Development of a CYBERnetic HAND prosthesis

A Pneumatic Stimulator was designed in coordination with the implantable electrodes for the external mechanical stimulation and to combine the stimulator with a recording system for nerve signals. It can be used in vivo experiments to investigate the reaction of sensory cells in the skin and the neural response on mechanical stimulation. To observe the exact moment on which the mechanical part of the pneumatic stimulator hits the area of interest, an ultrasonic sensor was incorporated at the stimulation tip. The signal generated by the ultrasonic sensor is available as a TTL-level signal at the output of the stimulator. By varying the control gas pressure the hardness of the stimulation can be controlled. Also different front-ends can be adapted to the cylinder of the stimulator.

The final prototype of the fully sensorized CYBERHAND five fingered biomechatronic prosthetic hand has been developed and integrated in the control system. The CYBERHAND biomechatronic hand has five underactuated fingers actuated by six DC motors. Five motors and five Bowden cables have been integrated in a specific mechanical structure (artificial forearm). Another motor is integrated in the palm and it is used for controlling the thumb opposition. A set of sensors have been integrated in the hand in order to provide both proprioceptive and exteroceptive information. Tension cable, force, joint angle, end stroke, and contact sensors have been integrated in the final prototype that is driven using six specific motor driving boards and two NI DAQ boards. All information and data about the prosthetic hand is available from the documents and video indicated in the section below. The official web site of the CYBERHAND project has been published at http://www.cyberhand.org. Public results and media coverage are available.

An ASIC with 4-channels amplifier 4ChRec was integrated without any digital control and a monolithic optically coupled prototype was developed for using in acute experiments in animal models. This amplifier has identical performances as that included in the ASIC "8ChStim4ChRec" with the advantage of having a low noise and being possible to place it near the electrode getting a better performance.

Longitudinal intrafascicular electrodes (LIFEs) placed inside the peripheral nerve have been developed in order to improve selectivity with respect to extraneural electrodes and to increase the signal-to-noise ratio of recordings. We evaluated the functional and morphological effects of either Pt wire LIFEs or polyimide-based thin-film LIFEs implanted in the rat sciatic nerve for 3 months. Functional results at 1 month indicated an initial decline in nerve conduction velocity and in the amplitude of muscle responses, which recovered during the following 2 months towards normal values. Morphological results showed that both types of LIFEs induced a mild scar response and a focal but chronic inflammatory reaction, which were limited to a small area around the electrode placed in the nerve. Both types of LIFEs can be considered biocompatible and cause reversible, minimal nerve damage.

An actuated artificial hand made of compliant material has been developed. The five fingers are articulated and are actuated using the underactuated approach and specific components for the transmission mechanism. The actuator can be integrated inside the palm. Two electromyographic electrodes have been used to control the opening and the closing of the hand. The main features of this artificial hand are: - Low cost fabrication and maintenance; - High cosmetics appearance; - Adaptable grasping capabilities; - Simple control strategies; - Low control burden for the user; - Anthropomorphic kinematics. The above listed features make this artificial hand suitable for prosthetic applications. The artificial hand and the control strategies have been described in detail in three conference papers: M.C. Carrozza, G. Cappiello, G. Stellin, F. Zaccone, F. Vecchi, S. Micera, P. Dario, "A Cosmetic Prosthetic Hand with Tendon Driven Under-Actuated Mechanism and Compliant Joints: Ongoing Research and Preliminary Results", in Proceedings of the 2005 IEEE International Conference on Robotics and Automation (ICRA 2005), Barcelona, Spain, April 2005, pp. 2672-2677. M.C. Carrozza, F. Zaccone, S. Micera, G. Cappiello, G. Stellin, F. Vecchi, P. Dario, An adaptive prosthetic hand with compliant joints and EMG-based control, in Proc. of MEC 05 Integrating Prosthetics and Medicine, August 17-19, 2005, pp. 62-68. M.C. Carrozza, G. Cappiello, G. Stellin, F. Zaccone, F. Vecchi, S. Micera, P. Dario, "On the Development of a Novel Adaptive Prosthetic Hand with Compliant Joints: Experimental Platform and EMG Control", International Conference on Intelligent Robots and Systems (IROS 2005). An Italian Patent (NoLU2003A000012) has been requested on September 15, 2003.

