Hsin-Lung Chen

Enteric-coated capsules filled with freeze-dried chitosan/poly(γ-glutamic acid) nanoparticles for oral insulin delivery

A pH-sensitive nanoparticle (NP) system composed of chitosan and poly(gamma-glutamic acid) was prepared for the oral delivery of insulin. The biodistribution study in a rat model showed that some of the orally administered NPs were retained in the stomach for a long duration, which might lead to the disintegration of NPs and degradation of insulin. To overcome these problems, we freeze-dried NPs and filled them in an enteric-coated capsule. The small angle X-ray scattering (SAXS) profiles indicated that the freeze-drying process did not significantly disrupt the internal structure of NPs; additionally, their pH-sensitivity was preserved and the insulin release was pH-dependent. The results obtained in the native PAGE analysis indicated that the released insulin molecules were neither fragmented nor aggregated. Upon oral administration, the enteric-coated capsule remained intact in the acidic environment of the stomach, but dissolved rapidly in the proximal segment of the small intestine. Consequently, all the NPs loaded in the capsule were brought into the small intestine, thus enhancing the intestinal absorption of insulin and providing a prolonged reduction in blood glucose levels. The relative bioavailability of insulin was found to be approximately 20%. These results suggest that the formulation developed in the study might be employed as a potential approach for the oral delivery of insulin.

pH-triggered injectable hydrogels prepared from aqueous N-palmitoyl chitosan: In vitro characteristics and in vivo biocompatibility

In-situ forming hydrogels triggered by environmental stimuli have emerged as a promising injectable strategy targeted for various biomedical applications. However, several drawbacks associated with temperature-stimulated hydrogels have been reported. Employing a hydrophobically-modified chitosan (N-palmitoyl chitosan, NPCS), we developed a pH-triggered hydrogel system which showed a rapid nanostructure transformation within a narrow pH range (pH 6.5-7.0). NPCS in an aqueous environment was found to be a shear-thinning fluid and exhibited an instant recovery of its elastic properties after shear thinning, thereby making it an injectable material. Additionally, aqueous NPCS, an associating polyelectrolyte, can be rapidly transformed into hydrogel triggered simply by its environmental pH through a proper balance between charge repulsion and hydrophobic interaction. This in-situ hydrogel system was shown to be nontoxic. Subcutaneous injection of aqueous NPCS (pH 6.5) into a rat model resulted in rapid formation of a massive hydrogel at the location of injection. The implanted hydrogel was found to be degradable and was associated with an initial macrophage response which decreased with time as the degradation proceeded. These results suggested that the developed NPCS hydrogel may be used as an injectable drug/cell delivery system.

A Thermoresponsive Bubble-Generating Liposomal System for Triggering Localized Extracellular Drug Delivery

The therapeutic effectiveness of chemotherapy is optimal only when tumor cells are subjected to a maximum drug exposure. To increase the intratumoral drug concentration and thus the efficacy of chemotherapy, a thermoresponsive bubble-generating liposomal system is proposed for triggering localized extracellular drug delivery. The key component of this liposomal formulation is the encapsulated ammonium bicarbonate (ABC), which is used to create the transmembrane gradient needed for a highly efficient encapsulation of doxorubicin (DOX). At an elevated temperature (42 °C), decomposition of ABC generates CO(2) bubbles, creating permeable defects in the lipid bilayer that rapidly release DOX and instantly increase the drug concentration locally. Because the generated CO(2) bubbles are hyperechogenic, they also enhance ultrasound imaging. Consequently, this new liposomal system encapsulated with ABC may also provide an ability to monitor a temperature-controlled drug delivery process.

Smart Multifunctional Hollow Microspheres for the Quick Release of Drugs in Intracellular Lysosomal Compartments

Prepared to self-destruct: when poly(D, L-lactic-co-glycolic acid) (PLGA) hollow microspheres containing NaHCO(3) entered the endocytic organelles of a live cell, the NaHCO(3) in the aqueous core reacted with protons that infiltrated from the compartment to generate CO(2) gas. The evolution of CO(2) bubbles led to the formation of small holes in the PLGA shell and thus rapid release of the encapsulated drug doxorubicin.

