Scientists at Northwestern University have become the first to design molecules that could lead to a breakthrough in bone repair. The designer molecules hold promise for the development of a bonelike material to be used for bone anomalies and have implications for the regeneration of other tissues and organs.
‘Recreating natural bone structure at the nanoscale level – the first level of bone structural hierarchy – is what we set out to do with our experiments, and we succeeded,’ said Northwestern postdoctoral fellow Jeffrey D. Hartgerink, the lead author of a paper reporting these results.
The molecules reportedly self-assemble into a three-dimensional structure that mimics the key features of human bone at the nanoscale level, including the collagen nanofibres that promote mineralisation and the mineral nanocrystals.
Collagen – the most abundant protein in the human body – is found in most human tissues, including the heart, eye, blood vessels, skin, cartilage and bone, and gives these tissues their structural strength.
When the synthetic nanofibres form they make a gel that could be used as a type of glue in bone fractures or in creating a scaffold for other tissues to regenerate. Because of its chemical structure, the nanofibre gel would encourage attachment of natural bone cells, helping to repair the fracture.
The findings also map out a path for the creation of many other materials by self-assembly and spontaneous mineralisation that take advantage of an inorganic material growing on an organic material (known as a composite) and which could be useful in electronics, photonics, magnetics and catalysis.
In the Northwestern study the researchers created self-assembled nanofibres that resemble the collagen fibrils of real bone in shape and size. When the nanofibres were exposed to solutions containing calcium and phosphate ions, the fibres became covered with hydroxyapatite crystals.
These thin, rectangular mineral wafers grew on the nanofibres in a direction parallel to the fibre’s length in the same way that hydroxyapatite crystal grows on collagen in the formation of real bone.
The assembly of the nanofibres themselves can be easily reversed by changing the pH level of the fibres’ environment. The fibres can also be polymerised or cross-linked by oxidation to give them additional strength, a process that also can be reversed.
The versatility of the nanofibre system is said to offer the possibility of using the organic fibres as cargo carriers, possibly for drug delivery to a specific point in the body. Natural enzymes found in the body can disassemble the fibres so that their cargo can be released.
‘These fibres are cell-friendly,’ said Samuel I. Stupp, Board of Trustees Professor of Materials Science, Chemistry and Medicine, who led the study. ‘Cells like to grow on them.’ This property could lead to the use of the nanofibres in tissue engineering.