|Carbon Fibre Composites in Orthopaedics|
Sangeeta Nangia, Soumitra Biswas
The Department of Science and Technology (DST), Govt. of India in association with the Defence Research & Development Organization (DRDO) has launched the Advanced Composites Mission aimed at promoting the technology of composite materials & products in Indian industry.
The Technology Information, Forecasting & Assessment Council (TIFAC), an autonomous organization under DST has been entrusted with the implementation of the mission-mode programme.
The success of the Advanced Composites Mission of TIFAC may possibly be gauged by the large array of projects initiated by the Mission across the country. The Mission initiatives cover a wide spectrum of developmental projects ranging from hi-tech brake-discs for aircraft to down-to-earth societal applications such as orthopaedics to alleviate human suffering.
The Mission has recently launched a project in collaboration with M/s. S H Pitkar Orthotools Pvt. Ltd., Pune for developing orthopaedic appliances to enhance surgical implants to international standards and thereby offering improved rehabilitation systems.
The project aims at developing components for orthopaedic applications based on polyether sulphone matrix reinforced with carbon fibre. This new material is being developed as a substitute for stainless steel currently being used for the external ring fixator for the bone-healing system.
What’s a Ring Fixator?
It is an exceptionally versatile circular external fixator. The system has good range of fasteners and other supporting devices of various sizes & lengths, which produce an excellent combination of bone segments including angulation, rotation, translation, lengthening and compression.
The basic principle behind the use of this apparatus is tissue regeneration through the principles of distraction histogenesis of bone and tissues. The apparatus is quite stable permitting weight bearing and joint functioning during the treatment. This technique of fitting external fixator on human body is commonly known as llizarov technique.
What is Ilizarov Technique?
The surgery of Poliomyelitis, Osteomyelitis etc. has always been considered unglamorous. Limb lengthening being considered esoteric, unsafe and unpredictable, deformity correction was considered uninteresting and unrewarding. There was simply no elegant or effective solution in sight and hence a large number of patients languished.
The conventional premise of orthopaedic surgery that the generation of new bones, muscles and nerve tissue is not possible has been belied by the Ilizarov technique. It is in this scenario that Prof. Ilizarov’s 'nuts and bolts' surgery came in like a whiff of fresh air from the Siberian wilderness.
The technique, first developed by Russian surgeon G. A. Ilizarov in 1951 but which remained little known till recent times, is being used to correct both congenital bone deformities and those acquired due to polio, bone infection and accidents.
It has been used with great success for a wide range of limb disorders such as fresh fractures, disunited and infected fractures with gaps & deformities. This technique is able to fix bony fragments with minimal invasion of the tissues and retained function.
Using the law of tension, stress transforms the tissues to their embryonic potential. The surgeon can lengthen and reshape limbs, heal the most recalcitrant of non-unions, straighten & align bones and stabilize joints with the ability of a craftsman. This technique has already gained immense popularity in Mumbai, Bangalore and Chennai & is now becoming popular in Delhi as well.
How is it performed?
Ilizarov ring fixator is a set of around 20 simple mechanical devices including rings, threaded rods, nuts, bolts and hinges. The stainless steel pins are jointed to steel rings/carbon composite rings with bolts and put under ideal tension. The two sets of rings are fixed at the two ends of a deformed bone.
These rings are supported by special 2 mm thick pins those are drilled into the bone as well as manually adjustable threaded rods that connect the rings at the two ends. By gradually strengthening the two rings apart, pressure is exerted on the bone below, stimulating cell growth and elongation.
Growth of the associated muscle, nerve, skin and blood vessel tissues takes place simultaneously. The patients are advised to distract the rods at the rate of 0.25 mm every six hours. The distraction is initiated at the recommended rate of 1 mm daily. On an average, it usually takes one month to increase the length by 1 cm
There is perfect lengthening without complications and every deformity can be corrected. The wires slightly larger than hypodermic needles cause minimal damage and have a low risk of infection.
The elongation of bones makes them weaker and without proper physiotherapy, it is difficult to regain the muscle powers. Physiotherapy plays a crucial role to ensure joint movement and proper blood supply.
This technique could also be used for cosmetic treatment. It would be a boon for the people who want to increase their height. Lengthening can be done in legs, thighs and arms leading to a possible increase in the height by about 30 cms. This is a long procedure requiring about seven to eight months for each leg.
Why Ring Fixator?
The benefits associated with the ring fixators are the following:
While the former is rare and preventable by a thorough knowledge of anatomy, the latter can be treated with antibiotics. The versatility of the fixator permits fine-tuning and precise control over the process. The cost of this technique works out to be Rs.30,000 to over Rs.100,000 depending on the treatment duration.
The present project aims at developing the external ring fixator based on Carbon Fibre and Polyther Sulphone matrix. The importance of advanced composites for future light-weight materials is derived from the high stiffness combined with high strength & low density of fibre backbone. In this respect, carbon fibre surpasses the more economic glass fibre.
More than 90% of the carbon fibres used today are high-tension fibres with a tensile strength of above 3500 MPa. The Young’s Modulus of this type of fibres with values around 250 GPa is much higher than the values of the aramid and glass fibres.
Carbon fibre has negative coefficient of expansion in axial direction, which makes them resistant to thermal shock. They also possess low coefficient of friction and very good fatigue characteristics. The dimensional stability and very low coefficient for thermal expansion are properties instrumental for its use in tooling. The reduced coefficient of friction than glass makes carbon fibre more effective against steel.
The ability of Carbon fibre composites to resist chemical environment depends principally on the matrix systems. With the suitable selection of the matrix resin, it is possible to manufacture composites that exhibit excellent resistance to chemicals. Therefore, using polyether sulphone as the matrix for carbon fibres makes an excellent combination of high chemical resistance.
In addition to heat deformation resistance, the polymer is also resistant to chemical change on heating. It is therefore, capable of absorbing a high degree of thermal and ionizing radiation without cross-linking.
The principal features of the polyhether sulphone are their exceptional resistance to creep, good high temperature resistance, rigidity and above all transparency and self extinguishing characteristics. The transparency characteristic of PES enables the composites to be radiolucent.
These excellent properties of carbon fibre and polyether sulphone and moreover, the compatibility of the fibre with PES matrix makes them suitable for such orthopaedic applications.
The stainless steel external fixators are found heavy for the patients. Composite fibre ring is not only lighter but also due to its radiolucency, it enables the surgeons read the X-rays with better accuracy. Moreover, the high strength to weight ratio of composite made of carbon fibre and engineering polymers makes it suitable for high impact strength, as needed for the surgical procedures.
It has been planned to develop the following items under this project:
As of now, the imported fixators, by way of rehabilitation aids, have limited reach due to their high costs. This project would aim, in a self-reliant fashion, to ensure that such rehabilitation aids reach the commoners.