This study I found suggest that instead of the traditional approach in tissue engineering where the scaffold where the stem cells or growth factor is placed is made of not very strong or elastic in terms of material and machanical properties, it might be possible to add a scaffold made out of polyacrylamide and a type of alginate hydrogel which has much better mechanical and material properties.
Update – Link seems to NOT work: New hydrogel may help cartilage regeneration research
Link #2 – New ‘hydrogel’ shows promise for cartilage repair in proof-of-concept trial
This link is nothing new to me but shows that in terms of the development of certain types of biomedical research into actual application, it has taken a long time. For the last decade or so scientists and researchers around the world have been using a stem cell w/ scaffold combination to regrow bones and cartilage. Only now has this news been reported, and from John’s Hopkins University. Like the article states, many defects seen in the articular cartilage in humans have been traditionally fixed using the microfracture surgery, where a small drill is done at the defect area. The marrow inside pours out, forming a layer of fibrocartilage which is just not as good as the hyaline cartilage that was there before. This scaffold idea which is supposed to be a ‘breakthrough” is really not. It might be that researchers at JHU have been trying out thousands of scaffold composition or formulation combinations before they finally found a good enough hydrogel/scaffold/alginate combination for stem cells to really grow. The combination of the idea of stem cell in scaffold along with microfracture surgery is not a big leap in understanding or application. I say that it was bound to happen eventually. The main thing I guess that is important is in showing that if you use the scaffold and microfracture in combination, it is much better than just going with the microfracture sugery route along.
The results are…
After six months, the researchers found that hydrogel recipients had new cartilage filling 86 per cent of their defects, on average, compared with just 64 per cent for patients with microfracture alone.
In addition, patients who received the hydrogel implant reported a greater improvement in their levels of knee pain.
Study #1 – Highly stretchable and tough hydrogels
Summary – Hydrogels has been used in many types of applications but they are not very good due to having certain types of mechanical properties. They are not very elastic and break after they are stretched even slightly. Compared to other materials like cartilage and rubber, the hydrogel does not have a very high fracture energy, making them much more brittle. At the current moment, multiple researchers are looking for ways to make a type of hydrogel that is much stronger and more elastic. There are already some synthetically made hydrogels that have a fracture energy of 100–1,000 J m^(-2) which is up to 2 magnitudes greater than average.
However, for this study, the researchers show that they have developed a new type of hydrogel that is much more elastic and have much higher fracture energy and stretchability. They report the synthesis of hydrogels from polymers forming ionically and covalently crosslinked network
These new synthetic hydrogels can stretch up to 20 X their length, have fracture energy around 9000 J/m^2 and be composed of 90% water.
They state that the gels’ toughness to the synergy of two mechanisms:
- crack bridging by the network of covalent crosslinks – Furthermore, the network of covalent crosslinks preserves the memory of the initial state, so that much of the large deformation is removed on unloading.
- hysteresis by unzipping the network of ionic crosslinks – The unzipped ionic crosslinks cause internal damage, which heals by re-zipping.
Implications For Height Increase Application
I personally think that the best and most likely alternative to the limb lengthening surgery is doing a type of synthetic tissue implant into the bone of a person. If we can create a strong enough type of growth plate in a scaffold formation, then it would definitely be a real alternative. This requires the understanding of stem cell mechanisms and tissue engineering practices. From tissue engineering practice, the use of scaffolds is very big. The use of hydrogels as scaffolds is very common, if not universal. I have been trying to figure out what types of hydrogels would be best to be used in combination with formed cartilage-bone tissue that is growing volumetrically.
As I stated in one of the most important posts on the website, we have been able to create growing cartilage tissue aka functional growth plates however I had stated that I worried that even if we implanted the cartilage into the body, they would not be able to withstand the loading by an adult human. This is why I felt that maybe we need to find a good enough transport system aka scaffold we can put not just stem cells in, but also expanding cartilage tissue. If the hydrogel scaffold is strong enough, the synthetic growth plate with strong & elastic scaffold combination being implanted would probably work, at least with multiple testing done.
From the study “Elastic, Superporous Hydrogel Hybrids of Polyacrylamide and Sodium Alginate“…
These hydrogels are distinguished from other porous hydrogels in terms of their pore sizes and the methods used to generate the pores. If any portion of a superporous hydrogel is exposed to water or aqueous fluids, fluid is immediately absorbed through the open channels to fill the whole space. This capillary-driven absorption mechanism helps dried superporous hydrogels to swell very quickly into a very large size.
These products are very resilient and resistant to compression and elongation. In their water-swollen state, elastic superporous hydrogels can be repeatedly stretched to almost twice their original length without breaking. These novel products may find applications in the development of drug and protein delivery systems, fast-dissolving tablets, occlusion devices for aneurysm treatment, scaffolding, cell culture, tissue engineering, water-absorbent pads, hygiene products (baby diapers, feminine pads) and many others.
It might be possible that we might use the Superporous hydrogels (SPHs) since they are made from hydrophilic polymers with so many pores and they also have the interesting property that the hydrogels EXPAND when they absorb water. It could be that the properties of Superporous hydrogels will be very good with the synthetic growth plate cartilage implanted since both will be expanding.