基于玻璃-PDMS复合结构的微型毛细管被动阀

微阀是微流控系统中起控制限流的重要组成器件。研究的微阀是一种基于微机械加工技术的无活动部件的单向被动阀,其利用通道表面张力的变化产生阻流作用,起到阀的作用。讨论了被动阀的工作机理,利用快速制备原型技术制作微阀,同时在玻璃表面制作憎水薄膜,将玻璃与PDMS基底贴合并施加一定的压力,即可实现微阀的简单封装。取去离子水进行测试,微阀可以成功的停住液流,最大可以产生1kPa的压力降。阀的操作模式试验表明,微阀适合于应用在低压、一次性使用的场合。     

Fabrication of topologically complex three-dimensional microfluidic systems in PDMS by rapid prototyping

This paper describes a procedure for making topologically complex three-dimensional microfluidic channel systems in poly(dimethylsiloxane) (PDMS). This procedure is called the "membrane sandwich" method to suggest the structure of the final system: a thin membrane having channel structures molded on each face (and with connections between the faces) sandwiched between two thicker, flat slabs that provide structural support. Two "masters" are fabricated by rapid prototyping using two-level photolithography and replica molding. They are aligned face to face, under pressure, with PDMS prepolymer between them. The PDMS is cured thermally. The masters have complementary alignment tracks, so registration is straightforward. The resulting, thin PDMS membrane can be transferred and sealed to another membrane or slab of PDMS by a sequence of steps in which the two masters are removed one at a time; these steps take place without distortion of the features. This method can fabricate a membrane containing a channel that crosses over and under itself, but does not intersect itself and, therefore, can be fabricated in the form of any knot. It follows that this method can generate topologically complex microfluidic systems; this capability is demonstrated by the fabrication of a "basketweave" structure. By filling the channels and removing the membrane, complex microstructures can be made. Stacking and sealing more than one membrane allows even more complicated geometries than are possible in one membrane. A square coiled channel that surrounds, but does not connect to, a straight channel illustrates this type of complexity.     

Production of new 3D scaffolds for bone tissue regeneration by rapid prototyping

The incidence of bone disorders, whether due to trauma or pathology, has been trending upward with the aging of the worldwide population. The currently available treatments for bone injuries are rather limited, involving mainly bone grafts and implants. A particularly promising approach for bone regeneration uses rapid prototyping (RP) technologies to produce 3D scaffolds with highly controlled structure and orientation, based on computer-aided design models or medical data. Herein, tricalcium phosphate (TCP)/alginate scaffolds were produced using RP and subsequently their physicochemical, mechanical and biological properties were characterized. The results showed that 60/40 of TCP and alginate formulation was able to match the compression and present a similar Young modulus to that of trabecular bone while presenting an adequate biocompatibility. Moreover, the biomineralization ability, roughness and macro and microporosity of scaffolds allowed cell anchoring and proliferation at their surface, as well as cell migration to its interior, processes that are fundamental for osteointegration and bone regeneration.     

Scaffolds for bone tissue engineering fabricated from two different materials by the rapid prototyping technique: PCL versus PLGA

Three dimensional tissue engineered scaffolds for the treatment of critical defect have been usually fabricated by salt leaching or gas forming technique. However, it is not easy for cells to penetrate the scaffolds due to the poor interconnectivity of pores. To overcome these current limitations we utilized a rapid prototyping (RP) technique for fabricating tissue engineered scaffolds to treat critical defects. The RP technique resulted in the uniform distribution and systematic connection of pores, which enabled cells to penetrate the scaffold. Two kinds of materials were used. They were poly(ε-caprolactone) (PCL) and poly(d, l-lactic-glycolic acid) (PLGA), where PCL is known to have longer degradation time than PLGA. In vitro tests supported the biocompatibility of the scaffolds. A 12-week animal study involving various examinations of rabbit tibias such as micro-CT and staining showed that both PCL and PLGA resulted in successful bone regeneration. As expected, PLGA degraded faster than PCL, and consequently the tissues generated in the PLGA group were less dense than those in the PCL group. We concluded that slower degradation is preferable in bone tissue engineering, especially when treating critical defects, as mechanical support is needed until full regeneration has occurred.     

