Development of a Three-Dimensional Multiscale Octree SBFEM for Viscoelastic Problems of Heterogeneous Materials

The multiscale method provides an effective approach for the numerical analysis of heterogeneous viscoelastic materials by reducing the degree of freedoms(DOFs).A basic framework of the Multiscale Scaled Boundary Finite Element Method(MsSBFEM)was presented in our previous works,but those works only addressed two-dimensional problems.In order to solve more realistic problems,a three-dimensional MsSBFEM is further developed in this article.In the proposed method,the octree SBFEM is used to deal with the three-dimensional calculation for numerical base functions to bridge small and large scales,the three-dimensional image-based analysis can be conveniently conducted in small-scale and coarse nodes can be flexibly adjusted to improve the computational accuracy.Besides,the Temporally Piecewise Adaptive Algorithm(TPAA)is used to maintain the computational accuracy of multiscale analysis by adaptive calculation in time domain.The results of numerical examples show that the proposed method can significantly reduce the DOFs for three-dimensional viscoelastic analysis with good accuracy.For instance,the DOFs can be reduced by 9021 times compared with Direct Numerical Simulation(DNS)with an average error of 1.87%in the third example,and it is very effective in dealing with three-dimensional complex microstructures directly based on images without any geometric modelling process.

Craniocerebral injury promotes the repair of peripheral nerve injury

The increase in neurotrophic factors after craniocerebral injury has been shown to promote fracture healing. Moreover, neurotrophic factors play a key role in the regeneration and repair of peripheral nerve. However, whether craniocerebral injury alters the repair of peripheral nerve injuries remains poorly understood. Rat injury models were established by transecting the left sciatic nerve and using a free-fall device to induce craniocerebral injury. Compared with sciat- ic nerve injury alone after 6-12 weeks, rats with combined sciatic and craniocerebral injuries showed decreased sciatic functional index, increased recovery of gastrocnemius muscle wet weight, recovery of sciatic nerve ganglia and corresponding spinal cord segment neuron mor- phologies, and increased numbers of horseradish peroxidase-labeled cells. These results indicate that craniocerebral injury promotes the repair of peripheral nerve injury.

Sericin protects against diabetes-induced injuries in sciatic nerve and related nerve cells

Sericin from discarded silkworm cocoons of silk reeling has been used in different fields, such as cosmetology, skin care, nutrition, and oncology. The present study established a rat model of type 2 diabetes by consecutive intraperitoneal injections of low-dose （25 mg/kg） streptozotocin. After intragastrical perfusion of sericin for 35 days, blood glucose levels significantly declined, and the expression of neurofilament protein in the sciatic nerve and nerve growth factor in L4-6 spinal ganglion and anterior horn cells significantly increased. However, the expression of neuropeptide Y in spinal ganglion and anterior horn cells significantly decreased in model rats. These findings indicate that sericin protected the sciatic nerve and related nerve cells against injury in a rat type 2 diabetic model by upregulating the expression of neurofilament protein in the sciatic nerve and nerve growth factor in spinal ganglion and anterior horn cells, and downregulating the expression of neuropeptide Y in spinal ganglion and anterior horn cells.

Estrogen intervention in microvascular morphology and choline acetyltransferase expression in rat hippocampal neurons in chronic cerebral ischemia

We observed dynamic changes in microvessels and a protective effect of estrogen on chronic cerebral ischemia ovariectomized rat models established through permanent occlusion of bilateral carotid arteries at 7, 14 and 21 days. The results revealed that estrogen improved microvasculature in the hippocampus of chronic cerebral ischemic rats, upregulated Bcl-2 protein expression, downregulated Bax protein expression, increased choline acetyltransferase expression in hippocampal cholinergic neurons, and suppressed hippocampal neuronal apoptosis. These findings indicate that estrogen can protect hippocampal neurons in rats with chronic cerebral ischemia.

Application of scaled boundary finite element method in static and dynamic fracture problems

The scaled boundary finite element method （SBFEM） is a recently developed numerical method combining advantages of both finite element methods （FEM） and boundary element methods （BEM） and with its own special features as well. One of the most prominent advantages is its capability of calculating stress intensity factors （SIFs） directly from the stress solutions whose singularities at crack tips are analytically represented. This advantage is taken in this study to model static and dynamic fracture problems. For static problems, a remeshing algorithm as simple as used in the BEM is developed while retaining the generality and flexibility of the FEM. Fully-automatic modelling of the mixed-mode crack propagation is then realised by combining the remeshing algorithm with a propagation criterion. For dynamic fracture problems, a newly developed series-increasing solution to the SBFEM governing equations in the frequency domain is applied to calculate dynamic SIFs. Three plane problems are modelled. The numerical results show that the SBFEM can accurately predict static and dynamic SIFs, cracking paths and load-displacement curves, using only a fraction of degrees of freedom generally needed by the traditional finite element methods.

