Jeong Ho Chang

In-situ synthesis of reactive hydroxyapatite nano-crystals for a novel approach of surface grafting polymerization

A novel approach to surface modification of hydroxyapatite (HAp) nano-crystals was described based on in-situ synthesis of surface thiol-functionalized HAp (HAp-SH) and subsequent grafting polymerization of ethylene glycol methacrylate phosphate (EGMP). Energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) analyses showed that thiol groups were introduced on HAp surfaces by adding 3-mercaptopropionic acid during hydrothermal synthesis of HAp nano-crystals. The radical chain transfer to surface thiol groups generated the sulfur-centered radicals on HAp nano-surfaces, which initiated the surface grafting polymerization of EGMP. Fourier transform infrared (FT-IR) spectroscopy and powder X-ray diffraction (XRD) analyses confirmed the grafting reaction on HAp surfaces. Zeta potentials of control HAp, thiol-functionalized HAp (HAp-SH), and PolyEGMP-grafted HAp in phosphate buffered saline (PBS) solutions (pH 7.4) were negative and decreased with increasing the amount of grafted PolyEGMP. TEM measurements and time-dependent phase monitoring suggested that the colloidal stability of PolyEGMP-grafted HAp over synthesized HAp nano-crystals in water dramatically increased without inter-crystal aggregation.

The Core–Shell Approach to Formation of Ordered Nanoporous Materials

This work describes a novel core-shell approach for the preparation of ordered nanoporous ceramic materials that involve a self-assembly process at the molecular level using MPEG-b-PDLLA bloack copolymers. This approach provides for rapid self-assembly and structural reorganization at room temperature. Selected MPEG-b-PDLLA block copolymers were synthesized with systematic variation of the chain lengths of the resident hydrophilic and hydrophobic blocks. This allows the micelle size to be systematically varied. Results from this work are used to understand the formation mechanism of nanoporous structures in which the pore size and wall thickness are closely dependent on the size of hydrophobic cores and hydrophilic shells of the block copolymer templates. The core-shell mechanism for nanoporous structure evolution is based on the size and contrasting micellar packing arrangements that are controlled by the copolymer.

Sustained drug release on temperature-responsive poly(N-isopropylacrylamide)-integrated hydroxyapatite

A hybrid temperature-responsive hydroxyapatite-poly(N-isopropylacrylamide) (HAP-PNIPAAm) gel has been synthesized by the interpenetration of PNIPAAm into a sintered HAP disk through a radical-initiated polymerization of NIPAAm monomers under N2 atmosphere, and shows sustained positive thermo-responsive drug release profile over a month at PBS buffer.

Functional scaffolds of bicontinuous, thermoresponsive L3-phase silica/hydroxyapatite nanocomposites

Silicified L3-poly(N-isopropylacrylamide)/hydroxyapatite nanocomposites have been prepared by the integration of a thermosensitive polymer and heterogeneous continuity in a 3-D interconnected porous structure for highly controlled drug release without initial burst release during step-wise temperature changes, and the in-vitro cytotoxicity test for biocompatibility is demonstrated.

Morphology control of hierarchically ordered ceramic materials prepared by surfactant-directed sol-gel mineralization of wood cellular structures

Abstract We here report the synthesis of ordered ceramic materials with hierarchy produced by an in-situ mineralization of ordered wood cellular structures with surfactant-templated sol-gel at different pHs. At low pH, a silicic acid is coated onto inner surface of wood cellular structure and it penetrates into pores left, where degraded lignin and hemicellulose are leached out, to form a positive replica, while at high pH the precipitating silica particles due to fast condensation clog the cells and pit structures to form a negative replica of wood. The calcined monoliths produced in different pHs contain ordered wood cellular structures, multi-layered cell walls, pits, vessels well-preserved with positive or negative contrasts, respectively. The surfactant-templated mineralization produces ordered hexagonal mesopores with 2nm in the cell walls after calcination.

Strategies for the Design and Synthesis of Hybrid Multifunctional Nanoporous Materials

This chapter discusses the design and synthesis of multifunctional active sites in ordered nanoporous materials. First, the formation of homogeneous molecular monolayer structures is described. Hybrid nanoporous materials modified with functional molecules and groups are widely investigated for many applications. The molecular chain conformations depend on the surface roughness of the pore channels. A step-wise growth model has been proposed to account for the step-wise pore dimension change. This paper also discusses the use of supercritical fluids as delivery media to improve the effectiveness of surface functionalization. This technique has been used successfully to synthesize size-exclusive microporous acid catalysts. Finally, the formation of architectured monolayer molecular structures is discussed. The use of imprinting or lithograph techniques allows the synthesis of hierarchical porous materials with tunable size-and-shape selective microporosity.

