基于先进生物材料的心肌细胞力——电微环境体外构建

心血管疾病是当前全球范围内导致人类死亡的首要原因, 心肌组织工程的发展为心血管疾病的治疗, 尤其是心肌组织再生修复提供了最有潜力的解决方案.心血管疾病的发生发展与细胞力--电微环境的变化密切相关. 近十几年, 随着先进生物材料和微纳生物制造技术的发展, 越来越多的研究表明, 细胞力--电微环境的调控对工程化心肌组织的成熟和功能化以及心肌组织再生修复具有重要意义. 本文首先阐明了在体心肌细胞所处力学微环境的生物学基础以及电信号的传导过程, 包括正常和疾病状态下心肌细胞所处的力--电微环境.其次调研了用于心肌组织工程的先进生物材料的研究现状.最后总结用于基底硬度与应力应变细胞微环境以及细胞电学微环境的构建和调控, 以及细胞对力--电微环境的生物学响应.%      

CD44-配体相互作用的生物力学与功能调控

作为一种广谱表达的细胞粘附分子, I型跨膜糖蛋白CD44(cluster of differentiation 44)参与细胞增殖、分化、迁移, 血管生成等生物学过程,对于介导细胞信号转导, 调节组织稳态等功能具有关键作用. 特别地,CD44-选择素、CD44 -透明质酸相互作用介导的细胞粘附动力学在经典炎症反应、肿瘤转移或组织特异的肝脏免疫中具有重要作用.该综述分别从细胞层次粘附动力学、二维与三维条件下的分子层次反应动力学、原子层次微观结构以及胞内信号转导通路等方面综述了CD44 -选择素、CD44 -透明质酸相互作用的研究进展及尚待回答的生物力学问题.力学、物理因素对生命活动的不可或缺性逐渐被研究者们接受,力学医学、力学免疫学、力学组学等新概念相继提出. 生理、病理条件下,CD44 -配体相互作用介导的细胞粘附必将受到血流剪切、基底硬度等力学、物理微环境的调控,但是其调控机制还远不清楚. 基于此,本文就CD44 -配体相互作用相关的未来研究方向做出展望, 主要包括:力学、物理因素如何调控CD44 -配体相互作用介导的细胞粘附动力学及其内在机制;CD44 -配体相互作用反应动力学的力学调控规律及结构基础是什么;以及力学作用下CD44 -配体相互作用原子层次的微观结构如何发生动态演化.本文可为深入理解CD44 -配体相互作用的生物学功能及其结构功能关系提供线索.      

骨组织细胞的力学调控研究

力学环境是影响骨组织细胞形成、增殖和功能成熟的一个重要因素. 骨细胞是力学感受细胞, 将力学信号传递给效应细胞; 成骨细胞、破骨细胞为力学效应细胞, 使骨形成和骨吸收处于动态平衡以维持骨力学稳定性. 目前对骨组织细胞间力学调控的机理仍不甚清楚. 综述了骨组织细胞力学生物学作用和细胞间力学调控的一些相关问题. 在概述了成骨细胞、骨细胞和破骨细胞的生物学特性基础上,阐述了骨重建力学调控理论,成骨细胞、骨细胞和破骨细胞生物力学效应和细胞间力学调控最新研究进展. 最后对骨组织细胞三维网络间力学调控研究做出展望.     

基于先进生物材料的心肌细胞力–电微环境体外构建

心血管疾病是当前全球范围内导致人类死亡的首要原因,心肌组织工程的发展为心血管疾病的治疗,尤其是心肌组织再生修复提供了最有潜力的解决方案.心血管疾病的发生发展与细胞力–电微环境的变化密切相关.近十几年,随着先进生物材料和微纳生物制造技术的发展,越来越多的研究表明,细胞力–电微环境的调控对工程化心肌组织的成熟和功能化以及心肌组织再生修复具有重要意义.本文首先阐明了在体心肌细胞所处力学微环境的生物学基础以及电信号的传导过程,包括正常和疾病状态下心肌细胞所处的力–电微环境.其次调研了用于心肌组织工程的先进生物材料的研究现状.最后总结用于基底硬度与应力应变细胞微环境以及细胞电学微环境的构建和调控,以及细胞对力–电微环境的生物学响应.     