Altered acetylcholinesterase levels in the spinal cord anterior horn and dorsal root ganglion following sciatic nerve ischemia

BACKGROUND： Peripheral nerve ischemia has been shown to result in ischemic fiber degenera-tion and axoplasmic transport disturbance. However, the effect on acetylcholinesterase （AChE） ex- pression in relevant cells following sciatic nerve ischemia remains unclear. OBJECTIVE： To observe AChE concentration changes following peripheral nerve ischemia. DESIGN, TIME AND SETTING： The present comparative observation, neuroanatomical experiment was performed at the Central Laboratory Animal of Chengde Medical College between 2006 and 2007. MATERIALS： A total of 20 healthy, adult, Wistar rats were randomized into two groups （n = 10）： 8-day ischemia and 14-day ischemia. METHODS： Ischemia injury was induced in the unilateral sciatic nerve （experimental side） through ligation of the common iliac artery. The contralateral side received no intervention, and served as the control side. Rats in the 8-day ischemia and 14-day ischemia groups were allowed to survive for 8 and 14 days, respectively. MAIN OUTCOME MEASURES： The L5 lumbar spinal cord and the L5 dorsal root ganglion were removed from both sides and sectioned utilizing a Leica vibrating slicer. AChE cellular expression was detected using Karnovsky-Root, and the number of AChE-positive cells and average gray value were analyzed using a MiVnt image analysis system. RESULTS： In the 8-day ischemia group, AChE-positive cell numbers were significantly less in the dorsal root ganglion and spinal cord anterior horn of the experimental side, but the average gray value was significantly greater, compared with the control side （P 〈 0.05）. These changes were more significant in the 14-day ischemia group than in the 8-day ischemia group （P 〈 0.01）. CONCLUSION： Peripheral nerve ischemia leads to decreased AChE expression in the associated cells in a time-dependent manner.

FINITE ELEMENT MODELLING OF COMPLEX 3D STATIC AND DYNAMIC CRACK PROPAGATION BY EMBEDDING COHESIVE ELEMENTS IN ABAQUS

This study proposes an algorithm of embedding cohesive elements in Abaqus and develops the computer code to model 3D complex cragk propagation in quasi-brittle materials in a relatively easy and efficient manner. The cohesive elements with softening traction-separation relations and damage initiation and evolution laws are embedded between solid elements in regions of interest in the initial mesh to model potential cracks. The initial mesh can consist of tetrahedrons, wedges, bricks or a mixture of these elements. Neither remeshing nor objective crack propagation criteria are needed. Four examples of concrete specimens, including a wedgesplitting test, a notched beam under torsion, a pull-out test of an anchored cylinder and a notched beam under impact, were modelled and analysed. The simulated crack propagation processes and load-displacement curves agreed well with test results or other numerical simulations for all the examples using initial meshes with reasonable densities. Making use of Abaqus＇s rich pre/post- processing functionalities and powerful standard/explicit solvers, the developed method offers a practical tool for engineering analysts to model complex 3D fracture problems.

Synthesis and Anti-HIV Activity of a Series of 6-Modified 2＇,3＇-Dideoxyguanosine and 2＇,3＇-Didehydro-2＇,3＇- dideoxyguanosine Analogs

In search of potential 2＇,3＇-dideoxyguanosine （ddG） and 2＇,3＇-didehydro-2＇,3＇-dideoxyguanosine （D4G） prodrugs, a series of 6-modified ddG, D4G analogs were synthesized and evaluated for their anti-HIV activities and cyto- toxities in cell-based assays. All analogs showed low cytotoxieities and some of them displayed benign anti-HIV activities. The active triphosphate forms in vivo, ddGTP and D4TTP, were also synthesized by a novel and facile ＂one-pot＂ method. The recognition of ddGTP and D4TTP by Taq, Therminater DNA polymerase and HIV reverse transcriptase （RT） incorporated in DNA/RNA strands were investigated by a non-radioactivity method and Km were determined.

Synthesis and Antitumor Activity Evaluation of γ-Monofluorinated and γγy-Difluorinated Goniothalamin Analogues

A series of novel γ,γ-difluorinated Goniothalamin analogues 4a--4i and 6a--6i were synthesized. The key steps included the construction of C-5 stereocenter adjacent to gem-difluoromethylene group by way of lipase AK catalyzed kinetic resolution, the introduction of aryl group via Stille coupling, and lactonization by 1,5-oxidative cycli- zation. These γ,γ-difluorinated Goniothalamin analogues 4a-4i and their enanfiomers 6a--6i, together with several corresponding 7-monofluorinated Goniothalamin analogues were biologically evaluated against four different cancer cell lines. Compound 7h showed a nearly equivalent potency as the parent （R）-Goniothalamin in the micromolar range. The different fluorine effects between fluoromethylene and gem-difluoromethylene on antitumor activity were discussed through the analysis of bioassay data.

Supramolecular Assembly Models of siRNA Delivery Systems

Small interfering RNA(siRNA)technology,which could be able to silence specific targeted mRNAs rapidly and efficiently,has been regarded as a novel and potent gene therapeutic approach for diseases,such as cancers,in-fections,inflammations and neurological disorders.However,some conspicuous intrinsic defects of siRNA including the poor cellular uptake,low biological stability,unfavorable pharmacokinetics and bio-distribution properties,have hindered further applications in clinic.Therefore,it is prerequisite to design safe and effective siRNA delivery systems for the successful development of siRNA-based various diseases therapeutics.This review aims to analyze and summarize these supramolecular assembly models in the process of siRNA delivery,namely recent nanotech-nological strategies for carrying siRNA by using diverse non-viral vehicles such as cationic liposomes,stable nucleic acid lipid particles(SNALPs),cationic polymers,cationic dendrimers,inorganic nanoparticles and others.Eventually,it is concluded with future perspectives of siRNA therapeutics in the field of non-viral carriers.