Methods for in vitro characterization of multichannel nerve tubes Godard C. de Ruiter, 1,2 Irene A. Onyeneho, 1 Ellen T. Liang, 1 Michael J. Moore, 3 Andrew M. Knight, 4 Martijn J.A. Malessy, 5 Robert J. Spinner, 2 Lichun Lu, 6 Bradford L. Currier, 6 Michael J. Yaszemski, 6 Anthony J. Windebank 4 1 Cellular Neurobiology Laboratory, Mayo Clinic, Rochester, Minnesota 2 Department of Neurologic Surgery, Mayo Clinic, Rochester, Minnesota 3 Department of Physiology and Biomedical Engineering, Mayo Clinic, Rochester, Minnesota 4 Department of Neurology, Mayo Clinic, Rochester, Minnesota 5 Department of Neurosurgery, Leiden University Medical Center, Leiden, the Netherlands 6 Department of Orthopedic Surgery, Mayo Clinic, Rochester, Minnesota Received 18 July 2006; revised 5 January 2007; accepted 26 January 2007 Published online 16 July 2007 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/jbm.a.31298 Abstract: Multichannel conduits have been developed for experimental peripheral nerve and spinal cord repair. We present a series of methods to characterize multichannel nerve tubes for properties of bending, deformation, swel- ling, and degradation and introduce a new method to test the permeability of multichannel nerve tubes from the rate of diffusion of different-sized fluorescent dextran mole- cules (10, 40, and 70 kDa). First, single-lumen nerve tubes made with different poly(lactic-co-glycolic acid) (PLGA) ratios (50:50, 75:25, and 85:15) were compared. One ratio (75:25 PLGA) was subsequently used to compare single- lumen and multichannel nerve tubes. Nerve tubes made with lower PLGA ratios were found to be more flexible than nerve tubes made with a higher PLGA ratio. For low ratios, however, swelling was also greater as a result of a faster rate of degradation. Multichannel structure did not interfere with the permeability of the tube; the rate of dif- fusion into multichannel 75:25 PLGA nerve tubes appeared to be even higher than that into single-lumen ones, but this was only significant for 70-kDa molecules. Also, multi- channel 75:25 PLGA nerve tubes were more flexible and, at the same time, more resistant to deformation. However, swelling significantly decreased the total cross-sectional lumen area, especially in multichannel 75:25 PLGA nerve tubes. Permeability, bending, deformation, swelling, and degradation are important properties to characterize in the development of multichannel nerve tubes. The methods presented in this study can be used as a basis for optimiz- ing these properties for future, possibly clinical, applica- tion. Ó 2007 Wiley Periodicals, Inc. J Biomed Mater Res 84A: 643–651, 2008 Key words: degradation; flexibility; nerve regeneration; permeability; swelling; tissue engineering INTRODUCTION Biodegradable single-lumen or hollow nerve tubes have been developed as an alternative to repair with an autologous nerve graft. 1–5 The disadvantages of using an autograft include donor-site morbidity, lim- ited availability, and size mismatch with the injured nerve. In comparison, nerve tubes are available off the shelf in different sizes. Multichannel conduits have been developed for experimental peripheral nerve 6,7 and spinal cord repair. 8–10 The multichannel structure provides more surface area for cell attachment and local release of incorporated growth factors. Also, the multichannel structure may better support regeneration across larger gaps by stabilizing the fibrin matrix, 11,12 and may better guide regenerating axons (de Ruiter GC, The author, or one or more of the authors, has received or will receive remuneration or other perquisites for per- sonal or professional use from a commercial or industrial agent in direct or indirect relationship to his authorship. Correspondence to: A.J. Windebank; e-mail: windebank. anthony@mayo.edu Contract grant sponsors: Mayo Clinic Department of Neurosurgery, VSB Fonds, Leids Universitair Fonds, Jan- neke Fruin-Helb beurs, Stichting Fundatie van de Vrijv- rouwe van Renswoude te’ s Gravenhage, Stichting Mitialto, Stichting Dr Hendrik Muller’s Vaderlandsch Fonds, Lustra and Jo Keur Fonds Contract grant sponsor: NIH; contract grant numbers: EB002390, NS40471 Contract grant sponsor: Mayo Clinic College of Medicine ' 2007 Wiley Periodicals, Inc.