The ability to control protein and cell positioning on a microscopic scale is crucial in many bio... more The ability to control protein and cell positioning on a microscopic scale is crucial in many biomedical applications, such as single cell studies. We have developed and investigated the grafting of poly(ethylene glycol) (PEG) brushes onto poly(d,l-lactide-co-glycolide) (PLGA) thin films, which can be micropatterned by exploiting their spontaneous dewetting on top of polystyrene (PS) films. Dense PEG brushes with excellent protein repellence were achieved on PLGA by using cloud point grafting conditions, and selective adsorption of proteins on the micropatterned substrates was achieved by exploiting the different affinity protein adsorption onto the PEG brushes and the PS holes. PEG-grafted PLGA films showed better resistance against spontaneous degradation in buffer than bare PLGA films, due to passivation by the thin PEG coating. The simplicity of dewetting and subsequent grafting approaches, coupled with the ability to coat and pattern nonplanar substrates give rise to possible applications of PEG-grafted PLGA films in single cell studies and cell cultures for tissue engineering.
Inspired by an example found in nature, the design of patterned surfaces with chemical and topogr... more Inspired by an example found in nature, the design of patterned surfaces with chemical and topographical contrast for the collection of water from the atmosphere has been of intense interest in recent years. Herein we report the synthesis of such materials via a combination of macromolecular design and polymer thin film dewetting to yield surfaces consisting of raised hydrophilic bumps on a hydrophobic background. RAFT polymerization was used to synthesize poly(2-hydroxypropyl methacrylate) (PHPMA) of targeted molecular weight and low dispersity; spin-coating of PHPMA onto polystyrene films produced stable polymer bilayers under appropriate conditions. Thermal annealing of these bilayers above the glass transition temperature of the PHPMA layer led to complete dewetting of the top layer and the formation of isolated PHPMA domains atop the PS film. Due to the vastly different rates of water nucleation on the two phases, preferential dropwise nucleation of water occurred on the PHPMA ...
Journal of colloid and interface science, Jan 15, 2015
Two-dimensional nanoparticles such as graphene oxide (GO) can serve as emulsion stabilizers due t... more Two-dimensional nanoparticles such as graphene oxide (GO) can serve as emulsion stabilizers due their ability to adsorb at oil-water (o/w) interfaces with high atom efficiency. The ability for GO to act as a surfactant is hypothesized to be highly dependent on the nature (i.e. polarity) of the oil phase, which has not considered previously. The stabilization energy associated with adsorption of GO sheets at an o/w interface was modelled as a function of the polarity of the oil phase using surface tension contributions terms and Hansen solubility parameters (HSPs). Oil-in-water (o/w) miniemulsions were prepared via ultrasonication in the presence of GO for a variety of different oil phases, and were studied using dynamic light scattering (DLS). The stabilization energy associated with GO adsorption was greater for non-polar oil phases compared to more polar oils. This behaviour is driven by the significant reduction in the oil-water interfacial tension as the polarity of the oil incr...
The preparation of hybrid hollow capsules consisting of a cross-linked polymer shell and a coatin... more The preparation of hybrid hollow capsules consisting of a cross-linked polymer shell and a coating of graphene oxide (GO) is demonstrated. The capsules are prepared by Pickering miniemulsion polymerization, exploiting the surface activity of GO for its use as a colloidal surfactant. This approach represents a simple and convenient route towards hollow carbon nanostructures for a variety of applications. The incorporation of surface-modified TiO2 nanoparticles into the interior of these capsules was also demonstrated.
The ability to control protein and cell positioning on a microscopic scale is crucial in many bio... more The ability to control protein and cell positioning on a microscopic scale is crucial in many biomedical applications, such as single cell studies. We have developed and investigated the grafting of poly(ethylene glycol) (PEG) brushes onto poly(d,l-lactide-co-glycolide) (PLGA) thin films, which can be micropatterned by exploiting their spontaneous dewetting on top of polystyrene (PS) films. Dense PEG brushes with excellent protein repellence were achieved on PLGA by using cloud point grafting conditions, and selective adsorption of proteins on the micropatterned substrates was achieved by exploiting the different affinity protein adsorption onto the PEG brushes and the PS holes. PEG-grafted PLGA films showed better resistance against spontaneous degradation in buffer than bare PLGA films, due to passivation by the thin PEG coating. The simplicity of dewetting and subsequent grafting approaches, coupled with the ability to coat and pattern nonplanar substrates give rise to possible applications of PEG-grafted PLGA films in single cell studies and cell cultures for tissue engineering.
