Nanoparticle-Water Interaction: Key to Effective Nanomedicine Development

The promise of nanomedicine – delivering drugs with pinpoint accuracy and minimizing side effects – hinges on understanding how engineered nanoparticles behave inside the human body. A new study from Arizona State University reveals a critical piece of that puzzle: the interaction between nanoparticles and water. Researchers have discovered that how water adheres to the surface of these tiny particles dramatically influences their biological performance, offering a pathway toward designing more effective and safer nanomedicines.

Published in the Proceedings of the National Academy of Sciences, the research directly measured what happens when water encounters nanoparticles coated with different biomolecules. This focus on “hydration energetics,” as the researchers call it, provides a fundamental thermodynamic framework for predicting how nanoparticles will interact with biological systems. The work, led by Alexandra Navrotsky, Regents Professor in the School of Molecular Sciences and Director of Arizona State University’s Center for Materials of the Universe, could address a long-standing challenge in the field.

Why Water Matters in Nanomedicine

“Water is necessary for all life,” Navrotsky explained. “And in medicine it is the first molecule that interacts with any nanoparticle surface in a biological environment. By directly measuring the energetics of water adsorption, One can quantify the interaction potential of the nanoparticle surface and better predict how it will behave in the body.” This is significant because, despite decades of research, nanomedicine has struggled to consistently deliver on its potential. The body’s defenses and complex biological barriers often prevent drugs from reaching their intended targets efficiently.

The challenge lies in controlling the nanoparticle’s journey through the body. Once introduced, these particles are immediately surrounded by water and biomolecules, forming a complex interface that dictates their stability, circulation time, how the immune system recognizes them, and how well they’re taken up by cells. Researchers have been exploring ‘Trojan horse’ strategies, using nanoparticle shells to protect and deliver medications, but understanding the initial water interaction was a missing piece of the puzzle.

Measuring Hydration Energetics

The ASU team focused on magnetite nanoparticles – iron oxide particles often used in biomedical applications – coated with three common biomolecules: bovine serum albumin (a protein), potato starch (a polysaccharide), and lauric acid (a fatty acid). Using a highly sensitive calorimetry–gas adsorption system, they meticulously measured how water interacted with each coating. They then compared these findings to uncoated magnetite and the free biomolecules themselves.

Their results revealed that each coating dramatically altered how water interacted with the nanoparticle surface, and its potential biological interactions. The bovine serum albumin coating, frequently used in drug delivery research, exhibited the strongest initial attraction to water. However, the study also revealed incomplete coverage, leaving patches of magnetite exposed. Kristina Lilova, Research Assistant Professor at Arizona State University’s Center for Materials of the Universe, explained, “The protein coating increases the surface interaction potential of the nanocomplex. But the existence of exposed magnetite regions introduces heterogeneity that may promote protein corona formation and immune recognition.” This “protein corona” – the unintentional binding of proteins from the body to the nanoparticle surface – can alter the particle’s behavior and potentially trigger an immune response, shortening its circulation time.

Starch and Fatty Acid Coatings: Unexpected Results

In contrast to the protein coating, starch-coated nanoparticles displayed a large hydrophilic (water-loving) surface area but a weaker interaction potential. The starch formed a dense shell around the magnetite core, limiting water access. Lilova suggests this could be beneficial for drug delivery, promoting mobility along cell membranes and reducing toxicity.

Perhaps the most surprising finding involved lauric acid. While free lauric acid doesn’t readily adsorb water, when bound to magnetite, it reorganized into a partial bilayer structure that strongly interacted with water. “The fatty acid rearranges into a partial bilayer with particularly strong hydrophilicity,” Lilova said. “That structure increases stability and may reduce immune activation compared to more hydrophobic surfaces.” This suggests that the way a molecule behaves in isolation isn’t necessarily how it will behave when attached to a nanoparticle.

Towards Rational Nanocarrier Design

Across all three coatings, the researchers identified hydration enthalpy – a measure of the energy released or absorbed when water interacts with a surface – as a key thermodynamic parameter governing surface hydrophilicity, heterogeneity, and biological interaction. This finding is crucial because it provides a quantifiable metric for predicting nanoparticle behavior. “Our findings indicate that surface functionalisation doesn’t just change chemistry – it fundamentally alters the thermodynamic landscape at the nano-bio interface,” Lilova stated. “By understanding primary hydration energetics, we can rationally engineer nanocarriers with tailored stability, immune interactions and drug delivery behaviour.”

Arizona State University is a hub for materials and nanoscience research, with faculty exploring designer electronic materials, molecular logic devices, and novel materials for energy conversion and storage. This research builds on that foundation, applying fundamental materials science principles to the complex challenges of nanomedicine.

What Comes Next: Validation and Application

The next steps involve validating these findings with a wider range of biomolecules and nanoparticle compositions. Researchers will also need to investigate how these hydration energetics translate to in vivo (within a living organism) performance. Further studies will focus on how these interactions affect drug release, targeting efficiency, and long-term biocompatibility. The ultimate goal is to develop a predictive model that allows scientists to design nanocarriers with specific properties, tailored to the needs of a particular drug and therapeutic application. This research provides a crucial thermodynamic foundation for designing nanocarriers with predictable biological reactivity, bringing us closer to truly rational nanomedicine, according to Navrotsky.