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功能高分子材料促进脊髓损伤后再生修复的研究进展

孙秀敏 庞卯 冯丰 刘斌 戎利民 何留民

引用本文:
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功能高分子材料促进脊髓损伤后再生修复的研究进展

    作者简介: 孙秀敏(1984—),女,博士后,研究方向为神经组织工程和脊髓损伤再生修复。E-mail: ermine2005@163.com;何留民,博士,长期专注于纳米医学与神经再生研究,在功能性自组装短肽纳米水凝胶的设计、聚合物功能化改性以及纳米支架多级信号诱导神经再生等方面进行了深入的研究。主持多项国家自然科学基金及省部级项目。先后入选“广东特支计划”科技创新青年拔尖人才计划、广州市珠江科技新星、广东省高等学校优秀青年教师培养计划。以第一作者/通讯作者在包括Biomaterials、ACS Appl Mater Interfaces、Acta Biomater、J Mater Chem等学术期刊上发表SCI论文40余篇,被引近2000次。以第一发明人授权中国发明专利2件,成功转让1件。自2015年起受邀在全国生物材料大会担任神经修复材料分会主席并作邀请报告.
    通讯作者: 何留民, helm9@mail.sysu.edu.cn
  • 中图分类号: O63

Research Progress of Functional Polymer for Spinal Cord Regeneration

    Corresponding author: HE Liumin, helm9@mail.sysu.edu.cn
  • CLC number: O63

  • 摘要: 脊髓损伤后损伤区域神经纤维束的破坏,导致损伤区域以下长久的感觉和运动功能丧失。损伤区域恶劣的微环境是脊髓损伤难以修复的一大问题,大量的炎症细胞聚集、细胞死亡、抑制因子的分泌等,进一步导致损伤区域神经细胞的二次死亡、胶质细胞过度增生、胶原纤维沉积等。不利的微环境不仅限制轴突的再生,同时损伤神经干细胞的功能,不利于神经干细胞向损伤区域迁移并向神经元分化。虽然近期的研究证明脊髓损伤后轴突在合适的基质环境下能够再生,但完全恢复目前还没有可行措施。近年来,高分子生物材料在脊髓损伤修复研究中取得了一定进展:高分子生物材料支架可以发挥多种功能:抑制空洞和瘢痕组织的形成,为再生轴突的生长提供支撑作用;调控细胞行为,诱导神经细胞生长和分化;抑制炎症细胞的非特异性渗入进而改善脊髓损伤区域的微环境;作为载体负载和释放药物、细胞和生物活性因子。本文结合本课题组的研究从生物材料种类、支架类型、微环境构建以及因子负载等方面在脊髓损伤修复中的应用研究进行了综述。为生物材料用于脊髓损伤的治疗提供基础研究方向。
  • 图 1  脊髓损伤后的病理生理示意图,细胞和细胞外基质在损伤区域沉积的过程:(a)脊髓损伤后急性期(0-72 h)损伤导致神经细胞死亡和大量炎性细胞迁移到损伤区域;(b)脊髓损伤后慢性期(损伤72 h之后),慢性空洞形成,星形胶质细胞反应性增生和细胞外基质的沉积

    Figure 1.  The schematic of SCI pathophysiology, cellular and extracellular composition of the spinal injury scar: (a) In the acute post-injury phase (0–72 h), neural cell death and the release of a number of inflammatory cell in the injury site; (b) In the chronic post-injury phase (after 72 h), a chronic cystic cavity develops, reactive astrocytes hypertrophy and extracellular deposition

    图 2  (a)脱细胞基质周围神经基质(DNM)和脱细胞脊髓基质(DSCM)(标尺为10 mm);(b)天然或脱细胞周围神经/脊髓组织学切片的 H&E 染色(箭头指示细胞核,标尺为25 μm);(c)消化和离子平衡后的DSCM预凝胶;(d)水凝胶;(e)COLI, DNM 和 DSCM水凝胶纳米纤维结构的 SEM显微图像(标尺=5 μm)。[65]

    Figure 2.  (a)Decellularized peripheral nerve matrix and decellularized spinal cord matrix,(Scale bars =10 mm); (b) Histological sections with H&E staining of the native or decellularized peripheral nerve/spinal cord, respectively (The arrows indicate cell nucleus. Scale bars = 25μm); (c) Pre-gel solution obtained after digestion and ionic balance of DSCM in a tilted vial;(d)The appearance of DSCM-gel after sol-gel transition;(e)SEM images of the nanofibrous structure in the COLI, DNM, and DSCM hydrogels. (Scale bars = 5 μm)[65]

    图 3  (a):ⅰ-实心的圆柱体,ⅱ-单通道管,ⅲ-5通道管,ⅳ-有核开放性结构,ⅴ-无核的开放性结构;(b)通道管模具设计线框图;(c)无核开放性结构设计模具;(d)有核开放性结构设计模具

    Figure 3.  (a)ⅰ-Solid cylinder, ⅱ-tube, ⅲ-channel, ⅳ-open-path without core, and ⅴ-open-path with out core; (b) Wireframe view of a mold for the channel design; (c) Open-path without a core mold blueprint; (d) Open-path with core blueprint[84]

    图 4  PLLA多通道导管制备装置示意图和不同结构多通道导管横截面的SEM照片[102]

    Figure 4.  Scheme of the systematized device for fabrication of multi-channel conduits and SEM images of the multi-channel conduits cross section[102]

    图 5  含生长因子的F/S水凝胶的形态特征:(a)含有生长因子的RADA16-IKVAV溶液与RADA16-RGD溶液混合形成的稳定水凝胶;(b)F/S水凝胶纤维和(c-e)不同生长因子的水凝胶纤维的AFM照片[139]

    Figure 5.  Morphological characteristics of the F/S hydrogel containing growth factors: (a) Stable hydrogel was formed by combining RADA16-IKVAV solution containing growth factors and RADA16-RGD solution;(b) Images of F/S hydrogel fiber and (c-e)those with different growth factors [139]

    图 6  模拟脊髓结构的3D打印支架:(a)3D打印机系统装置;(b)3D打印机打印的连续层结构;(c)正常大鼠脊髓轴突NF200染色结果(上方白质中轴突高度排列成平行阵列,下方灰质中轴突为无序结构);(d)脊髓中相关功能轴突线状排列区域(束)(运动系统用绿色表示,感觉系统用蓝色表示)

    Figure 6.  3D-printed scaffold mimics the spinal cord architecture: (a) 3D-printer setup; (b) 3D printing creates a structure with one continuous layer; (c) Heavy chain neurofilament (NF200) labeling of axons in rat spinal cord (The axons in the white matter (top of the panel) are highly organized into parallel arrays traveling from rostral to caudal. The axons in the gray matter (bottom of the panel) are not linear);(d) Axonal projections in the spinal cord are linearly organized into regions (fascicles) containing axons of related function (Motor systems are shown in green and sensory systems are shown in blue)[147]

    表 1  生物材料支架负载生物活性因子的研究

    Table 1.  Investigations of biomaterial scaffolds loaded with neurotrophic factors

