Daojun Liu

A poly(L-lysine)-based hydrophilic star block co-polymer as a protein nanocarrier with facile encapsulation and pH-responsive release.

A hydrophilic star block co-polymer was synthesized, characterized, and evaluated as a protein nanocarrier. The star block co-polymer was composed of a hyperbranched polyethylenimine (PEI) core, a poly(L-lysine) (PLL) inner shell, and a poly(ethylene glycol) (PEG) outer shell. The model protein insulin can be rapidly and efficiently encapsulated by the synthesized polymer in aqueous phosphate buffer at physiological pH. Complexation between PEI-PLL-b-PEG and insulin was investigated using native polyacrylamide gel electrophoresis. The uptake of enhanced green fluorescent protein into Ad293 cells mediated by PEI-PLL-b-PEG was also investigated. The encapsulated insulin demonstrated sustained release at physiological pH and showed accelerated release when the pH was decreased. The insulin released from the star block co-polymer retained its chemical integrity and immunogenicity.

Water Soluble Star-block Copolypeptides: Towards Biodegradable Nanocarriers for Versatile and Simultaneous Encapsulation

The synthesis of water soluble star-block copolypeptides and their encapsulation properties are described. The star-block copolypeptides, obtained by ring-opening polymerization of amino acid N-carboxyanhydrides, consist of a PEI core, a hydrophobic polyphenylalanine or polyleucine inner shell, and a negatively charged polyglutamate outer shell. The encapsulation study showed that these water soluble, amphiphilic star-block copolypeptides could simultaneously encapsulate versatile compounds ranging from hydrophobic to anionic and cationic hydrophilic guest molecules.

Poly(L-lysine)-based star-block copolymers as pH-responsive nanocarriers for anionic drugs.

Star-block copolymers PEI-g-(PLL-b-PEG) with a branched polyethylenimine (PEI) core, a poly(l-lysine) (PLL) inner shell, and a poly(ethylene glycol) (PEG) outer shell have been synthesised and evaluated as potential nanocarriers for anionic drugs. The star-block copolymers were synthesised by a ring-opening polymerisation of ɛ-benzyloxycarbonyl-L-lysine N-carboxyanhydride initiated by the peripheral primary amino groups of PEI, surface modification with activated PEG 4-nitrophenyl carbonate, and subsequent deprotection of benzyl groups on the side chains of the PLL inner shell. The synthesised star-block copolymers were characterised by (1)H NMR, gel permeation chromatography (GPC), and dynamic light scattering (DLS). The encapsulation properties of these star-block copolymers were characterised by spectrophotometric titration and dialysis. These techniques demonstrated that anionic model dyes, such as methyl orange and rose Bengal, and the model drug diclofenac sodium can be encapsulated efficiently by PEI-g-(PLL-b-PEG) at physiological pH. The entrapped model compounds demonstrated sustained release at physiological pH and accelerated release when the pH was either increased to 10.0-11.0 or decreased to 2.0-3.0. The efficient encapsulation as well as the pH-responsive releasing properties of these star-block copolymers could be potentially used in the controlled release of anionic drugs.

Controlled biosilification using self-assembled short peptides A6K and V6K

We report the molecular self-assembly of two amphiphilic peptides (A6K and V6K) and the application of their self-assemblies as organic templates to direct biosilica formation. Under ambient conditions, A6K self-assembled into nanotubes 2.7 nm tall and approximately 1 μm to 2 μm long. In contrast, V6K self-assembled into lamellar-stack nanostructures approximately 4 nm tall and under 100 nm long. The self-assembled peptide nanostructures were used as organic templates to direct biosilica formation. Comparing with the self-assembled structures formed by the peptide/anions system, novel silica morphologies can be obtained by changing the peptide composition, using different anions, and applying electrostatic/flow fields. We observed that the presence of anions is important but not enough to produce ordered silica structures with novel morphologies. This study provides further understanding of silica biomineralization tailored by assembled peptides, which offers a simple but efficient method to control the formation of inorganic material.

Amphiphilic cylindrical copolypeptide brushes as potential nanocarriers for the simultaneous encapsulation of hydrophobic and cationic drugs

Cylindrical copolypeptide brushes PLLF-g-(PLF-b-PLG) with poly(L-lysine-co-L-phenylalanine) (PLLF) as the backbone and poly(L-phenylalanine)-b-poly(L-glutamic acid) (PLF-b-PLG) as the side chains have been synthesized and evaluated as drug delivery carriers. The synthesized copolypeptide brushes were characterized by (1)H NMR, gel permeation chromatography (GPC), and transmission electron microscopy (TEM). In aqueous solution, the copolypeptide brushes adopt cylindrical morphologies and resemble unimolecular polymeric micelles with a hydrophobic poly(L-phenylalanine) core and a hydrophilic poly(L-glutamate) shell. An encapsulation study demonstrated that these water soluble, biodegradable copolypeptide brushes encapsulate hydrophobic compounds and cationic hydrophilic guest molecules simultaneously. Furthermore, the encapsulated cationic model compounds exhibit a pH-responsive releasing property.

