Researchers from the University of Connecticut have developed a biodegradable composite made from silk fibres that can be used to repair load-breaking broken bones safely and effectively.
In the paper ‘High performance resorbable composites for load-bearing bone fixation devices’, published in the Journal of the Mechanical Behaviour of Biomedical Materials, Professor Mei Wei and associate professor Dianyun Ziang tested silk fibroin, a protein found in the strong silk fibres spun by spiders. They used various composite forms to optimise the compound’s strength, flexibility and biodegradability.
“Our results are really high in terms of strength and flexibility, but we feel that if we can get every component to do what we want them to do, we can get even higher,” said Wei.
The team had to ensure the composite was strong enough to support bones as they heal, but not so strong that it bears more weight than the bone itself, which can lead to the recovered bone being weaker than it was before the break. The composite also needs to be flexible enough to enable patients to retain their natural range of motion and mobility during the healing process.
The researchers produced a composite consisting of long silk fibres and fibres of polylactic acid, a biodegradable thermoplastic derived from corn starch and sugar cane. The fibres are dipped in a solution where each is coated with particles of hydroxyapatite, the calcium phosphate mineral found in teeth and bones, before being packed in layers on a small steel frame and pressed into a dense composite bar.
The composite is strong and resilient, and reportedly capable of supporting broken legs through months of recovery, before degrading after a year. No surgery is required to remove the composite. The team has started tests on derivatives of the composite, including forms that incorporate a single crystalline form of the hydroxyapatite for greater strength, and a variation of the coating mixture to maximise its weight-bearing properties.
Wei and Ziang were joined in the study by Bryant Heimbach, a PhD candidate and materials scientist, and Beril Tonyali, a student of materials science and engineering, both from the university.