Abstract
Surgical intervention followed by physical therapy remains the major way to repair damaged nerves and restore function. Imaging constitutes promising, yet underutilized, approaches to improve surgical and postoperative techniques. Dedicated methods for imaging nerve regeneration will potentially provide surgical guidance, enable recovery monitoring and postrepair intervention, elucidate failure mechanisms and optimize preclinical procedures. Herein, we present an outline of promising innovations in imaging-based tracking of in vivo peripheral nerve regeneration. We emphasize optical imaging because of its cost, versatility, relatively low toxicity and sensitivity. We discuss the use of targeted probes and contrast agents (small molecules and nanoparticles) to facilitate nerve regeneration imaging and the engineering of grafts that could be used to track nerve repair. We also discuss how new imaging methods might overcome the most significant challenges in nerve injury treatment.
Graphical abstract
Papers of special note have been highlighted as: • of interest; •• of considerable interest
References
- 1. . The epidemiology of upper extremity injuries presenting to the emergency department in the United States. Hand 7(1), 18–22 (2012).
- 2. . A classification of peripheral nerve injuries producing loss of function. Brain 74(4), 491–516 (1951).
- 3. . Three types of nerve injury. Brain 66(4), 237–288 (1943).
- 4. The role of current techniques and concepts in peripheral nerve repair. Plast. Surg. Int. 2016, 4175293 (2016).
- 5. . Tissue engineered constructs for peripheral nerve surgery. Eur. Surg. 45(3), 122–135 (2013).
- 6. . A biomaterials approach to peripheral nerve regeneration: bridging the peripheral nerve gap and enhancing functional recovery. J. R. Soc. Interface 9(67), 202–221 (2012).
- 7. . Pathways regulating modality-specific axonal regeneration in peripheral nerve. Exp. Neurol. 265, 171–175 (2015). •• Review of potential pharmacological therapies and novel opportunities in nerve repair.
- 8. . The blood–nerve barrier in Wallerian degeneration: a sequential long-term study. Muscle Nerve 12, 627–635 (1989).
- 9. . The cellular and molecular basis of peripheral nerve regeneration. Mol. Neurobiol. 14(1–2), 67–116 (1997).
- 10. . Interactions between Schwann cells and macrophages in injury and inherited demyelinating disease. Glia 56(14), 1566–1577 (2008).
- 11. . Strategies for inducing the formation of bands of Bungner in peripheral nerve regeneration. Biomaterials 30(29), 5251–5259 (2009).
- 12. . Outcome measures of peripheral nerve regeneration. Ann. Anat. 193(4), 321–333 (2011).
- 13. . Repair Schwann cell update: adaptive reprogramming, EMT, and stemness in regenerating nerves. Glia 67(3), 421–437 (2019).
- 14. . Advances in nerve guidance conduit-based therapeutics for peripheral nerve repair. ACS Biomater. Sci. Eng. 3(7), 1221–1235 (2017). • Review of nerve guidance conduit engineering including topographic, biophysical and biochemical properties.
- 15. Peripheral nerve surgery: the role of high-resolution MR neurography. Am. J. Neuroradiol. 33(2), 203–210 (2012).
- 16. . Clinical neurophysiology and imaging of nerve injuries: preoperative diagnostic work-up and postoperative monitoring. Plast. Aesthetic Res. 2(4), 149 (2015).
- 17. . Visualization of peripheral nerve regeneration. Neural Regen. Res. 9(10), 997–999 (2014).
- 18. . Magnetic resonance imaging of the digital nerves of the hand: anatomy and spectrum of pathology. Curr. Problems Diagn. Radiol. 47(1), 42–50 (2018).
- 19. . Peripheral nerve reconstruction after injury: a review of clinical and experimental therapies. BioMed. Res. Int. 2014, 698256 (2014). • Overview of peripheral nerve injury treatment.
- 20. Processed nerve allografts for peripheral nerve reconstruction: a multicenter study of utilization and outcomes in sensory, mixed, and motor nerve reconstructions. Microsurgery 32(1), 1–14 (2012).
- 21. . Progress of nerve bridges in the treatment of peripheral nerve disruptions. J. Neurorestoratol. 4, 107–113 (2016).
- 22. . Reorganization and orientation of regenerating nerve fibres, perineurium, and epineurium in preformed mesothelial tubes – an experimental study on the sciatic nerve of rats. J. Neurosci. Res. 6, 265–281 (1981).
