Development of the Fibrillar and Microfibrillar Structure During Biomimetic Mineralization of Wood

Wood is a hierarchical composite, consisting at its lowest hierarchy level of crystalline cellulose elementary fibrils with diameters of 2–4 nm embedded in a matrix of hemicelluloses and lignin. At the micrometer scale, it has a cellular architecture resembling a honeycomb structure. The transformation of the hierarchical wood structure into a silica replica has been reported recently. Its formation process and structural details are studied in this contribution. First, a silica/biopolymer composite is prepared by wood delignification and cell‐wall modification, followed by silica precursor infiltration and condensation. The calcination process is monitored to gain insight into the structure development upon decomposition of the biopolymers. The material changes its architecture gradually from fibrillar structures of 10–20 nm in diameter with homogeneous electron density, into fibrils of 8–10 nm in diameter with inhomogeneous electron density, exhibiting internal sub‐fibrillar structures of about 2 nm in diameter. The steps of the successful replication of the cellulose elementary fibrils into nanopores of similar diameter and orientation in a fibrillar silica matrix are demonstrated. These nanopore replicas of the original cellulose are wound in a steep helix within the macropore walls. These advanced materials may have lightweight structural applications and the nanopores may be advantageous for molecular separation.     

Nanomanipulation and aggregation limitations of self-assembling structural proteins

Collagen, the most abundant protein on Earth, is used as a platform for studying three major hurdles of nanotechnology: (1) What is the aggregation limit in self-assembling systems? (2) What is the smallest scale at which matter can be reliably and repeatedly organized? (3) Where do the natural boundaries lie in what is achievable via directed manipulation at the nanoscale? Through work involving a mechanics-based model for predicting the radial aggregation limit of collagen fibrils using translation length, axial and torsional stiffness of the tropocollagen model, and specific binding sites, the 20-500 nm diameter distribution of collagen is explored, verifying previous atomic force microscopy data. Preliminary micromanipulation of collagen fibers with the Zyvex S100 also implicate the necessary steps to be taken in proposed nanomanipulation experiments. Results presented implicate: (1) That the aggregation limit of collagen fibrils and perhaps other structural proteins may be predicted by the mechanical properties of its molecular subunits wherein the outer portions of the fibril are in tension balanced by compressive stresses within the inner portions, (2) That currently the top-down style of nanomanipulation must be improved via advances in computational imaging if it is to keep pace with advancements which have been made at the microscale, and (3) That there exist tightly constrained paths which must be followed in order to create beneficial mutations at the molecular level.     

Three-dimensional meshwork structure of glomerular basement membrane revealed by chemical treatment

In order to study the three-dimensional ultrastructure of the glomerular basement membrane (GBM), isolated GBM was treated with elastase, sodium dodecyl sulfate, and 2-mercaptoethanol and examined by transmission electron microscopy using ultrathin sectioning method and stereoscopic view. This treatment revealed clearly three-dimensional meshwork structure of GBM mainly composed of type IV collagen. Numerous regular polygonal small pores were present in the meshwork structure. The average short dimension of the small pores was 4.1 +/- 1.8 nm and the average long dimension was 4.8 +/- 2.2 nm. Our present results further support the molecular sieve theory of the basement membrane.     

Regenerating axons and their growth cones observed by scanning electron microscopy

A predenervated sciatic nerve segment, which had been treated by repeated freezing and thawing to kill Schwann cells, was grafted to the original sciatic nerve in the rat. Three to five days later, the graft was chemically fixed and treated by KOH-collagenase digestion, a treatment which selectively removes almost all non-cellular elements including the collagen fibrils and basal laminae from the tissue, thus making it possible to observe regenerating axons by scanning electron microscopy. Debris of degraded Schwann cells and myelin sheaths remained in the form of "columns", and several thick (2-3 microns in diameter) and thin (less than 1 micron in diameter) axons ran singly or in bundles on such "cell debris columns." Thick axons have an almost straight contour, while there were various swellings at intervals along the thin axons. In most cases, the growing tips of regenerating axons were swollen as growth cones ranging from 2 microns to 5 microns in diameter. Growth cones exhibited fusiform to polygonal variations in structure and had only a few filopodial processes on the surface.     

