Experimental and analytical studies on steel scaffolds under eccentric loads

Steel scaffolds collapse quite often in many places with a considerable number of reported casualties, but their behaviour has not been studied to the extent of many other permanent structures. This paper investigates the effect of eccentric loads on steel scaffolding systems used in construction sites. The type of scaffold considered here is the door-shaped steel scaffold with an inner reinforced gable sub-frame. The single-side cross-brace scaffolding systems with various eccentric loads are mainly focused on two issues, namely, the unrestrained boundary and the removal of cross-braces at the access location. This study shows that regardless of the lowest layer of cross-brace in a scaffold being removed or not, the critical load of a scaffolding system under an eccentric load is the lowest, whereas that of scaffolding system under a concentric load is the maximum. If the bottom jack base of a scaffolding system in construction sites is strengthened to a fixed end, the critical load of this scaffolding system will be greatly increased. If a scaffolding system is erected more than 8 stories high, the critical load of the scaffolding system with the fixed end base can be increased to 2.4 times that with the hinged base. However, whether the cross-braces at the lowest story of a scaffolding system are removed or not, the simulated scaffolding test indicates that the critical load of a used scaffolding system under the eccentric load is the lowest and its load reduction also appears significant.     

Porous poly (lactic-co-glycolide) microsphere sintered scaffolds for tissue repair applications

In this paper, a new route to preparing porous poly (lactic-co-glycolide) (PLGA) scaffolds for bone tissue repair applications was developed. Novel porous PLGA scaffolds were fabricated via microsphere sintered technique and gas forming technique. Ammonium bicarbonate was used to regulate porosity of these porous scaffolds. Porosity of the scaffolds, and cell attachment, viability and proliferation on the scaffolds were evaluated. The results indicated that PLGA porous scaffolds were with the porosity from around 30% to 95% by regulating ammonium bicarbonate content from 0 to 10%. We also found that PLGA porous microsphere scaffolds benefited cell attachment and viability. Taken together, the achieved porous scaffolds have controlled porosity and also support mesenchymal stem cell proliferation, which could serve as potential scaffolds for bone repair applications.     

In vitro cellular response to hydroxyapatite scaffolds with oriented pore architectures

The objective of the present work was to evaluate the in vitro cellular response to hydroxyapatite (HA) scaffolds with oriented pore architectures. Hydroxyapatite scaffolds with approximately the same porosity (65–70%) but two different oriented microstructures, described as ‘columnar’ (pore diameter = 90–110 μm) and ‘lamellar’ (pore width = 20–30 μm), were prepared by unidirectional freezing of suspensions. The response of murine MLO-A5 cells, an osteogenic cell line, to these scaffolds was evaluated using assays of MTT hydrolysis, alkaline phosphatase (ALP) activity, and alizarin red staining. While the cellular response to both groups of scaffolds was better than control wells, the columnar scaffolds with the larger pore width provided the most favorable substrate for cell proliferation and function. These results indicate that HA scaffolds with the columnar microstructure could be used for bone repair applications in vivo.     

基于形函数控制的组织工程骨架孔隙结构实体建模方法

组织工程支架在组织工程研究中起着重要作用,它不仅为特定的细胞提供结构支撑作用,而且能引导组织再生和控制组织结构。从几何建模的角度,寻找一种通用的组织工程骨架实体建模方法：采用有限元中六面体单元对实体模型进行网格剖分;利用有限元中的八结点六面体形函数将参数域中的基本孔隙单元映射为空间域中各种不规则孔隙几何单元。利用布尔并运算构建实体的造孔单元。再与整个实体轮廓模型(CT/MRI)进行逻辑差运算,就可以得到组织工程骨架模型。研究表明：通过有限元单元剖分方法,有效地解决了组织工程骨架孔隙体元的分布计算等技术问题,相对随机几何方法,具有很好的技术操作性和高效性。通过剖分单元约束和孔隙体元变形构型方法的应用,可大大提高骨组织孔隙形状的自然性。     

A Review of 3D Printing Technology for Medical Applications

Donor shortages for organ transplantations are a major clinical challenge worldwide. Potential risks that are inevitably encountered with traditional methods include complications, secondary injuries, and limited source donors. Three-dimensional (3D) printing technology holds the potential to solve these limitations; it can be used to rapidly manufacture personalized tissue engineering scaffolds, repair tissue defects in situ with cells, and even directly print tissue and organs. Such printed implants and organs not only perfectly match the patient’s damaged tissue, but can also have engineered material microstructures and cell arrangements to promote cell growth and differentiation. Thus, such implants allow the desired tissue repair to be achieved, and could eventually solve the donor-shortage problem. This review summarizes relevant studies and recent progress on four levels, introduces different types of biomedical materials, and discusses existing problems and development issues with 3D printing that are related to materials and to the construction of extracellular matrix in vitro for medical applications.     

