Controlled drug delivery from swellable hydroxypropylmethylcellulose matrices: model-based analysis of observed radial front movements

Characterisation, slow-release, and antibacterial properties of carboxymethyl chitosan/inulin hydrogel film loaded with novel antilisterial durancin GL

This paper reports the development of a hydrogel film with antibacterial activity and controlled release characteristics. Carboxymethyl chitosan (CMCS) is grafted onto durancin GL and inulin via a mediated reaction between N-hydroxysuccinimide and 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride. Rheology tests, Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy, and lap shear tests confirmed the formation of a stable chemical cross-linking and excellent adhesion hydrogel with 4 % CMCS and 8 % inulin. The CMCS/inulin hydrogel film loaded with durancin GL appears transparent and uniform. FTIR spectroscopy results reveal the interaction mode among CMCS, inulin, durancin GL, and the hydrogel film structure. Cross-linking improved thermal stability and water-vapour barrier performance. The hydrophobicity of CMCS/inulin @Durancin GL increased under a durancin GL concentration of 0.036 g/30 mL, and the release of active substances is prolonged. In-vitro antibacterial capacity and salmon preservation experiments show that the addition of durancin GL enhanced the antibacterial activity of the hydrogel film. Therefore, CMCS/inulin@Durancin GL hydrogel films can be used as fresh-keeping packaging materials in practical applications.

Analysis of NSAIDs in Rat Plasma Using 3D-Printed Sorbents by LC-MS/MS: An Approach to Pre-Clinical Pharmacokinetic Studies

Analytical sample preparation techniques are essential for assessing chemicals in various biological matrices. The development of extraction techniques is a modern trend in the bioanalytical sciences. We fabricated customized filaments using hot-melt extrusion techniques followed by fused filament fabrication-mediated 3D printing technology to rapidly prototype sorbents that extract non-steroidal anti-inflammatory drugs from rat plasma for determining pharmacokinetic profiles. The filament was prototyped as a 3D-printed sorbent for extracting small molecules using AffinisolTM, polyvinyl alcohol, and triethyl citrate. The optimized extraction procedure and parameters influencing the sorbent extraction were systematically investigated by the validated LC-MS/MS method. Furthermore, a bioanalytical method was successfully implemented after oral administration to determine the pharmacokinetic profiles of indomethacin and acetaminophen in rat plasma. The Cmax was found to be 0.33 ± 0.04 µg/mL and 27.27 ± 9.9 µg/mL for indomethacin and acetaminophen, respectively, at the maximum time (Tmax) (h) of 0.5–1 h. The mean area under the curve (AUC0–t) for indomethacin was 0.93 ± 0.17 µg h/mL, and for acetaminophen was 32.33± 10.8 µg h/mL. Owing to their newly customizable size and shape, 3D-printed sorbents have opened new opportunities for extracting small molecules from biological matrices in preclinical studies.

Phase-Field Model for Drug Release of Water-Swellable Filaments for Fused Filament Fabrication

This paper treats the drug release process as a phase-field problem and a phase-field model capable of simulating the dynamics of multiple moving fronts, transient drug fluxes, and fractional drug release from swellable polymeric systems is proposed and validated experimentally. The model can not only capture accurately the positions and movements of the distinct fronts without tracking the locations of fronts explicitly but also predict well the release profile to the completion of the release process. The parametric study has shown that parameters including water diffusion coefficient, drug saturation solubility, drug diffusion coefficient, initial drug loading ratio, and initial porosity are critical in regulating the drug release kinetics. It has been also demonstrated that the model can be applied to the study of swellable filaments and has wide applicability for different materials. Due to explicit boundary position tracking being eliminated, the model paves the way for practical use and can be extended for dealing with geometrically complex drug delivery systems. It is a useful tool to guide the design of new controlled delivery systems fabricated by fused filament fabrication.