ABSTRACT The ability to control protein and cell positioning on a microscopic scale is crucial in... more ABSTRACT The ability to control protein and cell positioning on a microscopic scale is crucial in many biomedical applications, such as tissue engineering and the development of biosensors. We demonstrate here that the assembly of collagen on patterned surfaces produced by the dewetting of metastable poly(N-vinylpyrrolidone) (PNVP) films on top of polystyrene films supports the adhesion and survival of a biologically relevant cell type, human endothelial cells. Micropatterning of Type 1 collagen was achieved on such substrates by exploiting the different protein affinity of the two polymers, the effect of treatment with an air plasma, and the control over the nanoscale assembly of collagen using different adsorption conditions. The simplicity of the dewetting approach, coupled with the ability to coat and pattern non-planar substrates, gives rise to possible applications in the coating of biological implants such as arterial stents.
ABSTRACT Dispersion polymerization of styrene has been performed in CO2-expanded ethanol at ≤9 MP... more ABSTRACT Dispersion polymerization of styrene has been performed in CO2-expanded ethanol at ≤9 MPa and 70 °C using PVP as stabilizer. The polymerizations proceeded with good colloidal stability, resulting in spherical particles of diameters of ∼2 μm. Pressurization with CO2 leads to an increase in particle size (∼1 μm in the corresponding CO2-free system), and a decrease in both polymerization rate and molecular weight. The main effect of CO2 is proposed to be its influence on the partitioning of monomer between the continuous and the particle phase–the results indicate that CO2-pressurization causes a reduction in monomer concentration in the particles. Overall, the results are consistent with literature data on the effects of the polarity of the continuous phase in dispersion polymerization of styrene in alcohols and alcohol/water mixtures.
The free-radical polymerization propagation rate coefficient (kp) of acrylic acid (AA) was calcul... more The free-radical polymerization propagation rate coefficient (kp) of acrylic acid (AA) was calculated using transition state theory and ab initio quantum chemistry in order to shed light on the very strong solvent effects observed experimentally. Calculations were performed using a gas-phase reaction simulation, and the contribution of solvent then taken into account using the Polarizable Continuum Model for two solvents—water
It has been found [ Thickett, SC; Gaborieau, M.; Gilbert, RG Macromolecules 2007,40, 4710−4720] t... more It has been found [ Thickett, SC; Gaborieau, M.; Gilbert, RG Macromolecules 2007,40, 4710−4720] that rate and characterization data on the seeded growth of latex particles electrosterically stabilized by a hairy layer of anchored poly(acrylic acid) (pAA) can be qualitatively and ...
We investigated the early and intermediate stages of the guided dewetting of polystyrene (PS) thi... more We investigated the early and intermediate stages of the guided dewetting of polystyrene (PS) thin films on chemically patterned silicon, achieved by micro-contact printing of non-wettable self-assembling monolayers of an alkylsilane. Two different types of ordered patterns could be achieved depending on the annealing temperature and time. Study of the dynamics of hole growth revealed a deviation of the growth profile from the trend on homogeneous substrates, attributed to the pinning of the PS rims on the borders of the hydrophobic regions. The ordered patterns produced could be useful in applications that require spatially localized features of controlled surface chemistry, such as studies in proteomics, single cell studies, and biosensors.
We investigated the morphology and dynamics of the dewetting of metastable poly(4-vinylpyridine) ... more We investigated the morphology and dynamics of the dewetting of metastable poly(4-vinylpyridine) (P4VP) thin films situated on top of polystyrene (PS) thin films as a function of the molecular weight and thickness of both films. We focused on the competition between the dewetting process, occurring as a result of unfavorable intermolecular interactions at the P4VP/PS interface, and layer inversion due to the lower surface energy of PS. By means of optical and atomic force microscopy (AFM), we observed how both the dynamics of the instability and the morphology of the emerging patterns depend on the ratio of the molecular weights of the polymer films. When the bottom PS layer was less viscous than the top P4VP layer (liquid-liquid dewetting), nucleated holes in the P4VP film typically stopped growing at long annealing times because of a combination of viscous dissipation in the bottom layer and partial layer inversion. Full layer inversion was achieved when the viscosity of the top P4VP layer was significantly greater (>10⁴) than the viscosity of the PS layer underneath, which is attributed to strongly different mobilities of the two layers. The density of holes produced by nucleation dewetting was observed for the first time to depend on the thickness of the top film as well as the polymer molecular weight. The final (completely dewetted) morphology of isolated droplets could be achieved only if the time frame of layer inversion was significantly slower than that of dewetting, which was characteristic of high-viscosity PS underlayers that allowed dewetting to fall into a liquid-solid regime. Assuming a simple reptation model for layer inversion occurring at the dewetting front, the observed surface morphologies could be predicted on the basis of the relative rates of dewetting and layer inversion.
