Implantable Nanogel Particles for Long-Term Drug Delivery

Bioengineers have developed an implantable drug dispensing mechanism based on heat sensitive nanogel membranes incorporated into magnetic nanoparticles.

Investigators from Children's Hospital Boston (MA, USA) were seeking a nonmechanical solution to the problem of long-term, modulated drug delivery for patients suffering from chronic pain or from diseases such as cancer or diabetes.

The investigators focused their work on a novel type of temperature-sensitive nanogel membrane made from poly(N-isopropylacrylamide). The drug of choice was encapsulated inside the membrane, which when heated relaxed to allow some of the drug to be dispensed. Upon cooling, the membrane regained a rigid state that prevented further dispersal of the drug. The nanogel membranes were combined into a tiny, implantable device along with magnetite nanoparticles that heated up when exposed to an external magnetic field.

Results of studies conducted on the implanted device, which were published in the September 8, 2009, online edition of the journal Nano Letters, revealed that drug delivery began within one to two minutes after exposure to the external magnetic field. Return of membrane rigidity and cessation of drug release, occurred five to 10 minutes after removal of the magnetic field. The magnetite particles were activated by temperatures higher than normal body temperatures, so they were not affected by the heat of a patient's fever or inflammation.

The membranes remained mechanically stable under tensile and compression testing, indicating their durability, showed no toxicity to cells, and were not rejected by the animals' immune systems. The total drug dose delivered was directly proportional to the duration of the "on" pulse, and the nanoparticles retained their switchable flux properties after 45 days of subcutaneous implantation.

"A device of this kind would allow patients or their physicians to determine exactly when drugs are delivered, and in what quantities," said Dr. Daniel Kohane, associate professor of anesthesiology at Children's Hospital Boston.

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