Rheological Characterization of Excipients

Nowadays, polymeric excipients are an important addition to complex tableting blends. Ingredients such as polylactic acid (PLA), poly-lactic glycolic acid (PLGA), and hydroxyl methyl cellulose and its derivatives are enabling formulators to apply an increasing number of manufacturing techniques such as spray drying, hot melt extrusion and lipid-based drug delivery. The properties of these polymers can directly affect the clinical efficacy, safety and quality of the finished drug, with molecular weight (MW), MW distribution and structural characteristics often identified as critical quality attributes (CQA). The processability and functional properties of polymeric excipients depend on their rheological behavior. Therefore, in order to obtain a more fully characterization of macromolecular or polymeric excipients and to further understand their variability, our excipient experts recommend evaluating the average molecular weight, molecular weight distribution and powder flow properties of your excipients.

Application of Rheological Measurements

• Characterization of the flow and deformation of drug products
• The application and acceptance of pharmaceutical formulations depend upon their rheological characteristics
• Study the stability and bioavailability of drugs

Figure 1. Rheological Characterization of Excipients. (Fischetti, T.; et al. 2020)

Our Capabilities

BOC Sciences can perform characterization of rheological characteristics of the most commonly used polymeric excipients to support the development of your different pharmaceutical dosage forms.

Molecular Weight Distributions (MWD) Testing of Excipients

In general, polymers are composed of repeated units (monomers) in long chains of different lengths and degrees of branching. Polymers are not homogeneous in molecular weight. The molecular weight distribution in a given polymer sample can be calculated as a ratio of weight-average molecular weight and number-average molecular weight. Knowledge of the molecular weight distribution of a polymeric excipient is also essential to establish a preliminary understanding of the relationship between structure and properties. We can perform molecular weight distribution tests on a variety of polymeric excipients including polydextrose, hydrogenated polydextrose, polyvinyl acetate, chitosan, polyethylene glycol, and hydroxypropyl cellulose. The molecular weight distribution tests are developed based on gel permeation chromatography (GPC) or size exclusion chromatography (SEC) with refractive index detection or viscosity detection.

Molecular Weight (MW) Testing of Excipients

Molecular weight is one of the key properties to characterize polymer products. For the pharmaceutical industry, the molecular weight of polymeric excipients often has a direct effect on their mechanical properties, thermal behavior and viscosity characteristics. Therefore, reliable molecular weight determination provides a rapid drug quality control check that can detect lot to lot variations. At BOC Sciences, our expert team performs high-quality molecular weight testing services on water-soluble polymeric excipients and natural excipients as well as organic soluble materials by using gel permeation chromatography (GPC) and dilute solution or intrinsic viscometer (IV) to help our customers accurately characterize the composition and variation of various excipients.

Figure 2. Control of Drug-Excipient Particle Enables Improved Powder Rheology. (Denise, Z. L. Ng.; et al. 2020）

Powder Flow Characteristics of Excipients

In tablet manufacturing, excipient is an non-active substance, usually in powdered form. During the formulation manufacturing process, excipients are added to the active pharmaceutical ingredient (API) of the formulation to increase its volume, improve its stability, and dilute the concentration of API to optimize its therapeutic properties, such as promoting drug absorption, reducing viscosity, or improving solubility. The flowability and compactibility of excipients are important to ensure that target tablet hardness and integrity are achieved. BOC Sciences therefore offers powder flow properties characterization of excipient to detect problems in the early stages of formulation development, which can then be mitigated or eliminated through the selection of excipient materials and appropriate process equipment.