Hydrophobic oligopeptide-based star-block copolymers as unimolecular nanocarriers for poorly water-soluble drugs.

Hydrophobic oligopeptide (HOP)-based star-block copolymers of the form PEI-g-(HOP-b-PEG) were synthesized, characterized and evaluated as nanocarriers for poorly water-soluble drugs. The designed PEI-g-(HOP-b-PEG) polymers were composed of a hyperbranched polyethylenimine (PEI) core, a HOP [i.e., oligo(l-tryptophan), oligo(l-phenylalanine), oligo(l-leucine), oligo(γ-benzyl-l-glutamate) and oligo(ɛ-benzyloxycarbonyl-l-lysine)] inner shell and a hydrophilic poly(ethylene glycol) (PEG) outer shell. The synthesized polymers were characterized using (1)H NMR, gel permeation chromatography (GPC) and transmission electron microscopy (TEM). Their micellization behavior was investigated by the dynamic light scattering (DLS) and fluorescence spectroscopy using pyrene as a probe; the results demonstrated that these star-block copolymers predominantly resembled unimolecular micelles, particularly when shorter HOP blocks and/or elongated PEG chains were incorporated. The encapsulation properties of these unimolecular micelles were evaluated using pyrene, oil-red O (OR) and doxorubicin (DOX) as guest hydrophobic compounds, which revealed that poorly water-soluble guests can be efficiently solubilized in PEI-g-(HOP-b-PEG) with a loading capacity of up to 10%. The encapsulated DOX demonstrated sustained release from PEI-g-(HOP-b-PEG). The synthesized star-block copolymers, given their structural versatility, water solubility and biodegradability, could potentially be used as unimolecular nanocarriers for the delivery of poorly water-soluble drugs.

Self-assembled peptide nanotubes as potential nanocarriers for drug delivery

The self-assembly of amphiphilic peptide I3K (Ac-I3K-NH2) and its potential application as a drug nanocarrier have been investigated. I3K monomers and nanotubular segments were initially the dominant species in aqueous solution and they gradually self-assembled into mature nanotubes with heights of approximately 12 nm and lengths of more than 1 μm. The encapsulation properties of the self-assembled peptide nanotubes were then investigated using model compound guests, including anionic hydrophilic methyl orange (MO) and hydrophobic oil red. It revealed that the model compounds could be efficiently encapsulated by I3K assemblies via electrostatic and hydrophobic interactions, respectively. Atomic force microscopy images demonstrated that variations in drug concentration did not significantly alter the structures of the peptide assemblies but could affect their sizes. Circular dichroism analyses indicated the predominance of β-sheet conformation associated with the self-assembled system regardless of drug concentrations. The in vitro releasing behavior of the encapsulated model drugs was also studied by the techniques of dialysis. The entrapped model drug MO exhibited an accelerated release as the solution pH was either decreased to 2.0–3.0 or increased to 10.0–11.0 but revealed a sustained release at physiological pH. These results demonstrated that these self-assembled peptide nanotubes could serve as potential drug nanocarriers with efficient encapsulation ability, and sustained and pH-responsive release properties.

Poly(ε-benzyloxycarbonyl-L-lysine)-grafted branched polyethylenimine as efficient nanocarriers for indomethacin with enhanced oral bioavailability and anti-inflammatory efficacy.

