Can Hydrogel Cartilage Repair Ever Work? U.S. Researchers Say Yes

In short

U.S. Researchers from esteemed institutions have created a type of hydrogel that they claim has proven to be effective in treating patients with damaged cartilage. Hydrogels as a potential solution for repair of articular cartilage defects are nothing new, and none have yet reached the market, so is this one different?

The claim is that the gel provides a platform for the stem cells to grow into cartilage cells, allowing for rejuvenation. Over time, so the claims go, the gel dissolves, leaving behind new cartilage.

Background

Medicalxpress.com has reported a new piece of published research from the journal Science Translational Medicine, on a hydrogel which apparently “thickens when exposed to light” (presumably cross-linking in some way), providing a lattice platform for the development of new cell growth. The piece, and indeed the publication, suggests that this new wonder material offers a solution to the hitherto intractable problem of articular cartilage damage. Given the potential to revolutionise joint treatment, we’ll suppress our healthy scepticism for a minute and dwell on the research over a few lines on medlatest.

Cartilage, the pliable material that coats the opposing surfaces of our joints, has the primary function of lubricating movement and to a degree protecting bones from the rigours of a mobile life. Injuries to cartilage or simple wear and tear can result in perforations that allow bones to rub against one another, resulting in pain and reduced joint mobility.

Once injured, whether through trauma or degeneration, articular cartilage doesn’t repair itself well, injury having a habit of propagating or progressing through a complex cascade of processes. So people end up eventually getting their joints replaced. Given the size of the commercial opportunity it’s no wonder that the quest is permanently on to find an alternative. And it’s no wonder the world’s researchers have turned to hydrogels, because these polymeric fillers are pretty innocuous things that often look white and soft, just like articular cartilage, and are often claimed to have cellular in-growth potential.

Surely they must provide a preferable alternative to joint replacement, or even the earlier stage therapeutic approach of microfracture, in which the surgeon uses a metal spike to penetrate and induce bleeding from underlying bone (which in turn creates a clot, which “sort of” modifies into a “sort of” cartilage-like material). Microfracture is a solution of sorts, but not a viable long term cure for a stoutly degenerative condition.

So, does implanting some hydrogel goop do a better job? Well according to the research, yes it does. First up, in an in vitro model the gel showed both deposition of cartilage-specific extracellular matrix in the hydrogel and apparent stimulation of adjacent cartilage tissue development by mesenchymal stem cells. So far so good.

Secondly, the team turned to a caprine model(that’s a goat to you and me). They first performed the standard microfracture procedure then applied the gel to the holes in the cartilage, then finished by bathing it in light to cause it to cross-link. Once satisfied that this was all do-able they turned to humans and treated 15 patients with the microfracture plus the gel vs a population with microfracture alone. Note that this was not a randomised study, just a pilot, but nonetheless the results look hopeful: MRI showed that treated patients achieved significantly higher levels of tissue fill compared to controls. “Magnetic resonance spin-spin relaxation times (T2) showed decreasing water content and increased tissue organisation over time”, both signs of good things. Treated patients had reportedly less pain compared with controls, which is probably not surprising given the immediate cushioning/protective effect of the material as compared with a raw, bone-on-bone, freshly fractured surface.

Sadly knee function  as measured by performing International Knee Documentation Committee (IKDC) scores increased to similar levels between the groups over the 6 months evaluated. Whether that fact trumps all the others remains to be seen, but it might suggest the gel’s gone and the microfractured surfaces have been left looking the same in each group… which would not be a great outcome.

All of which may leave us pretty much where we started. Intuitively, and even in the lab it looks like hydrogels, especially this one, have a chance. But the reality is that the inside of our joints is a hostile place in which the delicate surfaces given to us when we’re born don’t always last the course. Expecting a sticky hydrogel to help us reverse a degenerative change is a long shot.

The researchers’ claims that “with further clinical testing, this practical biomaterials strategy has the potential to improve the treatment of articular cartilage defects”, might be a wee bit optimistic. As for medxpress.com’s interpretation that the results have been positive enough to suggest that the gel will likely become a standard treatment for cartilage repair “in the very near future”, that may be jumping the gun proper.

Source: Medxpress.com, Science Translational Medicine

Ref: Human Cartilage Repair with a Photoreactive Adhesive-Hydrogel Composite, Sci Transl Med 9 January 2013: Vol. 5, Issue 167, p. 167ra6 DOI: 10.1126/scitranslmed.3004838