Crystallization induced microstructure of polymer blends consisting of two crystalline constituents

Abstract The crystallization kinetics and semicrystalline morphology of a polymer blend consisting of two crystalline components, poly(ethylene oxide) (PEO) and poly(ethylene succinate) (PES), have been investigated. PEO and PES were miscible in the melt. Slight dilution with PEO ( w PEO ≤0.2) promoted the crystallization kinetics of PES because of enhanced segmental mobility upon blending. Further increase in PEO content reduced the PES crystallization rate owing to the dominant effect of depression in crystallization driving force. The semicrystalline morphology of PEO/PES blends was probed by small-angle X-ray scattering (SAXS). At temperatures between the melting point of PEO ( T m PEO ≈59°C) and that of PES ( T m PES ≈101°C), the blend was a crystalline/amorphous system. Both crystallizations via direct cooling to 70°C (where only PES crystallized) and direct cooling to 40°C (where two components crystallized simultaneously) followed by heating to 68°C (to melt PEO crystals) created a high extent of interfibrillar segregation coupled with a minor extent of interlamellar incorporation of amorphous PEO. At temperatures below T m PEO , where the blend was a crystalline/crystalline system, direct cooling to 40°C (one-step crystallization) generated two separate lamellar stack (LS) domains: one containing almost pure PES lamellae and the other consisting of mixed PEO and PES lamellae. Crystallization at 70°C followed by cooling to room temperature (two-step crystallization) also yielded two separate LS domains, due to the crystallization of PEO within the interfibrillar regions.

Nanostructure and Hydrogen Spillover of Bridged Metal-Organic Frameworks

The metal-organic frameworks (MOF) with low and medium specific surface areas (SSA) were shown to be able to adsorb hydrogen via bridged spillover at room temperature (RT) up to an amount of full coverage of hydrogen in the MOF. Anomalous small-angle X-ray scattering was employed to investigate the key relationship between the structures and storage properties of the involved materials. It was found that the tunable imperfect lattice defects and the 3D pore network in the MOF crystal are the most critical structures for RT hydrogen uptake rather than the known micropores in the crystal, SSA, and Pt catalyst structure.

Spherulitic crystallization behavior of Poly(ε-caprolactone) with a wide range of molecular weight

Poly(e-caprolactone) (PCL) with a wide range of molecular weight (MW) has been prepared via fractionation by either precipitating PCL/chloroform solutions into different amounts of methanol or adding methanol into PCL/tetrahydrofuran (THF) solutions. The samples with M n ranging from 1900 to 64 700 were used to investigate the MW effects on the spherulite growth rate, nucleation density, and equilibrium melting point (T m 0 ) of PCL. The variation of spherulite growth rate with MW exhibited a maximum rather than a conventional monotonic drop. The existence of such a maximum was rationalized by considering the interplay between the effects of MW on T m 0 and segmental mobility. A growth kinetic formula proposed by Hoffman was employed to extract the crystal surface free energy product (σσ e ). In contrast to the conventional Lauritzen-Hoffman analysis which was based on the growth rates measured at different crystallization temperatures (T c ) for a given MW, the present analysis was based on the growth rates measured for different MW at a given T c . The spherulite nucleation density was found to be higher for the sample with larger MW, and this observation was interpreted based on the individual effects of MW on the primary nucleation rate and spherulite growth rate. An increase in MW promoted the nucleation rate much more significantly compared with its effect on the growth rate, and this in turn led to a higher nucleation density. An unusual morphology due to the segregation of uncrystallizable short chains into the interfibrillar regions of the spherulites was also observed for PCL with M n = 1900.

The characteristics, biodistribution and bioavailability of a chitosan-based nanoparticulate system for the oral delivery of heparin.

