Circumvention of pH-dependent release from ethylcellulosecoated pellets

Dressman, J.B.; Derbin, George; Ismailos, George; Jarvis, Christopher; Ozturk, Asuman; Palsson, Bernhard Ø.; Wheatley, Thomas

doi:10.1016/0168-3659(95)00042-7

Cited by 19 publications

(10 citation statements)

References 3 publications

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“…Figure 1 shows the DSC scan of an ethylcellulose ®lm with the Tg determined by the half-Cp method, where DCp is half the change of the complete transition. The values were 121Á3 and 123Á1 C, which are in agreement with those previously reported (Selinger & Brine 1988;Dressman et al 1995;Sakellariou & Rowe 1995). DSC of Surelease ®lms ( Figure 2) showed a discontinuity between 20 C and 60 C, that could be related to its softening point (35 C) determined previously by thermomechanical analysis (Iyer et al 1990).…”

Section: Determination Of Tgsupporting

confidence: 90%

“…Furthermore, the Tg is affected by storage conditions (Aulton 1995), water content (Hancock & Zogra® 1994;Wang et al 1997) and the addition of plasticizers (Selinger & Brine 1988; Van der Voort Maarschalk et al 1998;Hogan 1995). Therefore, the Tg of polymers is a critical factor not only in the ®lm formation during coating (Okhamafe & York 1988Keshikawa & Nakagami 1994) but also in compaction (Van der Voort Maarschalk et al 1998) and drug release (Okhamafe & York 1989;Dressman et al 1995).…”

mentioning

confidence: 99%

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Use of Dynamic Differential Scanning Calorimetry in Identifying Glass Transition Temperatures of Ethylcellulose and Surelease Films

Velasco

Ford

Rajabi‐Siahboomi

1999

Pharmacy and Pharmacology Communications

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The thermal properties of ethylcellulose and Surelease films were evaluated by differential scanning calorimetry (DSC) and dynamic differential scanning calorimetry (DDSC). DDSC is a novel thermoanalytical technique that allows the identification of glass transitions when they are overlapped by other phenomena such as decomposition or dehydration. Films containing different amounts of plasticizer (triethyl citrate) were prepared from solutions of ethylcellulose in acetone. Additionally, films were prepared from Surelease dispersions at different coalescent temperatures. DSC was sensitive enough to identify the glass transitions in ethylcellulose films but not in Surelease films. DDSC, because it separates the heat flow into two components—loss and storage curves—allowed the identification of the glass transitions in the storage curve. The addition of different amounts of triethyl citrate to ethylcellulose films led to a reduction in the glass transition temperature (Tg). The Tg temperature in Surelease films decreased with an increase in the temperature of coalescence, probably because at higher temperatures the movement of the polymer strands was higher and enhanced the action of the plasticizers included in the Surelease film. For simple polymeric films containing ethylcellulose, Tg values were identified by DSC and DDSC was not required. However, for Surelease films, containing materials of different molecular weight, plasticizers and variable moisture content, DDSC was required.

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Section: Determination Of Tgsupporting

confidence: 90%

mentioning

confidence: 99%

Use of Dynamic Differential Scanning Calorimetry in Identifying Glass Transition Temperatures of Ethylcellulose and Surelease Films

Velasco

Ford

Rajabi‐Siahboomi

1999

Pharmacy and Pharmacology Communications

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“…These charged groups produce an electrostatic repulsion force among themselves, which influences the expansion of the gel network. 17,18 Therefore, some controlled drug release devices have been developed based on pH-sensitive swelling characteristics of polyelectrolyte hydrogels. 19 A series of gels prepared from sodium 2-acrylamido-2-methylpropyl sulfonate (NaAMPS), N-3-dimethylamino propylacrylamide (NDAPA) and betaine were reported by Wada et al 20 They found that the amphoteric gel containing an equimolar of the NDAPA and NaAMPS (50/50) showed the lowest transition temperature and swelling ratios among the amphoteric gels, which was similar to that of NIPAAm gels.…”

Section: Introductionmentioning

confidence: 99%

Thermoreversible hydrogels X: Synthesis and swelling behavior of the (N-isopropylacrylamide-co-sodium 2-acrylamido-2-methylpropyl sulfonate) copolymeric hydrogels

Lee

Yuan

2000

J. Appl. Polym. Sci.

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“…18 Thus, some controlled drug release devices based on the pHsensitive swelling characters of polyelectrolyte hydrogels have been developed. 19 The hydrolysis of polyacrylamide (PAAm) gels, equilibrated in aqueous solution of high pH or formed from an initial highly basic solution (with pH of 11 or 12), led to extensive swelling of the gels when placed in pure water. 20 Ilavsky reported the presence of charges (due to the hydrolysis of the PAAm chain) in the collapse of PAAm gels.…”

Section: Introductionmentioning

confidence: 99%

pH-thermoreversible hydrogels. I. Synthesis and swelling behaviors of the (N-isopropylacrylamide-co-acrylamide-co-2-hydroxyethyl methacrylate) copolymeric hydrogels

Lee

Shieh

1999

J. Appl. Polym. Sci.

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A series of pH-thermoreversible hydrogels that exhibited volume phase transition was synthesized by various molar ratios of N-isopropylacrylamide (NIPAAm), acrylamide (AAm), and 2-hydroxyethyl methacrylate (HEMA). The influence of environmental conditions such as temperature and pH value on the swelling behavior of these copolymeric gels was investigated. Results showed that the hydrogels exhibited different equilibrium swelling ratios in different pH solutions. Amide groups could be hydrolyzed to form negatively charged carboxylate ion groups in their hydrophilic polymeric network in response to an external pH variation. The pH sensitivities of these gels also depended on the AAm content in the copolymeric gels; thus the greater the AAm content, the higher the pH sensitivity. These hydrogels, based on a temperature-sensitive hydrogel, demonstrated a significant change of equilibrium swelling in aqueous media between a highly solvated, swollen gel state and a dehydrated network response to small variations of temperature. pH-thermoreversible hydrogels were used for a study of the release of a model drug, caffeine, with changes in temperature.

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Circumvention of pH-dependent release from ethylcellulosecoated pellets

Cited by 19 publications

References 3 publications

Use of Dynamic Differential Scanning Calorimetry in Identifying Glass Transition Temperatures of Ethylcellulose and Surelease Films

Use of Dynamic Differential Scanning Calorimetry in Identifying Glass Transition Temperatures of Ethylcellulose and Surelease Films

Thermoreversible hydrogels X: Synthesis and swelling behavior of the (N-isopropylacrylamide-co-sodium 2-acrylamido-2-methylpropyl sulfonate) copolymeric hydrogels

pH-thermoreversible hydrogels. I. Synthesis and swelling behaviors of the (N-isopropylacrylamide-co-acrylamide-co-2-hydroxyethyl methacrylate) copolymeric hydrogels

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