Strong silky scaffold for bone repair
doi:10.1038/nindia.2012.68 Published online 8 May 2012
On a structure made out of pure silk — some silk fibres and a little silk solution — researchers have now been able to grow bone tissue from human bone marrow. They say this strong silky scaffold could be useful in regenerating many other human tissue systems and could have broad applications in regenerative medicine1.
A lot of orthopaedic research of the day veers around making biomaterials for bone tissue regeneration. Silk scaffolds have also been used in the past for the purpose. However, most biomaterials currently being used do not show great compressive strength required for load-bearing bone grafts.
This is the issue that the new protein-protein composite biomaterial tries to address. It is made up of solubilised and reconstituted silk fibroin from silkworm fibres. Researchers from Tufts University, Massachusetts, USA, Indian Institute of Technology, Guwahati and National Institute of Rehabilitation, Mexico got together to derive these components through 'selective chemical hydrolysis' of silkworm fibres.
"Surprisingly, we generated microfibers whose length we could control through the chemistry and time of chemical hydrolysis," says David Kaplan of Tufts University, one of the key collaborators. The microfibers run from a few microns long to hundreds of microns depending on the conditions used in the process. The microfibers were formed into composite materials with silk solution, and then into porous sponges to support cell and tissue growth.
"The mechanical properties of the silk composites are surprisingly strong, at least near the lower end of native bone tissue," Kaplan adds. The scientists generated bone tissue from human bone marrow derived mesenchymal stem cells in vitro on these composite materials. "This is an interesting side of composite research where different forms of the same material – in this case fibres and solution of silk – are shown to interact cohesively to produce reinforced materials imparting great strength," says Biman Mandal from IIT Guwahati.
A theory in materials science says longer length reinforced fibres in a composite are more effective in distributing load than smaller ones, leading to stronger composites. "This is a proof of concept of that theory," Mandal says.
These robust, all-silk scaffolds can play a valuable role as temporary biodegradable 3D support for native cells to grow and regenerate. The control over mechanical properties could be further used to regenerate many other human tissue systems, Mandal adds.
The researchers have filed for a US patent on the work.
- Mandal, B. B. et al. High-strength silk protein scaffolds for bone repair. P. Natl. Acad. Sci. USA. doi: 10.1073/pnas.1119474109 (2012)