【作者】 刘彬；

【导师】 蔡绍皙； 李校堃；

【作者基本信息】 重庆大学 ， 生物医学工程， 2008， 博士

【摘要】 由各种外伤原因所导致的周围神经损伤或者断裂,会给伤者造成肢体感觉和运动功能的下降或者丧失。对于周围神经断裂类的损伤,若断裂缺口较大时,就须借助于对缺口进行桥接移植手术才能使断裂了的周围神经得到再生修复。目前采用的移植体有自体移植体和神经支架,但自体移植来源有限且会带来供体部位的后遗症。在神经支架研究方面,由于非降解材料可能导致神经压迫和二次手术的必要性,所以近年的工作主要趋向于生物可降解支架材料的研究和开发。截至2006年底,美国FDA已经批准了NeuraGen、SaluBridge、Neurolac、Neuro Matrix、Neuroflex和Neurotube等品牌的神经导管用于临床;我国也有几家单位正在申报国家三类医疗器械批文。尽管如此,由于所使用的材料不同,其促周围神经损伤修复的效果也很有差异;同时,它们基本都不适用于长段神经缺损的修复,故开展神经支架的研究仍有必要。基于以上原因,本论文拟研制出一种以猪皮来源的细胞外基质(ECM)粉末和聚乳酸-聚羟基乙酸共聚物(PLGA)为主要原料、对神经生长因子(NGF)有缓慢释放功能的促周围神经损伤修复的支架;通过体外检测及动物实验来评估其作为促周围神经损伤修复支架的可行性。具体内容主要包括以下几个方面:①制备出了猪皮来源的ECM粉末。经H.E染色及扫描电子显微镜观测,没有观测到细胞残留;经琼脂糖凝胶电泳分析,未检测到核酸残留。②制备出了具有生物活性的NGF明胶微球。经激光粒径分布仪检测,微球的粒径介于1μm和20μm之间,平均粒径主要分布在8μm和12μm之间;毛细管电泳检测结果显示微球对NGF的封载率为80.50%。③通过添加弱碱性物质,达到了中和PLGA在降解过程中所产生的酸性产物以稳定组织pH的目的。对于纯的PLGA,随着降解时间的推移,降解液的pH值逐渐下降;不同种类的弱碱性调节剂与PLGA复合后都能对降解液的pH起到一定的调节作用,但效果各异;相同种类的弱碱性添加剂对降解液pH的影响与添加百分比相关;碳酸氢钠的调节作用最明显,使降解液的pH值一直处于碱性状态;壳聚糖的调节功效相对较平稳缓慢,使降解液的pH值一直处于酸性状态和平稳下降趋势;而碱性氨基酸添加剂的作用则处于中间状态,先使降解液上调成碱性,然后再下调为酸性,使降解液的pH值保持在中性附近;当组氨酸的添加量为5%和10%时,对降解液pH的影响差异不显著;而当添加剂为精氨酸和赖氨酸时,在高添加剂量下其对降解液pH值的影响比在低添加剂量下的作用更显著;当赖氨酸的添加量为5%时,在试验考察期内,其使降解液的pH值保存在7.28~6.62间,是最适合的添加方式。④通过对由PLGA和ECM的不同混合比例所制备的支架进行比较发现,随着支架中ECM含量的增加,材料中的孔隙的在形态及孔径的大小分布上越不均匀;材料的断裂强度逐渐增大,当ECM含量在达到20-30%时为最大值,然后逐渐降低;材料的断裂伸长率逐渐降低;吸水率逐渐增大;失重率逐渐增大;降解速率逐渐增大。综合评价认为,材料中ECM的最佳含量应在20-30%。⑤通过对不同组织工程原材料的筛选以及配伍比例的探讨和制备方法的摸索,制备出了目标支架。⑥体外测试结果显示,本目标支架的断裂强度为8.308MPa,断裂伸长率为38.98 %,弹性模量为77.27 MPa。扫描电子显微镜观测发现,支架中PLGA和ECM发生了物理共混并形成了蜂窝状结构。在8周的考察期内,支架质量损失了15.6%,羟脯氨酸的累计释放率为62.8%。在第30d仍能检测到支架对NGF的释放。扫描电子显微镜观测结果显示雪旺氏细胞(SC)能够在支架上粘附、穿行。⑦动物实验初步实验结果显示,本目标支架在兔坐骨神经部位生物相容性良好,无炎症反应,无过敏反应。通过对动物实施本目标支架移植后,在术后第5周术部神经实现了愈合,在术部神经的愈合中有雪旺氏细胞的参与。综上所述,本支架具有对NGF进行缓慢释放的功能并保持了NGF的生物活性;无细胞毒性,并对雪旺氏细胞的生长有促进作用;其三维结构为雪旺氏细胞在支架中的穿行提供了前提;其力学指标和生物可降解特性符合神经支架的要求;在支架中添加弱碱性物质是中和PLGA在降解过程中所产生的酸性物质的有效方法。本支架的力学性质、生物活性、生物相容性、生物可降解性符合神经支架的要求,可以作为一种候选的神经支架。更多还原

