Chun-Wen Hsiao

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.

Electrical coupling of isolated cardiomyocyte clusters grown on aligned conductive nanofibrous meshes for their synchronized beating

Myocardial infarction is often associated with abnormalities in electrical function due to a massive loss of functioning cardiomyocytes. This work develops a mesh, consisting of aligned composite nanofibers of polyaniline (PANI) and poly(lactic-co-glycolic acid) (PLGA), as an electrically active scaffold for coordinating the beatings of the cultured cardiomyocytes synchronously. Following doping by HCl, the electrospun fibers could be transformed into a conductive form carrying positive charges, which could then attract negatively charged adhesive proteins (i.e. fibronectin and laminin) and enhance cell adhesion. During incubation, the adhered cardiomyocytes became associated with each other and formed isolated cell clusters; the cells within each cluster elongated and aligned their morphology along the major axis of the fibrous mesh. After culture, expression of the gap-junction protein connexin 43 was clearly observed intercellularly in isolated clusters. All of the cardiomyocytes within each cluster beat synchronously, implying that the coupling between the cells was fully developed. Additionally, the beating rates among these isolated cell clusters could be synchronized via an electrical stimulation designed to imitate that generated in a native heart. Importantly, improving the impaired heart function depends on electrical coupling between the engrafted cells and the host myocardium to ensure their synchronized beating.

Multifunctional core-shell polymeric nanoparticles for transdermal DNA delivery and epidermal Langerhans cells tracking

Skin is a highly immune-reactive tissue containing abundant antigen-presenting cells such as Langerhans cells (LCs), and thus is a favorable site for DNA immunization. This study developed a multifunctional core-shell nanoparticle system, which can be delivered transdermally into the epidermis via a gene gun, for use as a DNA carrier. The developed nanoparticles comprised a hydrophobic PLGA core and a positively-charged glycol chitosan (GC) shell. The core of the nanoparticles was used to load fluorescent quantum dots (QDs) for ultrasensitive detection of Langerhans cell migration following transdermal delivery, while a reporter gene was electrostatically adsorbed onto the GC shell layer of the nanoparticles. Results of fluorescence spectrophotometry, transmission electron microscopy, energy dispersive X-ray analysis, and X-ray diffraction measurement confirmed that the prepared nanoparticles had a core-shell structure with QDs in their core area. The surface charge of nanoparticles depended strongly on pH environment, enabling the intracellular release of the loaded DNA via a pH-mediated mechanism. Using a mouse model, this study demonstrated that bombardment of nanoparticles transfected DNA directly into LCs present in the epidermis; the transfected LCs then migrated and expressed the encoded gene products in the skin draining lymph nodes. These observation results suggest that the developed nanoparticle system is suitable for monitoring and fine-tuning important functional aspects of the immune system, in conjunction with the loaded fluorescence, and thus has potential for use in immunotherapy and vaccine development.

Enhancement of efficiencies of the cellular uptake and gene silencing of chitosan/siRNA complexes via the inclusion of a negatively charged poly(γ-glutamic acid)

Although advantageous for siRNA packing and protection, chitosan (CS)-based complexes may lead to difficulties in siRNA release once they arrive at the site of action, due to their electrostatic interactions. To assist the intracellular release of siRNA and thus enhance its effectiveness in gene silencing, we incorporated a negatively charged poly(γ-glutamic acid) (γ-PGA) into CS/siRNA complexes. The inclusion of γ-PGA did not alter the complex-formation ability between CS and siRNA; additionally, their cellular uptake was significantly enhanced. The results obtained in our molecular dynamic simulations indicate that the binding between CS and siRNA remained stable in the cytosol environment. In contrast, the compact structure of the ternary CS/siRNA/γ-PGA complexes was unpacked; such a structural unpackage may facilitate the intracellular release of siRNA. In the gene silencing study, we found that the inclusion of γ-PGA into complexes could significantly expedite the onset of gene knockdown, enhance their inhibition efficiency and prolong the duration of gene silencing. These findings may be attributed to the fact that there were significantly more CS/siRNA/γ-PGA complexes internalized into the cells in company with their more rapid intracellular unpackage and release of siRNA when compared with their binary counterparts in the absence of γ-PGA. The aforementioned results suggest that CS/siRNA/γ-PGA complexes can be an efficient vector for siRNA transfection.

An Implantable Depot That Can Generate Oxygen in Situ for Overcoming Hypoxia-Induced Resistance to Anticancer Drugs in Chemotherapy

In the absence of adequate oxygen, cancer cells that are grown in hypoxic solid tumors resist treatment using antitumor drugs (such as doxorubicin, DOX), owing to their attenuated intracellular production of reactive oxygen species (ROS). Hyperbaric oxygen (HBO) therapy favorably improves oxygen transport to the hypoxic tumor tissues, thereby increasing the sensitivity of tumor cells to DOX. However, the use of HBO with DOX potentiates the ROS-mediated cytotoxicity of the drug toward normal tissues. In this work, we hypothesize that regional oxygen treatment by an implanted oxygen-generating depot may enhance the cytotoxicity of DOX against malignant tissues in a highly site-specific manner, without raising systemic oxygen levels. Upon implantation close to the tumor, the oxygen-generating depot reacts with the interstitial medium to produce oxygen in situ, effectively shrinking the hypoxic regions in the tumor tissues. Increasing the local availability of oxygen causes the cytotoxicity of DOX that is accumulated in the tumors to be significantly enhanced by the elevated production of ROS, ultimately allaying the hypoxia-induced DOX resistance in solid malignancies. Importantly, this enhancement of cytotoxicity is limited to the site of the tumors, and this feature of the system that is proposed herein is unique.

