Customisation of Textile Surgical Implants
Julian G Ellis
Ellis Developments Ltd
Special Lecturer, Department of Medical and Surgical Sciences, University of Nottingham
An article written in 1999 (but still relevant)
The paper describes the development of embroidery for the manufacture of textile surgical implants. A new range of implants can be customised for individual patients requiring repair of abdominal aortic aneurysms, a vascular condition that kills some 10,000 people in the UK alone each year. Dimensions of the diseased arteries are obtained from scans, and using CADCAM methods a customised implant can be rapidly produced.
The customisation of other implants using this method is also described.
Keywords: Embroidery, surgical implants, aneurysms.
When considering the design of a surgical implant, it is essential that the implant fits properly so that it gives the maximum benefit to the patient, whether it be a vascular implant, orthopaedic, spinal or has another application.
Many implants are available in a small range of sizes, for example, the component for an artificial hip that fits into the femur may come in perhaps five sizes and the cup which fits into the pelvis in another five. This is a perfectly satisfactory number for the range of sizes of patients encountered, because the surgical method used can accommodate slight variations in the size of the patient. However, for some products the range of sizes required is considerable, as the fit must be perfect, and adaptations cannot be made during the operation. This is particularly relevant when minimally invasive (or “keyhole”) surgical techniques are employed. This paper describes a project and its outcome to develop a system for the relining of the major arteries requiring customisation of the implant for each patient.
2. Abdominal Aortic Aneurysms
The problem relates to the endovascular repair of abdominal aortic aneurysms (AAA). An aneurysm is a bulge in the wall of a blood vessel, and AAA’s are aneurysms that occur in the main artery from the heart towards the legs. They kill some 10,000 people a year in the UK alone. If the aneurysm bursts, there is significant internal bleeding which is frequently fatal unless dealt with very promptly.
Traditionally, the aorta has been repaired with a major operation, involving the opening up of the body cavity, moving the intestines and other organs aside to gain access to the aorta and lower arteries. The arteries are clamped, the diseased portion of artery cut out and a woven or knitted polyester tube sewn in its place. This process has given adequate results for over 45 years. However, the disease, which particularly affects male smokers over the age of 60, is often required to be carried out on the very frail and elderly people or those with other conditions which may make the major operation required using this technique too risky to carry out. It is also usual for the patient to require intensive care after the operation which will take up a scarce and expensive (some £1500 per day) bed in an ITU. In order to overcome this difficulty, in recent years there has been a move towards developing 'keyhole' surgical methods to treat the condition in order to reduce trauma to the patient.
In essence, the endovascular repair method involves making a small hole in the femoral artery and inserting a 7-mm diameter catheter. Under x-ray control, this is passed up above the diseased section of artery. An implant is then passed up the catheter. The implant may carry hooks, which bed themselves into the main healthy artery wall above the diseased portion. Next, the catheter is slowly withdrawn leaving the implant behind. It is essential that the implant forms a blood tight seal above the diseased section and a blood tight seal below the diseased section. The result is that the diseased portion of artery is excluded by the textile tube within it and the risk of the aneurysm bursting is largely removed.
To fit the patient properly, a large number of measurements must be made of the artery, as shown in Fig 1. To fit all sizes of artery likely to be presented to the surgeon some 1900 different sizes would be required to be stocked. This is clearly unreasonable and therefore each implant must be customised to fit the patient. This customisation is usually carried out with the use of Computer Aided Tomography, commonly known as a CAT scan.
3. Computer Aided Tomography
CAT is similar to an ordinary x-ray, but multiple x-rays are oriented at different angles around the body (Fig 2). A computer is then used to extrapolate a three-dimensional image from the various two-dimensional images. From this resultant three-dimensional image (Fig 3) dimensions can be taken and the required dimensions for the implant determined. A straightforward order form can then be completed and the details sent to the manufacturer for processing and production of the implant.
