These images show the structure of the newly created hydrogel at different magnifications.
Image credit: Mark Tibbitt
The use of gels to deliver drugs is an increasing area of interest for researchers. While conventional liquid solutions allow drugs to be dispersed throughout the body straight away, gel-based solutions can release drugs over long periods of time.
In addition, gels can be molded into certain shapes, allowing drug delivery to specific parts of the body. But there is a problem with current drug-delivery gels; once molded, they cannot be reshaped, meaning they often need to be implanted with surgery.
The research team - co-led by Mark Tibbitt of the Koch Institute for Integrative Cancer Research at Massachusetts Institute of Technology (MIT) - set out to tackle this problem.
Hydrogel made of polymer-containing nanoparticles and cellulose
According to Tibbitt and colleagues, researchers have previously created drug-delivery hydrogels using chemical connections between polymers - long chains of molecules - that are irreversible.
The researchers note that while such gels are extremely tough - a feature needed to withstand long-term use - it can be very difficult to alter their shape once they are molded.
In the past, scientists have attempted to tackle this issue by developing proteins that assemble into hydrogels by themselves, but the MIT team says such a process is complex. In their study, they adopted a simpler approach.
The researchers used nanoparticles consisting of PEG-PLA copolymers, which are widely used for drug delivery. In order to form their new hydrogel, the researchers combined these PEG-PLA copolymers with another polymer called cellulose.
Since most nanoparticles have a weak bond with polymer chains, the connection between the PEG-PLA copolymer-containing nanoparticles and cellulose was loose. As such, each connection is able to soften under physical stress, allowing the hydrogel to be injected through a syringe.
However, when such stress is absent, the nanoparticle and cellulose form new connections, meaning its toughness is restored.
"Now you have a gel that can change shape when you apply stress to it, and then, importantly, it can re-heal when you relax those forces. That allows you to squeeze it through a syringe or a needle and get it into the body without surgery," explains Tibbitt.
New hydrogel can deliver two drugs simultaneously
The team notes that because the hydrogel is made up of two components, it can be used to deliver two different drugs simultaneously.
The PEG-PLA copolymers have the ability to carry and deliver hydrophobic small-molecule drugs, such as those used for chemotherapy, while polymers like cellulose can carry hydrophilic molecules, such as antibodies and growth factors - drugs that stimulate cellular growth.
On injecting the hydrogel under the skin of mice, the team found it effectively delivered one hydrophobic and one hydrophilic drug over a period of several days.
Not only can the hydrogel offer targeted drug delivery, the researchers say each component of the gel can be modified so each drug can be delivered at different rates, meaning it could be tailored to a patient's individual needs.
The team is currently investigating how the new hydrogel can be used to deliver anti-angiogenesis drugs to treat macular degeneration - an eye disease that affects more than 10 million people in the US.
At present, patients with macular degeneration receive a monthly injection with anti-angiogenesis drugs, which work by reducing the growth of sight-impairing blood vessels. The MIT team believes the new hydrogel could be used to deliver these drugs over several months, which could limit the need for injections.
Because the new hydrogel can deliver growth factors, the researchers say it could also be effective for the repair of damaged heart tissue following a heart attack.
In addition, it could be used to treat cancer patients following the surgical removal of tumors. The team explains that the gel could be laced with a chemical that attracts remaining cancer cells toward it, alongside a chemotherapy drug that destroys the cancer cells, reducing the risk of cancer recurrence.
Last month, Medical News Today reported on another study published in Nature Communications, in which researchers detailed the development of a "triggered release" drug-delivery mechanism using nanoparticles.