Characterization of hot extruded Mg/SiC nanocomposites fabricated by casting

Mg–1%SiC nanocomposites were fabricated using an ultrasonic cavitation based casting method, resulting in the dispersion of the reinforcing SiC nanoparticles to form Mg–metal matrix nanocomposite (Mg–MMNC) billets. The MMNC billets were then processed using hot extrusion at 350 °C. Micrographic observations illustrate a significant grain size reduction and the presence of microbands that align the SiC nanoparticles parallel to the direction of extrusion for Mg–MMNCs. Observations from the cross-section at 90° of the extrusion direction show uniform nanoparticles dispersion. Results from the extruded Mg–MMNCs tensile testing at different temperatures (25, 125 and 177 °C) reveal an increase of the yield strength, ultimate tensile strength, and ductility values as compared to the un-reinforced and extruded Mg-alloy; such increase was also observed from the microhardness testing results where an increase from 19 to 34% was measured.     

Characterization of thermoplastic polyurethane/polylactic acid (TPU/PLA) tissue engineering scaffolds fabricated by microcellular injection molding

Polylactic acid (PLA) and thermoplastic polyurethane (TPU) are two kinds of biocompatible and biodegradable polymers that can be used in biomedical applications. PLA has rigid mechanical properties while TPU possesses flexible mechanical properties. Blended TPU/PLA tissue engineering scaffolds at different ratios for tunable properties were fabricated via twin screw extrusion and microcellular injection molding techniques for the first time. Multiple test methods were used to characterize these materials. Fourier transform infrared spectroscopy (FTIR) confirmed the existence of the two components in the blends; differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) confirmed the immiscibility between the TPU and PLA. Scanning electron microscopy (SEM) images verified that, at the composition ratios studied, PLA was dispersed as spheres or islands inside the TPU matrix and that this phase morphology further influenced the scaffold's microstructure and surface roughness. The blends exhibited a large range of mechanical properties that covered several human tissue requirements. 3T3 fibroblast cell culture showed that the scaffolds supported cell proliferation and migration properly. Most importantly, this study demonstrated the feasibility of mass producing biocompatible PLA/TPU scaffolds with tunable microstructures, surface roughnesses, and mechanical properties that have the potential to be used as artificial scaffolds in multiple tissue engineering applications.     

固溶温度对等离子快速成形Inconel625合金组织的影响

为了优化快速成形零件组织和力学性能,利用脉冲等离子焊接快速成形工艺制备了Inconel625合金薄壁零件.采用扫描电镜、透射电镜研究了固溶温度对成形零件组织的影响规律.结果表明:沉积态组织以胞状枝晶为主,具有较强生长取向性的外延枝晶组织特征,同时,在枝晶间隙析出大量的Laves相和少量的MC碳化物.经过720℃/1 h的固溶处理,金相组织没有发生明显变化,但导致γ″(Ni3Nb)相的析出.经850℃固溶处理,组织中的Laves相部分被溶解,生成了针状δ相.当固溶温度升高到980℃,Laves相几乎完全溶解,δ相发生了部分回溶.而经过1 080℃固溶处理,消除了元素的偏析和Laves相,但再结晶导致晶粒严重长大.980℃是最佳的固溶处理温度.     

Ni含量对多孔Cu-Ni合金孔隙率的影响

为研究Ni含量对孔隙率的影响,在氢气高压气氛中利用连铸法制备了藕状多孔Cu-Ni合金,分析了氢溶解度和糊状区宽度.结果表明:随着Ni含量的增加,合金凝固时的糊状区宽度不断增大,而孔隙率减小;糊状区宽度的不断增大,一方面造成气孔在长大时吸收液相中溶质氢原子越来越少,另一方面造成溶质氢原子进入到气孔的通道越来越曲折.气孔长大时吸收溶质氢原子的差别是孔隙率变化的主要原因.     

