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方法文章

用于构建血管化组织和类器官的微流控生物打印技术

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DOI:

10.3791/55957

2017年8月11日

* These authors contributed equally

本文内容

摘要

我们提供一种基于微流控生物打印策略的通用方案,用于构建微纤维血管床,其中可进一步将第二种细胞类型接种于该微纤维结构的间隙空间,以生成带血管化的组织和类器官。

摘要

构建具有血管化的组织结构和类器官历来具有挑战性。本文介绍了一种基于微流控生物打印的新型方法,用于生成由多层交错水凝胶微纤维组成的支架。为实现平稳的生物打印,设计了一种包含同轴结构的微流控打印头,该打印头的芯层流动中挤出复合生物墨水,鞘层流动则携带交联溶液,并将其安装于生物打印机上。通过将甲基丙烯酰化明胶(GelMA)与海藻酸盐(一种在特定二价离子存在下可发生瞬时离子交联的多糖)混合,先实现海藻酸盐的快速离子交联,再对GelMA组分进行二次光交联以达到永久性稳定,利用该生物打印策略可获得微纤维支架。重要的是,包埋在生物打印微纤维内的内皮细胞在16天的培养过程中能够形成类似血管的管腔样结构。该内皮化微纤维支架可进一步作为血管床,通过在微纤维的间隙空间中接种第二类细胞,构建出具有血管化的组织。微流控生物打印为高保真、便捷地工程化构建血管化组织提供了一种通用策略。

引言

组织工程旨在构建功能性组织替代物,可用于替换、修复或增强人体内受损或病变的组织1,2,3,4,通常通过目标细胞类型与生物活性分子的组合实现5,6和生物材料7,8,9,10近年来,组织工程技术也越来越多地被用于生成 体外 模拟其重要功能的组织和器官模型 体内 对应物,可用于药物开发等应用,以替代传统的过度简化的平面细胞培养11,12,13,14,15,16,17,18,19在这两种情况下,重现人体组织的复杂微结构和层次化结构的能力,对于实现工程化组织的功能至关重要。10,特别是如何将血管网络整合到工程化组织中,目前备受关注,因为血管化是该领域面临的最大挑战之一20,21,22,23.

迄今为止,已有多种方法被开发用于在工程化组织构建物中形成血管结构,并在不同程度上取得了成功8。例如,内皮细胞的自组装可形成微血管网络24;递送促血管生成生长因子可诱导持续的新生血管化25,26;使用血管前体细胞和周细胞可促进内皮细胞的生长与组装24,27;设计支架材料的特性可实现对血管化的精确调控28,29;而细胞片技术则便于对血管层结构进行便捷操作30。然而,这些策略尚无法实现对血管空间分布模式的控制,常导致工程化组织构建物内血管分布随机,因而可重复性有限。近年来,生物打印技术作为一种具有推动作用的技术类别,因其能够在自动化或半自动化条件下以高保真度和高重复性沉积复杂的组织结构,展现出解决这一挑战的巨大潜力31,32,33。牺牲式生物打印34,35,36,37,38、嵌入式生物打印39,40,41以及中空结构生物打印/生物制造42,43,44,45,46,47,48,49,50,51,52,53均已被证明可实现血管组织或血管化组织的构建。

最近开发出一种用于制备微纤维支架的微流控生物打印策略,该方法通过同轴喷头的内核输送由海藻酸钠和甲基丙烯酰化明胶(GelMA)组成的复合生物墨水,同时通过喷头外层鞘流输送氯化钙(CaCl2)溶液54,55。两种流体的共挤出实现了海藻酸钠组分的即时物理交联,从而形成微纤维,随后的光交联则确保了多层微纤维支架的永久稳定。值得注意的是,包埋在生物打印微纤维中的内皮细胞能够增殖并迁移至微纤维周边,形成类似管腔的结构,模拟血管床54,55。这些经生物打印并内皮化的血管床可进一步接种所需的次级细胞类型,以构建具有血管化的组织55。因此,本方案详细描述了基于同轴喷嘴设计的微流控生物打印策略,为组织工程和类器官建模中的血管化组织便捷制备提供了可行路径。