【Abstract】 Peripheral nerve defects caused by various kinds of trauma can result in motor and sensory disabilities. Direct end-to-end suturing is suggested for a short nerve injury. For larger nerve defects or gaps, implantation of a nerve graft is often necessary to bridge the proximal and distal nerve stumps for facilitating nerve regeneration and functional recovery. At present, to recover the disrupted nerve is clinically carried out by autograft, but there still exist certain limits and disadvantages: the donator source limitation for autograft, and the accompanying risks in harvesting autograft. To overcome those disadvantages, artificial nerve scaffold has been developed and showed great potentiality. In recent research, biodegradation never conduits have attracted much more attention. By the end of 2006, there are some conduits that were FDA approved for clinic, including SaluBridge Nerve cuff, Neurolac nerve conduit, Neuro Matrix, Neuroflex and Neurotube. In our country, a few of institutions are applying for national medical equipment certificates. However, different kinds of conduits have different effectiveness on nerve regeneration. In addition, these present treatments are served for small defects (several millimeters) and do not address larger peripheral nerve injuries. Thus, it was deserved to further develop new nerve scaffolds to satisfy the requirement of clinical using.Polylactic acid-polyglycolic acid (PLGA) has been widely utilized in tissu engineering, due to its good biocompatibility, biodegradation and easy fabrication. But the scaffold fabricated by PLGA is fragile and hard. So it is essential to compounded PLGA with other kinds of materials in order to improve its biomechanics. Meanwhile, acidity from PLGA degradation in vivo could result in local acid collection, which would change the pH stabilization of tissue. Thus how to overcome this problem is should be taken consideration.Moreover, studies confirm the addition of nerve growth factors [NGFs] into artificial nerve scaffold can promote its regeneration and repair, however, due to the very short half-life time of NGFs in vivo, thus sustained release of NGFs is required for them to function better.It is well known that porcine-derived extracellular matrix (ECM) has good biocompability and will not cause the risk that sufferer is infected with porcine endogenous retrovirus. ECM, which is composed with collagen and a little laminin and fibronectin, has been shown to play a significant role in axonal regeneration. However it is difficult to fabricate a nerve scaffold with ECM molecules directly. As porcine-derived ECM has favourable hydrophilicity and water insoluble, we mixed ECM with PLGA to fabricate a compound conduit, which could keep its shape in vivo for a long time.In this study, we manufactured a compound nerve scaffold with porcine-derived ECM and PLGA, which could release NGF sustainly. The compound scaffold was evaluated by vitro testing and animal experiments. The concrete contents are as follows:①Porcine-derived extracellular matrix was prepared by enzymolysis. The matrix was underwent H-E Staining, SEM observation and DNA remains assay to ensure the pigskin free of cell. It was seen cells have been completely removed by H.E staining and scanning electron macrograph (SEM) observation. The result of DNA remains assay showed that there is no DNA band in acellular matrix.②Gelatin microballoon with bioactive NGF was fabricated. By laser particle diameter distribution device testing, it was found that the particle diameter was range from 1μm to 20μm and the mean diameter from 8μm to12μm. The encanpsulation ratio of NGF is 80.50% by capillary electrophoresis.③Alkaline substance added into the scaffold could neutralize acidoid from degradation of PLGA to maintain tissue pH. As for pure PLGA, the pH of degradation solution will decrease gradually as it was degradated in purified water. Variety kinds of weak base moderators, which were combinated with PLGA, could regulate the pH of degradation solution. But the regulated effectiveness vary with the kinds of moderator and the percentage of moderator added to the PLGA. According to our experiment, all the basic additives investigated in the experiment showed good potential to relieve the level of acid collection in the course of PLGA degradation. Among those, the relieving ability of NaHCO3 was in the top, basic amino acid in the moderate, while Algin and chitosan ranked lower. 5% addition of Lysine produced a best outcome that is the pH remainning at 7.28~6.62.④Comparing the compound scaffolds with different mixture ratio of PLGA and ECM, the results were as follows : (1) The pore diamater and the appearance were vary with the increasement of the content of ECM in the scaffold; (2)the breaking strength increased up to the peak with the extent of ECM in the scaffold increasing to 20%~30%; (4) the breaking extensibility decreased gradually with increment of ECM in scaffold; (5) the max water-uptake and mass losing rate of conduits increased with the increment of ECM in the scaffold during the degradation period. By comprehend evaluation; it is considered that the most optimization content of ECM in scaffold is about 20%~30%.⑤Target scaffold has been fabricated.⑥According to test in vitro, the result displayed as follows: (1)Mechanical testing showed that the breaking strength was about 8.308MPa, the breaking extensibility was about 38.98 % and the elastic modulus was about 77.27 MPa. (2) SEM result showed PLGA has mixed with ECM to form cellular structure. (3) During 8 weeks of degradation in vitro, and the mass loss ratio was about 15.6%, the accumulative releas rate of hydroxyproline is 62.8%. (4) The release of NGF could be still detected on the 30th day. (5) Cells could adhere to the scaffold and extend on it.⑦The results of animal experiment suggested that the scaffold implanted into rat’s sciatic nerve has good biocompatibility, no inflammation and is free of hypersensitive response.To sum up, the scaffold could release NGF sustainedly and protect NGF from denaturation; it was free of cytotoxicity and could promote Schwann cells’growth; it’s three dimensional structure is the prerequisite of SCs extended on it; it has appropriate mechanics property and good bio-degradablity; Addition alkaline substance is an effective method for neutralization acidoid from PLGA. So the compound scaffold may be a potential artificial nerve scaffold.更多还原