机械应力刺激对体外肺腺癌细胞增殖的影响

通过FX-4000柔性基底加载系统研究了不同波形的周期性拉伸对人肺腺癌A549细胞株增殖的影响,应用Image—pro图像处理软件对A549细胞株在心形波、三角波及方波等拉伸应变下的增殖动力学变化进行了分析。实验结果表明：在collagenⅠ基底膜上,应变为0％～20％,频率为0．5Hz及1．0Hz,加载时间为2h时,与对照组比较,方波刺激组细胞生长明显受到抑制,三角波与心形波刺激组细胞增殖率无明显差异。研究表明：A549细胞株对体外的生理应变作出响应时,方波的抑制作用最佳,而拉伸频率的影响并不明显。     

羟基磷灰石纳米粒子对肝癌增殖活性的影响

为了研究HAP纳米粒子对肝癌细胞的增殖能力及生物学行为的影响，采用均匀沉淀法制备了均匀分散的纳米尺度的HAP纳米粒子。以0．56mmol/的HAP纳米粒子与Bel-7402肝癌细胞作用4d后，细胞行Feulgen染色和AgNOR染色，显微镜观察标本、图像分析系统定量分析肝癌细胞的DNA和AgNOR。结果显示HAP纳米粒子能降低Bel-7402细胞的DNA含量，减少细胞的AgNOR数量，与对照纽比较均有显著性差异（P〈0．01）。HAP纳米粒子能减弱肝癌细胞的增殖活性，可能是通过抑制DNA的合成，以及减少AgNOR数量而抑制rRNA的合成，发挥抗癌作用。     

不同拉伸应变率下金纳米线拉伸力学行为的分子动力学模拟

采用分子动力学方法模拟了不同拉伸应变率下金纳米线的拉伸力学行为。模拟结果表明，相同截面尺寸、拉伸温度、拉伸方向的金纳米线在较高的拉伸应变率下，屈服强度较大，屈服发生的较早；更高应变率下的金纳米线在屈服时对应的应变更大，并且更容易发生二次屈服。金纳米线的弹性模量随着拉伸应变率的增大有所增加，但是幅度不是很明显。     

不同拉伸应变率下金纳米线拉伸力学行为的分子动力学模拟

采用分子动力学方法模拟了不同拉伸应变率下金纳米线的拉伸力学行为。模拟结果表明,相同截面尺寸、拉伸温度、拉伸方向的金纳米线在较高的拉伸应变率下,屈服强度较大,屈服发生的较早;更高应变率下的金纳米线在屈服时对应的应变更大,并且更容易发生二次屈服。金纳米线的弹性模量随着拉伸应变率的增大有所增加,但是幅度不是很明显。     

纯化肝细胞生长因子对肝癌细胞的增殖刺激作用

利用ＤＥＡＥ纤维素层析、ＦＰＬＣ和ＨＰＬＣ分离，从人胎肝中获得了纯化的特异刺激肝来源细胞ＤＮＡ合成的肝细胞生长因子（ＨＧＦ）。进一步研究表明，ＨＧＦ明显刺激人肝癌细胞的增殖，其刺激活性具有量效关系，并诱导肝癌细胞从Ｇ０／Ｇ１期进入Ｓ期。本研究为探讨ＨＧＦ作用机理建立了模型。     

基于Hela细胞的失巢凋亡现象时序评价模型的建立及测量验证方法研究北大核心CSCD

失巢凋亡作为一种特殊的程序化细胞死亡形式,在机体发育、组织自身平衡、疾病发生和肿瘤转移中起重要作用。利用贴壁增殖表皮细胞系海拉(Hela)细胞作为模型,通过对比贴壁细胞悬浮后悬浮时间对细胞活性的影响,深入探讨了细胞失巢凋亡现象。研究考察了悬浮5 min、30 min、1 h, 2 h, 4 h和8 h后的活细胞数量,以及重新贴壁培养后对细胞活性(即贴壁24 h后活细胞增殖数量)的影响。结果表明:悬浮时间可导致海拉细胞数量减少及活性降低,在细胞实验过程中应当严格控制悬浮细胞接种时长。     