- 23. Axonal growth arrests after an increased accumulation of Schwann cells expressing senescence markers and stromal cells in acellular nerve allografts. Tissue Eng. Part A 22(13–14), 949–961 (2016).
- 24. . Collagen tube conduits in peripheral nerve repair: a retrospective analysis. Hand 5(3), 273–277 (2010).
- 25. . Fibronectin, collagen, fibrin – components of extracellular matrix for nerve generation. Topics Tissue Engineering 3, 1–26 (2017).
- 26. Short and long gap peripheral nerve repair with magnesium metal filaments. J. Biomed. Mater. Res. Part A 105(11), 3148–3158 (2017).
- 27. A biosynthetic nerve guide conduit based on silk/SWNT/fibronectin nanocomposite for peripheral nerve regeneration. PLoS ONE 8(9), e74417 (2013).
- 28. . The effect of high outflow permeability in asymmetric poly(dl-lactic acid-co-glycolic acid) conduits for peripheral nerve regeneration. Biomaterials 27(7), 1035–1042 (2006).
- 29. A 3D-engineered porous conduit for peripheral nerve repair. Sci. Rep. 7, 46038 (2017).
- 30. Prompt peripheral nerve regeneration induced by a hierarchically aligned fibrin nanofiber hydrogel. Acta Biomater. 55, 296–309 (2017).
- 31. . Novel conductive polypyrrole/silk fibroin scaffold for neural tissue repair. Neural Regen. Res. 13(8), 1455–1464 (2018).
- 32. Finely tuned temporal and spatial delivery of gdnf promotes enhanced nerve regeneration in a long nerve defect model. Tissue Eng. Part A 21(23–24), 2852–2864 (2015).
- 33. Immunoengineering nerve repair. PNAS 114(26), E5077–E5084 (2017).
- 34. Controlling dispersion of axonal regeneration using a multichannel collagen nerve conduit. Biomaterials 31(22), 5789–5797 (2010).
- 35. A physicochemically optimized and neuroconductive biphasic nerve guidance conduit for peripheral nerve repair. Adv. Healthcare Mater. 6(24), 1700954 (2017).
- 36. . 3D printed polymeric hydrogels for nerve regeneration. Polymers 10(9), 1041 (2018).
- 37. Nerve guides manufactured from photocurable polymers to aid peripheral nerve repair. Biomaterials 49, 77–89 (2015).
- 38. Multichanneled nerve guidance conduit with spatial gradients of neurotrophic factors and oriented nanotopography for repairing the peripheral nervous system. ACS Appl. Mater. Interfaces 9(43), 37623–37636 (2017). • Multimodal nerve guidance conduit including neurotrophic concentration gradients, guidance microchannels and tuned biophysical properties.
- 39. . Adipose-derived stem cells enhance peripheral nerve regeneration. J. Plast. Reconstr. Aesthetic Surg. 63(9), 1544–1552 (2010).
- 40. Transgenic SCs expressing GDNF-IRES-DsRed impair nerve regeneration within acellular nerve allografts. Biotechnol. Bioeng. 114(9), 2121–2130 (2017).
- 41. 3D bioprinting of scaffolds with living Schwann cells for potential nerve tissue engineering applications. Biofabrication 10(3), 035014 (2018).
- 42. . 3D bio-printed scaffold-free nerve constructs with human gingiva-derived mesenchymal stem cells promote rat facial nerve regeneration. Sci. Rep. 8(1), 6634 (2018).
- 43. . The synaptic receptor Lrp4 promotes peripheral nerve regeneration. Nat. Commun. 9(1), 2389 (2018).
- 44. Molecular sequelae of topographically guided peripheral nerve repair. Ann. Biomed. Eng. 42(7), 1436–1455 (2014).
- 45. . Roles of nitric oxide and ethyl pyruvate after peripheral nerve injury. Inflamm. Regen. 37, 20 (2017).
- 46. . MRI appearance of nerve regeneration in a surgically repaired ulnar nerve. Eur. J. Trauma Emerg. Surg. 36(1), 73–75 (2010).
- 47. . Nanotechnology for Biomedical Imaging and Diagnostics: From Nanoparticle Design to Clinical Applications. John Wiley & Sons, NJ, USA (2014). • Extensive review of innovative in vivo imaging techniques.
- 48. . Noninvasive imaging of peripheral nerves. Cells Tissues Organs 200(1), 69–77 (2014).
