Yamini Jadcherla, Student, Melanie Urbanchek, PhD, Mohammad Reza Abidian, BS, PhD, Brent Egeland, MD, Rachel Marie Miriani, MS, Kirsten Schroeder, Student, Eugene D. Daneshvar, MS, Katie Ewing, Student, William M. Kuzon, Jr, MD, PhD, Daryl Richard Kipke, PhD, and Paul S. Cederna, MD.
Introduction: Strategies for improving nerve
regeneration through nerve gaps include the development of new biological and
synthetic materials, such as poly
(3, 4-ethylenedioxythiophene) or PEDOT,
which is an electrically conducting polymer. PEDOT functions similar to a wire;
it increases electrical signals within the nerve in order to compensate for the
lack of nerves.
Materials
&Methods: We
constructed a grafting material to augment regenerated nerve conduction. We
incorporated PEDOT, as the lining of an agarose-based hydrogel tube. We tested
the following concepts: 1) nerve fibers regenerate through a nerve graft
containing PEDOT, and 2) successfully reinnervate target skeletal muscles. We
tested four synthetic materials as peripheral nerve conduits; two of which
included PEDOT. The recovery of these two grafts was compared with a control
nerve autograft. The groups compared were: nerve autograft (AUTO), polydimethylsiloxane (PDMS), plain agarose (AG-P/Hydrogel),
agarose with a spiral layer of PEDOT lining (S-OT), and agarose completely
lined with PEDOT (F-DOT). Rat peroneal nerve was lesioned and repaired with a
12 mm long interpositional graft or conduit (n=5 per group). Following a 90 day
recovery period, muscle force properties were measured by stimulating the
peroneal nerve proximal to the repair. Nerve histology was performed. Data was
collected with bright-light microscopy and with integrated morphometry analysis
software.
Results & Conclusion: Review of mid-graft histology (Figure 1) indicates there are
regenerating nerve fibers in all the grafts. When ranked on nerve fiber density
(nerve count/total area), the group order is AUTO>PDMS>S-DOT =
F-DOT>>AG-P. Nerve fibers grew beside the agarose and the PEDOT but not
through it. Muscle contractile forces indicate muscle fibers were successfully
reinnervated in all groups except the AG-P/ Hydrogel group (Table 1). Nerve
fibers regenerate through a nerve graft containing PEDOT and successfully
reinnervate target skeletal muscles. Based on the latter half of Table 1,
quantitative analysis confirms that nerve fiber density ranks in the order
mentioned above. Measurements taken were % Neural Area, which calculates the
percentage of nerves over the whole region. % Neural Debris calculates the
percentage of debris over the entire region.� % Collagen is the amount of
collagen in the region. Axon: Fiber Ratio is calculated as the total area of
the axoplasm: total area of the nerve. After analysis of these measurements, it
can be concluded that PEDOT is the best synthetic material out of the four
grafts in terms of muscle force and the aforementioned measurements.
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.
Table 1. Summary of Statistical Test Data by Graft Material |
| Graft Material |
| AUTO (Control) | PDMS | AG-P (Hydrogel) | S-DOT | F-DOT |
Sample size | 4 | 5 | 5 | 5 | 5 |
EDL muscle force (mN) | 2118�988 | 628�743* | 7�11* | 243�536* | 125�174* |
TA muscle force (mN) | 5453�3555 | 1095�1558* | 3.0�3.2* | 521�1107* | 564�1023* |
EDL muscle mass (mg) | 108�30.3 | 67.0�27 | 50.0�7.5* | 60�16* | 54�6.4* |
TA muscle mass (mg) | 385�168 | 203�86* | 144�17* | 178�52* | 189�29* |
Nerve Count | 176 | 38 | 0 | 2 | 4 |
Nerve Fiber Density | 7.96x10-3 | 1.65 x10-3 | 0 | 8.64x10-5 | 1.73 x 10-4 |
% Neural Area | 54.80 % | 1.72% | 0 % | 0.11% | 0.16% |
% Neural Debris | 2.69 % | 7.37% | 37.94% | 17.18% | 11.54% |
% Collagen | 42.51% | 90.90% | 62.06 % | 82.71% | 88.30% |
Axoplasm: Nerve Fiber Ratio | 0.30 | 0.33 | N/A | 0.17 | 0.22 |
Values are group mean�SD. * Indicates statistically different from AUTO group, p<0.05. AUTO = autograft; PDMS = silicone graft; AG-P = agarose alone graft; S-DOT = agarose with a spiral layer of PEDOT, and F-DOT = agarose completely lined with PEDOT. EDL=extensor digitorum longus muscle; TA = Tibialis Longus muscle. |