COMSOL Multiphysics® modelling of oxygen diffusion through a cellulose nanofibril conduit employed for peripheral nerve repair

Abstract

Background Peripheral nerve injury can cause significant impairment, and the current methods for facilitating repair, particularly over distances greater than approximately 1 mm, are not entirely effective. Allografts, autografts, and synthetic conduits are three of the most common surgical interventions for peripheral nerve repair; however, each has limitations including poor biocompatibility, adverse immune responses, and the need for successive surgeries. A potential new method for promoting peripheral nerve repair that addresses the shortcomings of current interventions is a biocompatible cellulose nanofibril (CNF) conduit that degrades in-vivo over time. Preliminary testing in multiple animal models has yielded positive results, but more information is needed regarding how the CNF conduit facilitates nutrient and gas flow. Results The current work employs 3D modelling and analysis via COMSOL Multiphysics® to determine how the CNF conduit facilitates oxygen movement both radially through the conduit walls and axially along the length of the conduit. Various CNF wall permeabilities, conduit lengths, and nerve-to-conduit diameter ratios have been examined; all of which were shown to have an impact on the resultant oxygen profile within the conduit. When the walls of the CNF conduit were modeled to have significant oxygen permeability, oxygen diffusion across the conduit was shown to dominate relative to axial diffusion of oxygen along the length of the conduit, which was otherwise the controlling diffusion mechanism. Conclusions The results of this study suggest that there is a complex relationship between axial and radial diffusion as the properties of the conduit such as length, diameter, and permeability are altered and when investigating various locations within the model. At low wall permeabilities the axial diffusion is dominant for all configurations, while for higher wall permeabilities the radial diffusion became dominant for smaller diameters. The length of the conduit did not alter the mechanism of diffusion, but rather had an inverse relationship with the magnitude of the overall concentration profile. As such the modeling results may be employed to predict and control the amount and distribution of oxygenation throughout the conduit, and hence to guide experimental conduit design.

Shielding the Nerve: A Systematic Review of Nerve Wrapping to Prevent Adhesions in the Rat Sciatic Nerve Model

“…Although Hernández-Cortés et al did not show an effect in preventing perineural adhesions using a cellulose-based wrapping material [25], cellulose has been examined with positive results in other research, including use around nerves and tendons to prevent adhesions [63][64][65]. Improved oxygen and glucose diffusion through cellulose conduits to nerves has been demonstrated [66,67]. Supporting the promising literature, Yamamoto et al showed perineural adhesion prevention after using a CMC-PE gel [17].…”

Convection-enhanced diffusion and directed withdrawal of methylene blue in agarose hydrogel using finite element analyses

“…Another tier of modeling (using COMSOL Multiphysics) focused on diffusion with variables other than fluid convection. Some setups include diffusion in porous media with temperature-induced variation in diffusivity [11], diffusion with a chemical reaction [12], diffusion in a porous media in an electric field [13], diffusion of solute amongst two fluids with one displacing the other [14], and diffusion in a liquid in a tube replicating nerve fibers containing semipermeable membranes for walls [15]. Furthermore, simulations of brain characteristics have been demonstrated with a probe compressing brain tissue [16], changes in chemical reactions with motion induced by probes [17], and a brain model with tumor growth represented as an advancing concentration profile of tumoral cellular spread [18].…”