Investigation of geometric imperfections and joint stiffness of support scaffold systems

This paper describes the findings from various site measurements of geometric imperfections of support scaffold systems, also known as falsework in industry. The measurements consist of out-of-straightness of the standards (uprights), out-of-plumb of the frame and loading eccentricity between the timber bearer and the U-head screw jack. The measurements were taken from different support scaffold construction sites before the pouring of concrete, representing actual initial geometric imperfections and loading eccentricity encountered in practice. The paper also reports the results of support scaffold joint tests. The tests were performed on randomly chosen used components to investigate the joint stiffness for rotations about vertical and horizontal axes. Tests were performed for various joint configurations (two-way, three-way, and four-way connections), bending axes, and loading directions. The statistical analysis of the data is presented in the paper for practical application in modelling and probabilistic assessment of support scaffold systems.     

支撑系统的模拟

对具有不同升降高度、升降机数量和杰克延性的3+3支撑系统的足尺试验进行数值模拟,分析支撑系统性能。介绍了模拟栓接节点、半刚性梁连接及底板偏心的方法。基于Ramberg-Osgood方程,考虑材料非线性,并考虑了轴线不直、表面与轴线不垂直等初始几何缺陷。通过足尺试验得到的破坏荷载和荷载-位移曲线,对非线性分析得到的极限荷载进行修正。数值结果与试验很吻合,表明采用几何非线性和材料非线性分析能很好地研究支撑系统的性能和极限承载力。分析了支撑系统模拟中的一些难题,建立了底板、U型头、栓接节点的力学模型。     

同轴骨组织工程支架降解特性研究

为使抗骨结核药物在病灶区长期维持一定浓度,并促进术后缺损处的骨修复,应用羟基磷灰石、聚乙烯醇、丝素蛋白作为药物载体材料,结合自制机械式挤出装置制备同轴梯度骨组织工程支架。为使骨组织工程支架顺利植入体内,且保证支架负载的药物持续缓慢地释放,现对药物载体材料骨组织工程支架降解性能进行测试。研究发现降解10周后,无丝素蛋白的单轴支架的降解率为40.14%,同轴骨组织工程支架降解率为28.15%,说明复合丝素后降解速率明显变缓,这为药物长期释放提供可能。降解10周后,降解液pH值为6.8,溶液呈弱酸性。高倍扫描电镜图显示同轴骨组织工程支架微孔结构分布均匀,孔径尺寸随降解时间延长不断变大,可为新骨生长提供空间。力学实验测试结果表明同轴骨组织工程支架降解10周后抗压强度是12.61MPa,满足人体松质骨承载要求。     

In vitro evaluation of borate-based bioactive glass scaffolds prepared by a polymer foam replication method

Borate-based bioactive glass scaffolds with a microstructure similar to that of human trabecular bone were prepared using a polymer foam replication method, and evaluated in vitro for potential bone repair applications. The scaffolds (porosity = 72 ± 3%; pore size = 250–500 μm) had a compressive strength of 6.4 ± 1.0 MPa. The bioactivity of the scaffolds was confirmed by the formation of a hydroxyapatite (HA) layer on the surface of the glass within 7 days in 0.02 M K₂HPO₄ solution at 37 °C. The biocompatibility of the scaffolds was assessed from the response of cells to extracts of the dissolution products of the scaffolds, using assays of MTT hydrolysis, cell viability, and alkaline phosphatase activity. For boron concentrations below a threshold value (0.65 mM), extracts of the glass dissolution products supported the proliferation of bone marrow stromal cells, as well as the proliferation and function of murine MLO-A5 cells, an osteogenic cell line. Scanning electron microscopy showed attachment and continuous increase in the density of MLO-A5 cells cultured on the surface of the glass scaffolds. The results indicate that borate-based bioactive glass could be a potential scaffold material for bone tissue engineering provided that the boron released from the glass could be controlled below a threshold value.     

Preparation of novel porous calcium silicate scaffold loaded by celecoxib drug using freeze drying technique: Fabrication,characterization and simulation

In the current investigation, the microarchitecture of bio-nanocomposite scaffold, which is fabricated by natural synthetic diopside and composed of magnetite nanoparticles (MNPs), is considered. The MNPs are tested with various weight fractions (0, 5, 10, and 15 wt%) and are manufactured by the freeze-drying technique using sodium alginate as base matrix for the first time. Due to the limitation of the mechanical properties of calcium phosphates (CaPs) and bioactive glasses (BG), clinical usage of calcium silicate ceramics (CSC) are greatly affected. Therefore, CSCs are produced with the incorporation of metal oxides into the base binary xCaO-ySiO₂, as well as the substitution of calcium ions. Furthermore, mechanical and biological properties of CSCs are enhanced, which are a result of the ability to give out bioactive ions and their distinct compositions. After that, the porous bio-nanocomposite scaffolds are investigated for biological and mechanical properties corresponding to hardness versus elastic modulus, apatite formation versus biodegradation rate, wetting properties versus roughness and electrical conductivity of the sample. Then, the composition, microstructure, and physical characteristics are also examined using different techniques such as X-ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM) which is equipped with energy-dispersive X-ray spectroscopy (EDX). The obtained outcomes show that addition of diopside bioceramic enhances the mechanical and physical properties of the samples. It is shown that the prepared porous bio-nanocomposite scaffolds, containing 10 wt% MNPs, represents a better agreement in serving as a bone graft for the cancer disease treatment and hyperthermia term. The results indicate that the specimen with 10 wt% MNPs in the bio-nanocomposite release the celecoxib drug easier, however, its has better porosity and mechanical behavior that make it suitable candidate for bone implantations.     