5083铝合金搅拌摩擦焊接头拉伸行为研究

目的 研究5083铝合金搅拌摩擦焊接（FSW）的组织、力学性能和拉伸应变,分析接头的拉伸行为。方法 采用数码相机、光学显微镜、电子扫描显微镜等表征分析方法,对焊缝的表面宏观成形、微观组织、断口形貌进行分析;利用拉伸机、三维数字动态散斑应变测量分析系统和显微维氏硬度计对接头的力学性能和拉伸应变进行测试。结果 不同焊接工艺参数下FSW接头的最低抗拉强度为305 MPa,断后延伸率达到了14%以上;焊核区拉伸应变沿板厚方向呈现上高下低和上宽下窄的不均匀梯度分布,发生了较大程度的变形强化,直到拉伸应力达到抗拉强度。断裂失效前300/120接头的最大拉伸应变在晶粒粗大的母材区,500/120和500/200接头的最大拉伸应变则位于晶粒尺寸差异较大的后退侧焊核区与热力影响区交界处。接头拉伸断口宏观上均为45°剪切韧性断裂,微观上均以韧窝韧性断裂为主,而高热输入500/120接头出现脆性断裂特征,其延伸率明显降低。结论 高热力耦合输入使铝合金FSW接头薄弱区发生转变,强韧性降低。     

SHCC的配制与拉伸性能研究

采用聚乙烯醇纤维(PVA)纤维作为增强材料,选定不同的粉煤灰掺量、石英砂级配、纤维掺量和养护工艺配制应变硬化水泥基复合材料(SHCC),研究上述因素对SHCC力学性能的影响。研究表明,随着粉煤灰掺量的增加,SHCC极限拉伸强度有少许削弱,但极限拉伸应变不断增加,均高于3%。随着养护龄期增加,SHCC极限拉伸应变呈现先增加后减小的趋势,但拉伸强度随龄期增加而增大。自然养护有利于维持SHCC的高极限拉伸应变;蒸汽养护能提高SHCC早期的极限拉伸强度,但蒸汽养护使SHCC的极限拉伸应变随着龄期增加而明显降低。当m(FA)/m(C)=1.6,2.0和2.4,Vf=2.0%时,采用较细的石英砂和自然养护,28d龄期的SHCC极限拉伸强度在4 MPa以上,极限拉伸应变在3%以上。     

金属涂层/聚合物复合体系的结构-力学行为

在单向拉伸和平面压缩金属涂层／聚合物复合体系的条件下，在体系的表面形成周期性的微观结构。综述了对这种周期性表面微结构的特点及其形成机理的研究，并介绍了该理论在地壳表面形貌形成机理研究中的应用。     

开放大孔海藻酸微球的制备及三维细胞培养应用

开放大孔微球能够帮助细胞-细胞和细胞-细胞外基质相互作用的形成，适合作为三维细胞培养支架。采用微流控技术和在线紫外引发交联法制备得到尺寸均一、大小可控的甲基丙烯酰化海藻酸(AlgMA)微球，利用冷冻干燥制孔法得到具有开放大孔的AlgMA微球。系统研究了内/外相流速比的变化和AlgMA浓度对微球尺寸、形貌和稳定性的影响，并以人肝癌细胞HepG2作为模型细胞，系统考察了AlgMA微球对细胞活性和增殖的影响。结果表明，当AlgMA质量分数为10%时，微球的复溶胀性能和孔洞结构最好，分别培养HepG2细胞24 h,48 h和72 h后，细胞活性均在85%以上，培养48 h和72 h后，相较于前一天细胞数量分别倍增了1.24倍和1.76倍。该研究工作为开放大孔海藻酸微球的制备提供了新方法。     

Modelling Residual Strains During Cycling of Ti–Ni and Ti–Ni–Cu Shape Memory Alloys in a Pseudoelastic Range of Behaviour Conditions

