• A scaffold made of silk–bone cement composite doped with silicon and zinc metal ions has been found to regenerate new bone tissue in rabbits in three months.
  • The newly formed bone forms a seamless joint with the existing bone and has blood vessels inside it.
  • Tests carried out on rabbits with defective thigh bone (femur) showed extensive bone formation of 73% at the end of 90 days compared with 49% in the case of scaffold made only of silk fibre.
  • Even at the end of 30 days, there was adequate bone regeneration and new blood vessel formation.
  • At the end of three months, the silk fibre had completely degraded leaving behind a homogeneous bone produced by rabbit bone cells.
  • The newly formed bone had healed the defective femur
  • The bone cement made of calcium phosphate becomes a part of the bone while the biocompatible metal ions (silicon and zinc) get leached out at the end of 90 days.
  • The scaffold is fabricated by first doping the bone cement with silicon and zinc and mixing the bone cement with chopped mulberry silk fibre.
  • The bone cement gets adsorbed on the silk fibre.
  • Liquid silk fibre is then added to bind the chopped fibre and bone cement; the liquid silk also makes the composite highly porous.
  • The silk–bone cement composite has higher density and strength, more surface area and high surface roughness, closely resembling a native bone.
  • The zinc and silicon ions get leached from the composite and activate bone and blood vessel cells.
  • This leads to faster regeneration of the bone tissue and blood vessel formation
  • By doping with these metal ions we are doing away with external addition of growth factor and also making the graft affordable.”
  • Silicon and zinc trigger a molecular response within the bone cells which makes them feel that they are lacking oxygen (triggering hypoxia response element).
  • So the bone cells start secreting pro-blood vessel forming (angiogenic) signals leading to vascularisation.
  • The compressive strength of silk fibre is about 40 kPa, while it is nearly double in the case of the silk–bone cement composite.
  • Though doping with the silicon and zinc metal ions reduces the mechanical properties, particularly the compressive strength, the bulk strength of the doped composite is sufficient to activate bone regeneration.