Cross-linked amylose as matrix for drug controlled release. X-ray and FT-IR structural analysis

For cross-linked amylose (CLA) tablets prepared by direct compression, a linear increase in cross-linking degree (cld) defined as percentage of epichlorohydrin cross-linker/polymer, generates non-monotonous variation of drug release time. Controlled release (up to 20–24 h) properties were obtained only for tablets from CLA (Contramid^TM) with relatively low cld (CLA-2 up to CLA-6). Moderate increase in cld (CLA-15) generates a sharp decrease in the release time (2–6 h). This is a particular characteristic of the CLA matrix. The controlled release properties were related to the X-ray pattern of the dry CLA network. The increase in cld induces a transition from B-type (double helix) to a predominat V-type (single helix) and to more amorphous conformation of CLA powders. Furthermore, FT-IR data indicated low free water content at low cld. For low cross-linked CLA, chains are closely located and stabilized by HO groups involved in hydrogen bonding and thus more resistant to hydration and more appropriate for the control of drug release.