Liquid ingress or matrix strength? Using magnesium stearate lubrication to distinguish tablet disintegration factors in MCC and lactose tablets

Tablet disintegration results from a competition between liquid penetration and subsequent disintegration-promoting mechanisms on one hand, and mechanical resistance of the tablet matrix on the other, but their relative contributions are difficult to separate experimentally. Here, magnesium stearate (MgSt) lubrication was used to distinguish these effects in microcrystalline cellulose (MCC) and α-lactose monohydrate (lactose) tablets, characterised by terahertz pulsed imaging to monitor liquid ingress kinetics and tensile strength testing. Increasing MgSt concentration slowed liquid ingress in both matrices, but disintegration times diverged. MCC disintegration was governed primarily by matrix resistance and was therefore accelerated by MgSt-induced weakening of the matrix. In contrast, lactose disintegration was governed primarily by liquid ingress kinetics and was consequently slowed by MgSt, as conventionally expected. Notably, the effect of porosity on disintegration times could be attributed to the same mechanistic principles in the two systems. The results indicate that matrix strength, not only liquid ingress, can be a dominant factor controlling disintegration kinetics. Overall, the findings support incorporating matrix strength as a distinct factor in disintegration testing and formulation design, with MgSt lubrication providing a useful strategy for identifying systems in which matrix resistance dominates disintegration.