Introduction Our ultimate goal is to interface peripheral nerve and muscle directly to electronics which power prosthetic devices. Existing electrode interfaces lack durability, sensitivity, fidelity, and are cumbersome. We envision a biological interface where an amputee nerve stump grows and synapses with in vivo developing muscle contained in a porous multi channel micro-electrode chamber treated with an intrinsically conductive polymer such as poly (3,4-ethylenedioxythiophene), or PEDOT. That our electrode sites have fuzzy coatings of PEDOT which is known to decrease impedance by 5 times and increase conduction speed, affords many benefits for recording from larger and more disperse muscle action potentials rather then from small compact nerve fascicles.
Methods We measured myocyte growth in the presence of container conditions and materials: 1) medium alone or 2) with: Biobrane, 3) smooth silicone sheeting, 4) acellular muscle, or 5) acellular muscle polymerized with PEDOT. We then also implanted acellular muscle with cultured muscle constructs into a rat hind limb amputee model. The rat peroneal nerve was divided, the proximal stump was sutured to an acellular muscle impregnated with PEDOT that had myoblasts cultured on it. The PEDOT, myoblasts, and nerve ending were contained in a 2 cm long BioBrane™.tube. The distal nerve stump was reflected and tacked to gluteus muscle; the incision was closed. At post operative day 50, the BioBrane™ container with nerve-muscle PEDOT interface was removed and processed histologically. Biocompatibility was confirmed if: robust myotube formation from mononuclear progenitor satellite cells occurred, cell proliferation was comparable to cells grown in medium alone, and there was continued myoblast growth plus nerve regeneration with in the implanted construct after 50 days.
Results Primary mixed cultures of myoblasts and fibroblasts were grown from adult rat soleus muscles. At confluence (P1, Day 7) primary cultures were passaged and cells were deposited on plates holding test materials. Cell number was determined at day 4 and day 7 after passage 2. Replicate plates were completed 3-6 times. Cell counts on days 4 and 7 during passage 2 showed no difference in cell viability (98%) across the 5 materials (power = 0.6) and more live cells at day 7 (186%) than at day 4 (p<0.05). Multinucleated myocytes and fibroblasts were observed on all plates. By day 14, myotubes were present as confirmed by desmin staining for each material. For containers implanted in vivo, histology verified nerve sprouts and small multinucleated muscles grew into the distal end of the BioBrane™ tubes and both myofibers and nerves were in the immediate proximity of PEDOT filled acellular muscle cytoskeltons.
Conclusion Biocompatibility of myoblasts growth and regenerating nerve with PEDOT was confirmed. Myotube formation from mononuclear progenitor satellite cells and cell proliferation were as robust as seen in the control for all other biomaterial cultures. After fifty days in vivo, the container of PEDOT and myoblasts had developed muscle fibers and nerve sprouts in close contact with the PEDOT. We conclude that PEDOT shows promise for incorporation into a living nerve endoprosthesis interface. The intrinsically conductive nature of this compatible PEDOT may prove advantageous to biologic interfaces with electronic components.
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