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方案

本方案中使用的新生大鼠心肌细胞取自2日龄的Sprague-Dawley大鼠,分离方法遵循Brigham and Women's医院机构动物护理和使用委员会批准的成熟操作流程56

1. 生物打印机的仪器安装

  1. 插入较小的钝针(例如,27G,1英寸)作为核心插入较大钝针的中心例如,18G,½英寸)作为鞘管,构建双层同轴微流体打印头;确保内层针头比外层鞘管略长(约1 mm)图1A)。通常通过手动调整对齐,但如有必要,可在内针和外针的尖端及管身两端暂时夹入适当尺寸的垫片,以辅助同心对齐。使用环氧树脂胶密封管身连接处,并在适用时从尖端一侧移除对齐用垫片。
  2. 将另一根针头(23G)反向插入中心针的针管中。  然后在套管针外针的侧壁上打一个孔,将一个尺寸匹配的金属连接器插入孔中,再用环氧树脂胶密封。
  3. 将打印头的两个入口分别通过两根PVC管连接至双通道注射泵,用于单独注入生物墨水和交联溶液。使用聚甲基丙烯酸甲酯(PMMA)制成的塑料支架将挤出装置固定在生物打印机的打印头上。
    注意:生物打印机的选择取决于设备的可获得性。在本研究中,我们已在多种市售生物打印机上成功测试了该装置。然而,原则上,任何配备x-y-z电动载物台的生物打印机均可实现与该微流体打印头的集成。

2. 生物打印微纤维血管床

  1. 使用海藻酸钠(4 w/v%,低黏度)和甲基丙烯酰化明胶(GelMA,1–2 w/v%)混合制备生物墨水57,58,以及光引发剂Irgacure 2959(0.2–0.5 wt.%)溶于含10 vol.%胎牛血清(FBS)的25 mM 2-[4-(2-羟乙基)哌嗪-1-基]乙磺酸(HEPES缓冲液,pH 7.4)中。
  2. 配制 0.3-M CaCl 溶液2 在含有10 vol.% FBS的HEPES缓冲液中作为交联载体溶液。
  3. 生物打印前立即使用0.05 w/v%胰蛋白酶处理5–10分钟,将人脐静脉内皮细胞(HUVECs)从培养瓶中消化下来,并将细胞重悬于生物墨水中,细胞浓度为5–10 × 10⁶ cells/mL6 细胞/mL。用移液器缓慢吹打混悬液5至10次,以确保均匀分布。
  4. 使用双通道注射泵以相同的流速(5 µL/min)开始生物墨水/交联液的注射。可让流体持续运行最多1分钟,直至流速稳定。随后,通过控制生物打印机以约4 mm/s的沉积速度启动打印头运动。图1B)。每次新设置时可能需要对这些速度进行微调,以确保最佳的生物打印效果。生物打印过程通常在室温(21 - 25 °C)下进行,但该温度也可根据需要调整。生物打印过程应能够实现海藻酸盐组分的快速离子交联,并沉积形成微纤维支架(图1B).
  5. 支架生物打印完成后,通过进一步光交联 GelMA 组分实现化学凝胶化,光照强度约为 5 - 10 mW/cm²2 紫外光(360 - 480 nm)照射 20 - 30 秒(图1C).
  6. 生物打印和交联完成后,用磷酸盐缓冲液(PBS)轻轻冲洗支架,以去除多余的 CaCl₂2. 将载有 HUVECs 的微纤维支架置于内皮细胞生长培养基(EGM)中,在 37 °C、5 vol.% CO₂ 的培养箱中进行培养2 培养长达16天,每隔至少2天更换一次培养基。在培养期间,于显微镜下观察HUVECs的形态。

