Are sugars the key to extending joint replacement lifetimes?

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An international research initiative partly taking place in Durham University’s Chemistry department, led by Dr Paul McGonigal, looks to take advantage of sugar polymers bound to a surface, and their interaction with surrounding water molecules as a technique for longer-lasting lubrication between surfaces. The highly efficient technique could be helpful in cars and other machinery to reduce wasted energy cheaply. The biocompatibility of the technique gives promising evidence that surface-bound sugar polymer interactions with water molecules can mimic natural lubricant (cartilage in natural joints) in artificial joint implants.

Joints can be defined as points in the body where two or more bones meet, for example at the hips and elbows. Friction between bones at joints reduces the efficiency of energy usage and can cause irreversible damage to bone structure by degrading the bone down. At natural joints, the constant cycle of cartilage breakdown and repair, in coordination with wear and tear caused mostly by physical activity, is what keeps the flexible, hinge-like mechanism between these bones moving freely by providing lubrication at the joint.

In most artificial joint replacements, current technology uses biopolymers at the joint surface that are easily damaged over time, resulting in an inevitable lack of lubrication eventually, and causing irreversible damage to the joint as a result.  This research describes supramolecular repair using sugars, from which their interaction with water molecules provides insight into how we can impersonate cartilage at artificial joints for longer lasting lubrication.

The technique uses a layer of sugar polymer on the artificial joint surface, on top of which layers of water molecules self-assemble and consequently become bound to it. The self-assembly of water molecules from surrounding bulk-solution was proven possible and effective in the investigation using confocal laser scanning microscopy to visualise the process. These water molecules relax when subjected to drag (the movement of bones at the joint), meaning that they can lower the coefficient of friction (COF) here to ‘’record levels”, and ultimately reduce the damage often caused at artificial replacements.

Image: Dr Paul McGonigal & Chem.

During investigations with pressure applied to mimic the impact on hip joints during exercise, two surfaces coated with PMPC materials (the polymer) laid against each other resulted in COFs of 0.01-0.05. Whilst these are already incredibly low, the fact that these can be lowered even further to 0.001 in optimised systems gives even greater hope for how the negative effects of friction can be practically eradicated at artificial joints with this technique.

As well as low friction, other criteria for optimum joint function at the lubrication surface include that of high resistance to stresses like high-impact events, malleability to respond to these stresses, and a simple repair mechanism for when inevitable degradation does occur. Supramolecular repair here does just that.

The specific yet versatile hydrogen bonds that can form between sugar monomers and surrounding water molecules are modifiable enough that any breakage can be easily reversed and repaired. Fast, convenient reformation of these non-covalent bonds can therefore easily respond to wear and tear as and when required. This clearly improves on current methods of covalently bound surface layers on artificial joints which are hard to manage and fix once damaged, and consequently, this technique proposes the further possibility of vast, promising improvement to artificial joint function.

Arguably, the most beneficial factor of this technique is that it makes use of naturally produced compounds in the body even though the joint is artificial. Once installed, the technique should work indefinitely by relying on water molecule self-assembly into layers. The body contains so much water that this shouldn’t be hard to maintain. This again makes repair to degradation easier as the resources for repair are readily available in our own bodies.

The fact that this technique alleviates the physical effects that cause degradation to bones at artificial joints, whilst taking advantage of the body’s own resources, provides an incredibly efficient and promising treatment at joint implants to extend their lifetimes. This could improve the lives of millions worldwide by mitigating long-term joint pain and avoiding the need for multiple surgeries during the joint replacement process.

Image: Mehmet Turgut Kirkgoz via Unsplash

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