Meidong Lang

Fabrication of uniform hollow mesoporous silica spheres and ellipsoids of tunable size through a facile hard-templating route

A facile hard-templating route has been successfully developed to fabricate uniform hollow mesoporous silica spheres and ellipsoids by using hematite as hard template. The outer diameter of the spherical mesoporous silica particles can be well adjusted in a sub-micrometric range (typically around 100–200nm) by selecting suitable hematite particles as core templates. The thickness of the mesoporous shell can be tuned independently at around 10nm by tailoring the amount of tetraethoxysilane and n-octadecyltrimethoxysilane mixture. Ellipsoidal hollow mesoporous silica particles are prepared as well for the first time when spindle shaped hematite particles are employed as core templates. In addition, these hollow mesoporous particles manifest high drug storage capacity (726 mg ibuprofen per gram) mainly and physically in the core part, hence justifying their promising applications as nanocarriers in drug delivery.

Fine tuning micellar core-forming block of poly(ethylene glycol)-block-poly(ε-caprolactone) amphiphilic copolymers based on chemical modification for the solubilization and delivery of doxorubicin.

This study aimed to optimize poly(ethylene glycol)-b-poly(ε-caprolactone) (PEG-b-PCL)-based amphiphilic block copolymers for achieving a better micellar drug delivery system (DDS) with improved solubilization and delivery of doxorubicin (DOX). First, the Flory-Huggins interaction parameters between DOX and the core-forming segments [i.e., poly(ε-caprolactone) (PCL) and poly[(ε-caprolactone-co-γ-(carbamic acid benzyl ester)-ε-caprolactone] (P(CL-co-CABCL))] was calculated to assess the drug-polymer compatibility. The results indicated a better compatibility between DOX and P(CL-co-CABCL) than that between DOX and PCL, motivating the synthesis of monomethoxy-poly(ethylene glycol)-b-poly[(ε-caprolactone-co-γ-(carbamic acid benzyl ester)-ε-caprolactone] (mPEG-b-P(CL-co-CABCL)) block copolymer. Second, two novel block copolymers of mPEG-b-P(CL-co-CABCL) with different compositions were prepared via ring-opening polymerization of CL and CABCL using mPEG as a macroinitiator and characterized by (1)H NMR, FT-IR, GPC, WAXD, and DSC techniques. It was found that the introduction of CABCL decreased the crystallinity of mPEG-b-PCL copolymer. Micellar formation of the copolymers in aqueous solution was investigated with fluorescence spectroscopy, DLS and TEM. mPEG-b-P(CL-co-CABCL) copolymers had a lower critical micelle concentration (CMC) than mPEG-b-PCL and subsequently led to an improved stability of prepared micelles. Furthermore, both higher loading capacity and slower in vitro release of DOX were observed for micelles of copolymers with increased content of CABCL, attributed to both improved drug-core compatibility and favorable amorphous core structure. Meanwhile, DOX-loaded micelles facilitated better uptake of DOX by HepG2 cells and were mainly retained in the cytosol, whereas free DOX accumulated more in the nuclei. However, possibly because of the slower intracellular release of DOX, DOX-loaded micelles were less potent in inhibiting cell proliferation than free DOX in vitro. Taken together, the introduction of CABCL in the core-forming block of mPEG-b-PCL resulted in micelles with superior properties, which hold great promise for drug delivery applications.

Folate-functionalized nanoparticles for controlled 5-Fluorouracil delivery

In this paper, folate conjugated poly(ε-caprolactone-co-4-maleate-ε-caprolactone) (P(CL-co-MCL)-folate) was prepared by a carbodiimide coupling reaction, i.e., the vitamin folic acid (FA) was covalently linked to the main chain of the maleate-functionalized polymer, poly(ε-caprolactone-co-4-maleate-ε-caprolactone) (P(CL-co-MCL)). Then the 5-Fluorouracil (5-FU) loaded nanoparticles of P(CL-co-MCL)-folate were achieved by solvent-evaporation method. Their properties were extensively studied by dynamic light scattering (DLS) and scan electron microscopy (SEM). DLS and SEM showed that the nanoparticles were in a well-defined spherical shape with a uniform size distribution. We also investigated the entrapment and in vitro release behavior, which indicated that the release speed of 5-FU could be well controlled and the release half-life period could reach 16.86h, which was 26.4 times longer than that of pure 5-FU. The in vitro targeting test displayed that the 5-FU loaded P(CL-co-MCL)-folate nanoparticles exhibited an enhanced cell inhibition because folate targeting increased the concentration of 5-FU loaded P(CL-co-MCL)-folate nanoparticles in the tumor cells with folate receptor overexpressed. Meanwhile, the tumor inhibition of 5-FU loaded P(CL-co-MCL)-folate nanoparticles was much higher than that of pure 5-FU and that of 5-FU loaded P(CL-co-MCL) nanoparticles. Therefore, P(CL-co-MCL)-folate nanoparticles would be highly beneficial for biomedical and pharmaceutical applications.