Abstract: Pseudoelastic behaviour of three types of Ti–Ni shape memory alloys in a pseudoelastic state has been studied under conditions of maximum strain‐ and maximum stress‐controlled cycling. Experimental results proved that residual deformation after unloading increases with the number of cycles; however, critical stress for the induction of martensite and the energy dissipated in one cycle decline during cycling. A higher critical stress for slip, and more intense cyclic dislocation hardening promoted by greater maximum deformation and greater maximum applied stresses, generally reduce the rate at which residual elongation grows with the number of cycles, and tend to stabilise the cyclic stress‐elongation diagrams. The small magnitude of critical stress for slip in low‐nickel alloys, and also cyclic strain hardening, induce greater internal stresses and a more marked decrease in critical stress for the induction of martensite as cycling progresses. Detailed analysis of plastic deformation propagation in cyclically loaded specimen helped develop a model of dependence of residual elongation on the number of cycles. This model enables identification of three main factors that govern the magnitude of residual elongation: one residual plastic elongation caused by dislocation hardening after the alloy is heat treated, and two cyclic strain hardening parameters describing how residual elongation grows with number of cycles, and how this residual elongation is reduced, as cycles increase, by the rising critical stress level for slip. The model has proved to yield very close agreement with experimental findings.     

In vitro biocompatibility of degradable biopolymers in cell line cultures from various ocular tissues: extraction studies

In vitro biocompatibility of 50:50 PDLGA, 85:15 PDLGA, and Inion GTR^TM membrane was evaluated in cell line cultures from various ocular tissues, in human corneal epithelial cells (HCE), rabbit stromal fibroblasts (SIRC), bovine corneal endothelial cells (BCE), human conjunctival epithelial cells (IOBA-NHC), and human retinal pigment epithelial cells (ARPE-19). To study the toxicity of degradation products, the biomaterials were extracted in phosphate buffered saline at 70 °C for 24 h. The cell cultures were exposed to biomaterial extract diluted in medium (1:1–1:8) and the biocompatibility was evaluated by the WST-1 cytotoxicity/cell proliferation test. In all experiments without pH neutralization, cell viability increased with decreasing biomaterial extract volume. The highest extraction ratio 1:1 of PDLGA 50:50 decreased viability from 5–20%, from the control level, depending on the cell type. The corresponding cell viability values for PDLGA 85:15 and Inion GTR membrane ranged from 47–87% and 66–92%, respectively. When the pH of biomaterial extract was neutralized, Inion GTR membrane and PDLGA 85:15 had no effect on viability. BCE, HCE, and IOBA-NHC appeared to the most sensitive cell types, while SIRC and ARPE-19 were more resistant. The results of our in vitro studies suggest that the polymers tested are satisfactorily biocompatible.     

A nonlinear mechanical model for the fatigue life of thin-film carbon nanotube supercapacitors

The effects of cyclic loading on the mechanical performance and fatigue life of a novel carbon nanotube supercapacitor are investigated. The highly flexible supercapacitor is a monolithic, pre-fabricated, fully functional film made of a nanostructured free-standing layer in which ions are stored within two vertically aligned multi-walled carbon nanotube (MWCNs) electrodes that are monolithically interspaced by a solution of microcrystalline cellulose in a room temperature ionic liquid electrolyte. To study the cyclic mechanical response of such nanostructured multilayer composite, an original framework is adopted by combining the equivalent continuum approach of Eshelby–Mory–Tanaka and a Weibull-like approach for the evolution of debonding carbon nanotubes electrodes. One- and three-layer models of the supercapacitor are proposed. Cyclic tests are numerically carried out in strain control. A fatigue life limit is determined by considering a confidence interval for the number of cycles corresponding to the states at which the effective elastic modulus of the partially debonded nanostructured portion of the supercapacitor is reduced by a percentage between 20% and 30%. The simulated cyclic tests yield Wholer-type fatigue curves showing the fatigue life limit as the maximum number of cycles N for each strain amplitude.The sensitivity of the fatigue life with respect to meaningful parameters such as the interfacial strength between the MWCNs and cellulose is investigated. Frequency-response functions of the multilayer nanostructured composite are further computed as function of the strain amplitude during cyclic tests.     