    Types of drug delivery strategiesBiomaterialsFactorOutcomeFrom
    Polymer micro/nanoparticlesPLGANGF and GDNFThe neurotrophins were released over 6 weeks in vitro and resulted in both tissue regeneration and functional improvements[163164]
    PLGAGDNFpromoted axon growth and functional improvement after SCI[165]
    nanoparticle20 nm nanoparticles were found along the spinal cord both rostral and caudal to the injection site, while 100 nm nanoparticles remained at the injection site[166]
    PEGnanoparticlelimit protein adsorption and macrophage engulfment[167]
    Short peptide series nanoparticleenhance nanoparticle deliveryacross the BBB[168]
    PLGA nanoparticleChABCDegraded glial scar, promoted functional recovery and axonal regeneration[169]
    Chemical crosslinkL-lactide, L-LA andε-caprolactone, ε-CLLoad factors[170]
    Electrospun collagen nanofibers,microbial transglutaminase (mTG)NT3Proteins were loaded at an efficiency of approximately 45%-48%, a sustained release of NT3 was obtained[171]
    collagenNT3, BDNF, bFGF, EphA4LBD and PlexinB1LBDFacilitated axonal and neuronal regeneration, remyelination and synapse formation of regenerated axons after SCI[34, 35, 37, 38]
    Physical blendFibrin gelsNT3, BDNFChABC, Rho inhibitor, GethrinPromote axonal regeneration and functional recovery[172, 173]
    hyaluronan/methyl cellulose (HAMC) hydrogelFGF2Increased angiogenesis[174]
    hyaluronan/methyl cellulose (HAMC) hydrogelerythropoietin(EPO)Attenuated inflammatory response and promoted neurogenesis[175]
    PCL core-shell structuresRetinoic acidsustained released of RA was obtained for at least 14 days, enhanced MSCs neuronal differentiation[176]
    PCL core-shell nanofibersAlbumin and lysozymeThe released lysozyme maintained its structure and bioactivity[177]
    PCL core-shell nanofibersplatelet-derived growth factor (PDGF)The protein with near zero-order kinetics and preserved bioactivity[178]
    Self-assembling peptide hydrogels FAQ SAPsChABCChABC was continuously released in vitro for 42 days, favored host neural regeneration and behavioral recovery[179]
    Particle/scaffold compositesPLA-PEG-PLAPLGA microparticlesGDNFBDNFBDNF was slowly released over a 56-day period, whereas a bolus of GDNF was released around 28 days[127]
    PLA-PEG-PLAhydrogelsPLGA microparticlesCNTFCNTF released from a degradable hydrogel was able to stimulate outgrowth of a significantly higher number of neurites[180]
    PLGmicroparticlesTGF-β1Expression of cytokines TNF-alpha, IL-12, and MCP-1 were decreased by at least 40% .[181]
    HAMCPLGA micro/nanoparticleFGF2Increased the density of neovascularization in the injured area.[182]
    Functional Multichannel Poly(Propylene Fumarate)-Collagen ScaffoldNT3Facilitated axonal and neuronal regeneration, remyelination and synapse formation of regenerated axons after SCI[36]
    PLLAGelatinNT3Decreased inflammatory responses and collagen/astrocytic scar formation. Promoted axonal regeneration and functional restoration[107]
    PLGA Multifunctional, multichannel bridgesHA microparticlesNT3BDNFEnhance axonal growth and promote regeneration[118]
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  • [1] ANJUM A, YAZID M D, FAUZI D M, et al. Spinal cord injury: Pathophysiology, multimolecular interactions, and underlying recovery mechanisms [J]. International Journal of Molecular Sciences,2020,21(20):7533. doi: 10.3390/ijms21207533
    [2] DIMITRIJEVIC M R, KAKULAS B A. Spinal cord injuries, human neuropathology and neurophysiology [J]. Acta Myol,2020,39(4):353-358.
    [3] YUAN S, SHI Z, CAO F, et al. Epidemiological features of spinal cord injury in china: A systematic review [J]. Frontiers in Neurology,2018,9:683. doi: 10.3389/fneur.2018.00683
    [4] KATOH H, YOKOTA K, FEHLINGS M G. Regeneration of spinal cord connectivity through stem cell transplantation and biomaterial scaffolds [J]. Frontiers in Cellular Neuroscience,2019,13:248. doi: 10.3389/fncel.2019.00248
    [5] DIMITRIJEVIC M R, DANNER S M, MAYR W. Neurocontrol of movement in humans with spinal cord injury [J]. Artificial Organs,2015,39(10):823-833. doi: 10.1111/aor.12614
    [6] MIEKISIAK G, LATKA D, JARMUZEK P, et al. Steroids in acute spinal cord injury: All but gone within 5 years [J]. World Neurosurgery,2019,122:e467-e471. doi: 10.1016/j.wneu.2018.09.239
    [7] DVORAK M F, NOONAN V K, FALLAH N, et al. The influence of time from injury to surgery on motor recovery and length of hospital stay in acute traumatic spinal cord injury: An observational Canadian cohort study [J]. J Neurotrauma,2015,32(9):645-654. doi: 10.1089/neu.2014.3632
    [8] LAI B Q, CHE M T, FENG B, et al. Tissue-engineered neural network graft relays excitatory signal in the completely transected canine spinal cord [J]. Adv Sci (Weinh),2019,6(22):1901240. doi: 10.1002/advs.201901240
    [9] LI G, CHE M T, ZENG X, et al. Neurotrophin-3 released from implant of tissue-engineered fibroin scaffolds inhibits inflammation, enhances nerve fiber regeneration, and improves motor function in canine spinal cord injury [J]. Journal of Biomedical Materials Research Part A,2018,106(8):2158-2170. doi: 10.1002/jbm.a.36414
    [10] MA Y H, ZENG X, QIU X C, et al. Perineurium-like sheath derived from long-term surviving mesenchymal stem cells confers nerve protection to the injured spinal cord [J]. Biomaterials,2018,160:37-55. doi: 10.1016/j.biomaterials.2018.01.015
    [11] SILVA N A, SOUSA N, REIS R L, et al. From basics to clinical: A comprehensive review on spinal cord injury [J]. Progress in Neurobiology,2014,114:25-57. doi: 10.1016/j.pneurobio.2013.11.002
    [12] ELLIOTT D I, TAM R, SEFTON M V, et al. Cell and biomolecule delivery for tissue repair and regeneration in the central nervous system [J]. Journal of Controlled Release,2014,190:219-227. doi: 10.1016/j.jconrel.2014.05.040
    [13] SENSHARMA P, MADHUMATHI G, JAYANT R D, et al. Biomaterials and cells for neural tissue engineering: Current choices [J]. Mater Sci Eng C Mater Biol Appl,2017,77:1302-1315. doi: 10.1016/j.msec.2017.03.264
    [14] NGUYEN A T, SATHE S R, YIM E K. From nano to micro: topographical scale and its impact on cell adhesion, morphology and contact guidance [J]. J Phys Condens Matter,2016,28(18):183001. doi: 10.1088/0953-8984/28/18/183001
    [15] ERMIS M, ANTMEN E, HASIRCI V. Micro and nanofabrication methods to control cell-substrate interactions and cell behavior: A review from the tissue engineering perspective [J]. Bioact Mater,2018,3(3):355-369. doi: 10.1016/j.bioactmat.2018.05.005
    [16] ZHANG Q, SHI B, DING J, et al. Polymer scaffolds facilitate spinal cord injury repair [J]. Acta Biomaterialia,2019,88:57-77. doi: 10.1016/j.actbio.2019.01.056
    [17] FUHRMANN T, ANANDAKUMARAN P N, SHOICHET M S. Combinatorial therapies after spinal cord injury: How can biomaterials help? [J]. Advanced Healthcare Materials,2017,6(10):1601130. doi: 10.1002/adhm.201601130
    [18] MADL C M, LESAVAGE B L, DEWI R E, et al. Maintenance of neural progenitor cell stemness in 3D hydrogels requires matrix remodelling [J]. Nature Materials,2017,16(12):1233-1242. doi: 10.1038/nmat5020
    [19] SRIDHARAN R, CAVANAGH B, CAMERON A R, et al. Material stiffness influences the polarization state, function and migration mode of macrophages [J]. Acta Biomaterialia,2019,89:47-59. doi: 10.1016/j.actbio.2019.02.048
    [20] TAY C Y, IRVINE S A, BOEY F Y, et al. Micro-/nano-engineered cellular responses for soft tissue engineering and biomedical applications [J]. Small,2011,7(10):1361-1378. doi: 10.1002/smll.201100046
    [21] MILLER C, JEFTINIJA S, MALLAPRAGADA S. Synergistic effects of physical and chemical guidance cues on neurite alignment and outgrowth on biodegradable polymer substrates [J]. Tissue Engineering,2002,8(3):367-378. doi: 10.1089/107632702760184646
    [22] ZHANG D, WU S, FENG J, et al. Micropatterned biodegradable polyesters clicked with CQAASIKVAV promote cell alignment, directional migration, and neurite outgrowth [J]. Acta Biomaterialia,2018,74:143-155. doi: 10.1016/j.actbio.2018.05.018
    [23] KRIPARAMANAN R, ASWATH P, ZHOU A, et al. Nanotopography: cellular responses to nanostructured materials [J]. J Nanosci Nanotechnol,2006,6(7):1905-1919. doi: 10.1166/jnn.2006.330
    [24] KOEGLER P, CLAYTON A, THISSEN H, et al. The influence of nanostructured materials on biointerfacial interactions [J]. Adv Drug Deliv Rev,2012,64(15):1820-1839. doi: 10.1016/j.addr.2012.06.001
    [25] HE L, TIAN L, SUN Y, et al. Nano-engineered environment for nerve regeneration: Scaffolds, functional molecules and stem cells [J]. Curr Stem Cell Res Ther,2016,11(8):605-617. doi: 10.2174/1574888X10666151001114735
    [26] DU B L, XIONG Y, ZENG C G, et al. Transplantation of artificial neural construct partly improved spinal tissue repair and functional recovery in rats with spinal cord transection [J]. Brain Research,2011,1400:87-98. doi: 10.1016/j.brainres.2011.05.019
    [27] GHASEMI-MOBARAKEH L, PRABHAKARAN M P, MORSHED M, et al. Application of conductive polymers, scaffolds and electrical stimulation for nerve tissue engineering [J]. J Tissue Eng Regen Med,2011,5(4):e17-e35. doi: 10.1002/term.383
    [28] THEOCHARIS A D, SKANDALIS S S, GIALELI C, et al. Extracellular matrix structure [J]. Adv Drug Deliv Rev,2016,97:4-27. doi: 10.1016/j.addr.2015.11.001
    [29] MARQUES C F, DIOGO G S, PINA S, et al. Collagen-based bioinks for hard tissue engineering applications: A comprehensive review [J]. J Mater Sci Mater Med,2019,30(3):32. doi: 10.1007/s10856-019-6234-x
    [30] LIAO S, NGIAM M, CHAN C K, et al. Fabrication of nano-hydroxyapatite/collagen/osteonectin composites for bone graft applications [J]. Biomedical Materials,2009,4(2):25019. doi: 10.1088/1748-6041/4/2/025019
    [31] YEH J Z, WANG D H, CHERNG J H, et al. A Collagen-based scaffold for promoting neural plasticity in a rat model of spinal cord injury [J]. Polymers (Basel),2020,12(10):2245. doi: 10.3390/polym12102245
    [32] KOURGIANTAKI A, TZERANIS D S, KARALI K, et al. Neural stem cell delivery via porous collagen scaffolds promotes neuronal differentiation and locomotion recovery in spinal cord injury [J]. NPJ Regen Med,2020,5:12. doi: 10.1038/s41536-020-0097-0
    [33] LI X, DAI J. Bridging the gap with functional collagen scaffolds: tuning endogenous neural stem cells for severe spinal cord injury repair [J]. Biomater Sci,2018,6(2):265-271. doi: 10.1039/C7BM00974G
    [34] HAN S, WANG B, JIN W, et al. The linear-ordered collagen scaffold-BDNF complex significantly promotes functional recovery after completely transected spinal cord injury in canine [J]. Biomaterials,2015,41:89-96. doi: 10.1016/j.biomaterials.2014.11.031
    [35] HAN S, YIN W, LI X, et al. Pre-clinical evaluation of CBD-NT3 modified collagen scaffolds in completely spinal cord transected non-human primates [J]. J Neurotrauma,2019,36(15):2316-2324. doi: 10.1089/neu.2018.6078
    [36] CHEN X, ZHAO Y, LI X, et al. Functional multichannel poly(propylene fumarate)-collagen scaffold with collagen-binding neurotrophic factor 3 promotes neural regeneration after transected spinal cord injury [J]. Advanced Healthcare Materials,2018,7(14):e1800315. doi: 10.1002/adhm.201800315
    [37] YANG Y, FAN Y, ZHANG H, et al. Small molecules combined with collagen hydrogel direct neurogenesis and migration of neural stem cells after spinal cord injury [J]. Biomaterials,2021,269:120479. doi: 10.1016/j.biomaterials.2020.120479
    [38] LIU W, XU B, XUE W, et al. A functional scaffold to promote the migration and neuronal differentiation of neural stem/progenitor cells for spinal cord injury repair [J]. Biomaterials,2020,243:119941. doi: 10.1016/j.biomaterials.2020.119941
    [39] ONUMA-UKEGAWA M, BHATT K, HIRAI T, et al. Bone marrow stromal cells combined with a honeycomb collagen sponge facilitate neurite elongation in vitro and neural restoration in the hemisected rat spinal cord [J]. Cell Transplantation,2015,24(7):1283-1297. doi: 10.3727/096368914X682134
    [40] YUAN N, TIAN W, SUN L, et al. Neural stem cell transplantation in a double-layer collagen membrane with unequal pore sizes for spinal cord injury repair [J]. Neural Regeneration Research,2014,9(10):1014-1019. doi: 10.4103/1673-5374.133160
    [41] MARCHAND R, WOERLY S. Transected spinal cords grafted with in situ self-assembled collagen matrices [J]. Neuroscience,1990,36(1):45-60. doi: 10.1016/0306-4522(90)90350-D
    [42] MA W, FITZGERALD W, LIU Q Y, et al. CNS stem and progenitor cell differentiation into functional neuronal circuits in three-dimensional collagen gels [J]. Experimental Neurology,2004,190(2):276-288. doi: 10.1016/j.expneurol.2003.10.016
    [43] PRABHAKARAN M P, VENUGOPAL J R, RAMAKRISHNA S. Mesenchymal stem cell differentiation to neuronal cells on electrospun nanofibrous substrates for nerve tissue engineering [J]. Biomaterials,2009,30(28):4996-5003. doi: 10.1016/j.biomaterials.2009.05.057
    [44] LABRADOR R O, BUTI M, NAVARRO X. Influence of collagen and laminin gels concentration on nerve regeneration after resection and tube repair [J]. Experimental Neurology,1998,149(1):243-252. doi: 10.1006/exnr.1997.6650
    [45] YOSHII S, OKA M, SHIMA M, et al. Bridging a spinal cord defect using collagen filament [J]. Spine (Phila Pa 1976),2003,28(20):2346-2351. doi: 10.1097/01.BRS.0000085302.95413.16
    [46] ALTINOVA H, HAMMES S, PALM M, et al. Dense fibroadhesive scarring and poor blood vessel-maturation hamper the integration of implanted collagen scaffolds in an experimental model of spinal cord injury [J]. Biomedical Materials,2020,15(1):15012. doi: 10.1088/1748-605X/ab5e52
    [47] ALTINOVA H, HAMMES S, PALM M, et al. Fibroadhesive scarring of grafted collagen scaffolds interferes with implant-host neural tissue integration and bridging in experimental spinal cord injury [J]. Regen Biomater,2019,6(2):75-87. doi: 10.1093/rb/rbz006
    [48] HO M T, TEAL C J, SHOICHET M S. A hyaluronan/methylcellulose-based hydrogel for local cell and biomolecule delivery to the central nervous system [J]. Brain Research Bulletin,2019,148:46-54. doi: 10.1016/j.brainresbull.2019.03.005
    [49] JENSEN G, HOLLOWAY J L, STABENFELDT S E. Hyaluronic acid biomaterials for central nervous system regenerative medicine [J]. Cells,2020,9(9):2113. doi: 10.3390/cells9092113
    [50] LAM J, TRUONG N F, SEGURA T. Design of cell-matrix interactions in hyaluronic acid hydrogel scaffolds [J]. Acta Biomaterialia,2014,10(4):1571-1580. doi: 10.1016/j.actbio.2013.07.025
    [51] MENG F, MODO M, BADYLAK S F. Biologic scaffold for CNS repair [J]. Regenerative Medicine,2014,9(3):367-383. doi: 10.2217/rme.14.9
    [52] ZAREI-KHEIRABADI M, SADROSADAT H, MOHAMMADSHIRAZI A, et al. Human embryonic stem cell-derived neural stem cells encapsulated in hyaluronic acid promotes regeneration in a contusion spinal cord injured rat [J]. International Journal of Biological Macromolecules,2020,148:1118-1129. doi: 10.1016/j.ijbiomac.2020.01.219