Engineering mechanical-electrical cell microenvironment in myocardium using advanced biomaterials

心血管疾病是当前全球范围内导致人类死亡的首要原因, 心肌组织工程的发展为心血管疾病的治疗, 尤其是心肌组织再生修复提供了最有潜力的解决方案.心血管疾病的发生发展与细胞力--电微环境的变化密切相关. 近十几年, 随着先进生物材料和微纳生物制造技术的发展, 越来越多的研究表明, 细胞力--电微环境的调控对工程化心肌组织的成熟和功能化以及心肌组织再生修复具有重要意义. 本文首先阐明了在体心肌细胞所处力学微环境的生物学基础以及电信号的传导过程, 包括正常和疾病状态下心肌细胞所处的力--电微环境.其次调研了用于心肌组织工程的先进生物材料的研究现状.最后总结用于基底硬度与应力应变细胞微环境以及细胞电学微环境的构建和调控, 以及细胞对力--电微环境的生物学响应.%     

细胞骨架生物力学进展

细胞骨架力学作为力学细胞生物学的一个新兴领域, 其研究方法突破传统细胞力学思想, 不再把活细胞简化为皮质膜包着的弹性、黏性或黏弹性连续介质体, 而是基于在细胞变形和功能中发挥重要作用的细胞骨架离散网络结构, 在微/纳米尺度建立一种集细胞形态和功能于一体的离散网络结构. 这种细胞骨架模型作为细胞变形和生化事件调控的纽带, 能从分子层次上阐述细胞运动、能量转换、信息传递、基因表达等重大生命活动的潜在机制,同时也能解释生物大分子间相互作用、受体/配体特异性相互作用、大分子自装配、细胞及分子层次的力学-化学耦合, 为定量研究细胞-亚细胞-生物大分子等在多种力学刺激下的响应建立了良好的平台, 对于理解生物模式形成、生物复杂性以及解决重大生物学难题具有深远意义. 本文基于细胞骨架三维离散网络结构特点及其生物学背景, 从生物力学角度详细阐述近几年国际上流行的细胞骨架模型理论分析和研究成果的最新进展.      

Biomechanics of stem cells

干细胞生物力学作为生物力学的重要分支和前沿学科,近年来在力学-生物学、力学-化学耦合等方面取得了重大进展,已成为生物力学乃至生物医学工程最活跃的领域之一,并对发生物学、干细胞生物学、组织修复、再生医学等相关领域产生重要影响.干细胞具有独特的力学性质,可感知、传递、转导和响应生理力学微环境的改变,从而调控干细胞的生长、分化等功能,体现出典型的力学-生物学耦合特征.本文将对干细胞的力学性质与细胞力学模型、在体力学环境对干细胞生长和分化的影响、干细胞对外界力学刺激的响应等方面加以综述.     

干细胞的生物力学研究

干细胞生物力学作为生物力学的重要分支和前沿学科,近年来在力学-生物学、力学-化学耦合等方面取得了重大进展,已成为生物力学乃至生物医学工程最活跃的领域之一,并对发育生物学、干细胞生物学、组织修复、再生医学等相关领域产生重要影响.干细胞具有独特的力学性质,可感知、传递、转导和响应生理力学微环境的改变,从而调控干细胞的生长、分化等功能,体现出典型的力学-生物学耦合特征.本文将对干细胞的力学性质与细胞力学模型、在体力学环境对干细胞生长和分化的影响、干细胞对外界力学刺激的响应等方面加以综述.     

磁场力及膜曲率对磁敏感薄膜-基底界面 黏附性能的影响与调控

界面黏附和脱黏的可调控在攀爬装置、黏附开关、机械抓手等方面具有重要的应用需求. 针对磁敏感薄膜-基底界面, 开展了薄膜初始曲率及外加磁场对界面黏附性能影响机制的研究. 首先实验制备了具有初始曲率的磁敏感薄膜, 分别开展了具有初始曲率的磁敏感薄膜-基底界面撕脱实验及理论研究, 研究了薄膜初始曲率、弯曲刚度和外加磁场强度对界面黏附性能的影响规律. 实验和理论结果一致表明: 具有初始曲率的磁敏感薄膜-基底界面黏附力随薄膜初始曲率的增大而减小, 而外加磁场能够有效提高界面黏附力;相比于初始零曲率薄膜-基底界面稳态撕脱力与薄膜弯曲刚度无关, 薄膜弯曲刚度减弱了具有初始曲率薄膜-基底界面的稳态撕脱力. 进一步从能量角度分析了界面等效黏附性能, 揭示了薄膜弯曲能、磁场势能、界面黏附能的相互竞争机制. 最后, 基于本文的实验及理论结果, 提出了一种磁场和薄膜初始曲率协同调控的简易机械抓手, 可连续实现物体的拾取、搬运和释放功能. 本文结果不仅有助于理解多场调控的界面可逆黏附机制, 对界面黏附可控的功能器件设计亦提供了一种新方法.      