An overview on the mathematical modeling of hydrogels' behavior for drug delivery systems

Hydrogels-based systems (HBSs) for drug delivery are nowadays extensively used and the interest in modeling their behavior is dramatically increasing. In this review a critical overview on the modeling approaches is given, quantitatively and qualitatively analyzing the publications on the subject, the trend of the publications per year and the type of modeling approaches. It was found that, despite the drug release fitting models (i.e. Higuchi's equation) are the most abundant, their use for HBSs is decreasing in the last years and luckily, considering the limiting assumption on which they were built, they will be confined to simple mathematical fitting equations. Within the mechanistic models the "multi-component" with the swelling approximation (mass transport only) and with the mechanics (fully coupled) are experiencing the highest growth rate, with much more interest toward the last one that, in the next years could be able to provide a first principles model. Statistical models, especially based on the response surface methodology, are rapidly spreading in the scientific community mainly thanks to their ability to be predictive, regardless of the phenomenology, in the analyzed design space with very low efforts. Neural Networks models for HBSs, in countertrend with their use in the pharmaceutical industry, have never take off preferring less data demanding statistical models.

Collagen-Hydroxypropyl Methylcellulose Membranes for Corneal Regeneration

To improve intraocular transparency of collagen matrices, hydroxypropyl methylcellulose (HPMC) was introduced for the first time into cross-linked collagen to form collagen-HPMC composite membranes. Light transmittance and refractive indices of the membranes are enhanced by incorporation of HPMC in comparison to the control of cross-linked collagen membranes. Maximum light transmittance of the collagen-HPMC membrane was up to 92%. In addition, their permeability of nutrients such as glucose, tryptophan, and NaCl was superior or comparable to that of human corneas. In vitro results demonstrated that the collagen-HPMC membrane supported adhesion and proliferation of human corneal epithelial cells (HCECs), showing good cytocompatibility to HCECs. The corneas maintained a smooth surface and clear stroma postoperatively after 7 months of implantation of collagen-HPMC membranes into the corneas of rabbits. The good intraocular biocompatibility was verified by maintaining a high optical clarity for over 6 months after transplantation. Hematoxylin and eosin staining results showed the growth of stromal keratocytes into the collagen-HPMC implants, indicating the ability of the collagen-HPMC membrane to induce corneal cell regeneration. Taken together, the collagen-HPMC membrane might be a promising candidate for use in corneal repair and regeneration.

In Vivo Evaluation of a PEO-Gellan Gum Semi-Interpenetrating Polymer Network for the Oral Delivery of Sulpiride

In this study, an optimized epichlorohydrin-crosslinked semi-interpenetrating polymer network xerogel matrix system (XePoMas) for the controlled delivery of sulpiride was prepared. The ability of XePoMas to sustain drug release was determined by in vitro and in vivo drug release experiments. Swelling of the xerogel over the 24-h experimental period ranged from 346 to 648%; swelling was observed to increase exponentially over the initial 8 h. In vitro drug release depicted a linear zero order drug release profile with an R ² value of 0.9956. The ability of the fabricated XePoMas to sustain drug release and enhance bioavailability of sulpiride in vivo was investigated by evaluating the plasma drug concentration over 24 h in the large pig model. The optimized XePoMas formulation was shown to increase intestinal absorption of sulpiride to a greater extent than the marketed product in vivo, with a C _max of 830.58 ng/mL after 15 h.

Drug release kinetics from carboxymethylcellulose-bacterial cellulose composite films

Composite films of sodium carboxymethyl cellulose and bacterial cellulose (NaCMC-BC) cross-linked with citric acid (CA) were prepared by solution casting method. Ibuprofen sodium salt (IbuNa) has been used to study the mechanism of drug release from composite films. Surface morphology was investigated by scanning electron microscopy (SEM) and proved that the BC content influences the aspect of the films. Fourier transformed infrared spectroscopy (FTIR) revealed specific peaks in IR spectra of composite films which sustain that NaCMC was cross-linked with CA. Starting from swelling observations, the release kinetic of IbuNa was described using a model which neglects the volume expansion due to polymer swelling and which considers non-linear diffusion coefficients for drug and solvent. The IbuNa release is also influenced by BC content, the drug release rate was decreasing with the increase of BC content.

"Rolling" phenomenon in twin screw granulation with controlled-release excipients

The developed knowledge regarding use of twin screw granulators for continuous wet granulation has been primarily limited to immediate release formulations in the literature. The present study highlights an issue previously unreported for wet granulation with twin screw extruders when using formulations containing controlled-release (CR) excipients. Long (3-10 mm), twisted noodle-like granules can be produced in the presence of these excipients that are difficult to control and are anticipated to create complications in downstream unit operations to the granulator. Working with two different CR excipients, METHOCEL™ K4M and Kollidon® SR, each blended at different ratios with a mixture of 80% α-lactose monohydrate/20% microcrystalline cellulose, these unique particles were found to be produced in the conveying elements of the extruder, arising from a rolling action at the top of the screw flights. The CR excipients adhesively strengthen the wetted mass, forming this undesired granule shape such that they persisted to the exit of the machine; the shape appeared most strongly affected by screw speed, producing particles of higher aspect ratio as speed was increased. Adjusting the concentration of these CR excipients in the formulation, the flow rate or the type of compression element used in the screws proved ineffective in controlling the problem. Rather, a re-design of the extruder screws was required to prevent generation of these extended-form granules.