直角坐标系下无向双环网络G(N;±1,±s)直径的研究

提出将直角坐标系引入无向双环网络的研究,通过直角坐标系,系统研究无向双环网络G(N;±1,±s)的直径、平均直径,验证直径的下界,得出平均直径的下界。最后给出直角坐标系下无向双环网络的仿真方法,该方法克服了传统L型瓦方法在无向双环网络研究中的不足,大大提升了无向双环网络的研究水平。     

太阳光度计定标方法和西安地区气溶胶光学特征的研究

利用西安理工大学2015~2018年的太阳光度计观测资料,在传统Langley法定标的基础上,利用期望平均法和拟合平均法获得了更为稳定的仪器定标系数,分析了西安地区气溶胶光学厚度和?ngstr?m波长指数的变化特征。研究结果表明:（1）仅用Langley法对仪器进行定标带来的误差较大,引入期望平均法与拟合平均法后,得到的仪器定标值更合理,有效解决了Langley法定标值波动较大的问题;（2）西安地区气溶胶光学厚度日变化呈现5种特征:平稳型、上升型、下降型、凹型和凸型,其中平缓型出现频率最低（3.55%）,凸型出现频率最高（34.25%）;（3） 500 nm气溶胶光学厚度季节均值为0.60±0.36,0.59±0.33,0.62±0.40,0.68±0.36,呈春夏低、秋冬高的季节变化趋势。?ngstr?m波长指数季节均值在夏季最大（1.06±0.33）,春季最小（0.81±0.32）。     

Cathepsins in the osteoclast

The mechanism by which bone collagen and other organic components are degraded by the osteoclast during osteoclastic bone resorption was unclear until the 1980s. Studies conducted since the early 1990s have identified lysosomal proteases, mainly cathepsins that are active at low pH, involved in osteoclastic bone resorption. Several cathepsins, such as cathepsins C, D, B, E, G and L, were initially demonstrated to take part in the degradation of organic bone matrix in osteoclasts. Cathepsin K, which has high proteolytic activity and localizes primarily in osteoclasts, was discovered in 1995. This first tissue-specific cathepsin was associated with pycnodysostosis, a genetic disorder observable as an osteopetrotic phenotype in cathepsin K-deficient mice. Cystatin C, an endogenous inhibitor of cysteine proteases, regulates the activity of cathepsin K. However, detailed morphological observations suggest that the organic bone matrix is degraded by not only cathepsin K, but also by matrix metalloproteinases or other cathepsins. The osteoclast possesses a unique endocytotic/exocytotic structure and each cathepsin is specifically localized in the osteoclast, which implies that each cathepsin contributes cooperatively to the process of osteoclastic bone resorption. Further studies may clarify the regulation of cathepsin activities and the roles of cathepsins during bone remodelling.     

Perichromatin granule-like granular structures in the nuclei of antral-follicular oocytes of the Chinese hamster

In the nuclei of antral-follicular oocytes of the Chinese hamster (Cricetulus griseus), numerous granular structures ranging from 60 nm to 250 nm in diameter were present in the nucleolar area, and a few were observed on the surface of heterochromatin materials and within the interchromatin space. When treated with bismuth staining en bloc after glutaraldehyde fixation (GA-Bi staining), these granular structures were shown to be composed of fine fibrils intensely contrasted with bismuth, indicating that these may be regarded as one type of perichromatin granule.     