    [53] THOMPSON R E, PARDIECK J, SMITH L, et al. Effect of hyaluronic acid hydrogels containing astrocyte-derived extracellular matrix and/or V2a interneurons on histologic outcomes following spinal cord injury [J]. Biomaterials,2018,162:208-223. doi: 10.1016/j.biomaterials.2018.02.013
    [54] KHAING Z Z, MILMAN B D, VANSCOY J E, et al. High molecular weight hyaluronic acid limits astrocyte activation and scar formation after spinal cord injury [J]. Journal of Neural Engineering,2011,8(4):46033. doi: 10.1088/1741-2560/8/4/046033
    [55] ZAVISKOVA K, TUKMACHEV D, DUBISOVA J, et al. Injectable hydroxyphenyl derivative of hyaluronic acid hydrogel modified with RGD as scaffold for spinal cord injury repair [J]. Journal of Biomedical Materials Research Part A,2018,106(4):1129-1140. doi: 10.1002/jbm.a.36311
    [56] HE Z, ZANG H, ZHU L, et al. An anti-inflammatory peptide and brain-derived neurotrophic factor-modified hyaluronan-methylcellulose hydrogel promotes nerve regeneration in rats with spinal cord injury [J]. Int J Nanomedicine,2019,14:721-732. doi: 10.2147/IJN.S187854
    [57] KUTIKOV A B, MOORE S W, LAYER R T, et al. Method and apparatus for the automated delivery of continuous neural stem cell trails into the spinal cord of small and large animals [J]. Neurosurgery,2019,85(4):560-573. doi: 10.1093/neuros/nyy379
    [58] HU M, SABELMAN E E, TSAI C, et al. Improvement of Schwann cell attachment and proliferation on modified hyaluronic acid strands by polylysine [J]. Tissue Engineering,2000,6(6):585-593. doi: 10.1089/10763270050199532
    [59] TUKMACHEV D, FOROSTYAK S, KOCI Z, et al. Injectable extracellular matrix hydrogels as scaffolds for spinal cord injury repair [J]. Tissue Eng Part A,2016,22(3-4):306-317. doi: 10.1089/ten.tea.2015.0422
    [60] MEDBERRY C J, CRAPO P M, SIU B F, et al. Hydrogels derived from central nervous system extracellular matrix [J]. Biomaterials,2013,34(4):1033-1040. doi: 10.1016/j.biomaterials.2012.10.062
    [61] GUO S Z, REN X J, WU B, et al. Preparation of the acellular scaffold of the spinal cord and the study of biocompatibility [J]. Spinal Cord,2010,48(7):576-581. doi: 10.1038/sc.2009.170
    [62] CRAPO P M, TOTTEY S, SLIVKA P F, et al. Effects of biologic scaffolds on human stem cells and implications for CNS tissue engineering [J]. Tissue Eng Part A,2014,20(1-2):313-323. doi: 10.1089/ten.tea.2013.0186
    [63] HONG J Y, SEO Y, DAVAA G, et al. Decellularized brain matrix enhances macrophage polarization and functional improvements in rat spinal cord injury [J]. Acta Biomaterialia,2020,101:357-371. doi: 10.1016/j.actbio.2019.11.012
    [64] CERQUEIRA S R, LEE Y S, CORNELISON R C, et al. Decellularized peripheral nerve supports Schwann cell transplants and axon growth following spinal cord injury [J]. Biomaterials,2018,177:176-185. doi: 10.1016/j.biomaterials.2018.05.049
    [65] XU Y, ZHOU J, LIU C, et al. Understanding the role of tissue-specific decellularized spinal cord matrix hydrogel for neural stem/progenitor cell microenvironment reconstruction and spinal cord injury [J]. Biomaterials,2021,268:120596. doi: 10.1016/j.biomaterials.2020.120596
    [66] YANG T L. Chitin-based materials in tissue engineering: applications in soft tissue and epithelial organ [J]. International Journal of Molecular Sciences,2011,12(3):1936-1963. doi: 10.3390/ijms12031936
    [67] GNAVI S, BARWIG C, FREIER T, et al. The use of chitosan-based scaffolds to enhance regeneration in the nervous system [J]. International Review of Neurobiology,2013,109:1-62.
    [68] HU X, ZHOU X, LI Y, et al. Application of stem cells and chitosan in the repair of spinal cord injury [J]. International Journal of Developmental Neuroscience,2019,76:80-85. doi: 10.1016/j.ijdevneu.2019.07.005
    [69] CHENG H, HUANG Y C, CHANG P T, et al. Laminin-incorporated nerve conduits made by plasma treatment for repairing spinal cord injury [J]. Biochem Biophys Res Commun,2007,357(4):938-944. doi: 10.1016/j.bbrc.2007.04.049
    [70] YANG Z, ZHANG A, DUAN H, et al. NT3-chitosan elicits robust endogenous neurogenesis to enable functional recovery after spinal cord injury [J]. Proc Natl Acad Sci U S A,2015,112(43):13354-13359. doi: 10.1073/pnas.1510194112
    [71] JI W C, LI M, JIANG W T, et al. Protective effect of brain-derived neurotrophic factor and neurotrophin-3 overexpression by adipose-derived stem cells combined with silk fibroin/chitosan scaffold in spinal cord injury [J]. Neurological Research,2020,42(5):361-371. doi: 10.1080/01616412.2020.1735819
    [72] ZHANG J, CHENG T, CHEN Y, et al. A chitosan-based thermosensitive scaffold loaded with bone marrow-derived mesenchymal stem cells promotes motor function recovery in spinal cord injured mice [J]. Biomedical Materials,2020,15(3):35020. doi: 10.1088/1748-605X/ab785f
    [73] ROWLEY J A, MADLAMBAYAN G, MOONEY D J. Alginate hydrogels as synthetic extracellular matrix materials [J]. Biomaterials,1999,20(1):45-53. doi: 10.1016/S0142-9612(98)00107-0
    [74] BOZZA A, COATES E E, INCITTI T, et al. Neural differentiation of pluripotent cells in 3D alginate-based cultures [J]. Biomaterials,2014,35(16):4636-4645. doi: 10.1016/j.biomaterials.2014.02.039
    [75] HOSSEINI S M, SHARAFKHAH A, KOOHI-HOSSEINABADI O, et al. Transplantation of neural stem cells cultured in alginate scaffold for spinal cord injury in rats [J]. Asian Spine J,2016,10(4):611-618. doi: 10.4184/asj.2016.10.4.611
    [76] KHOSRAVIZADEH Z, RAZAVI S, BAHRAMIAN H, et al. The beneficial effect of encapsulated human adipose-derived stem cells in alginate hydrogel on neural differentiation [J]. J Biomed Mater Res B Appl Biomater,2014,102(4):749-755. doi: 10.1002/jbm.b.33055
    [77] SUN J, TAN H. Alginate-based biomaterials for regenerative medicine applications [J]. Materials (Basel),2013,6(4):1285-1309. doi: 10.3390/ma6041285
    [78] SITOCI-FICICI K H, MATYASH M, UCKERMANN O, et al. Non-functionalized soft alginate hydrogel promotes locomotor recovery after spinal cord injury in a rat hemimyelonectomy model [J]. Acta Neurochir (Wien),2018,160(3):449-457. doi: 10.1007/s00701-017-3389-4
    [79] GUNTHER M I, WEIDNER N, MULLER R, et al. Cell-seeded alginate hydrogel scaffolds promote directed linear axonal regeneration in the injured rat spinal cord [J]. Acta Biomaterialia,2015,27:140-150. doi: 10.1016/j.actbio.2015.09.001
    [80] LIU S, SANDNER B, SCHACKEL T, et al. Regulated viral BDNF delivery in combination with Schwann cells promotes axonal regeneration through capillary alginate hydrogels after spinal cord injury [J]. Acta Biomaterialia,2017,60:167-180. doi: 10.1016/j.actbio.2017.07.024
    [81] BECHARA S L, JUDSON A, POPAT K C. Template synthesized poly(epsilon-caprolactone) nanowire surfaces for neural tissue engineering [J]. Biomaterials,2010,31(13):3492-3501. doi: 10.1016/j.biomaterials.2010.01.084
    [82] DONOGHUE P S, LAMOND R, BOOMKAMP S D, et al. The development of a epsilon-polycaprolactone scaffold for central nervous system repair [J]. Tissue Eng Part A,2013,19(3-4):497-507. doi: 10.1089/ten.tea.2012.0382
    [83] PATEL B B, SHARIFI F, STROUD D P, et al. 3D Microfibrous scaffolds selectively promotes proliferation and glial differentiation of adult neural stem cells: A platform to tune cellular behavior in neural tissue engineering [J]. Macromolecular Bioscience,2019,19(2):e1800236. doi: 10.1002/mabi.201800236
    [84] WONG D Y, LEVEQUE J C, BRUMBLAY H, et al. Macro-architectures in spinal cord scaffold implants influence regeneration [J]. J Neurotrauma,2008,25(8):1027-1037. doi: 10.1089/neu.2007.0473
    [85] SILVA N A, SOUSA R A, FRAGA J S, et al. Benefits of spine stabilization with biodegradable scaffolds in spinal cord injured rats [J]. Tissue Eng Part C Methods,2013,19(2):101-108. doi: 10.1089/ten.tec.2012.0264
    [86] FLYNN L, DALTON P D, SHOICHET M S. Fiber templating of poly(2-hydroxyethyl methacrylate) for neural tissue engineering [J]. Biomaterials,2003,24(23):4265-4272. doi: 10.1016/S0142-9612(03)00334-X
    [87] HWANG D H, KIM H M, KANG Y M, et al. Combination of multifaceted strategies to maximize the therapeutic benefits of neural stem cell transplantation for spinal cord repair [J]. Cell Transplantation,2011,20(9):1361-1379. doi: 10.3727/096368910X557155
    [88] LI X, YANG C, LI L, et al. A therapeutic strategy for spinal cord defect: Human dental follicle cells combined with aligned PCL/PLGA electrospun material [J]. Biomed Research International,2015,2015:197183.
    [89] GOMEZ J C, EDGAR J M, AGBAY A M, et al. Incorporation of retinoic acid releasing microspheres into pluripotent stem cell aggregates for inducing neuronal differentiation [J]. Cellular and Molecular Bioengineering,2015,8(3):307-319. doi: 10.1007/s12195-015-0401-z
    [90] GELAIN F, PANSERI S, ANTONINI S, et al. Transplantation of nanostructured composite scaffolds results in the regeneration of chronically injured spinal cords [J]. ACS Nano,2011,5(1):227-236. doi: 10.1021/nn102461w
    [91] LAN H N, GAO M, LIN J, et al. Three-dimensional aligned nanofibers-hydrogel scaffold for controlled non-viral drug/gene delivery to direct axon regeneration in spinal cord injury treatment [J]. Scientific Reports,2017,7:42212.
    [92] FITZGERALD R, BASS L M, GOLDBERG D J, et al. Physiochemical characteristics of poly-L-lactic acid (PLLA) [J]. Aesthetic Surgery Journal,2018,38(suppl_1):S13-S17. doi: 10.1093/asj/sjy012
    [93] PANG X, ZHUANG X, TANG Z, et al. Polylactic acid (PLA): Research, development and industrialization [J]. Biotechnology Journal,2010,5(11SI):1125-1136.
    [94] BELLINI D, CENCETTI C, SACCHETTA A C, et al. PLA-grafting of collagen chains leading to a biomaterial with mechanical performances useful in tendon regeneration [J]. J Mech Behav Biomed Mater,2016,64:151-160. doi: 10.1016/j.jmbbm.2016.07.006
    [95] CHEN W, CHEN S, MORSI Y, et al. Superabsorbent 3D scaffold based on electrospun nanofibers for cartilage tissue engineering [J]. ACS Appl Mater Interfaces,2016,8(37):24415-24425. doi: 10.1021/acsami.6b06825
    [96] DENG Q Y, LI S R, CAI W Q, et al. Poly-lactic acid and agarose gelatin play an active role in the recovery of spinal cord injury [J]. Neuroscience Bulletin,2006,22(2):73-78.
    [97] CAI J, ZIEMBA K S, SMITH G M, et al. Evaluation of cellular organization and axonal regeneration through linear PLA foam implants in acute and chronic spinal cord injury [J]. Journal of Biomedical Materials Research Part A,2007,83(2):512-520.
    [98] HURTADO A, CREGG J M, WANG H B, et al. Robust CNS regeneration after complete spinal cord transection using aligned poly-L-lactic acid microfibers [J]. Biomaterials,2011,32(26):6068-6079. doi: 10.1016/j.biomaterials.2011.05.006
    [99] BARROCA N, MAROTE A, VIEIRA S I, et al. Electrically polarized PLLA nanofibers as neural tissue engineering scaffolds with improved neuritogenesis [J]. Colloids Surf B Biointerfaces,2018,167:93-103. doi: 10.1016/j.colsurfb.2018.03.050
    [100] IZADPANAHI M, SEYEDJAFARI E, AREFIAN E, et al. Nanotopographical cues of electrospun PLLA efficiently modulate non-coding RNA network to osteogenic differentiation of mesenchymal stem cells during BMP signaling pathway [J]. Mater Sci Eng C Mater Biol Appl,2018,93:686-703. doi: 10.1016/j.msec.2018.08.023
    [101] YANG F, MURUGAN R, WANG S, et al. Electrospinning of nano/micro scale poly(L-lactic acid) aligned fibers and their potential in neural tissue engineering [J]. Biomaterials,2005,26(15):2603-2610. doi: 10.1016/j.biomaterials.2004.06.051
    [102] ZENG C G, XIONG Y, XIE G, et al. Fabrication and evaluation of PLLA multichannel conduits with nanofibrous microstructure for the differentiation of NSCs in vitro [J]. Tissue Eng Part A,2014,20(5-6):1038-1048. doi: 10.1089/ten.tea.2013.0277
    [103] SUN X, BAI Y, ZHAI H, et al. Devising micro/nano-architectures in multi-channel nerve conduits towards a pro-regenerative matrix for the repair of spinal cord injury [J]. Acta Biomaterialia,2019,86:194-206. doi: 10.1016/j.actbio.2018.12.032
    [104] PATIST C M, MULDER M B, GAUTIER S E, et al. Freeze-dried poly(D, L-lactic acid) macroporous guidance scaffolds impregnated with brain-derived neurotrophic factor in the transected adult rat thoracic spinal cord [J]. Biomaterials,2004,25(9):1569-1582. doi: 10.1016/S0142-9612(03)00503-9
    [105] BINAN L, TENDEY C, de CRESCENZO G, et al. Differentiation of neuronal stem cells into motor neurons using electrospun poly-L-lactic acid/gelatin scaffold [J]. Biomaterials,2014,35(2):664-674. doi: 10.1016/j.biomaterials.2013.09.097
    [106] HURTADO A, MOON L D, MAQUET V, et al. Poly (D, L-lactic acid) macroporous guidance scaffolds seeded with Schwann cells genetically modified to secrete a bi-functional neurotrophin implanted in the completely transected adult rat thoracic spinal cord [J]. Biomaterials,2006,27(3):430-442. doi: 10.1016/j.biomaterials.2005.07.014
    [107] SUN X, ZHANG C, XU J, et al. Neurotrophin-3-loaded multichannel nanofibrous scaffolds promoted anti-inflammation, neuronal differentiation, and functional recovery after spinal cord injury [J]. ACS Biomaterials Science & Engineering,2020,6(2):1228-1238.
    [108] LEE S Y, JUNG E, PARK J H, et al. Transient aggregation of chitosan-modified poly(D, L-lactic-co-glycolic) acid nanoparticles in the blood stream and improved lung targeting efficiency [J]. J Colloid Interface Sci,2016,480:102-108. doi: 10.1016/j.jcis.2016.07.006
    [109] WANG J, LI D, LI T, et al. Gelatin tight-coated poly(lactide-co-glycolide) scaffold incorporating rhBMP-2 for bone tissue engineering [J]. Materials (Basel),2015,8(3):1009-1026. doi: 10.3390/ma8031009
    [110] WILEMS T S, SAKIYAMA-ELBERT S E. Sustained dual drug delivery of anti-inhibitory molecules for treatment of spinal cord injury [J]. Journal of Controlled Release,2015,213:103-111. doi: 10.1016/j.jconrel.2015.06.031
    [111] HAN F Y, THURECHT K J, WHITTAKER A K, et al. Bioerodable PLGA-based microparticles for producing sustained-release drug formulations and strategies for improving drug loading [J]. Frontiers in Pharmacology,2016,7:185.
    [112] XIONG Y, ZHU J X, FANG Z Y, et al. Coseeded Schwann cells myelinate neurites from differentiated neural stem cells in neurotrophin-3-loaded PLGA carriers [J]. Int J Nanomedicine,2012,7:1977-1989.
    [113] ZHANG Y Q, HE L M, XING B, et al. Neurotrophin-3 gene-modified Schwann cells promote TrkC gene-modified mesenchymal stem cells to differentiate into neuron-like cells in poly(lactic-acid-co-glycolic acid) multiple-channel conduit [J]. Cells Tissues Organs,2012,195(4):313-322. doi: 10.1159/000327724
    [114] HE L, ZHANG Y, ZENG C, et al. Manufacture of PLGA multiple-channel conduits with precise hierarchical pore architectures and in vitro/vivo evaluation for spinal cord injury [J]. Tissue Eng Part C Methods,2009,15(2):243-255. doi: 10.1089/ten.tec.2008.0255
    [115] TENG Y D, LAVIK E B, QU X, et al. Functional recovery following traumatic spinal cord injury mediated by a unique polymer scaffold seeded with neural stem cells [J]. Proc Natl Acad Sci U S A,2002,99(5):3024-3029. doi: 10.1073/pnas.052678899
