New Hydrogel for Tissue Engineering

One of the most important considerations to make in tissue engineering is the kind of material you use, because it has to be both capable of sustaining the constant stress placed on it by the body and still be biocompatible. This can make it very difficult to replace or grow new tissues with synthetic materials because oftentimes something that is strong enough might have too high toxicity levels, and something that's proven to be perfectly safe might simply be inadequate for the job.

Hydrogels can be very stretchy.

 

An example of such a material that has been troublesome in the past are hydrogels. As the name suggests, these are composed mostly of liquid yet behave as a solid because of their structure. The liquid molecules are dispersed throughout a solid and are cross-linked in such a way that makes them have a jelly-like consistency.

Because they are both water-based and biocompatible, hydrogels make ideal candidates for tissue engineering applications such as cartilage replacements or usage in spinal disks. However, the problem lies in their weakness. Current hydrogels have been very brittle and thus unsuitable, so many researchers have been attempting to create a hydrogel that would be stretchy and strong enough to suffice.

At last, Harvard researchers have had a break-through. The hydrogel they created is made of two common polymers, polyacrylamide and alginate, combined in an 8:1 ratio, and although the two polymers aren't very impressive on their own, their combination is tough, self-healing, and can be stretched to 21 times its original length without breaking.

The alginate chains bond weakly with one another and trap calcium ions, and when the hydrogel is stretched, the bonds but not the chains break, thus releasing the calcium ions and allowing the gel to expand. However, the stretchiness is increased when the alginate is combined with polyacrylamide because of the grid-like, cross-linking phenomenon that occurs.

The polyacrylamide chains bond very tightly with the alginate chains, so the breaking of bonds diffuses across a wide area rather than being concentrated in one place and risking a crack or tear. The self-healing comes in because the alginate chains are able to re-form the ionic bonds between them, essentially renewing the hydrogel.