Electrophoretic deposition of nanocrystalline TiO2 particles on porous TiO2-x ceramic scaffolds for biomedical applications

Nanocrystalline TiO₂ coated scaffolds offers the possibility to be used in bone tissue regeneration providing not only space for new tissue formation, but also to enhance bioactivity of the implant. In the present study, direct current electrophoretic deposition (EPD) was chosen as simple and low cost technique to coat 3D porous structure of TiO_2-x ceramic. Suspension for EPD was prepared suspending nanocrystalline TiO₂ particles in isopropanol and adding triethanolamine as dispersant. TiO₂ particles were electrophoretically deposited on the surface of TiO_2-x scaffolds through varying EPD time and applied voltage. The scaffold pore structure was maintained after applying the coating by EPD. The deposition of nanocrystalline TiO₂ coating can be a smart strategy to impart bioactive properties to the 3D scaffold, allowing formation of spherical hydroxyapatite particles on the coated scaffolds after immersion in simulated body fluid. In vitro cell studies does not show cytotoxic effect of nanocrystalline TiO₂ coated scaffolds.     

An investigation of cell adhesion and growth on micro/nano-scale structured surface—Self-assembled micro particles as a scaffold

A controlled cellular behavior (adhesion, migration and growth) on a scaffold is a technical issue on development of cultured cell applications such as biosensor and tissue engineering. The present paper describes fundamental experiments about effects of some micro/nano-scale structures on cell adhesion and growth. Micro/nano-scale structures of scaffold are fabricated by both top-down and bottom-up processes using some unique materials. For fine spherical particles, they are self-assembled on a substrate. The micro/nano-structured particles provide non-angular and regularly-arranged surface asperity with two-dimensional opal structure, which is also permeable to a culture solution because of fine gaps among assembled particles. Some polymers are formed into an array of micro-ridges with rectangular cross-section by nano-imprint process. Most cells are selectively adhered on micro-structured silica particles, while a flat surface has low affinity for the cells. The present study intends to explain a preferential surface for cell adhesion and growth in terms of geometry and biochemical property of micro-structure.     

Nylon mesh-based 3D scaffolds for the adherent culture of neural stem/progenitor cells

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Synthesis of Poly-L-Lactide for Scaffold Materials by Melt-Solid Polycondensation

Poly-L-lactide (PLLA) with low viscosity average molecular mass for scaffold materials was synthesized by melt-solid condensation polymerization and characterized by IR, XRD, and ¹H-NMR. The influences of catalyst (LaCl₃/C₇H₈SO₃) concentration, polymerization temperature and polymerization time on the viscosity average molecular mass of poly-L-lactide acid (PLLA) were investigated. Poly-L-lactide with a viscosity average relative molecular mass of about 7.2 × 10⁴ was obtained when melt-solid polycondensation was conducted with first preheating at 110°C for 4 h and solid polycondensation at 150°C for 20 h; the catalyst concentration was 0.4 wt. %. PLLA was made into porous materials by using sodium hydrogen carbonate particulates as the porogen to foam. Scanning electron microscope observation indicates that the sample is highly porous and well distributed with good interconnections between pores and the pore size of porous materials in the range of 300–500 μm and it can be used as scaffold for bone tissue engineering.     

Investigation of biphasic calcium phosphate/gelatin nanocomposite scaffolds as a bone tissue engineering

The porous scaffold of nanobiphasic calcium phosphate (n-BCP) and gelatin from bovine skin type B was prepared by freeze-drying method. The porogen which used was Naphthalene. EDC (N-(3-dimethyl aminopropyl)-N′-ethyl carbodiimide hydrochloride) for stabilization of gelatin by cross-linking method was used. The scaffold was characterized by SEM, XRD and FTIR. As a result, a biocompatible scaffold with good cell attachment, facility in formation in desired shapes and simplicity in production were prepared for bone tissue engineering.