Human endurance

Engineers and scientists are co-operating more closely in the hunt for robust, cost-effective materials to produce artificial replacements for the human body which do not trigger rejection. Andrew Lee reports.

The relentless demand on healthcare providers to provide better, more efficient treatment is fuelling increased research into new medical materials.

From hips to heart valves, replacing the body’s natural systems with artificial replacements poses a range of challenges for the engineering and medical communities.

Such materials must be robust enough to meet the unique demands of the human body over many years. In some engineering applications it may be possible to replace a component regularly with minimal fuss.

In the case of the human body, repeat operations to upgrade medical implants can be at best traumatic and at worst fatal.

The materials used in medical applications must also be acceptable to the human body. Rejection of a component by the body can result in major complications.

A third factor is expense. With an ageing population demanding increasingly high standards of medical care, the materials must be cost-effective to manufacture and apply. Significant research is under way to overcome these challenges, requiring new levels of close co-operation between engineers and scientists.

A £4.3m institute has just opened at Queen’s University Belfast to provide leading-edge research into polymer biomaterials, also known as medical plastics.

The Medical Polymers Research Institute (MPRI) brings together teams from the university’s departments of mechanical and chemical engineering, and its school of pharmacy, to develop new materials for applications such as plastic ventilator tubes, catheters, medical implants and prosthetics.

The Belfast centre will attempt to overcome problems such as infection and blocked drainage tubes that occur when rejection of medical plastics occurs.

Researchers are also concentrating on highly specific applications for advanced medical materials. One example is work under way at Loughborough University to develop new implants for people needing facial reconstruction due to a congenital disfigurement or following cancer treatment or a serious injury.

Loughborough has been given more than £200,000 by the Department of Health’s New and Emerging Applications of Technology (NEAT) programme to research the implants.

A key component of the work will be the application of rapid prototyping technology to allow the implants to be custom-made quickly to suit the needs of each individual patient.

Loughborough is investigating the use of laser sintering to build in a few hours an implant that would take several weeks to manufacture using current methods.

A 3D model would be taken of the area needing reconstruction using non-intrusive CT or MRI scans. The model is broken down into 2D sections that are then built up layer by layer using laser sintering techniques.

The new implants would be made from a mixture of a polymer and a bioactive ceramic, chosen for their ability to bond with bone.

Dr. Russell Harris of the Wolfson School of Mechanical and Manufacturing Engineering, leading the project, claimed it has the potential to ‘revolutionise’ the treatment options for people needing reconstructive surgery.

‘These materials could be harnessed with a hi-tech but established production technique for the direct, quick custom-manufacture of bone implants that will integrate themselves within the body and require only one surgical operation.’

The refinement of the types of materials to be used by the Loughborough team is a major focus of the bio-engineering research community.

One key area is the development of scaffolds – support structures implanted into the body on which natural cells can grow to form replacement tissue.

The scaffolds are intended to degrade at the same rate as new tissue develops, leaving nothing but healthy new biological structures at the end of the process.

However, finding material for the scaffolds that does not trigger rejection by the body has proved a problem.

A team at the University of Westminster is about to begin a project to create a new material to make scaffolds for both hard and soft tissue replacement, with applications in range of medical procedures including heart valves, eye cell implants and bone grafts.

The Westminster team is working with bacteria that can be used to create unique polymers for use in scaffolds, changing the conditions in which the bacteria grow to produce a wide variety of materials.

According to the university, the key aspect of the project is the use of a new strain of bacteria that has the ability to create hitherto unknown polymers.

These will be combined with a type of glass, 45S5 Bioglass, that provides an ideal surface to which cells can attach themselves in the scaffold material.

The researchers claim that the resulting Bioglass composites will have unique properties with the potential to solve tissue engineering problems that are beyond the scope of existing materials.

Researchers in the medical field are also looking for ways to extend the range of applications for existing materials through modification.

A project team at Sheffield University is looking to produce a biocompatible glass-ionomer cement (GIC). According to Sheffield, GIC bone cements are widely used in dentistry, but have seen their wider clinical application to ear, nose and throat (ENT) surgery limited due to concerns over their biocompatibility.

Specific concerns are that conventional GICs can leach aluminium ions associated with nerve damage and bone defects. They can also lack both transparency to X-rays and a distinctive colour to bone tissue – highly desirable properties for medical procedures.

The Sheffield team plans to co-operate with the biomaterials industry to produce an aluminium-free bone cement by replacing aluminium with iron, and achieve X-ray visibility by substituting calcium with strontium.

An industrial partner, Cornithian Medical, will provide additional support to the academics. Sheffield said the company has extensive experience in ENT surgery, and would contribute financial backing, materials and expertise to the project. The EPSRC is also backing the Westminster and Sheffield initiatives.