- 49. 18F-fluorodeoxyglucose positron emission tomography/computed tomography in a case of malignant peripheral nerve sheath tumor: an unusual presentation. Indian J. Nucl. Med. 28(3), 168–170 (2013).
- 50. . Imaging of peripheral nerve sheath tumors with pathologic correlation: pictorial review. Eur. J. Radiol. 52(3), 229–239 (2004).
- 51. . Substrate-mediated nanoparticle/gene delivery to MSC spheroids and their applications in peripheral nerve regeneration. Biomaterials 35(9), 2630–2641 (2014).
- 52. Iodine-enhanced micro-CT imaging of soft tissue on the example of peripheral nerve regeneration. Contrast Media Mol. Imaging 2019, 7483745 (2019).
- 53. . The utility of ultrasound in the assessment of traumatic peripheral nerve lesions: report of 4 cases. Neurosurg. Focus 39(3), E3 (2015).
- 54. . Label-free photoacoustic microscopy of peripheral nerves. J. Biomed. Optics 19(1), 16004 (2014).
- 55. . (18)F-FDG PET/MRI can be used to identify injured peripheral nerves in a model of neuropathic pain. J. Nuclear Med. 52(8), 1308–1312 (2011).
- 56. In vivo optical microscopy of peripheral nerve myelination with polarization sensitive-optical coherence tomography . J. Biomed. Optics 20(4), 046002 (2015).
- 57. Nerve-highlighting fluorescent contrast agents for image-guided surgery. Mol. Imaging 10(2), 91–101 (2011).
- 58. Current and future imaging of the peripheral nervous system. Diagn. Interv. Imaging 95(1), 17–26 (2014).
- 59. . In vivo diffusion tensor imaging, diffusion kurtosis imaging, and tractography of a sciatic nerve injury model in rat at 9.4T . Sci. Rep. 8(1), 12911 (2018).
- 60. . Quantitative magnetic resonance (MR) neurography for evaluation of peripheral nerves and plexus injuries. Quant. Imaging Med. Surg. 7(4), 398–421 (2017).
- 61. In vivo MR microneurography of the tibial and common peroneal nerves . Radiol. Res. Practice 2014, 780964 (2014).
- 62. . Peripheral nerve tissue engineering and regeneration observed using MRI. In: Magnetic Resonance Imaging in Tissue Engineering. Kotecha M Magin RL Mao JJ (Eds). John Wiley & Sons, Inc., NJ, USA, 367–381 (2017).
- 63. Assessment of nerve degeneration by gadofluorine M-enhanced magnetic resonance imaging. Ann. Neurol. 57(3), 388–395 (2005).
- 64. . Peripheral nerve imaging (chapter 40). Neuroimaging: Part 2 (40), 811–826 (2016).
- 65. Oral manganese as an MRI contrast agent for the detection of nociceptive activity. NMR Biomed. 25(4), 563–569 (2012).
- 66. . The peripheral nerves: update on ultrasound and magnetic resonance imaging. Clin. Exp. Rheumatol. 36(Suppl. 114), S145–S158 (2018).
- 67. . High resolution ultrasound in the evaluation and management of traumatic peripheral nerve injuries: review of the literature. Oman Med. J. 29(5), 314–319 (2014).
- 68. Ultrasound diagnosis of postoperative complications of nerve repair. World Neurosurg. 115, 320–323 (2018).
- 69. Performance of ultrasound-guided peripheral nerve blocks by medical students after one-day training session. Cureus 11(1), e3911 (2019).
- 70. . On the feasibility of imaging peripheral nerves using acoustic radiation force impulse imaging. Ultrason. Imaging 31(3), 172–182 (2009).
- 71. . Clinical application of photoacoustic imaging to the evaluation of diabetic polyneuropathy. Diabetes 67(Suppl. 1), 582-P (2018).
- 72. . Label-free in vivo imaging of peripheral nerve by multispectral photoacoustic tomography. J. Biophoton. 9(1–2), 124–128 (2016).
- 73. Fluorescence imaging of nerves during surgery. Ann. Surg. 270(1), 69–76 (2019). • Overview of fluorescent nerve imaging agents.
- 74. . Imaging in the era of molecular oncology. Nature 452(7187), 580–589 (2008).
- 75. . Penetration depth of photons in biological tissues from hyperspectral imaging in shortwave infrared in transmission and reflection geometries. J. Biomed. Optics 21(12), 126006 (2016).
- 76. . Shortwave-infrared (SWIR) emitters for biological imaging: a review of challenges and opportunities. Nanophotonics 6(5), 1043–1054 (2017).
