What Determines Medicine Viscosity?
Student Summary by Hayden Byun
Original Source: Fabrizio Camerin et al., Science Journal for Kids and Teens, March 2026
https://www.sciencejournalforkids.org/wp-content/uploads/2026/03/antibody-medicine_article.pdf; https://www.pnas.org/doi/suppl/10.1073/pnas.2425974122
Abstract
Background: Medicine takes on several different forms and has various ways of entering our bodies, such as through syringes and pills. This is because the physical properties of a medicine, including its viscosity (thickness of the substance), determine how it can be given; this affects the affordability of healthcare. Some people are unable to access proper medical care, especially for cancer or autoimmune diseases. Because medicines for these types of diseases are viscous, they must be injected into the patient intravenously (through the veins) inside a hospital.
Objective: Scientists wanted to detect the property that is making certain medicines—specifically those containing monoclonal antibodies—more viscous than others. (Monoclonal antibodies are proteins engineered to imitate the role of antibodies that our bodies naturally produce.) The researchers set out to test whether the density of antibody molecules packed into the solution and the electrostatic interactions between the proteins were causing the substances to become viscous.
Method: Researchers used computer models called coarse-grained models, which simplify antibodies by grouping several atoms into single beads. This made it possible to study many molecules at once instead of tracking the incredibly complex structure of amino acids, which are the molecules that make up antibodies. Each bead showed the average electrostatic charge of the amino acids in that region of the antibody. They formulated three different models of individual antibodies (Model A, Model B, Model C), each made of nine beads. Model A was the simplest, with one uniform charge spread evenly across the antibody. Model B had uneven charges — negative, positive, and neutral — mapped from the real amino acids. Model C was the same as Model B, but also included ions in the solution surrounding the antibody. For each model, scientists examined various antibody concentrations and compared their results to previous laboratory values.
Results: It was discovered that the viscosity of the antibody solution increased with higher concentration. In regions where there were opposite charges, antibodies were more prone to clustering, or grouping together, contributing to less flow in the medicinal substance itself (high viscosity). These clusters were temporary. Because the charged regions also interacted with ions in the solution, the antibodies were stabilized and stayed clustered for longer, even when their charges were the same. Model C seemed most consistent with real lab results.
Conclusion: This study found that both the interactions between antibodies and the interactions between antibodies and ions are needed to explain why these medicines get so thick, and that future models must include both. With the knowledge from this study, experts could reformulate these medicines to take on different, more accessible forms, and with further development could possibly transform hospital IV treatments into syringe injections that patients can take at home. This study has shown that by using computer modeling, researchers can see and investigate microscopic objects in depth. This finding may eventually allow scientists to create cheaper, more available treatments for cancer and other diseases.
