The Experts below are selected from a list of 198 Experts worldwide ranked by ideXlab platform
Nicholas A. Peppas - One of the best experts on this subject based on the ideXlab platform.
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observation of swelling process and Diffusion Front position during swelling in hydroxypropyl methyl cellulose hpmc matrices containing a soluble drug
Journal of Controlled Release, 1999Co-Authors: Paolo Colombo, Ruggero Bettini, Nicholas A. PeppasAbstract:The behavior of gel layer thickness in swellable hydroxypropyl methyl cellulose matrices loaded with increasing amounts of soluble and colored drug and exhibiting swelling, Diffusion and erosion Fronts, was studied using a colorimetric technique. The effect of the drug loading on the Front position in the gel layer, in particular, on the presence of a Diffusion Front and its movement, was investigated. In addition, the swelling, Diffusion and erosion Front positions at different releasing times were measured and a theoretical analysis of the overall process was provided. It was found that the Diffusion Front was visible in systems with more than 30% drug, due to the presence of an undissolved drug layer. The physical analysis of such systems clearly showed the importance of drug solubility and loading in the observation of the Diffusion Front.
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drug Diffusion Front movement is important in drug release control from swellable matrix tablets
Journal of Pharmaceutical Sciences, 1995Co-Authors: Paolo Colombo, Ruggero Bettini, G Massimo, Pier Luigi Catellani, Patrizia Santi, Nicholas A. PeppasAbstract:Swellable controlled release devices of buflomedil pyridoxalphosphate in hydroxypropyl methylcellulose were prepared, and their swelling and release behavior was investigated. The drug release as a function of time was investigated for various system parameters. Three distinct Fronts were observed during the swelling and release processes, i.e., a swelling, a drug Diffusion, and an erosion Front. The drug Diffusion Front could be readily determined due to the drug's yellow color. The relative positions of the Fronts and the drug release rate were studied as functions of the initial porosity and the molecular weight of the polymer carrier. It was shown that the drug Diffusion Front best describes the overall release behavior of the system. The fractional drug release was a strong function of the dissolved drug gel layer thickness, which separates the Diffusion Front from the erosion Front. The effect of drug solubility was also investigated by altering the pH and the ionic strength of the dissolution medium. It was shown that as drug solubility increased, the undissolved drug gel layer thickness decreased, again showing the importance of the movement of the Diffusion Front in controlling the overall release.
Karen Turnquest - One of the best experts on this subject based on the ideXlab platform.
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influence of base additives on the reaction Diffusion Front of model chemically amplified photoresists
Journal of Vacuum Science & Technology B, 2007Co-Authors: Bryan D Vogt, Shuhui Kang, Vivek M Prabhu, Ashwin Rao, Eric K Lin, Sushil K Satija, Karen TurnquestAbstract:The effects of amine base quencher on the photoacid catalyzed deprotection reaction-Diffusion Front in model photoresists were measured by combination of neutron reflectivity and Fourier transform infrared spectroscopy. Modulation in the location of the base with respect to the diffusing photoacid catalyst changes the spatial reaction extent and illuminates the complex role of the base on the shape of the reaction-Diffusion Front. Despite similar total extents of reaction, a comparison between uniform base and model photodegradable base distributions demonstrates distinct reaction time and base concentration effects on the deprotection profile shape. These differences arise from the modification of the initial deprotection extent due to both the neutralization of the photoacid and the influence of the changing photoresist composition on the reaction-Diffusion process. The use of the model photodegradable base results in a sharper Front due to these effects. Lastly, aqueous hydroxide development of these l...
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measurements of the reaction Diffusion Front of model chemically amplified photoresists with varying photoacid size
Macromolecules, 2006Co-Authors: Bryan D Vogt, Shuhui Kang, Vivek M Prabhu, Eric K Lin, Sushil K Satija, Karen TurnquestAbstract:Neutron reflectivity and Fourier transform infrared spectroscopy measurements are used to profile the deprotection reaction−Diffusion Front with nanometer resolution in a model photoresist polymer using three perfluoroalkane-based photoacid generators (PAG) with varying chain lengths. As expected, the spatial extent of the deprotection reaction Front increases with decreasing PAG size. Although the total extent of deprotection increases with increasing postexposure bake time for each PAG, the reaction−Diffusion of deprotection does not propagate continuously into the photoresist polymer. The form of the deprotection reaction Front changes because the Diffusion process is affected by the changing polymer composition. The data are well described by a reaction−Diffusion model that includes a simple acid-trapping term and does not require a varying PAG diffusivity. This high-resolution profiling, together with modeling, illustrates details of the coupled Diffusion and deprotection reaction processes that affe...
Ruggero Bettini - One of the best experts on this subject based on the ideXlab platform.
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observation of swelling process and Diffusion Front position during swelling in hydroxypropyl methyl cellulose hpmc matrices containing a soluble drug
Journal of Controlled Release, 1999Co-Authors: Paolo Colombo, Ruggero Bettini, Nicholas A. PeppasAbstract:The behavior of gel layer thickness in swellable hydroxypropyl methyl cellulose matrices loaded with increasing amounts of soluble and colored drug and exhibiting swelling, Diffusion and erosion Fronts, was studied using a colorimetric technique. The effect of the drug loading on the Front position in the gel layer, in particular, on the presence of a Diffusion Front and its movement, was investigated. In addition, the swelling, Diffusion and erosion Front positions at different releasing times were measured and a theoretical analysis of the overall process was provided. It was found that the Diffusion Front was visible in systems with more than 30% drug, due to the presence of an undissolved drug layer. The physical analysis of such systems clearly showed the importance of drug solubility and loading in the observation of the Diffusion Front.