Functionalised gold nanoparticles for selective induction of in vitro apoptosis among human cancer cell lines

The interaction of citrate- and polyethylene imine (PEI)-functionalised gold nanoparticles (GNP) with cancer cell lines with respect to the cellular response was studied. It was found that GNP/citrate nanoparticles were able to induce apoptosis in human carcinoma lung cell lines A549, but GNP/PEI did not show any reduction in the viability of the cells in human breast cancer cell line MCF-7 and A549 cell lines. FACS data confirmed that the number of apoptotic cells increased with increase in the concentration of GNP/citrate nanoparticles. Decline in cellular expansion and changes in the nuclear morphology were noted after the treatment of GNP/citrate nanoparticles on A549 cell lines, which itself is a direct response for stress induction. The induction of cellular apoptosis was further confirmed by DNA fragmentation assay. These data confirm the potential of GNP/citrate nanoparticle to evoke cell-specific death response in the A549 cell lines.     

Enzymatic activation of a peptide functionalised gold nanoparticle system for prodrug delivery

Gold nanoparticles (GNPs) with a monolayer of peptides were synthesized as a potential tumour activated cancer drug delivery system. The prodrug system was achieved by the attachment of two varying lengths of peptides to GNPs: An 18 amino acid peptide sequence encompassing a shorter fluorescent labelled (coumarin) six amino acid peptide sequence. The longer peptide chain included the sequence D-AFK that is selectively cleavable by the over-expression of proteases in the vicinity of cancer cells. The protease-mediated exposure of the coumarin was demonstrated by the incubation of peptide capped GNPs with adenocarcinomic human alveolar basal epithelial A549 cells and madin-darby bovine kidney epithelial cells. Confocal laser scanning microscopy studies revealed enhanced fluorescence emission intensities in the cancer cell line as compared to the intensity exhibited by the healthy cell line. This work suggests that GNPs functionalised with a cytotoxic agent or fluorophore encapsulated by longer peptide strands may find useful applications for development of GNPs with therapeutic or diagnostic studies.     

Silver nanoparticles reduce the apoptosis induced by tumor necrosis factor-α

Silver nanoparticles (AgNPs) are widely known to have anti-inflammatory properties, but the exact mechanism underlying this anti-inflammatory effect is not clearly understood. Tumor necrosis factor-α (TNFα) is a major pro-inflammatory cytokine that is expressed in the early stage of cell inflammation and induces apoptosis by several known pathways. Our study aimed to investigate the effect of AgNPs on the response of lung epithelial cells to TNFα and the molecular mechanism of this response. Lung epithelial cell line NCI-H292 cells were exposed to AgNPs (5 µg/mL) and/or TNFα (20 ng/mL) for 24 h, then cellular uptake was analyzed using flow cytometry. Our results showed that AgNPs were taken up by cells in a dose-dependent manner and that the cellular uptake ratio of AgNPs was significantly increased in the presence of TNFα. Apoptosis assays indicated that exposure to AgNPs significantly decreased the apoptotic effect of TNFα. Confocal microscopy was used to localize the tumor necrosis factor receptor 1 (TNFR1) and revealed that TNFR1 localized on the surface of cells exposed to TNFα. In contrast, TNFR1 localized inside cells exposed to both AgNPs and TNFα, with very few receptors scattered on the cell membrane. The results indicated that AgNPs reduced the cell surface TNFR1 expression level. The results suggested that the reduction of surface TNFR1 reduced cellular response to TNFα, resulting in an anti-apoptotic effect.     

The effect of prior cyclic loading variables on the creep behaviour of ex-service Type 316H stainless steel

Abstract

Initial tests have been conducted for a systematic survey of the effect of prior cyclic loading on subsequent creep properties. Samples of 316H stainless steel were subjected to prior cyclic loading at 550°C at different combinations of strain range and cycles experienced. These samples were then remachined into uniaxial creep specimens and tested under a constant load at 250 MPa at 550°C.

