A Bi‐Layer PVA/CMC/PEG Hydrogel with Gradually Changing Pore Sizes for Wound Dressing

Wound dressings are vital for cutaneous wound healing. In this study, a bi‐layer dressing composed of polyvinyl alcohol/carboxymethyl cellulose/polyethylene glycol (PVA/CMC/PEG) hydrogels is produced through a thawing–freezing method based on the study of the pore size of single‐layer hydrogels. Then the physical properties and healing of full‐thickness skin defects treated with hydrogels are inspected. The results show that the pore size of the single‐layer PVA/CMC/PEG hyrogel can be controlled. The obtained non‐adhesive bi‐layer hydrogels show gradually increasing pore sizes from the upper to the lower layer and two layers are well bonded. In addition, bi‐layer dressings with good mechanical properties can effectively prevent bacterial penetration and control the moisture loss of wounds to maintain a humid environment for wounds. A full‐thickness skin defect test shows that bi‐layer hydrogels can significantly accelerate wound closure. The experiment indicates that the bi‐layer PVA/CMC/PEG hydrogels can be used as potential wound dressings.     

基于遗传-细菌觅食组合算法的非线性模型优化

文中提出一种遗传-细菌觅食组合优化算法以解决非线性模型优化问题。该方法先使用遗传算法进行全局搜索,并缩小最优解的搜索范围;再使用细菌觅食优化算法在该局部范围内执行局部搜索。这种组合搜索策略可以增强算法的收敛性,并能有效地均衡全局搜索和局部搜索。文中利用单峰、多峰和复杂多峰等非线性函数模型验证所提算法的性能。实验结果表明,组合算法的计算精度和效率分别比遗传算法和细菌觅食优化算法提高了30%和50%,表明该组合算法具有更快的收敛速度,更高的求解精度,适用于大规模多极值的非线性问题。     

纳米微结构表面与石墨烯薄膜的界面黏附特性研究

石墨烯性能的发挥受石墨烯表面形貌的影响,而石墨烯表面形貌则与基底密切相关.石墨烯在纳米微结构表面的吸附与剥离可以为石墨烯的功能化制备和转移提供理论基础.分子动力学模拟能提供石墨烯在纳米微结构表面的吸附构型和剥离特性等详细信息,可以弥补实验的不足.本文利用LAMMPS分子动力学模拟软件,从吸附能角度研究了石墨烯在矩形微结构表面的黏附特性,并进一步探讨了石墨烯从矩形微结构表面剥离的行为.研究表明:石墨烯的吸附构型在矩形微结构表面的转变是连续的,但由部分贴合状态向完全贴合状态的转变是一个反复的过程,当石墨烯完全贴合微结构表面时吸附能最大;从微结构表面剥离石墨烯时,剥离力会出现周期性的波动.剥离过程表现为两种形式:完全贴合时,石墨烯是直接滑过槽底;而当悬浮构型或部分贴合构型时,石墨烯是直接从微结构表面分离.本文给出了平均剥离力随微结构尺寸参数变化的理论公式,该公式与模拟结果拟合较好.此外,随着剥离角度的变大,平均剥离力先变大后变小,从平整基底表面剥离具有Stone-Wales缺陷结构的石墨烯会使剥离力变大.研究结果可为探究石墨烯在纳米微结构表面的剥离行为、揭示其黏附机理提供理论参考.     

Si单晶片切削液挂线性能的研究

Si片线切割过程中,切削液的挂线性能直接影响切片表面质量、切片速率、线锯寿命以及晶片成品率.为满足超大规模集成电路对Si衬底表面质量的要求,改进线切割液的性能,对影响线切割液性能的因素进行了分析,并通过实验对线切割液的挂线性能进行了研究,找到了比较适合Si片切割且挂线性能较好的切削液配比.     

Effect of plasma treatments on interface adhesion between SiOCH ultra-low-k film and SiCN etch stop layer

The effect of different plasma treatments on the interfacial bonding configurations and adhesion strengths between porous SiOCH ultra-low-dielectric-constant film and SiCN etch stop layer have been investigated in this study. From X-ray photoelectron spectroscopic analyses, interlayer regions of about 10 nm thick with complicated mixing bonds were found at SiOCH/SiCN interfaces. With plasma treatments, especially H₂/NH₃ two-step plasma, a carbon-depletion region of about 30 nm thick with more Si-O related bonds of high binding energy formed at the interface. Furthermore, the adhesion strengths of the SiOCH/SiCN interfaces were measured by nanoscratch and microscratch tests. For the untreated interface, the adhesion energy was obtained as about 0.22 and 0.44 J/m² by nanoscratch and microscratch tests, respectively. After plasma treatments, especially the H₂/NH₃ treatment, the interfacial adhesion energy was effectively improved to 0.41 and 0.89 J/m² because more Si-O bonds of high binding energy formed at the interfaces.     

