Von Cresce - Academia.edu (original) (raw)

Papers by Von Cresce

Applied Physics Letters, 2001

... Phys. 71, 5107 (1992). V. Seshu Bai, SM Bhagat, R. Krishnan, and M. Seddat, J. Magn. Magn. Ma... more ... Phys. 71, 5107 (1992). V. Seshu Bai, SM Bhagat, R. Krishnan, and M. Seddat, J. Magn. Magn. Mater. 147, 97 (1995). JR Cullen, in Handbook of Science and Technology, edited by KHJ Buschow (VCH, Weinheim, 1990), Chap. 16, Vol. III B. ...

Langmuir, 2010

Efforts were made to differentiate the contributions to the so-called "ion transfer" barrier at t... more Efforts were made to differentiate the contributions to the so-called "ion transfer" barrier at the electrolyte/graphite junction from two distinct processes: (1) desolvation of Li þ before it enters graphene interlayer and (2) the subsequent migration of bare Li þ through the ad hoc interphase. By leveraging a scenario where no substantial interphase was formed on Li þ intercalation hosts, we were able to quantify the distribution of "ion transfer" activation energy between these two interfacial processes and hence identify the desolvation process of Li þ as the major energy-consuming step. The result confirmed the earlier belief that the rate-determining step in the charging of a graphitic anode in Li þ intercalation chemistry relates to the stripping of solvation sheath of Li þ , which is closely interwoven with the interphasial resistance to Li þ migration.

The study of interfaces is important in understanding biological interactions, including cellular... more The study of interfaces is important in understanding biological interactions, including cellular signaling and virus infection. This thesis is an original effort to examine the interaction between a block copolymer and both a protein and a virus. Block copolymers intrinsically form nanometer-scale structures over large areas without expensive processing, making them ideal for the synthesis of the nanopatterned surfaces used in this study. The geometry of these nanostructures can be easily tuned for different applications by altering the block ratio and composition of the block copolymer. Block copolymers can be used for controlled uptake of metal ions, where one block selectively binds metal ions while the other does not. 5-norbornene-2,3-dicarboxylic acid is synthesized through ring-opening metathesis polymerization. It formed spherical domains with spheres approximately 30 nm in diameter, and these spheres were then subsequently loaded with nickel ion. This norbornene block copolymer was tested for its ability to bind histidine-tagged green fluorescent protein (hisGFP), and it was found that the nickel-loaded copolymer was able to retain hisGFP through chelation between the histidine tag and the metal-containing portions of the copolymer surface. Poly(styrene-b-4-vinylpyridine) (PS/P4VP) was also loaded with nickel, forming a cylindrical microstructure. The binding of Tobacco mosaic virus and Tobacco necrosis virus was tested through Tween 20 detergent washes. Electron microscopy allowed for observation of both block copolymer nanostructures and virus particles. Results showed that Tween washes could not remove bound Tobacco mosaic virus from the surface of PS/P4VP. It was also seen that the size and tunability of block copolymers and the lack of processing needed to attain different structures makes them attractive for many applications, including microfluidic devices, surfaces to influence cellular signaling and growth, and as a nanopatterning surface for organized adhesion.

Acta Biomaterialia, 2009

This paper examines the interaction between a block copolymer and a virus. A poly(styrene-b-4-vin... more This paper examines the interaction between a block copolymer and a virus. A poly(styrene-b-4-vinylpyridine) block copolymer was loaded with nickel, and cast from a selective solvent mixture to form a cylindrical microstructure (PS/P4VP-Ni). The nickel ions were confined within the P4VP block of the copolymer. The binding of tobacco mosaic virus (TMV) and tobacco necrosis virus on microphase-separated PS/P4VP-Ni was examined. A staining technique was developed to simultaneously visualize virus and block copolymer structure by transmission electron microscopy. Electron microscopy revealed virus particles associated with block copolymer microphase-separated domains, even after extensive washes with Tween. In contrast, virus associated with PS/P4VP block copolymers lacking Ni were readily removed by Tween. The cylinder long axis of the microstructure was oriented using a hot press and a cooled channel die for quenching, resulting in PS/P4VP cylinders that had a strong anisotropic directional preference. When exposed to flowing solutions of TMV, the PS/P4VP-Ni surface exhibited an ability to retain TMV in a partially aligned state, when the direction of flow coincided with the long axis of the PS/P4VP-Ni cylinders. These results suggest that Coulombic interactions provide a robust means for the binding of virus particles to block copolymer surfaces.