Improvement of Polymer Flooding Using in-Situ Releasing of Smart Nano-Scale Coated Polymer Particles in Porous Media

The main purpose of this paper is modeling and simulation of in-situ releasing of smart nano-sized core-shell particles at the water-oil interface during polymer flooding. During the polymer flooding process, when these nano-particles reach the water-oil interface, migrate to the oil phase and the hydrophobic layer of them dissolves in this phase. After dissolution of this protective nano-sized layer, the hydrophilic core containing a water-soluble ultra high molecular weight polymer diffuses back into the water phase and with dissolving in this phase, dramatically increases viscosity of flooding water in the neighborhood of the water-oil interface. In this study, two different time-dependent dissolution models are implemented. A swellable-chain disentanglement model with concentration-dependent diffusion coefficient is considered for dissolution of the core polymer into the aqueous phase, whereas, surface chain disentanglement with constant diffusion coefficient is considered for dissolution of the shell polymer in the oil phase. Using finite difference scheme, the governing equations are numerically solved by defining some dimensionless parameters for the main parameters as well as the moving boundaries. In addition, some experimental flooding tests in micromodel were carried out to experimentally investigate the recovery factor of using these particles compared to those of the conventional polymer flooding.

Sol-Gel Behavior of Hydroxypropyl Methylcellulose (HPMC) in Ionic Media Including Drug Release

Sol-gel transformations in HPMC (hydroxypropyl methylcellulose) are being increasingly studied because of their role in bio-related applications. The thermo-reversible behavior of HPMC is particularly affected by its properties and concentration in solvent media, nature of additives, and the thermal environment it is exposed to. This article contains investigations on the effects of salt additives in Hofmeister series on the HPMC gelation. Various findings regarding gelation with salt ions as well as with the ionic and non-ionic surfactants are presented. The gel formation in physiological salt fluids such as simulated gastric and intestine fluids is also examined with the interest in oral drug delivery systems. The processes of swelling, dissolution and dispersion of HPMC tablets in simulated bio-fluids are explored and the release of a drug from the tablet affected by such processes is studied. Explanations are provided based on the chemical structure and the molecular binding/association of HPMC in a media. The test results at the body or near-body temperature conditions helped in understanding the progress of the gelation process within the human body environment. The detailed interpretation of various molecule level interactions unfolded the sol-gel mechanisms and the influence of a few other factors. The obtained test data and the established mathematical models are expected to serve as a guide in customizing applications of HPMC hydrogels.

Drug loading into and drug release from pH- and temperature-responsive cylindrical hydrogels

Hydrogels that undergo deformation upon appropriate changes in pH or temperature have considerable promise as drug delivery vehicles. Drug uptake in swelling and nonswelling cylindrical hydrogels and drug release from these into a target fluid are investigated here. A mathematical model for hydrogel-solution composite, a composite of a distributed parameter system (cylindrical hydrogel) and a lumped parameter system (surrounding solution), is developed. The polymer network displacement in a swelling/deswelling hydrogel is described by a stress diffusion coupling model. The analytical solution for network displacement is used to predict solvent intake by swelling hydrogels, solvent efflux from deswelling hydrogels, and changes in pressure, porosity, and effective drug diffusivity. These in turn influence drug uptake during and after hydrogel swelling and drug release from hydrogel during and after deswelling. Numerical results illustrate benefits of hydrogel swelling for drug loading and merits of different modes of drug release. Drug uptake and drug release by temperature-responsive hydrogels are compared with those by hydrogels not subject to deformation.

Magnetic resonance imaging and image analysis for assessment of HPMC matrix tablets structural evolution in USP Apparatus 4

PURPOSE

The purpose of the study was to present a methodology for the processing of Magnetic Resonance Imaging (MRI) data for the quantification of the dosage form matrix evolution during drug dissolution. The results of the study were verified by comparison with other approaches presented in literature.

