Edible solid foams as porous substrates for inkjet-printable pharmaceuticals
The aim of this study was to investigate new porous flexible substrates, i.e., solid foams that would serve as a carrier with a high ink absorption potential for inkjet printable pharmaceuticals. Propranolol hydrochloride was used as a model active pharmaceutical ingredient (API). Pharmaceutically approved and edible cellulose derivatives and gums together with different additives were evaluated as a base for the substrate. Different methods for preparation of a solid foam such as freeze-drying, vacuum oven drying and drying at room temperature were explored. Only freeze-drying of the polymeric solutions resulted in the desired porous and flexible, but mechanically stable, soft sponge-like substrates with hydroxypropyl methylcellulose (HPMC)-based solid foams being the most suitable for the use in continuous inkjet printing. The plasticized HPMC foams had a superior absorption capacity and fast penetration speed for the different solvents due to the open cell pore structure and higher porosity as compared to nonplasticized additive-free foams, although, the latter were less hygroscopic. The produced solid foams were well suited for inkjet printing of high volumes of API-containing ink. The inkjet-printed API was immediately released from the dosage forms upon contact with the dissolution medium. This work demonstrates that the fabricated solid foams, based on plasticized HPMC, show a great potential as porous carriers in the fabrication of high dose dosage forms by inkjet printing.