Xiuli Zhuang

Stimuli‐Sensitive Synthetic Polypeptide‐Based Materials for Drug and Gene Delivery

Stimuli-sensitive synthetic polypeptides are unique biodegradable and biocompatible synthetic polymers with structures mimicking natural proteins. These polymers exhibit reversible secondary conformation transitions and/or hydrophilic-hydrophobic transitions in response to changes in environmental conditions such as pH and temperature. The stimuli-triggered conformation and/or phase transitions lead to unique self-assembly behaviors, making these materials interesting for controlled drug and gene delivery applications. Therefore, stimuli-sensitive synthetic polypeptide-based materials have been extensively investigatid in recent years. Various polypeptide-based materials, including micelles, vesicles, nanogels, and hydrogels, have been developed and tested for drug- and gene-delivery applications. In addition, the presence of reactive side groups in some polypeptides facilitates the incorporation of various functional moieties to the polypeptides. This Review focuses on recent advances in stimuli-sensitive polypeptide-based materials that have been designed and evaluated for drug and gene delivery applications. In addition, recent developments in the preparation of stimuli-sensitive functionalized polypeptides are discussed.

One-step preparation of reduction-responsive poly(ethylene glycol)-poly (amino acid)s nanogels as efficient intracellular drug delivery platforms†

A series of disulfide-core-cross-linked poly(ethylene glycol)-poly(amino acid)s star copolymers were synthesized through one-step ring-opening polymerization of L-phenylalanine N-carboxyanhydride (L-Phe NCA) and L-cystine N-carboxyanhydride (L-Cys NCA) with amino group terminated poly(ethylene glycol) monomethyl ether (mPEG-NH2) as macroinitiator. The reduction-responsive PEG-poly(amino acid)s nanogels (NGs) were prepared by directly dispersing the resultant PEG-poly(amino acid)s in phosphate buffer solution at pH 7.4. Dynamic light scattering (DLS) measurements showed that the reducible NG swelled in response to 10 mM glutathione (GSH). Doxorubicin (DOX), an anthracycline anticancer drug, was loaded into the NGs. The in vitro release results revealed that the release behaviors could be adjusted by GSH concentration, and poly(amino acid)s content and composition. The intracellular DOX release results showed that enhanced intracellular DOX release occurred in GSH pretreated Henrietta Lacks (HeLa) cells. In vitro methyl thiazolyl tetrazolium (MTT) assays indicated that the NGs were biocompatible, and DOX-loaded NG showed higher cellular proliferation inhibition towards GSH pretreated HeLa cells than that of non-pretreated cells. Therefore, the NGs can efficiently deliver anticancer drugs into tumor cells and inhibit cell proliferation, rendering highly promising for targeted intracellular delivery of operative chemotherapeutic drugs in cancer therapy.

Polylactic acid (PLA): Research, development and industrialization

Polylactide (PLA) is a biodegradable, aliphatic polyester derived from lactic acid. It has similar mechanical properties to polyethylene terephthalate, but has a significantly lower maximum continuous use temperature. PLA products can be recycled after use either by remelting and processing the material a second time or by hydrolyzing to lactic acid, the basic chemical. In this review, the technologies for polymerization of the lactic acid and the comparison of physical, thermal and mechanical properties, biodegradability, and biocompatibility of the PLA and copolymers with other similar polymers are described.

Biocompatible reduction-responsive polypeptide micelles as nanocarriers for enhanced chemotherapy efficacy in vitro

To develop biocompatible reduction-responsive micellar systems for efficient intracellular drug delivery, disulfide-linked block copolymers of methoxyl poly(ethylene glycol) (mPEG) and poly(ε-benzyloxycarbonyl-l-lysine) (PZLL) were synthesized through ring-opening polymerization of ε-benzyloxycarbonyl-l-lysine N-carboxyanhydride with amino group terminated disulfide functionalized mPEG as macroinitiator. The copolymers self-assembled into micelles in phosphate buffered saline (PBS) at pH 7.4 through direct dissolution and dialysis methods. The micelles were revealed to have excellent hemocompatibilities, and cell and tissue compatibilities, which rendered them with potential for drug delivery applications. Doxorubicin (DOX), an anthracycline antitumor drug, was loaded into the micelles through nanoprecipitation with a drug loading efficiency of about 30 wt%. The in vitro DOX release from all DOX-loaded micelles was accelerated in PBS with 10.0 mM GSH, mimicking intracellular reductive conditions. DOX-loaded micelles showed higher cellular proliferation inhibition towards glutathione monoester pretreated HeLa (a human cervical cell line) and HepG2 cells (a human hepatoma cell line) as compared to unpretreated or buthionine sulfoximine pretreated cells. The above results indicated that the biocompatible reduction-responsive micelles have vast potential in targeted intracellular delivery of antitumor drugs to achieve enhanced efficacy in malignancy therapy.

