Special biomedical materials that can be injected as a liquid and turn into a solid inside our bodies - called thermogels - could provide a less-invasive way to deliver drugs or treat wounds. Scientists at Penn State have developed a new design for these materials that further improves their properties and may hold particular promise for use in tissue regeneration, the researchers said.
The team reported their findings in the March issue of the journal Advanced Functional Materials.
Thermogels are special materials that can transform from liquid to gel when triggered by heat, like going from room temperature to body temperature. While this work was tested as a proof of concept in a buffer solution that matches the pH and temperature of cellular systems, the scientists said the technology shows promise for biomedical applications. Gels, for example, could be introduced in the human body by a simple injection without the need for surgery. But controlling how the hydrogel forms remains challenging and can result in weak and unstable thermogels.
The researchers created "patchy" nanoparticle-based thermogel materials - meaning they have sticky areas that encourage the nanoparticles to assemble in a more controlled way when heated. This improves mechanical properties and potentially allows scientists to fine-tune the materials for different biomedical applications, said Urara Hasegawa, assistant professor of materials science and engineering at Penn State and lead author of the study.
"This is exciting in terms of the development of next-generation biomedical materials," Hasegawa said. "It's currently very difficult to control how thermogel materials form inside the body. This new approach addresses that challenge, and we think it can have a great impact on biomaterial development."
Biomedical thermogel materials are typically made up of micelles - nano-sized, ball-shaped structures that can carry drugs or other medical treatments and protect them from prematurely breaking down in our bodies to help control their release. The micelles' surface becomes sticky at body temperature, causing the material to aggregate, or form into, macroscopic hydrogel material. But it is difficult to control how they group together as they form into solids, the scientists said.
"If you have a particle and the whole surface is sticky, it's going to lump together and basically create a dense structure with defects that make the gel brittle," Hasegawa said. "Our idea is to instead use the particles as a building block and try to make a more ordered structure."
The patchy micelles they developed have sticky spots - essentially like arms reaching out that give the materials places to connect. The patches can help the micelles to form a structure without defects. And altering the number of these sticky patches may enable the scientists to control the structure of the materials and tweak thermogels for different applications, Hasegawa said.
"You can imagine that if we can control the number of these hands, we can actually control the assembling nature of the materials," she said. "Our work showed that if you change the sticky patches, then you can control mechanical properties."
The method may be especially appealing for soft tissue reconstruction, like following a cancer removal surgery, Hasegawa said. In those cases, thermogels could serve as tissue scaffolds, structures that provide a framework for cells to stick to and form new, healthy tissue. The new materials could be tailored to better match specific targeted soft tissues.
"If you are thinking of a hydrogel material you want to implant into the body, traditionally you need to do a surgical procedure," Hasegawa said. "But surgery can lead to infections, and people dealing with an illness or the elderly may have a much harder time recovering. If we can inject a solution in liquid form that becomes gel, we can avoid surgical procedures."
The scientists said future research is required to test the feasibility of the materials as soft tissue substituents/scaffolds in biological systems like cells and animals.
Also contributing from Penn State were Ralph Colby, professor of materials science and engineering and chemical engineering; Enrique Gomez, professor of chemical engineering; Esther Gomez, associate professor of chemical engineering; Andre van der Viles and Sarah Kiemle, assistant research professors; Masoud Ghasemi and Joshua Del Mundo, postdoctoral scholars; and Binru Han, doctoral candidate.
Shota Fujii, assistant research professor at the University of Massachusetts Amherst, also contributed.
The U.S. National Science Foundation, the U.S. Department of Energy and a Penn State Wilson Research Initiation Grant supported this work.