Self-assembly of pH-sensitive mixed micelles based on linear and star copolymers for drug delivery.

Comicellization of a star block copolymer poly(ε-caprolactone)-block-poly(diethylamino)ethyl methacrylate (S(PCL-b-PDEAEMA)) and a linear block copolymer methoxy poly(ethylene glycol)-block-poly(ε-caprolactone) (mPEG-b-PCL) was developed to enhance the stability and lower the cytotoxicity of the micelles. The two copolymers self-assembled into the mixed micelles with a common PCL core surrounded by a mixed PDEAEMA/mPEG shell in aqueous solution. This core-shell structure was transformed to the core-shell-corona structure at high pH due to the collapse of the PDEAEMA segment. The properties of the polymeric micelles were greatly dependent on the weight ratio of the two copolymers and the external pH. As increasing the mPEG-b-PCL content, the size and the zeta potential of the mixed micelles were lowered while the pH-dependent stability and the biocompatibility were improved. Moreover, an increase in pH accelerated the release of indomethacin (IND) from the mixed micelles in vitro. These results augured that the mixed micelles could be applied as a stable pH-sensitive release system.

Preparation of polysaccharide derivates chitosan-graft-poly(ɛ-caprolactone) amphiphilic copolymer micelles for 5-fluorouracil drug delivery.

Biodegradable graft copolymer, chitosan-graft-poly(ɛ-caprolactone) (CS-g-PCL) was synthesized via ring opening polymerization and characterized by (1)H NMR and FTIR spectroscopy. Then graft copolymers were self-assembled into micelles as drug delivery system. To evaluate drug-polymer compatibility, the Flory-Huggins interaction parameter between 5-fluorouraci (5-Fu) and hydrophobic segment was calculated. The result was in agreement with experimental data from drug loading content and drug loading efficiency. Meanwhile, DLS and TEM were utilized to evaluate the trend of particle size and morphology in aqueous solution with different repeating units of ɛ-CL. The in vitro drug release data was fitted with three kinetic models, usually applied in the drug delivery system. Results indicated that the release of 5-Fu was controllable and the release half-time could reach as long as 54.46 h, much slower than that of free 5-Fu. Cytotoxicity evaluation and cellular apoptosis study suggested good biocompatibility of CS-g-PCL micelles. Moreover, 5-Fu loaded micelles could delay the release of drug and exert comparable cytotoxicity against A549 cells.

Dual-response nanocarrier based on graft copolymers with hydrazone bond linkages for improved drug delivery.

Core-shell micelles with biodegradability, thermo- and pH-response were successfully demonstrated by poly(2-oxepane-1,5-dione-co-epsilon-caprolactone) (P(OPD-co-CL)) grafted with hydrophilic segments of amine-terminated poly(N-isopropylacrylamide) (At-PNIPAM). To compare with the graft copolymer, P(OPD-co-CL) block PNIPAM polymer was also prepared. The micelles with core-shell structure were formed with both graft and block copolymers by self-assembly in aqueous solutions, of which PNIPAM shell is thermo-response. Furthermore, P(OPD-co-CL)-g-PNIPAM also showed pH-sensitivity, which was attributed to the acid-cleavable property of the hydrazone bond. The low critical micelle concentrations (CMCs) of graft polymers and block polymers were 6.7 mg/L and 14.3mg/L, respectively, which indicated the formation of stable micelles. Both drug-free and drug-loaded micelles were in uniformly spherical shape observed by transmission electron microscopy (TEM). The sizes of the drug-free and drug-loaded micelles prepared from graft polymer were 123.5 nm and 146.5 nm, respectively, and the sizes of those prepared from block polymer were 197.5 nm and 211.5 nm, respectively. The lower critical solution temperature (LCST) for the graft polymer was 34.3 degrees C, while that for the block polymer was 28.1 degrees C, demonstrating a thermo-response. The graft polymeric micelles exhibited thermo-triggered decelerated release at pH 7.4, and pH-triggered accelerated release at 25 degrees C in vitro release test, indicating that the graft polymeric micelles could be a promising site-specific drug delivery system for enhancing the bioavailability of the drug in targeted pathological areas.

Fabrication of three-dimensional poly(ε-caprolactone) scaffolds with hierarchical pore structures for tissue engineering.

The physical properties of tissue engineering scaffolds such as microstructures play important roles in controlling cellular behaviors and neotissue formation. Among them, the pore size stands out as a key determinant factor. In the present study, we aimed to fabricate porous scaffolds with pre-defined hierarchical pore sizes, followed by examining cell growth in these scaffolds. This hierarchical porous microstructure was implemented via integrating different pore-generating methodologies, including salt leaching and thermal induced phase separation (TIPS). Specifically, large (L, 200-300 μm), medium (M, 40-50 μm) and small (S, <10 μm) pores were able to be generated. As such, three kinds of porous scaffolds with a similar porosity of ~90% creating pores of either two (LS or MS) or three (LMS) different sizes were successfully prepared. The number fractions of different pores in these scaffolds were determined to confirm the hierarchical organization of pores. It was found that the interconnectivity varied due to the different pore structures. Besides, these scaffolds demonstrated similar compressive moduli under dry and hydrated states. The adhesion, proliferation, and spatial distribution of human fibroblasts within the scaffolds during a 14-day culture were evaluated with MTT assay and fluorescence microscopy. While all three scaffolds well supported the cell attachment and proliferation, the best cell spatial distribution inside scaffolds was achieved with LMS, implicating that such a controlled hierarchical microstructure would be advantageous in tissue engineering applications.

