Background

The Facial Nerve can be damaged at a peripheral level by a stroke or, for example by trauma or infection within the face or the ear. In these cases the facial muscles are paralysed with little or no chance of spontaneous recovery. This research focuses on the potential utilisation of a Shape Memory Alloy (SMA) to replace the function of the Facial Nerve, which will allow in conjunction with passive reconstructive methods, a patient to regain limited but active movement of the mouth corner. Paralysis of the mouth corner is a very disabling both functionally and cosmetically, speech and swallowing are hampered and the patient loses saliva, with presents a social problem.  

Methods

This work addresses the design activity by implementing a methodology utilising integrated methods for achieving successful product engineering. Research and development is related to the investigation of the utilisation of an SMA to supplement the “passive” technique. Operational design and development work has already been undertaken in relation to a SMA being controlled by a dedicated electronic control interface and power supply. The interface measures the active potential of the healthy Zygomatic muscle by means of electromyography (EMG) and produces a signal to control the actuation of the SMA. The research centres on the entire device ultimately being implantable, similar to a pacemaker or deep brain stimulator.

Results

To identify the key parameters of the EMG sensing device the system testing strategy needed to ascertain the output signal from the device for a range of facial movements. Data was collected relating to five different ‘levels’ of smile with a sampling period of 30 seconds for each ‘level’.  Experimental work confirmed that there is definite viability for the precise control of an SMA system based on EMG data. The next stage            of development will address the issue of a ‘tuneable’ dedicated controller for this specific SMA control application and will also examine the potential integration and control of Electroactive Polymers (EAP’s).  

Conclusions

The first stages in assessing both the strengths and limitations of SMA’s towards resolving biomechanical problems and relieving disability have been undertaken. Experimental work to date has confirmed there is definite viability for the precise control of an SMA system based on EMG data. A considerable amount of research and developmental work has still to be undertaken before the system can be considered effective for precise control. The research and experimental work undertaken to date provides a firm foundation for the further development of the EMG/SMA control system for an animatronic head and, in addition will potentially provide proof of principle for effective and real time EMG/SMA or EMG/EAP control.