Yunge Fan

Biodegradable and temperature-responsive polyurethanes for adriamycin delivery

To develop biodegradable polymers with temperature-sensitivity, a series of polyurethanes consisting of poly (ethylene glycol) (PEG) and L-lysine ester diisocyanate (LDI) were synthesized, and the structure and molecule weight of the polymers were examined by (1)H NMR, FT-IR, gel permeation chromatography (GPC). The solution properties of the copolymers were studied by turbidity measurement and size measurement. Polyurethanes could form nanoparticles by sonication in water. No temperature-sensitivity was observed with the polyurethane nanoparticles composed of PEG1000 and PEG1500. On the contrary, LDI-PEG600 exhibited a reversible temperature-responsive behavior in aqueous solution. The transition temperature (T(c)) of LDI-PEG600 with methyl ester of LDI was higher than that of LDI-PEG600 with butyl ester side chain. The polymers were then used to encapsulate adriamycin (ADR) by the dialyzing method from dimethylformamide solution against water. ADR could be successfully encapsulated into the polyurethane nanoparticles. The ratio of ADR release from polymeric nanoparticles increased sharply above the T(c), while the release was suppressed below the T(c).

A novel delivery system of doxorubicin with high load and pH-responsive release from the nanoparticles of poly (α,β-aspartic acid) derivative.

A poly (amino acid)-based amphiphilic copolymer was utilized to fabricate a better micellar drug delivery system (DDS) with improved compatibility and sustained release of doxorubicin (DOX). First, poly (ethylene glycol) monomethyl ether (mPEG) and DOX were conjugated onto polyasparihyazide (PAHy), prepared by hydrazinolysis of the poly (succinimide) (PSI), to afford an amphiphilic polymer [PEG-hyd-P (AHy-hyd-DOX)] with acid-liable hydrazone bonds. The DOX, chemically conjugated to the PAHy, was designed to supply hydrophobic segments. PEGs were also grafted to the polymer via hydrazone bonds to supply hydrophiphilic segments and prolong its lifetime in blood circulation. Free DOX molecules could be entrapped into the nanoparticles fabricated by such an amphiphilic polymer (PEG-hyd-P (AHy-hyd-DOX)), via hydrophobic interaction and π-π stacking between the conjugated and free DOX molecules to obtain a pH responsive drug delivery system with high DOX loaded. The drug loading capacity, drug release behavior, and morphology of the micelles were investigated. The biological activity of micelles was evaluated in vitro. The drug loading capacity was intensively augmented by adjusting the feed ratio, and the maximum loading capacity was as high as 38%. Besides, the DOX-loaded system exhibited pH-dependent drug release profiles in vitro. The cumulative release of DOX was much faster at pH 5.0 than that at pH 7.4. The DOX-loaded system kept highly antitumor activity for a long time, compared with free DOX. This easy-prepared DDS, with features of biocompatibility, biodegradability, high drug loading capacity and pH-responsiveness, was a promising controlled release delivery system for DOX.

Preparation and tunable temperature sensitivity of biodegradable polyurethane nanoassemblies from diisocyanate and poly(ethylene glycol)

The development of temperature-responsive and biodegradable polymeric nanoparticles with tunable temperature sensitivity is of great interest. In this study, alternating polyurethanes were synthesized from diisocyanate (L-lysine ethyl ester diisocyanate (LDI) or hexamethylene diisocyanate (HDI)) and poly(ethylene glycol) (PEG) of different molecular weights. The resulting polyurethanes were then used to prepare nanoparticles either by direct dispersion in water or by nanoprecipitation. The temperature-responsive property of the polyurethane nanoparticles was evaluated by UV-visible transmittance experiments and dynamic light scattering. During the heating–cooling cycling, the LDI-PEG series showed almost no change except LDI-PEG600, but the HDI-PEG series exhibited reversible dispersion–aggregation changes. The nanoparticles were spherical at temperatures below or above the cloud point, as observed by transmission electron microscopy. The cloud point temperature of the alternative polymers was found to depend on both the hydrophilic–hydrophobic balance of the alternative chain and polymer concentration. The degradation test in vitro revealed a fall of less than 20% of polymer molecular weight within 12 days. The transition temperature was close to human body temperature, which could have great potential in biomedical fields.

Polyelectrolyte complex nanoparticles of amino poly(glycerol methacrylate)s and insulin.

