ABSTRACT Cell adhesion to a biomaterial surface depends on surface topography and functionality. ... more ABSTRACT Cell adhesion to a biomaterial surface depends on surface topography and functionality. We have investigated osteoblast-like cell attachment, spreading, function, and adhesion on model silicon oxide and silicone surfaces by immobilizing RGD, the well-know cell-binding domain, via aminopropyltriethoxysilane (APTS) linkers. After surface characterization, cells are seeded on control, APTS and RGD-APTS surfaces and incubated in a serum free medium for up to 6 h. Whereas attachment densities are similar, cell spreading and cytoskeletal organization are enhanced on APTS-RGD relative to APTS. A significant increase in osteogenic markers supports enhanced cell function on RGD-APTS. Cells on RGD-APTS display discrete focal adhesion plaques. Adhesive strength is evaluated by a spinning-disc device. Cells seeded on silicone membranes modified by RGD attach, proliferate and display enhanced bioactivity and mineral formation. Cells exposed to 2% cyclic strain also display enhanced function.
Most research on polymer composites has focused on adding discrete inorganic nanofillers to a pol... more Most research on polymer composites has focused on adding discrete inorganic nanofillers to a polymer matrix to impart properties not found in polymers alone. However, properties such as ion conductivity and mechanical reinforcement would be greatly improved if the composite exhibited an interconnected network of inorganic and polymer phases. Here, we fabricate bicontinuous polymer-infiltrated scaffold metal (PrISM) composites by infiltrating polymer into nanoporous gold (NPG) films. Polystyrene (PS) and poly(2-vinylpyridine) (P2VP) films are infiltrated into the ∼43 nm diameter NPG pores via capillary forces during thermal annealing above the polymer glass transition temperature (Tg). The infiltration process is characterized in situ using spectroscopic ellipsometry. PS and P2VP, which have different affinities for the metal scaffold, exhibit slower segmental dynamics compared to their bulk counterparts when confined within the nanopores, as measured through Tg. The more attractive P2VP shows a 20 °C increase in Tg relative to its bulk, while PS only shows a 6 °C increase at a comparable molecular weight. The infiltrated polymer, in turn, stabilizes the gold nanopores against temporal coarsening. The broad tunability of these polymer/metal hybrids represents a unique template for designing functional network composite structures with applications ranging from flexible electronics to fuel cell membranes.
FIE '98. 28th Annual Frontiers in Education Conference. Moving from 'Teacher-Centered' to 'Learner-Centered' Education. Conference Proceedings (Cat. No.98CH36214)
ABSTRACT Nanocomposite thin films, composed of a binary polymer mixture and mobile nanoparticles,... more ABSTRACT Nanocomposite thin films, composed of a binary polymer mixture and mobile nanoparticles, undergo a unique phase evolution mechanisms incorporating wetting and phase separation. According to recent simulations, the addition of hard mobile particles may significantly impact both the dynamics and mechanism of phase separation (Ginzburg et al., PRL, 1998). Despite current technical and theoretical interests, polymer blend thin films containing nanoparticles have received little experimental interest because reliable sample preparation, such as particle dispersion, is difficult and the need for multiple techniques for following phase separation, wetting and particle partitioning. Using our prior understanding of phase evolution in PMMA/SAN thin film blends as a foundation (Wang et al., J.Chem Phys., 2000), we next investigate how the addition of spherical silica nanoparticles impacts phase dynamics. Because of the complexity of the problem, various characterization tools are utilized in this study, including optical microscopy, AFM, RBS, FReS, SEM, and TEM. The addition of particles is found to distort the phase evolution mechanism and, in agreement with simulations, retard the growth kinetics. Wetting layer growth was also influenced by the nanoparticles.
ABSTRACT Spontaneous delivery of nanoparticles towards a surface or interface is an important top... more ABSTRACT Spontaneous delivery of nanoparticles towards a surface or interface is an important topic in technologies ranging from smart materials to drug delivery. Here, we present examples of self-assembly of nanoparticles (silica, gold, and silver) in homopolymer and polymer blend (PMMA:SAN) systems that are driven by surface and interfacial interactions. For example, silica nanoparticles grafted with methyl groups partition into dPMMA-rich phases upon annealing. For a critical blend, FRES and RBS are used to show that both the dPMMA and nanoparticles, respectively, undergo surface-directed-spinodal-decomposition. The lateral pattern formation of the nanoparticles and polymer domains are observed with SFM. Experiments including PMMA-grafted Au nanoparticles will also be presented. As an alternative approach for fabricating nanoparticle composites, a silver complex is blended with SAN:PMMA and annealed to create in-situ silver nanoparticles ( 4 nm). These nanoparticles are observed to segregate to the air/polymer interface and modify the phase-separation kinetics relative to the blend without nanoparticles.
