Like Jim and Huckleberry Finn floating down the Mississippi River “mighty free and easy and comfortable on a raft,” that’s how medicines eventually brush up against a hurt that needs to be healed — by riding free and easy on the river of blood inside a vein.
But now chemists at Penn State, looking for a better way to heal cracks in bones, have invented a more-energetic, more-targeted system. They have used tiny self-powered nanoparticles to transport medicine directly to a bone as soon as it cracks.
The energy that revs the motors of these nanoparticles and sends them rushing toward the crack comes from a surprising source — the crack itself.
“When a crack occurs in a bone, it disrupts the minerals in the bone, which leach out as charged particles — as ions —that create an electric field, which pulls negatively charged particles toward the crack,” said professor of chemistry Ayusman Sen, a leader of the research team.
“Our experiments have shown that a biocompatible particle can quickly and naturally deliver an osteoporosis drug directly to a newly cracked bone.”
Sen said that the formation of this kind of an electric field is a well-known phenomenon, but other scientists previously had not used it as both a power source and homing beacon to actively deliver bone-healing medications to the sites most at risk for fracture or active deterioration.
“It is a novel way to deliver medicines,” he said.
Microcracks lead to broken bones in patients with osteoporosis and other medical conditions. To find a way to heal the cracks before they grow into breaks, Sen and his graduate student, Vinita Yadav, teamed up with the biomedical-engineering lab of professor Mark Grinstaff at Boston University. The scientists then did a series of experiments in each of their labs. A scientific paper that describes these experiments is published this month in the international chemistry journal “Angewandte Chemie.”
Sen and Yadav’s first series of experiments tested their novel way to deliver medicines in a model system using bone from a human tibia and femur and very small fluorescent particles called quantum dots.
“We added fluorescence to these particles because fluorescence makes them so easy to see under a microscope.” Sen said.
This first series of tests showed that negatively charged quantum dots did, indeed, move toward and pile up on a newly formed crack.
The scientists next tested their system using a natural biological material — a protein molecule — to see if it would perform on human bone as well as the synthetic quantum dots behaved. The results of these tests were encouraging. So Sen and his team set the bar even higher, doing their next set of experiments with nanomotors made from both a biological material and a synthetic material. They wanted to see if they could attach the biological material — a drug used to treat osteoporosis — onto a synthetic material that could carry it, like a nanotruck, to a crack in a human bone. The synthetic material the scientists selected to carry the osteoporosis drug has been approved by the Federal Drug Adminstration and is in wide use in medical devices. The goal of this set of experiments was to make a self-powered nanotruck that could carry the osteoporosis drug and would have a good chance of being safe for use inside the human body.
Like the nanoparticles in the previous tests, the FDA-approved nanotruck material had a little fluorescent molecule attached to it so its movements could be seen under a microscope. “Our experiments show that this bio-safe nanomotor can, in fact, successfully carry the osteoporosis drug to a fresh crack in a human bone,” Sen said. He explained that, even when these nanomotors were loaded with millions of molecules of their bone-healing cargo, each one still was 30 to 40 times smaller than a red blood cell.
In a final set of experiments, done in the Grinstaff lab at Boston University, graduate student Jonathan Freedman tested the same osteoporosis drugon live human bone cells.
“The treated bone cells proliferated as compared with those that were not treated with the osteoporosis drug, which confirms other studies that have shown that this drug is effective in repairing human bones,” Sen said.
“What makes our nanomotors different is that they can actively and naturally deliver medications to a targeted area,” he said. “Current methods, in contrast, involve taking a drug and hoping that some of it gets to where it is needed for healing.”
Now that this nanomotor-powered medication-delivery system has gotten a start in Sen’s lab, it will need many more tests and much further development, of course, before it may be proven safe and effective for preventing broken bones in patients with conditions like osteoporosis.
Barbara Kennedy is a science writer in Penn State’s Eberly College of Science.