IEEE Transactions on Magnetics, 2001

We report magnetic resonance results on (0.3-8 μm) films of c-axis oriented barium ferrite grown ... more We report magnetic resonance results on (0.3-8 μm) films of c-axis oriented barium ferrite grown by pulsed laser deposition on sapphire substrates. By optimizing the growth and annealing parameters, we have observed numerous (up to 25) spin wave resonance modes as well as nearly intrinsic ferromagnetic resonance linewidth of 23 Oe at 58 GHz, when the applied field is parallel

The formation of self-assembled ZnO nanoclusters on Si and SiO2/Si surfaces, using diblock copoly... more The formation of self-assembled ZnO nanoclusters on Si and SiO2/Si surfaces, using diblock copolymers and wet chemical processing compatible with semiconductor manufacturing, is reported. The diblock copolymers, consisting of a majority polymer (norbornene) and a minority polymer (norbornene-dicarboxcylic acid), were synthesized with a block repeat unit ratio of 400 (majority block) to 50 (minority block), to obtain spherical microphase separation for the minority block and hence a spherical morphology for the metal oxide nanoclusters. The self-assembly of the inorganic nanoparticles was achieved at room temperature in the liquid phase by incorporating ZnCl2 precursor dopant that associates with the minority polymer, then solidifying the copolymer on the semiconductor surface, and using wet chemical processing to substitute the chlorine atoms with oxygen, and form ZnO. Fourier transform infrared (FTIR) and X-ray photoemission (XPS) spectroscopy confirmed the association of the ZnCl2 with the minority block and the formation of ZnO after polymer treatment with the wet chemical process. Transmission electron microscopy (TEM) showed spherical morphology of the ZnO nanoclusters as targeted, and a relatively narrow size distribution ranging between 7 and 15 nm. The doped diblock copolymer was spin-cast on Si and SiO2/Si wafers, and its photolithographic patterning, metallization, and reactive ion etching using CF4/O2 were developed

Macromolecules, 2006

Exploiting the microphase separation of block copolymers is a facile method of synthesizing nanom... more Exploiting the microphase separation of block copolymers is a facile method of synthesizing nanometer-sized structures. The interactions of recombinant proteins with block copolymer surfaces displaying nanoscale order could be used to investigate intercellular signaling and for creating arrays of nanoreactors for lab-on-a-chip applications. A block copolymer of norbornene and norbornenedicarboxylic acid (NOR/NORCOOH) was synthesized and its hydrophilic block loaded with metal ions. Protein binding ability was examined by exposing the metal-loaded copolymer film to histidine-tagged green fluorescent protein (hisGFP), washing with detergent to remove nonspecifically bound protein, and measuring the surface fluorescence. Results showed that nickel ions on the copolymer surface had superior hisGFP binding ability to copper and iron. Further investigation comparing the binding of hisGFP and GFP lacking the histidine tag showed that the nickel templated block copolymer was binding only hisGFP. It was concluded that the chelation between nickel on the polymer surface and histidine groups on the protein is the only significant binding force in the hisGFP-copolymer system.

