Mechanical properties and structure of swollen crosslinked high amylose starch tablets

Crosslinked high amylose starch (CLHAS) has been introduced as an excipient for controlled oral drug delivery. The kinetics of delivery is governed by the diffusion of the medication through a hydrogel matrix, which forms as water penetrates the CLHAS tablet. The formation of the gel from the compre ssed spray-dried starch powder comes from pseudo-crosslinking of particles by the self-assembly of amylose and amylopectin segments into double helice s. Tablets reach equilibrium swelling after more than 24 It and contain abo ut 200% water. They demonstrated nearly reversible non-linear viscoelastic properties. Under compression, water flows out and vice-versa for decompres sion suggesting a sponge-like behaviour. A series of tablets fabricated und er increasing compression force in the dry state showed a decrease of wet e quilibrium stiffness with increasing fabrication pressure. Scanning electro n microscopy on freeze-dried tablets reveals a fine porous texture at the s urface of the tablets, which forms, in the first minutes of water penetrati on. On the other hand the internal texture which develops over longer perio ds has much larger pores which account for the high equilibrium water conte nt and the observed sponge-like behaviour. (C) 2002 Elsevier Science Ltd. A ll rights reserved.