肿瘤及其微环境的力学问题

肿瘤微环境包括肿瘤细胞、间质细胞、细胞外基质等.其在肿瘤的生长和发展过程中起着关键作用.肿瘤的微环境与正常组织的微环境有着显著的不同.肿瘤中的压应力对微环境有着多方面的影响, 例如, 可调控血管与淋巴管的功能, 造成代谢异常和间质高压, 压缩间隙基质, 增大药物输运的困难, 促进间质细胞变异并诱导肿瘤细胞转移. 因此, 肿瘤中的力学因素引起了广泛关注.本文总结了肿瘤及其微环境力学问题的研究进展, 讨论了肿瘤微环境中应力产生、药物输运、肿瘤转移等问题, 介绍了肿瘤微环境正常化的策略及其对肿瘤治疗的意义.      

Mechanosensing of substrate stiffness regulates focal adhesions dynamics in cell

Cell mechanical recognition of extracellular matrix determines the cell activities and functions. Focal adhesions are part of the cell mechanosensing machinery and, operating at the very dynamic interface between cell and extracellular matrix, can operate this recognition and trigger conformational, functional and behavioral modification of the cell. To investigate how the dynamic of assembly and disassembly of focal adhesion are influenced by the substrate mechanics we developed a novel procedure. The analysis consists of the over time tracking of focal adhesion structures in a stable cell line of NIH/3T3 expressing fluorescent pmKate2-paxillin. From collected signals and by their autocorrelation we evaluated the average lifetime and assembly rate of focal adhesion as function of substrate stiffness. Further, by signals cross-correlation we obtained information about the mechanical nature of cytoskeleton and its network. This quantitative approach to focal adhesion dynamics characterization was presented in this study as an investigation tool for cell mechanobiology.     

Non-slipping adhesive contact between mismatched elastic spheres: A model of adhesion mediated deformation sensor

A generalized JKR model is established for non-slipping adhesive contact between two dissimilar elastic spheres subjected to a pair of pulling forces and a mismatch strain. We discuss the full elastic solution to the problem as well as the so-called non-oscillatory solution in which tension and shear tractions along the contact interface is decoupled from each other. The model indicates that the mismatch strain has significant effect on the contact area and the pull-off process. Under a finite pulling force, a pair of adhering spheres is predicted to break apart spontaneously at a critical mismatch strain. This study suggests an adhesion mediated deformation sensing mechanism by which cells and molecules can detect mechanical signals in the environment via adhesive interactions.     

Some basic questions on mechanosensing in cell–substrate interaction

Cells constantly probe their surrounding microenvironment by pushing and pulling on the extracellular matrix (ECM). While it is widely accepted that cell induced traction forces at the cell–matrix interface play essential roles in cell signaling, cell migration and tissue morphogenesis, a number of puzzling questions remain with respect to mechanosensing in cell–substrate interactions. Here we show that these open questions can be addressed by modeling the cell–substrate system as a pre-strained elastic disk attached to an elastic substrate via molecular bonds at the interface. Based on this model, we establish analytical and numerical solutions for the displacement and stress fields in both cell and substrate, as well as traction forces at the cell–substrate interface. We show that the cell traction generally increases with distance away from the cell center and that the traction-distance relationship changes from linear on soft substrates to exponential on stiff substrates. These results indicate that cell adhesion and migration behaviors can be regulated by cell shape and substrate stiffness. Our analysis also reveals that the cell traction increases linearly with substrate stiffness on soft substrates but then levels off to a constant value on stiff substrates. This biphasic behavior in the dependence of cell traction on substrate stiffness immediately sheds light on an existing debate on whether cells sense mechanical force or deformation when interacting with their surroundings. Finally, it is shown that the cell induced deformation field decays exponentially with distance away from the cell. The characteristic length of this decay is comparable to the cell size and provides a quantitative measure of how far cells feel into the ECM.     

Morphological Responses of Vascular Endothelial Cells Induced by Local Stretch Transmitted Through Intercellular Junctions

It has been well established that mechanical stimuli including fluid shear stress and cyclic stretch play a key role in endothelial cell (EC) remodeling. However, in contrast to global remodeling to these mechanical stimuli, little is known of how local mechanical forces are transmitted through cells to induce cell remodeling leading to alteration in cell functions. In this study, we demonstrated that EC remodeling can be exerted by local tension generated in a neighboring EC. In this technique, a glass microneedle was used to apply local stretch in an EC in confluent monolayer and the resulting tension is transmitted to a neighboring EC across intercellular junctions. Local stretch induced reorientation and elongation of ECs parallel to the direction of stretch associated with reorganization of stress fibers. In addition, recruitment of Src homology 2-containing tyrosine phosphatase-2, binding to intercellular adhesion molecules platelet-endothelial cellular adhesion molecules-1, was selectively observed at the force-transmitted intercellular junctions after application of local stretch. These findings suggest that intercellular junctions can not only transmit but also sense local forces, and are potentially involved in EC mechanotransduction pathways.     

