Influence of Addition of Hyaluronic Acid (HA) on the Properties of Collagen/HA Composite Scaffolds

In order to develop a scaffolding material for tissue regeneration, porous matrices containing varying composites of collagen and hyaluronic acid (HA) (from 1:0 to 0:1) were fabricated using a freeze-drying method. The effect of the composition on the morphology, hydrophilicity, swelling behavior, mechanical properties, and in vitro cytotoxicity was investigated. The results showed that all the scaffolds had an interconnected pore structure with sufficient pore size for use as a support for the growth of fibroblasts. The addition of HA improved the swelling property, but reduced the compressive strength. The contact angle decreased with increasing HA content. In in vitro cytotoxicity tests using fibroblastic cells, the collagen/HA scaffolds showed no toxicity. All these results suggest that collagen/HA composite scaffolds are a potential candidate for tissue engineering scaffolds.     

The influence of polymer concentrations on the structure and mechanical properties of porous polycaprolactone-coated hydroxyapatite scaffolds

Polycaprolactone (PCL)-coated porous hydroxyapatite (HA) composite scaffolds were prepared by combining polymer impregnating method with dip-coating method. Three different PCL solution concentrations were used in dip-coating process to improve the mechanical properties of porous HA scaffolds. The results indicated that as the concentration of PCL solution increases the compressive strength significantly increased from 0.09 MPa to 0.51 MPa while the porosity decreased from 90% to 75% for the composite scaffolds. An interlaced structure was found inside the pore wall for all composite scaffolds due to the penetration of PCL. The porous HA/PCL composite scaffolds dip-coated with 10% PCL exhibited optimal combination of mechanical properties and pore interconnectivity, and may be a potential bone candidate for the tissue engineering applications.     

Preparation and Characterization of Poly(L-lactide-co-glycolide-co-ε-caprolactone) Scaffolds by Thermally Induced Phase Separation

Abstract

The technique of thermally induced phase separation (TIPS) is favorable for the fabrication of a porous scaffold due to a number of advantages. In this work the poly(L-lactide-co-glycolide-co-ε-caprolactone) (PLLGC) terpolymer was synthesized by melt copolymerization and porous scaffolds thereof from its solution in 1,4-dioxane were fabricated by using the TIPS method. The effects of fabrication parameters, including polymer concentration and freezing temperature, on the morphology, pore size and mechanical properties were studied. The results showed that the average pore size of the PLLGC porous scaffold increased with a decrease in PLLGC concentration and the pore size resulting from freezing at 4?°C (about 20–100?μm) was significantly larger than for other samples (20–50?μm) frozen at lower temperatures. The porosity of the scaffolds decreased with increasing PLLGC concentration or decreasing freezing temperature. On the other hand, the compressive strength of the scaffolds increased with the increase of PLLGC concentration or the decrease of freezing temperature, as would be expected. The present results can be applied in design to control the processing parameters of TIPS for a scaffold with desired pore morphology.     

Modeling of heterogeneous surfaces and characterization of porous materials by extending density functional theory for the case of amorphous solids

A method of characterization of carbonaceous materials using nongraphitized carbon black as a reference is considered. The Tarazona density functional theory was applied to amorphous solids to describe nitrogen adsorption on nongraphitized carbon black. This allows us to describe energetic heterogeneity without the need to invoke any energy distribution functions. To derive the pore size distribution (PSD) of porous carbon whose pore walls are non-graphitized, we used the entropy concept in the regularization method. With this approach PSD is more well-behaved than that obtained with the usual means. We applied this new theory to study the effects of technological parameters on porous structure of a series of activated carbon.     