Synthesis and characterization of polycaprolactone / poly(ethylene oxide) / polylactide tri-component copolymers

Polycaprolactonel/poly(ethylene oxide)/polylactide tri-component copolymers (PCEL) with different compositions were synthesized by copolymerization of e-caprolactone and L-lactide in the presence of poly(ethylene glycol) using stannous octoate as a catalyst. The copolymers were purified and characterized by various analytical techniques such as GPC, FT-IR, H NMR, 13C NMR, DSC, and X-ray diffractometry. It was evidenced that these copolymers were pure tri-component compounds which exhibited partially random chain structures, and possessed good mechanical properties and variable biodegradability.

In Situ Controlled Release of rhBMP-2 in Gelatin-Coated 3D Porous Poly(ε-caprolactone) Scaffolds for Homogeneous Bone Tissue Formation

In tissue engineering, incorporation of bone morphogenetic protein-2 (BMP-2) into biomaterial scaffolds is an attractive strategy to stimulate bone repair. However, suboptimal release of BMP-2 remains a great concern, which may cause unfavorable bone formation as well as severe inflammation. In this study, genipin-cross-linked gelatin entrapped with recombinant human BMP-2 (rhBMP-2) was exploited to decorate the interior surface of three-dimensional porous poly(ε-caprolactone) (PCL) scaffolds. With gelatin-coating, PCL scaffolds demonstrated enhanced water uptake and improved compressive moduli. Intriguingly, a unique release profile of rhBMP-2 composed of a transient burst release followed by a sustained release was achieved in coated scaffolds. These coated scaffolds well supported growth and osteogenesis of human mesenchymal stem cells (hMSCs) in vitro, indicating the retaining of rhBMP-2 bioactivity. When hMSCs-seeded scaffolds were implanted subcutaneously in nude mice for 4 weeks, better bone formation was observed in gelatin/rhBMP-2-coated scaffolds. Specifically, the spatial distribution of newly formed bone was more uniform in gelatin-coated scaffolds than in uncoated scaffolds, which displayed preferential bone formation at the periphery. These results collectively demonstrated that gelatin-coating of porous PCL scaffolds is a promising approach for delivering rhBMP-2 to stimulate improved bone regeneration.

Synthesis, characterization, fluorescence labeling and cellular internalization of novel amine -functionalized poly(ethylene glycol)- block -poly(ε-caprolactone) amphiphilic block copolymers

We report in this paper a facile way to prepare novel amine-functionalized monomethoxy-poly(ethylene glycol)-b-poly(e-caprolactone) (mPEG-b-PCL) amphiphilic block copolymers, which are subsequently fluorescently labeled. In our synthetic route, monomethoxy-poly(ethylene glycol)-b-poly[e-caprolactone-co-γ-(carbamic acid benzyl ester)-e-caprolactone] [mPEG-b-P(CL-co-CABCL)] copolymers were synthesized viaring-opening polymerization (ROP) of e-caprolactone (CL) and a newly developed monomer, γ-(carbamic acid benzyl ester)-e-caprolactone (CABCL) at varied ratios using mPEG as macroinitiator and Sn(Oct)2 as catalyst. Subsequent deprotection upon removal of carbobenzoxy (Cbz) group yielded monomethoxy-poly(ethylene glycol)-b-poly(e-caprolactone-co-γ-amino-e-caprolactone) [mPEG-b-P(CL-co-ACL)] copolymers bearing primary amine functional groups on the PCL block. The structures of polymers were characterized with NMR, FT-IR and GPC techniques. These amphiphilic block copolymers self-assembled into micelles in aqueous solution and the critical micelle concentration (CMC) was dependent on the compositions of the copolymers. In addition, the particle size and morphology of micelles were studied with DLS and TEM, respectively. In vitro study demonstrated that the micelles were nontoxic to human fibroblasts based on MTT and live/dead assays. Furthermore, a proof-of-concept usage of amino groups for bioconjugation was illustrated by tagging the copolymer with a fluorophore, fluorescein isothiocyanate (FITC). Internalization of FITC-labeled micelles by fibroblast cells was observed under fluorescence microscopy. Through facile conjugation of chemical moieties such as drugs, peptides, proteins or fluorophores, micelles prepared with these amine-functionalized mPEG-b-PCL copolymers hold great promise in biomedical applications.