Enhancement of efficiency of chitosan-based complexes for gene transfection with poly(γ-glutamic acid) by augmenting their cellular uptake and intracellular unpackage

As a cationic polysaccharide, chitosan (CS) has been identified for its potential use as a non-viral vector for exogenous gene transfection. However, owing to their electrostatic interactions, CS complexes may cause difficulties in gene release upon their arrival at the site of action, thus limiting their transfection efficiency. In this work, an attempt is made to facilitate the release of a gene by incorporating a negatively-charged poly(γ-glutamic acid) (γPGA) into CS complexes in order to diminish their attractive interactions. The mechanisms of exploiting γPGA to enhance the transfection efficiency of CS complexes are elucidated. The feasibility of using this CS/γPGA-based system for DNA or siRNA transfer is explored as well. Additionally, potential of the CS/γPGA formulation to deliver disulfide bond-conjugated dual PEGylated siRNAs for multiple gene silencing is also examined. Moreover, the genetic use of pKillerRed-mem, delivered using complexes of CS and γPGA, to express a membrane-targeted KillerRed as an intrinsically generated photosensitizer for photodynamic therapy is described.

Injectable Cell Constructs Fabricated via Culture on a Thermoresponsive Methylcellulose Hydrogel System for the Treatment of Ischemic Diseases

Cell transplantation via direct intramuscular injection is a promising therapy for patients with ischemic diseases. However, following injections, retention of transplanted cells in engrafted areas remains problematic, and can be deleterious to cell-transplantation therapy. In this Progress Report, a thermoresponsive hydrogel system composed of aqueous methylcellulose (MC) blended with phosphate-buffered saline is constructed to grow cell sheet fragments and cell bodies for the treatment of ischemic diseases. The as-prepared MC hydrogel system undergoes a sol-gel reversible transition upon heating or cooling at ≈32 °C. Via this unique property, the grown cell sheet fragments (cell bodies) can be harvested without using proteolytic enzymes; consequently, their inherent extracellular matrices (ECMs) and integrative adhesive agents remain well preserved. In animal studies using rats and pigs with experimentally created myocardial infarction, the injected cell sheet fragments (cell bodies) become entrapped in the interstices of muscular tissues and adhere to engraftment sites, while a minimal number of cells exist in the group receiving dissociated cells. Moreover, transplantation of cell sheet fragments (cell bodies) significantly increases vascular density, thereby improving the function of an infarcted heart. These experimental results demonstrate that cell sheet fragments (cell bodies) function as a cell-delivery construct by providing a favorable ECM environment to retain transplanted cells locally and consequently, improving the efficacy of therapeutic cell transplantation.

Inflammation-Induced Drug Release by using a pH-Responsive Gas-Generating Hollow-Microsphere System for the Treatment of Osteomyelitis

In the conventional treatment of osteomyelitis, the penetration of antibiotics into the infected bone is commonly poor. To ensure that the local antibiotic concentration is adequate, this work develops an injectable calcium phosphate (CP) cement in which is embedded pH-responsive hollow microspheres (HMs) that can control the release of a drug according to the local pH. The HMs are fabricated using a microfluidic device, with a shell of poly(D,L-lactic-co-glycolic acid) (PLGA) and an aqueous core that contains vancomycin (Van) and NaHCO3. At neutral pH, the CP/HM cement elutes a negligible concentration of the drug. In an acidic environment, the NaHCO3 that is encapsulated in the HMs reacts with the acid rapidly to generate CO2 bubbles, disrupting the PLGA shells and thereby releasing Van locally in excess of a therapeutic threshold. The feasibility of using this CP/HM cement to treat osteomyelitis is studied using a rabbit model. Analytical results reveal that the CP/HM cement provides highly effective local antibacterial activity. Histological examination further verifies the efficacy of the treatment by the CP/HM cement. The above findings suggest that the CP/HM cement is a highly efficient system for the local delivery of antibiotics in the treatment of osteomyelitis.

Disulfide bond-conjugated dual PEGylated siRNAs for prolonged multiple gene silencing

Many human diseases carry at least two independent gene mutations, further exacerbating clinical disorders. In this work, disulfide bond-conjugated dual PEGylated siRNAs were synthesized, capable of specifically targeting and silencing two genes simultaneously. To achieve efficient delivery, the conjugated siRNAs were formulated with the cationic chitosan together with an anionic polymer, poly(γ-glutamic acid) (γPGA), to form a ternary complex. Experimental results indicate that the incorporated γPGA could significantly enhance their intracellular delivery efficiency, allowing for reduction of the disulfide bond-conjugated PEGylated siRNAs delivered to the PEGylated siRNAs in the reductive cytoplasmic environment. The PEGylated siRNAs could more significantly increase their enzymatic tolerability, effectively silence multiple genes, and prolong the duration of their gene silencing capability than the unmodified siRNAs could. Silencing of different genes simultaneously significantly contributes to the efforts to treat multiple gene disorders, and prolonged duration of gene silencing can reduce the need for frequent administrations.

Injectable Microbeads with a Thermo-Responsive Shell and a pH-Responsive Core as a Dual-Switch-Controlled Release System

Treating inflammation with a dual-switch-controlled release system: The release of a drug from the developed microbead system occurs only in response to both an increase in local temperature and an acidic environmental pH. This dual-switch-controlled release system has the advantages of distinguishing between inflamed and healthy tissues to improve treatment efficacy.