Influence of Nano-Bioactive Glass (NBG) Content on Properties of Gelatin-Hyaluronic Acid/NBG Composite Scaffolds

The development of three-dimensional (3-D) scaffolds with highly open porous structure is one of the most important issues in tissue engineering. A novel nanocomposite scaffold of gelatin (Gel), hyaluronic acid (HA), and nano-bioactive glass (NBG) was prepared by blending NBG with a Gel and HA solution followed by lyophilization. The effects of NBG content on the properties of the Gel-HA/NBG composite scaffolds, including the morphologies, porosity, compressive strength, swelling behavior, cell viability and alkaline phosphatase (ALP) activity, were investigated. Porous composite scaffolds with interconnected pores were obtained and the pores became cylindrical with increasing NBG content. The porosity percent and swelling ability decreased with increasing NBG content; however, the compressive strength, cell viability and ALP activity were enhanced. All the results showed the addition of NBG particles can improve the physicochemical and biological properties and the Gel-HA/NBG composite scaffolds exhibited good potential for tissue engineering applications.     

Preparation and Properties of Novel Maleated Poly (D,L-lactide-co-glycolide) Porous Scaffolds for Tissue Engineering

Three-dimensional biodegradable porous scaffolds play an important role in tissue engineering. A new polymer based on maleated poly(lactic-co-glycolic acid) (MPLGA) was synthesized using direct melt copolymerization from maleic anhydride (MAH), D, L-lactide, and glycolide monomers. MPLGA porous biodegradable scaffolds were prepared by a solution-casting/salt-leaching method. The effects of content and size of the NaHCO₃ porogen on the compressive strength of the MPLGA scaffolds were investigated, and the effect of content of the porogen on the porosity of the MPLGA scaffolds was also studied. The results indicated that MAH was grafted onto PLGA successfully and MPLGA scaffolds with interconnective and open pore structure were obtained. Increasing content of NaHCO₃ porogen resulted in an increase of porosity and decrease of the compressive strength of the MPLGA scaffolds with the compressive strength of the scaffolds also decreasing with increasing porogen size.     

Dielectric constant of porous ultra low-k dielectrics by fractal-Monte Carlo simulations

The effective dielectric constant of porous ultra low-k dielectrics is simulated by applying the fractal geometry and Monte Carlo technique in this work. Based on the fractal character of pore size distribution in porous media, the probability models for pore diameter and for effective dielectric constant are derived. The proposed model for the effective dielectric constant is expressed as a function of the dielectric coefficient of base medium and the volume fractions of pores and base medium, fractal dimension for pores, the pore size, as well as random number. The Monte Carlo simulations combined with the fractal geometry are performed. The predictions by the present simulations are shown in good accord with the available experimental data. The proposed technique may have the potential in analyzing other properties such as electrical conductivity and thermal conductivity in porous ultra low-k dielectrics.     

等离子喷涂层原生性孔隙几何结构的分形及统计特性

孔隙是等离子喷涂涂层原生性结构, 对涂层的耐磨损、耐腐蚀、耐高温等性能具有显著影响, 是涂层参数优化的重要指标之一. 因此, 对涂层孔隙结构特征参数的全面表征对于更加精确地评价涂层质量具有重要意义. 本文将概率统计方法、分形方法与数字图像分析技术相结合, 研究了等离子喷涂涂层原生性孔隙数量、形态、尺寸及其分布等结构特征参数表征方法及孔隙的成形机理. 首先通过改变喷涂功率得到不同孔隙状态的Fe基合金涂层, 随后采用数字图像分析技术对涂层截面孔隙的扫描电子显微形貌图进行处理, 最后通过Weibull统计模型分析了孔隙周长及面积的尺寸分布特征, 并利用基于分形思想的面积-周长幂率研究了孔隙不规则形态的定量表征方法. 在实验过程中, 为了分析涂层孔隙的成形机理, 采用Spraywatch在线监测喷涂粒子的飞行状态. 结果表明: 分形维数能够表征孔隙的不规则形态, 分形维数越大, 孔隙面积越大或边界形态越复杂, 并且其与孔隙的成形机理之间存在良好的映射关系; 孔隙面积及周长的尺寸分布均服从明显的两项Weibull分布特征, 孔隙尺寸较小时, 形状参数β 较大, 而孔隙尺寸较大时, 则反之; 喷涂功率对孔隙尺寸的聚集特点产生不同程度的影响, 随着喷涂功率的增加, 粒子的融化状态逐渐改善, 孔隙的尺寸明显降低; 而当孔隙面积(周长)小于特征值时, 相同尺寸的孔隙概率密度值则越来越接近, 说明孔隙功率的变化对小尺寸孔隙出现的概率影响较小.     