Surface modification of bioactive glass nanoparticles and the mechanical and biological properties of poly(L-lactide) composites

Novel bioactive glass (BG) nanoparticles/poly(L-lactide) (PLLA) composites were prepared as promising bone-repairing materials. The BG nanoparticles (Si:P:Ca=29:13:58 weight ratio) of about 40nm diameter were prepared via the sol-gel method. In order to improve the phase compatibility between the polymer and the inorganic phase, PLLA (M(n)=9700Da) was linked to the surface of the BG particles by diisocyanate. The grafting ratio of PLLA was in the vicinity of 20 wt.%. The grafting modification could improve the tensile strength, tensile modulus and impact energy of the composites by increasing the phase compatibility. When the filler loading reached around 4 wt.%, the tensile strength of the composite increased from 56.7 to 69.2MPa for the pure PLLA, and the impact strength energy increased from 15.8 to 18.0 kJ m(-2). The morphology of the tensile fracture surface of the composite showed surface-grafted bioactive glass particles (g-BG) to be dispersed homogeneously in the PLLA matrix. An in vitro bioactivity test showed that, compared to pure PLLA scaffold, the BG/PLLA nanocomposite demonstrated a greater capability to induce the formation of an apatite layer on the scaffold surface. The results of marrow stromal cell culture revealed that the composites containing either BG or g-BG particles have much better biocompatibility compared to pure PLLA material.

Intracellular microenvironment responsive PEGylated polypeptide nanogels with ionizable cores for efficient doxorubicin loading and triggered release

Two kinds of reduction and pH responsive disulfide-cross-linked poly(ethylene glycol)-polypeptide copolymers were prepared through one-step ring-opening polymerization of γ-benzyl-L-glutamate N-carboxyanhydride (BLG NCA) or e-benzyloxycarbonyl-L-lysine N-carboxyanhydride (ZLL NCA) and L-cystine N-carboxyanhydride (LC NCA) with amino group terminated monomethoxy poly(ethylene glycol) (mPEG-NH2) as macroinitiator. Then, the copolymers were deprotected and dispersed in phosphate buffered saline, yielding PEG-polypeptide nanogels. Doxorubicin (DOX), a model anticancer drug, was effectively loaded into nanogels via electrostatic and hydrophobic interactions. The DOX release from all DOX-loaded nanogels was accelerated in intracellular reductive and acidic conditions, which controlled by Fickian diffusion and nanogels swelling. The enhanced intracellular DOX release was observed in glutathione monoester (GSH-OEt) pretreated HeLa cells. DOX-loaded nanogels showed higher cellular proliferation inhibition towards GSH-OEt pretreated HeLa and HepG2 cells than to unpretreated or buthionine sulfoximine (BSO) pretreated cells. Hemolysis tests indicated that nanogels were hemocompatible, and the presence of nanogels could reduce the hemolysis ratio (HR) of DOX significantly. These features suggest that the nanogels can efficiently load and deliver DOX into tumor cells and enhance the inhibition of cellular proliferation in vitro, providing a favorable platform to construct an efficient drug delivery system for cancer therapy.

Preparation of photo-cross-linked pH-responsive polypeptide nanogels as potential carriers for controlled drug delivery

Diblock and triblock copolymers, including poly(ethylene glycol monomethyl ether)-b-poly(L-glutamic acid-co-γ-cinnamyl-L-glutamate) (mPEG-b-P(LGA/CLG)) and poly(L-glutamic acid-co-γ-cinnamyl-L-glutamate)-b-poly(ethylene glycol)-b-poly(L-glutamic acid-co-γ-cinnamyl-L-glutamate) (P(LGA/CLG)-b-PEG-b-P(LGA/CLG)), were synthesized by ring-opening polymerization (ROP) of γ-benzyl-L-glutamate-N-carboxyanhydride (BLG-NCA) monomer with PEG-based macroinitiator, deprotection of the benzyl groups and subsequent chemical modification with cinnamyl alcohol. The structures of copolymers were confirmed by 1H NMR and GPC analyses. Pyrene-probe-based fluorescence technique revealed that these diblock and triblock copolymers could self-assemble into micelles in aqueous solution at pH 7.4 spontaneously, with PEG shells and P(LGA/CLG) cores. Under UV-irradiation at λ = 254 nm, the P(LGA/CLG) blocks in the cores of the micelles were cross-linked through the photodimerization of the cinnamyloxy groups, yielding nanogels. The nanogels were characterized by 1H NMR, FT-IR, SEM, AFM and DLS. The nanogels were pH-responsive and their properties could be tuned by varying the compositions of block copolymers. In vitro MTT assay demonstrated that the nanogels were biocompatible to HeLa cells, rendering their potential for drug delivery applications. Rifampin as a model drug was loaded into the nanogels. The in vitro rifampin release behaviors of nanogels could be affected by both the compositions of block copolymers and solution pH. These properties indicated that the pH-responsive nanogels fabricated by photo-cross-linking polypeptide micelles can be used as drug carriers for intelligent drug delivery.