Amino poly(glycerol methacrylate)s (PGOHMAs) were synthesized from linear or star-shaped poly(glycidyl methacrylate)s (PGMA)s via ring opening reactions with 1,2-ethanediamine, 1,4-butanediamine and diethylenetriamine, respectively. The resulting cationic polymers were employed to form polyelectrolyte complexes (PECs) with insulin. Parameters influencing complex formation were investigated by dynamic light scattering (DLS). PECs in the size range of 100-200 nm were obtained under optimal conditions, i.e., the pH value of PECs was 5.58-6.27, the concentration of NaCl was 0.02 mol/L, and insulin-polymer weight ratio was 0.8. The insulin association efficiency (AE) of current system increased with zeta potentials of PECs. Circular dichroism (CD) analysis corroborated that the structure of insulin in the PEC nanoparticles was preserved after lyophilization. Fourier transform infrared (FT-IR) and X-ray diffraction (XRD) experiments demonstrated that weak physical interactions between insulin and amino PGOHMAs play an important role in the formation of PECs. The release of insulin depends on both structure and architecture of amino PGOHMAs. These PECs would be potentially useful for mucosal administration.

Amino poly(glycerol methacrylate)s for oligonucleic acid delivery with enhanced transfection efficiency and low cytotoxicity

To improve the transfection activity and reduce cell cytotoxicity of polycations with antisense oligonucleotide (AON), poly(glycidyl methacrylate)s (PGMAs) were modified with different amines, i.e., methylethylamine (MEA), 2-amino-1-butanol (2-ABO) and 4-amino-1-butanol (4-ABO). The structures of resulting polymers were well characterized and their thermal properties were studied by differential scanning calorimetry (DSC). The amino PGMA could self-assemble with AON in a Tris buffer solution, resulting in narrowly distributed polymer/AON complexes with a size of 0.1–0.3 μm at an amine-group-of-polymer/phosphate-group-of-nucleotide ratio (N/P ratio) of 0.5–3. Spherical nanoparticles of the complexes were visualized using atomic force microscopy (AFM), and the gel electrophoresis and zeta potential assay evidenced the formation of complexes at relatively low N/P ratios. Stability of the complexes towards dissociation was tested using ethidium bromide displacement assay. Protection of the incorporated AON against DNase I degradation was also evaluated. An increased charge ratio and a synergistic effect of hydrogen bonding in this system contributed to the increased stability of the complex, which prevents the incorporated AON from nuclease degradation. In vitro cytotoxicity experiments on COS-7 cells showed that all amino PGMAs displayed lower toxicity compared to the control PEI25k, except for the polymers with a relatively high molecular weight (30 kDa). In addition, the MEA modified linear and star-shaped PGMA (Mn in the range of 15–20 kDa) as well as 4-ABO modified linear PGMA complexes exhibited higher transfection efficiencies in vitro, compared to PEI25k. These results demonstrated that amino PGMAs with suitable amine groups and molecular weight can be used as safe and efficient AON delivery polymers.

Carboxylated poly(glycerol methacrylate)s for doxorubicin delivery

Poly(glycerol methacrylate)s (PGOHMAs) were successfully synthesized via the hydrolysis of the epoxy groups on linear and/or star-shaped poly(glycidyl methacrylate)s (PGMAs). Further modification of the hydroxyl groups on PGOHMAs with succinic anhydride (SA) or 1,2-cyclohexanedicarboxylic anhydride (CDA) resulted in a new type of polyacid polymer, namely, PGOHMACOOH for short, which was then employed to prepare pH-sensitive assemblies using dialysis method. The carboxylated polymers were quite effective in the encapsulation of doxorubicin hydrochloride (DOX) by electrostatic interaction. Compared with poly(acrylic acid) (PAA), the star-shaped PGOHMA modified with CDA exhibited higher encapsulation efficiency and loading capacity, as well as better pH-responsive release profile. Scanning electron microscope images showed that the polymeric nanoparticles before and after encapsulation of DOX were spherical in shape. The encapsulation efficiency, loading capacity and release properties of these polymers were found to rely on their backbone architectures and the type of carboxylated functionalities. By fine-tuning these factors to achieve optimal properties, such type of polymeric materials holds promise as an attractive and effective drug delivery vehicle.

pH-Responsive Self-Assembly and conformational transition of partially propyl-esterified poly(α,β-l-aspartic acid) as amphiphilic biodegradable polyanion