    [116] SLOTKIN J R, PRITCHARD C D, LUQUE B, et al. Biodegradable scaffolds promote tissue remodeling and functional improvement in non-human primates with acute spinal cord injury [J]. Biomaterials,2017,123:63-76. doi: 10.1016/j.biomaterials.2017.01.024
    [117] THOMAS A M, KUBILIUS M B, HOLLAND S J, et al. Channel density and porosity of degradable bridging scaffolds on axon growth after spinal injury [J]. Biomaterials,2013,34(9):2213-2220. doi: 10.1016/j.biomaterials.2012.12.002
    [118] TUINSTRA H M, AVILES M O, SHIN S, et al. Multifunctional, multichannel bridges that deliver neurotrophin encoding lentivirus for regeneration following spinal cord injury [J]. Biomaterials,2012,33(5):1618-1626. doi: 10.1016/j.biomaterials.2011.11.002
    [119] TUINSTRA H M, MARGUL D J, GOODMAN A G, et al. Long-term characterization of axon regeneration and matrix changes using multiple channel bridges for spinal cord regeneration [J]. Tissue Eng Part A,2014,20(5-6):1027-1037. doi: 10.1089/ten.tea.2013.0111
    [120] YANG Y, de LAPORTE L, ZELIVYANSKAYA M L, et al. Multiple channel bridges for spinal cord injury: Cellular characterization of host response [J]. Tissue Eng Part A,2009,15(11):3283-3295. doi: 10.1089/ten.tea.2009.0081
    [121] MOORE M J, FRIEDMAN J A, LEWELLYN E B, et al. Multiple-channel scaffolds to promote spinal cord axon regeneration [J]. Biomaterials,2006,27(3):419-429. doi: 10.1016/j.biomaterials.2005.07.045
    [122] NEHRT A, HAMANN K, OUYANG H, et al. Polyethylene glycol enhances axolemmal resealing following transection in cultured cells and in ex vivo spinal cord [J]. J Neurotrauma,2010,27(1):151-161. doi: 10.1089/neu.2009.0993
    [123] LU X, PERERA T H, ARIA A B, et al. Polyethylene glycol in spinal cord injury repair: A critical review [J]. J Exp Pharmacol,2018,10:37-49. doi: 10.2147/JEP.S148944
    [124] FAN C, WANG D. A biodegradable PEG-based micro-cavitary hydrogel as scaffold for cartilage tissue engineering [J]. European Polymer Journal,2015,72:651-660. doi: 10.1016/j.eurpolymj.2015.02.038
    [125] KIM C. PEG-assisted reconstruction of the cervical spinal cord in rats: Effects on motor conduction at 1h [J]. Spinal Cord,2016,54(10):910-912. doi: 10.1038/sc.2016.72
    [126] REN S, LIU Z, WU Q, et al. Polyethylene glycol-induced motor recovery after total spinal transection in rats [J]. CNS Neuroscience & Therapeutics,2017,23(8):680-685.
    [127] LAMPE K J, KERN D S, MAHONEY M J, et al. The administration of BDNF and GDNF to the brain via PLGA microparticles patterned within a degradable PEG-based hydrogel: Protein distribution and the glial response [J]. Journal of Biomedical Materials Research Part A,2011,96A(3):595-607. doi: 10.1002/jbm.a.33011
    [128] GROUS L C, VERNENGO J, JIN Y, et al. Implications of poly (N-isopropylacrylamide)-g-poly(ethylene glycol) with codissolved brain-derived neurotrophic factor injectable scaffold on motor function recovery rate following cervical dorsolateral funiculotomy in the rat [J]. J Neurosurg Spine,2013,18(6):641-652. doi: 10.3171/2013.3.SPINE12874
    [129] LI X, LIU X, CUI L, et al. Engineering an in situ crosslinkable hydrogel for enhanced remyelination [J]. Faseb Journal,2013,27(3):1127-1136. doi: 10.1096/fj.12-211151
    [130] PIANTINO J, BURDICK J A, GOLDBERG D, et al. An injectable, biodegradable hydrogel for trophic factor delivery enhances axonal rewiring and improves performance after spinal cord injury [J]. Experimental Neurology,2006,201(2):359-367. doi: 10.1016/j.expneurol.2006.04.020
    [131] CIGOGNINI D, SATTA A, COLLEONI B, et al. Evaluation of early and late effects into the acute spinal cord injury of an injectable functionalized self-assembling scaffold [J]. PLoS One,2011,6(5):e19782. doi: 10.1371/journal.pone.0019782
    [132] GOKTAS M, CINAR G, ORUJALIPOOR I, et al. Self-assembled peptide amphiphile nanofibers and peg composite hydrogels as tunable ECM mimetic microenvironment [J]. Biomacromolecules,2015,16(4):1247-1258. doi: 10.1021/acs.biomac.5b00041
    [133] LU J, WANG X. Biomimetic self-assembling peptide hydrogels for tissue engineering applications [J]. Advances in Experimental Medicine and Biology,2018,1064:297-312.
    [134] RASPA A, CARMINATI L, PUGLIESE R, et al. Self-assembling peptide hydrogels for the stabilization and sustained release of active Chondroitinase ABC in vitro and in spinal cord injuries [J]. Journal of Controlled Release,2020,330:1208-1219.
    [135] MATSON J B, STUPP S I. Self-assembling peptide scaffolds for regenerative medicine [J]. Chem Commun (Camb),2012,48(1):26-33. doi: 10.1039/C1CC15551B
    [136] ZHANG S, GREENFIELD M A, MATA A, et al. A self-assembly pathway to aligned monodomain gels [J]. Nature Materials,2010,9(7):594-601. doi: 10.1038/nmat2778
    [137] LIU Y, YE H, SATKUNENDRARAJAH K, et al. A self-assembling peptide reduces glial scarring, attenuates post-traumatic inflammation and promotes neurological recovery following spinal cord injury [J]. Acta Biomaterialia,2013,9(9):8075-8088. doi: 10.1016/j.actbio.2013.06.001
    [138] IWASAKI M, WILCOX J T, NISHIMURA Y, et al. Synergistic effects of self-assembling peptide and neural stem/progenitor cells to promote tissue repair and forelimb functional recovery in cervical spinal cord injury [J]. Biomaterials,2014,35(9):2617-2629. doi: 10.1016/j.biomaterials.2013.12.019
    [139] LIU H, XU X, TU Y, et al. Engineering microenvironment for endogenous neural regeneration after spinal cord injury by reassembling extracellular matrix [J]. ACS Appl Mater Interfaces,2020,12(15):17207-17219. doi: 10.1021/acsami.9b19638
    [140] KIM B S, CHO C S. Injectable hydrogels for regenerative medicine [J]. Tissue Engineering and Regenerative Medicine,2018,15(5):511-512. doi: 10.1007/s13770-018-0161-7
    [141] HUNT J A, CHEN R, van VEEN T, et al. Hydrogels for tissue engineering and regenerative medicine [J]. Journal of Materials Chemistry B,2014,2(33):5319-5338. doi: 10.1039/C4TB00775A
    [142] AKBARI A, JABBARI N, SHARIFI R, et al. Free and hydrogel encapsulated exosome-based therapies in regenerative medicine [J]. Life Sciences,2020,249:117447. doi: 10.1016/j.lfs.2020.117447
    [143] MANTHA S, PILLAI S, KHAYAMBASHI P, et al. Smart hydrogels in tissue engineering and regenerative medicine [J]. Materials (Basel),2019,12(20):3323.
    [144] SLAUGHTER B V, KHURSHID S S, FISHER O Z, et al. Hydrogels in regenerative medicine [J]. Advanced Materials,2009,21(32-33):3307-3329. doi: 10.1002/adma.200802106
    [145] WILLERTH S M, SAKIYAMA-ELBERT S E. Approaches to neural tissue engineering using scaffolds for drug delivery [J]. Adv Drug Deliv Rev,2007,59(4-5):325-338. doi: 10.1016/j.addr.2007.03.014
    [146] QU W, CHEN B, SHU W, et al. Polymer-based scaffold strategies for spinal cord repair and regeneration [J]. Front Bioeng Biotechnol,2020,8:590549. doi: 10.3389/fbioe.2020.590549
    [147] LI G, CHE M T, ZHANG K, et al. Graft of the NT-3 persistent delivery gelatin sponge scaffold promotes axon regeneration, attenuates inflammation, and induces cell migration in rat and canine with spinal cord injury [J]. Biomaterials,2016,83:233-248. doi: 10.1016/j.biomaterials.2015.11.059
    [148] KOFFLER J, ZHU W, QU X, et al. Biomimetic 3D-printed scaffolds for spinal cord injury repair [J]. Nature Medicine,2019,25(2):263-269. doi: 10.1038/s41591-018-0296-z
    [149] JOUNG D, TRUONG V, NEITZKE C C, et al. 3D Printed stem-cell derived neural progenitors generate spinal cord scaffolds [J]. Advanced Functional Materials,2018,28(39):1801850. doi: 10.1002/adfm.201801850
    [150] MUHEREMU A, AO Q. Past, present, and future of nerve conduits in the treatment of peripheral nerve injury [J]. Biomed Research International,2015,2015:237507.
    [151] DALY W, YAO L, ZEUGOLIS D, et al. A biomaterials approach to peripheral nerve regeneration: Bridging the peripheral nerve gap and enhancing functional recovery [J]. Journal of the Royal Society Interface,2012,9(67):202-221. doi: 10.1098/rsif.2011.0438
    [152] RAMBURRUN P, KUMAR P, CHOONARA Y E, et al. A review of bioactive release from nerve conduits as a neurotherapeutic strategy for neuronal growth in peripheral nerve injury [J]. Biomed Research International,2014,2014:132350.
    [153] de LAPORTE L, YAN A L, SHEA L D. Local gene delivery from ECM-coated poly(lactide-co-glycolide) multiple channel bridges after spinal cord injury [J]. Biomaterials,2009,30(12):2361-2368. doi: 10.1016/j.biomaterials.2008.12.051
    [154] DUMONT C M, MARGUL D J, SHEA L D. Tissue engineering approaches to modulate the inflammatory milieu following spinal cord injury [J]. Cells Tissues Organs,2016,202(1-2):52-66. doi: 10.1159/000446646
    [155] de RUITER G C, MALESSY M J, YASZEMSKI M J, et al. Designing ideal conduits for peripheral nerve repair [J]. Neurosurgical Focus,2009,26(2):E5. doi: 10.3171/FOC.2009.26.2.E5
    [156] FRANTZ C, STEWART K M, WEAVER V M. The extracellular matrix at a glance [J]. Journal of Cell Science,2010,123(Pt 24):4195-4200.
    [157] GUO J S, QIAN C H, LING E A, et al. Nanofiber scaffolds for treatment of spinal cord injury [J]. Current Medicinal Chemistry,2014,21(37):4282-4289. doi: 10.2174/0929867321666140815124648
    [158] HE L, TIAN L, SUN Y, et al. Nano-engineered environment for nerve regeneration: Scaffolds, functional molecules and stem cells [J]. Curr Stem Cell Res Ther,2016,11(8):605-617. doi: 10.2174/1574888X10666151001114735
    [159] SIMITZI C, RANELLA A, STRATAKIS E. Controlling the morphology and outgrowth of nerve and neuroglial cells: The effect of surface topography [J]. Acta Biomaterialia,2017,51:21-52. doi: 10.1016/j.actbio.2017.01.023
    [160] LI X, ZHANG C, HAGGERTY A E, et al. The effect of a nanofiber-hydrogel composite on neural tissue repair and regeneration in the contused spinal cord [J]. Biomaterials,2020,245:119978.
    [161] HARVEY A R, LOVETT S J, MAJDA B T, et al. Neurotrophic factors for spinal cord repair: Which, where, how and when to apply, and for what period of time? [J]. Brain Research,2015,1619:36-71. doi: 10.1016/j.brainres.2014.10.049
    [162] MOHTARAM N K, MONTGOMERY A, WILLERTH S M. Biomaterial-based drug delivery systems for the controlled release of neurotrophic factors [J]. Biomedical Materials,2013,8(2):22001. doi: 10.1088/1748-6041/8/2/022001
    [163] MENEI P, DANIEL V, MONTERO-MENEI C, et al. Biodegradation and brain tissue reaction to poly(D, L-lactide-co-glycolide) microspheres [J]. Biomaterials,1993,14(6):470-478. doi: 10.1016/0142-9612(93)90151-Q
    [164] GARBAYO E, MONTERO-MENEI C N, ANSORENA E, et al. Effective GDNF brain delivery using microspheres--a promising strategy for Parkinson's disease [J]. Journal of Controlled Release,2009,135(2):119-126.
    [165] PEAN J M, MENEI P, MOREL O, et al. Intraseptal implantation of NGF-releasing microspheres promote the survival of axotomized cholinergic neurons [J]. Biomaterials,2000,21(20):2097-2101. doi: 10.1016/S0142-9612(00)00141-1
    [166] ANDRIEU-SOLER C, AUBERT-POUESSEL A, DOAT M, et al. Intravitreous injection of PLGA microspheres encapsulating GDNF promotes the survival of photoreceptors in the rd1/rd1 mouse [J]. Molecular Vision,2005,11:1002-1011.
    [167] WANG Y C, WU Y T, HUANG H Y, et al. Sustained intraspinal delivery of neurotrophic factor encapsulated in biodegradable nanoparticles following contusive spinal cord injury [J]. Biomaterials,2008,29(34):4546-4553. doi: 10.1016/j.biomaterials.2008.07.050
    [168] NANCE E A, WOODWORTH G F, SAILOR K A, et al. A dense poly(ethylene glycol) coating improves penetration of large polymeric nanoparticles within brain tissue [J]. Science Translational Medicine,2012,4(149):119r-149r.
    [169] GAO H, PANG Z, JIANG X. Targeted delivery of nano-therapeutics for major disorders of the central nervous system [J]. Pharm Res,2013,30(10):2485-2498. doi: 10.1007/s11095-013-1122-4
    [170] AZIZI M, FARAHMANDGHAVI F, JOGHATAEI M T, et al. ChABC-loaded PLGA nanoparticles: A comprehensive study on biocompatibility, functional recovery, and axonal regeneration in animal model of spinal cord injury [J]. Int J Pharm,2020,577:119037. doi: 10.1016/j.ijpharm.2020.119037
    [171] BAOLIN G, MA P X. Synthetic biodegradable functional polymers for tissue engineering: A brief review [J]. Science China: Chemistry,2014,57(4):490-500. doi: 10.1007/s11426-014-5086-y
    [172] LIU T, XU J, CHAN B P, et al. Sustained release of neurotrophin-3 and chondroitinase ABC from electrospun collagen nanofiber scaffold for spinal cord injury repair [J]. Journal of Biomedical Materials Research Part a,2012,100(1):236-242.
    [173] TAYLOR S J, MCDONALD J R, SAKIYAMA-ELBERT S E. Controlled release of neurotrophin-3 from fibrin gels for spinal cord injury [J]. Journal of Controlled Release,2004,98(2):281-294. doi: 10.1016/j.jconrel.2004.05.003
    [174] LORD-FONTAINE S, YANG F, DIEP Q, et al. Local inhibition of Rho signaling by cell-permeable recombinant protein BA-210 prevents secondary damage and promotes functional recovery following acute spinal cord injury [J]. J Neurotrauma,2008,25(11):1309-1322. doi: 10.1089/neu.2008.0613
    [175] WANG Y, COOKE M J, MORSHEAD C M, et al. Hydrogel delivery of erythropoietin to the brain for endogenous stem cell stimulation after stroke injury [J]. Biomaterials,2012,33(9):2681-2692. doi: 10.1016/j.biomaterials.2011.12.031
    [176] CHEW S Y, WEN J, YIM E K, et al. Sustained release of proteins from electrospun biodegradable fibers [J]. Biomacromolecules,2005,6(4):2017-2024. doi: 10.1021/bm0501149
    [177] JIANG X, CAO H Q, SHI L Y, et al. Nanofiber topography and sustained biochemical signaling enhance human mesenchymal stem cell neural commitment [J]. Acta Biomaterialia,2012,8(3):1290-1302. doi: 10.1016/j.actbio.2011.11.019
    [178] JIANG H, HU Y, LI Y, et al. A facile technique to prepare biodegradable coaxial electrospun nanofibers for controlled release of bioactive agents [J]. Journal of Controlled Release,2005,108(2-3):237-243. doi: 10.1016/j.jconrel.2005.08.006
    [179] LIAO I C, CHEW S Y, LEONG K W. Aligned core-shell nanofibers delivering bioactive proteins [J]. Nanomedicine (Lond),2006,1(4):465-471. doi: 10.2217/17435889.1.4.465
    [180] BURDICK J A, WARD M, LIANG E, et al. Stimulation of neurite outgrowth by neurotrophins delivered from degradable hydrogels [J]. Biomaterials,2006,27(3):452-459. doi: 10.1016/j.biomaterials.2005.06.034
    [181] LIU J, ZHANG J, ZHANG X, et al. Transforming growth factor-beta 1 delivery from microporous scaffolds decreases inflammation post-implant and enhances function of transplanted islets [J]. Biomaterials,2016,80:11-19. doi: 10.1016/j.biomaterials.2015.11.065
    [182] CAICCO M J, COOKE M J, WANG Y, et al. A hydrogel composite system for sustained epi-cortical delivery of Cyclosporin A to the brain for treatment of stroke [J]. Journal of Controlled Release,2013,166(3):197-202. doi: 10.1016/j.jconrel.2013.01.002
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  • 收稿日期:  2021-01-18
  • 网络出版日期:  2021-03-31

