Polymers used to influence cell fate in 3D geometry: New trends

The extracellular matrix (ECM) is a hydrogel-like structure comprised of several different biopolymers, encompassing a wide range of biological, chemical, and mechanical properties. The composition, organization, and assembly of the ECM play a critical role in cell function. Cellular behavior is guided by interactions that occur between cells and their local microenvironment, and this interrelationship plays a significant role in determining physiological functions. Bioengineering approaches have been developed to mimic native tissue microenvironments by fabricating novel bioactive hydrogel scaffolds. This review explores material designs and fabrication approaches that are guiding the design of hydrogels as tissue engineered scaffolds. As the fundamental biology of the cellular microenvironment is often the inspiration for material design, the review focuses on modifications to control bioactive cues such as adhesion molecules and growth factors, and summarizes the current applications of biomimetic scaffolds that have been used in vitro as well as in vivo.     

Cellular Response of Limbal Stem Cells on Poly (Hydroxybuthyrate-co-Hydroxyvalerate) Porous Scaffolds for Ocular Surface Bioengineering

The aim of this study was to develop a modified-porous poly (3-hydroxybutyrate-co-3- hydroxyvalerate) (PHBV) scaffold for limbal stem cell (LSC) expansion that can serve as a potential alternative substrate to replace human amniotic membrane. The human limbal stem cell was used to evaluate the biocompatibility of substrates (porous scaffold, human amniotic membrane and thermoresponsive substrate) based on their viability, proliferation, and attachment ability. Biocompatibility results indicated that the all substrates were highly biocompatible, as LSCs could favorably attach and proliferate on the scaffold surface. Microscopic figures showed that the human limbal stem cell was firmly anchored to the substrates and were able to retain a normal corneal stem cell phenotype. Microscopic analyses illustrated that cells infiltrated the porous scaffold and successfully formed a three-dimensional corneal epithelium, which was viable for two weeks. Gene expression results revealed no change in the expression profile of LECs grown on scaffold when compared to those grown on human amniotic membrane or thermo responsive substrate. In addition, porous PHBV substrate provides not only a milieu supporting LSCs expansion, but also serve as a useful alternative carrier for ocular surface tissue engineering and could be used as an alternative substrate to amniotic membrane.     

Compressive and flexural properties of novel polylactic acid/hydroxyapatite/yttria-stabilized zirconia hybrid nanocomposite scaffold

The mechanical property is a crucial factor in the design of bone tissue engineering scaffolds. In the current study, novel PLLA (Poly-L-lactic acid)–Hydroxyapatite (HA)–yttria-stabilized zirconia (YSZ) nanocomposite scaffold with various compositions was prepared and characterized. The effect of HA and YSZ contents on the mechanical behavior of the resultant composites was investigated. TEM micrograph revealed that HA particles are needle-like in shape and nano in size. Scanning electron microscopy (SEM) micrograph also showed that YSZ powder is in granule form and submicron size. SEM disclosed that all scaffolds had a highly interconnected porous structure and X-ray diffractometry revealed that there were some molecular interactions between PLA (Polylactic acid), HA, and YSZ in the composites. The results depicted that introducing YSZ to the nanocomposite leads to a significant increase in compressive strength, modulus, and densification strain. In addition, flexural strength and modulus showed an upward trend by adding YSZ particles to scaffolds. It should be noted that PLA–20%HA–20%YSZ indicates the highest strength and modulus in both compression and bending tests, though, it did not demonstrate the proper strain compared to other scaffolds. Thus, PLA–15%HA–15%YSZ has been reported as the best candidate due to appropriate strength and strain. Also, energy absorption in nanocomposites showed an upward trend by increasing the amount of YSZ particles. It was found that the strength of samples was declined after being soaked in simulated body fluid. However, scaffolds with HA underwent more decrease in strength compared to samples containing YSZ.     

Alginate Based Scaffolds for Cartilage Tissue Engineering: A Review

Abstract

Many people, especially old and middle-aged, suffer from pain and disabilities caused by cartilage degradation. There are many surgical methods for cartilage treatment, however, none of them have shown acceptable results in long-term. Tissue engineering would be an acceptable approach for cartilage treatment. This includes cells, a carrier such as a matrix scaffold and signaling molecule. An ideal scaffold for cartilage tissue engineering should meet some requirements includes biocompatibility, biodegradability, and sufficient mechanical characteristic. While there are many suitable scaffolds made by natural and synthesis polymers, alginate- a natural polymer- has received good attention. Alginate offers many advantages for cartilage treatment; it has great potential in having tunable mechanical properties and easy manufacturing process. In the present paper, focusing on alginate as main scaffold constructive component, different studies on alginate based scaffolds in the form of physically, chemically and biologically crosslinked hydrogel, sponge, fiber, micro/nano particles and 3?D printed for articular cartilage tissue engineering are discussed and reviewed.     

Polyhydroxybutyrate (PHB) Scaffolds as a Model for Nerve Tissue Engineering Application: Fabrication and In Vitro Assay

In this study, we fabricated PHB scaffolds by solid/liquid phase separation method. The properties of fabricated scaffolds were investigated using SEM, DMTA, and DSC. Our studies noticed that for an approach to scaffolds that contain tubular morphology and better mechanical properties, the solution should be frozen near crystallization temperature. For in vitro evaluation, the P19 mouse embryonal cell line was used as a model system. Results notice that cells attach and differentiate to the nerve cell. In vitro assay shows that it is a suitable model for use as a platform for neural tissue engineering applications.     

超临界CO2／盐析法制备聚乳酸多孔支架材料

利用盐析／超临界CO2复合方法制备了一系列的PDLLA及PDLLA—PEG三维多孔支架材料．利用这种方法可以避免使用有机溶剂，不需较高温度，降低常规气体发泡法所需的较长时间．制备的三维多孔支架的孔隙率最高达80％，孔与孔之间相互连通，孔径大小为100～500μm，符合组织工程支架的一般要求．此外还详细研究了CO2压力、温度、浸润时间等条件的变化对多孔材料的形貌和孔隙率的影响．     

扣件式钢管脚手架优化设计的算法与实现

以一落地式卸料平台的扣件式钢管脚手架搭设方案为例,探讨了脚手架步距,立杆纵、横向间距等参数的优化计算方法.在此基础上,给出不同长度钢管的配置方案、需用数量的选择途径.     

导轨式整体爬升脚手架强度验算

以导轨式整体爬升脚手架为研究对象，取标准层层高≤3.6m,Lmax≤6.8m的单元架体，并且针对工程的具体要求取最大值做为计算参数，施工前对架体的局部重要受力杆件如穿墙螺栓、斜拉杆、连接板进行了强度验算，同时也对受力点结构砼的抗压强度进行了验算。验算结果满足强度要求，从而在理论上为导轨式整体爬升脚手架施工应用提供了安全保证。     

骨组织工程支架材料及其力学性能

骨组织工程的研究是组织工程最为活跃的领域之一,如何制备理想的骨支架材料是当前的一个研究热点.通过人们的努力,目前已有多种骨组织工程支架材料问世.综述了各类骨组织工程支架材料的优缺点,对比了它们的力学性能,并对骨组织工程的前景进行了展望.     

巧用脚手架加快工程进度的方法

在某大型商场的正立面改造扩建工程中,巧妙搭设外承重脚手架,改变了常规的施工顺序,将传统的从下至上依次施工变为多层钢筋、模板立体施工,因不需要下一层混凝土施工完毕便可进行上一层的模板支撑、梁植筋、钢筋绑扎的施工,从而缩短混凝土浇筑的间隔时间,达到加快进度的目的。