When a drug nanoparticle enters the bloodstream, it doesn't release its cargo on a predictable schedule—some particles empty quickly, others hoard their payload, and a few barely let go of anything at all. A team at Barcelona's Institute of Materials Science (ICMAB-CSIC) has now made this hidden reality visible, revealing that standard drug-delivery science has been blind to critical variations within populations of supposedly identical particles.
This matters because precision medicine depends on getting the right dose to the right place at the right time. Nanocarriers—tiny vehicles made from materials like the biodegradable polymer PLGA—are among the most promising tools for transporting therapeutic molecules, proteins, and RNA to damaged tissues or tumors. But until now, researchers have relied on population averages that mask the behavior of individual particles, the way an average temperature tells you nothing about whether some rooms are freezing while others burn.
Working with colleagues from the Institute for Advanced Chemistry of Catalonia (IQAC) and the University of Parma, researchers Anna Solé and Anna Roig applied a microscopy technique called dSTORM to track single nanoparticles over 30 days. They used different fluorescent labels on both the polymer shell and the encapsulated protein (albumin, serving as a model drug), allowing them to watch both components simultaneously as they changed. What they saw was striking: enormous variation in release behavior that disappeared completely in aggregate statistics.
Some nanoparticles released a significant portion of their cargo in the first days, while others held onto most of it for much longer. All particles showed an initial rapid phase followed by sustained release until the polymer fully degraded, accompanied by swelling and diameter increases. But the range between fast releasers and slow releasers was dramatic—and, crucially, invisible in traditional measurements.
"There is increasing evidence that the clinical response depends on when, where and how much cargo is released in each part of the body," Solé and Roig explain. Those differences in timing and dose could be the difference between a treatment that works and one that triggers side effects. A particle that dumps its contents too quickly might cause localized toxicity; one that holds on too long might never reach therapeutic levels.
The methodology itself is transferable to other types of nanocarriers, opening two immediate research directions: better understanding of existing delivery systems and improved design of future therapies. The work forms part of Solé's doctoral thesis, developed alongside medical teams working toward targeted nanocarriers for organs like the lungs and brain, with the goal of improving regeneration in damaged tissue.
This kind of granular visibility—seeing not just what happens on average, but what happens to each particle—represents a quiet but significant shift in nanomedicine. It acknowledges that precision medicine cannot be built on population averages alone. The next generation of drug therapies may depend on designing nanocarriers that don't just work on average, but work reliably for every single dose.