Adhesion and Reliability of Anisotropic Conductive Films (ACFs) Joints on Organic Solderability Preservatives (OSPs) Metal Surface Finish

The effect of final metal finishes of Cu electrodes on the adhesion and reliability of anisotropic conductive film (ACF) joints was investigated. Two different metal surface finishes, electroless Ni/immersion Au (ENIG) and organic solderability preservatives (OSPs) coated on Cu, were selected in this study for ACF bonding. The adhesion strength of ACF/OSP joints was higher than that of ACF/bare Cu and ACF/ENIG joints. The fracture sites of the ACF/bare Cu and ACF/ENIG joints were ACF/metal interfaces, while those of ACF/OSP joints were inside the ACF. Transmission electron microscope (TEM) and Fourier-transform infrared (FT-IR) analyses showed that the OSP coating layer on the Cu electrodes reacted with the epoxy resin of the ACFs but still remained at the bonding interface. According to the in-depth X-ray photoelectron spectroscopy (XPS) analysis, additional C-N bonds formed after the OSP-epoxy reaction and the outermost nitrogen of the OSP layer participated in curing of the epoxy resin of the ACF. Therefore, the OSP layer acted as an adhesion promoter to ACFs. Furthermore, this role of the OSP layer enhanced the reliability of the ACF/OSP joints under high temperature and humid environments, as compared to the ACF/ENIG joints.     

Theoretical Prediction and Experimental Measurement of the Degree of Cure of Anisotropic Conductive Films (ACFs) for Chip-On-Flex (COF) Applications

The degree of cure of anisotropic conductive films (ACFs) was theoretically predicted and experimentally measured to investigate the effect of the degree of cure of ACFs on the electrical and mechanical stability of ACF joints and the␣reliability of chip-on-flex (COF) assemblies. The cure reaction of ACFs, observed by an isothermal differential scanning calorimetry (DSC) analysis, followed an autocatalytic cure mechanism, and the degree of cure of ACFs as a function of time and temperature was mathematically derived from an autocatalytic cure kinetics model. To simulate the ACF temperature field accurately during the COF bonding process, the thermal properties of the ACF such as the thermal diffusivity (α), specific heat capacity (C _p), and thermal conductivity (λ) were characterized experimentally. The degrees of cure of ACFs as functions of the bonding time during the COF bonding process were theoretically predicted by the incorporation of autocatalytic kinetics modeling and ACF temperature simulation. The predicted degrees of cure of ACFs were well matched with the experimental data measured by attenuated total reflectance/Fourier-transform infrared (ATR/FT-IR) analysis. The contact resistances of the ACF joints and the peel adhesion strengths of the COF assemblies were evaluated for electrical and mechanical interconnection stability. According to these results, the ACF contact resistances decreased and the ACF peel adhesion strengths increased as the degree of cure of ACFs increased. In addition, to investigate the effect of the degree of cure of ACFs on the reliability of COF assemblies, an 85°C/85% relative humidity (85°C/85% RH) test was performed. These results showed that the reliability of COF assemblies also strongly depends on the degree of cure of the ACFs.     

Biological Assemblies Provide Novel Templates for the Synthesis of Biocomposites and Facilitate Cell Adhesion

Mechanical mismatch and the lack of interactions between implants and the natural tissue environment are major drawbacks in bone tissue engineering. Biomaterials mimicking the self‐assembly process and the composition of the bone matrix should provide new routes for fabricating biomaterials possessing novel osteoconductive and osteoinductive properties for bone repair. In the present study, bioinspired strategies are employed to design de novo self‐assembled chimeric protein hydrogels comprising leucine zipper motifs flanking a dentin matrix protein 1 domain, which is characterized as a mineralization nucleator. Results show that this chimeric protein could function as a hydroxyapatite nucleator in pseudo‐physiological buffer with the formation of highly oriented apatites similar to biogenic bone mineral. It could also function as an inductive substrate for osteoblast adhesion, promote cell surface integrin presentation and clustering, and modulate the formation of focal contacts. Such biomimetic “bottom‐up” construction with dual osteoconductive and osteoinductive properties should open new avenues for bone tissue engineering.     

The study of low temperature hydrothermal growth of ZnO nanorods on stents and its applications of cell adhesion and viability

The hydrothermal growths of the ZnO nanorods with the densities ranging from 157 to 73 nanorods/μm² were achieved by diluting the ZnO seed solution. However, the ZnO seed nanocrystals started to agglomerate for the seed solution diluted below 1% of the original nano-crystalline solutions and resulted in the formation of clustered nanorods. With the assistance of a surfactant, Triton X-100, the nanorod density can be further reduced to 4 nanorods/μm². The diameters of the nanorods depended on the concentration of the seed solution and agitation speed of the nanorod growth solution. More diluted seed solution used and less agitation of the growth solution, the larger diameter of the nanorods was obtained. This indicated that the nanorod growth mechanism was controlled by the diffusion of reactants. With sufficient agitation of the growth solution, the nanorod can be uniformly grown with subjects on any arbitrary geometry. We have demonstrated ZnO nanorods growth on both inside and outside of biliary stents as well as on nitinol wires used as metal stents. The effect of nanorod density on the NIH 3T3 and HUVEC cells growth was also investigated in this study and the results suggested nanorod-coating to be a suitable method for controlling cell adhesion and viability on implantable devices.     

Biocompatibility of various ferrite nanoparticles evaluated by in vitro cytotoxicity assays using HeLa cells

Magnetic nanoparticles for thermotherapy must be biocompatible and possess high thermal efficiency as heating elements. The biocompatibility of Fe₃O₄ (20-30 nm), ZnFe₂O₄ (15-30 nm) and NiFe₂O₄ (20-30 nm) nanoparticles was studied using a cytotoxicity colony formation assay and a cell viability assay. The Fe₃O₄ sample was found to be biocompatible on HeLa cells. While ZnFe₂O₄ and NiFe₂O₄ were non-toxic at low concentrations, HeLa cells exhibited cytotoxic effects when exposed to concentrations of 100 μg/ml nanoparticles.