Molecular Pharmaceutics, 2008

Transient expression levels, vector dissemination and toxicities associated with adenoviral vecto... more Transient expression levels, vector dissemination and toxicities associated with adenoviral vectors have prompted the usage of matrices for localized and controlled gene delivery. Two recombinant silk-elastinlike protein polymer analogues, SELP-47K and SELP-415K, consisting of different lengths and ratios of silk and elastin units, were previously shown to be injectable hydrogels capable of matrix-mediated controlled adenoviral gene delivery. Reported here is a study of spatiotemporal control over adenoviral gene expression with these SELP analogues in a human tumor xenograft model of head and neck cancer using whole animal imaging. Real-time images of viral expression levels indicate that polymer concentration and polymer structure are predominant factors that affect viral release and, thus, viral transfection. Decrease in polymer concentration and increase in polymer elastin content results in greater release, probably due to changes in the network structure of the hydrogel. To better understand this relationship, macro- and microstructural properties of the hydrogels were analyzed using dynamic mechanical analysis (DMA) and transmission electron microscopy (TEM). The results confirm that the concentration and the elastin content of the protein polymer affect the pore size of the hydrogel by changing the physical constraints of the SELP fibril network and the degree of hydration of the SELP fibrils. The potential to modulate viral release using SELP hydrogel delivery vehicles that can be injected intratumorally by minimally invasive techniques holds significant promise for the delivery of therapeutic viruses.

Polymer, 2003

Ring opening metathesis polymerization (ROMP) with Grubbs's catalyst was used to synthesize narro... more Ring opening metathesis polymerization (ROMP) with Grubbs's catalyst was used to synthesize narrow polydispersity (PDI)diblock copolymers of norbornene (NOR) and norbornenedicarboxylic acid (NORCOOH). Norbornene (NOR) and 5-norbornene-2,3,-dicarboxylic acid bis trimethylsilyl ester (NORCOOTMS) were used as precursor monomers for thepolymerization. [NORCOOTMS]m/[NOR]n was converted to [NORCOOH]m/[NOR]n by precipitating the polymer solution in a mixture of methanol, acetic acid, and water. The conversion to 5-norbornene-2,3-dicarboxylic acid was evidenced by 1H NMR. By polymerizing the bulkier NORCOOTMS precursor monomer first, lower PDIs were observed for the completed [NORCOOH]m/[NOR]n block copolymers in comparison to copolymers where the NOR block was polymerized first. The PDI of the diblock copolymers of [NORCOOH]m/[NOR]n decreased with increase in block length ofthe precursor NORCOOTMS monomer. This study shows that the PDI can be controlled by selecting a monomer with appropriate functionality as the starting block of the block copolymer to control the rate of propagation, Rp, as an alternative of using additives to change the reactivity of the catalyst.

Polymer, 2009

Silk–elastinlike protein polymer, SELP-815K, with eight silk and fifteen elastin units and a lysi... more Silk–elastinlike protein polymer, SELP-815K, with eight silk and fifteen elastin units and a lysine (K) modified elastin, was genetically engineered with longer silk and elastin units compared to existing hydrogel forming analogs (SELP-415K and SELP-47K). Hydrogels of the three SELPs (with similar MWs) were investigated for their structure–function relationships. Results indicate that equilibrium swelling ratio in these hydrogels is a function of polymer structure, concentration, cure time and ionic strength of media. Swelling was not influenced by the changes in pH. Storage moduli observed by dynamic mechanical analysis and the Debye–Bueche correlation length obtained from small-angle neutron scattering provided structural insight that suggests the cross-linking densities in these hydrogels follow the order SELP-47K > SELP-815K > SELP-415K. These results allude to the importance of the length of elastin blocks in governing the spacing of the cross-linked hydrogel network and that of silk in governing the stiffness of their 3-dimensional structures.

Solid-state Electronics, 2002

The formation of self-assembled ZnO nanoclusters using diblock copolymers, is reported. The diblo... more The formation of self-assembled ZnO nanoclusters using diblock copolymers, is reported. The diblock copolymers, consisting of a majority polymer (norbornene) and a minority polymer (norbornene-dicarboxcylic acid), were synthesized with a block repeat unit ratio of 400/50, to obtain spherical microphase separation and hence a spherical morphology for the metal oxide nanoclusters. The self-assembly of the inorganic nanoparticles was achieved at room temperature in the liquid phase, using ZnCl 2 precursor dopant and wet chemical processing compatible with semiconductor manufacturing to convert to ZnO. FTIR and XPS spectroscopy, confirmed the association of the ZnCl 2 precursor with the minority block and the formation of ZnO, while TEM showed the spherical morphology of ZnO nanoparticles as targeted, and a relatively narrow size distribution ranging between 7 and 15 nm.