Abdominal Aortic Aneurysms and Embroidered Implants
Abdominal aortic aneurysms (AAA's) are responsible for the death of some 10,000 people each year in the UK alone. These swellings in the wall of the main aorta are liable to rupture, with massive blood loss into the abdominal cavity.
The condition is more common in males, with approximately 5% of men over the age of 60 developing them. For the last 40 years the conventional treatment has been to open the abdomen to remove the diseased portion of the artery, and sew a tube of polyester in its place. However, the operation is risky for a number of patient groups, requires a long hospital stay, usually including several days in intensive care.
In recent years surgeons have been developing minimally invasive techniques for the repair of AAA's. This usually requires a small opening in the leg to obtain access to the femoral artery, and uses an X-ray unit with image intensifier to monitor the progress of the procedure. Because the trauma to the patient is less intense, the level of hospital aftercare is considerably reduced.
The major research and development project we managed, was known as the SITE project (Surgical Implants using the Techniques of Embroidery). Details can be seen by following the link above.
The UK Department of Health has for many years supported research and development in health devices. Their current programme, known as Health Technology Devices, supports collaborative research projects in a very wide range of devices ranging from surgical implants to walking aids.
The previous programme known as MedLink had slightly different objectives but provided 50% funding support for projects. This scheme provided an ideal support process for a project that Ellis Developments Ltd set up and managed.
The Professor of Vascular Surgery at the University of Nottingham, Brian Hopkinson had been greatly interested in the repair of abdominal aortic aneurysms using minimally invasive (keyhole) surgery for a number of years. However, he was not entirely satisfied with the devices being developed, so he and I discussed the requirements of his ideal device one evening at his home. Ellis Developments had, already developed the concept of using embroidery technology to produce customised surgical implants and using the technology to produce graft stents was a process ideally suited to its facility for producing customised devices. Work carried out by Professor Hopkinson's team had indicated that a device to fit all the patients they were likely to treat would need some 1900 different shapes and sizes of device to be produced. It was clearly impossible to produce this range using conventional weaving or knitting techniques, but embroidery provides the flexibility to produce customised devices.
Commercial embroidery processes have been developed to facilitate the production of very low numbers of customised devices. For example, embroidered name tags on company uniforms and other garment decoration. A commercial embroidery machine is a development of a simple lockstitch sewing machine with a computer controlled pantograph moving the work piece under the stitching head with great precision. Software packages for designing for the machines are readily available and their adaptation for use for surgical implants did not require any changes to the software.
Aortic aneurysms are weaknesses in the walls of a major blood vessel which, if they burst, cause internal bleeding within the patient. Aneurysms in the main artery, the abdominal aorta, give rise to some 10,000 deaths each year in the UK alone. Traditional treatment for several decades has been to use a woven (or sometimes knitted) polyester tube. In a major operation the diseased artery is clamped above and below the diseased portion, the diseased section removed and the polyester stitched into its place. . The patient population is normally older people, who often have other disease, and the operation has a high post-operative mortality rate. The benefit of using minimally invasive techniques is that they are less stressful to the patient and can sometimes even be done under a local anaesthetic, avoiding the need for a more dangerous general anaesthetic.
Keyhole surgery for the repair of abdominal aortic aneurysms involves the surgeon making a small incision in the femoral artery at the top of the leg and pushing a 7 mm catheter up through the blood vessels to reach the diseased section. The whole operation is carried out using x-ray techniques with image intensifiers to assist the surgeon in locating the position of the insertion system. Originally the repair devices known as a stent grafts, were pulled through the catheter. However, as the process has developed more sophisticated and easier to use insertion devices have been developed.
Although the insertion catheter is only 7 mm in diameter, the implant may be required to expand within the patient to a diameter of 34 mm or even larger: the main aorta carries a considerable amount of blood.
In order to provide the springiness required to incorporate this expansion we decided to use a superelastic wire made of nitinol (an alloy mainly of nickel and titanium which also has shape memory properties). The springiness is not only required to provide the self-expansion properties of the device, but also provide a blood-tight seal against the wall of the artery at both the top and the bottom of the device, which bridges the diseased section of artery.
A collaboration was set up between the University of Nottingham, Pearsalls Limited (who are the licensee of our embroidered implant process technology) and Lombard Medical of Didcot, Oxfordshire. We applied to the MedLink scheme for a project of a value of some £320,000, of which half was funded by the government. We found that one of the major benefits of receiving government funding was not just the financial support but also the support and contact given by the representative of the programme management committee and his extensive contacts.
Much of the initial development work was based on the design of the positioning of the shape memory alloy wire, which was attached to a 100% polyester micro fibre fabric. The configuration of the wire on the base fabric is critical in obtaining not only a fabric which will expand and provide a blood tight seal as required but will also prevent the tubular structure from kinking as the patient moves about and therefore obstructing the flow of blood from the heart towards the leg.
As work progressed studies were important in confirming the feasibility of inserting the device reliably and accurately inside the patient.
By the time the project ended (which took about 3 years), we had a device which we believed to be safe from a biocompatibility point of view as well as being safe for insertion into patients. A steady roll out programme is in hand where the pioneer surgeon, Professor Hopkinson teaches surgeons and later supervises them in the insertion of devices. The surgeons he trains can then teach other centres so the device is steadily rolled out across the world.
We expect Lombard to have considerable commercial success with this device in saving the lives of very many patients.
Ellis Developments Limited
Nottinghamshire, United Kingdom
Julian Ellis will be delighted to hear from you.
Telephone on +44 (0) 7976 425899
We are based at Far Close, Rolleston Road, Fiskerton, Southwell, Nottinghamshire, NG25 0UJ, United Kingdom