Compatibility between Drugs and Polymer in Nanoparticles Produced by the Miniemulsion‐Solvent Evaporation Technique

Abstract Encapsulation of poorly soluble drugs in polymer nanoparticles is a common strategy to increase bioavailability of drugs. The miniemulsion‐solvent evaporation technique is widely used for encapsulating drugs in polymer nanoparticles because it is a versatile process, allowing many drug–polymer pair combinations. However, above a critical concentration of drug, which depends on the drug and polymer, nanoparticles tend to precipitate. Herein, the importance of drug solubility and miscibility in the polymer phase for selecting the optimal polymer matrix is investigated. Ibuprofen, naproxen methyl ester, and naproxen, as models for poorly soluble drugs, are encapsulated with various loadings in polycaprolactone nanoparticles by the miniemulsion‐solvent evaporation method. The miscibility between drug and polymer is estimated by calculating Flory–Huggins interaction parameters (χ) from differential scanning calorimetry measurements and calculating the difference in Hansen solubility parameter of drugs and polymer. Both values can be used for determining the feasibility of the drug encapsulation in polymer nanoparticles.