Characterization of PSD of activated carbons by using slit and triangular pore geometries

A mixed geometry model for activated carbons, representing the porous space as a collection of an undetermined proportion of slit and triangular pores, is developed, evaluated theoretically and applied to the characterization of a controlled series of samples of activated carbon obtained from the same precursor material. A method is proposed for the determination of the Pore Size Distribution (PSD) for such a mixed geometry model, leading to the unique determination of the proportion of pores of the two geometries fitting adsorption data. By using the Grand Canonical Monte Carlo (GCMC) simulation method in the continuum space, families of N2 adsorption isotherms are generated both for slit and triangular geometry corresponding to different pore sizes. The problem of the uniqueness in the determination of the PSD by fitting an adsorption isotherm using the mixed geometry model is then discussed and the effects of the addition of triangular pores on the PSD are analyzed by performing a test where the adsorption isotherm corresponding to the known PSD is generated and used as the “experimental” isotherm. It is found that a pure slit geometry model would widen the PSD and shift it to smaller sizes, whereas a pure triangular geometry model would produce the opposite effect. The slit and triangular geometry families of isotherms are finally used to the fit experimental N₂ adsorption data corresponding to a family of activated carbons obtained from coconut shells through a one-step chemical activation process with phosphoric acid in air, allowing for the determination of the micropore volume, the proportion of slit and triangular pores and the PSD corresponding to the mixed geometry. The same experimental data were fit using both the conventional slit pore model and the mixed geometry model. From the analysis of the effect of different preparation procedures on the resulting PSDs, it is concluded that the proposed mixed geometry model may probably better capture the morphology and energetics of activated carbons prepared by chemical activation under mild temperatures.     

Highly porous 3D nanofibrous scaffolds processed with an electrospinning/laser process

Electrospinning has been widely used to produce micro/nanosized fibres. Although the method is very simple, easy, and effective for obtaining nanosized material, the fabrication of three dimensional (3D) shapes comprised of micro/nanofibres has been a major obstacle for use in tissue engineering. In this study, a new electrospinning method to fabricate controllable 3D micro/nanofibrous structure (with thickness over 3 mm) is suggested. The fabricated 3D fibrous structure was fully porous and successfully consisted of submicron-sized fibres. However, the pores in the 3D fibrous structure were too small (5–10 μm), so we used a femtosecond laser process to achieve enough cell infiltration and proliferation in the thickness direction of the 3D structure. By controlling appropriate processing conditions, we can successfully fabricate a highly porous 3D micro/nanofibrous structure with various pore sizes ranging from 189 ± 28 μm to 380 ± 21 μm. The fabricated 3D fibrous scaffolds were assessed for in vitro biological capabilities by culturing osteoblast like cells (MG63). Compared with the rapid-prototyped PCL scaffold, the 3D fibrous scaffold exhibited significantly higher biological activities (initial cell attachment and cell proliferation) due to the topographical structure of micro/nanofibres.     

Effect of the internal microstructure in rapid-prototyped polycaprolactone scaffolds on physical and cellular properties for bone tissue regeneration

Biomedical scaffolds should be designed to optimize their inter-microstructure to enable cell infiltration and nutrient/waste transport. To acquire these properties, several structural parameters, such as pore size, pore shape, porosity, pore interconnectivity, permeability, and tortuosity are required. In this study, we explored the effect of tortuosity on the viable cell proliferation and mineralization of osteoblast-like-cells (MG63) in polycaprolactone scaffolds. For analysis, we designed four different scaffolds of various tortuosities ranging from 1.0 to 1.3 under the same porosity (56?%) and 100?% pore interconnectivity. The pore size of the scaffolds was set as 150 and 300?μm, and a mixture of these sizes. We found that despite the porosity being same, the elastic modulus was dependent on the pore size of the scaffolds due to the distributed stress concentration. In addition, the relative water movement within scaffolds was also related to the internal microstructure. Cell viability and Ca²⁺ deposition of the cell-seeded scaffolds showed that the proliferation of viable cells and mineralization in the scaffolds with appropriate tortuosity (1.2) was relatively high compared to those of the scaffolds displaying low (1.05 and 1.1) or high (1.3) tortuosity. Our findings indicated that the internal microstructure of the scaffolds may influence not only the physical properties, but in addition the cellular behavior.     