- 77. . Comparison of imaging techniques for tracking cardiac stem cell therapy. J. Nuclear Med. 48(12), 1916–1919 (2007). • Comprehensive review on fluorescence lifetime investigation techniques
- 78. . Fluorescence lifetime measurements and biological imaging. Chem. Rev. 110(5), 2641–2684 (2010).
- 79. . Fluorescence lifetime imaging ophthalmoscopy. Prog. Retin. Eye Res. 60, 120–143 (2017).
- 80. Improved intraoperative visualization of nerves through a myelin-binding fluorophore and dual-mode laparoscopic imaging. PLoS ONE 10(6), e0130276 (2015).
- 81. In vivo imaging of porcine gastric enteric nervous system using confocal laser endomicroscopy & molecular neuronal probe . J. Gastroenterol. Hepatol. 31(4), 802–807 (2016).
- 82. . Visualizing peripheral nerve regeneration by whole mount staining. PLoS ONE 10(3), e0119168 (2015).
- 83. Comprehensive evaluation of peripheral nerve regeneration in the acute healing phase using tissue clearing and optical microscopy in a rodent model. PLoS ONE 9(4), e94054 (2014).
- 84. . Fluorescently-tagged anti-ganglioside antibody selectively identifies peripheral nerve in living animals. Sci. Rep. 5, 15766 (2015).
- 85. Retrograde labeling in peripheral nerve research: it is not all black and white. J. Reconstr. Microsurg. 23(7), 381–389 (2007).
- 86. Prototype nerve-specific near-infrared fluorophores. Theranostics 4(8), 823–833 (2014).
- 87. Design and synthesis of near-infrared fluorescent probes for imaging of biological nitroxyl. Sci. Rep. 5, 16979 (2015).
- 88. A NIR dye for development of peripheral nerve targeted probes. MedChemComm 3(6), 685–690 (2012).
- 89. . In vivo imaging of axonal transport in murine motor and sensory neurons . J. Neurosci. Methods 257, 26–33 (2016).
- 90. Imaging of radicals following injury or acute stress in peripheral nerves with activatable fluorescent probes. Free Radic. Biol. Med. 101, 85–92 (2016).
- 91. . Evaluation of peripheral nerve regeneration via in vivo serial transcutaneous imaging using transgenic Thy1-YFP mice. Exp. Neurol. 232(1), 7–14 (2011).
- 92. . A small molecule screen identifies in vivo modulators of peripheral nerve regeneration in zebrafish. PLoS ONE 12(6), e0178854 (2017).
- 93. . Macroscopic in vivo imaging of facial nerve regeneration in Thy1-GFP rats. JAMA Facial Plast. Surg. 17(1), 8–15 (2015).
- 94. Visualizing changes in brain-derived neurotrophic factor (BDNF) expression using bioluminescence imaging in living mice. Sci. Rep. 7(1), 4949 (2017).
- 95. . Label-free in vivo imaging of myelinated axons in health and disease with spectral confocal reflectance microscopy. Nat. Med. 20(4), 443–449 (2014).
- 96. Wide-field functional microscopy of peripheral nerve injury and regeneration. Sci. Rep. 8(1), 14004 (2018).
- 97. . High-resolution in vivo imaging of peripheral nerves using optical coherence tomography: a feasibility study.
J. Neurosurg.
doi:10.3171/2019.2.JNS183542 (2019) (Epub ahead of print). - 98. . Peripheral nerve nanoimaging: monitoring treatment and regeneration. AAPS J. 19(5), 1304–1316 (2017). • Review of neuronal molecular imaging using nanoscopic constructs.
- 99. . Myelin-targeted, texaphyrin-based multimodal imaging agent for magnetic resonance and optical imaging. Contrast Media Mol. Imaging 11(6), 492–505 (2016).
- 100. . Novel nanoimaging strategies for noninvasive graft monitoring in vascularized composite allotransplantation. Curr. Transplant. Rep. 5(4), 369–372 (2018).
- 101. . Clinically translatable nanotheranostic platforms for peripheral nerve regeneration: design with outcome in mind. Proc. SPIE 10508 (2018).
- 102. . Laser-activated perfluorocarbon nanodroplets: a new tool for blood brain barrier opening. Biomed. Optics Express 9(9), 4527–4538 (2018).
