scattering and spectroscopy methods. Light scattering reveals that the interaction with lysozyme causes shrinkage of the self-assembled nanoparticles in the case of the hydrophobic-polyelectrolyte-hydrophilic sequence. In the polyelectrolyte-hydrophobic-hydrophilic sequence, the opposite trend is observed. Small angle neutron scattering confirms the existence of micellar and fractal aggregates and the complexation with lysozyme. The pH-dependence of the interactions and the stability of the hybrid protein/polymer nanoparticles upon salt addition are tested. The native conformation of the protein is found to be preserved during complexation. This study reveals that both micellar and fractal aggregates made of amphiphilic triblock polyelectrolytes are capable of loading with oppositely charged proteins in a controllable manner, tuned primarily by the structure of the triblock terpolymer.

Synthesis of Thermoresponsive Chitosan-graft-Poly(N-isopropylacrylamide) Hybrid Copolymer and Its Complexation with DNA.

A hybrid synthetic-natural, thermoresponsive graft copolymer composed of poly(N-isopropyl acrylamide) (PNIPAM) side chains, prepared via RAFT polymerization, and a chitosan (Chit) polysaccharide backbone, was synthesized via radical addition-fragmentation reactions using the "grafting to" technique, in aqueous solution. ATR-FTIR, TGA, polyelectrolyte titrations and 1H NMR spectroscopy were employed in order to validate the Chit-g-PNIPAM copolymer chemical structure. Additionally, 1H NMR spectra and back conductometric titration were utilized to quantify the content of grafted PNIPAM side chains. The resulting graft copolymer contains dual functionality, namely both pH responsive free amino groups, with electrostatic complexation/coordination properties, and thermoresponsive PNIPAM side chains. Particle size measurements via dynamic light scattering (DLS) were used to study the thermoresponsive behavior of the Chit-g-PNIPAM copolymer. Thermal properties examined by TGA showed that, by the grafting modification with PNIPAM, the Chit structure became more thermally stable. The lower critical solution temperature (LCST) of the copolymer solution was determined by DLS measurements at 25-45 °C. Furthermore, dynamic and electrophoretic light scattering measurements demonstrated that the Chit-g-PNIPAM thermoresponsive copolymer is suitable of binding DNA molecules and forms nanosized polyplexes at different amino to phosphate groups ratios, with potential application as gene delivery systems.

Chitosan-Based Nanoparticles for Nucleic Acid Delivery: Technological Aspects, Applications, and Future Perspectives.

Chitosan is a naturally occurring polymer derived from the deacetylation of chitin, which is an abundant carbohydrate found mainly in the shells of various marine and terrestrial (micro)organisms. Chitosan has been extensively used to construct nanoparticles (NPs), which are biocompatible, biodegradable, non-toxic, easy to prepare, and can function as effective drug delivery systems. Moreover, chitosan NPs have been employed in gene and vaccine delivery, as well as advanced cancer therapy, and they can also serve as new therapeutic tools against viral infections. In this review, we summarize the most recent developments in the field of chitosan-based NPs intended as nucleic acid delivery vehicles and gene therapy vectors. Special attention is given to the technological aspects of chitosan complexes for nucleic acid delivery.

Development of Double Hydrophilic Block Copolymer/Porphyrin Polyion Complex Micelles towards Photofunctional Nanoparticles.

The electrostatic complexation between double hydrophilic block copolymers (DHBCs) and a model porphyrin was explored as a means for the development of polyion complex micelles (PICs) that can be utilized as photosensitive porphyrin-loaded nanoparticles. Specifically, we employed a poly(2-(dimethylamino) ethyl methacrylate)-b-poly[(oligo ethylene glycol) methyl ether methacrylate] (PDMAEMA-b-POEGMA) diblock copolymer, along with its quaternized polyelectrolyte copolymer counterpart (QPDMAEMA-b-POEGMA) and 5,10,15,20-tetraphenyl-21H,23H-porphine-p,p',p″,p'''-tetrasulfonic acid tetrasodium hydrate (TPPS) porphyrin. The (Q)PDMAEMA blocks enable electrostatic binding with TPPS, thus forming the micellar core, while the POEGMA blocks act as the corona of the micelles and impart solubility, biocompatibility, and stealth properties to the formed nanoparticles. Different mixing charge ratios were examined aiming to produce stable nanocarriers. The mass, size, size distribution and effective charge of the resulting nanoparticles, as well as their response to changes in their environment (i.e., pH and temperature) were investigated by dynamic and electrophoretic light scattering (DLS and ELS). Moreover, the photophysical properties of the complexed porphyrin along with further structural insight were obtained through UV-vis (200-800 nm) and fluorescence spectroscopy measurements.

Complexation of lysozyme with poly(sodium(sulfamate-carboxylate)isoprene).

The complexation between hen egg white lysozyme (HEWL) and a novel pH-sensitive and intrinsically hydrophobic polyelectrolyte poly(sodium(sulfamate-carboxylate)isoprene) (SCPI), was investigated by means of dynamic, static, and electrophoretic light scattering and isothermal titration calorimetry measurements. The complexation process was studied at both pH 7 and 3 (high and low charge density of the SCPI, respectively) and under low ionic strength conditions for two polyelectrolyte samples of different molecular weights. The solution behavior, structure, and effective charge of the formed complexes proved to be dependent on the pH, the [-]/[+] charge ratio, and the molecular weight of the polyelectrolyte. Increasing the ionic strength of the solution led to vast aggregation and eventually precipitation of the complexes. The interaction between HEWL and SCPI was found to be mainly electrostatic, associated with an exothermic enthalpy change. The structural investigation of the complexed protein by fluorescence, infrared, circular dichroism spectroscopic, and differential scanning calorimetric measurements revealed no signs of denaturation upon complexation.