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drug Diffusion Front movement is important in drug release control from swellable matrix tablets
Journal of Pharmaceutical Sciences, 1995Co-Authors: Paolo Colombo, Ruggero Bettini, G Massimo, Pier Luigi Catellani, Patrizia Santi, Nicholas A. PeppasAbstract:Swellable controlled release devices of buflomedil pyridoxalphosphate in hydroxypropyl methylcellulose were prepared, and their swelling and release behavior was investigated. The drug release as a function of time was investigated for various system parameters. Three distinct Fronts were observed during the swelling and release processes, i.e., a swelling, a drug Diffusion, and an erosion Front. The drug Diffusion Front could be readily determined due to the drug's yellow color. The relative positions of the Fronts and the drug release rate were studied as functions of the initial porosity and the molecular weight of the polymer carrier. It was shown that the drug Diffusion Front best describes the overall release behavior of the system. The fractional drug release was a strong function of the dissolved drug gel layer thickness, which separates the Diffusion Front from the erosion Front. The effect of drug solubility was also investigated by altering the pH and the ionic strength of the dissolution medium. It was shown that as drug solubility increased, the undissolved drug gel layer thickness decreased, again showing the importance of the movement of the Diffusion Front in controlling the overall release.
Paolo Colombo - One of the best experts on this subject based on the ideXlab platform.
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observation of swelling process and Diffusion Front position during swelling in hydroxypropyl methyl cellulose hpmc matrices containing a soluble drug
Journal of Controlled Release, 1999Co-Authors: Paolo Colombo, Ruggero Bettini, Nicholas A. PeppasAbstract:The behavior of gel layer thickness in swellable hydroxypropyl methyl cellulose matrices loaded with increasing amounts of soluble and colored drug and exhibiting swelling, Diffusion and erosion Fronts, was studied using a colorimetric technique. The effect of the drug loading on the Front position in the gel layer, in particular, on the presence of a Diffusion Front and its movement, was investigated. In addition, the swelling, Diffusion and erosion Front positions at different releasing times were measured and a theoretical analysis of the overall process was provided. It was found that the Diffusion Front was visible in systems with more than 30% drug, due to the presence of an undissolved drug layer. The physical analysis of such systems clearly showed the importance of drug solubility and loading in the observation of the Diffusion Front.
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drug Diffusion Front movement is important in drug release control from swellable matrix tablets
Journal of Pharmaceutical Sciences, 1995Co-Authors: Paolo Colombo, Ruggero Bettini, G Massimo, Pier Luigi Catellani, Patrizia Santi, Nicholas A. PeppasAbstract:Swellable controlled release devices of buflomedil pyridoxalphosphate in hydroxypropyl methylcellulose were prepared, and their swelling and release behavior was investigated. The drug release as a function of time was investigated for various system parameters. Three distinct Fronts were observed during the swelling and release processes, i.e., a swelling, a drug Diffusion, and an erosion Front. The drug Diffusion Front could be readily determined due to the drug's yellow color. The relative positions of the Fronts and the drug release rate were studied as functions of the initial porosity and the molecular weight of the polymer carrier. It was shown that the drug Diffusion Front best describes the overall release behavior of the system. The fractional drug release was a strong function of the dissolved drug gel layer thickness, which separates the Diffusion Front from the erosion Front. The effect of drug solubility was also investigated by altering the pH and the ionic strength of the dissolution medium. It was shown that as drug solubility increased, the undissolved drug gel layer thickness decreased, again showing the importance of the movement of the Diffusion Front in controlling the overall release.
Bryan D Vogt - One of the best experts on this subject based on the ideXlab platform.
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influence of base additives on the reaction Diffusion Front of model chemically amplified photoresists
Journal of Vacuum Science & Technology B, 2007Co-Authors: Bryan D Vogt, Shuhui Kang, Vivek M Prabhu, Ashwin Rao, Eric K Lin, Sushil K Satija, Karen TurnquestAbstract:The effects of amine base quencher on the photoacid catalyzed deprotection reaction-Diffusion Front in model photoresists were measured by combination of neutron reflectivity and Fourier transform infrared spectroscopy. Modulation in the location of the base with respect to the diffusing photoacid catalyst changes the spatial reaction extent and illuminates the complex role of the base on the shape of the reaction-Diffusion Front. Despite similar total extents of reaction, a comparison between uniform base and model photodegradable base distributions demonstrates distinct reaction time and base concentration effects on the deprotection profile shape. These differences arise from the modification of the initial deprotection extent due to both the neutralization of the photoacid and the influence of the changing photoresist composition on the reaction-Diffusion process. The use of the model photodegradable base results in a sharper Front due to these effects. Lastly, aqueous hydroxide development of these l...
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measurements of the reaction Diffusion Front of model chemically amplified photoresists with varying photoacid size
Macromolecules, 2006Co-Authors: Bryan D Vogt, Shuhui Kang, Vivek M Prabhu, Eric K Lin, Sushil K Satija, Karen TurnquestAbstract:Neutron reflectivity and Fourier transform infrared spectroscopy measurements are used to profile the deprotection reaction−Diffusion Front with nanometer resolution in a model photoresist polymer using three perfluoroalkane-based photoacid generators (PAG) with varying chain lengths. As expected, the spatial extent of the deprotection reaction Front increases with decreasing PAG size. Although the total extent of deprotection increases with increasing postexposure bake time for each PAG, the reaction−Diffusion of deprotection does not propagate continuously into the photoresist polymer. The form of the deprotection reaction Front changes because the Diffusion process is affected by the changing polymer composition. The data are well described by a reaction−Diffusion model that includes a simple acid-trapping term and does not require a varying PAG diffusivity. This high-resolution profiling, together with modeling, illustrates details of the coupled Diffusion and deprotection reaction processes that affe...