Vapor Pressure Assisted Void Growth and Cracking of Polymeric Films and Interfaces

Pores and cavities form at filler particle-polymer matrix interfaces, at polymer film-silicon substrate interfaces as well as in molding compounds of IC packages. Moisture diffuses to these voids. During reflow soldering, surface mount plastic encapsulated devices are exposed to temperatures between 210 to 260°C. At these temperatures, the condensed moisture vaporizes. The rapidly expanding water vapor can create internal pressures within the voids that reach 3–6 MPa. These levels are comparable to the yield strengths of epoxy molding compounds and epoxy adhesives, whose glass transition temperatures T _g range between 150 to 300°C. Under the combined action of thermal stress and high vapor pressure (relative to the yield strength at T _g), both pre-existing and newly nucleated voids grow rapidly and coalesce. In extreme situations, vapor pressure alone could drive voids to grow and coalesce unstably causing film rupture, film-substrate interface delamination and cracking of the plastic package.Vapor pressure effects on void growth have been incorporated into Gurson's porous material model and a cohesive law. Crack growth resistance-curve calculations using these models show that high vapor pressure combined with high porosity bring about severe reduction in the fracture toughness. In some cases, high vapor pressure accelerates void growth and coalescence resulting in brittle-like interface delamination. Vapor pressure also contributes a strong tensile mode component to an otherwise shear dominated interface loading. An example of vapor pressure related IC package failure, known as popcorn cracking, is discussed.     

载荷对壁虎刚毛束的摩擦各向异性特性影响的实验研究

用离体壁虎刚毛阵列在自制微黏附摩擦测试台上对预加载荷对刚毛摩擦与黏着的各向异性特性的影响进行了实验研究.实验结果表明,在逆壁虎刚毛自然弯曲方向卷出实现脱附时, 刚毛所受摩擦力与法向力成正比,摩擦系数为0.6;沿顺刚毛自然弯曲方向卷入实现黏附时, 随预载荷增加摩擦力增加,法向力由黏附力变为斥力.在同等预载荷下,卷入方向的摩擦力是卷出方向的2倍以上. 本文提出了摩擦各向异性特征参数,对壁虎刚毛的黏着与摩擦各向异性进行了定量表征, 这种特性是由刚毛的弯曲及多等级结构决定的. 关键词： 壁虎刚毛 黏着 摩擦 各向异性     

Remote Switching of Elastic Movement of Decorated Ligand Nanostructures Controls the Adhesion-Regulated Polarization of Host Macrophages

Design of materials with remote switchability of the movement of decorated nanostructures presenting cell-adhesive Arg-Gly-Asp ligand can decipher dynamic cell-material interactions in decorated ligand nanostructures. In this study, the decoration of ligand-bearing gold nanoparticles (ligand-AuNPs) on the magnetic nanoparticle (MNP) with varying ligand-AuNP densities is demonstrated, which are flexibly coupled to substrate in various MNP densities to maintain constant macroscopic ligand density. Magnetic switching of upward (“Upper Mag”) or downward (“Lower Mag”) movement of varying ligand-AuNPs is shown via stretching and compression of the elastic linker, respectively. High ligand-AuNP densities promote macrophage adhesion-regulated M2 polarization that inhibits M1 polarization. Remote switching of downward movement (“Lower Mag”) of ligand-AuNPs facilitates macrophage adhesion-regulated M2 polarization, which is conversely suppressed by their upward movement (“Upper Mag”), both in vitro and in vivo. These findings are consistent with human primary macrophages. These results provide fundamental understanding into designing materials with decorated nanostructures in both high ligand-AuNP density and downward movement of the ligand-AuNPs toward the substrate to stimulate adhesion-regulated M2 polarization of macrophages while suppressing pro-inflammatory M1 polarization, thereby facilitating tissue-healing responses.     