功能高分子材料促进脊髓损伤后再生修复的研究进展

    通讯作者: 何留民, helm9@mail.sysu.edu.cn
    作者简介: 孙秀敏(1984—),女,博士后,研究方向为神经组织工程和脊髓损伤再生修复。E-mail: ermine2005@163.com;何留民,博士,长期专注于纳米医学与神经再生研究,在功能性自组装短肽纳米水凝胶的设计、聚合物功能化改性以及纳米支架多级信号诱导神经再生等方面进行了深入的研究。主持多项国家自然科学基金及省部级项目。先后入选“广东特支计划”科技创新青年拔尖人才计划、广州市珠江科技新星、广东省高等学校优秀青年教师培养计划。以第一作者/通讯作者在包括Biomaterials、ACS Appl Mater Interfaces、Acta Biomater、J Mater Chem等学术期刊上发表SCI论文40余篇,被引近2000次。以第一发明人授权中国发明专利2件,成功转让1件。自2015年起受邀在全国生物材料大会担任神经修复材料分会主席并作邀请报告
  • 中山大学附属第三医院脊柱外科,广东省微创脊柱外科工程技术研究中心,广东省微创脊柱外科质量控制中心,广州 510630

摘要: 脊髓损伤后损伤区域神经纤维束的破坏,导致损伤区域以下长久的感觉和运动功能丧失。损伤区域恶劣的微环境是脊髓损伤难以修复的一大问题,大量的炎症细胞聚集、细胞死亡、抑制因子的分泌等,进一步导致损伤区域神经细胞的二次死亡、胶质细胞过度增生、胶原纤维沉积等。不利的微环境不仅限制轴突的再生,同时损伤神经干细胞的功能,不利于神经干细胞向损伤区域迁移并向神经元分化。虽然近期的研究证明脊髓损伤后轴突在合适的基质环境下能够再生,但完全恢复目前还没有可行措施。近年来,高分子生物材料在脊髓损伤修复研究中取得了一定进展:高分子生物材料支架可以发挥多种功能:抑制空洞和瘢痕组织的形成,为再生轴突的生长提供支撑作用;调控细胞行为,诱导神经细胞生长和分化;抑制炎症细胞的非特异性渗入进而改善脊髓损伤区域的微环境;作为载体负载和释放药物、细胞和生物活性因子。本文结合本课题组的研究从生物材料种类、支架类型、微环境构建以及因子负载等方面在脊髓损伤修复中的应用研究进行了综述。为生物材料用于脊髓损伤的治疗提供基础研究方向。