The ability to control protein and cell positioning on a microscopic scale is crucial in many bio... more The ability to control protein and cell positioning on a microscopic scale is crucial in many biomedical applications, such as single cell studies. We have developed and investigated the grafting of poly(ethylene glycol) (PEG) brushes onto poly(d,l-lactide-co-glycolide) (PLGA) thin films, which can be micropatterned by exploiting their spontaneous dewetting on top of polystyrene (PS) films. Dense PEG brushes with excellent protein repellence were achieved on PLGA by using cloud point grafting conditions, and selective adsorption of proteins on the micropatterned substrates was achieved by exploiting the different affinity protein adsorption onto the PEG brushes and the PS holes. PEG-grafted PLGA films showed better resistance against spontaneous degradation in buffer than bare PLGA films, due to passivation by the thin PEG coating. The simplicity of dewetting and subsequent grafting approaches, coupled with the ability to coat and pattern nonplanar substrates give rise to possible applications of PEG-grafted PLGA films in single cell studies and cell cultures for tissue engineering.
Inspired by an example found in nature, the design of patterned surfaces with chemical and topogr... more Inspired by an example found in nature, the design of patterned surfaces with chemical and topographical contrast for the collection of water from the atmosphere has been of intense interest in recent years. Herein we report the synthesis of such materials via a combination of macromolecular design and polymer thin film dewetting to yield surfaces consisting of raised hydrophilic bumps on a hydrophobic background. RAFT polymerization was used to synthesize poly(2-hydroxypropyl methacrylate) (PHPMA) of targeted molecular weight and low dispersity; spin-coating of PHPMA onto polystyrene films produced stable polymer bilayers under appropriate conditions. Thermal annealing of these bilayers above the glass transition temperature of the PHPMA layer led to complete dewetting of the top layer and the formation of isolated PHPMA domains atop the PS film. Due to the vastly different rates of water nucleation on the two phases, preferential dropwise nucleation of water occurred on the PHPMA ...
Journal of colloid and interface science, Jan 15, 2015
Two-dimensional nanoparticles such as graphene oxide (GO) can serve as emulsion stabilizers due t... more Two-dimensional nanoparticles such as graphene oxide (GO) can serve as emulsion stabilizers due their ability to adsorb at oil-water (o/w) interfaces with high atom efficiency. The ability for GO to act as a surfactant is hypothesized to be highly dependent on the nature (i.e. polarity) of the oil phase, which has not considered previously. The stabilization energy associated with adsorption of GO sheets at an o/w interface was modelled as a function of the polarity of the oil phase using surface tension contributions terms and Hansen solubility parameters (HSPs). Oil-in-water (o/w) miniemulsions were prepared via ultrasonication in the presence of GO for a variety of different oil phases, and were studied using dynamic light scattering (DLS). The stabilization energy associated with GO adsorption was greater for non-polar oil phases compared to more polar oils. This behaviour is driven by the significant reduction in the oil-water interfacial tension as the polarity of the oil incr...
The preparation of hybrid hollow capsules consisting of a cross-linked polymer shell and a coatin... more The preparation of hybrid hollow capsules consisting of a cross-linked polymer shell and a coating of graphene oxide (GO) is demonstrated. The capsules are prepared by Pickering miniemulsion polymerization, exploiting the surface activity of GO for its use as a colloidal surfactant. This approach represents a simple and convenient route towards hollow carbon nanostructures for a variety of applications. The incorporation of surface-modified TiO2 nanoparticles into the interior of these capsules was also demonstrated.
The ability to control protein and cell positioning on a microscopic scale is crucial in many bio... more The ability to control protein and cell positioning on a microscopic scale is crucial in many biomedical applications, such as single cell studies. We have developed and investigated the grafting of poly(ethylene glycol) (PEG) brushes onto poly(d,l-lactide-co-glycolide) (PLGA) thin films, which can be micropatterned by exploiting their spontaneous dewetting on top of polystyrene (PS) films. Dense PEG brushes with excellent protein repellence were achieved on PLGA by using cloud point grafting conditions, and selective adsorption of proteins on the micropatterned substrates was achieved by exploiting the different affinity protein adsorption onto the PEG brushes and the PS holes. PEG-grafted PLGA films showed better resistance against spontaneous degradation in buffer than bare PLGA films, due to passivation by the thin PEG coating. The simplicity of dewetting and subsequent grafting approaches, coupled with the ability to coat and pattern nonplanar substrates give rise to possible applications of PEG-grafted PLGA films in single cell studies and cell cultures for tissue engineering.
