Phase separation drug-polymer

Microcapsules of PCL and its copolymers may be prepared by aircoating (fluidized bed), mechanical, and, most commonly, solution methods. Typically, the solution method has involved emulsification of the polymer and drug in a two-phase solvent-nonsolvent mixture (e.g., CH2Cl2/water) in the presence of a surfactant such as polyvinyl alcohol. Residual solvent is removed from the tnicrocapsules by evaporation or by extraction (70). Alternatively, the solvent combination can be miscible provided one of the solvents is high-boiling (e.g., mineral spirits) phase separation is then achieved by evaporation of the volatile solvent (71). The products of solution methods should more accurately be called microspheres, for they... 

Chloropromazine (8—34 wt% loading) has been microencapsulated in PCL-cellulose propionate blends by the emulsion solvent evaporation method (61). Phase separation for some ratios of the two polymers was detectable by SEM. The release rate from microcapsules in the size range of 180-250 pm in vitro (Fig. 11) was directly proportional to the PCL content of the blend, the half-life (50% drug release)... 

If the drug and polymer are miscible in their Luid state, then as discussed in Section Thermodynamic Perspective of Miscibility and Phase Separation in Solid Dispersions, the mixture may or may not undergo phase separation during solidiLcation, thereby inLuencing the structure of solid dispersion. 

Quantitative PXRD and thermal analysis have been used to determine solid solubility of drugs in polymeric carrier [132-134], When phase separation occurs in solid dispersion, it results in formation of a drug-rich phase and a polymer-rich phase. The polymer-rich phase could retain, either by restricting molecular mobility or by interacting with drug, a certain portion of drug within its matrix. 

The portion of drug that remains trapped within the polymer may be estimated by measurfggf he the polymer-rich phase. In instances whl ef polymer-rich phase issimilartothatof neat polymer, a complete phase separation may be assumed. In other instances, the differ gsolid solubility of drug in polymer. As shown in Figure 18.12, phase separation of trehalose was observed from dextran solid dispersions in the 4-day and 34-day samples. However, a certain fraction of trehalose remained miscible with dextran as indicated by the substantially low... 

Coacervation phase separation. This technique is used to microencapsulate water-soluble drugs. The core material (drug) is suspended in a nonaqueous polymer solution (coating material), and the polymer is made to form a uniform coat by various approaches, such as temperature change, addition of an incompatible polymer, addition of a nonsolvent, or addition of a salt. 

Emulsion phase separation. Water-soluble drugs are fabricated in the form of microcapsules by this method. An aqueous phase containing dissolved drug and an organic phase containing polymer are emulsified. Then polymer is phase separated using the techniques such as temperature change, addition of salts, etc. A nonsolvent then is used to harden the microspheres. 

Generally, all the mechanisms of polymer coacervation involve some sort of phase separation, thereby producing more or less dense coacervate microdroplets. These microdroplets can either engulf an additional component, such as a dissolved drug, or deposit on solid surfaces, which is typically used for coating solid particles added to the system, e.g., drug particles or living cells. 

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