Composite Artificial Limbs

Road accidents inflict grievous injuries to people. Loss of a limb by amputation can be a traumatic experience for such accident victims. Other factors such as congenital defects, bone deformities and constricted bone growth also add to the number of physically challenged people.

Composites, the wonder material serves the mankind with the advanced rehabilitation aid. The industry is really moving towards composite material because they are lighter in weight, easier to work with & more durable.

The artificial leg developed initially in the world has been an exoskeleton, which was more of a cosmetic replacement than a functional one. Though these appear like natural limbs, they cannot provide normal gait to a person and also comfortable for usability. The world has already directed its efforts to fabricate endoskeleton type of artificial limbs. The endoskeleton replicates the functionality of bones for load bearing and involves proper mechanical joints for normal gait. It essentially consists of a tubular unit, which meets the mechanical properties of the bones in order to provide uniform distribution of stresses (load sharing). The entire tubular unit is provided with a durable and cosmetic leg shaped covering made of polymeric foam. The endoskeleton type of artificial limbs use more & more light weight composites with carbon or glass fibre and polymer matrix.

In India, commonly used artificial legs are exoskeleton type made of high density polyethylene. Though the imported endoskeleton type of limbs are available in India, they are very expensive. As physical deformities aggravate the economic woes of the victims in our country, it calls for an indigenous development to restore the functional normalcy of physically challenged people at an affordable price.

On assessing the present scenario towards improving design, functional requirement and aesthetics of the artificial limbs in India, the Advanced Composite Mission of TIFAC launched a project on developing 'composite artificial limbs for physically handicapped' in collaboration with M/s. Mohana Orthotics & Prosthetic Centre, Chennai (Madras). The Department of Aeronautical Engineering, Madras Institute of Technology (MIT), Chennai has been extending technology support in terms of design, prototype development and complete testing of composite limbs. The project activities involve mechanical design & its validation, prototype development & productionization by suitable fabrication techniques & equipment.

The below-the-knee endoskeleton artificial limbs developed under the project are lighter in weight and better appearance than ever before with improved gait for the patients. This below-the-knee endoskeleton limb consists of five parts: a FRP tubular structure fabricated by filament winding of glass fibre in epoxy matrix, top & bottom connectors made by injection moulding of glass filled nylon, a polyurethane foot with composite keel embedded in it and a polypropylene socket to accommodate the amputee stump. The socket made of polypropylene is patient specific and does not create any problems like pressure sores even for diabetic patients. The FRP tube connects the socket to the foot. The connectors between the socket & tube and tube & the foot can be adjusted for angular alignment of the limb.

A very innovative design approach has been adopted for designing FRP keel for providing improved strength & flexibility in the foot piece. All the components of the limb have been designed on the basis of theoretical analysis using CAD software (CSA/NASTRAN) for typical compression loads at different angles, momentary impact etc. All the five parts and the socket are adjustable to meet individual requirements and to take care of static & dynamic alignment patterns.

The evaluation of individual components and also of the entire endoskeleton assembly for compressive & bending strength has been carried out. A simulated endurance test has been conducted for 5-year service life of the artificial limb considering average stance duration of 0.5 seconds for normal gait and three hours walking time per day thus testing the limb for 39.42 million cycles to simulate the life of 5 years. A 3-D modelling of the endoskeleton with all the embedded components considering actual properties of various materials was also carried out. Such type of below the knee artificial limbs would cost only Rs.6000-6500/- only as against Rs.40,000/- for the imported ones.

The indigenously developed artificial limb looks like a natural foot, it is sturdy, durable, waterproof and made of locally available material. The unique design of this composite limb permits walking, cycling and even driving a vehicle by a person physically challenged otherwise. A whole lot of innovative technology inputs from Madras Institute of Technology, Chennai has been instrumental in developing a user friendly & world-class artificial limb with excellent market potential in India and abroad.

Prototype artificial limbs developed under the project have been fitted to the patients for large-scale field trials.

For further information, please contact

Proprietor
# 154, MTH Road, Villi Vakkam
Chennai - 600 049, India