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MONITORING 
(1) Minimal corrosion and erosion by body 
fluid; 
(2) Fatigue resistance to repeated stress; 
and 
(3) Minimum body reaction to limit the 
increase of threshold due to peri- 
electrode fibrosis. 
Multistranded wires of gold, platinum, stainless 
steel, and Elgiloy are used; however, coils or 
helical-wound multistranded wires provide bet- 
ter flexibility and less fatigue. Elgiloy is re- 
ported to have the best fatigue resistance, but 
corrodes seriously when used as an anode. Plat- 
inum electrodes have minimum corrosion and 
erosion when used for biphasic stimulation 
pulses. Bipolar electrodes are generally more 
effective than monopolar ones. 
Many electrode problems remain to be solved. 
For brain stimulation, high density electrodes 
of the order of 1000 electrodes per cm^ and the 
associated electronic circuits and systems are 
still to be developed. 
Tissue damage resulting from electrical stim- 
ulation using "non-toxic electrodes" can be 
caused by: 
(1) Gas generation due to large current 
density ; 
(2) Heat generated at the electrode site ; 
(3) Toxic material generated by electrode- 
chemical reaction at the electrode site ; 
(4) Mechanical stress caused by the elec- 
trode assembly. 
These are subjects to be studied carefully to- 
gether with the threshold of stimulation. 
Although now in its infancy, stimulation is 
believed to have great potential. Many appli- 
cations of stimulation to control pain, hormone 
secretion, mental disturbance, and to partially 
compensate for defective organs can be sug- 
gested. 
PROBLEMS IN IMPLANT TELEMETRY 
AND STIMULATION 
The following problems are the major re- 
search or development direction for designing 
implant instrumentation, telemetry and stim- 
ulation systems. 
Circuit and System Design 
Current implant instruments have relatively 
low reliability and poor stability compared to 
space or industrial electronics because of size 
and weight limitations. With micropower de- 
vices and integrated circuits (medium or large 
scale), more complex functions can be designed 
to consume less power and occupy much less 
space. Therefore, it is possible now to improve 
reliability, accuracy and stability of implant 
instruments within size and weight limitations. 
Packaging Material and Techniques 
Size and weight limitations also impose heavy 
requirements on packaging material and tech- 
niques, particularly for long term implants. 
Materials that can protect electronic circuits 
and power supply from harsh body environ- 
ment for a period of a few years are still to be 
developed. Current materials including wax, 
epoxy and glass require too much weight and 
volume. 
Body Reaction and Implant Techniques 
Body reaction to implant instruments has 
not been thoroughly studied. Besides reaction at 
the implant site, total body reaction and possi- 
ble long term side-effects should be studied. For 
example, (a) pressure exerted by the implant 
due to the weight has an effect on local circula- 
tion; and (b) besides the toxicity of foreign 
material, effects of surface conditions and shape 
of the implant package are to be studied. 
Power Supply 
A small, compact, lightweight power supply 
over a long period of time for implant instru- 
ments is another necessary component to be 
designed. The nuclear battery, solid electrolyte 
battery, and body energy converters present 
attractive directions of pursuit. 
Implant Transducers 
New design of implant transducers is needed 
to meet the overall requirements of size and 
weight. Current transducers, except electrodes, 
are not suitable for implant telemetry applica- 
tions, and the design of transducers generally 
