Kevin S. Jack

Improving Adsorbent Properties of Cage-like Ordered Amine Functionalized Mesoporous Silica with Very Large Pores for Bioadsorption

In this paper, we report the successful synthesis of amine-functionalized FDU-12-type mesoporous silica with a very large pore (30.2 nm) and a highly ordered mesostructure by using 3-aminopropyltriethoxysilane (APTES) as an organosilane source. Small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) measurements confirmed that the materials possessed a face-centered cubic (space group Fm3m) mesostructure. Different techniques were used to obtain a significant pore and entrance size enlargement: low synthesis temperature and high hydrothermal treatment temperature. The amount of amine organosilane influenced the mesostructure of the mesoporous silica. It was found that the addition of inorganic salt (KCl) could help to maintain an ordered structure of the large pore mesoporous material. X-ray photoelectron spectroscopy (XPS), solid-state magic-angle spinning (MAS) 13C nuclear magnetic resonance (NMR) and thermogravimetric analysis (TGA) verified the incorporation of amine functional groups on the surface of the materials. The addition of amine organosilane extended the synthesis temperature domain of ordered FDU-12 materials. The amine functional group significantly enhanced the adsorption capacity of the mesoporous materials, e.g., the amine functionalized mesoporous silica had 8-fold higher bovine serum albumin (BSA) adsorption capacity than that of the unfunctionalized one. It also had 2 times higher adsorption capacity for large cellulase enzymes. The amine functional group introduced positively charged groups on the surface of the mesoporous silica, which created strong electrostatic interactions between the protein and the silica.

The fabrication and characterization of biodegradable HA/PHBV nanoparticle-polymer composite scaffolds

This study reports the fabrication and characterization of nano-sized hydroxyapatite (HA)/poly(hydroxyabutyrate-co-hydroxyvalerate) (PHBV) polymer composite scaffolds with high porosity and controlled pore architectures. These scaffolds were prepared using a modified thermally induced phase-separation technique. This investigation focuses on the effect of fabrication conditions on the overall pore architecture of the scaffolds and the dispersion of HA nanocrystals within the composite scaffolds. The morphologies, mechanical properties and in vitro bioactivity of the composite scaffolds were investigated. It was noted that the pore architectures could be manipulated by varying phase-separation parameters. The HA particles were dispersed in the pore walls of the scaffolds and were well bonded to the polymer. The introduction of HA greatly increased the stiffness and strength, and improved the in vitro bioactivity of the scaffolds. The results suggest these newly developed nano-HA/PHBV composite scaffolds may serve as an effective three-dimensional substrate in bone tissue engineering.

One-pot synthesis of block copolymers in supercritical carbon dioxide: a simple versatile route to nanostructured microparticles.

We present a one-pot synthesis for well-defined nanostructured polymeric microparticles formed from block copolymers that could easily be adapted to commercial scale. We have utilized reversible addition-fragmentation chain transfer (RAFT) polymerization to prepare block copolymers in a dispersion polymerization in supercritical carbon dioxide, an efficient process which uses no additional solvents and hence is environmentally acceptable. We demonstrate that a wide range of monomer types, including methacrylates, acrylamides, and styrenics, can be utilized leading to block copolymer materials that are amphiphilic (e.g., poly(methyl methacrylate)-b-poly(N,N-dimethylacrylamide)) and/or mechanically diverse (e.g., poly(methyl methacrylate)-b-poly(N,N-dimethylaminoethylmethacrylate)). Interrogation of the internal structure of the microparticles reveals an array of nanoscale morphologies, including multilayered, curved cylindrical, and spherical domains. Surprisingly, control can also be exerted by changing the chemical nature of the constituent blocks and it is clear that selective CO(2) sorption must strongly influence the block copolymer phase behavior, resulting in kinetically trapped morphologies that are different from those conventionally observed for block copolymer thin films formed in absence of CO(2).