Complex Formation Between Lysozyme and Stabilized Micelles with a Mixed Poly(ethylene oxide)/Poly(acrylic acid) Shell.

The electrostatic complexation between lysozyme and stabilized polymeric micelles (SPMs) with a poly(acrylic acid) (PAA) or a mixed poly(ethylene oxide)/poly(acrylic acid) (PEO/PAA) shell (SPMs with a mixed shell, SPMMS) and a temperature-responsive poly(propylene oxide) (PPO) core was investigated by means of dynamic, static, and electrophoretic light scattering. The SPMs and different types of SPMMS used resulted from the self-assembly of PAA-PPO-PAA triblock copolymer chains, or PAA-PPO-PAA and PEO-PPO-PEO triblock copolymer chain mixtures (with varying chain lengths and molar ratios) in aqueous solutions at pH 10 and the subsequent cross-linking of their PPO cores via loading and photo-cross-linking of pentaerythritol tetraacrylate (PETA). The solution behavior, structure and properties of the formed complexes at pH 7 and 0.01 M ionic strength, were studied as a function of the protein concentration in the solution (the concentration of the stabilized micelles was kept constant) or equivalently the ratio of the two components. The complexation process and properties of the complexes proved to be dependent on the protein concentration, while of particular interest was the effect of the structure of the shell of the SPMs on the stability/solubility of the complexes. Finally, the fluorescence and mid infrared spectroscopic investigation of the structure of the complexed protein showed that, although a small stretching of the protein molecules occurred in some cases, no protein denaturation takes place upon complexation.

Complexation of cationic-neutral block polyelectrolyte with insulin and in vitro release studies.

Insulin (INS) was incorporated into complexes with the block polyelectrolyte quaternized poly[3,5-bis(dimethylaminomethylene)hydroxystyrene]-b-poly(ethylene oxide) (QNPHOSEO), which is a cationic-neutral block polyelectrolyte. Light scattering techniques are used in order to examine the size, the size distribution and the ζ-potential of the nanocarriers in aqueous and biological media, which are found to depend on the ratio of the components and the physicochemical parameters during and after complex preparation. Circular dichroism and infrared spectroscopy, employed to investigate the structure of the complexed INS, show no alteration of protein structure after complexation. In vitro release profiles of the entrapped protein are found to depend on the ratio of the components and the solution conditions used during preparation of the complexes.

Solution behavior of poly(sodium(sulfamate-carboxylate)isoprene), a pH sensitive and intrinsically hydrophobic polyelectrolyte.

The solution properties of a novel pH sensitive and intrinsically hydrophobic polyelectrolyte poly(sodium(sulfamate-carboxylate)isoprene) (SCPI) were investigated by means of dynamic, static, and electrophoretic light-scattering and fluorescence spectroscopy techniques. Because of the pH dependent charge density of the polyelectrolyte chain, the dynamics and structure of the solution were studied at both pH 7 (high charge density) and pH 3 (low charge density) and at low ionic strength conditions for two samples of different molecular weights. In all cases, a fast and a slow diffusive mode were observed. The fast mode is attributed to the diffusion of isolated polyelectrolyte chains, while the slow mode denotes the presence of multichain domains in solution, formed by electrostatic and/or hydrophobic interactions. The size and density of the multichain domains were reduced with decreasing charge density and molecular weight. Effective charge of the particles does not depend appreciably on solution pH, while fluorescence spectroscopy revealed the presence of hydrophobic domains in the studied systems. It was found that increasing temperature resulted in the compaction of both isolated chains and multichain domains due to the hydrophobic effect. Furthermore the increase of the ionic strength of the solution led to a partial dissociation of the multichain domains at short times and at pH 7, while it led to increased aggregation and precipitation at pH 3 and long times. The performed experiments allowed for a separation of the electrostatic and hydrophobic contributions to the self-assembly of the particular polyelectrolyte systems.

Self-assembled nanoparticles from a block polyelectrolyte in aqueous media: structural characterization by SANS.

We present a small angle neutron scattering (SANS) study of polystyrene-b-sodium (sulfamate/carboxylate) isoprene (PS-PSCI) nanoparticles in aqueous media. The SANS experiments are complemented by static and dynamic light scattering measurements. A detailed analysis of the scattering form factor obtained by SANS for the self-assembled block polyelectrolyte spherical nanoparticles implies a two-region power-law model for the radial volume fraction profiles. The theoretically predicted scaling of the osmotic brush regime phi(r) approximately r(-2) for the inner region and the osmotic annealing brush regime phi(r) approximately r(-8/3) for the outer region are in agreement with our experimental findings. A concentrated shell of PSCI polyelectrolyte chains collapsed on the polystyrene core is needed in the form factor analysis so that the aggregation number of the nanoparticles is self-consistent. The self-assembled nanoparticles are found to be kinetically frozen i.e. their aggregation number is not sensitive to the solution conditions and is defined by the preparation protocol. The size of the spherical nanoparticles tends to decrease upon the addition of salt and the drop of pH.