The promise of nanomedicine – delivering drugs with pinpoint accuracy to fight disease – has long been hampered by the body’s own defenses. Now, research from Arizona State University suggests a key to overcoming those hurdles lies in understanding how nanoparticles interact with water. A new study, published in the Proceedings of the National Academy of Sciences, reveals that the way nanoparticles are coated dramatically influences their behavior within the body, offering a pathway toward more effective and safer treatments.
For decades, scientists have envisioned nanoparticles as microscopic delivery vehicles, ferrying medication directly to cancerous tumors or infected tissues. But the human body is a complex environment, and these tiny particles often face immediate challenges – being intercepted by the immune system, failing to reach their target, or triggering unwanted side effects. This new research focuses on a fundamental, often overlooked aspect of this interaction: the role of water.
The ASU team, led by Alexandra Navrotsky, Regents Professor in the School of Molecular Sciences and Director of the Center for Materials of the Universe, directly measured the energetics of water adsorption on nanoparticles coated with different biomolecules. This means they quantified how strongly water molecules bind to the surface of these particles, and how that binding affects their biological performance. The findings establish hydration enthalpy as a key parameter in predicting how nanoparticles will behave once inside the body.
The Critical Role of Water
“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, we can quantify the interaction potential of the nanoparticle surface and better predict how it will behave in the body.” This understanding is crucial due to the fact that the initial interaction with water dictates a nanoparticle’s stability, its ability to evade the immune system, and its effectiveness in delivering its therapeutic payload.
The researchers studied magnetite nanoparticles – iron oxide particles – 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, comparing the results to uncoated magnetite and the free biomolecules themselves.
Protein Coatings: A Patchy Interaction
Nanoparticles coated with bovine serum albumin, frequently used in drug delivery research, exhibited the strongest initial interaction with water. The coating created numerous binding sites, suggesting a strong potential for interaction. Still, the study revealed a surprising detail: total water uptake was lower than with the free protein, indicating incomplete coverage and exposed patches of the underlying magnetite.
“The protein coating increases the surface interaction potential of the nanocomplex,” said Kristina Lilova, Research Assistant Professor at Arizona State University’s Center for Materials of the Universe. “But the existence of exposed magnetite regions introduces heterogeneity that may promote protein corona formation and immune recognition.” This “protein corona” – the accumulation of proteins on the nanoparticle surface – can signal the immune system, potentially leading to the particle being cleared from the body before it reaches its target.
Starch as a Shield, and the Surprise of Lauric Acid
In contrast, the starch coating created a dense shell around the magnetite core, limiting water access and resulting in a weaker interaction potential. According to Lilova, “The weaker interaction potential of the starch coating and its relatively large hydrophilic surface area suggest more dynamic and reversible binding,” which could be beneficial for drug delivery by promoting mobility along cell membranes and reducing toxicity.
Perhaps the most unexpected finding involved lauric acid. While free lauric acid doesn’t readily adsorb water, when bound to the magnetite nanoparticles, it reorganized into a partial bilayer structure that strongly interacted with water. “The fatty acid rearranges into a partial bilayer with very strong hydrophilicity,” Lilova explained. “That structure increases stability and may reduce immune activation compared to more hydrophobic surfaces.”
Towards “Rational Nanomedicine”
Across all three coatings, the researchers established hydration enthalpy as a key thermodynamic parameter governing surface hydrophilicity, heterogeneity, and biological interaction. This means that by understanding how different coatings affect water interaction, scientists can begin to rationally design nanocarriers with specific properties – tailored stability, reduced immune response, and optimized drug delivery behavior.
“Our findings show 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.”
This research offers a promising step toward overcoming the long-standing challenges in nanomedicine, potentially leading to more effective treatments for a range of diseases, including cancer. The team hopes these findings will inform the design of targeted drug delivery systems, advanced imaging agents, and innovative cancer therapies.
“This research provides a thermodynamic foundation for designing nanocarriers with predictable biological reactivity. It moves us one step closer to truly rational nanomedicine,” Navrotsky concluded.
The researchers are continuing to investigate the interplay between nanoparticle coatings, water interactions, and biological systems. The next phase of their work will focus on testing these findings in more complex biological environments, bringing the promise of truly targeted nanomedicine closer to reality.
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