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Confined crystallization of drug in directionally freeze-dried water-soluble template
Lee, Hyeseung,Lee, Jonghwi Elsevier 2015 Journal of industrial and engineering chemistry Vol.21 No.-
<P><B>Abstract</B></P> <P>The applicability of confined crystallization is limited by the use of extra template materials unsuitable for oral dosage forms. In consideration of this limitation, mannitol was processed into a template with well controlled pores. This template was used for the subsequent confined crystallization of a model drug, resulting in drug/mannitol composite powders processable into the common operations of oral solid dosage forms. The confined crystallization produced a significant melting point depression, caused by a significant particle size reduction, but did not alter the crystal polymorphism. The <I>in vitro</I> release of drug was significantly improved by the confined crystallization.</P>
Anisometric nanocomposite hydrogels with temperature responsive compartments
Lee, Sona,Kim, Hyun Jun,Chang, Seung Hwan,Lee, Jonghwi The Royal Society of Chemistry 2013 SOFT MATTER Vol.9 No.2
<P>Recently, anisometric structures, which are popular in nature but uncommon in artificial materials, have been actively investigated for the development of novel materials designed for sensors, optical systems, scaffolds, <I>etc.</I> In this study we investigated the hypothesis that the symmetry of two-compartment hydrogels influences their temperature responsive behavior and drug diffusivity. Composite hydrogels with isometric and anisometric compartments were prepared using poly(<I>N</I>-isopropylacrylamide), poly(acrylamide), and nanoclay. The anisometric hydrogel showed a markedly smaller volume transition and equilibrium swelling ratio than its isometric counterpart, possibly because of more restriction from the two-compartment structure. Furthermore, water retention and the release of cilostazol were significantly sustained in the case of the anisometric hydrogel. By incorporating Ag nanoparticles into one compartment, an IR responsive transition was achieved, which showed the consistent effect of the anisometric structure. Finite element analysis further confirmed the difference found in the experimental results by presenting a prevailing von Mises stress in the anisometric case. This study provides a novel engineering strategy for hydrogel properties and a fundamental understanding valuable for designing anisometric hydrogel materials.</P> <P>Graphic Abstract</P><P>Hydrogels with temperature responsive compartments were prepared, the structure of which was designed to be either anisometric or isometric. The anisometric hydrogel experienced more restriction from the misfit of the two compartments, resulting in highly concentrated shear stress, sustained drug release and a lower volume transition. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c2sm26979a'> </P>
Lee, Min Kyung,Rich, Max H.,Shkumatov, Artem,Jeong, Jae Hyun,Boppart, Marni D.,Bashir, Rashid,Gillette, Martha U.,Lee, Jonghwi,Kong, Hyunjoon Wiley (John WileySons) 2015 Advanced Healthcare Materials Vol.4 No.2
<P>This study demonstrates that a new method to align microparticles releasing bioactive molecules in microchannels of a hydrogel allows the guiding of growth direction and spacing of vascular networks.</P>
Cryoprotectants for freeze drying of drug nano-suspensions: Effect of freezing rate
Lee, Min Kyung,Kim, Min Young,Kim, Sujung,Lee, Jonghwi Wiley Subscription Services, Inc., A Wiley Company 2009 Journal of Pharmaceutical Sciences Vol.98 No.12
<P>Drug nanoparticles are often prepared in a liquid medium, and a drying method such as freeze drying is used to convert them to an oral solid dosage form. When the dried form is reconstituted in an aqueous system, it may be redispersed to achieve its original particle size. The redispersibility of dried nanoparticles depends on the parameters of the freeze drying process. In this study, an apparatus with a freezing rate gradient was used to systematically investigate the effect of cryoprotectants on the redispersibility of nanoparticles as a function of freezing rate. Sucrose, lactose, mannitol, and polyethylene glycol were used as cryoprotectants for a naproxen nano-suspension. A fast freezing rate and a high cryoprotectant concentration were generally favored. However, under certain conditions, a slower freezing rate resulted in better redispersibility. This is probably because slow freezing can produce a more cryo-concentrated liquid phase, and the concentrated cryoprotectant in the liquid phase can more effectively protect the nanoparticles. An irreversible aggregation map was constructed as a function of the freezing rate and the cryoprotectant concentration, and shows both the favorable and unfavorable effects of cryoprotectants. © 2009 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 98:4808–4817, 2009</P>
A nano-frost array technique to prepare nanoporous PVDF membranes.
Lee, Min Kyung,Lee, Jonghwi RSC Pub 2014 Nanoscale Vol.6 No.15
<P>Frost, the solid deposition of water vapor from humid air, forms on the surface of a solid substrate when its temperature drops below the freezing point of water. In this study, we demonstrate how this natural phenomenon can be applied to develop novel nanoporous materials. The solvent annealing of polyvinylidene fluoride (PVDF) infiltrated into nanopores induced template-directed dewetting thus preparing nanoembossing films. Then, water nanodroplets formed on the cold polymer nanopatterned surfaces following the embossing patterns, similar to dew formation on the ground. Subsequently, the nanodroplets were frozen and then removed by freeze-drying. This nano-frost array technique produced nanoporous PVDF membranes with an average thickness of 250 ( 48) nm. It was revealed that the nanopatterned surface formed by solvent annealing played an important role in achieving a nano-frost array with an adjustable size. Additionally, the freezing process led to significant changes of the PVDF crystallinity and polymorphism. Our results prove that the nano-frost array technique can be broadly used to design ordered nanoporous structures and provide new prospects in nanomaterial fields.</P>