Hydrogel that outperforms cartilage could be in human knees in 2023

Joint pain is a common ailment of aging, thanks to cartilage’s tendency to wear out. Now, researchers at Duke University have developed a new hydrogel that’s stronger and more durable than the real thing, which could make for longer lasting knee implants.

Natural cartilage plays an important role in cushioning joints, but unfortunately it doesn’t regenerate itself very well after damage by age or injury. Current treatment options are usually limited to pain medication, physical therapy, or if things progress too far, a total knee reconstruction. But if the Duke team’s new work pans out, a better option might soon be available.

Soft and flexible, hydrogels have been investigated as potential cartilage replacement materials, but most of them have been too weak to support much weight. In 2020 the Duke team created a hydrogel that had properties that were as good as natural cartilage – and now they’ve developed a version that surpasses the real thing.

The new hydrogel is made up of cellulose fibers, which make the material strong while being stretched, infused with polyvinyl alcohol that helps it return to its original shape. The team also tweaked its manufacturing method too – rather than freezing and thawing it like most hydrogels, they annealed it like glass, which triggers more crystal formation in the polymer network.

The end result is a hydrogel with a tensile strength (withstanding stretching) of 51 Megapascals (MPa), and a compressive strength (withstanding pressure) of 98 MPa. That’s 26% higher tensile strength and 66% higher compressive strength than natural cartilage, the team says. It’s also five times the tensile strength and twice the compressive strength of other hydrogels made by freezing and thawing.

A sample of the new cartilage-replacing hydrogel, attached to its titanium base for an implantable device Benjamin Wiley, Duke University

In other tests, the team used a machine to rub their artificial cartilage against natural cartilage a million times, under pressure similar to that on the knee during walking. And again, the artificial version proved to be three times more wear-resistant than natural cartilage.

Hydrogels have historically been tricky to anchor to bone in a knee joint, so the team also experimented with an implantable device to fix that. The hydrogel is cemented and clamped to a titanium base, which is then attached to a hole left by the damaged cartilage. This boasted a shear strength of 2 MPa, which is 68% stronger than natural cartilage’s grasp on bone.

The team says that implants made of the material are currently being tested in sheep, with human clinical trials to follow as soon as April 2023.

The research was published in the journal Advanced Functional Materials.