Polymer films containing nanoparticles are of technological interest because fillers can alter th... more Polymer films containing nanoparticles are of technological interest because fillers can alter the mechanical, electrical and optical properties. Recently, several numerical studies have investigated the impact of mobile nanoparticles on phase separation dynamics (see eg. Ginzburg et al., PRL (1999), Tang & Ma, JCP (2002), Laradji & MacNevin, JCP (2003)). Here, we present the first systematic experimental study of phase
The thermodynamic factors that affect the dispersion of polymer-brush grafted gold nanorods (NR) ... more The thermodynamic factors that affect the dispersion of polymer-brush grafted gold nanorods (NR) in polymer matrix films have been studied by experiment and theory. When brush and matrix have a favorable interaction, such as poly(ethylene oxide) (PEO)-NR/ poly(methyl methacrylate) (PMMA) and polystyrene (PS)-NR / poly(2,6-dimethyl-p-phenylene oxide) (PPO), nanorods are uniformly dispersed. For PEO-NRs in PMMA, the NRs are regularly spaced and well dispersed, independent of the ratio of the degree of polymerization of the matrix (P) to that of the brush (N), namely P/N. As the NR volume fraction increases, the local orientation of the nanorods increases, whereas the macroscopic orientation remains isotropic. When the brush and matrix are similar (i.e., PS-NR / PS and PEO-NR / PEO), the nanorods randomly disperse for P/N 2 (i.e., wet brush), but align side-by-side in aggregates for P/N 2. UV-visible spectroscopy and discrete dipole approximation (DDA) calculations demonstrate that sur...
ABSTRACT To fully utilize their optical absorption and polarizing abilities, the dispersion of Au... more ABSTRACT To fully utilize their optical absorption and polarizing abilities, the dispersion of Au nanorods (NRs) in a matrix, such as a polymer film, must be controlled. By functionalizing NRs with a polymer brush chemically similar to the matrix, NR dispersion and aggregation can be controlled by varying the ratio of brush (N) to matrix (P) chain length. For P/N > 2, aggregates containing mainly side-by-side arrangements of NRs are observed. Here, polystyrene (PS) functionalized Au NRs are incorporated into miscible thin film blends of PS and poly(2,6-dimethyl-p-phenylene oxide) (PPO) (P/N ≈ 30) and characterized using a combination of transmission electron microscopy (TEM) and UV–visible spectroscopy (UV–vis). As the volume fraction of PPO (PPO) increases from 0.00 to 0.50, the NRs remain mainly aggregated; however, at PPO = 0.75 they begin to disperse and finally completely disperse in a pure PPO matrix. Correspondingly, the longitudinal surface plasmon resonance peak undergoes a red shift, consistent with improved dispersion (i.e., individual NRs). A novel outcome of this work is to utilize UV–vis to detect nanometer-scale changes in Au nanorod dispersion. To understand the role of the PPO matrix chains, which favorably interact with the PS brush, self-consistent field theory (SCFT) calculations were performed to determine the brush and matrix density profiles. The brush profile is initially parabolic for PPO < 0.25 and has a thickness that is nearly the radius of gyration of the brush. However, for PPO = 0.50, the brush begins to stretch because of PPO matrix chain penetration. Finally, for PPO = 0.75 and 1.00, the brush thickness increases by about 50%. These SCFT results help interpret the dispersion of nanorods determined from TEM and UV–vis.
... Ithaca, NY 14853, USA and Dwain M. White General Electric Corporate Research and Development,... more ... Ithaca, NY 14853, USA and Dwain M. White General Electric Corporate Research and Development, Schenectady, NY 12301, USA (Received 27 ... of the Dow Chemical Company for characterizing the molecular weight of the PXE samples and D. Walsh of DuPont for making his ...
