Controlled Release

Fan, L.T.; Singh, Satish Kumar

doi:10.1007/978-3-642-74507-2

Cited by 66 publications

(9 citation statements)

References 121 publications

(228 reference statements)

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“…Here, where the transport couples also to the mass transfer in the surrounding liquid, we base the analysis on the pseudo-steady-state assumption. This requires that the concentration profile in the shell is always at steady state with respect to the movement of the shell boundaries and the concentration at r out . At steady state, the rate of transport to the core through the spherical shell is where C in ′ and C out ′ are the concentrations of A in the shell at r in and r out , respectively.…”

Section: Theorymentioning

confidence: 99%

Drug-Eluting Polyacrylate Microgels: Loading and Release of Amitriptyline

Al-Tikriti

Hansson

2020

J. Phys. Chem. B

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We investigated the loading of an amphiphilic drug, amitriptyline hydrochloride (AMT), onto sodium polyacrylate hydrogels at low ionic strength and its release at high ionic strength. The purpose was to show how the self-assembling properties of the drug and the swelling of the gel network influenced the loading/release mechanisms and kinetics, important for the development of improved controlled-release systems for parenteral administration of amphiphilic drugs. Equilibrium studies showed that single microgels (∼100 μm) in a large solution volume underwent a discrete transition between swollen and dense states at a critical drug concentration in the solution. For single macrogels in a small solution volume, the transition progressed gradually with increasing amount of added drug, with swollen and dense phases coexisting in the same gel; in a suspension of microgels, swollen and collapsed particles coexisted. Time-resolved micropipette-assisted microscopy studies showed that drug self-assemblies accumulated in a dense shell enclosing the swollen core during loading and that a dense core was surrounded by a swollen shell during release. The time evolution of the radius of single microgels was determined as functions of liquid flow rate, network size, and AMT concentration in the solution. Mass transport of AMT in the surrounding liquid, and in the dense shell, influenced the deswelling rate during loading. Mass transport in the swollen shell controlled the swelling rate during release. A steady-state kinetic model taking into account drug self-assembly, core–shell phase separation, and microgel volume changes was developed and found to be in semiquantitative agreement with the experimental loading and release data.

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Section: Theorymentioning

confidence: 99%

Drug-Eluting Polyacrylate Microgels: Loading and Release of Amitriptyline

Al-Tikriti

Hansson

2020

J. Phys. Chem. B

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“…In descriptions of membrane transport, it is common to write P = KD I , where K is an equilibrium constant describing the partitioning of the diffusing species between membrane and solution . The interpretation derives from Fick's first law for the case of diffusing species forming an ideal solution in the membrane, obviously not the case for the surface phase.…”

Section: Theorymentioning

confidence: 99%

Ion-Exchange Controls the Kinetics of Deswelling of Polyelectrolyte Microgels in Solutions of Oppositely Charged Surfactant

2005

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The kinetics of deswelling of sodium polyacrylate microgels (radius 30-140 microm) in aqueous solutions of dodecyltrimethylammonium bromide is investigated by means of micropipet-assisted light microscopy. The purpose of the study is to test a recent model (J. Phys. Chem. B 2003, 107, 9203) proposing that the rate of the volume change is controlled by the transport of surfactant from the solution to the gel core (ion exchange) via the surfactant-rich surface phase appearing in the gel during the volume transition. Equilibrium swelling characteristics of the gel network in surfactant-free solutions and with various amounts of surfactant present are presented and discussed with reference to related systems. A relationship between gel volume and degree of surfactant binding is determined and used in theoretical predictions of the deswelling kinetics. Experimental data for single gel beads observed during deswelling under conditions of forced convection are presented and compared with model calculations. It is demonstrated that the dependences of the kinetics on initial gel size, the surfactant concentration in the solution, and the liquid flow rate are well accounted for by the model. It is concluded that the deswelling rates of the studied gels are strongly influenced by the mass transport of surfactant between gel and solution (stagnant layer diffusion), but only to a minor extent by the transport through the surface phase. The results indicate that, during the volume transition, swelling equilibrium (network relaxation/transport of water) is established on a relatively short time scale and, therefore, can be treated as independent of the ion-exchange kinetics. Theoretical aspects of the kinetics and mechanisms of surfactant transport through the surface phase are discussed.

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“…At steady state the rate of transport of surfactant into a spherical gel is where n s,g is the number of moles of surfactant in the gel and D II is the effective diffusion coefficient in the stagnant layer. In the present case where C s,2 is constant the solution to the differential equation (8) can be written as 39 where t U is the time for fractional attainment of equilibrium U ( t ) and C g is the total concentration of positive ions in the gel.…”

Section: Theorymentioning

confidence: 99%

Shrinking Kinetics of Polyacrylate Gels in Surfactant Solution

Göransson

Hansson

2003

J. Phys. Chem. B

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Volume transition of covalently cross-linked sodium polyacrylate gels (micrometer-sized) due to the absorption of dodecyltrimethylammonium bromide from bulk aqueous solution is studied by means of light and fluorescence microscopy. The volume transition occurs in a narrow range of surfactant concentrations. In the presence of 0.01 M sodium bromide in the solution, the equilibrium volume is reduced typically 50 times for surfactant concentrations larger that 4 × 10-4 M. During the transition, a collapsed, surfactant-rich, surface phase is formed, enclosing the swollen gel core. Evidence is found for equilibrium between the core and surface phase in the collapsed state of the gel. The relation to surfactant self-assembly in solutions of linear polyion and in centimeter-sized gels is discussed. The kinetics of diffusion-controlled shrinking is analyzed theoretically. The model considers the transport of surfactant from the bulk, through the “stagnant” liquid layer and the surface phase, to the gel core. During shrinking, the osmotic swelling of the gel is assumed to be in quasi-equilibrium with the bulk and calculated using a recent model for equilibrium swelling of phase-separated gels (Hansson et al. J. Phys. Chem. B 2002, 106, 9777). The kinetic model is used to analyze time-resolved experimental shrinking curves. The result suggests that the shrinking is controlled by stagnant layer diffusion of surfactant, and that the relative swelling at intermediate stages during the collapse is the same as for slab gels of the same composition. The lag time measured before shrinking starts is longer than the time expected for the surfactant concentration to exceed the critical aggregation concentration in the gels, suggesting that the gels are arrested for some time in a metastable state before the surface phase starts to form.

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Controlled Release

Cited by 66 publications

References 121 publications

Drug-Eluting Polyacrylate Microgels: Loading and Release of Amitriptyline

Drug-Eluting Polyacrylate Microgels: Loading and Release of Amitriptyline

Ion-Exchange Controls the Kinetics of Deswelling of Polyelectrolyte Microgels in Solutions of Oppositely Charged Surfactant

Shrinking Kinetics of Polyacrylate Gels in Surfactant Solution

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