Electrospinning biomaterials for tendon repair
Scientists at The University of Manchester, UK, are investigating the use of electrospun polycaprolactone nanofibres to regenerate damaged tendons.
Because the bundle of fibres replicates the morphology of tendon tissue, researchers envisage that the synthetic structure will perform the mechanical function of the tendon while it repairs itself, as well as act as a temporary scaffold to promote cell migration and new tissue formation.
Hydrolysis of the polymer causes it to degrade as the injury heals. However, the rate of polymer degradation must match the rate of new tissue growth for effective load transfer.
‘All levels of tissue regeneration come with their own difficulties that need to be addressed,’ says Lucy Bosworth of the Department of Biomaterials at Manchester.
‘The main issue with tendon regeneration is the ability to provide an environment desirable for cells that would allow them to secrete matrix (ECM) of the correct type – collagen type I – and with an orientation parallel to the direction of load application.’
With current techniques, such as autografts and allografts, inferior scar tissue often forms leading to chronic pain and recurrent problems. Bosworth explains, ‘Scar tissue forms due to rapid cellular production of collagen type III, known to be biomechanically inferior to collagen type I, causing poor alignment of collagen and insufficient infiltration with tendon cells’.
The polycaprolactone fibres inhibit scar tissue formation by encouraging cells to secrete collagen type I matrix.
‘By replicating the structure of the tendon, cells should not be deterred by the scaffold’s presence and ought to be able to migrate along the bundle axis. Materials that are too stiff or elastic would not promote desirable tissue formation,’ adds Bosworth.
The scaffold is formed by spinning a polymer solution of biocompatible polycaprolactone onto the surface of a liquid reservoir and drawing it using a needle tip to form a fine bundle of about 46µm, with fibres about 640nm in width.
Solution concentration, polymer molecular weight, solution flow-rate, applied voltage, and the distance between the needle-tip and the fibre collector are carefully monitored during electrospinning to ensure fibres are of the correct diameter.
Dr David Farrar, Biomaterials Technology Manager at the Smith and Nephew Research Centre in Heslington, UK, suggests there is a ‘clinical need’ for this technology in tendon repair, and observes that electrospinning, which is still new to the biomaterials sector, is ‘interesting for producing nanofibres that create the right environment physically for the cells’.
He says the ‘simplicity’ of the process lends itself to be scaled up for industry.
He adds, ‘The key test is how it performs in vivo and then there is the challenge of scaling that up in bigger animal models.
'The material, polycaprolactone, is a well established biomaterial. But it is not strong and is a slow degrading material [degradation can take about three years], so we would be concerned about it having sufficient strength [and] slowing down new tissue growth in its place. The other issue is, will enough cells migrate into the scaffold and quickly enough?’
Another approach that may be considered is pre-seeding the scaffold with the patient’s cells prior to suturing it to the affected area.
Research will now focus on pre-clinical tests in the Achilles heal of a mouse, exploring control of biodegradation in terms of strength retention and mass loss.