Star-block copolymers PEI-g-PZLL with a branched polyethylenimine (PEI) core and multiple grafted poly(ε-benzyloxycarbonyl-L-lysine) (PZLL) peripheral chains were designed, synthesized, and evaluated as nanocarriers for indomethacin (IND). In an aqueous solution, PEI-g-PZLL self-assembled into spherical nanoparticles capable of encapsulating IND at high loading capacity and loading efficiency. Differential scanning calorimetry and X-ray diffraction measurements indicated that IND was molecularly or amorphously dispersed in the nanoparticles. Fourier transform infrared spectra revealed the presence of multiple intermolecular interactions, including hydrogen bonding, electrostatic forces, π-π stacking and hydrophobic interactions, between the block copolymer and the IND molecules. IND-loaded nanoparticles exhibited fast release under intestinal pH. Compared with raw IND, the utilization of PEI-g-PZLL as a carrier significantly enhanced the oral bioavailability of IND and improved its protective effect on renal ischemia-reperfusion injury, as evidenced by in vivo pharmacokinetic and pharmacodynamic studies. Cytotoxicity assay, histological observation and cellular uptake study suggested that PEI-g-PZLL was fairly biocompatible. All these results indicated that star-block copolymers PEI-g-PZLL could be used as efficient nanocarriers for IND and other poorly water-soluble drugs. STATEMENT OF SIGNIFICANCE The use of polyethylenimine (PEI) as an oral drug delivery carrier is limited because it is not biodegradable and the use of higher molecular weight PEI leads to improved efficiency but also increased cytotoxicity. The design of functionalized PEIs with low cytotoxicity and high efficiency is crucial for developing a successful oral drug delivery system. In our study, poly(ε-benzyloxycarbonyl-L-lysine) (PZLL)-grafted branched PEI (PEI-g-PZLL) was reported as an oral nanocarrier for indomethacin (IND). The low cytotoxicity and biodegradability, well-defined self-assembled nano-sized polymeric micelles, high loading capacity and loading efficiency, amorphous state of the encapsulated IND, as well as the enhanced oral bioavailability of IND, makes the copolymer PEI-g-PZLL a promising nanocarrier for the oral administration of IND and possibly other poorly water-soluble drugs.

Morphology-controlled synthesis of silica materials templated by self-assembled short amphiphilic peptides

Molecular self-assembly has evolved into a robust and powerful bottom-up approach for constructing biomaterials. In this paper, we report the molecular self-assembly of synthetic short amphiphilic peptides (Ac-I3K-NH2, Ac-A3K-NH2, and Ac-A9K-NH2) and their applications as specific biomineralization templates to investigate mechanisms controlling biosilica morphologies. In pure water, variation of peptide compositions from Ac-I3K-NH2 to Ac-A3K-NH2 and Ac-A9K-NH2 resulted in altered self-assembly into nanotubes, lamellar stack nanostructures, and nanofibrils, respectively. Addition of phosphate ions did not result in noticeable morphological variation in the self-assembled nanostructures of Ac-I3K-NH2 and Ac-A3K-NH2, but favored growth of the Ac-A9K-NH2 peptide to form long nanofibrils, suggesting that phosphate ions tune peptide aggregation via different mechanisms. The self-assembled nanomaterials were then utilized as organic templates to direct biosilica formation. Our results indicate that the nature of the peptide/anion complex and external forces were important factors in producing ordered biosilica structures. Because of the exceptional stability of Ac-I3K-NH2 self-assemblies, silica intermediates tended to precipitate directly at the peptide surface, whereas Ac-A3K-NH2 and Ac-A9K-NH2 self-assemblies mediated re-assembly of large sizes of biosilica particles from twinned crystals. Our findings demonstrate the potential use of self-assembled templates and biomimetic conditions for controlling morphologies of inorganic materials.

Gadolinium-conjugated star-block copolymer polylysine-modified polyethylenimine as high-performance T1 MR imaging blood pool contrast agents

Core–shell copolymers have received widespread attention because of their unique properties, such as suitable for surface modification and increasing the functionality. Thus, they have been increasingly used in many fields including biomedical, pharmaceutical, electronics and optics. Here, a new core–shell copolymer system was developed to synthesize potential blood pool contrast agent (CA) for magnetic resonance imaging (MRI). The novel CA with high T1 relaxivity was synthesized by conjugating gadolinium (Gd) chelators onto star-block copolymer polyethylenimine-grafted poly(L-lysine) (PEI–PLL) nanoparticles (NPs). The T1 relaxivity of PEI–PLL–DTPA–Gd NPs measured on a 7.0 T small animal MRI scanner was 8.289 mM−1 s−1, higher than that of T1 contrast agents widely used in the clinic, such as Gd–DTPA (also known as Magnevist, r1 = 4.273 mM−1 s−1). These results show that PEI–PLL–DTPA–Gd exhibits more efficient T1 MR contrast enhancement compared to Gd–DTPA. More importantly, the PEI–PLL–DTPA–Gd core–shell NPs exhibited extremely low toxicity when measured against the HepG2 cell line over a similar concentration rang of Magnevist. In in vivo experiments, PEI–PLL–DTPA–Gd not only displayed good T1 contrast enhancement for the abdominal aorta, but also showed prolonged blood circulation time compared with Gd–DTPA, which should enable longer acquisition time, for MR and MR angiographic images, with high resolution in clinical practice. PEI–PLL–DTPA–Gd NPs have potential to serve as high T1 relaxivity blood pool MRI CA in the clinic.