ABSTRACT Cell adhesion to a biomaterial surface depends on surface topography and functionality. ... more ABSTRACT Cell adhesion to a biomaterial surface depends on surface topography and functionality. We have investigated osteoblast-like cell attachment, spreading, function, and adhesion on model silicon oxide and silicone surfaces by immobilizing RGD, the well-know cell-binding domain, via aminopropyltriethoxysilane (APTS) linkers. After surface characterization, cells are seeded on control, APTS and RGD-APTS surfaces and incubated in a serum free medium for up to 6 h. Whereas attachment densities are similar, cell spreading and cytoskeletal organization are enhanced on APTS-RGD relative to APTS. A significant increase in osteogenic markers supports enhanced cell function on RGD-APTS. Cells on RGD-APTS display discrete focal adhesion plaques. Adhesive strength is evaluated by a spinning-disc device. Cells seeded on silicone membranes modified by RGD attach, proliferate and display enhanced bioactivity and mineral formation. Cells exposed to 2% cyclic strain also display enhanced function.
Most research on polymer composites has focused on adding discrete inorganic nanofillers to a pol... more Most research on polymer composites has focused on adding discrete inorganic nanofillers to a polymer matrix to impart properties not found in polymers alone. However, properties such as ion conductivity and mechanical reinforcement would be greatly improved if the composite exhibited an interconnected network of inorganic and polymer phases. Here, we fabricate bicontinuous polymer-infiltrated scaffold metal (PrISM) composites by infiltrating polymer into nanoporous gold (NPG) films. Polystyrene (PS) and poly(2-vinylpyridine) (P2VP) films are infiltrated into the ∼43 nm diameter NPG pores via capillary forces during thermal annealing above the polymer glass transition temperature (Tg). The infiltration process is characterized in situ using spectroscopic ellipsometry. PS and P2VP, which have different affinities for the metal scaffold, exhibit slower segmental dynamics compared to their bulk counterparts when confined within the nanopores, as measured through Tg. The more attractive P2VP shows a 20 °C increase in Tg relative to its bulk, while PS only shows a 6 °C increase at a comparable molecular weight. The infiltrated polymer, in turn, stabilizes the gold nanopores against temporal coarsening. The broad tunability of these polymer/metal hybrids represents a unique template for designing functional network composite structures with applications ranging from flexible electronics to fuel cell membranes.
FIE '98. 28th Annual Frontiers in Education Conference. Moving from 'Teacher-Centered' to 'Learner-Centered' Education. Conference Proceedings (Cat. No.98CH36214)
ABSTRACT Nanocomposite thin films, composed of a binary polymer mixture and mobile nanoparticles,... more ABSTRACT Nanocomposite thin films, composed of a binary polymer mixture and mobile nanoparticles, undergo a unique phase evolution mechanisms incorporating wetting and phase separation. According to recent simulations, the addition of hard mobile particles may significantly impact both the dynamics and mechanism of phase separation (Ginzburg et al., PRL, 1998). Despite current technical and theoretical interests, polymer blend thin films containing nanoparticles have received little experimental interest because reliable sample preparation, such as particle dispersion, is difficult and the need for multiple techniques for following phase separation, wetting and particle partitioning. Using our prior understanding of phase evolution in PMMA/SAN thin film blends as a foundation (Wang et al., J.Chem Phys., 2000), we next investigate how the addition of spherical silica nanoparticles impacts phase dynamics. Because of the complexity of the problem, various characterization tools are utilized in this study, including optical microscopy, AFM, RBS, FReS, SEM, and TEM. The addition of particles is found to distort the phase evolution mechanism and, in agreement with simulations, retard the growth kinetics. Wetting layer growth was also influenced by the nanoparticles.
ABSTRACT Spontaneous delivery of nanoparticles towards a surface or interface is an important top... more ABSTRACT Spontaneous delivery of nanoparticles towards a surface or interface is an important topic in technologies ranging from smart materials to drug delivery. Here, we present examples of self-assembly of nanoparticles (silica, gold, and silver) in homopolymer and polymer blend (PMMA:SAN) systems that are driven by surface and interfacial interactions. For example, silica nanoparticles grafted with methyl groups partition into dPMMA-rich phases upon annealing. For a critical blend, FRES and RBS are used to show that both the dPMMA and nanoparticles, respectively, undergo surface-directed-spinodal-decomposition. The lateral pattern formation of the nanoparticles and polymer domains are observed with SFM. Experiments including PMMA-grafted Au nanoparticles will also be presented. As an alternative approach for fabricating nanoparticle composites, a silver complex is blended with SAN:PMMA and annealed to create in-situ silver nanoparticles ( 4 nm). These nanoparticles are observed to segregate to the air/polymer interface and modify the phase-separation kinetics relative to the blend without nanoparticles.
