Cell receptor and surface ligand density effects on dynamic states of adhering circulating tumor cells

Dynamic states of cancer cells moving under shear flow in an antibody-functionalized microchannel are investigated experimentally and theoretically. The cell motion is analyzed with the aid of a simplified physical model featuring a receptor-coated rigid sphere moving above a solid surface with immobilized ligands. The motion of the sphere is described by the Langevin equation accounting for the hydrodynamic loadings, gravitational force, receptor-ligand bindings, and thermal fluctuations; the receptor-ligand bonds are modeled as linear springs. Depending on the applied shear flow rate, three dynamic states of cell motion have been identified: (i) free motion, (ii) rolling adhesion, and (iii) firm adhesion. Of particular interest is the fraction of captured circulating tumor cells, defined as the capture ratio, via specific receptor-ligand bonds. The cell capture ratio decreases with increasing shear flow rate with a characteristic rate. Based on both experimental and theoretical results, the characteristic flow rate increases monotonically with increasing either cell-receptor or surface-ligand density within certain ranges. Utilizing it as a scaling parameter, flow-rate dependent capture ratios for various cell-surface combinations collapse onto a single curve described by an exponential formula.     

Low melting point agarose as a protection layer in photolithographic patterning of aligned binary proteins

A novel photolithography method to build aligned patterns of two different proteins is presented. Chessboard patterns of 125 microm x 125 microm squares are constructed on a silicon dioxide substrate, using standard photoresist chemistries in combination with low-temperature oxygen plasma etching. Low-melting-point agarose (LMPA) is used to protect underlying protein layers and, at the appropriate stage, the digestive enzyme GELase (EPICENTRE) is used to selectively remove the prophylactic LMPA layers. Two antibodies, mouse-IgG and human-IgG, were immobilized and patterned by this procedure. The patterned antibodies maintained the specificity of their antigen-antibody binding, as demonstrated by fluorescence microscopy. In addition, normalized fluorescence intensity profiles illustrate that the patterned proteins layers are uniform (standard deviations below 0.05). Finally, a trypsin activity test was conducted to probe the effect of the patterning protocol on immobilized enzymes; the results imply that this photolithographic process using LMPA as a protection layer preserves 70% of immobilized enzyme activity.     

A high-performance microsystem for isolating circulating tumor cells

A unique flow field pattern in a bio-functional microchannel is utilized to significantly enhance the performance of a microsystem developed for selectively isolating circulating tumor cells from cell suspensions. For high performance of such systems, disposal of maximum non-target species is just as important as retention of maximum target species; unfortunately, most studies ignore or fail to report this aspect. Therefore, sensitivity and specificity are introduced as quantitative criteria to evaluate the system performance enabling a direct comparison among systems employing different techniques. The newly proposed fluidic scheme combines a slow flow field, for maximum target-cell attachment, followed by a faster flow field, for maximum detachment of non-target cells. Suspensions of homogeneous or binary mixtures of circulating breast tumor cells, with varying relative concentrations, were driven through antibody-functionalized microchannels. Either EpCAM or cadherin-11 transmembrane receptors were targeted to selectively capture target cells from the suspensions. Cadherin-11-expressing MDA-MB-231 cancer cells were used as target cells, while BT-20 cells were used as non-target cells as they do not express cadherin-11. The attachment and detachment of these two cell lines are characterized, and a two-step attachment/detachment flow field pattern is implemented to enhance the system performance in capturing target cells from binary mixtures. While the system sensitivity remains high, above 0.95, the specificity increases from about 0.85 to 0.95 solely due to the second detachment step even for a 1 : 1000 relative concentration of the target cells.     

Isolation of circulating tumor cells under hydrodynamic loading using microfluidic technology(基于微流控技术在流体动力载荷下分离循环肿瘤细胞)

在世界范围内, 癌症的死亡率仍在逐年上升. 循环肿瘤细胞(circulating tumor cells, CTCs) 是指从原发肿瘤脱落并进入血液循环系统的细胞, 可能引发肿瘤转移并入侵其他正常组织和器官. 因此, CTCs 的检测结果可以作为癌症病人疗效和预后的评价指标. 但是CTCs 的数量及其稀少, 使得CTCs 的检测尤为困难. 在癌症转移的病人中, 每毫升血液约含有10-100 个CTCs. 利用经生物活性材料表面修饰的微流控器件, 可以从血液中分离出CTCs. 这是一项跨学科的挑战, 需要来自不同学科背景的专家们共同参与, 如细胞生物学、表面化学、流体力学及微纳加工技术等. 该文首先介绍了CTCs 的细胞生物学基础, 然后总结了当前分离CTCs 的主要微流控技术, 包括基于细胞-- 配体作用、磁力作用和过滤等, 最后综述了基于微流控技术的CTC 检测和计数、在体CTC 成像等最新研究进展.      

Engineering Aqueous Fiber Assembly into Silk‐Elastin‐Like Protein Polymers

Self‐assembled peptide/protein nanofibers are valuable 1D building blocks for creating complex structures with designed properties and functions. It is reported that the self‐assembly of silk‐elastin‐like protein polymers into nanofibers or globular aggregates in aqueous solutions can be modulated by tuning the temperature of the protein solutions, the size of the silk blocks, and the charge of the elastin blocks. A core‐sheath model is proposed for nanofiber formation, with the silk blocks in the cores and the hydrated elastin blocks in the sheaths. The folding of the silk blocks into stable cores—affected by the size of the silk blocks and the charge of the elastin blocks—plays a critical role in the assembly of silk‐elastin nanofibers. Furthermore, enhanced hydrophobic interactions between the elastin blocks at elevated temperatures greatly influence the nanoscale features of silk‐elastin nanofibers.

     

Nanoparticle dispersion laser

Lasing action from a dispersion of nanoparticles is reported for the first time to our knowledge. The nanoparticles are Nd(2)O(3) modified with dimethyldichlorosilane (DMDCS) in dimethylsulfoxide. The laser was pumped with a pulsed laser at 802 nm and yielded 2.7 mJ with a slope efficiency of 50%. This was compared to a standard Nd-doped phosphate glass that yielded very similar results in the same setup.