Polyimide sieve electrodes were implanted between the severed ends of the sciatic nerve in rats. The degree of axonal regeneration through the electrode was examined by physiological and histological methods from 2 to 12 months postimplantation. Regeneration was successful in all animals implanted. The number of regenerated myelinated fibers increased from 2 to 6 months, when it was similar to control values. The majority of myelinated fibers crossing the via holes and regenerated through the distal nerve had a normal appearance. However, in a few cases decline of target reinnervation and loss of regenerated nerve fibers was found from 6 to 12 months postimplantation. Motor axons labeled by ChAT immunoreactivity regenerated scattered within minifascicles, although they were found at higher density at the periphery of the regenerated nerve. The number of ChAT-positive axons was markedly lower distally than proximally to the sieve electrode. Retrograde tracing studies indicate that the sieve electrode is not an obstacle for the regrowth of sensory fibers, but partially hinders motor fibers regeneration. They also suggest that fine fibers may be at advantage over large ones to regenerate through the regenerative electrode.

We evaluated nerve regeneration in an experimental nerve amputee model in the rat sciatic nerve. Morphological results show that regeneration occurred into a silicone blind chamber, with a large number of axonal profiles indicative of regenerative sprouting. The number of axonal profiles counted at the distal level was sustained over 9 months follow-up, indicating that regenerated axons are maintained even in absence of distal targets. Reconnection of the distal nerve to foreign targets improved the patter of nerve regeneration, decreasing the number of abnormal sprouts.

A monolithic prototype was designed and fabricated to carry out the electrical characterization and in vivo testing of ASIC "8ChStim/4ChRec". This prototype can be used with different electrode types such as sieve, cuff and Life. The system is optically coupled with the external controller allowing to be used in acute experiments.

A bidirectional inductive telemetric link was developed for energy and data transmission. The internal transceiver is based in an ASIC and implements a communication protocol and data (de)modulation. An OOK modulation is used getting a bit rate up to 1Mbps in both directions at a distance of 2cm.

Development of regenerative type electrodes and accessories to form interfaces with nerves of behaving animals for stimulation and recording of neural signals. -A laboratory version of a telemetry system for sieve electrode with multiplexer (FAMS II). -Design and manufacturing of a new version of the regeneration-type interface. A 27 channel implantable microelectrode with integrated multiplexer (FAMS II) was built. A transcutaneous connector for connection to the implantable telemetric system was fabricated.

Peripheral nerve injuries are rarely followed by complete return of function. Deficits are particularly important for motor function, resulting in paralysis and muscle atrophy. In different groups of rats the sciatic nerve was either crushed or transected and repaired by direct suture or by tube repair using silicone or collagen tubes. After 60 days, nerve regeneration was assessed by electrophysiological and functional tests, nerve morphology and immunohistochemistry against choline acetyltransferase (ChAT) for labeling motor axons. Suture and tube repair resulted in similar levels of muscle reinnervation, but significantly lower than after nerve crush. Recovery of walking track pattern was poor in all groups after nerve section. The numbers of regenerated myelinated fibers and of ChAT+ fibers were similar to control values after nerve crush, but increased after section and repair. The normal fascicular architecture and grouping of ChAT+ fibers were maintained after nerve crush but lost after section and repair, where motor fibers were scattered within small regenerated fascicles throughout the nerve. The loss of fascicular organization was related to the deficient recovery of locomotor function. Thus, labeling of motor axons by ChAT immunohistochemistry provides useful information for the study of the degree and specificity of nerve regeneration.

Flexible, 4 channel polyimide based cuff electrode for FES application were designed with monolithic (CNM) amplifier (P-MOS) and filter integrated to the substrate. An advantage of the cuff electrode is the easy implantation at the site of recording or stimulation, causing minor irritation to tissue even for chronic application. The possible applications are recording action potentials from different nerves to monitor neural signals and/or to understand the post surgical conditions of the nerve.

Polyimide sieve electrodes were implanted between the severed ends of the sciatic nerve in rats. After regeneration took place during 3-7 months, the electrodes were used for stimulation and recording from the regenerated nerve fibers. Comparison of neural recordings has been made between regenerative electrodes, cuff electrodes and microneedle electrodes.

An ASIC with 8-channels stimulator and 4-channels neural recording amplifier ("8ChStim/4ChRec") was developed. The main performances of electrical stimulator are: current range up to 5mA in four scales with 6 bits resolution (2, 5, 20 and 50uA); programmable stimuli waveform; 1 us pulse width resolution; stimulation frequency from 7 to 300Hz and burst capability. The main characteristics of recording amplifiers are: very low noise [5nV/sqr(Hz)], programmable gain and bandwidth and high CMRR. This ASIC can be used to implement a general purpose neural stimulator and recording device using different electrodes such as cuff, sieve or life.

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