Heparin is a potent anticoagulant; however, it is poorly absorbed in the gastrointestinal tract. In this study, we developed a nanoparticle (NP) system shelled with chitosan (CS) for oral delivery of heparin; the NPs were prepared by a simple ionic gelation method without chemically modifying heparin. The drug loading efficiency of NPs was nearly 100% because a significantly excess amount of CS was used for the CS/heparin complex preparation. The internal structure of the prepared NPs was examined by small angle X-ray scattering (SAXS). The obtained SAXS profiles suggest that the NPs are associated with a two-phase system and consist of the CS/heparin complex microdomains surrounded by the CS matrix. The stability of NPs in response to pH had a significant effect on their release of heparin. No significant anticoagulant activity was detected after oral administration of the free form heparin solution in a rat model, while administration of NPs orally was effective in the delivery of heparin into the blood stream; the absolute bioavailability was found to be 20.5%. The biodistribution of the drug carrier, (99m)Tc-labeled CS, in rats was studied by the single-photon emission computed tomography after oral administration of the radio-labeled NPs. No significant radioactivity was found in the internal organs, indicating a minimal absorption of CS into the systemic circulation. These results suggest that the NPs developed in the study can be employed as a potential carrier for oral delivery of heparin.

Real-time visualization of pH-responsive PLGA hollow particles containing a gas-generating agent targeted for acidic organelles for overcoming multi-drug resistance

Chemotherapy research highly prioritizes overcoming the multi-drug resistance (MDR) effect in cancer cells. To overcome the drug efflux mediated by P-glycoprotein (P-gp) transporters, we developed pH-responsive poly(D,L-lactic-co-glycolic acid) hollow particles (PLGA HPs), capable of delivering doxorubicin (DOX) into MDR cells (MCF-7/ADR). The shell wall of PLGA HPs contained DiO (a hydrophobic dye), and their aqueous core carried DOX hydrochloride salt and sodium bicarbonate, a gas-generating agent when present in acidic environments. Both DiO and DOX could serve as fluorescence probes to localize HPs and visualize their intracellular drug release in real-time. Real-time confocal images provided visible evidences of the acid-responsive intracellular release of DOX from PLGA HPs in MDR cells. Via the macropinocytosis pathway, PLGA HPs taken up by cells experienced an increasingly acidic environment as they trafficked through the early endosomes and then matured into more acidic late endosomes/lysosomes. The progressive acidification of the internalized particles in the late endosomes/lysosomes generated CO(2) bubbles, leading to the disruption of HPs, prompt release of DOX, its accumulation in the nuclei, and finally the death of MDR cells. Conversely, taken up via a passive diffusion mechanism, free DOX was found mainly at the perimembrane region and barely reached the cell nuclei; therefore, no apparent cytotoxicity was observed. These results suggest that the developed PLGA HPs were less susceptible to the P-gp-mediated drug efflux in MDR cells and is a highly promising approach in chemotherapy.

Crystallization induced microstructure of crystalline/crystalline poly(vinylidenefluoride)/poly(3-hydroxybutyrate) blends probed by small angle X-ray scattering

Abstract The lamellar morphology of a melt-miscible blend consisting of two crystalline constituents, poly(vinylidene fluoride) (PVDF) and poly(3-hydroxybutyrate) (PHB), has been investigated by small angle X-ray scattering (SAXS). Owing to the proximity of melting points, PVDF and PHB crystallized over essentially the same temperature range, and consequently created a crystalline/crystalline state with the morphology characterized by the spatial arrangement of PVDF and PHB lamellae. Irrespective of the crystallization temperatures ( T c ), the SAXS patterns revealed the presences of two lamellar stack (LS) domains, where one contained mainly PVDF lamellae (PVDF LS domain) and the other primarily consisted of PHB lamellae (PHB LS domain). The interlamellar (IL) regions of both LS domains were found to contain mixed amorphous PVDF and PHB. The blends crystallized at higher T c exhibited smaller SAXS invariants. This observed T c dependence was connected with the disparity in crystallization kinetics that gave rise to different LS domain sizes at different T c s.