This study investigated the basic physico-chemical property and binding functionality of commonly used commercial direct compression binders/fillers. The compressibility of these materials was also analyzed using compression parameters derived from the Heckel, Kawakita, and Cooper-Eaton equations. Five classes of excipients were evaluated, including microcrystalline cellulose (MCC), starch, lactose, dicalcium phosphate (DCP), and sugar. In general, the starch category exhibited the highest moisture content followed by MCC, DCP, lactose, and finally sugar; DCP displayed the highest density, followed by sugar, lactose, starch, and MCC; the material particle size is highly processing dependent. The data also demonstrated that MCC had moderate flowability, excellent compressibility, and extremely good compact hardness; with some exceptions, starch, lactose, and sugar generally exhibited moderate flowability, compressibility, and hardness; DCP had excellent flowability, but poor compressibility and hardness. This research additionally confirmed the binding mechanism that had been well documented: MCC performs as binder because of its plastic deformation under pressure; fragmentation is the predominant mechanism in the case of lactose and DCP; starch and sugar perform by both mechanisms.
Biodegradable polymer hydrogel networks based on hydrophilic dextran derivative of allyl isocyanate (dex-AI) and hydrophobic poly (D,L) lactide diacrylate macromer (PDLLAM) were synthesized, and their swelling and morphological properties were studied. During a 2-day incubation, the higher the PDLLAM composition in the hydrogel, the slower the swelling as well as the lower the extent of swelling were. A 3D porous network structure was observed by scanning electron microscope. The rate of formation of this 3D porous network structure depended on the hydrophilicity of the components, their composition ratio, and the degradation time. The highly hydrophilic dex-AI component facilitated the formation of this 3D porous network structure at an earlier immersion period, while the degradability of the PDLLAM component would make this 3D porous network structure more open at a later immersion period. Indomethacin, a low molecular weight and moderately hydrophobic drug, was incorporated into the hydrogels for the release study in pH 7.4 phosphate buffer solution at 37 degrees C. The release kinetics suggested, as the PDLLAM composition increased, the indomethacin diffusion coefficient (D) and release half life time (t(1/2)) decreased, while the release index n increased. The controlled release mechanism was determined by the combination of three factors: the rate and degree of formation of swelling-induced 3D porous structure in the hydrogel, the hydrolytic degradation of PDLLAM components, and the hydrophobic interaction between PDLLAM and IDM.
ABSTRACT:A new class of biodegradable hydrogels, consisting of hydrophobic poly(D,L)-lactic acid (PDLLA) and hydrophilic dextran segments with a polymer network structure, was synthesized with UV photopolymerization. Unsaturated vinyl groups first were introduced onto the PDLLA and dextran polymer backbones, then followed by a crosslinking reaction of diacrylate-terminated PDLLA and dextran acrylate. The chemical crosslinking forced the hydrophobic PDLLA and hydrophilic dextran segments to mix with each other in the network hydrogels. The new polymers were characterized by standard polymer characterization methods such as NMR, Fourier transform infrared spectroscopy, and gel permeation chromatography. The effects of reaction time, temperature, and molar ratio of the reactants on the incorporation of acrylate onto the polymer backbone were examined. A series of hydrogels with different dextran/PDLLA composition ratios was prepared, and their swelling behaviors were studied. These new bicomponent network hydrogels had a wide range of hydrophilicity to hydrophobicity that was difficult to achieve in totally hydrophilic hydrogels.
The controlled release of insulin from a series of biodegradable hybrid hydrogel network containing dextran derivative of allyl isocyanate (dex-AI) and poly (D,L) lactide diacrylate macromer (PDLLAM) over a wide range of composition ratio was investigated. Laser confocal scanning microscope was used to understand the insulin dispersion and release mechanism in the hydrogels. We found that the dispersion of insulin in the hydrogel network appeared to become less homogeneous as the PDLLAM composition in the hydrogel increased. The increase in hydrogel degradability imparted by PDLLAM incorporation shifted the hydrogel to a more open structure at a later release time, which facilitated the release rate and extent of insulin. From the result of release kinetics study (i.e., diffusion coefficient), insulin release occurred through diffusion and degradation controlled mechanisms. In addition, a comparison of the release characteristics of indomethacin, insulin and bovine serum albumin from the hydrogel network showed that the following parameters determined the release kinetics: drug molecular weight and size, hydrogel swellability and degradability, drug solubility in water and the hydrophobic interaction between drugs and the hydrogel network.
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