Homotopic root repair.23, 25, 26, 36 a | Intradural repair of ventral roots S1 and S2 in a cat model using a tubulation technique (exemplified for S1). The cylinder consists of mesh sheets and filter material, rolled into a tube around nerves and secured by ligatures or silver clips. b | Extradural bilateral repair of S1 and S2 ventral and dorsal roots in a canine model using end-on-end realignment and suturing (exemplified for ventral S1 and S2). One site is surrounded by a silicone sheath to enable delivery of BDNF. Bilaterally, a nerve cuff electrode is placed immediately proximal to the repair site to assess neurally evoked bladder emptying via FES. Abbreviations: BDNF, brain-derived neurotrophic factor; CG, coccygeal segment; FES, functional electrical simulation; IVF, intervertebral foramen; L, lumbar; S, sacral.