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Membranized Coacervate Microdroplets: from Versatile Protocell Models to Cytomimetic Materials
Accounts of Chemical Research ( IF 16.4 ) Pub Date : 2023-01-10 , DOI: 10.1021/acs.accounts.2c00696
Ning Gao 1, 2 , Stephen Mann 1, 2, 3, 4
Affiliation  

Although complex coacervate microdroplets derived from associative phase separation of counter-charged electrolytes have emerged as a broad platform for the bottom-up construction of membraneless, molecularly crowded protocells, the absence of an enclosing membrane limits the construction of more sophisticated artificial cells and their use as functional cytomimetic materials. To address this problem, we and others have recently developed chemical-based strategies for the membranization of preformed coacervate microdroplets. In this Account, we review our recent work on diverse coacervate systems using a range of membrane building blocks and assembly processes. First, we briefly introduce the unusual nature of the coacervate/water interface, emphasizing the ultralow interfacial tension and broad interfacial width as physiochemical properties that require special attention in the judicious design of membranized coacervate microdroplets. Second, we classify membrane assembly into two different approaches: (i) interfacial self-assembly by using diverse surface-active building blocks such as molecular amphiphiles (fatty acids, phospholipids, block copolymers, protein–polymer conjugates) or nano- and microscale objects (liposomes, nanoparticle surfactants, cell fragments, living cells) with appropriate wettability; and (ii) coacervate droplet-to-vesicle reconfiguration by employing auxiliary surface reconstruction agents or triggering endogenous transitions (self-membranization) under nonstoichiometric (charge mismatched) conditions. We then discuss the key cytomimetic behaviors of membranized coacervate-based model protocells. Customizable permeability is achieved by synergistic effects operating between the molecularly crowded coacervate interior and surrounding membrane. In contrast, metabolic-like endogenous reactivity, diffusive chemical signaling, and collective chemical operations occur specifically in protocell networks comprising diverse populations of membranized coacervate microdroplets. In each case, these cytomimetic behaviors can give rise to functional microscale materials capable of promising cell-like applications. For example, immobilizing spatially segregated enzyme-loaded phospholipid-coated coacervate protocells in concentrically tubular hydrogels delivers prototissue-like bulk materials that generate nitric oxide in vitro, enabling platelet deactivation and inhibition of blood clot formation. Alternatively, therapeutic protocells with in vivo vasoactivity, high hemocompatibility, and increased blood circulation times are constructed by spontaneous assembly of hemoglobin-containing cell-membrane fragments on the surface of enzyme-loaded coacervate microdroplets. Higher-order properties such as artificial endocytosis are achieved by using nanoparticle-caged coacervate protocell hosts that selectively and actively capture guest nano- and microscale objects by responses to exogenous stimuli or via endogenous enzyme-mediated reactions. Finally, we discuss the current limitations in the design and programming of membranized coacervate microdroplets, which may help to guide future directions in this emerging research area. Taken together, we hope that this Account will inspire new advances in membranized coacervate microdroplets and promote their application in the development of integrated protocell models and functional cytomimetic materials.

中文翻译:

膜化凝聚层微滴:从多功能原始细胞模型到细胞模拟材料

尽管源自反电荷电解质的缔合相分离的复杂凝聚层微滴已成为自下而上构建无膜、分子拥挤的原始细胞的广泛平台,但封闭膜的缺失限制了更复杂的人造细胞的构建及其使用作为功​​能性细胞模拟材料。为了解决这个问题,我们和其他人最近开发了基于化学的策略,用于预制凝聚层微滴的膜化。在这个帐户中,我们回顾了我们最近使用一系列膜构件和组装工艺在不同凝聚层系统上的工作。首先,我们简要介绍凝聚层/水界面的不寻常性质,强调超低界面张力和宽界面宽度作为理化特性,在膜化凝聚层微滴的明智设计中需要特别注意。其次,我们将膜组装分为两种不同的方法:(i)通过使用不同的表面活性构建块进行界面自组装,例如分子两亲物(脂肪酸、磷脂、嵌段共聚物、蛋白质-聚合物缀合物)或纳米级和微米级物体(脂质体、纳米颗粒表面活性剂、细胞碎片、活细胞)和适当润湿性;(ii)通过使用辅助表面重建剂或触发内源性转变(自膜化)来凝聚液滴到囊泡的重构)在非化学计量(电荷不匹配)条件下。然后我们讨论基于膜化凝聚层的模型原始细胞的关键细胞模拟行为。可定制的渗透性是通过分子拥挤的凝聚层内部和周围膜之间的协同作用实现的。相比之下,代谢样内源性反应、扩散化学信号和集体化学操作特别发生在由不同种群的膜化凝聚层微滴组成的原始细胞网络中。在每种情况下,这些细胞模拟行为都可以产生能够用于类细胞应用的功能性微型材料。例如,在体外,使血小板失活并抑制血块形成。或者,治疗性原始细胞在体内血管活性、高血液相容性和增加的血液循环时间是通过在载酶凝聚层微滴表面自发组装含血红蛋白的细胞膜碎片而构建的。人工内吞等高阶特性是通过使用纳米颗粒笼状凝聚层原始细胞宿主实现的,这些宿主通过对外源刺激的反应或通过内源酶介导的反应选择性地主动捕获客体纳米级和微米级物体。最后,我们讨论了膜化凝聚层微滴设计和编程的当前局限性,这可能有助于指导这一新兴研究领域的未来方向。综合起来,
更新日期:2023-01-10
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