A simple method to prepare hybrid hydroxyapatite scaffold mimicking nature bone

The physio-chemical properties of natural bone are significantly determined by the biological environment. Thus, it is desirable to prepare advanced bone tissue engineered scaffold by mimicking nature bone formation process. In this study, we proposed a new simple method (physio-chemical mixing) to prepare a hybrid hydroxyapatite (HA) scaffolds mimicking nature bone. Nano powder phases constitution was studied by SEM, XRD, and TEM. The results founded that the simple method could affect the physio-chemical properties (i.e., compositions and morphologies) of HA scaffolds. Moreover, the scaffolds prepared could have mimicked the nature bone.     

Factors governing the dimensional accuracy and fracture modes under compression of regular and shifted orthogonal scaffolds

Direct ink writing allows controlling the structure of tissue engineering scaffolds. The aim of this work was to study the effects of the in silico pattern design on the dimensional accuracy of tricalcium phosphate scaffolds and of the loading direction on the compressive strength and fracture modes. Regular and shifted scaffolds showed anisotropic shrinkage during drying and isotropic shrinkage during sintering. Shifted layers induced bending stresses when compressed longitudinally, resulting in lower compressive strength. The transverse Young’s modulus and compressive strength were higher than the longitudinal ones for both regular and shifted structures. Strand deflections were more pronounced in shifted structures. Finite element modelling suggested that such deflections considerably increased the effective transverse modulus of the shifted scaffolds, thus increasing the related compressive strength. In conclusion, shifted scaffolds performed similarly to regular ones in the transverse direction but were less mechanically reliable under the longitudinal direction.     

On the mechanical and biological properties of bredigite-magnetite (Ca7MgSi4O16-Fe3O4) nanocomposite scaffolds

The aim of the present study was to study the mechanical and biologocal properties of the bredigite-magnetite (Ca₇MgSi₄O₁₆-Fe₃O₄) nanocomposite with various amounts of magnetite (0, 10, 20 and 30 wt%). According to the obtained results, the properties of the constructed scaffolds have an extreme dependence on the magnetite content. In this research, the bredigite-30 wt% magnetite as the optimum sample showed a fracture toughness of 2.69 MPa m^1/2 and a Young's modulus of 29 GPa. Increasing bredigite content led to the increase of pH values in the SBF solution. This was originated from the interchange/interaction of Ca²⁺ ion on the scaffold surface. The sample containing 10 wt% magnetite presented a rocky and irregular surface while that of 30 wt% illustrated a smooth and flat outer layer with coarse projections. The results confirmed that the biodegradation rate of the pure bredigite is more than that of 20 wt% sample. The event is originated from the dissolution of the Si ions of the bridigite particles in the absence of magnetite.     

Novel Fe2O3-doped glass /chitosan scaffolds for bone tissue replacement

In this study quaternary bioglass system (BG) SiO₂–CaO–Na₂O–P₂O₅ doped with Fe₂O₃ was prepared by the sol–gel method. Furthermore, 3D scaffolds were designed through blending Fe₂O₃ -doped bioglass with chitosan to obtain various compositions of scaffolds by the freeze-drying technique. The thermal behavior, morphological properties, porosity (%), mechanical properties and physicochemical properties of BG and scaffolds were evaluated by DSC/TGA, TEM, SEM, liquid displacement method, universal testing machine, XRD and FTIR. In addition, the in vitro bioactivity of the prepared scaffolds was studied in phosphate buffer saline (PBS) through the determination of PBS ions concentrations, as well as the degradation and the observation of precipitated calcium phosphate layer by SEM coupled with EDX and FTIR behavior. The cell viability of the prepared scaffolds was conducted against Baby Hamster Kidney fibroblasts (BHK-21) cell line. The presence of Fe₂O₃ decreased the T_g (from 513 to 390?°C) and the size decreased (from 20.89 to 50.81–13.92–27.87?nm). The scaffolds porosity (%) decreased upon Fe₂O₃ doping but the mechanical strength increased. Cell viability results for the designed scaffolds demonstrated acceptable cell viability compared with normal cells. Therefore, the designed scaffolds are promoted as regenerated materials that can be used for bone tissue replacement.