METHODS

A commercially available, HPMC-based quetiapine fumarate tablet was studied with a 4.7T MR system. Imaging was performed inside an MRI probe-head coupled with a flow-through cell for 12 h in circulating water. The images were segmented into three regions using threshold-based segmentation algorithms due to trimodal structure of the image intensity histograms.

RESULTS

Temporal evolution of dry glassy, swollen glassy and gel regions was monitored. The characteristic features were observed: initial high expansion rate of the swollen glassy and gel layers due to initial water uptake, dry glassy core disappearance and maximum area of swollen glassy region at 4 h, and subsequent gel layer thickness increase at the expense of swollen glassy layer.

CONCLUSIONS

The temporal evolution of an HPMC-based tablet by means of noninvasive MRI integrated with USP Apparatus 4 was found to be consistent with both the theoretical model based on polymer disentanglement concentration and experimental VIS/FTIR studies.

Evaluation of Galactomannan from Gleditsia Sinensis Lam. as Sustained Release Material in Colonic Drug Delivery

The galactomannan from endosperm of G. sinensis seeds was used as sustained release material in the matrix tablets prepared at different concentration of 5, 10 and 15 % corresponding to formulations of G5, G10 and G15, for the release of theophylline. The drug release behaviors of the systems were investigated, including the swelling and morphological studies and texture analysis. The dissolution tests were conducted in 0.1 M hydrochloric acid and pH 6.8 phosphate buffered saline. The results of release studies demonstrated that G10 with 10 % galactomannan concentration showed a better control of the drug release profiles. The percents of cumulative drug released in 24 h were 98.8, 90.2 and 83.4 % for G5, G10 and G15, respectively. All the systems exhibited the typical morphological behavior of a swellable matrix. Results of texture analysis on the swollen tablets confirmed that diffusion drug release mechanism played the major role in G10 and G15 systems while the drug delivery kinetic towards an erosion/relaxation mechanism for G5 matrix tablets.

The use of hypromellose in oral drug delivery

Hypromellose, formerly known as hydroxypropylmethylcellulose (HPMC), is by far the most commonly employed cellulose ether used in the fabrication of hydrophilic matrices. Hypromellose provides the release of a drug in a controlled manner, effectively increasing the duration of release of a drug to prolong its therapeutic effect. This review provides a current insight into hypromellose and its applicability to hydrophilic matrices in order to highlight the basic parameters that affect its performance. Topics covered include the chemical, thermal and mechanical properties of hypromellose, hydration of the polymer matrices, the mechanism of drug release and the influence of tablet geometry on drug-release rate. The inclusion of drug-release modifiers within hypromellose matrices, the effects of dissolution media and the influence of both the external environment and microenvironment pH within the gel matrix on the properties of the polymer are also discussed.

Modelling of diclofenac sodium diffusion from swellable and water-soluble polyethylene oxide matrices

Objectives

The main objective of this study was to develop a mathematical model for the characterization of diclofenac sodium diffusion from polyethylene oxide (PEO) matrices. A model was developed on the basis of the diffusion theory accounting for the characteristics of the polymer: swelling with subsequent dissolution in water. The concentration-dependent diffusion of drug and water was taken into account. Experimental data were analysed using a computer software program as an aid for solving partial differential equations.

Methods

Six formulations of matrix tablets with different drug-excipient ratios were prepared using low-molecular-weight PEO as a matrix-forming material. For obtaining drug release data, dissolution studies were performed and water uptake by pure PEO matrices was studied as well.

Key findings

A good agreement of the developed model with experimental results was demonstrated. Some anomalies in drug diffusion were observed and their origin was questioned. Changes in the parameters characterizing the process of diffusion are attributed to glassy-rubbery polymer transitions. Additional interpretation of this phenomenon on the basis of percolation theory is also provided.

Conclusions

The obtained model has the ability to predict the required characteristics of matrices for desired drug release. The composition of batches with undesirable release properties can be predetermined and avoided in manufacturing.

