Polyvinylamine-based capsules: a mechanistic study of the formation using alginate and cellulose sulphate

Capsules based on sodium alginate (SA) and sodium cellulose sulphate (SCS), have been prepared using polyvinylamines (PVAm) of varying intrinsic viscosities. The resulting capsules are relatively dense in nature, revealing a bursting force which is four times that observed for the classical SA/SCS/polymethylene-co-guanidine chemistry. Molar mass cutoffs were typically in the 10-70 kDa range. A mechanistic study was carried out where the reaction time, ionic strength and pH of the reaction mixture, as well as the stoichiometry of the polyanion blend and the PVAm molar mass were varied. It is postulated that both the SA-PVAm and the SCS-PVAm binary interactions contribute to the mechanical properties and the permeability of the resulting capsules. The polyvinylamine-based chemistry offers interesting alternatives to the PMCG system in that it provides a means to produce capsules at low, or zero, ionic strengths. Subtle changes in the pH, or the SA:SCS ratio, can also be used to tune the bursting force quite sensitively. The most appropriate capsules, for transplantation, would likely be formed at polyanion levels of 1.2 wt% with a PVAm molar mass below 17 kDa.