- 103. Noninvasive photoacoustic and fluorescence sentinel lymph node identification using dye-loaded perfluorocarbon nanoparticles. ACS Nano 5(1), 173–182 (2011).
- 104. . (18)F-FDG positron emission tomography as a novel diagnostic tool for peripheral nerve injury. J. Neurosci. Methods 317, 11–19 (2019).
- 105. . PET/SPECT molecular imaging in clinical neuroscience: recent advances in the investigation of CNS diseases. Quant. Imaging Med. Surg. 5(3), 433–447 (2015).
- 106. Multimodal assessment of nervous and immune system responses following sciatic nerve injury. Pain 154(12), 2782–2793 (2013).
- 107. Combining micro-computed tomography with histology to analyze biomedical implants for peripheral nerve repair. J. Neurosci. Methods 255, 122–130 (2015).
- 108. . Myelinated mouse nerves studied by x-ray phase contrast zoom tomography. J. Struct. Biol. 192(3), 561–568 (2015).
- 109. Angiogenesis in tissue-engineered nerves evaluated objectively using MICROFIL perfusion and micro-CT scanning. Neural Regen. Res. 11(1), 168–173 (2016).
- 110. . In vivo coherent anti-Stokes Raman scattering imaging of sciatic nerve tissue. J. Microsc. 225(2), 175–182 (2007).
- 111. Application of Raman spectroscopy for visualizing biochemical changes during peripheral nerve injury in vitro and in vivo . J. Biomed. Optics 18(11), 116011 (2013).
- 112. . Rapid and accurate peripheral nerve imaging by multipoint Raman spectroscopy. Sci. Rep. 7(1), 845 (2017).
- 113. . Common aspects influencing the translocation of SERS to biomedicine. Curr. Med. Chem. 25(35), 4638–4652 (2018). • Overview of the use of surface-enhanced Raman scattering nanoparticles for in vivo imaging.
- 114. . Imaging strategies for tissue engineering applications. Tissue Eng. Part B Rev. 21(1), 88–102 (2015).
- 115. Iron oxide-labeled collagen scaffolds for non-invasive MR imaging in tissue engineering. Adv. Funct. Mater. 24(6), 754–762 (2014).
- 116. : US
2011/0243852 (2011). - 117. . Wound healing monitoring using near infrared fluorescent fibrinogen. Biomed. Optics Express 1(1), 285–294 (2010).
- 118. . Real-time molecular imaging throughout the entire cell cycle by targeted plasmonic-enhanced Rayleigh/Raman spectroscopy. Nano Lett. 12(10), 5369–5375 (2012).
- 119. . Direct conversion of human fibroblasts into Schwann cells that facilitate regeneration of injured peripheral nerve in vivo . Stem Cells Transl. Med. 6(4), 1207–1216 (2017).
- 120. Biomarkers of nerve regeneration in peripheral nerve injuries: an emerging field. In: Biomarkers of Brain Injury and Neurological Disorders. Wang KKW Zhang Z Kobeissy FH (Eds). CRC Press, FL, USA, 650 (2014). • Describes potential nerve regeneration imaging targets.
- 121. . Roles of channels and receptors in the growth cone during PNS axonal regeneration. Exp. Neurol. 223(1), 38–44 (2010).
- 122. Prostanoid receptor EP1 and Cox-2 in injured human nerves and a rat model of nerve injury: a time-course study. BMC Neurology 6, 1 (2006).
- 123. . The origin and development of glial cells in peripheral nerves. Nat. Rev. 6(9), 671–682 (2005).
- 124. . Nanotechnology in peripheral nerve repair and reconstruction.
Adv. Drug Deliv. Rev.
doi:10.1016/j.addr.2019.01.006 (2019) (In Press). - 125. . The role of exosomes in peripheral nerve regeneration. Neural Regen. Res. 10(5), 743–747 (2015).
- 126. . Laminin targeting of a peripheral nerve-highlighting peptide enables degenerated nerve visualization. PNAS 45(113), 12774–12779 (2016).
- 127. Nerve-targeted probes for fluorescence-guided intraoperative imaging. Theranostics 8(15), 4226–4237 (2018).
- 128. . G-CSF prevents caspase 3 activation in Schwann cells after sciatic nerve transection, but does not improve nerve regeneration. Neuroscience 334, 55–63 (2016).
- 129. Activatable molecular systems using homologous near-infrared fluorescent probes for monitoring enzyme activities in vitro, in cellulo, and in vivo . Mol. Pharm. 6(2), 416–427 (2009).