English Abstract

    • 脊髓损伤(spinal cord injury,SCI)是一种神经系统疾病,全球每年约有25~50万人患病。脊髓损伤发生于机动车事故、跌倒、暴力和运动损伤等,而道路交通事故是最常见的原因[1]。在美国/中国每年约有1.7/10万新增病例,男性占4/5,发病率最高年龄组是16~30岁[2]。然而,只有不到1%的SCI病人通过治疗可以恢复,大多数患者存在不同程度的残疾,不仅为患者的身心健康带来伤害,而且给家庭、社会经济带来沉重的负担[3],是严重威胁人类健康的重大疾病之一。

      急性脊髓损伤通常是由于脊柱的突然损伤致骨折或椎体脱位而引起[4]。脊髓损伤分为两个阶段,即原发性损伤和继发性损伤,如图1。原发性损伤包括神经实质破坏、轴突网络破坏、出血和胶质膜破坏,脊髓损伤严重程度的主要决定于初始破坏程度和脊髓受压的持续时间[1]。继发性损伤分为急性期、亚急性期和慢性期。原发性损伤期之后,急性继发性损伤期表现为血管损伤、离子失衡、兴奋性毒性、自由基产生、钙内流增加、脂质过氧化、炎症、水肿、坏死等病理生理特征[1]。亚急性继发损伤期表现为神经元凋亡、轴突脱髓鞘、沃勒变性、轴突重塑、胶质瘢痕形成等特征。慢性继发损伤期的特征是囊腔形成、轴突回缩、纤维及胶质瘢痕成熟等[5]

      图  1  脊髓损伤后的病理生理示意图,细胞和细胞外基质在损伤区域沉积的过程:(a)脊髓损伤后急性期(0-72 h)损伤导致神经细胞死亡和大量炎性细胞迁移到损伤区域;(b)脊髓损伤后慢性期(损伤72 h之后),慢性空洞形成,星形胶质细胞反应性增生和细胞外基质的沉积

      Figure 1.  The schematic of SCI pathophysiology, cellular and extracellular composition of the spinal injury scar: (a) In the acute post-injury phase (0–72 h), neural cell death and the release of a number of inflammatory cell in the injury site; (b) In the chronic post-injury phase (after 72 h), a chronic cystic cavity develops, reactive astrocytes hypertrophy and extracellular deposition

    • 目前临床上对脊髓损伤修复的早期治疗主要采用手术和激素治疗。对于急性创伤、慢性压迫性和嵌顿性损伤,在损伤后24 h内进行脊髓减压手术,有利于改善神经系统紊乱及后续运动功能的恢复[6]。另外,针对脊髓损伤急性阶段,临床上还采用皮质类固醇药物如甲基强的松龙来控制早期急性炎症。但是研究也显示,高剂量用药超过48 h会引起消化道出血、感染等严重并发症,甚至造成多器官的损害,而且激素类药物对脊髓损伤的治疗效果目前还不确定[7]

      在急性期之后,脊髓损伤患者会进入相对稳定的慢性阶段,在此阶段,临床上主要以护理和康复训练为主。与此同时,围绕促进脊髓组织神经再生的治疗措施也在持续探索中,这也是脊髓损伤治疗和修复研究领域中的热点和难点。国内外已经开展了大量研究,主要采用细胞移植,分子药物或(和)生物材料支架等治疗策略和方法。

      细胞移植和分子药物治疗可以为损伤区域提供细胞和营养支持,同时也可以改善损伤区域微环境,主要表现为调节免疫反应,分泌促再生因子,促进损伤区域神经再生和轴突髓鞘化等作用[8-11]。但是,由于损伤区域缺乏桥接物的支撑,移植的细胞或营养因子等因脑脊液循环难以定植,导致细胞和生物活性因子不能有效发挥作用[12, 13]

      近几年研究发现,生物支架材料在治疗脊髓损伤的过程起着重要作用。支架材料本身的结构性能可以调控损伤区域微环境,促进轴突再生和动物行为学功能恢复[14]。另外,可以与细胞和生物活性分子一起以一种综合的方式来达到恢复、维持或提高组织功能恢复的目的。而生物支架材料的引入不仅能够填充损伤区域的缺损,为再生的组织提供引导,同时可以为种子细胞提供支撑和引导,加载多种活性物质和营养因子等[15, 16]。因此生物材料支架是神经组织工程修复的关键。

    • 组织再生支架设计的主要功能是用来仿生天然细胞外基质(ECM)组织结构填充损伤区域空洞,并且能够引导组织再生,同时可以作为细胞或生物活性因子的载体[17]。因此,理想的支架应该具有如下属性和特征:(1)良好的生物相容性、与宿主能够很好地整合、不能引起免疫反应、较好的生物活性和理想的电荷密度;(2)只有在受伤部位完全再生时才会生物降解,且降解产物无毒性,易于被机体清除;(3)理想的物理机械特性,与周围组织具有相适应的弹性模量,能够与周围组织更好地融合;(4)完全相互连通的几何结构,有利于交换;(5)理想的表面特性,可以调控细胞的行为,对轴突具有物理导向作用;(6)易功能化,能够根据需要负载细胞或因子。一个理想的神经支架应具有包括力学性能、生物化学特征、拓扑结构和电子信号等在内的多种优势[18-28]。这些优势帮助支架模拟体内组织的原生细胞外基质,通过提供更好的接触导向来促进神经轴突生长和细胞的黏附、增殖、迁移和生存。

    • 生物材料可以从天然或合成聚合物中获得,不管是天然生物材料或者是合成生物材料在应用中各有优缺点。

    • 天然材料相比合成材料所具有的优势:一些材料本身是ECM组分,存在原生的配体环境,固有的生物活性,并经历过自然重构。因此,移植后能够与宿主组织良好地整合,更容易实现从实验到临床的转化。在神经组织工程中用于支架设计的天然高分子材料常用的细胞基质成分有:胶原蛋白、明胶、透明质酸、脱细胞基质等,以及非细胞外基质成分:壳聚糖和海藻酸盐等。

      (1)胶原蛋白:胶原蛋白是人体中含量最多、分布最广的蛋白质,也是研究最广泛的ECM成分之一。目前已有28种不同亚型被鉴定出来,它们的特征都是三螺旋状结构[29, 30]。由于胶原蛋白抗原性低、生物相容性和生物降解性好,已成为脊髓损伤修复中研究最多的天然高分子材料。

      首先,胶原具有大量的结合位点,可以负载生物活性因子或细胞等,适合细胞的黏附、增殖和分化等特点[31-33]。例如,中科院戴建武团队长期采用同轴排列的胶原纤维束功能性结合NT3, BDNF, bFGF, LDN193189, SB431542, CHIR99021, P7C3-A20, EphA4LBD和PlexinB1LBD等因子和药物,并负载神经干细胞(Neural stem cell, NSC)进行脊髓损伤再生修复,能明显减小损伤区域的空洞、减弱胶质细胞反应性增生、促进神经干细胞分化为神经元、促进轴突再生和髓鞘化,最终促进动物行为学功能的恢复[34-38]。采用蜂窝状胶原蛋白海绵结构支架[39]或胶原纤维膜[40]负载间充质干细胞(MSC)或NSC也可以促进干细胞分化为神经元,改善再生微环境,促进动物行为学功能的恢复。

      另外,由于胶原蛋白模量与人体软组织强度相似,纤维可以吸水膨胀,因此可以制成可注射水凝胶支架原位注射到脊髓损伤区域。Marchand等[41]将胶原水凝胶注射到损伤区域形成胶原纤维网络,可以促进细胞迁移到损伤区域和轴突再生。胶原蛋白可制备成与神经组织更加相似的纳米纤维结构,因此也是促进神经再生比较理想的支架[42]。有研究将胶原制成纳米纤维结构支架,发现可以促进干细胞分化为神经元并表达神经元相关蛋白[43]

      然而,胶原如果处理不好,也会成为神经再生的障碍[44, 45]。Brook课题组[46, 47]制备Ⅰ型胶原支架,在脊髓修复中发现支架周围会形成纤维和胶质瘢痕,不利于与宿主组织进行整合。支架内微血管不够成熟,血-脊髓屏障改造不良。

      (2)透明质酸:透明质酸(HA)是一种线性的、无分支的非硫化糖胺(GAG),是由重复的二糖(β-1,4-D-葡糖醛酸(称为尿酸)和β-1,3-N-乙酰葡萄糖胺)组成的一种长链多糖,是细胞外基质HA的重要组成部分[48-50]。HA在体内可酶解成不同分子量的透明质酸[51]。研究发现,高分子量HA可提高神经再生修复功能[52, 53]。低分子量HA可促进血管生成。另外还有研究显示,HA能够刺激生物活性因子如血管内皮生长因子(VEGF)和脑源性神经营养因子(BDNF)的分泌,促进脊髓损伤后的神经元存活和轴突再生髓鞘化等[54]

      HA水凝胶相互连接的多孔结构可以输送营养,促进细胞、血管和神经的渗透。因此被用来作为药物、因子和细胞的理想载体[55]。He等[56]制备的透明质酸-甲基纤维素(HAMC)水凝胶负载BDNF和抗炎因子KAFAK,能够减少促炎因子释放和空洞胶质瘢痕的形成,促进神经元存活和轴突再生。而HA水凝胶负载人NSC,可促进人NSC存活、分化为神经谱系细胞,促进动物行为学功能恢复[57]

      但HA黏附性较差,需要对其进行修饰。同时,因HA的水溶性较强,可通过交联剂来将其转化为可注射的形式[58]。Zaviskova等[55]使用精氨酸、甘氨酸和天门冬氨酸序列(RGD)修饰HA的可注射水凝胶支架负载MSC,可以减少星形胶质细胞增生,促进血管组织再生。Sakiyama-Elbert课题组[53]利用透明质酸水凝胶混合星形胶质细胞来源的脱细胞基质与V2a中间神经元,可减少巨噬细胞/小胶质细胞聚集和胶质瘢痕的形成,促进轴突长入损伤区域。

      (3)组织来源脱细胞基质材料:脱细胞基质生物材料由原生动物组织脱细胞制备而成。其优势是可以较好地保留原组织或器官的细胞外基质蛋白成分、活性因子和天然的3D结构,具有良好的生物相容性和非免疫原性,力学性质、降解模式与组织一致[51]。脊髓损伤修复所用的的ECM主要来于脑、脊髓和外周神经组织[59]。来源于脊髓的脱细胞基质主要由糖氨基葡聚糖(透明质酸)和蛋白聚糖组成,另外还包括:层黏连蛋白、轴突导向因子-1、巢蛋白、络丝蛋白、腱糖蛋白以及生长因子,如FGF-2和EGF等[60]

      目前关于脱细胞基质的研究虽不够充分,但它却是一种非常有潜力的修复材料,也是近期研究的热点。Guo等[61]移植脊髓来源的脱细胞基质支架,可使损伤区域渗透的T-细胞数量明显减少。Crapo等[62]比较了猪中枢神经系统3个不同部位(脑源性、脊髓源性和视神经源性)来源的脱细胞基质支架,证实支架中均残留有NGF、bFGF和VEGF等神经营养因子,并能促进PC12细胞的增殖、迁移和分化。Hong等[63]移植猪源性脑脱细胞基质水凝胶,可以促进巨噬细胞向M2型极化和动物行为学功能的恢复。Cerqueira等[64]移植大鼠周围神经脱细胞基质水凝胶负载雪旺细胞(SC),可提高其在损伤区域的存活率,并促进轴突再生和髓鞘化。全大萍课题组[65]制备外周神经来源的脱细胞基质、鼠尾胶原Ⅰ型水凝胶和脊髓来源的脱细胞基质水凝胶(图2),研究表明脊髓来源的水凝胶能够为脊髓损伤区域提供更有利的微环境,促进损伤区域神经干细胞的募集和向神经元方向分化,促进轴突再生。

      图  2  (a)脱细胞基质周围神经基质(DNM)和脱细胞脊髓基质(DSCM)(标尺为10 mm);(b)天然或脱细胞周围神经/脊髓组织学切片的 H&E 染色(箭头指示细胞核,标尺为25 μm);(c)消化和离子平衡后的DSCM预凝胶;(d)水凝胶;(e)COLI, DNM 和 DSCM水凝胶纳米纤维结构的 SEM显微图像(标尺=5 μm)。[65]