Poly(alpha,beta-L-aspartate) (PAsp) was partially esterified to afford an amphiphilic biodegradable polyanion, poly(sodium aspartate-co-propyl aspartate) (PAsp-Na/PAsp-P). The synthesized polyanion could be assembled into the nano-scaled aggregates in aqueous medium. The aggregate morphologies were studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) as a function of pH. It was demonstrated that micellization of this random copolymer occurred with stimulus of pH changes to form various morphological micelles. The copolymer existed as precipitate at low pH (pH<2). When pH increased to 4, the polymers were associated into spherical micelles with the core of poly(propyl aspartate) (PAsp-P) hydrophobic units and shell of some negatively charged poly(sodium aspartate) (PAsp-Na) units. At higher pH (pH>5), toroidal nanostructures of the micelles were formed because rigid polyamide chains directly assemble into the large hollow spheres. The CD study showed that the conformation underwent a transition between alpha-helix and random coil at pH 3-7. The cooperative transitions were regulated by the degree of ionization of carboxylic side chains. When they were protonated (neutralized), the molecular backbone was in favor of the regular helical structure; when deprotonated (ionized), the electrostatic repulsions among side chains destabilized the intramolecular hydrogen bonds, thus randomizing the regular conformation.

Synthesis of a novel zwitterionic biodegradable poly (α,β-l-aspartic acid) derivative with some l-histidine side-residues and its resistance to non-specific protein adsorption

A novel zwitterionic polypeptide derivative, denoted as His-PAsp/PAsp, was successfully synthesized by amidation of Poly (α,β-L-aspartic acid) with L-histidine methyl ester. Turbidity, zeta potential and ¹H NMR measurements were used to study the aggregation behaviors of His-PAsp/PAsp under different pH values. The modified polypeptide derivative composed of electro-negatively carboxylic and electro-positively imidazole residues randomly so as to bear opposite charges at pH values above or below the isoelectric point. When the zwitterionic polypeptide was coated on silicon wafer as a model substrate material, the absorption resistance of fibrinogen, a blood protein resulting in the blood coagulation cascade, on the coated surface was measured. It was found that the adsorption amount of fibrinogen on the polypeptide-coated surface depended on the dose of the polypeptide on silicon wafer. Obvious resistance of the fibrinogen adsorption on the polypeptide-coated surface was observed. Since its good biodegradability and superior anti-protein-fouling property, this pH-responsive zwitterionic polypeptide is a promising candidate for surface modification in many biomedical applications, including medical implants, drug delivery carriers, and biosensors.

Layer-by-layer supramolecular assemblies based on linear and star-shaped poly(glycerol methacrylate)s for doxorubicin delivery†

Hollow microcapsules, composed of pH responsive polyelectrolytes via a layer-by-layer (LBL) adsorption technique, were prepared. Linear or star-shaped poly(glycerol metha crylate)s (PGOHMAs) modified with 1,4-butanediamine and 1,2-ethanediamine (EDA) were synthesized and used as polycations. Poly(acrylic acid) was employed as polyanion and SiO2 (about 170 nm) as template. After LBL absorption, SiO2 cores were removed by HF treatment. The particle size and zeta potential were measured by dynamic light scattering, showing that the diameter of star-shaped amino-PGOHMA was larger than linear counterpart. The LBL assembly and core-etching process were evidenced by scanning electron microscope, transmission electron microscope, and energy dispersive spectrometer. The cytotoxicity experiments on human umbilical vein endothelial cells were carried out to evaluate the toxicity of LBL assembly. The star-shaped and EDA-modified PGOHMA exhibited better cell viability. The microcapsules were then used to load an anticancer drug, doxorubicin hydrochloride. High loading capacity (about 42%) and entrapment efficiency (84%) were obtained for star-shaped polymer-based microcapsules. The cumulative release rate was evaluated in vitro, showing faster release at an acidic condition compared to neutral pH. Confocal laser scanning microscopy evidenced the successful cellular uptake of DOX-loaded microparticles.

Synthesis of amphiphilic poly(tetraethylene glycol succinate) and the thermosensitivity of its aggregation in water.

Amphiphilic biodegradable polyester, poly(tetraethylene glycol succinate) (PTEGSuc), was synthesized via melt polycondensation of tetraethylene glycol and succinic acid on catalysis of p-toluenesulfonic acid. It was observed that PTEGSuc could self-assemble into micelles in water. In addition, thermosensitivity of PTEGSuc aggregation in water was first found in the experiment, and the critical aggregation temperatures could be controlled by solution concentration. Transmission electron microscopy was used to investigate the micellar morphologies of PTEGSuc in different solvents. It was found that particle shape is almost round although the micellar morphology is different depending on the solvent used. Based on the perfect properties, especially in micelle formation and thermosensitivity, PTEGSuc is promising in biomedical field as carrier of drug delivery system, scaffold of tissue engineering, and other medical devices.