Engineering Functional Collagen Scaffolds: Cyclical Loading Increases Material Strength and Fibril Aggregation

Variation in collagen fibril diameter in nature is a major factor determining biological material properties. However, the mechanism resulting in this fibril diameter difference is not clear and generally assumed to be cell‐dependent. It is certainly not possible so far to engineer this into implantable scaffold materials. This gap in our knowledge is crucial for the fabrication of truly biomimetic tissue‐like materials. We have tested the idea that fibril diameter can be regulated directly without cell involvement, using cyclical mechanical loading to promote fibril fusion. Specific loading regimes increased collagen fibril diameter (> 2 fold) in direct relation to cycle number, whilst thin fibrils disappeared. Tensile properties increased, producing a 4.5 fold rise in break strength. This represents the first demonstration of direct cyclical load‐promoted fibril fusion and provides a direct relation with material properties. The ability to control material properties in this way makes it possible to fabricate truly biomimetic collagen materials without cells.     

Imaging saponin-induced structural changes in neural processes with atomic force microscopy

Temporal changes in the structure of neuronal processes in the presence of saponin were studied by atomic force microscopy in a fluid medium. After saponin treatment, concavities were formed on the surface of some neurites and fibrous structures in other neurites were splayed. The vertical height of these splayed fibrils or fibrillar bundles ranged from 13 to 370 nm, and the horizontal width was less than 500 nm. These findings suggest that formation of concavities and separation of bundled fibrils occurred simultaneously in saponin-treated neurites.     

A sulphur matrix complex,elastic fibril composed of a fine core of amorphous elastin and microfibrils was largely accumulated in the aortic intima of aged rats

We examined elastic fibrils in the aortic intima of aged rats with elastin staining, elastase digestion and X-ray microanalysis. The innermost elastic lamina, heavily stained by a brief treatment with azure II-toluidine blue without heating, was thin and fragmented, and an amorphous substance that stained weakly to moderately was accumulated in the thick subendothelial space of 26-28-month-old rat aortas. The substance was always present in the intimas; to a large extent in the aged rats but rarely in 5-month-old rats, and disappeared after digestion with elastase. The amorphous substance was identified as elastic fibrils approximately 0.1-0.2 microm in diameter under an electron microscope with tannic acid-uranyl acetate/lead citrate staining. Elastase digestion revealed that elastic fibrils were composed of a number of microfibrils, which were 10-12 nm in diameter, in and around a fine core of amorphous elastin. X-ray microanalysis revealed a clear peak of sulphur in the elastic fibrils.     

Transparent,Anisotropic Biofilm with Aligned Bacterial Cellulose Nanofibers

Cellulose nanofibrils are attractive as building blocks for advanced photonic, optoelectronic, microfluidic, and bio‐based devices ranging from transistors and solar cells to fluidic and biocompatible injectable devices. For the first time, an ultrastrong and ultratough cellulose film, which is composed of densely packed bacterial cellulose (BC) nanofibrils with hierarchical fibril alignments, is successfully demonstrated. The molecular level alignment stems from the intrinsic parallel orientation of crystalline cellulose molecules produced by Acetobacter xylinum. These aligned long‐chain cellulose molecules form subfibrils with a diameter of 2–4 nm, which are further aligned to form nanofibril bundles. The BC film yields a record‐high tensile strength (≈1.0 GPa) and toughness (≈25 MJ m^?3). Being ultrastrong and ultratough, yet the BC film is also highly flexible and can be folded into desirable shapes. The BC film exhibits a controllable manner of alignment and is highly transparent with modulated optical properties, paving the way to enabling new functionalities in mechanical, electrical, fluidic, photonics, and biocompatible applications.     

Synthesis and Characterization of Silica Nanotubes with Radially Oriented Mesopores

Hierarchical silica nanotubes with radially oriented mesoporous channels perpendicular to the central axis of the tube were synthesized by using self‐assembled chiral anionic surfactant, co‐structure directing agent (CSDA) and silica precursor. The average inner diameter and the wall thickness were ∼94, ∼62, and ∼62 nm and to ∼27, ∼33, and ∼45 nm, respectively, by manipulating the synthesis gel composition, while the diameter of the wall mesopores was kept constant at ∼4 nm. These materials with such a unique structure were produced only with chiral surfactant and achiral or racemic surfactant did not give rise to mesoporous silica nanotubes. The existence of helicity in the lipid bilayer template was confirmed by means of circular dichroism spectroscopy. The mesoporous penetrating from outside to inside of silica nanotubes are thought to originate from the initial formation of self‐assembled lipid tubes with helical bilayers, which in turn re‐assemble to form the mesopores in the wall of the nanotubes upon addition of co‐structure directing agent and silica source.     