Biomimetic formation of apatite on the surface of porous gelatin/bioactive glass nanocomposite scaffolds

There have been several attempts to combine bioactive glasses (BaGs) with biodegradable polymers to create a scaffold material with excellent biocompatibility, bioactivity, biodegradability and toughness. In the present study, the nanocomposite scaffolds with compositions based on gelatin (Gel) and BaG nanoparticles in the ternary SiO₂-CaO-P₂O₅ system were prepared. In vitro evaluations of the nanocomposite scaffolds were performed, and for investigating their bioactive capacity these scaffolds were soaked in a simulated body fluid (SBF) at different time intervals. The scaffolds showed significant enhancement in bioactivity within few days of immersion in SBF solution. The apatite formation at the surface of the nanocomposite samples confirmed by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and X-ray powder diffraction (XRD) analyses. In vitro experiments with osteoblast cells indicated an appropriate penetration of the cells into the scaffold's pores, and also the continuous increase in cell aggregation on the bioactive scaffolds with increase in the incubation time demonstrated the ability of the scaffolds to support cell growth. The SEM observations revealed that the prepared scaffolds were porous with three dimensional (3D) and interconnected microstructure, pore size was 200-500 μm and the porosity was 72-86%. The nanocomposite scaffold made from Gel and BaG nanoparticles could be considered as a highly bioactive and potential bone tissue engineering implant.     

基于相场方法的孔隙尺度油水两相流体流动模拟

基于真实岩心颗粒粒径分布,利用过程法构建疏松砂岩油藏的三维孔隙结构模型,利用相场方法建立两相流体流动数学模型并利用有限元方法进行求解,研究驱替速度、流体性质、润湿性对剩余油分布以及采出程度的影响.结果表明：驱替速度的增大和油水粘度比的减小会导致较大的毛管数,进而有利于采出程度的提高;就润湿性而言,水湿条件下毛管力是水驱油的动力,而在油湿条件下是阻力,因此水湿岩心采出程度更高.同时,从孔隙尺度对油水渗流机理及剩余油分布机理进行揭示,结果表明：由于多孔介质的复杂孔隙结构,流体在流经不同孔隙时呈现不同的流动特征,进而对油水两相流整体的压力分布、流速分布造成重要影响.     

Impurity effects on ionic-liquid-based supercapacitors

Small amounts of an impurity may affect the key properties of an ionic liquid and such effects can be dramatically amplified when the electrolyte is under confinement. Here the classical density functional theory is employed to investigate the impurity effects on the microscopic structure and the performance of ionic-liquid-based electrical double-layer capacitors, also known as supercapacitors. Using a primitive model for ionic species, we study the effects of an impurity on the double layer structure and the integral capacitance of a room temperature ionic liquid in model electrode pores and find that an impurity strongly binding to the surface of a porous electrode can significantly alter the electric double layer structure and dampen the oscillatory dependence of the capacitance with the pore size of the electrode. Meanwhile, a strong affinity of the impurity with the ionic species affects the dependence of the integral capacitance on the pore size. Up to 30% increase in the integral capacitance can be achieved even at a very low impurity bulk concentration. By comparing with an ionic liquid mixture containing modified ionic species, we find that the cooperative effect of the bounded impurities is mainly responsible for the significant enhancement of the supercapacitor performance.     