Microstructure and mechanical properties of titanium components fabricated by a new powder injection molding technique

A powder injection molding (PIM) binder system has been developed for reactive metals such as titanium that employs an aromatic compound as the primary component to facilitate easy binder removal and mitigate problems with carbon contamination. In the study presented here, we examined the densification behavior, microstructure, and mechanical properties of titanium specimens formed by this process using naphthalene as the principle binder constituent. In general, it was found that tensile strengths could be achieved comparable to wrought titanium in the PIM-formed specimens, but that maximum elongation was less than expected. Chemical and microstructural analyses indicate that this process does not add oxygen to the material,suggesting that the use of higher purity powder and further process optimization should lead to significant improvements in ductility.     

Influence of raw powder preparation routes on properties of hydroxyapatite fabricated by 3D printing technique

A comparison between two routes of raw powder preparation, namely spray drying and grinding, for 3D printing of hydroxyapatite was carried out. Hydroxyapatite particles prepared by the spray drying technique were spherical in shape whereas the grinding route gave irregular-shaped agglomerates. Spray-dried powders had higher tap density than milled powders, however milled powders yielded 3DP specimens with greater green density and strength. After sintering at 1300 °C for 1 and 5 h, samples fabricated from milled powders showed a 32% higher in sintered density, a 20% lower in porosity and approximately two times higher flexural modulus and strength than samples fabricated from spray-dried powders. This difference was related to the better packing characteristics of milled powders which promoted improved inter- and intra-particle densification during high temperature sintering compared to the spray-dried powders which yielded only high intra-particle densification, but lower inter-particle densification.     

Nickel aluminide (Ni3Al) fabricated by reactive infiltration

Nickel aluminide Ni₃Al in the single phase form, with grain size 10 m, porosity 5%, tensile strength 425 MPa, modulus 92 GPa and ductility 9.5% at room temperature, was fabricated by reactive infiltration at 800 °C of liquid aluminium into a porous preform containing 78 vol % nickel and made by sintering 3–7 m size nickel particles. Without sintering, the preform contained 58 vol % nickel and reactive infiltration resulted in an aluminium-matrix NiAl₃ particle ( 50 m size) composite and extensive growth of Ni-Al needles from the preform to the excess liquid aluminium around the preform.     

Gas sensing property of perovskite SrTi(1-x)Fe(x)O3_delta fabricated by thick film planar technology

Planar sensor of SrTi(1-x)Fe(x)O3-delta, x = 0.4 and 0.6, with perovskite structure was fabricated on alumina substrate using thick film technology. Electrical resistance was measured as a function of thermal treatment conditions, atmosphere, time and temperature. Sensing property was also measured as a function of temperature and the gases of O2, CH4, CO, CO2, NO and NO2. The resistance of SrTi(1-x)Fe(x)O3-delta is lower than those of SrTiO3 or SrFeO3. TCR (temperature coefficient of resistance) of zero over 550 degrees C was measured for the composition of SrTi(1-x)Fe(x)O3-delta after thermal treatment at 1100 degrees C in air atmosphere only. The perovskite SrTi(1-x)Fe(x)O3-delta didn't show any response to CH4, CO, CO2, NO and NO2, but an excellent response and recovery characteristics with oxygen concentration.     

Characterization of the small molecule based organic thin film fabricated by electrospray deposition technique

A novel route for the fabrication of the SM based 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) organic thin film by electrospray deposition (ESD) technique has been presented in this paper. The tailoring of the film thickness was also performed by varying the number of deposition passes at a constant substrate speed. The structural and optical characterizations of the fabricated BCP thin film were thoroughly investigated. The energy gap of the fabricated thin film was measured to be 3.5 eV. Furthermore, the electrical performance of the BCP thin film was verified by performing current–voltage measurement of the prototype organic diode device having fabricated BCP film as a buffer layer. The current density–voltage characteristic curve of the organic device showed non linear diode like behavior, thereby confirming the proper interference established between organic diode adjacent layers. At low voltage, the device showed ohmic conduction, where as the space charged limited current and trap charge limited current mechanism have been found to be dominant in the fabricated organic device at higher voltage. Overall, the results suggest that the ESD approach will be promising for organic semiconductor device fabrication at low cost and with low material loss.     

