With trials on rabbit models showing promise, the next tests will be on larger animals
A scaffold made of silk composite functionalised with copper-doped bioactive glass to facilitate faster bone regeneration has been developed by researchers at Indian Institute of Technology (IIT) Guwahati. The scaffold seeded with stem cells was found to differentiate into bone cells, facilitate growth of blood vessels and successfully integrate the newly formed bone cells with the native bone.
The researchers were able to replicate the results in rabbits using functionalised non-mulberry silk composite. Rabbits with scaffolds implanted at the site of bone injury showed successful growth of bone cells and integration with the native bone at the end of three months.
Commercially available synthetic grafts have a failure rate of about 25% and 30-60% complication rates. This is due to slower bonding with native bone and poor blood vessel growth.
The team led by Prof. Biman Mandal from the Department of Bioscience and Bioengineering at IIT Guwahati developed the silk composite by adding chopped silk fibre to liquid silk. Unlike pure silk, the silk composite has greater strength. The addition of bioglass further enhanced the strength of the composite.
Besides other kinds, both mulberry and non-mulberry silk composites were tested. The non-mulberry silk composite was found to be superior in all respects. The RGD sequence in non-mulberry silk is a cell binding site and helps in better cell attachment and proliferation. As a result, more stem cells get attached to the composite leading to better bone tissue formation with time.
Besides enhancing the strength of the composite, the minerals from the bioglass gets deposited on the composite making it rougher. “Bone cells prefer rough surfaces and the scaffold mimics the native bone surface architecture,” says Prof. Mandal. Bioglass also helps in stem differentiation. “We found stem cells differentiating into bone cells with the formation of extracellular matrix similar to natural bone,” he says.
The doped copper plays a crucial role in stabilising the gene responsible for blood vessel formation. The gene, in turn, regulates the downstream angiogenesic factors thus helping blood vessel formation.
Copper also plays a role in attracting endothelial cells (which forms the inner lining of blood vessels) present nearby to the bone defect site making blood vessel formation possible.
The mulberry silk composite degrades and gets desorbed by the body at a faster rate than the non-mulberry silk. The rate of silk composite degradation should match the rate of new tissue formation else the bone that forms will tend to be weaker. “The non-mulberry silk material will be replaced completely in a few years. Since bone healing is slow, the silk material should not degrade quickly,” Prof. Mandal says.
The researchers tested the potential of the composites in repairing bone defects in rabbits and found more than 80% bone formation at the end of 30 days. “In the rabbits, the scaffolds promoted new bone tissue formation and growth of blood vessels. The resorbable nature of the scaffolds enabled them to degrade inside the body while being replaced with viable bone tissue in the small focal sized bone defects. No remnants of the scaffold were seen,” says Joseph Christakiran Moses from the institute’s Department of Bioscience and Bioengineering and first author of a paper published in the journal Advanced Healthcare Materials.
“The results from rabbit models are very promising. We would like to undertake trials on larger animals such as sheep and goat,” says Prof. Mandal. “Since we use green methodology, the prospects of regulatory clearance are brighter.”