3. 构建血管化组织

  1. 当 HUVECs 迁移至支架微纤维的边缘并形成管腔样结构时(图 1D),取出支架并轻轻将其放置在疏水性表面(例如,聚二甲基硅氧烷 [PDMS] 板)上。使用一片无菌滤纸,利用毛细作用小心地将支架间质空间中的所有培养基去除。
  2. 立即在支架顶部加入一滴(约 20 - 40 µL)以 1 - 10 × 106 个细胞/mL 密度悬浮于培养基中的第二类细胞(例如,心肌细胞),使液滴渗入支架的整个间质空间(图 1E)。将该装置置于培养箱中(37 °C,5 vol.% CO2,95% 相对湿度)孵育 0.5 - 2 小时,以使细胞黏附到各个微纤维上。在此期间监测液滴大小,确保无明显蒸发发生。
  3. 通过在 PBS 溶液中轻轻振荡清洗支架,以去除未黏附的细胞,并将构建物置于相应的培养基中继续培养,直至形成所需的血管化组织。

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结果

微流控生物打印策略可实现利用低粘度生物墨水直接挤出打印微纤维支架54,55如图所示 图2A,一种尺寸为6的支架 × 6 × 6 mm3 含有 >30层微纤维可在10分钟内完成生物打印。海藻酸盐组分与CaCl₂的即时离子交联2 在生物打印过程中保持了优异的结构完整性,而随后对GelMA组分进行的物理光交联则确保了生物打印微纤维支架的长期稳定性,如所示的俯视图和侧视图所示 图2B和图2C在此方案指定的生物打印条件下制备的微纤维直径约为100 - 150 µm 直径会随着时间因肿胀而略有增加。

生物打印过程,包括生物墨水的微流控挤出、离...

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讨论

同轴打印头的构建是实现成功微流体生物打印的关键步骤,可同时从核心输送生物墨水,从鞘层输送交联剂。本方案中,示例打印头采用27G针头作为核心,18G针头作为外壳;但该方法可轻松扩展至使用不同规格针头的多种组合。然而,针头尺寸的改变会导致各相流体输送量发生变化,因此需要进一步优化生物墨水和交联剂的流速(可通过两个独立的注射泵分别调节,而非使用双通道泵),以及可能还需调整生物打印机的沉积速度。

本实验方案中参数(针头尺寸、流速和沉积速度)的组合,使得生物打印的微纤维在沉积后立即形成直径约为120 µm的结构,在培养基中平衡后会膨胀至约150 µm55。由于微纤维层之间无间隙,该尺寸也大致等于生物打印结构的层厚。生物打印微纤维的直径是这三个参数共同作用的结果54,63;打印头核心针头的尺寸和生物墨水流速与微纤维直径呈正相关,而包层针头的尺寸、交联剂的流速以及沉积速度则与微纤维直径呈负相关。通过控制打印头和/或电动平台的运动,可...

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披露

作者声明不存在利益冲突。

致谢

作者谨此致谢 美国国立卫生研究院国家癌症研究所独立之路奖(K99CA201603)

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材料

本文使用的材料清单
姓名公司目录编号评论
来自褐藻的海藻酸钠Sigma-AldrichA0682生物试剂,经植物细胞培养测试,低粘度,粉末状
猪皮来源A型明胶Sigma-AldrichG2500凝胶强度300
光引发剂Irgacure 2959(2-羟基-4'-(2-羟基乙氧基)-2-甲基苯丙酮)Sigma-Aldrich41089698%
HEPES缓冲液Sigma-AldrichH08871 M,pH 7.0 - 7.6,经无菌过滤,生物试剂,适用于细胞培养
胎牛血清 Thermo Fisher Scientific10438026经认证,热灭活,符合美国农业部批准地区标准
二水合氯化钙Sigma-AldrichC5080BioXtra,≥99.0%
磷酸盐缓冲液Thermo Fisher Scientific10010023pH 7.4
人脐静脉内皮细胞Angio-ProteomiecAP-0001人脐静脉内皮细胞(HUVECs)
表达GFP的人脐静脉内皮细胞Angio-ProteomiecAP-0001GFP表达GFP的人脐静脉内皮细胞(GFPHUVECs)
内皮细胞生长培养基LonzaCC-3162EGM-2 BulletKit
Dulbecco’s改良Eagle培养基 Thermo Fisher Scientific12430054高糖,含HEPES
Sylgard 184硅酮弹性体试剂盒Ellsworth Adhesives184 SIL ELAST KIT 0.5KG透明0.5 kg装试剂盒
紫外固化灯系统Excelitas TechnologiesOmniCure S2000带智能紫外传感器的点光源紫外固化系统

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