Synthesis and characterization of novel biodegradable and electroactive hydrogel based on aniline oligomer and gelatin.

A biodegradable electroactive hydrogel (AP-g-GA), aniline pentamer (AP) grafting gelatin (GA), is synthesized by a coupling reaction between the carboxyl group of AP and the amino side group of GA in aqueous solution. The electroactivity of the physical hydrogel is confirmed by UV-vis and CV. The hydrophobic AP changes the hydrogels porous structure of the natural GA and the gel-time, which is confirmed by the rheological behavior of the AP-g-GA and GA. With an increase in the content of AP, the hydrogel gradually forms a porous structure, from honeycomb to bamboo raft. The porous scaffolds can be crosslinked with 3.5% EDC in 90% ethanol. MTT assays show that the AP-g-GA exhibits reduced cytotoxicity compared to EM AP due to the introduction of the biocompatible GA moiety. The in vitro cell cultures suggest that the AP-g-GA#1 (with 1.9% AP) shows the best biocompatibility and cell adhesion ability.

Versatile synthesis of temperature-sensitive polypeptides by click grafting of oligo(ethylene glycol)

A series of novel temperature-sensitive polypeptides were synthesized by ring opening polymerization (ROP) of γ-propargyl-L-glutamateN-carboxyanhydride (PLG-NCA) and subsequent click reaction between the pendant alkyne groups and 1-(2-methoxyethoxy)-2-azidoethane (MEO2-N3) or 1-(2-(2-methoxyethoxy)ethoxy)-2-azidoethane (MEO3-N3). The efficient click grafting and structure of the resultant copolymers were verified by 1H NMR, 13C NMR and GPC. All the copolymers hold α-helix conformation, and could self-assemble into amphiphilic nanoparticles in aqueous solution with hydrodynamic radii (Rh) of 32.3–62.8 nm. The graft copolymers exhibited sharp temperature-dependent phase transitions, and the LCST could be adjusted from 22.3 to 74.1 °C by varying the molecular weight, the length of the OEG side chain, the polymer concentration and salt concentration. MTT assays revealed that the graft copolymers exhibited no detectable cytotoxicity at all test concentrations up to 1 mg mL−1. In vitrodegradation tests demonstrated that the graft copolymers could be degraded by proteinase K. The drug release behaviors from the PPLG112-g-MEO2 nanoparticles were evaluated at 37 °C and 15 °C using doxorubicin (DOX) as a model drug. The drug release behavior displayed thermosensitivity, and a sustained release profile was observed at physiological temperature. These results suggested that the novel biodegradable and biocompatible polypeptide derivatives with adjustable temperature sensitivity could be a promising material for biomedical applications.

Crystallization Behavior of Asymmetric PLLA/PDLA Blends

The effects of the addition of poly(D-lactide) (PDLA) on the crystallization behavior of poly(L-lactide)(PLLA) were investigated by means of differential scanning calorimetry (DSC) and temperature-dependent X-ray diffraction(XRD). When the blends were cooled from different temperatures (250, 240, and 190 °C) at the rate of cooling of 5 °C/min, stereocomplex (sc) crystallites could stay at diverse states. Accordingly, the stereocomplexes acted as a nucleation agent exerting distinct effects on PLLA crystallization. The speculated mechanisms of the stereocomplex formation and the effectiveness as a nucleating agent are schematically described. Moreover, temperature-dependent XRD was carried out to further investigate the melt-crystallization behavior of PLLA/PDLA blends in real time. Temperature-dependent XRD results indicated that even at 240 °C the stereocomplex crystallites in all blend samples existed clearly, which could not be detected by DSC. These XRD results further suggest that the onset T(c) values for the PLLA α-form crystals formation were 160, 120, 140, and 160 °C, respectively, for neat PLLA, PLLA/PDLA 95/5, 90/10, and 80/20 as well as 70/30 samples.