Bhangra, K

Choi, D

Knowles, J

Phillips, J

Shipley, R

English

UCL Discovery

European Cells and Materials Vol. NN. Suppl. N, 20xx (page htu)                                                         ISSN 1473-2262                                                  http://www.ecmjournal.org  Mechanical testing of nerve guidance conduit materials for peripheral nerve repair KS Bhangra1,2,3, JC Knowles1, R Shipley3,4, D Choi5 and JB Phillips1,2,3 1Biomaterials & Tissue Engineering, UCL Eastman Dental Institute, 2Pharmacology, UCL School of Pharmacy, 3UCL Centre for Nerve Engineering, 4Mechanical Engineering, UCL Engineering, 5Brain repair and Rehabilitation, UCL Institute of Neurology   INTRODUCTION: A long-standing challenge in the development of nerve guidance conduits (NGCs) is to achieve a balance between required mechanical strength to withstand physiological stresses whilst mimicking natural nerve biomechanics to support endogenous peripheral nerve repair. Currently, there are several FDA-approved NGCs [1], however the stiffness of these hollow tubes tends to be greater than that of a nerve since they must maintain a patent lumen [2]. Conversely, conduits with an internal framework of engineered tissue can have a reduced stiffness [3]. In this study, we carried out tensile tests to investigate the breaking force of a rat sciatic nerve and that of potential NGC replacement materials, in particular natural and synthetic membranes.  METHODS: Sciatic nerves were harvested from Sprague-Dawley rats (200 – 260 g). Nerves had a diameter of 1.33 ± 0.32 mm and a length of 20 mm. Two collagen-based membranes and a Poly Lactic Acid (PLA)-based material were also evaluated, namely CM-A, CM-B and PLA. Material thickness was determined using a contact angle measurement machine (CAM 200, KSV Instruments). Samples were then prepared by cutting the membranes into an hourglass shape with a width of 10 ± 1 mm, a height of 20 ± 1 mm and a central width of 5 ± 1 mm. Each membrane was hydrated in phosphate buffered saline for 5 minutes prior to mechanical testing. Tensile testing was performed with a 10 mm gauge length in uniaxial tension using a Bose Electroforce 3200 machine with an extension rate of 10 mm/min. Ultimate tensile stress (UTS) refers to the amount of force per unit of initial cross-sectional area at tensile failure. RESULTS: Results reveal that CM-A is thinnest of the tested membranes, closely followed by CM-B, whereas the PLA-based membrane was the thickest (Table 1).  Figure 1 shows that the sciatic nerve has a UTS of 3.4 ± 0.4 N/mm2, whereas a sheet of CM-A is considerably less at 0.9 ± 0.2 N/mm2. The CM-B material has a break force that is greater than that of CM-A, 1.7 ± 0.2 N/mm2. The PLA-based membrane has the greatest break force compared to the other membranes and most similar to a sciatic nerve, at 2.4 ± 0.3 N/mm2. Table 1. Thickness of prospective NGC materials.  Material Thickness, mm Collagen-based membrane A 0.29 ± 0.03 Collagen-based membrane B 0.33 ± 0.02 PLA-based membrane 0.37 ± 0.03 Fig. 1: Ultimate tensile stress for sciatic nerve, CM-A, CM-B and PLA- based membranes. Data are means ± SEM, where n = 4. Statistical analysis was performed using one-way ANOVA, ns: non significant, **p<0.01, ***p<0.001. DISCUSSION & CONCLUSIONS: The UTS of the collagen membranes were approximately 75% (CM-A) and 50% (CM-B) less than that of a sciatic nerve, suggesting they may not be suitable as NGCs as a single sheet. Statistical analysis revealed significant differences between collagen-based membranes and sciatic nerve but no difference between the sciatic nerve and PLA-based membrane. Our data suggest that this particular PLA-membrane could be used as a potential NGC material for peripheral nerve repair. Future work would involve developing materials with similar properties to nerve.  REFERENCES: [1] Kehoe et al. (2012). Injury. 43(5), pp. 553-72. [2] Yao et al. (2010). Tissue Eng Part C; 16, pp. 1585-1596. [3] Ruiter et al. 2009. Neurosurgey Focus. 26 (2) E5 pp. 1-9. 

Mechanical testing of nerve guidance conduit materials for peripheral nerve repair

https://discovery.ucl.ac.uk/10084224/1/Knowles_AAM_Kulraj%20TCES%20Draft%20V3%20JBP.pdf

Mechanical testing of nerve guidance conduit materials for peripheral nerve repair

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