The Anson Stent-Graft implant is made using our patented embroidery technology. Embroidery is the ideal textile manufacturing approach for producing a customised implant. It is a highly computerised process and, because of the general requirements of customisation for the manufacture of, for example, customised baseball hats or name badges, the technology has been developed to make the manufacture of low volumes and even 'one offs' economical.
3-Dimensional image of aneurysm developed from CAT Scan
Embroidered Straight implant
We have adapted the technology for the development of our surgical implant systems in conjunction with Pearsalls Limited and Anson Medical. In this particular case the implant is manufactured by embroidering a superelastic wire with shape memory characteristics onto a microfibre polyester base cloth. Firstly, the bare wire is heat set in a furnace to the required dimensions (dictated by the size of the patient's diseased artery). Next, an embroidery pattern is developed on a computer u sing a highly automated CAD system. The wire is then attached to the base cloth using an embroidery machine and the finished embroidery sewn into a tube (Fig 4). Including the heat setting, this process currently takes approximately 6 hours. After manufacture (in a clean room), the implant is pre-loaded into an insertion system and the whole sent off for sterilisation using gamma irradiation. It is then sent to the hospital.
With the frailest of patients the operation can even be carried out under local anaesthetic and many patients treated endovascularly do not even need intensive care, with consequent financial savings.
5. Other Customised Implants
Other products for surgical implants that can be produced using embroidery techniques to customise the implant include shoulder repair systems, spinal disc replacement systems and muscle transfer systems (suitable for children suffering from cerebral palsy).
In the example of replacement of the intervertebral discs of the spine, an embroidered textile which is wrapped around a biocompatible silicone block. The block has properties which are much like those of a natural spinal disc, but embroidery technology permits the manufacture of a textile which can be formed around the silicone. The embroidery is made on a soluble base material, which is dissolved away, to leave a fabric with optimised fibre architecture. Of note are the reinforced screw holes, which permit the textile to be fixed to the vertebrae with bone screws, and after the tissue ingrowth which quickly occurs, gives a structure which mimics the natural ligaments which would have secured the original spinal disc in place. Non-covered discs are in danger of being displaced from the intervertebral space by movements of the patient: the embroidered cover minimises this risk.
Embroidered implants offer a convenient and effective method of producing complex textile shapes which can be customised according to the needs of individual patients.
The project was a collaborative project run with financial help from the Department of Health, under the MedLink programme. The collaborators were the Department of Vascular Surgery, University of Nottingham led by Professor Brian Hopkinson, Pearsalls Limited of Taunton, Somerset and ourselves, Ellis Developments Limited from Nottingham. The project was later joined by Anson Medical Limited, of Didcot, Oxfordshire, who have developed a new delivery system for the device, and are marketing the device.
7. References and Bibliography
1. PCT International Patent Application WO99/37242 Reinforced Graft
2. Surgical Implants using the Techniques of Embroidery. MedLINK Project report on behalf of the project collaborators, January 2000. Ellis Developments Ltd
3. European Patent Application 96303741.1 Textile Surgical Implants
4. UK Patent Application 9510637.3 Device for the repair of the rotator cuff of the shoulder
5. International Patent WO 99/00074 Surgical Implant
6. McLeod ARM, Neumann, L, Ellis JG, Butcher P. The Nottingham Rotator Cuff Augmentation Device Comrades in Arms - Engineers and Surgeons, I MechE April 2001
7. Ellis JG Engineering and Surgical Textiles by Embroidery, Textile Institute 80th World Conference, Manchester, April 2000
8. Ellis JG Surgical Implants using Embroidery Techniques UK Liaison Committee for Sciences Allied to Medicine and Biology, Medical and Biological new Technology, Fourth International Conference, Brunel, 1999
9. Ellis JG and Hopkinson BR The Endoscopic repair of Abdominal Aortic Aneurysms using embroidered textiles. Link Medical Implants Seminar, Meriden, 1998