High Throughput Magnetic Separation for Human DNA by Aminosilanized Iron Oxide Nanoparticles

This work describes the preparation of functionalized magnetic nanoparticles (MNPs) and their bioapplication to human DNA separation. Silica coated MNPs were prepared by changing the volume ratio of tetraethyl orthosilicate (TEOS) for controlled coating thickness on the original nanoparticle of MNPs. The sol-gel process in silica coating on MNPs surface was adapted for relatively mild reaction condition, low-cost, and surfactant-free. And then amino functionalized magnetic nanoparticles were synthesized using amine groups as surface modifiers. The result of adsorption efficiency for human DNA with amino-functionalized silica coated MNPs was calculated as a function of the number of amine groups.

The Selective Protein Separations with Polyaminofunctionality on Controlled Silica Coating-Layers of Magnetic Nanoparticles

This work reported the development of the high throughput protein separation process with molecularly assembled silica-coated magnetic nanoparticles as a function of amino group numbers such as mono-, di-, and tri-aminofunctionality, in which the range of silica coating thicknesses were optimized to be interacted with protein. The protein separation efficiency was demonstrated as a function of each aminofunctional group and the particle sizes of the silica coated magnetic nanoparticles. The particles were prepared by the chemical precipitation of Fe2+ and Fe3+ salts with a molar ratio of 1:2 under basic solution. The silica coated magnetic nanoparticles were directly produced by the sol-gel reaction of a tetraethyl orthosilicate (TEOS) precursor, in which the coating layer serves as a biocompatible and versatile group for further biomolecular functionalization. To effectively capture the proteins, silica coated magnetic nanoparticles need to be functionalized reproducibly on the silica surface, and three kinds of amino functional groups were adapted as a function of number of amine using the mono-, di-, and tri-aminopropylalkoxysilanes.

The Preparation of Bone-Mimetic Sol-Gel Nanoporous Scaffold of L3-Phase Silica/Hydroxyapatite

This work presented the highly controlled drug delivery system to achieve the suppression of the burst release at initial time and long term release of drug with cancellous bone mimetic nanoporous structures. The materials were prepared by the integration of synthesized inorganic hydroxyapatite (HA) and the hybrid gels of bicontinuous sponge-phased L 3 silicate and thermo-responsive poly(N-isopropylacrylamide) (L 3 -PNIPAm gels). The materials were designed to have the three dimensionally interconnected heterogeneous porosity of macro- and mesoporosity, in which the HA has the macroporosity of 150 μm to be impregnated the drug into the pores and the L 3 -PNIPAm gels have mesoporosity of 5 nm to regulate the temperature sensitive drug-release through the pore channels and polymeric network, respectively. Consequently, these bone-mimetic system gave the highly long term drug release over the 60 days with suppressing the burst release and was able to control the releasing rate per time by the change of the HA and PNIPAm composition ratios.

Functional bone-mimetic scaffolds of bicontinuous, thermo-responsive L3-phase silica/hydroxyapatite nanocomposites

This work presents the highly controlled drug delivery system free from the burst release at an initial stage and equipped with the capability of long term drug release. The nanoporous drug releasing reservoir was combined with porous body resembling cancellous bone. The materials were prepared by the integration of synthesized inorganic hydroxyapatite (HA) and the hybrid gels of bicontinuous sponge-phased L3 silicate and thermo-responsive poly(N-isopropylacrylamide) (L3-PNIPAm gels). The materials were designed to have the three dimensionally interconnected heterogeneous porosity of macro- and mesoporosity, in which the HA has the macroporosity of 150μm to be impregnated the drug into the pores and the L3-PNIPAm gels have mesoporosity of 5 nm to regulate the temperature sensitive drug-release through the pore channels and polymeric network, respectively. Consequently, this bone-mimetic system gave the highly long term drug release over the 60 days without the burst release. The release rate could be controlled with the change of the HA and PNIPAm composition ratios. The structural characterization was achieved by TEM, SEM, XRD, Micro-Raman spectroscopy, BET, and the direct contact cytotoxicity test was also described.