At the hard-to-soft tissue interface

Materials World magazine
1 Mar 2010
An example of a simulated design for the cement bracket

Three-dimensional printed, calcium phosphate cement brackets may improve the bond between hard and soft tissue during ligament repair.

Researchers at the University of Birmingham, UK, are simulating different geometries so that there is maximum surface area for gripping both tissue types when placed at their interface.

The potential for stress concentrations caused by sharp corners is also being minimised.

In the next phase, the team will use surface modification to enhance adhesion at either end of the bracket. The 3D printing process, conducted at ambient temperatures, enables heat-sensitive biomolecules to be attached.

The research aims to overcome problems with ligament and tendon reconstruction, which involves either taking a soft tissue or a bone graft. The former is less painful but takes longer to heal, due to the graft’s weaker fixation to the bone. The latter, meanwhile, requires painful bone harvesting and implantation but achieves effective bone-to-bone healing.

‘We are producing something that has the advantage of the bone-to-bone graft without the harvesting procedure,’ claims Dr Liam Grover at Birmingham.

Creating bioresorbable brackets to replace the conventional metal screws that affix the hamstring soft tissue graft to the bone could reduce the potential for infection and tearing. It would also eliminate the need for invasive screw removal post-healing.

‘We are hoping that this interfacial regenerator will dissolve and blend the materials together, avoiding stress concentrations,’ says Grover.

He also proposes that the brackets will enhance bonding between the bone and engineered implantable soft tissue bioscaffolds. These constructs are increasingly being investigated to eliminate the need for grafting altogether. If the brackets’ biodegradation could match that of the scaffold, a complete system for repair might be available.

David Farrar, Technology Manager for Biomaterials at Smith and Nephew Research Centre in Heslington, UK, sees potential in using 3D printing to produce a variety of geometries, with the ability for surface modification at low temperatures. However, he says manufacturing scale up would need exploring.

Furthermore, he questions the need for such a part for artificially engineered constructs as ‘most [researchers] use a fibrous scaffold. The fibre provides strength [and] a means of fixing the scaffold into bone’. The brackets might, nonetheless, help form a ‘biological interface’, he acknowledges.

The question is ‘whether the cell-seeded-gel encased inside the brackets would have adequate access to the culture medium for exchange of nutrients and waste products’.

The group at Birmingham, in collaboration with other scientists in the USA, Germany and the UK, has completed a preliminary study. It has produced brackets at a laboratory scale via 3D powder printing from CAD models. Investigations will continue to optimise the morphology and surface.