Apr 18, 2011
UV treatment builds better nanofibres for tissue engineering
Researchers at Louisiana State University Health Sciences Center (LSUHSC), New Orleans, US, have developed a novel technique to produce biocompatible and biodegradable cross-linked polycarbonate nanofibrous materials that can be used as scaffolds for improving or replacing human tissues, organs and blood vessels.
This new technique is called photochemical reactive electrospinning, which uses a strong electrical field to draw jets from a solution containing cross-linkable polymers and deposit them onto a rotating drum forming nanofibres. During the process, the jet passes through strong UV light, which makes the fibrous material more resilient by inducing photocross-linking and photopolymerization reactions.
Biocompatible and biodegradable
Nanofibres of natural and synthetic polymers have been fabricated by numerous methods including self-assembly and electrospinning. The main advantage of these nanofibrous materials is that they have a huge surface area and high surface activity. These properties are desirable for engineering and biomedical applications, such as scaffolds for tissue repair and drug release. However, the main drawback of nanofibres is that they are often very fragile (weak) and susceptible to attack by chemicals, solvents and enzymes, which results in fast dissolution or degradation.
On the other hand, the nanofibres of some biodegradable polymers, such as poly(L-lactic acid) (PLA), are relatively stable in water and cell culture media, but these fibres have relatively low hydrophilicity (not ideal for cell attachment and growth). Their degradation products (lactic acid) have high acidity and may cause allergic reactions or inflammation.
The main challenge associated with biocompatible and biodegradable nanofibres is how to make them more hydrophilic to facilitate cell attachment and growth, and at the same time make them more resistant to water and enzymes that may be present in the human body to avoid premature degradation. To achieve this goal, the nanofibres are often cross-linked by some chemical cross-linkers, such as glutaraldehyde, but these chemical cross-linkers are usually toxic to cells and tissues.
Reporting their results in the journal Biomedical Materials, the researchers synthesized poly(dihydroxycarbonate) from L-tartic acid – a naturally occurring compound that is both cost-effective and environmentally friendly compared with petroleum-based raw materials. The method involves grafting a methacrylate group onto the polycarbonate and using photochemical reactive electrospinning to make cross-linked polycarbonate nanofibers. The advantages of aliphatic polycarbonates over PLA are that they are more hydrophilic and the degradation products are less acidic.
Benefits of cross-linking
The team investigated the effect of cross-linking the fibres on the chemical and mechanical properties of the material, as well as their biodegradability when treated with five different enzymes. Results showed that the fabricated materials were more resistant to solvents and had greater thermal stability and mechanical properties compared with the nanofibres that were not cross-linked. When treated with enzymes, the nanofibres showed a decrease in biodegradability as cross-linking increased, meaning that they would be resistant to enzymes when inserted into the body.
On top of this, the technology was shown to be very fast, which could aid mass production and showed a high affinity for cells, ideal when trying to fabricate tissue.
A key feature of reactive electrospinning is that the chemical, biological and mechanical properties of the nanofibres can be fine-tuned (by changing the content of the cross-linkable groups such as methacrylate and the UV intensity) without using toxic chemicals. This will provide new opportunities for designing and fabricating new materials for specific biomedical or engineering applications.
More information can be found in the journal Biomedical Materials.
About the author
Xiaoming Xu is head of the Division of Biomaterials at Louisiana State University Health Sciences Center (LSUHSC), New Orleans, US.