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Page 6 of 10 Amin. Plast Aesthet Res 2022;9:24 https://dx.doi.org/10.20517/2347-9264.2021.119

Multielectrode arrays have multiple electrode needles permitting multi-site recording and stimulation
[60]
penetrating the nerve at varying depths perpendicularly along the length of the nerve . The concern is
intraneural damage and the potential for poor stability of recorded signals over time. A single array
[61]
implanted in cat sciatic nerve for 350 days found persistent inflammation , and electrically stimulating a
large population of afferents via a single electrode is unnatural and can evoke paraesthesia’s .
[62]
Regenerative electrodes
Regenerative electrodes are the most invasive yet have the greatest contact with the largest number of axons.
The earliest example, devised 50 years ago, is the “sieve electrode”. Fine holes reside close to the nerve, and
as fibres regenerate, they regrow through holes for selective stimulation. The prospect of growth factor
[63]
delivery targeting specific neural populations electrodes will enable targeted delivery , and seems a
plausible method considering our understanding of how nerves attempt to regenerate. Nerve regrowth takes
time, and some concerns are that motor and sensory axons regrow in a disarrayed fashion than intact
[64]
nerves . Small unmyelinated axons have a higher growth capacity than large, myelinated axons, favouring
[65]
centrally located small axons and large at the periphery of the electrode . Promising results after 30
months is observed in cats . One potential avenue for exploration includes the guidance of regenerating
[66]
axons into small fascicles via neurite growth promotion down microchannels augmented by neurotrophic
factors or scaffolds . This has been seen to work well experimentally in the tibial nerve of rats .
[67]
[67]
Limitations of ENG decoding include overcoming the fibrotic response, minimised by increasing the degree
of charge stimulated with further concerns about neural injury .
[68]
FUTURE CHALLENGES IN DEVELOPING LOWER LIMB BIONIC TECHNOLOGY
Commercially available prostheses do not have volitional control, especially where it is needed, the ankle.
We know that sensorimotor interruption after limb loss leads amputees to have reduced confidence in
maintaining balance, increasing falls risk and bearing greater cognitive burden . Humans combine
[69]
sensory, visual, vestibular, cognitive, and proprioceptive inputs to their surrounding environment . A
[70]
sensory neuroprosthesis that modulated stimulated-evoked sensation in response to interactions between
the prosthesis and the environment was developed to study unilateral lower-limb amputees and their
adaptation to the loss of plantar sensation. Six BKAs were compared with 14 able-bodied individuals, and
they demonstrated higher foot placement accuracy. They were able to demonstrate that sensory
neuroprosthesis provides modulated feedback of plantar pressure that improves lower limb performance in
[70]
locomotor tasks .
Prostheses are heavy, need power, often noisy and require skilled repair when damaged. This is especially
pertinent to overcome these barriers considering compliance declines with time for prostheses . Modern
[71]
bionic prostheses limit data transfer across biological-mechanical interfaces, making them slow with low
bandwidth with wireless communication a priority, in addition to lead migration and fracture occurring in
24%-50% of events and wireless chips question how such systems can be appropriately powered [72,73] .
Similarly, electromagnetic interference can arise from the interface as a result of tissue reactions with blood,
matrix formation, inflammation, granulation tissue, foreign body reaction and fibrosis with the potential for
a hypersensitivity reaction . Long-term stability and reliability need further insight, and one avenue of
[74]
research is tissue engineered neural interfaces that integrate encapsulated neural cells within the electrode to
mitigate scar tissue formation and increase biocompatibility .
[75]

CONCLUSION
Outcomes after lower extremity trauma continue to improve. The growing expertise in preoperative,
intraoperative, and postoperative management of complex cases, embedded within specialist centres, is now