Hydrogel success calls for jolly good knees-up

By Wai Lang Chu

- Last updated on GMT

US scientists believe they may have developed an unusual material
that has similar physical properties of gelatine, remaining intact
even when deformed over 1,000 per cent. Its make up gives hope to
the 355 million arthritis sufferers worldwide.

In worst case scenarios painful surgery is required to drill holes in and reinforce affected joints. This is followed by months of rehabilitation and physiotherapy making the treatment a long and painful one for the patient. It is hoped that this new material can be directed to a material and prosthetic device for use in the treatment of arthritis and to supplement or replace cartilage. In a paper presented at the March Meeting of the American Physical Society, scientists from Hokkaido University in Japan described the work achieved on the unique double-network hydrogels. First discovered by researchers at Hokkaido in 2003, the team discovered the addition of a second polymer to the hydrogel made them so tough they compared favourably with cartilage tissue which can withstand enormous amounts of pressure over a considerable time period. Most conventionally prepared hydrogels, materials that are 80 to 90 per cent water held in a polymer network, easily break apart like gelatine. By using the National Institute of Standards and Technology (NIST) neutron research facility, the researchers were able to show how the molecules in the gel sustain such large deformations. "Initial work using NIST's neutron scattering techniques to explore the structure of the gel found unexpected results​," the paper explained. "The two polymers were attracted to each other, despite the fact that one polymer is negatively charged and the other neutral, and can withstand a certain force before they can be pulled apart​." The total amount of force endured by the polymer pair was amplified tremendously due to there being many contacts along each long chain. Essentially, it was the efficacy of stress transfer between the long added chain and gel network that determined the toughening mechanism in DN-gels. Scientists believe that uncovering the details of the molecular structure would allow for more precise design of the next generation of hydrogels. Human cartilage, especially in the knee joint, goes through a process of constant daily destruction and regeneration under everyday stresses. With this potential cartilage substitution the researchers believe a good synthetic cartilage could endure under the rigors of the body before needing to be replaced. Current treatments for arthritis are varied with physiotherapy and more invasive treatments such as orthopaedic surgery and the introduction of artificial joint components being the preferred methods. Non-steroidal anti-inflammatory agents have been used with some success but these agents may counterproductively hamper proteoglycan synthesis in collagen and cartilage as well as have undesirable side effects. Cortisone injections also weaken cartilage with time. Soft compliant materials used to replace the cartilage have been developed to absorb the load on the joint and to distribute the load evenly. Whilst silicone rubber has been used as a prosthetic device, the difficulty with these devices is securing the devices in place using various anchoring systems. Hyaluronates and hyaluronic acids have also been used for prosthetics and administered by injection into the intra-articular cavity of knees for the long-term relief of pain and improvement on the function of the knee joint. It has adequate viscosity and elasticity but has been prone to sheering due to mechanical stress and is biodegradable and has faced resorption problems. More details of the paper: 'A molecular model for toughening in double-network hydrogels. Presented at the March Meeting of the American Physical Society, March 11, 2008, New Orleans, La. Session: J25.00006,' can be found here​.

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