Silk route to healthy joints

Scientists grow cartilage tissue from silkworm protein

By Biplab Das
Published: Tuesday 15 November 2011

Osteoarthritis is one of the most common diseases affecting the elderly. The degenerative joint disease is mainly due to cartilage loss. Usually such patients are put on painkillers, but they give temporary relief from excruciating pain in joints. Overuse of the antibiotics may also cause stomach ulcer and bleeding.

Thus, the only way out is replacement of the damaged cartilage. Researchers have tried several natural biomaterials such as collagen, chitosan and cellulose as well as synthetic biomaterials like polylactic acid to synthesise cartilage in lab but to no avail. None can effectively mimic the function and structure of human cartilage tissue.

Now researchers from Indian Institute of Technology, Kharagpur, have succeeded in growing cartilage tissue from fibroin protein. The protein is isolated from the larvae of Indian tropical tasar silkworm which feeds on non-mulberry plants. Recent studies have shown that fibroin is an excellent biomaterial for tissue engineering in the form of films, gels, powders and scaffolds (see “Bone again”, Down To Earth, May 1-15, 2009). This motivated the IIT team to test the potential of fibroin isolated from both non-mulberry and mulberry silkworms.

They found that the non-mulberry silkworm protein helped synthesise better scaffolds—platforms made of fibroin protein on which cartilage tissue grow—due to a unique amino acid sequence. They then carried out further experiments to analyse non-mulberry silk protein’s ability to form scaffolds and grow cartilage tissue in lab. They prepared scaffolds using fibroin protein and seeded chondrocytes or cartilage-forming cells on it.

The chondrocytes were isolated from bovine cartilage. They also compared seeded scaffolds with non-seeded ones. After two weeks of culture, the seeded scaffolds had greater weight than that of non-seeded. Live cells were 75-85 per cent more in seeded scaffolds. At the end of two weeks, the seeded scaffolds showed increased levels of sulfated glycosaminoglycan and collagen—two main constituents of chondrocytes. “The cells were also able to produce cartilaginous extra cellular matrix (ECM), a complex mixture of carbohydrates, proteins and minerals that are parts of cartilage tissue,” says lead researcher Subhas C Kundu. “These scaffolds could also be used to grow human cartilage tissue,”’ he adds.

The findings of the study will appear in the December 2011 issue of Biomaterials.

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