Poly(5-nitroindole) Thin Film as Conductive and Adhesive Interfacial Layer for Robust Neural Interface

Poly(3,4-ethylenedioxythiophene) (PEDOT) has emerged as a promising neural interface material, but the weak adhesion of PEDOT to substrates adversely affects its reliability and practical application. Although adhesive interfacial layers have been explored to enhance the adhesion of PEDOT, their poor conductivity seriously compromises the performance of neural electrodes. It is a great challenge to develop an adhesive interfacial layer with excellent electrical properties. Herein, utilizing the advantages of polyindole derivatives, conductive polymers which have various functional groups for potential interface bonding, a conductive, adhesive, and biocompatible poly(5-nitroindole) (PIN-5NO₂) interfacial layer is developed to enhance the adhesion of PEDOT to metal electrodes. The conjugated PIN-5NO₂ with its superior electrical property can be prepared by electropolymerization of 5-nitroindole; however, the electrografting of amino groups, which is reduced from nitro groups in 5-nitroindole can provide strong adhesion with the gold (Au) substrate. With PIN-5NO₂ as an adhesive interfacial layer, the resultant Au/PIN-5NO₂/PEDOT electrode exhibits excellent electrochemical property, superb stability, and biocompatibility for high-performance neural interface. The in vivo evaluation of Au/PIN-5NO₂/PEDOT electrocorticographic microelectrodes demonstrates superior capacity to capture the neural dynamics of the brain. The novel strategy would offer a new insight for the construction of high-performance neural electrodes with high stability for neural interface application.     

A Highly-Adhesive and Self-Healing Elastomer for Bio-Interfacial Electrode

Stretchable electrodes are playing important roles in the measurement of bio-electrical signals especially in wearable electronic devices. These electrodes usually adopt commercial elastomers such as polydimethylsiloxane or polystyrene-ethylene-butylene-styrene as substrates, which result in poor stability and reliability due to weak interfacial adhesion between electrodes and human skin. Here, dopamine is introduced into the hydrogen bonding based elastomer as pendent groups. The elastomer shows both mechanical strength and adhesion strength at the same time. It exhibits high stress at break (1.9 MPa) and high fracture strain (5100%). Significantly, it exhibits a high adhesive strength (≈62 kPa) and underwater adhesive strength (≈16 kPa) with epithelial tissue. Thus, a stretchable bio-interfacial electrode is fabricated by spray-coating silver nanowires on the elastic substrate, which is stretchable, self-healable, and highly adhesive and suitable for electromyogram measurement.     

MMP-2 Responsive Unidirectional Hydrogel-Electrospun Patch Loading TGF-β1 siRNA Polyplexes for Peritendinous Anti-Adhesion

Bio-derived hydrogel patch systems exhibit promising potential in localized drug delivery for the prevention and treatment of various diseases. However, the uncontrolled release from the hydrogel patch both in time and space, is not an optimal strategy for peritendinous anti-adhesion, leading to transient effect and unnecessary diffusion of therapeutics. Here, an innovative composite anti-adhesion patch is designed for on-demand and unidirectional polyplexes delivery to inhibit fibroblasts proliferation and collagen deposition by silencing fibrosis gene transforming growth factor-β1 (TGF-β1). Firstly, a metalloproteinase-2 (MMP-2) degradable hydrogel is prepared by crosslinking allyl glycidyl ether (AGE) modified carboxymethyl chitosan (CMCS-AGE) with MMP-2 substrate peptide CPLGLAGC (MMP-2 sp). Then, the hydrogel loading TGF-β1 siRNA polyplexes are attached onto polycaprolactone (PCL) electrospun fibers to form a composite bilayer patch. The hydrogel–electrospun fibers (H–E) patch shows MMP-2-responsive and unidirectional release behaviors of encapsulated TGF-β1 siRNA polyplexes and associated gene silencing effect on TGF-β1, leading to the inhibition of fibroblasts proliferation. Moreover, after implanting the H–E patch by wrapping the repaired tendon, the formation of adhesion tissue is responsively attenuated in MMP-2 overexpression microenvironment. This study presents a promising approach employing a composite bilayer patch with on-demand and unidirectional delivery strategy for peritendinous anti-adhesion.     

