Hydrogels Assessed for Biomedical Uses

Scientists are studying hydrogel, a hydrophilic polymer chain with similar flexibility to natural tissue, for new biomedical uses.

Dr. Jie Zheng, associate professor of chemical and biomolecular engineering, and Dr. Robert Weiss, a professor and chair of polymer engineering at the University of Akron (OH, USA), are among the most recent to add to the mounting research of hydrogels, the gelatinous substance that, because of its toughness and plasticity, has several biomedical applications, including cartilage repair, implants for minimally invasive surgery and drug delivery.

Because, as Dr. Zheng reported, “all existing methods to prepare double-network hydrogels involve multiple-step processes, which are tedious and time-consuming.” Dr. Zheng and his team developed a simple, effective, and one-pot technique (in which reactions occur in one as opposed to several pots) to synthesize double-network hydrogels—that is, hydrogels composed of two networks of polymer chains, one rigid, the other ductile.

Dr. Zheng not only made the synthesis of these hydrogels more effective but also made the hydrogels tougher. Most hydrogels are weak and brittle, “suffering from low mechanical strength, poor toughness, and/or limited extensibility and recoverability,” Dr. Zheng remarked. His hydrogels, however, “exhibit high mechanical properties, excellent recoverable properties, and a unique, free-shapeable property,” he stated, making them potential replacements for load-bearing soft tissues such as muscle, cartilage, tendon, and blood vessels.

Dr. Weiss also has synthesized a more resilient brand of hydrogel, a shape memory hydrogel, which can be curved and stretched and fixed into temporary shapes. When exposed to an external stimulus, such as temperature, light, moisture, or an electric field, shape memory polymers recover their original, permanent shape.

Dr.Weiss’s shape memory hydrogels are thermally actuated, so that they stretch and change shape when heated, and they retain this temporary shape when cooled. Biocompatible, shape memory hydrogels have the potential to be used for minimally invasive surgery and drug delivery, Dr. Weiss noted. “Shape memory may be useful for deployment of hydrogels in biomedical applications using less invasive methods ... for example, one can implant a compact form of the device that would deploy into the usable shape after it is implanted,” he said.

A small form of the shape memory hydrogel may be inserted into the body, for instance, where, upon absorbing bodily fluids, it expands into the chosen shape of the implant, thereby filling a wound or replacing tissue. The permeable hydrogels can also be packed with drugs and positioned into the body, where the sponge-like gel biodegrades and releases the drugs from its pores.

The researchers published their findings January 7, 2013, in the journal ACS Macro Letters. Dr. Zheng’s application has received provisional approval for a patent, and his article, coauthored by Zheng and his UA research colleagues, Drs. Qiang Chen, Lin Zhu, Chao Zhao, and Qiuming Wang, was published June 14, 2013, online in the journal Advanced Materials.

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