Submicron resolution deep UV photolithography

A vacuum contact printing technique was used to evaluate the resolution limits of deep UV photolithography with a 300±30 nm exposure band. For the first time, an array of 200 chip sites containing 0.5 ?m meander patterns 3 cm long was clearly resolved in AZ 2415 positive resist across 2 in diameter silicon wafers.     

Oriented Strontium Carbonate Nanocrystals within Collagen Films for Flexible Piezoelectric Sensors

Bone, assembled by mineralized collagen fibrils, displays piezoelectric properties under external stimulation to affect tissue growth. The mineralized collagen fibrils consist of collagen and oriented inorganic nanocrystals. Inspired from the unique structures and piezoelectric effect of mineralized collagen fibrils, the intrafibrillar mineralization of oriented strontium carbonate nanocrystals is achieved in vitro, which also exhibits good piezoelectric properties. The amorphous strontium carbonate precursors penetrate from the gap zones and fill gradually into the whole space within the collagen fibrils, and transform into a co-oriented crystalline phase. Isolated mineralized collagen fibrils with organized SrCO₃ nanocrystals acquire good flexible properties and inverse piezoelectric responses with an effective piezoelectric coefficient of 3.45 pm V⁻¹, much higher than individual collagen (1.12 pm V⁻¹) and SrCO₃ crystals (0.092 pm V⁻¹). These results may indicate that the organic and inorganic components synergistically contribute to the piezoelectric effect of bone. Furthermore, devices of flexible piezoelectric thin films assembled by SrCO₃ mineralized collagen fibrils exhibit a regular open-circuit voltage of 1.2 V under compressive stress and a stable cycling short-circuit current of 80 nA under a bending mode. It can also facilitate the development of promising piezoelectric sensors.     

Statistical analysis of collagen alignment in ligaments byscale-space analysis

Injuries to ligaments in the knee are common in sports and other physical activities. Some clinical methods are available for qualitatively evaluating the degree of ligament injury and healing. It is, however, desirable to objectively assess the healing of ligaments and to predicate optimal treatment on quantitative measurements of their structure. Information such as areas of coverage and spatial orientations of collagen fibrils, for example, may provide important information about the internal structure of ligament tissues. Since normal ligament tissues are made up of collagen fibrils which are highly organized, they can be considered as oriented piecewise linear patterns. In this paper, we propose a computational technique for statistical analysis of collagen alignment in ligament images using the scale-space approach. In this method, a ligament image is preprocessed by a sequence of filters which are second derivatives of two-dimensional Gaussian functions with different scales. This gives a set of zero-crossing maps (the scale space) from which a stability map is generated. Significant linear patterns are captured by analyzing the stability map. The directional information in terms of orientation distributions of the collagen fibrils in the image and the area covered by the fibrils in specific directions are extracted for statistical analysis. Examples illustrating the performance of this method with scanning electron microscope images of the collagen fibrils in healing rabbit medial collateral ligaments are presented in this paper.     