Preparation of Polycaprolactone Tissue Engineering Scaffolds by Improved Solvent Casting/Particulate Leaching Method

The classic solvent casting/particulate leaching method to fabricate PCL scaffolds was improved by using a centrifugal technology, a direct bonding process in preparing salt matrices and a technology of vacuum treatment under heating in the desolvation process. Series operations of preshaping, centrifuging, casting and desolvating were employed during the scaffold's manufacture. The scaffold's properties were characterized including micro‐structures, pore dimensions, porosity and hydrophilicity. The results show that centrifugal technology can improve the pore uniformity of scaffolds. In the bonding process, well‐interconnected porous structures were formed if water content was between 2～7%. The distribution of pore dimensions was from 10 to 80 μm, and the porosities were about 89%. Generally, the porosities formed by vacuum treatment at high temperature are greater than those formed by vacuum treatment at ambient temperature in the desolvation process. The fabricated porous PCL scaffolds with good elasticity and desired thickness could be a good choice for application in soft tissue engineering.     

Morphology and Pore Size Distribution of Biocompatible Interconnected Porous Poly(L-lactic acid) Foams with Nanofibrous Structure Prepared by Thermally Induced Liquid–Liquid Phase Separation

Biocompatible, highly interconnected microporous poly(L-lactic acid) (PLLA) foams with nanofibrous structure, containing pores with average diameter below 1 μm and fibers with diameters of 10² nm scale, were prepared through the thermally induced liquid–liquid phase separation (TIPS) method consisting of quenching of the PLLA solution, freeze extraction with ethanol, and vacuum drying. Diverse foam morphologies were obtained by systematically changing parameters involved in the TIPS process, such as polymer concentration, solvent composition, and quenching temperatures. The morphology of different foams was examined by scanning electron microscopy to characterize the pore size and the pore size distribution. The results showed that most porous foams had a nanofibrous structure with interconnected open pores. In the case of using tetrahydrofuran (THF) as solvent, the higher the PLLA concentration, the smaller the average pore diameter and the narrower the pore size distribution. In the case of using the mixed solvents of THF/DOX (1,4-dioxane) with higher than 6/4 volume ratio, there appeared a maximum value of average pore diameter and a widest pore size distribution at 0.09 g/mL PLLA concentration. The average pore diameter of the foams increased with increasing DOX content in the mixed solvent and ranged from 0.2 to 0.9 μm depending on the process parameters. When the DOX content reached 60% by volume, the morphology of the foams contained some large closed pores with diameter ranging from 1 to 10 μm. By decreasing the quenching temperature, the average pore diameter of foams decreased and the pore size distribution became narrower. All the pore size distribution fit F-distribution equations.     

Phase transitions of fluids confined in porous silicon: A differential calorimetry investigation

The phase transitions of non-polar organic fluids and of water, confined in the pores of porous silicon samples, were investigated by Differential Scanning Calorimetry (DSC). Two types of PS samples (p^- and p⁺ type) with different pore size and morphology were used (with spherical pores with a radius of about 1.5 nm and cylindrical shape with a radius of about 4 nm respectively). The DSC results clearly show that the smaller the pores are, the larger is the decrease in the transition temperature. Moreover, a larger hysteresis between melting and freezing is observed for p⁺ type than for p^- type samples. A critical review of the thermodynamical properties of small particles and confined fluids is presented and used to interpret and discuss our DSC results. The effects of the chemical dissolution as well as the influence of anodization time are presented, showing that thick p⁺ type porous silicon layers are non-homogeneous. The DSC technique which was used for the first time to investigate fluids confined in porous silicon, enables us to deduce original information, such as the pore size distribution, the decrease in the freezing temperature of confined water, and the thickness of non-freezing liquid layer at the pore wall surface. Received: 11 May 1998 / Revised and Accepted: 29 July 1998     

高质量规则多孔氧化铝模板的制备

在合适的条件下利用阳极氧化高纯铝片，可以获得多孔结构的氧化铝，其孔径大小和排列方式都很均匀.由于孔的深度不受限制，因此可以制备出孔深很大的多孔氧化铝.这种多孔结构可以用作制备纳米材料的模板.利用0.3mol/L的草酸溶液在40V的直流电压下，采用二步氧化法获得了高质量的氧化铝多孔模板，其典型孔径值为40—70nm，孔间距约110nm，深度可达毫米量级.分析了溶液温度对结果的影响，比较了单步法和两步法获得的样品的多孔结构，认为低温下的二步氧化法可以获得很好的多孔氧化铝模板. 关键词： 纳米材料 多孔氧化铝 二步氧化法