CHAPTER II Materials (Experimental protocol)

CHAPTER II

Materials (Experimental protocol)

The experimental work has been done in the laboratory of Neurophysiology of the Universitat Autonoma de Barcelona (UAB), under the guide of professor Xavier Navarro, during the period from April to July of 2007. The surgical implantation of electrodes, and animal invasive procedures have been directly performed by Prof. Navarro.

2.1. Electrodes used

During the experimentation three types of electrodes have been implanted and tested: • Tripolar spiral cuff ([1],[2])

• Twelve polar cuff

• Thin-film longitudinal intrafascicular electrodes (Tf-LIFEs)

More precisely four different devices of tripolar cuffs have been implanted; four different models of twelve polar cuffs have been used and five different models of LIFEs have been used. Hence the electrodes variability was taken into consideration.

2.1.1 Cuff electrodes implant

Tripolar polyimide cuff electrodes (with 3 parallel ring Pt electrodes) with a diameter of 1.0, 1.2 mm and 1.6 mm were used. Surgical implantation has been done in 12 female Sprague-Dawley rats

Fig.2.1. Photograph of rat sciatic nerve with tripolar cuff electrode implanted (the three platinum rings can be observed)

The interconnect ribbon was routed through the muscle and skin excision, avoiding tension, and the plastic connector was positioned over the skin of the lateral side of the hindlimb and secured in a place with surgical tape.

Twelve polyimide cuff electrodes (with 12 punctual Pt electrodes) with a diameter of 1.0, 1.2 mm and 1.6 mm have been implanted as well. The surgical procedure is similar as described for the Tripolar cuffs (Fig.2.2.).

Fig.2.2. Photograph of rat sciatic nerve with twelve polar cuff implanted (Punctual Pt sites can be observed)

During recordings, the animals were placed over a warm flat streamer controlled by a hot water circulating pump, and the hindpaw skin temperature maintained above 32°C .The experimental procedures followed the recommendation of the European Union for the care and use of laboratory animals and were approved by the Ethical Committee of the UAB.

2.1.2. LIFEs implant

The rat’s sciatic nerve was exposed and a segment at the midthigh carefully freed from surrounding tissues. Then the tungsten needle was firmly held with a pair of Dumont fine forceps perpendicular

A)

B)

Fig.2.3. (A) Schema illustrating the surgical implantation of a LIFE. The tungsten needle was threaded along the nerve and then used to pull the electrode linked by the filament. Then the needle was pulled out leaving the electrode inside the nerve. The needle was removed by cutting the polyimide filament (dashed line)

B) Photograph of rat sciatic nerve with a Tf-LIFE implanted.

entry

exit

2.2. In-vivo experimental set-up

In the Fig.2.4. a schematic of the complete experimental set-up is illustrated.

Fig.2.4. Schema of experimental set-up.

All the experiments were performed in a Faraday shielded cage in order to avoid electromagnetic noise. The standard tripolar configuration was used for signal recording. Signals were fed in differential form to a preamplifier (Isolated Microamplifier, FHC Inc), with analogical band-pass

External Connector Microelectrode amplifier Noise eliminator AD board Computer Sensory stimuli:

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The experimental setup is imposed in order to record sensory and efferent information essential for eventual fully-bidirectional control of a hand prosthesis. The choice of adequate stimuli is essential, since they have to be physiologically relevant. Here are explained the reasons for choosing presented stimuli set.

• Before manipulating any object the prosthesis user should be aware of the fact that the prosthesis has reached the object . Hence touch continuous stimulation is needed. It has been simulated by touching with Von Fray filaments of different values applied at different sites of the hindpaw. The applied values used where: 5.18, 5.88, 6.65. The sites of the hindpaw where stimuli has been applied where: pads A, B, C, D. For mapping of rat’s hindpawn see [14].

• Slip information is indispensable, because during manipulation (e.g. lifiting object vertically) a person provides optimized grip force. Also, this information could be useful if the weight of the object increases (e.g. filling the glass-the classic case in which EMG based prosthesis fails). In order to stimulate this type of sensory information two types of stimulus were applied: brushing the haired skin(See Fig.2.5.) of the dorsum of the foot (very weak slip) and scratch on the sole (fast, strong slip information).

• Moreover, it should be perceptible whether an object to be grasped is safe for the human hand. Then, nociceptive stimuli produced by pinching a toe on the ipsilateral paw were applied.

• For natural use of prosthesis the user has to be conscious where is spatially located his hand/fingers (without looking at them). Three types of proprioceptive stimuli were applied: flexion of the fourth toe, maximal paw flexion and foot fast flexion.

• Finally the efferent information is necessary to obtain control signals for prosthesis actuation. With this objective painful pinch was applied at the contralateral paw, while recording efferent activity induced by spinal reflex arcs.

After the experimental work, we obtained 52 recordings (ENG signals) which can be used for data-elaboration processing.