Harim Bae

Directed Blood Vessel Growth Using an Angiogenic Microfiber/Microparticle Composite Patch

IO N Therapeutic angiogenesis has emerged as a promising strategy to treat various acute and chronic vascular diseases and to enhance tissue repair and regeneration. Revascularization therapies are commonly conducted by administering angiogenic growth factors, such as vascular endothelial growth factor (VEGF). [ 1 , 2 ] Successful angiogenic therapies rely greatly on the ability to engineer mature and functional neovessels, uniformly distributed within target tissues. Immature blood vessels with non-uniform distributions often stimulate an infl ammatory response and a limited therapeutic effi cacy. [ 3 , 4 ] This study presents an angiogenic microfi ber patch that releases angiogenic growth factors along aligned fi bers and subsequently directs the spacing and orientation of mature and functional neovessels. The angiogenic microfi ber patch was prepared by electrostatically binding electrosprayed VEGF-encapsulating poly(lactide-co-glycolide) (PLGA) microparticles with electrospun poly(lactide) (PLA) microfi bers. The PLGA microparticles released VEGF in a sustained manner, while the straightly aligned PLA fi bers guided cells to adhere along their orientation. Finally, microfi ber patches implanted in vivo resulted in the formation of neovessels, with controlled spacings and directionalities, together with a signifi cant increase in the blood vessel density. The angiogenic microfi ber patch developed in this study will be broadly useful for studying neovessel growth and will also signifi cantly improve the quality of clinical treatments requiring neovascularization. Several vascular biological studies have demonstrated that the spatiotemporal organization of multiple angiogenic growth factors and cytokines in tissues control the directional growth and spacing of neovessels during development and self-healing. [ 5 ]

Interconnection of electrospun nanofibers via a post co-solvent treatment and its open pore size effect on pressure-retarded osmosis performance

Design of support layer structures for asymmetric thin film composite membranes has drawn keen attention to improve the power density for salinity gradient power based on pressure-retarded osmosis. This study has interests on electrospun nanofiber-based support layers, and the effects of its open pore sizes are attractively stated. To control the open pore size, a counter charge deposition method was introduced. To retain the open pore size, all the nanofibers were interconnected by a post co-solvent treatment technology. For a thin film composite membrane, an interfacial polymerization was used to fabricate a polyamide active layer on the electrospun nanofiber-based support layers. It was found that although the maximum power density achieved with an open pore size of 2.4 μm2 was 0.14 W/m2, it increased significantly up to 9.5 W/m2 when the pore size was reduced to 0.65 μm2. The cause is the salt flux which increases with increasing the open pore sizes under applied pressures.

Morphology control of eprosartan crystals via polymer-directed crystallization

Improving the stability, processability and bioavailability of drug crystals is important during the development of most drugs. In traditional crystal engineering, different crystallization conditions are used to tailor the properties of crystals, often improving one property at the cost of another, or simply optimizing both properties. The influence of soluble polymers on the particle morphology of crystals during the crystallization of eprosartan was investigated to explore the possibility of improving the properties of the drug crystals. The presence of polyethylenimine (PEI) during the crystallization of eprosartan induced the self-assembly of small primary crystals into larger aggregates without changing the crystal polymorph. In particular, spherical aggregates of an ordered structure were obtained when eprosartan was crystallized by changing the pH from 12 to 4.2 in the presence of PEI. This technique of polymer-directed crystallization is promising for the property engineering of drug crystals, which has been limited by a few crystallization variables to date.

Fabrication of Asymmetric Porous Hydrophilic Nanofiber Mat Using a Co-solvent Post-treatment Technology

Nanofiber has been widely used for a variety of applications due to high mechanical strength as well as high porosity. For improvement of performance of each application, facile and cost-effect technologies have been developed to tune the structure and surface of nanofibers. In this study, asymmetric nanofiber mats were fabricated using a co-solvent post-treatment technology. First, polyethersulfone solutions of low concentrations were electrosprayed to fabricate particles, and then electrospun nanofibers were consequently deposited onto them. Using a co-solvent post-treatment technology, asymmetric porous nanofiber mats were simply fabricated by enhancing the adhesion among all the interconnection points among fibers as well as particles. Especially, when Pluronic F127 was dissolved in the co-solvent solution, it was facile fabricating asymmetric porous nanofiber mats with hydrophilic surface modification.

Polymer-directed Crystallization of Sibutramine using Cellulose Derivatives

Nonclassical pathway of crystallization has been utilized to modify the properties and morphologies of inorganic and organic/inorganic materials. In here, the polymer-directed crystallization method has been applied to the pharmaceutical active ingredient to assess the applicability for as a particle engineering tool. The polymer-directed crystallization was successful to modifying the crystal size, habit and morphology, but it was not effective to discover the novel polymorphs of Sibutramine (SB). SB was selected as a model drug and polyacrylic acid (PAA), polyethylene imine (PEI) and chitosan (CHI) were added as a crystallization pathway modifier. SB was crystallized via drowning crystallization using methanol or ethanol as a solvent and water as a non-solvent. The significant interactions between polymer and the drug were confirmed by measuring the solubility of the drug in presence of polymer during the crystallization. The crystal forms of SB are characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and optical microscope (OM). The polymer-directed crystallization seems to be able to modify the crystal properties of pharmaceutical active ingredient, which is critical in determining the bioavailability, processability, and stability.