Mechanical Stimulation of Growth Plate Chondrocytes: Previous Approaches and Future Directions

Growth plate cartilage resides near the ends of long bones and is the primary driver of skeletal growth. During growth, both intrinsically and extrinsically generated mechanical stresses act on chondrocytes in the growth plate. Although the role of mechanical stresses in promoting tissue growth and homeostasis has been strongly demonstrated in articular cartilage of the major skeletal joints, effects of stresses on growth plate cartilage and bone growth are not well established. Here, we review the literature on mechanobiology in growth plate cartilage at macroscopic and microscopic scales, with particular emphasis on comparison of results obtained using different methodological approaches, as well as from whole animal and in vitro experiments. To answer these questions, macroscopic mechanical stimulators have been developed and applied to study mechanobiology of growth plate cartilage and chondrocytes. However, the previous approaches have tested a limited number of stress conditions, and the mechanobiology of a single chondrocyte has not been well studied due to limitations of the macroscopic mechanical stimulators. We explore how microfluidics devices can overcome these limitations and improve current understanding of growth plate chondrocyte mechanobiology. In particular, microfluidic devices can generate multiple stress conditions in a single platform and enable real-time monitoring of metabolism and cellular behavior using optical microscopy. Systematic characterization of the chondrocytes using microfluidics will enhance our understanding of how to use mechanical stresses to control the bone growth and the properties of tissue-engineered growth plate cartilage.

     

Growth and remodeling of load-bearing biological soft tissues

The past two decades reveal a growing role of continuum biomechanics in understanding homeostasis, adaptation, and disease progression in soft tissues. In this paper, we briefly review the two primary theoretical approaches for describing mechano-regulated soft tissue growth and remodeling on the continuum level as well as hybrid approaches that attempt to combine the advantages of these two approaches while avoiding their disadvantages. We also discuss emerging concepts, including that of mechanobiological stability. Moreover, to motivate and put into context the different theoretical approaches, we briefly review findings from mechanobiology that show the importance of mass turnover and the prestressing of both extant and new extracellular matrix in most cases of growth and remodeling. For illustrative purposes, these concepts and findings are discussed, in large part, within the context of two load-bearing, collagen dominated soft tissues—tendons/ligaments and blood vessels. We conclude by emphasizing further examples, needs, and opportunities in this exciting field of modeling soft tissues.     

Probing the mechanosensitivity in cell adhesion and migration: Experiments and modeling

Cell adhesion and migration are basic physiological processes in living organisms. Cells can actively probe their mechanical micro-environment and respond to the external stimuli through cell adhesion. Cells need to move to the targeting place to perform function via cell migration. For adherent cells, cell migration is mediated by cell-matrix adhesion and cell-cell adhesion. Experimental approaches, especially at early stage of investigation, are indispensable to studies of cell mechanics when even qualitative behaviors of cell as well as fundamental factors in cell behaviors are unclear. Currently, there is increasingly accumulation of experimental data of measurement, thus a quantitative formulation of cell behaviors and the relationship among these fundamental factors are highly needed. This quantitative understanding should be crucial to tissue engineering and biomedical engineering when people want to accurately regulate or control cell behaviors from single cell level to tissue level. In this review, we will elaborate recent advances in the experimental and theoretical studies on cell adhesion and migration, with particular focuses laid on recent advances in experimental techniques and theoretical modeling, through which challenging problems in the cell mechanics are suggested.     

ADVANCES IN EXPERIMENTAL APPROACHES FOR INVESTIGATING CELL AGGREGATE MECHANICS

Cells tend to form hierarchy structures in native tissues.Formation of cell aggregates in vitro such as cancer spheroids and embryonic bodies provides a unique means to study the mechanical properties and biological behaviors/functions of their counterparts in vivo.In this paper,we review state-of-the-art experimental approaches to assess the mechanical properties and mechanically-induced responses of cell aggregates in vitro.These approaches are classified into five categories according to loading modality,including micropipette aspiration,centrifugation,compression loading,substrate distention,and fluid shear loading.We discussed the advantages and disadvantages of each approach,and the potential biomedical applications.Understanding of the mechanical behavior of cell aggregates provides insights to physical interactions between cells and integrity of biological functions,which may enable mechanical intervention for diseases such as atheromatosis and cancer.