Design and evaluation of a novel matrix type multiple units as biphasic gastroretentive drug delivery systems

A biphasic gastroretentive floating drug delivery system with multiple-unit mini-tablets based on gas formation technique was developed to maintain constant plasma level of a drug concentration within the therapeutic window. The system consists of loading dose as uncoated core units, and prolonged-release core units are prepared by direct compression process; the latter were coated with three successive layers, one of which is seal coat, an effervescent (sodium bicarbonate) layer, and an outer polymeric layer of polymethacrylates. The formulations were evaluated for quality control tests, and all the parameters evaluated were within the acceptable limits. The system using Eudragit RL30D and combination of them as polymeric layer could float within acceptable time. The drug release was linear with the square root of time. The rapid floating and the controlled release properties were achieved in this present study. When compared with the theoretical release profile, the similarity factor of formulation with coating of RS:RL (1:3)-7.5%, was observed to be 74, which is well fitted into zero-order kinetics confirming that the release from formulation is close to desired release profile. The stability samples showed no significant change in dissolution profiles (p > 0.05). In vivo gastric residence time was examined by radiograms, and it was observed that the units remained in the stomach for about 5 h.

Drug-eluting polymer implants in cancer therapy

BACKGROUND

Drug-eluting polymer implants present a compelling parenteral route of administration for cancer chemotherapy. With potential for minimally invasive, image-guided placement and highly localized drug release, these delivery systems are playing an increasingly important role in cancer management. This is particularly true as the use of labile proteins and other bioactive molecules is likely to increase in the upcoming years.

OBJECTIVE

In this review, we present the current trends in the application of Pre-formed and in situ-forming systems as drug-eluting implants for cancer chemotherapy.

METHODS

We outline the clinically available options as well as up-and-coming technologies and their advantages and challenges. We also describe ongoing related innovations with image-guided drug delivery, mathematical modeling of implanted delivery systems and implanted drug delivery in combination with other therapies.

RESULTS/CONCLUSION

Whether used alone or combined with other minimally invasive procedures, drug-eluting polymeric implants will play a significant role in the future of cancer management.

Noncross-Linked Copolymers of Dimethylaminoethyl Methacrylate and Methacrylic Acid as Oral Drug Carriers

The purpose of this study was to synthesize new water-soluble ampholytic copolymers consisting of tertiary amine and carboxylic acid pendent groups for oral drug carriers. The polymers were prepared with a 1:1 molar ratio of dimethylaminoethyl methacrylate and methacrylic acid by free radical polymerization. After polymerization, polymer rods were recovered, dissolved (or swollen) in de-ionized water, and freeze-dried before obtaining fine powders. Drug release experiments with various drugs, representing a variety of drug solubility and types of amine, were carried out with compressed tablets (total weight of 600 mg) containing a variety of basic drugs in pH's of 1.5 and 7. Surprisingly, zero-order release kinetics even from a tablet geometry has been obtained with drug loading ranging from 20-50%. Drug release in pH 7 maintains a zero-order rate up to 80-85% release after a slight initial burst, whereas in pH 1.5 one may not find the initial burst and zero-order kinetics is extended up to 90-95% release. Drug release becomes faster in pH 1.5 than pH 7 due to the faster rate of protonation of the tertiary amine in acidic conditions. The release of basic drugs in pH 1.5 is not significantly different even with varying solubility and types of amine (primary, secondary, and tertiary). However, different drug release profiles in pH 7 are observed with different types of amine and solubility.

Directly Compressed Mini Matrix Tablets Containing Ibuprofen: Preparation and Evaluation of Sustained Release

Directly compressed mini tablets were produced containing either hydroxypropylmethylcellulose (HPMC) or ethylcellulose (EC) as release controlling agent. The dynamics of water uptake and erosion degree of polymer were investigated. By changing the polymer concentration, the ibuprofen release was modified. In identical quantities, EC produced a greater sustaining release effect than HPMC. Different grades of viscosity of HPMC did not modify ibuprofen release. For EC formulations, the contribution of diffusion was predominant in the ibuprofen release process. For HPMC preparations, the drug release approached zero-order during a period of 8 h. For comparative purposes, tablets with 10 mm diameter were produced.

