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Biocompatible, shape memory hydrogels, implant coating that promotes bone growth

Biocompatible, shape memory hydrogels, implant coating that promotes bone growth

A squishy, synthetic, flexible, mostly water and almost as tough as rubber hydrogel developed by scientists at The University of Akron. The team is exploring new biomedical uses for this polymer-based product. Dr. Jie Zheng, associate professor of chemical and biomolecular engineering, and Dr. Robert Weiss, Hezzleton E. Simmons professor and chair of polymer engineering, are among the most recent to contribute to the growing 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. The team developed a simple, efficient and one-pot method (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. The team not only made the synthesis of these hydrogels more efficient – but also made the hydrogels tougher. These hydrogels exhibit high mechanical properties, excellent recoverable properties, and a unique, free-shapeable property," Weiss says, making them promising replacements for load-bearing soft tissues like cartilage, tendon, muscle and blood vessels. Weiss also has synthesized a tougher brand of hydrogel, a "shape memory hydrogel," which can be bent 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. These shape memory hydrogels are thermally actuated, meaning 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. For example, a small form of the shape memory hydrogel may be inserted into the body, where, upon absorbing bodily fluids, it expands into the desired shape of the implant, thus filling a wound or replacing tissue. The permeable hydrogels can also be loaded with drugs and placed into the body, where the sponge-like gel biodegrades and releases the drugs from its pores.

A team of MIT researchers, led by Paula Hammond, developed a new bone implant adhesive likely to change the future of orthopedic surgery. Researchers used nanotechnology to create an implant coating that promotes bone growth on and around the implant. In lab tests on rats, the adhesive proved to be up to four or five times stronger than the standard bone cement. The top coating consists of nanolayers containing the growth factor BMP-2. Over time, the layers break down and release BMP-2 which stimulates new bone cell growth. The bottom coating consists of bone-like ceramic which attracts new bone cells. The new bone cells attach to the ceramic like a “superglue,” as per Nisarg Shah, the lead author. Furthermore, the coating can be custom built to control how much and how fast BMP-2 is released. This is important when the healing process requires continuous hormone release over a long period, according to Medical Daily. Today, surgeons use bone cement to attach implants to bone, but this adhesive polymer has some significant flaws. Bone cement often deteriorates over time and fractures. Also, because the body recognizes the cement as foreign, it builds scar tissue around the implant, making it difficult for the bone to attach. Researchers expect the new nanocoating to solve these problems. This new bone implant “superglue” could spare future generations the pain and expense of revision surgeries. The only downside to this orthopedic advancement is the cost of an implant would likely increase. As a result, the new implant coating should first be applied to the elderly and those with preexisting conditions like osteoporosis. Those patients are already at a risk of failure and would benefit more than most implant patients. Professor Hammond anticipates the new implant adhesive will become a product in four to five years following trials with larger animals. Should tests prove successful, the implant nanocoating could transform the field of bone surgery, vastly improving many patients’ quality of life.

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