Characterization and mechanical performance comparison of multiwalled carbon nanotube/polyurethane composites fabricated by electrospinning and solution casting

Multiwalled carbon nanotube/polyurethane (MWNT/PU) composites were prepared by electrospinning and solution casting. The morphological and thermal properties, and mechanical performance of the nanofiber and film composites were characterized and compared. The tensile strength of neat PU film was 9-fold higher than that of neat PU nanofibrous mat. The incorporation of MWNTs increased the tensile strength and modulus of the composite nanofibers by 69% and 140%, respectively, and 62% and 78%, respectively for composite films. The MWNT/PU composites showed an improved thermal degradation behavior, with the incorporation of low MWNT content in the composites.     

溶胶-凝胶法制备BiFeO3铁电薄膜的结构和特性

采用 sol gel 方法在 Pt/Ti/SiO2/Si 衬底上制备出纯相铁酸铋薄膜。采用热分析方法研究了凝胶的化学变化和析晶过程。分析讨论了退火温度对薄膜的结构和形貌的影响。并用 XRD、SEM 等手段对样品在不同温度条件退火处理后的薄膜相和形貌进行了分析。在800℃时采用层层退火方式,有效抑制 Fe价态转化,从而降低了电子波动引发的氧空位数目,制备出纯铁相高电阻率的BiFeO3 铁电薄膜,并观测到饱和电滞回线,其 Ps 和 Pr 分别为 6.9μC/cm2 和 2.8μC/cm2。     

Microstructural characterization of the γ-TiAl alloy samples fabricated by direct laser fabrication rapid prototype technique

A direct laser fabrication technique (DLF) has been used to fabricate near net shape samples of a γ-TiAl alloy using gas atomized Ti₄₈A1₄₈Mn₂Nb₂ alloy powder as a feed stock material. The microstructures of these Ti₄₈A1₄₈Mn₂Nb₂ laser treated samples have been characterized using optical, scanning (SEM) and transmission electron microscopy (TEM), both immediately after laser fabrication and after heat treatments. The microstructural studies have shown that the microstructure is heterogeneous in nature and extremely fine in comparison with the conventionally processed material. The process parameters such as laser power and laser scanning speed greatly influence the morphology and the microstructure of the laser treated samples. Heat treatments for a number of process conditions have been carried out to examine the stability of the microstructure which remains stable up to 973 K and rapid grain coarsening occurs at 1273 K. A fully recrystallized and uniform microstructure is obtained after annealing at 1073 K for 24 h and compositional heterogeneity present in the laser-fabricated samples is eliminated. Annealing in the a phase field followed by air cooling and annealing in (α₂ + γ) phase region gives rise to a homogeneous and uniform microstructure. However, the microstructure is much coarser than the microstructure of the DLF samples.     

Porous Ti6Al4V scaffolds directly fabricated by 3D fibre deposition technique: Effect of nozzle diameter

3D porous Ti6Al4V scaffolds were successfully directly fabricated by a rapid prototyping technology: 3D fibre deposition. In this study, the rheological properties of Ti6Al4V slurry was studied and the flow rate was analyzed at various pressures and nozzle diameters. Scaffolds with different fibre diameter and porosity were fabricated. ESEM observation and mechanical tests were performed on the obtained porous Ti6Al4V scaffolds with regard to the porous structure and mechanical properties. The results show that these scaffolds have 3D interconnected porous structure and a compressive strength which depends on porosity at constant fibre diameters and on the fibre diameter at constant porosity. These Ti6Al4V scaffolds are expected to be constructs for biomedical applications.