Editorial Feature

Building the Human Body: The Bionic Hand

Recent reports have highlighted the change in quality of life of an amputee using the most advanced bebionic3 hand. The new bionic hand achieves complete balance in terms of aesthetics, functionality and technology. The bebionic hand features high strength, flexible grip patterns and adjustable grip speed when compared to other myoelectric hands. In addition, a natural silicone skin covers the hand and it is available in different shades. This hand is capable of being monitored and controlled in a wireless manner with the help of bebalance, flexible programming software and smart electronics. All these unique features and technology enable the hand to offer excellent performance and versatility. BeBionic demonstrates the functional capabilities to the bebionic hand technology in the following video:

What is it made of?

The biomechatronic hand is provided with three fingers – thumb, index and middle fingers - for facilitating a tripod grasp. A finger actuator system is controlled by two micro-actuators that operate proximal interphalangeal (PIP) and metacarpo-phalangeal (MP) joints, respectively. These actuators are included in the palm and proximal phalange, respectively.  

The biomechatronic hand performs the grasping action in two phases that include:

  • Reaching and shape-adapting phases
  • Grasping phase with thumb opposition.

The degrees of freedom are drastically reduced with the incorporation of heavy actuators resulting in the generation of high-grip forces to facilitate a stable grasp. The index and middle fingers comprise three phalanxes and palm housing for accommodating a proximal actuator. The palm and the proximal phalange are equipped with two micro-motors. The key features of this biomechatronic hand are low energy consumption, light weight, controllability and natural appearance.

Research

Egermann M et al (2009) carried out a study to estimate an acceptance rate of myoelectric prostheses in children between 2 and 5 years of age and suffering from unilateral upper limb deficiency. The results showed that all the children quickly adapted to using the prosthetic hand. Around 76% of the subjects were found to be using the prosthetic device efficiently at the mean observation time of 2.0±1.3 years. Furthermore, the usage of prosthetics was more in children who underwent intensive occupational training. Also, the overall drop-out rate is low in preschool children when compared to adults. Hence, it was concluded that preschool children can be benefited by myoelectric hand prostheses as the acceptance rate is significantly influenced by amputation level.  

Significant research work related to prosthetic hands includes the development of a sensory feedback system by Antfolk C et al (2010) to resolve the problem of insufficient sensory feedback received by the humeral amputees. This system employs a tactile display, five actuators and control electronics. The team initially studied the application of force levels on the forearm skin of the subject during the operation of the system. They also examined the possibilities of integrating the proposed system with a myoelectric control system, as artifacts would generate in the recorded myoelectric signals upon the skin displacement during operation. Following this, the analysis of EMG recordings was carried out.

Based on the force discrimination and spatial resolution, the sensory feedback system was applied on two non-amputated subjects. The results proved that proportional force were generated by the system with respect to the angle of control. Elimination of artefacts using filters resulted in the integration of the myoelectric system with the sensory feedback system. Also, the differentiation of tactile sensation was achieved when the system was applied on two healthy subjects. Hence, it was concluded that the proposed system is capable of producing conscious sensory feedback during object manipulation.

Current Status of Research

Although many self-contained robotic prosthetic hands for transradial amputation level have been developed so far, none of them fit properly. This problem can be resolved by adopting a large bandwidth human-machine interface for perception and control. Cipriani C et al (2011) developed the SmartHand that promises to fit into transradial amputees perfectly.

This SmartHand having 16 degrees of freedom can be employed as a tool for neuro-controlled upper limb prosthetics research. It includes four brushed DC motors for producing motion. A key feature of this model is the ability of its actuation system to allow the hand to stably perform grips involved in daily activities. It has a maximum speed similar to that of commercial prostheses. Slippage tests also revealed that the hand can stably grasp objects weighing 3.6 kg with certain friction and cylindrical prehensile pattern.

Future studies focus on the enhancement of grip power of the hand. Research efforts are also focusing on the aesthetics of this technology with the development of cosmetic, protective gloves. Future experiments are also keen to bridge the gap between the bionic hand and the nervous system through the application of neural electrodes.

Sources and Further Reading

  • Egermann M, Kasten P, Thomsen M. Myoelectric hand prostheses in very young children. International Orthopaedics. 2009;33:1101–1105.
  • Antfolk C, Balkenius C, Lundborg G, Rosén B, Sebelius F. Design and technical construction of a tactile display for sensory feedback in a hand prosthesis system. BioMedical Engineering OnLine. 2010; 9.
  • Cipriani C, Controzzi M, Carrozza MC. The SmartHand transradial prosthesis. Journal of NeuroEngineering and Rehabilitation. 2011; 8(29).

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