Polymer films containing nanoparticles are of technological interest because fillers can alter th... more Polymer films containing nanoparticles are of technological interest because fillers can alter the mechanical, electrical and optical properties. Recently, several numerical studies have investigated the impact of mobile nanoparticles on phase separation dynamics (see eg. Ginzburg et al., PRL (1999), Tang & Ma, JCP (2002), Laradji & MacNevin, JCP (2003)). Here, we present the first systematic experimental study of phase
The thermodynamic factors that affect the dispersion of polymer-brush grafted gold nanorods (NR) ... more The thermodynamic factors that affect the dispersion of polymer-brush grafted gold nanorods (NR) in polymer matrix films have been studied by experiment and theory. When brush and matrix have a favorable interaction, such as poly(ethylene oxide) (PEO)-NR/ poly(methyl methacrylate) (PMMA) and polystyrene (PS)-NR / poly(2,6-dimethyl-p-phenylene oxide) (PPO), nanorods are uniformly dispersed. For PEO-NRs in PMMA, the NRs are regularly spaced and well dispersed, independent of the ratio of the degree of polymerization of the matrix (P) to that of the brush (N), namely P/N. As the NR volume fraction increases, the local orientation of the nanorods increases, whereas the macroscopic orientation remains isotropic. When the brush and matrix are similar (i.e., PS-NR / PS and PEO-NR / PEO), the nanorods randomly disperse for P/N 2 (i.e., wet brush), but align side-by-side in aggregates for P/N 2. UV-visible spectroscopy and discrete dipole approximation (DDA) calculations demonstrate that sur...
ABSTRACT To fully utilize their optical absorption and polarizing abilities, the dispersion of Au... more ABSTRACT To fully utilize their optical absorption and polarizing abilities, the dispersion of Au nanorods (NRs) in a matrix, such as a polymer film, must be controlled. By functionalizing NRs with a polymer brush chemically similar to the matrix, NR dispersion and aggregation can be controlled by varying the ratio of brush (N) to matrix (P) chain length. For P/N > 2, aggregates containing mainly side-by-side arrangements of NRs are observed. Here, polystyrene (PS) functionalized Au NRs are incorporated into miscible thin film blends of PS and poly(2,6-dimethyl-p-phenylene oxide) (PPO) (P/N ≈ 30) and characterized using a combination of transmission electron microscopy (TEM) and UV–visible spectroscopy (UV–vis). As the volume fraction of PPO (PPO) increases from 0.00 to 0.50, the NRs remain mainly aggregated; however, at PPO = 0.75 they begin to disperse and finally completely disperse in a pure PPO matrix. Correspondingly, the longitudinal surface plasmon resonance peak undergoes a red shift, consistent with improved dispersion (i.e., individual NRs). A novel outcome of this work is to utilize UV–vis to detect nanometer-scale changes in Au nanorod dispersion. To understand the role of the PPO matrix chains, which favorably interact with the PS brush, self-consistent field theory (SCFT) calculations were performed to determine the brush and matrix density profiles. The brush profile is initially parabolic for PPO < 0.25 and has a thickness that is nearly the radius of gyration of the brush. However, for PPO = 0.50, the brush begins to stretch because of PPO matrix chain penetration. Finally, for PPO = 0.75 and 1.00, the brush thickness increases by about 50%. These SCFT results help interpret the dispersion of nanorods determined from TEM and UV–vis.
... Ithaca, NY 14853, USA and Dwain M. White General Electric Corporate Research and Development,... more ... Ithaca, NY 14853, USA and Dwain M. White General Electric Corporate Research and Development, Schenectady, NY 12301, USA (Received 27 ... of the Dow Chemical Company for characterizing the molecular weight of the PXE samples and D. Walsh of DuPont for making his ...
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