Design and evaluation of matrix-based controlled release tablets of diclofenac sodium and chondroitin sulphate

The purpose of the present study was to develop and characterize an oral controlled release drug delivery system for concomitant administration of diclofenac sodium (DS) and chondroitin sulfate (CS). A hydrophilic matrix-based tablet using different concentrations of hydroxypropylmethylcellulose (HPMC) was developed using wet granulation technique to contain 100 mg of DS and 400 mg of CS. Formulations prepared were evaluated for the release of DS and CS over a period of 9 hours in pH 6.8 phosphate buffer using United States Pharmacopeia (USP) type II dissolution apparatus. Along with usual physical properties, the dynamics of water uptake and erosion degree of tablet were also investigated. The in vitro drug release study revealed that HPMC K100CR at a concentration of 40% of the dosage form weight was able to control the simultaneous release of both DS and CS for 9 hours. The release of DS matched with the marketed CR tablet of DS with similarity factor (f(2)) above 50. Water uptake and erosion study of tablets indicated that swelling followed by erosion could be the mechanism of drug release. The in vitro release data of CS and DS followed Korsmeyer-Peppas and zero-order kinetics, respectively. In conclusion, the in vitro release profile and the mathematical models indicate that release of CS and DS can be effectively controlled from a single tablet using HPMC matrix system.

Doxorubicin and beta-lapachone release and interaction with micellar core materials: experiment and modeling

Polymer micelles with two different core-forming blocks, poly(d,l -lactide) (PLA) and poly(epsilon-caprolactone) (PCL), but the same coronal material, poly(ethylene glycol) (PEG), were investigated in this study as nanoscopic drug carriers. The release of two different drugs, doxorubicin (DOX) and beta-lapachone (beta-lap), from PEG(5k)-b-PCL(5k) and PEG(5k)-b-PLA(5k) micelles was studied at pH 5.0 and 7.4. Mathematical solutions of both Higuchi's model and Fickian diffusion equations were utilized to elucidate the differences between the micelle core materials for the two drugs. The neutral and smaller of the two drugs tested, beta-lap, demonstrated faster, pH-independent release, suggesting that no substantial changes occurred in either micelle core at lower pH. In contrast, the release rate of DOX was found to noticeably increase at lower pH with a larger cumulative amount of drug released. Different core materials were shown to have considerable influence on the release kinetics of both drugs: in both cases, the more hydrophobic PCL core showed slower drug release rates compared with the less hydrophobic PLA core.

Compressed matrix core tablet as a quick/slow dual-component delivery system containing ibuprofen

The purpose of the present research was to produce a quick/slow biphasic delivery system for ibuprofen. A dual-component tablet made of a sustained release tableted core and an immediate release tableted coat was prepared by direct compression. Both the core and the coat contained a model drug (ibuprofen). The sustained release effect was achieved with a polymer (hydroxypropyl methylcellulose [HPMC] or ethylcellulose) to modulate the release of the drug. The in vitro drug release profile from these tablets showed the desired biphasic release behavior: the ibuprofen contained in the fast releasing component was dissolved within 2 minutes, whereas the drug in the core tablet was released at different times (approximately 16 or >24 hours), depending on the composition of the matrix tablet. Based on the release kinetic parameters calculated, it can be concluded that the HPMC core was suitable for providing a constant and controlled release (zero order) for a long period of time.

A mechanistic model of controlled drug release from polymer millirods: Effects of excipients and complex binding

The incorporation of different cyclodextrin (CD) excipients such as HPbeta-CD, beta-CD, gamma-CD or alpha-CD into polymer millirods for complexing beta-lapachone (beta-lap), a potent anti-cancer drug, significantly improved the drug release kinetics with various drug release patterns. However, such a complex system requires a mechanistically based model in order to provide a quantitative understanding of the many molecular events and processes that are essential for the rational development of millirod implants. This study focuses on mathematical modeling of drug release from PLGA cylindrical millirods. This millirod system incorporates multiple components: a PLGA matrix; excipient in free and complex forms; drug in free, bound, and crystalline forms. The model characterizes many dynamic transport and complexation processes that include radial diffusion, excipient complexation and crystalline drug dissolution. Optimal estimates of the model parameters were obtained by minimizing the difference between model simulation and experimentally measured drug release kinetics. The effects of different drug loadings on the drug release rate were simulated and compared with other data to validate this model. Whereas our model can simulate all the experimental data, the Higuchi model can simulate only some of them. Furthermore, our model incorporates mechanisms by which the processes underlying drug release from a polymer matrix can be quantitatively analyzed. These processes include drug entrapment/dissolution in the matrix, drug recrysallization, and supersaturation. This modeling study shows that complex binding capacity, which affects drug initial conditions, drug-polymer interactions, and bound drug behavior in aqueous solution, is crucial in controlling drug release kinetics.