ABSTRACT The ability to control protein and cell positioning on a microscopic scale is crucial in... more ABSTRACT The ability to control protein and cell positioning on a microscopic scale is crucial in many biomedical applications, such as tissue engineering and the development of biosensors. We demonstrate here that the assembly of collagen on patterned surfaces produced by the dewetting of metastable poly(N-vinylpyrrolidone) (PNVP) films on top of polystyrene films supports the adhesion and survival of a biologically relevant cell type, human endothelial cells. Micropatterning of Type 1 collagen was achieved on such substrates by exploiting the different protein affinity of the two polymers, the effect of treatment with an air plasma, and the control over the nanoscale assembly of collagen using different adsorption conditions. The simplicity of the dewetting approach, coupled with the ability to coat and pattern non-planar substrates, gives rise to possible applications in the coating of biological implants such as arterial stents.
ABSTRACT Dispersion polymerization of styrene has been performed in CO2-expanded ethanol at ≤9 MP... more ABSTRACT Dispersion polymerization of styrene has been performed in CO2-expanded ethanol at ≤9 MPa and 70 °C using PVP as stabilizer. The polymerizations proceeded with good colloidal stability, resulting in spherical particles of diameters of ∼2 μm. Pressurization with CO2 leads to an increase in particle size (∼1 μm in the corresponding CO2-free system), and a decrease in both polymerization rate and molecular weight. The main effect of CO2 is proposed to be its influence on the partitioning of monomer between the continuous and the particle phase–the results indicate that CO2-pressurization causes a reduction in monomer concentration in the particles. Overall, the results are consistent with literature data on the effects of the polarity of the continuous phase in dispersion polymerization of styrene in alcohols and alcohol/water mixtures.
The free-radical polymerization propagation rate coefficient (kp) of acrylic acid (AA) was calcul... more The free-radical polymerization propagation rate coefficient (kp) of acrylic acid (AA) was calculated using transition state theory and ab initio quantum chemistry in order to shed light on the very strong solvent effects observed experimentally. Calculations were performed using a gas-phase reaction simulation, and the contribution of solvent then taken into account using the Polarizable Continuum Model for two solvents—water
It has been found [ Thickett, SC; Gaborieau, M.; Gilbert, RG Macromolecules 2007,40, 4710−4720] t... more It has been found [ Thickett, SC; Gaborieau, M.; Gilbert, RG Macromolecules 2007,40, 4710−4720] that rate and characterization data on the seeded growth of latex particles electrosterically stabilized by a hairy layer of anchored poly(acrylic acid) (pAA) can be qualitatively and ...
We investigated the early and intermediate stages of the guided dewetting of polystyrene (PS) thi... more We investigated the early and intermediate stages of the guided dewetting of polystyrene (PS) thin films on chemically patterned silicon, achieved by micro-contact printing of non-wettable self-assembling monolayers of an alkylsilane. Two different types of ordered patterns could be achieved depending on the annealing temperature and time. Study of the dynamics of hole growth revealed a deviation of the growth profile from the trend on homogeneous substrates, attributed to the pinning of the PS rims on the borders of the hydrophobic regions. The ordered patterns produced could be useful in applications that require spatially localized features of controlled surface chemistry, such as studies in proteomics, single cell studies, and biosensors.
We investigated the morphology and dynamics of the dewetting of metastable poly(4-vinylpyridine) ... more We investigated the morphology and dynamics of the dewetting of metastable poly(4-vinylpyridine) (P4VP) thin films situated on top of polystyrene (PS) thin films as a function of the molecular weight and thickness of both films. We focused on the competition between the dewetting process, occurring as a result of unfavorable intermolecular interactions at the P4VP/PS interface, and layer inversion due to the lower surface energy of PS. By means of optical and atomic force microscopy (AFM), we observed how both the dynamics of the instability and the morphology of the emerging patterns depend on the ratio of the molecular weights of the polymer films. When the bottom PS layer was less viscous than the top P4VP layer (liquid-liquid dewetting), nucleated holes in the P4VP film typically stopped growing at long annealing times because of a combination of viscous dissipation in the bottom layer and partial layer inversion. Full layer inversion was achieved when the viscosity of the top P4VP layer was significantly greater (>10⁴) than the viscosity of the PS layer underneath, which is attributed to strongly different mobilities of the two layers. The density of holes produced by nucleation dewetting was observed for the first time to depend on the thickness of the top film as well as the polymer molecular weight. The final (completely dewetted) morphology of isolated droplets could be achieved only if the time frame of layer inversion was significantly slower than that of dewetting, which was characteristic of high-viscosity PS underlayers that allowed dewetting to fall into a liquid-solid regime. Assuming a simple reptation model for layer inversion occurring at the dewetting front, the observed surface morphologies could be predicted on the basis of the relative rates of dewetting and layer inversion.
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Papers by Stuart Thickett