*2.2.3 Twin screw extrusion*

In twin screw extrusion (TSE) technique, the mixing of materials is carried out in a device known as a twin screw extruder in which milling of the starting materials is carried out below their melting points. Proficient intermixing and high surface interaction and consequently enhanced co-crystal formation are achieved without using the solvent provided by this method [25, 26]. The two co-/counter-rotating screws are accompanied by twin screw units in a solitary barrel. Screw activity offers immediate intermixing and mobility of components sideways the span of the barrel. The materialization of four model co-crystals consumes a 16 mm TSE with four manageable temperature regions as reported by Daurio et al. Theophylline:citric acid, carbamazepine:saccharin, nicotinamide:cinnamic acid, and caffeine:oxalic acid cocrystals were formed by slight grinds of the dry fine particles of both starting components *via* the extruder. The effect of heat on the alteration to a co-crystal was specific to the co-crystal arrangement described, with no ostensive temperature effect on the co-crystal of carbamazepine:saccharin and robust temperature effect on the cocrystal of cinnamic acid: nicotinamide. In a different investigation, the same authors reported a saccharin:AMG-157 co-crystal formed from twin screw extrusion and solution crystallization. Co-crystals from TSE were presented to have augmented bulk density, surface region, and movement characteristics compared to those prepared from solution crystallization.
