Introduction: Artificial limbs though helpful lack sensory feedback from distal prosthetic regions. Our ultimate goal is to interface limb sensors (heat and pressure transducers) with sensory peripheral nerve. In a preliminary step, we seek an active nerve interface to increase localized charge density and reduce interface biofouling and scarring long term. Poly(3,4-ethylenedioxythiophene) (PEDOT) is an electrically-conductive nanopolymer which enhances recording and may confer these desired characteristics.

Methods: Sensory protection was evaluated across 12mm auto and four fabricated grafts (n=5 per group) following nerve coaptation with PEDOT lined peroneal nerve grafts in the rat (Fig 1). On postoperative day (POD) 90, sensory function was evaluated by measuring reaction time to heat or cold application on the foot pad and response to foot pressure removal when lifting the rat. Sensory protection tests were validated against muscle force and nerve conduction values also measured on POD 90.

Results: Reaction times were fit to ordinal scales as was toe spread for comparisons. Response to heat and toe spread showed recovery similar to Control in both the AUTO and S-DOT graft groups while the F-DOT group scored statistically lower on these measures (Fig 2). Sensory test validation with muscle force and nerve conduction show significant relationships for toe spread; and heat sensation (Tables 1&2). Both heat and cold sensation require more than a motor response to evaluate.

Conclusion: Inclusion of some PEDOT (S-DOT) but not 100% PEDOT (F-DOT) in a synthetic graft lining statistically benefits early recovery of sensory protection when compared with autograft and control conditions. PEDOT, by aiding charge density and reducing scarring, could provide a stable interface for sensory transduction.

 

Table 1. Summary for Linear Regression Coefficients (R) Calculated by Separately Regressing Sensory Protection Data on Muscle Force Data collected on post operative day 90.
	% Heat Sensation Recovered		% Toe Spread Recovered		% Cold Sensation Recovered		Tibialis Anterior Muscle Force
EDL Muscle Force	R= .24, (n=23)		R= 0.67*, (n=23)		R=0.33, (n=19)		R= 0.97*, (n=24)
*Regression analysis was significant, p<0.05. Data were for rats in the surgical graft repair groups, AUTO, PDMS, AG-P, S-DOT, and F-DOT. Maximal EDL and TA muscle forces were recorded in situ with stimulation distal to the graft.
Table 2. Summary for Pearson Correlation Coefficients (r) for Sensory Protection Data and Nerve Conduction Data collected on post operative day 90.
	Heat Sensation Recovered	Toe Spread Recovered		Cold Sensation Recovered		Rheobase		Chronaxie
Graft Impedance	r= -0.42*, (n=24)	r= 0.16, (n=24)		r=-0.20, (n=19)		r=0.41*, (n=24)		r=0.42*, (n=24)
Peak velocity	r= -0.37, (n=16)	r= -0.60*, (n=16)		r=--0.03, (n=12)		r=0.82*, (n=16)		r=0.81*, (n=16)
*Correlation analysis was significant, p<0.05. Nerve conduction amplitude was recorded with stimulation at the sciatic notch proximal to the graft while recording in the EDL muscle.

The views expressed in this work are those of the authors and do not necessarily reflect official Army policy. This work was supported by the Department of Defense Multidisciplinary University Research Initiative (MURI) program administered by the Army Research Office under grant W911NF0610218.