聚酰亚胺衬底CIGS薄膜附着性的改善

为改善聚酰亚胺(PI)衬底Cu(In,Ga)Se2(CIGS)薄膜的附着性,提出在NaF沉积前预先在Mo层上蒸发沉积100nm厚的In-Ga-Se(IGS)薄膜的新掺Na工艺。结果表明:这种IGS-NaF-CIGS式新工艺可显著改善CIGS薄膜的附着,而且CIGS薄膜材料和器件特性没有显著退化;新工艺促进了NaInSe2的生成,减少了In-Se二元相的残余,但也造成薄膜电阻率的升高和电池填充因子的下降,进而导致制备的PI衬底CIGS电池的转换效率由9.8%降至9.0%。综合考虑附着性的改善和器件效率的轻微下降,新工艺利大于弊,有很好的应用前景。     

Inhomogeneous Friction Behaviour of Nanoscale Phase Separated Layered CuInP2S6

Mechanical friction leads to wear and energy dissipation, and its control is of high importance in new-generation miniature electromechanical devices. 2D materials such as graphene are considered to be excellent solid lubricants due to their ultralow friction and have attracted considerable research interest. Unique friction properties are discovered in various other 2D materials. However, the friction of functional van der Waals materials which have potential applications in novel nanoelectronics, like ferroelectric copper indium thiophosphate, has barely been studied. Herein, the study reports on the observation of inhomogeneous friction behavior existing in copper-deficient CuInP₂S₆ (Cu_0.2In_1.26P₂S₆), which exhibits a nanoscale phase separation of polar and non-polar crystalline phases. The paraelectric In_4/3P₂S₆ phase exhibits higher friction than the ferroelectric CuInP₂S₆ phase, while phase boundaries between the two phases, interestingly, display the lowest friction. The origin of this phenomenon is attributed to different lattice strains of phases together with the presence of large strains at the nanoscale phase boundaries, which also manifests in the nonuniform tip-sample adhesion force. The findings provide new insights into nanoscale device design and wear behavior of a phase-separated van der Waals ferroelectric, which may help to reduce the power consumption of friction-exhibiting devices and extend their service life.     

Bioinspired Mineral–Organic Bone Adhesives for Stable Fracture Fixation and Accelerated Bone Regeneration

The use of hydrogel‐based bone adhesives has the potential to revolutionize the clinical treatment of bone repairs. However, severe deficiencies remain in current products, including cytotoxicity concerns, inappropriate mechanical strength, and poor fixation performance in wet biological environments. Inspired by the unique roles of glue molecules in the robust mechanical strength and fracture resistance of bone, a design strategy is proposed using novel mineral–organic bone adhesives for strong water‐resistant fixation and guided bone tissue regeneration. The system leveraged tannic acid (TA) as a phenolic glue molecule to spontaneously co‐assemble with silk fibroin (SF) and hydroxyapatite (HA) in order to fabricate the inorganic–organic hybrid hydrogel (named SF@TA@HA). The combination of the strong affinity between SF and TA along with sacrificial coordination bonds between TA and HA significantly improves the toughness and adhesion strength of the hydrogel by increasing the amount of energy dissipation at the nanoscale. This in turn facilitated adequate and stable fixation of bone fracture in wet biological environments. Furthermore, SF@TA@HA promotes the regeneration of bone defects at an early stage in vivo. This work presents a type of bioinspired bone adhesive that is able to provide stable fracture fixation and accelerated bone regeneration during the bone remodeling process.     

基于车辆底盘阴影的车辆精确分割算法研究

在基于视频的智能交通系统中,利用车辆底盘阴影特征,并结合车辆边缘及稳定背景和可信前景等特征,抑制局部遮挡导致的车辆粘连问题,将遮挡的车辆准确分离。实验结果表明,车辆底盘特征能较好地用于粘连车辆的精确分割。