Surface Modified Cellulose Nanocrystals for Drug Polymorph Screening

Abstract

A major design consideration for active pharmaceutical ingredients (APIs) for oral drug delivery is the crystalline form of the API itself. The solubility, and thus bioavailability, depends greatly on the crystal structure and it is essential to select an appropriate polymorph that is stable over the shelf life of the drug and has acceptable solubility. However, due to the sensitivity of the polymorph formation to a variety of conditions, including solvent, temperature, impurities, mixing procedure, size of crystallizer, and more, it is challenging to control the crystallization and identify all the potential polymorphs that may form. Thus, improved techniques for screening and control are needed. Gel phase crystallization uses two methods to affect polymorph formation: particles within the gel provide a surface for heterogeneous nucleation and the pores within the gel allow for confined homogenous nucleation. By changing the surface of cellulose nanocrystals (CNCs), we can change the heterogenous nucleation sites and thus provide a variety of crystallization environments in one tool, valuable for a screening process. CNCs have a high surface area covered with readily-modifiable hydroxyl groups, which enable the production of CNCs with various surface functionalities. These surfaces can be used to form gels via network formation in organic solvents, which promotes API crystallization into a variety of different polymorphs. In this work, we develop supramolecular organogel systems based on CNC derivatives to be used as a favorable environment for crystallizing APIs. Using a variety of amines, including long-chain amines, diamines, and branched amines, we studied the network formation between oxidized cellulose molecules and the resulting API crystallizaiton. The high surface area of the nanocellulose provides a high concentration of interaction sites and the small size of the modified nanocellulose particles has interesting performance in promoting assembly and packing of the composite gel for use in crystallization screening.