s1 ) was synthesized by ring opening polymerization of d , l - lactide 34 . the mpeg - pdlla micelles with a weight concentration of 2.0 the procedure for isolation of the spinal cord white matter was described previously 8 and can be found in supplementary information . the compression injury was inflicted by a constant displacement of 530 sec compression of the spinal cord using modified forceps possessing a spacer until the cap dropped to 0 mv 14 . for local application of micelles , immediately after injury , the spinal cord white matter strips were kept in perfusing krebs solution at the speed of 2.0 ml / min controlled by a peristaltic pump for 10 min . then the perfusion was stopped and 500 l of 2.0 mg / ml micelle solution was added gently to the 1.0 ml krebs solution in the central compartment , leading to a final concentration of 0.67 mg / ml . following the micelle treatment , the spinal cord strips were thoroughly rinsed with krebs solution . cars and tpef imaging was carried out on a multimodal nonlinear optical microscope shown in fig . the tpef signal was generated by a mode - locked 200-fs ti : sapphire oscillator ( mira 900 , coherent inc . , santa clara , ca , usa ) . all protocols for this experiment were approved by the purdue animal care and use committee . the tenth thoracic ( t10 ) spine was removed by laminectomy and the t10 spinal cord segment was constantly compressed for 15 sec by the modified forceps under aseptic condition as described previously 9 . prior to the compression injury , all rats were anesthetized deeply with the mixture of 90 mg / kg ketamine and 5 mg / kg xylazine . after the compression injury , the laminectomy was closed by suturing the muscle with 3 - 0 prolene followed by the use of 7.5 mm michel wound clips ( fine science tools , foster city , ca , usa ) to close the skin incision . rats were randomized into three groups : 1 ml micelle ( 1.8 mg / ml in saline ; n=14 ) , 1 ml peg ( 30% in saline n=12 ) , and isovolumetric doses of saline ( n=12 ) . animals were caged individually 1 week before the surgery and then 4 weeks post surgery . for post - operation pain management , the analgesics buprenorphine ( 0.050.10 mg / kg ) were given every 12 h through subcutaneous injection during anesthesia recovery and for the first 3 days post surgery . one rat in the micelle treated group and one rat in the peg group were excluded from the study due to the abnormally high bbb score on day 0 . two rats in the peg group , one rat in the micelle group and two rats in the control group suffered from kidney fail during the first week post surgery thus were sacrificed . the locomotor recovery of the animals was determined by using the 21-point bbb open - field locomotor scale 23 . the test was conducted by two observers , with one observer being blind to the treatments . two observers scored independently and made an agreement on the score before the scores were finalized . locomotor scoring was conducted on day 0 at 6 h post - injury , day 1 and subsequently once per week for 4 weeks . samples were immuno - processed with glial fibrillary acidic protein ( gfap ) to detect reactive astrocytes and ed-1 to detect activated microglial cells and macrophages using standard procedures 37 , 38 . long - evans adult male rats were randomized into micelle treated group ( n=3 ) or saline treated group ( n=3 ) . each animal received 1 ml micelle ( 1.8 mg / ml suspended in saline ) or saline solution through tail vein injection . blood samples ( 1 ml ) were drawn through the jugular vein at day 1 , day 7 and day 42 post treatment . hematology study and serum analysis the rats were then sacrificed and tissues including liver , kidney , and spleen were fixed in 10% neutral buffered formalin for at least 48 h , embedded into paraffin . sections of 5 m thickness were stained with haematoxylin and eosin in purdue university histopathology lab . s1 ) was synthesized by ring opening polymerization of d , l - lactide 34 . the mpeg - pdlla micelles with a weight concentration of 2.0 the procedure for isolation of the spinal cord white matter was described previously 8 and can be found in supplementary information . the compression injury was inflicted by a constant displacement of 530 sec compression of the spinal cord using modified forceps possessing a spacer until the cap dropped to 0 mv 14 . for local application of micelles , immediately after injury , the spinal cord white matter strips were kept in perfusing krebs solution at the speed of 2.0 ml / min controlled by a peristaltic pump for 10 min . then the perfusion was stopped and 500 l of 2.0 mg / ml micelle solution was added gently to the 1.0 ml krebs solution in the central compartment , leading to a final concentration of 0.67 mg / ml . following the micelle treatment , cars and tpef imaging was carried out on a multimodal nonlinear optical microscope shown in fig . the tpef signal was generated by a mode - locked 200-fs ti : sapphire oscillator ( mira 900 , coherent inc . , santa clara , ca , usa ) . all protocols for this experiment were approved by the purdue animal care and use committee . the tenth thoracic ( t10 ) spine was removed by laminectomy and the t10 spinal cord segment was constantly compressed for 15 sec by the modified forceps under aseptic condition as described previously 9 . prior to the compression injury , all rats were anesthetized deeply with the mixture of 90 mg / kg ketamine and 5 mg / kg xylazine . after the compression injury , the laminectomy was closed by suturing the muscle with 3 - 0 prolene followed by the use of 7.5 mm michel wound clips ( fine science tools , foster city , ca , usa ) to close the skin incision . rats were randomized into three groups : 1 ml micelle ( 1.8 mg / ml in saline ; n=14 ) , 1 ml peg ( 30% in saline n=12 ) , and isovolumetric doses of saline ( n=12 ) . animals were caged individually 1 week before the surgery and then 4 weeks post surgery . for post - operation pain management , the analgesics buprenorphine ( 0.050.10 mg / kg ) were given every 12 h through subcutaneous injection during anesthesia recovery and for the first 3 days post surgery . one rat in the micelle treated group and one rat in the peg group were excluded from the study due to the abnormally high bbb score on day 0 . two rats in the peg group , one rat in the micelle group and two rats in the control group suffered from kidney fail during the first week post surgery thus were sacrificed . the locomotor recovery of the animals was determined by using the 21-point bbb open - field locomotor scale 23 . the test was conducted by two observers , with one observer being blind to the treatments . two observers scored independently and made an agreement on the score before the scores were finalized . locomotor scoring was conducted on day 0 at 6 h post - injury , day 1 and subsequently once per week for 4 weeks . samples were immuno - processed with glial fibrillary acidic protein ( gfap ) to detect reactive astrocytes and ed-1 to detect activated microglial cells and macrophages using standard procedures 37 , 38 . long - evans adult male rats were randomized into micelle treated group ( n=3 ) or saline treated group ( n=3 ) . each animal received 1 ml micelle ( 1.8 mg / ml suspended in saline ) or saline solution through tail vein injection . blood samples ( 1 ml ) were drawn through the jugular vein at day 1 , day 7 and day 42 post treatment . hematology study and serum analysis the rats were then sacrificed and tissues including liver , kidney , and spleen were fixed in 10% neutral buffered formalin for at least 48 h , embedded into paraffin . sections of 5 m thickness were stained with haematoxylin and eosin in purdue university histopathology lab .
spinal cord injury ( sci ) results in immediate disruption of neuronal membranes followed by extensive secondary neurodegenerative processes . 
 a key approach for repair of sci is sealing the damaged membranes early . here 
 we show that axonal membranes injured by compression can be effectively repaired by using self - assembled monomethoxy poly(ethylene glycol)-poly(d , l - lactic acid ) di - block copolymer micelles ( 60 nm diameter ) . 
 injured spinal tissue incubated with micelles showed rapid restoration of compound action potential and reduced calcium influx into axons . 
 much lower micelle concentration is required for treatment than the positive control , polyethylene glycol . 
 intravenously injected micelles effectively recovered the locomotor function and reduced the volume and inflammatory response of the lesion in sci rats . 
 the micelles showed no adverse effects after systemic administration to live rats . 
 our results suggest that copolymer micelles can interrupt the spread of primary sci damage with minimal toxicity .