Researchers devise method of producing composite scaffolds

According to Pennsylvania University, bioengineered replacements for tendons, ligaments, the meniscus of the knee and other tissues require recreation of the architecture of these tissues in three dimensions.

These fibrous, collagen-based tissues located throughout the body have an ordered structure that gives them their robust ability to bear extreme mechanical loading.

Many labs have been designing treatments for anterior cruciate ligament and meniscus tears of the knee and rotator cuff injuries.

One approach has involved the use of scaffolds made from nanosized fibres, which can guide tissue to grow in an organised way.

However, the fibres’ widespread application in orthopaedics has been slowed because cells do not readily colonise the scaffolds if fibres are too tightly packed.

Loose structure

Robert L Mauck, professor of orthopaedic surgery and bioengineering, and Brendon M Baker, previously a graduate student in the Mauck lab at the university’s Perelman School of Medicine, have developed and validated a new technology in which composite nanofibrous scaffolds provide a loose enough structure for cells to colonise without impediment but can still instruct cells how to lay down new tissue.

Their findings appear online this week in the Proceedings of the National Academy of Sciences.

‘These are tiny fibres with a huge potential that can be unlocked by including a temporary, space-holding element,’ said Mauck in a statement.

By using electrospinning, the team is said to have made composites containing two distinct fibre types: a slow-degrading polymer and a water-soluble polymer that can be selectively removed to increase or decrease the spacing between fibres.

The fibres are made by electrically charging solutions of dissolved polymers, causing the solution to erupt as a fine spray of fibres that fall onto a rotating drum and collect as a stretchable fabric.

This textile can then be shaped for medical applications and cells can be added, or it can be implanted directly into damaged tissue for neighbouring cells to colonise.

Increasing the proportion of the dissolving fibres is claimed to have enhanced the ability of host cells to colonise the nanofibre mesh and eventually migrate to achieve a uniform distribution and form a three-dimensional tissue.

Despite the removal of more than 50 per cent of the initial fibres, the remaining scaffold was a sufficient architecture to align cells and direct the formation of a highly organised extracellular matrix by collagen-producing cells.

This, in turn, is said to have led to a biologic material with tensile properties nearly matching human meniscus tissue in lab tests of tissue mechanics.

‘This approach transforms what was once an interesting biomaterials phenomenon — cells on the surface of nanofibrous mats — into a method by which functional, three-dimensional tissues can be formed,’ said Mauck.

It is a marked step forward in the engineering of load-bearing fibrous tissues and will eventually find widespread applications in regenerative medicine, according to the authors.

Mauck and his team are currently testing these materials in a large animal model of meniscus repair and for other orthopaedic applications.