      Figure 2.  (a)Decellularized peripheral nerve matrix and decellularized spinal cord matrix,(Scale bars =10 mm); (b) Histological sections with H&E staining of the native or decellularized peripheral nerve/spinal cord, respectively (The arrows indicate cell nucleus. Scale bars = 25μm); (c) Pre-gel solution obtained after digestion and ionic balance of DSCM in a tilted vial;(d)The appearance of DSCM-gel after sol-gel transition;(e)SEM images of the nanofibrous structure in the COLI, DNM, and DSCM hydrogels. (Scale bars = 5 μm)[65]

      (4)壳聚糖:壳聚糖主要存在于甲壳类动物如昆虫、螃蟹、虾以及细菌和真菌的细胞壁中,它具有与糖胺聚糖相似的结构和性质,是细胞外基质的主要成分[66],和构建神经再生支架的理想选择[67, 68]。Yao课题组[69]移植壳聚糖支架,海藻酸盐支架、壳聚糖-海藻酸盐复合支架,其中的壳聚糖支架与另两种支架相比获得较多的再生轴突纤维,并且胶质细胞较少。Cheng等[69]左脊髓损伤部位移植内部填充层黏连蛋白(LN)的壳聚糖神经导管,可降低炎症细胞反应,促进轴突再生和动物行为学功能恢复。李晓光课题组[70]移植壳聚糖多孔支架负载NT3,可促进神经干细胞分化为成熟神经元并促进动物行为学功能恢复。Ji等[71]移植负载BDNF和NT3丝素蛋白-壳聚糖支架,可促进GAP-43神经纤维的再生,减少GFAP的反应性增生,和Caspase-3的表达。Zhang等[72]移植负载MSC的壳聚糖水凝胶支架,可减少胶质瘢痕的形成和细胞死亡,抗炎抗氧化作用。

      (5)海藻酸盐:海藻酸是一种天然的、由棕色藻类和细菌获得的线性多糖。它由(1-4)-连接β-D-曼纽酸(M)和α-l-磺酸单体(G)组成,具有较好的生物相容性、生物降解性、非抗原性和螯合性等优点[73],并且具有增强干细胞向神经元分化并表达神经元相关标记物的潜能,是神经干细胞移植的理想载体[74-76]。Sun等[77]研究证实高G的海藻酸盐珠能促进NSC神经保护因子的分泌。Sitoci-Ficici等[78]将海藻酸盐水凝胶移植入2 mm脊髓损伤动物模型中,可改善大鼠行为学功能。文献[79, 80]制备的海藻酸盐各向异性毛细管水凝胶支架,负载BDNF和BMSC后,通道内仍有大量BMSC存活,轴突再生并沿毛细管定向生长。

    • 与天然材料相比合成生物材料的优势是:含有的杂质、病原体或污染物相对较少,对批量处理的可变性更低,具有生物可降解性、非炎症性、非毒性等特点。另外,还具有可改变的机械和物理特性。被广泛用于制造支架的合成聚合物主要包括聚己内酯(PCL)、聚乳酸(PLLA)、聚乙醇酸-乳酸共聚物(PLGA)等。

      (1)PCL:PCL是一种玻璃化温度较低、室温下较柔软、呈橡胶态的半结晶性聚合物。具有高弹性、低毒性、良好的力学性能、可生物降解和生物相容性较好的特点[81]。另外,PCL能够促进神经干细胞向少突胶质细胞方向分化和轴突髓鞘的形成,是脊髓损伤组织工程修复中较理想的材料[82, 83]

      Wong等[84]利用PCL模仿灰质或白质结构设计了几种不同微结构的支架(图3),将其移植入全横断脊髓损伤动物模型中,其开放式的微通道结构更有利于轴突的再生和髓鞘化并在轴向引导的作用下生长。Silva等[85]制备的淀粉-PCL的3D复合支架可以保护损伤区域并促进动物行为学功能的恢复。Flynn等[86]移植的PCL/pHEMA复合支架,其中的pHEMA凝胶纵向通道可以定向引导脊髓损伤轴突再生。

      图  3  (a):ⅰ-实心的圆柱体,ⅱ-单通道管,ⅲ-5通道管,ⅳ-有核开放性结构,ⅴ-无核的开放性结构;(b)通道管模具设计线框图;(c)无核开放性结构设计模具;(d)有核开放性结构设计模具

      Figure 3.  (a)ⅰ-Solid cylinder, ⅱ-tube, ⅲ-channel, ⅳ-open-path without core, and ⅴ-open-path with out core; (b) Wireframe view of a mold for the channel design; (c) Open-path without a core mold blueprint; (d) Open-path with core blueprint[84]

      PCL支架作为因子和细胞的理想载体在治疗脊髓损伤中也被广泛应用。Hwang等[87]制备的PCL支架负载NT-3和NSC,能促进轴突再生和动物行为学功能恢复。Li等[88]利用PCL/PLGA支架负载人牙囊细胞(hDFCs),可促进移植细胞的存活。Gomez等[89]将PCL制备成微球,并封装反式维甲酸(RA),然后与人诱导多能干细胞(hiPSCs)共培养,可使神经元标记相关蛋白TUJ1表达增加。采用电纺丝制备RA/PCL支架并负载hiPSCs后,可促进干细胞向神经元分化。

      PCL常被用于电纺丝制备各种膜纤维结构。Gelain等[90]利用电纺丝制备PCL/PLGA复合微管支架,用RADA16修饰负载生长因子,不仅促进了轴突沿着电纺丝纤维方向定向再生,而且促进了血管再生和动物行为学功能恢复。Lam等[91]利用电纺丝制备的3D纳米纤维水凝胶支架负载小非编码RNA和蛋白质后,未引发过度炎症反应和瘢痕组织形成,并可促进轴突再生。

      (2)PLLA:PLLA无毒、在体内可以被代谢吸收、机械加工性能良好[92, 93],而且获得各国食品和药品管理局(FDA)的批准[94, 95]

      PLLA支架本身不仅能填充空洞起到桥接作用,而且能够促进细胞迁移、轴突再生并与周围宿主组织整合,最终促进动物行为学功能恢复[96]。移植PLLA多孔多通道支架,可以促进细胞的黏附,减少损伤区域空洞的形成和轴突的再生[97, 98]

      由于纳米纤维结构的PLLA支架与中枢神经系统的ECM结构相似,因此它在神经组织工程中得到了广泛应用。PLLA纳米纤维结构支架比表面积大、孔隙率高、孔径分布宽(50~350 nm)[99, 100],可以促进神经干细胞分化为神经元[101]。全大萍课题组[102, 103]利用低温相分离-模具注射技术制备出微纳米纤维结构的PLLA多通道神经导管(图4),体外细胞种植NSC后,纳米纤维结构的支架更有利于NSC分化为神经元,将其移植入脊髓损伤动物模型中,可以减少炎症细胞聚集、星形胶质细胞的反应性增生和胶原纤维的沉积,促进神经再生,并沿通道定向生长,最终促进动物行为学功能恢复。

      图  4  PLLA多通道导管制备装置示意图和不同结构多通道导管横截面的SEM照片[102]

      Figure 4.  Scheme of the systematized device for fabrication of multi-channel conduits and SEM images of the multi-channel conduits cross section[102]

      纳米纤维结构支架是细胞和因子移植的理想载体。Patist等[104]移植负载BDNF的PLLA支架,促进了轴突和血管的再生。Binan等[105]采用电纺丝技术,制备出以PLLA为核,明胶负载视黄酸小分子为壳的双层结构纤维支架,它可以促进NSC增殖并定向分化为运动神经元。Hurtado[106]利用PLLA负载SC促进了轴突再生和动物行为学功能恢复。Sun等[107]采用PLLA纳米纤维多通道支架导管内填充负载NT3的明胶海绵,移植入全横断脊髓损伤模型中,可以减少炎症细胞的激活和胶原纤维的沉积,促进神经干细胞募集并分化为神经元,促进动物行为学功能恢复。

      (3)PLGA:PLGA是乙交酯和丙交酯的无规共聚物,可生物降解、无毒性且易成膜,用于制作神经组织工程中的支架时,可调控其渗透率、变形、柔韧性等[108-110]。目前,PLGA不仅可以制备成导管和水凝胶支架,而且可以制备成微球作为因子或药物的载体[111]

      全大萍课题组[112, 113]采用模具灌注的方法,制备了PLGA多纵向通道支架负载NT3,经体外NSC和SC共培养后,可以将NSC分化为成熟神经元,并表达突触小泡蛋白[114]。移植入脊髓损伤动物模型中,支架内有神经突触形成并表达突出小泡蛋白。Teng课题组[115]利用由PLGA与多聚赖氨酸制备的多通道支架负载NSC治疗脊髓损伤,可使轴突再生标志蛋白GAP-43表达上调。

      Langer课题组[116]研制的PLGA多孔结构支架,可减少炎性细胞聚集,减少星形胶质细胞增生,促进轴突再生。Shea课题组[117-120]采用发泡-微粒过滤-模具成型的方法制备出的不同通道和不同孔隙率的PLGA微孔支架,可随着通道数目的增多,使再生轴突密度也增加,孔隙率较高的支架能促进更多细胞迁移到损伤区域。Yaszemski课题组[121]研究证实,22通道较7通道支架中的再生轴突提高了7倍,450 μm通道内的轴突数量是660 μm通道内的2倍,纤维组织环的面积则减少了1/2。

      (4)PEG :水溶性聚醚类聚合物PEG是一种表面活性剂,它可以促进细胞膜的流动和融合,降低细胞膜的通透性[122]。在急性脊髓损伤阶段,PEG可以封闭细胞膜,对神经细胞产生保护作用[123, 124]。Kim[125]和Ren[126]等分别将PEG600直接移植于急性和慢性脊髓损伤动物模型中,减少了炎性细胞迁移到损伤区域并促进了轴突再生。

      另外,PEG也可与其他材料复合作为细胞或因子的载体,实现因子的持续缓慢释放。Lampe将PEG水凝胶与PLGA微球复合并负载BDNF和GDNF后,可以明显减少胶质瘢痕的形成[127]。Grous等[128]将聚异丙基丙烯酰胺(PNIPAAm)与PEG水凝胶复合并负载BDNF后,可促进轴突生长和动物行为学功能恢复。Li等[129]将PEG交联HA和明胶制备的复合水凝胶支架,负载少突胶质细胞后,可促进细胞的存活和再生轴突的髓鞘化。Piantino等[130]制备的PEG水凝胶支架偶联NT3后,可以促进轴突再生和改善动物行为学功能。

      (5)自组装多肽(SAP):SAP是通过设计氨基酸序列,依据温度和pH变化自组装而成的纳米纤维水凝胶支架[131]。SAP孔隙率高、比表面积大,有利于细胞的黏附和增殖,同时其生物相容性好,可降解吸收,易功能化等特性[132-134],使其在脊髓损伤组织工程修复中应用比较广泛。SAP的主要缺点是成本高,水凝胶的力学性能不足[135, 136]

      研究证实K2(QL)6K2自组装水凝胶可以减少损伤区域炎症反应和胶质瘢痕的形成,促进轴突再生和动物行为学功能恢复[137, 138]。本课题组[139]利用RADA16-IKVAV负载CNTF, aFGF, EGF, PDGF-AA和RADA16-RGD负载BDNF, NT-3, IGF, bFGF, GDNF, β-NGF,制备的功能自组装多肽(F/S)水凝胶(图5),植入脊髓损伤动物模型中,可以促进损伤区域内源性神经干细胞的募集、增殖,并向神经元方向分化,促进髓鞘化轴突再生和最终动物行为学功能的恢复。

      图  5  含生长因子的F/S水凝胶的形态特征:(a)含有生长因子的RADA16-IKVAV溶液与RADA16-RGD溶液混合形成的稳定水凝胶;(b)F/S水凝胶纤维和(c-e)不同生长因子的水凝胶纤维的AFM照片[139]

      Figure 5.  Morphological characteristics of the F/S hydrogel containing growth factors: (a) Stable hydrogel was formed by combining RADA16-IKVAV solution containing growth factors and RADA16-RGD solution;(b) Images of F/S hydrogel fiber and (c-e)those with different growth factors [139]

    • 在脊髓损伤组织工程修复中,生物材料支架移的主要作用是提供物理桥接和引导作用,以及作为种子细胞或生物活性因子的载体。目前,常见的支架类型主要有可注射用水凝胶支架和预制成型植入型支架两种。

