Alginates as tablet disintegrants: Understanding disintegration mechanisms and defining ranges of applications.

Alginates are biopolymers that have been investigated for their use in food and medical fields. Minimal information is available regarding their potential application as tablet superdisintegrants. Here we studied the disintegration action of sodium alginate (SA), calcium alginate (CA) and alginic acid (AA). Initially, we characterised the swelling and wicking abilities and the disintegration mechanism of pure disintegrants. We found that the liquid uptake of both CA and AA is more swelling-driven in phosphate buffer and more wicking-driven in hydrochloric acid and water. CA acts by shape-recovery, AA by a combination of swelling and shape-recovery mechanisms. SA cannot be used as disintegrant due to gelling. In the second part of the paper, the disintegration time of formulations with different physico-chemical properties and different alginate concentrations (i.e. 4% and 10%) was measured, thus delivering a direct readout for the ranges of application of alginates as tablets disintegrants. The main observations are: i) CA and AA often provide very rapid disintegration, similarly to the superdisintegrants used as controls; ii) the action of CA is more susceptible to the medium conditions than AA; iii) CA underperforms in hard tablets containing a binder; iv) both CA and AA have slightly slower disintegration than other superdisintegrants in tablets containing a hydrophobic component. While the suitability of CA as a disintegrant is formulation- and medium- dependent, AA appears as a promising tablet superdisintegrant, particularly for the development of uncomplicated hydrophilic formulations for the nutraceutical and supplement industry, where natural ingredients are favoured.