Matrix remodeling and cytological changes during spontaneous cartilage repair

During the repair of articular cartilage, type I collagen (COL1)-based fibrous tissues change into a mixture of COL1 and type II collagen (COL2) and finally form hyaline cartilaginous tissues consisting of COL2. In order to elucidate the changes that occur in the matrix during cartilage repair and the roles of fibroblasts and chondrocytes in this process, we generated a minimal cartilage defect model that could be spontaneously repaired. Defects of 0.3?mm were created on the patellofemoral articular cartilage of rats using an Er:YAG laser and were observed histologically, ultrastructurally and histochemically. At week 2 after this operation, fibroblastic cells were found to be surrounded by COL1 throughout the area of the defect. These cells became acid phosphatase positive by week 4, both taking in and degrading collagen fibrils. Thereafter, the cells became rounded, with both COL1 and 2 evident in the matrix, and showed immunolocalized matrix metalloproteinase-1 or -9. In the region of the bone marrow, the cells became hypertrophic and were surrounded mainly by COL2 and proteoglycans. By the eighth week, the cartilaginous matrix was found to contain abundant COL2, in which collagen fibrils of various diameters were arranged irregularly. These morphological changes suggested that the fibroblastic cells both produce and resolve the matrix and undertake remodeling to become chondrocytes by converting from a COL1- into a COL2-dominant matrix. This process eventually forms new articular cartilage, but this is not completely identical to normal articular cartilage at the ultrastructural level.     

Low-Temperature Synthesis of Fe-Doped ZnO Nanotubes

We report on the synthesis Zn_1?x Fe _x O nanotubes with average tube diameter of 60?nm to 100?nm and wall thickness of about 20?nm. The nanotubes were synthesized by a low-temperature electrochemical process, and their morphology was found to be sensitive to the electrolyte concentration and growth time. The maximum Fe doping achieved by this process was estimated to be approximately 4?wt.%. High-resolution transmission electron microscopy and x-ray diffraction showed good crystalline quality of the doped and undoped nanotubes with preferential growth along the wurtzite c-axis. The Fe-doped nanotubes exhibit wurtzite crystal structure with an increase in the c-axis lattice constant when compared with the undoped nanotubes, indicative of the fact that Fe ions substitute for Zn as 2+ ions in the ZnO crystal lattice. Further evidence of Fe as a substitutional dopant is provided by Raman and photoluminescence spectroscopy. A comparison of the effective magnetic moment in the undoped and doped nanotubes reveals the presence of four unpaired electrons in the Fe-doped sample and zero unpaired electrons for the undoped sample.     

Dispersion minimisation in single-mode fibres over a wide spectral range

The waveguide and material dispersion are investigated for various silica-based single-mode optical fibres with arbitrary refractive-index profiles. It is shown that in the case of the doubly clad optical fibre with an index difference between the core and the outer cladding ?1=1% and that between the inner cladding and the outer ?2=?1%, the diameter of the core 2a=7.2 ?m, and the thickness of the inner cladding t=0.3a, the total dispersion is reduced within ± 1 ps/km/nm over a wide spectral range of ?=1.35?1.67 ?m.     

基于负染－电镜的Aβ体外聚集表征测试要点分析

本文应用电镜负染色技术,对阿尔茨海默病（ Alzheimer′s disease, AD）中所涉及的β淀粉样肽（β?amyloid peptide,Aβ）的聚集规律进行了分析。通过对样品的浓度、pH值、温度和时间等设置系列梯度,以及调整负染试剂的种类、浓度和染色时间,优化了Aβ寡聚体样品制备以及电镜观察的最佳条件,获得了清晰的Aβ纤维图像并用以估算纤维长度。实验结果表明：经过六氟异丙醇给予单体化处理,并溶于无水二甲基亚砜（ DMSO）的Aβ（100μmol·L－1）,在pH7?2的PBS中4℃孵育24 h,Aβ寡聚体形态清晰,且Aβ42寡聚体比Aβ40寡聚体聚集趋势更明显。在pH 8?0的硼酸缓冲液中,Aβ42（40μmol·L－1）在37℃孵育72 h后,纤维形成明显;而Aβ纤维样品经过煮沸后再制备负染样品,所得电镜图像更为清晰,便于对纤维长度和结构进一步分析。因此电镜负染色技术,可作为一种快捷,直观的Aβ体外聚集形貌表征的质控方法。