(203d) Novel Method of Evaluating Liquid Absorption with Intra-Particle Pore of Pharmaceutical Porous Materials Using a Capillary Rise Method

Porous materials are attractive stuff for pharmaceutical particulate designing, such as for powdering oily drugs and improving the solubility of poorly soluble drugs formulated in dosage form. Understanding the mechanism of liquid absorption into intra pores and interstices of porous carrier particles should be important to effectively load active pharmaceutical ingredients (APIs) with the carriers. Although there is no useful practical method to measure the amount of liquid or API solution absorbed intra-particle pores and interstices of particles separately, in the bulk powder handling process. In this study, we established a simple and practical method to evaluate the liquid absorption behavior of porous carriers using a force tensiometer (K12, KRÜSS GmbH) with a probe for packing the porous carriers, which is based on the capillary rise method described with Washburn equation. Porous calcium silicate with petal-like pores (Florite^®-RE, Tomita Pharmaceutical Co., Ltd.) was used as a model porous material to absorb liquid and APIs.

First, the liquid absorption properties for the bulk powder of porous calcium silicate were evaluated using several solvents such as water, ethanol, and glycerin. Using the apparatus probe filled with bulk powder could estimate the apparent net absorption capacity of porous carriers including intra-particle pores and interstices of particles.

Differently-sized tablets with the same amount of porous material were prepared under different compression pressures for liquid absorption study using a tensiometer to evaluate the apparent amount of liquid present in intra-particle pores/interstices of particles. The amount of liquid trapped in interstices of particles decreased with decreasing tablet volume. Therefore, we could estimate the amount of liquid in the intra-particle pores quantitatively by performing liquid absorption study using the differently-sized tablets with the same weight of porous carriers.

API-loaded particles were prepared by absorbing API solution into porous carriers and the presence of API molecules in intra-particle pores/interstices of particles was evaluated. No free API was found on the surface of the prepared particles, and it was considered that the API was absorbed in intra-particle pores. The specific surface area of API-loaded carriers decreased with the increasing amount of absorbed API. These findings also suggested that the API was absorbed in intra-particle pores. To conclude, a tensiometer method with compressed porous materials having different volumes can provide practically a promising method to evaluate liquid absorption characteristics for pharmaceutical applications.