On the absolute calibration of bench-top small-angle X-ray scattering instruments: a comparison of different standard methods

Absolute calibration relates the measured (arbitrary) intensity to the differential scattering cross section of the sample, which contains all of the quantitative information specific to the material. The importance of absolute calibration in small-angle scattering experiments has long been recognized. This work details the absolute calibration procedure of a small-angle X-ray scattering instrument from Bruker AXS. The absolute calibration presented here was achieved by using a number of different types of primary and secondary standards. The samples were: a glassy carbon specimen, which had been independently calibrated from neutron radiation; a range of pure liquids, which can be used as primary standards as their differential scattering cross section is directly related to their isothermal compressibility; and a suspension of monodisperse silica particles for which the differential scattering cross section is obtained from Porods law. Good agreement was obtained between the different standard samples, provided that care was taken to obtain significant signal averaging and all sources of background scattering were accounted for. The specimen best suited for routine calibration was the glassy carbon sample, due to its relatively intense scattering and stability over time; however, initial calibration from a primary source is necessary. Pure liquids can be used as primary calibration standards, but the measurements take significantly longer and are, therefore, less suited for frequent use.

Control of the orientation of symmetric poly(styrene)-block-poly(D,L-lactide) block copolymers using statistical copolymers of dissimilar composition

The interactions of block copolymers with surfaces can be controlled by coating those surfaces with appropriate statistical copolymers. Usually, a statistical copolymer comprised of monomer units identical to those of the block copolymer is used; that is, typically a poly(styrene)-stat-poly(methyl methacrylate) (PS-stat-PMMA) is used to direct the alignment of poly(styrene)-block-poly(methyl methacrylate) (PS-block-PMMA), and poly(styrene)-stat-poly(2-vinylpyridine) (PS-stat-P2VP) has been used for poly(styrene)-block-poly(2-vinylpyridine) (PS-block-P2VP). Reports of controlling the orientation of block copolymers with statistical copolymers with a dissimilar composition are limited. Here, we demonstrate that this method can be further extended to show that PS-stat-PMMA can be used to control the wetting properties of poly(styrene)-block-poly(D,L-lactide) (PS-block-PDLA). Surfaces were modified with a series of cross-linked PS-stat-PMMA-stat-glycidyl methacrylate terpolymers, and the surface chemistries and energies were assessed using angle-dependent X-ray photoelectron spectroscopy and the two-liquid harmonic method, respectively. From these experiments, an expected neutral compositional window was identified for symmetrical PS-block-PDLA. Moreover, high-resolution SEM, AD-XPS, and grazing-incidence SAXS measurements were used to evaluate the morphology of PS-block-PDLA as a function of the surface composition of the underlying cross-linked copolymer films, and the neutral composition was found to range from 32 to 38 mol % of PS, in the bulk polymer. Ultimately, we demonstrated the determination of nonpreferential surface compositions that allow the self-assembly of lamellae with sizes in the sub-10 nm regime that are oriented perpendicular to the substrate. These findings have important implications for the use of PS-block-PDLA block copolymers in directed self-assembly, most specifically in advanced lithographic processes.

Protein delivery using nanoparticles based on microemulsions with different structure-types

Poly(alkylcyanoacrylate) nanoparticles based on microemulsions with different structure-types and containing insulin as a model protein were prepared and characterised in this study. A phase diagram of the pseudoternary system isopropyl myristate, caprylocaproyl macrogolglycerides, polyglycerol oleate and water was established. All compounds used in this study were pharmaceutically acceptable and biocompatible. The area in the phase diagram containing optically isotropic, monophasic systems was designated as the microemulsion region. Systems within this region were identified as water-in-oil (w/o), bicontinuous and oil-in-water (o/w) microemulsions with viscosity, conductivity, differential scanning calorimetry and self-diffusion NMR. The size distributions of the resulting nanoparticles prepared by interfacial polymerisation from selected microemulsions using ethyl (2) cyanoacrylate and butyl (2) cyanoacrylate were unimodal but template- and monomer-dependent and ranged from 160 to 400 nm. Entrapment and release of insulin were also studied. Entrapment ranged from 11.5 to 20.9% and a near zero-order release was observed after an initial burst. Release of insulin was monitored for 6h. Insulin-loaded nanoparticles were 320-350 nm in size. The microemulsion-structure was retained during the polymerisation process as determined by NMR. This study showed that these microemulsions with flexible formulation possibilities for the solubilisation of peptides and proteins depending on their microstructure could serve well as a platform for designing encapsulation processes for oral delivery of insulin.

