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In this study, the dissolution properties of celecoxib (CX) solid dispersions manufactured from Eudragit 4155F and polyvinylpyrrolidone (PVP) were evaluated. Hot-melt extrusion (HME) technology was used to prepare amorphous solid dispersions of drug/polymer binary systems at different mass ratios. The drug concentrations achieved from the dissolution of PVP and Eudragit 4155F solid dispersions in phosphate buffer, pH 7.4 (PBS 7.4) were significantly greater than the equilibrium solubility of CX (1.58 μg/mL). The degree of supersaturation increased significantly as the polymer concentration within the solid dispersion increased. The maximum drug concentration achieved by PVP solid dispersions did not significantly exceed the apparent solubility of amorphous CX. The predominant mechanism for achieving supersaturated CX concentrations in PBS 7.4 was attributed to stabilization of amorphous CX during dissolution. Conversely, Eudragit 4155F solid dispersions showed significantly greater supersaturated drug solutions particularly at high polymer concentrations. For example, at a drug/polymer ratio of 1:9, a concentration of 100 μg/mL was achieved after 60 min that was stable (no evidence of drug recrystallization) for up to 72 h. This clearly identifies the potential of Eudragit 4155F to act as a solubilizing agent for CX. These findings were in good agreement with the results from solubility performed using PBS 7.4 in which Eudragit 4155F had been predissolved. In these tests, Eudragit 4155F significantly increased the equilibrium solubility of CX. Solution (1)H NMR spectra were used to identify drug/polymer interactions. Deshielding of CX aromatic protons (H-1a and H-1b) containing the sulfonamide group occurred as a result of dissolution of Eudragit 4155F solid dispersions, whereas deshielding of H-1a protons and shielding of H-1b protons occurred as a result of the dissolution of PVP solid dispersions. In principle, it is reasonable to suggest that the different drug/polymer interactions observed give rise to the variation in dissolution observed for the two polymer/drug systems.

The interest in hot-melt extrusion (HME) as a drug delivery technology for the production of glass solutions is growing rapidly. HME glass solutions have a tendency to recrystallize during storage and also typically have a very dense structure, restricting the ingress of dissolution fluid and retarding drug release. In this study, we have used HME to manufacture glass solutions containing celecoxib (CX) and polyvinylpyrrolidone (PVP) and have assessed the use of supercritical carbon dioxide (scCO2) as a pore-forming agent to enhance drug release. Differential scanning calorimetry confirmed the formation of glass solutions following extrusion. All extrudates exhibited a single glass transition temperature (Tg), positioned between the Tg values of CX and PVP. The instability of glass solutions is a significant problem during storage. Stabilization may be improved through the appropriate choice of excipient to facilitate drug–polymer interactions. The Gordon–Taylor equation showed that the Tg values of all extrudates expected on ideal mixing were lower than those observed experimentally. This may be indicative of drug–polymer interactions that decrease free volume and elevate the Tg. Molecular interactions between CX and PVP were further confirmed using Fourier transform infrared and Raman spectroscopy. Storage stability of the extrudates was shown to be dependent on drug loading. Samples containing a higher CX loading were less stable, which we ascribed to decreased Tg and hence increased mobility within the drug–polymer matrix. The solubility of CX was improved through the formulation of extruded glass solutions, but release rate was relatively slow. Exposure of extrudates to scCO2 had no effect on the solid-state properties of CX but did produce a highly porous structure. The drug-release rate from extrudates after scCO2 exposure was significantly higher.

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The objective of this study was to investigate the role of amorphous domain of polyethylene oxide (PEO), a semicrystalline polymer, on the stability of drug/PEO solid dispersion. Molecular dispersion of drugs within hydrophilic low molecular weights PEOs (solid solution) has been demonstrated as a viable approach to enhance the dissolution properties and hence the oral bioavailability of poorly soluble drugs. In this system, the drug molecules are dissolved within the amorphous domain of the polymer and a miscible amorphous drug/polymer combination can result in a decrease of the polymer crystallinity, and hence increasing its amorphous fraction. This may result in increasing the drug solubility in the polymer hence affecting the stability of drug/polymer solid dispersion system. PEO is a highly crystallisable semi-crystalline polymer in natural and a rapid decrease in the amorphous fraction of the polymer may occur immediately after hot-melt extrusion resulting a forced migration of amorphous drug into nearby amorphous region. Thus, the actual concentrations of the drug within PEO solid dispersion were much higher than the concentration that we intended. Therefore, we are proposing a novel method of stabilising the amorphous drug/PEO solid dispersion by stabilising the amorphous region of PEO using another amorphous polymer. Inclusion of a miscible polymer that can increase the glass transition (Tg) of PEO (antiplasticization) or/and form strong inter-polymer interactions was used to enhance the stability of the amorphous PEO. In this study, the effects of inter-polymer interactions and miscibility between PEO and an amorphous polymer of high Tg, Eudragit ® S100, on the stability of the amorphous PEO and consequently the PEO/drug celecoxib (CX) solid dispersion was studied. Hot-melt extrusion (HME) was used to prepare different ratios of binary polymer blends of PEO/S100 (70/30, 50/50 and 30/70 w/w) and ternary solid dispersion systems containing pre-defined drug loading within the PEO/S100 polymer blends. Results from differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA) suggested a great miscibility between PEO and S100 polymer blends particularly in the 50/50 ratio. After immediately HME, single Tg was observed in all ternary systems that increase with increasing S100 amount (antiplasticization). The completely absence of PXRD crystalline Bragg's peaks also suggested the full amorphous CX/polymer solid dispersion has been produced. Upon storage, CX crystallized rapidly from the CX/PEO (30/70) system within 3 days at 40°C and 75% RH, whereas it remained stable without crystallization up to 4 weeks within CX/(PEO/S100) 30/(50/50) system. Interestingly, both the stability of the amorphous PEO and CX were greater in the ternary system containing the polymer blend at 50/50 ratio than other systems. Despite of the lower Tg of 30/(50/50) system than 30/(30/70) one, the former was more stable. This indicates that the antiplasticization effects by Eudragit ® S100 were not the ...

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The properties of hydrogels, in particular their high biocompatibility and water sorption uptake, make hydrogels very attractive in drug delivery and biomedical devices. These favorable features of hydrogels are compromised by certain structural limitations such as those associated with their low mechanical strength in the swollen state. This review highlights the most important challenges that may seriously affect the practical implementation of hydrogels in clinical practice and the solutions that may be applied to overcome these limitations.