The initial results from specimens subject to prior cyclic loading show significant decreases in the minimum true creep strain rate of between 30 and 94%. A consistent decrease in the minimum creep strain rate was found with increases in both the strain range of the prior cyclic loading and the number of cycles experienced by the sample. In addition, the prior-cyclic loading has significantly changed the shape of the creep curve to varying degrees depending upon the applied cyclic loading.     

Age-dependent changes in microscale stiffness and mechanoresponses of cells

Cellular ageing can lead to altered cell mechanical properties and is known to affect many fundamental physiological cell functions. To reveal age-dependent changes in cell mechanical properties and in active mechanoresponses, the stiffness of human fibroblasts from differently aged donors was determined, as well as the cell's reaction to periodic mechanical deformation of the culture substrate, and the two parameters were correlated. A comparison of the average Young's moduli revealed that cells from young donors (<25 years) are considerably stiffer than cells from older donors (>30 years). The reduced stiffness of cells from the older donor group corresponds to the measured decrease of actin in these cells. Remarkably, cells from the older donor group show a significantly faster reorganization response to periodic uniaxial tensile strain than cells from the young donor group. The impact of a reduced amount of actin on cell stiffness and cell reorganization kinetics is further confirmed by experiments where the amount of cellular actin in cells from the young donor group was decreased by transient siRNA knockdown of the actin gene. These cells show a reduced stiffness and enhanced reorganization speed, and in this way mimic the properties and behavior of cells from the older donor group. These results demonstrate that mechanical properties of human fibroblasts depend on the donor's age, which in turn may affect the cells' active responses to mechanical stimulations.     

Plasma polymer coated surfaces for serum-free culture of limbal epithelium for ocular surface disease

The potential use of plasma polymer coatings as substrates for serum-free expansion of limbal epithelial cells was investigated. Preliminary studies using a human corneal epithelial cell line showed that acrylic acid-coated surfaces performed better than allyl amine and allyl alcohol coated surfaces in terms of cell metabolic activity and confluence as assessed using the MTT assay. Subsequently, the proliferation and maturity of primary human limbal epithelial cells in co-culture with growth arrested 3T3 fibroblasts on a range of acrylic acid plasma coated surfaces, octadiene plasma coated surfaces and tissue culture plastic was investigated using MTT and cytokeratin 3 immunostaining. The cells performed better in the presence of serum on all surfaces. However, the acrylic acid coated surfaces successfully sustained a serum-free fibroblast/epithelial cell co-culture. The metabolic activity of the epithelial cells was superior on the acrylic acid coated surfaces than on tissue culture plastic in serum-free conditions and their levels of differentiation were not significantly higher than in the presence of serum. These results suggest that these surfaces can be used successfully for the serum-free expansion of human limbal epithelial cells.     

The influence of the surface chemistry of silver nanoparticles on cell death

The influence of the surface chemistry of silver nanoparticles (AgNPs) on p53 mediated cell death was evaluated using human dermal fibroblast (HDF) and lung cancer (A549) cells. The citrate reduced AgNPs (C-AgNPs) were modified with either lactose (L-AgNPs) or a 12-base long oligonucleotide (O-AgNPs). Both unmodified and modified AgNPs showed increased concentration and time dependent cytotoxicity and genotoxicity causing an increased p53 up-regulation within 6 h and led to apoptotic or necrotic cell deaths. The C-AgNPs induced more cytotoxicity and cellular DNA damage than the surface modified AgNPs. Modifying the C-AgNPs with lactose or the oligonucleotide reduced both necrotic and apoptotic cell deaths in the HDF cells. The C-AgNPs caused an insignificant necrosis in A549 cells whereas the modified AgNPs caused necrosis and apoptosis in both cell types. Compared to the O-AgNPs, the L-AgNPs triggered more cellular DNA damage, which led to up-regulation of p53 gene inducing apoptosis in A549 cells compared to HDF cells. This suggests that the different surface chemistries of the AgNPs cause different cellular responses that may be important not only for their use in medicine but also for reducing their toxicity.