Phosphorylation of alginate: Synthesis, characterization, and evaluation of in vitro mineralization capacity

Phosphorylation of alginate was achieved using a heterogeneous urea/phosphate reaction. The degree and stereoselectivity of phosphorylation as well as the effects on the physical properties of the polysaccharide were investigated by Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectroscopies, inductively coupled plasma optical-emission spectroscopy (ICP-OES), and size exclusion chromatography (SEC). Multidimensional NMR studies of the phosporylated alginate revealed that phosphorylation of the M residues occurred predominantly at the C3 (equatorial) carbon of the polysaccharide ring. In addition, a more comprehensive assignment of the (1)H NMR spectrum of alginate, compared with those previously reported in the literature, is provided here. Hydrogel materials were formed from ionically cross-linked blends of phosphorylated alginate and alginate. These blended hydrogels showed an enhanced resistance to degradation by chelating agents compared with cross-linked alginate hydrogels and a reduction in their mineralization potential.

Understanding the roles of nanoparticle dispersion and polymer crystallinity in controlling the mechanical properties of HA/PHBV nanocomposites

Nano-sized hydroxyapatite (HA) particles stabilized using poly(acrylic acid) (PAA) as a dispersing agent, and sonic energy to further increase dispersion, were blended with poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) using a precipitation/gelation method to produce HA/PHBV nanocomposites with up to 16% by weight of HA content. The level of HA nanoparticle dispersion was monitored in the precursor dispersions prior to composite production and in the nanocomposites by a range of techniques including visual observation, turbidity measurements and electron microscopy, and the roles of the dispersing agent and the sonic energy in controlling the dispersion of HA particles in both the precursor dispersions and the final composites as well as their effects on the compressive strength and Youngs modulus were investigated. It was found that HA suspensions treated with both PAA and sonic energy possessed significantly better colloidal stability compared to untreated suspensions or suspensions treated with either PAA or sonic energy. This, in turn, resulted in better dispersion of HA nanoparticles in the composites and higher compressive moduli as a function of the particle loading. This enhancement in stiffness of the composites was attributed primarily to the increased surface area of the HA filler in the more highly dispersed samples, but also to an observed increase in the crystalline content achievable after annealing of the samples. It is proposed that this increase in crystallinity is due to the more highly dispersed particles acting as nucleation sites for the crystallization of the PHBV at the particle interface, which, in turn, leads to enhancement of the bonding between the matrix and filler.

High Curie temperature Bi1.85Mn0.15Te3 nanoplates

Bi(1.85)Mn(0.15)Te(3) hexagonal nanoplates with a width of ~200 nm and a thickness of ~20 nm were synthesized using a solvothermal method. According to the structural characterization and compositional analysis, the Mn(2+) and Mn(3+) ions were found to substitute Bi(3+) ions in the lattice. High-level Mn doping induces significant lattice distortion and decreases the crystal lattice by 1.07% in the a axis and 3.18% in the c axis. A high ferromagnetic state with a Curie temperature of ~45 K is observed in these nanoplates due to Mn(2+) and Mn(3+) ion doping, which is a significant progress in the field of electronics and spintronics.

EUVL compatible LER solutions using functional block copolymers

Directed self assembly (DSA) of block copolymers is an emerging technology for achieving sub-lithographic resolution. We investigate the directed self assembly of two systems, polystyrene-block-poly-DL-lactic acid (PS-b-PDLA) and PSb- poly(methyl methacrylate). For the PS-b-PDLA system we use an open source EUVL resist and a commerciallyavailable underlayer to prepare templates for DSA. We investigate the morphology of the phase separated domains and compare the LER of the resist and the PS-PDLA interface. For the PS-b-PMMA system we again use an open source resist, but the annealing conditions in this case require crosslinking of the resist prior to deposition of the block copolymer. For this system we also investigate the morphology of the phase separated domains and compare the LER of the resist and the PS-PMMA interface.