    • 水凝胶具有如下优点:(1)很好的生物相容性;(2)伴随着组织再生可通过水解和酶的方式降解;(3)物理结构可调控,孔隙率高、渗透性强,有利于细胞的黏附、迁移和生长;(4)较高的含水量和微纳多孔结构,是因子和细胞的理想载体,也可为细胞提供营养代谢和物质交换场所;(5)可注射,适合于挤压伤、挫伤、全/半横断模型,特别是在挤压伤模型中,通过微创的方式注射到损伤区域,可以根据损伤区域的结构特点自行形成与损伤结构契合的支架形态[140, 141]。主要缺点是的强度较低、降解速率过快,不能够满足移植细胞的长期存活和组织再生需要,这也是限制可注射水凝胶的应用的关键因素。根据水凝胶的材料来源,可注射水凝胶可以分为人工合成材料水凝胶(聚乙烯醇类、聚丙烯酸及其衍生物等)[142, 143]和天然材料来源水凝胶(蛋白质类、多糖类等)[144, 145]

    • 预制成型支架制备工艺主要有:相分离、注射成型、气体发泡、熔融铸造和3D打印等技术。制备的支架主要类型为:多孔海绵、导管和3D设计模型。预制成型支架是一种在体外制备成型,需要开放性手术植入损伤区域的一种支架。这种支架的特点是:(1)可根据研究目的制备具有特定宏观和微/纳米结构的支架;(2)降解速率慢,可长期为轴突生长和组织再生提供支撑和引导作用;(3)主要适用于规整的半横断或全横断的损伤模型中;(4)作为细胞或因子的载体,可以实现对细胞或因子的长时间负载和缓慢释放[146]

      研究显示,预制成型支架在脊髓损伤修复中具有重要作用,并且支架的宏观结构形态、微/纳结构、机械强度、表面性能、降解速率和化学生物活性分子组成等相关参数等对细胞的命运、损伤微环境的改善和轴突再生等均有不同程度的影响,但目前仍然有很多问题需要深入探索。多孔海绵结构和3D打印技术(图6)在脊髓损伤中的研究主要作用体现在支架的桥接、负载细胞和生长因子等方向,对支架的内部精细结构并没有详细的探讨[147]。另外,3D打印技术还处于探索阶段,后续的细胞和动物学研究相对较少。本节主要介绍神经导管在脊髓损伤中的研究进展[148, 149]

      图  6  模拟脊髓结构的3D打印支架:(a)3D打印机系统装置;(b)3D打印机打印的连续层结构;(c)正常大鼠脊髓轴突NF200染色结果(上方白质中轴突高度排列成平行阵列,下方灰质中轴突为无序结构);(d)脊髓中相关功能轴突线状排列区域(束)(运动系统用绿色表示,感觉系统用蓝色表示)

      Figure 6.  3D-printed scaffold mimics the spinal cord architecture: (a) 3D-printer setup; (b) 3D printing creates a structure with one continuous layer; (c) Heavy chain neurofilament (NF200) labeling of axons in rat spinal cord (The axons in the white matter (top of the panel) are highly organized into parallel arrays traveling from rostral to caudal. The axons in the gray matter (bottom of the panel) are not linear);(d) Axonal projections in the spinal cord are linearly organized into regions (fascicles) containing axons of related function (Motor systems are shown in green and sensory systems are shown in blue)[147]

      神经导管(NGC)是由生物材料制成的一种用于神经修复的支架。神经导管的几何管状结构是由神经内膜、神经束膜和神经外膜演化而来,可以设计成不同的形状,如管状、纤维状和矩阵型[150]。设计最初目的是为了替代神经移植。在神经导管修复的过程中,通道对轴突生长的引导机制被称为接触导向机制,并且可以结合功能需要对形貌、纤维走向,表面光滑度等进行设计以改善其性能[151]。另外神经导管与细胞、ECM和神经营养因子的结合,可以有效模拟有利于轴突再生的微环境,这一支架结构特点被称为人工细胞外基质或信号龛。研究表明这种修复适用于短距离(4 cm)内的神经损伤,可以引导神经再生,并防止神经的异常再生[152-154]

      影响神经导管性能的主要因素有:(1)渗透性,决定了导管内外营养成分的交换,调控不同种类细胞的渗入;(2)弹性,确保损伤界面周围组织不被压迫损伤;(3)膨胀和降解,降解产物的积累会导致导管的膨胀压迫周围组织,因此需要通过调控通道数目、大小和共聚物等来控制导管的膨胀程度[155]。另外,在神经再生过程中,导管降解性应遵循一定的趋势,确保对轴突的引导作用,并根据轴突生长的需要降解退出;(4)表面弯曲,可为轴突的生长提供引导信息;(5)合并微丝,可为轴突生长提供形貌引导[21]

      近几年来,神经导管的研究相对较多的是通道的引导作用,但到目前为止研究仍然不够充分,一些参数仍需要优化,如通道壁的结构仍是值得关注的问题,通道壁及通道之间不同纤维/超微结构对轴突的接触导向及损伤微环境的调节亦是亟待解决的问题。

    • 天然ECM是由多种蛋白质、蛋白聚糖、糖蛋白、氨基聚糖和纤维等构成的3D微/纳米纤维结构网络,纤维直径50~500 nm。组织工程支架修复脊髓损伤的另一个重要策略就是模仿天然ECM结构,并负载生物活性物质,调控细胞行为和组织再生微环境[156]。支架在宏观结构上的合适孔径,有利于营养交换和细胞的迁移和长入;在微观结构上其特定的微/纳米纤维结构,可调控细胞的行为[157]

      组织工程支架材料的种类、硬度及材料的结构(孔隙,沟槽,多通道及纤维尺寸等)性能可以调节脊髓损伤处的微环境。另外,支架材料的微纳拓扑结构可以影响细胞的黏附、增殖、迁移和分化等命运[158],而且可以影响细胞-基质之间的相互作用[15, 159]。纳米纤维结构比表面积较大,有利于促进蛋白的吸附,进而有利于细胞的黏附、增殖和神经干细胞向神经元方向分化。纳米纤维结构支架较多孔结构支架可更明显地调控不同种类细胞渗入损伤区域,减少炎症细胞的渗入、星形胶质细胞增生和胶原纤维沉积在损伤区域,促进损伤区域神经干细胞的募集和轴突再生,促进巨噬细胞向M2型极化[160]。而微纳米纤维结构如何调控细胞行为,以及其调控微环境的机制均不清楚,仍需要探索和研究。

    • 目前,静脉注射、腹腔注射和鞘内注射等主要给药方式存在局部易感染、二次损伤、药物流失,半衰期短等特点。因此,迫切需要一种稳定长效的给药方法。生物支架材料作为药物或因子的负载和递送系统,不仅对药物起一定的保护作用,同时可以为损伤区域提供稳定持续的给药微环境,最大限度地发挥药物对微环境改善和对轴突再生的促进作用。目前,在中枢神经再生中关于生物支架材料相关负载因子并控制释放的研究主要集中在以下几个方面(详见表1):(1)聚合物微/纳颗粒,主要用于亲水性和疏水性分子药物的控制释放;如:PLGA,PCL等微/纳米颗粒;(2)化学交联,主要是采用交联剂将生物活性因子与材料以化学键的方式结合,主要应用在合成材料;(3)物理共混,一种是直接将生物活性因子与生物材料混合,随着材料的降解逐步释放因子;另一种是根据物质带电荷和亲疏水等性能的不同,使材料与因子相互吸附,从而将因子固定在材料表面和内部,常见于水凝胶(SAP、透明质酸等)、聚合物支架(PCL等)和电纺丝纤维内部等负载因子;(4)复合材料缓释系统,主要是聚合物或水凝胶支架与微/纳米颗粒复合,这种方法能为因子的释放提供更好的定位,并实现顺序释放;另外一种常见的支架材料复合释放系统,即生物活性材料负载因子修饰聚合物支架,在生物活性材料降解的过程中,实现因子的释放。复合材料释放系统,通过设计既可以实现生物活性因子的持续稳定释放,而且可以根据材料的特点,特定设计生物活性因子的释放空间、地点和顺序,不同的损伤修复阶段释放不同的有效因子,将会为神经修复提供最有效的帮助[12,161, 162]

      Types of drug delivery strategiesBiomaterialsFactorOutcomeFrom
      Polymer micro/nanoparticlesPLGANGF and GDNFThe neurotrophins were released over 6 weeks in vitro and resulted in both tissue regeneration and functional improvements[163164]
      PLGAGDNFpromoted axon growth and functional improvement after SCI[165]
      nanoparticle20 nm nanoparticles were found along the spinal cord both rostral and caudal to the injection site, while 100 nm nanoparticles remained at the injection site[166]
      PEGnanoparticlelimit protein adsorption and macrophage engulfment[167]
      Short peptide series nanoparticleenhance nanoparticle deliveryacross the BBB[168]
      PLGA nanoparticleChABCDegraded glial scar, promoted functional recovery and axonal regeneration[169]
      Chemical crosslinkL-lactide, L-LA andε-caprolactone, ε-CLLoad factors[170]
      Electrospun collagen nanofibers,microbial transglutaminase (mTG)NT3Proteins were loaded at an efficiency of approximately 45%-48%, a sustained release of NT3 was obtained[171]
      collagenNT3, BDNF, bFGF, EphA4LBD and PlexinB1LBDFacilitated axonal and neuronal regeneration, remyelination and synapse formation of regenerated axons after SCI[34, 35, 37, 38]
      Physical blendFibrin gelsNT3, BDNFChABC, Rho inhibitor, GethrinPromote axonal regeneration and functional recovery[172, 173]
      hyaluronan/methyl cellulose (HAMC) hydrogelFGF2Increased angiogenesis[174]
      hyaluronan/methyl cellulose (HAMC) hydrogelerythropoietin(EPO)Attenuated inflammatory response and promoted neurogenesis[175]
      PCL core-shell structuresRetinoic acidsustained released of RA was obtained for at least 14 days, enhanced MSCs neuronal differentiation[176]
      PCL core-shell nanofibersAlbumin and lysozymeThe released lysozyme maintained its structure and bioactivity[177]
      PCL core-shell nanofibersplatelet-derived growth factor (PDGF)The protein with near zero-order kinetics and preserved bioactivity[178]
      Self-assembling peptide hydrogels FAQ SAPsChABCChABC was continuously released in vitro for 42 days, favored host neural regeneration and behavioral recovery[179]
      Particle/scaffold compositesPLA-PEG-PLAPLGA microparticlesGDNFBDNFBDNF was slowly released over a 56-day period, whereas a bolus of GDNF was released around 28 days[127]
      PLA-PEG-PLAhydrogelsPLGA microparticlesCNTFCNTF released from a degradable hydrogel was able to stimulate outgrowth of a significantly higher number of neurites[180]
      PLGmicroparticlesTGF-β1Expression of cytokines TNF-alpha, IL-12, and MCP-1 were decreased by at least 40% .[181]
      HAMCPLGA micro/nanoparticleFGF2Increased the density of neovascularization in the injured area.[182]
      Functional Multichannel Poly(Propylene Fumarate)-Collagen ScaffoldNT3Facilitated axonal and neuronal regeneration, remyelination and synapse formation of regenerated axons after SCI[36]
      PLLAGelatinNT3Decreased inflammatory responses and collagen/astrocytic scar formation. Promoted axonal regeneration and functional restoration[107]
      PLGA Multifunctional, multichannel bridgesHA microparticlesNT3BDNFEnhance axonal growth and promote regeneration[118]

      表 1  生物材料支架负载生物活性因子的研究

      Table 1.  Investigations of biomaterial scaffolds loaded with neurotrophic factors

    • 生物材料支架在脊髓损伤修复研究中已经取得了较大进展,但仍然存在诸多问题,生物材料支架如何再现天然细胞外基质的功能,在材料的制备过程中,其生物力学、模量、多孔结构、微纳米结构等性能的调控以及对细胞行为的影响仍然是未来需要研究的重点。

      目前,转化医学已经成为衡量一个国家生命科学与医学发展水平的重要标志之一,生物材料作为转化医学的重要组成部分,在包括脊髓损伤在内的多种疾病治疗中有着巨大的应用潜力及市场需求。然而,生物材料支架移植在脊髓损伤中的临床应用还有很长的路要走。生物材料支架本身性能对细胞行为和微环境调控的机制仍不清楚,需进一步阐明神经调控及修复等机制,为生物材料在脊髓损伤临床转化中的应用奠定坚实的基础。

      生物材料同时又是组织工程再生修复的核心,更好地利用生物材料这个载体,结合细胞、生物活性因子、药物等调控脊髓损伤再生微环境,重建神经功能环路,是未来脊髓损伤修复研究中的核心内容。

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