Porous biomedical composite microspheres developed for cell delivering scaffold in bone regeneration

Microspherical particles have attracted great interest as a delivery system of tissue cells in regenerative engineering. For hard tissue regeneration, here we exploited porous biomedical composite microspheres of hydroxyapatite-polycaprolactone (HA-PCL). The pore channels within the microsphere was facilitated by using camphene as the porogen, where the initial HA-PCL-camphene mixture in chloroform was solidified and the camphene was then sublimed to leave pore channels within the HA-PCL microspheres. The pore size increased with increasing camphene concentration, resulting in the generation of macropores (> 50 μm). Rat bone marrow mesenchymal stem cells were shown to proliferate actively on the porous microspheres penetrating deeply into the pore channels. Results suggest future applications of the porous composite microsphere as a cell delivery scaffold for bone tissue regeneration.     

纳米羟基磷灰石/壳聚糖复合膜的制备和表征

以壳聚糖(chitosan,CS)为高分子相,纳米羟基磷灰石(nano-hydroxyapatite,n-HA)为无机相,采用溶液共混和真空下溶剂挥发的方法制备了n-HA/CS复合膜,通过SEM、XRD、FTIR、接触角及力学性能等测试对此复合膜进行分析和表征.结果表明,复合膜具有非对称结构,上表面组分主要是CS,下表面组分是n-HA和CS复合体,并在底部形成了一层致密层,中间是疏松层;复合膜中CS与HA之间存在一定的化学键合并复合均匀,没有明显的相分离,且复合膜中的HA为类似于自然骨矿物相的弱结晶结构.复合膜的非对称结构对其接触角也有一定的影响,反映了膜表面亲、疏水性的不同,为细胞的粘附和旺长提供了一定的微环境.复合膜干态下的拉伸强度和断裂伸长率较纯CS膜的低,而在湿态时却较纯CS膜高.     

Development and cell response of a new biodegradable composite scaffold for guided bone regeneration

Composites of biodegradable polymers with different calcium phosphate ceramics and glasses, have been developed as scaffolds for applications in bone-tissue engineering. In this work, phosphate glass particles have been incorporated into the polymer, poly(95L/5DL) lactic acid (PLA) and porous structures were elaborated. Their porosity, compressive mechanical properties and biological response were evaluated. Interconnected structures with evenly distributed pores and a porosity as high as 97% were obtained. The incorporation of glass particles into the polymer showed to have a positive effect in the mechanical properties of the foams. Indeed, the compressive modulus increased from 74.5 to 120 KPa and the compressive strength from 17.5 to 20.1 KPa for the PLA and the PLA/glass foams, respectively. The biological response was evaluated by means of the MTT test, the materials resulted to be noncytotoxic.     

Electrospun composite nanofibers for tissue regeneration

Nanotechnology assists in the development of biocomposite nanofibrous scaffolds that can react positively to changes in the immediate cellular environment and stimulate specific regenerative events at molecular level to generate healthy tissues. Recently, electrospinning has gained huge momentum with greater accessibility of fabrication of composite, controlled and oriented nanofibers with sufficient porosity required for effective tissue regeneration. Current developments include the fabrication of nanofibrous scaffolds which can provide chemical, mechanical and biological signals to respond to the environmental stimuli. These nanofibers are fabricated by simple coating, blending of polymers/bioactive molecules or by surface modification methods. For obtaining optimized surface functionality, with specially designed architectures for the nanofibers (multi-layered, core-shell, aligned), electrospinning process has been modified and simultaneous 'electrospin-electrospraying' process is one of the most lately introduced technique in this perspective. Properties such as porosity, biodegradation and mechanical properties of composite electrospun nanofibers along with their utilization for nerve, cardiac, bone, skin, vascular and cartilage tissue engineering are discussed in this review. In order to locally deliver electrical stimulus and provide a physical template for cell proliferations, and to gain an external control on the level and duration of stimulation, electrically conducting polymeric nanofibers are also fabricated by electrospinning. Electrospun polypyrrole (PPy) and polyaniline (PAN) based scaffolds are the most extensively studied composite substrates for nerve and cardiac tissue engineering with or without electrical stimulations, and are discussed here. However, the major focus of ongoing and future research in regenerative medicine is to effectively exploit the pluripotent potential of Mesenchymal Stem Cell (MSC) differentiation on composite nanofibrous scaffolds for repair of organs.     

Method for enhancing bioavailability of myricetin based on self‐assembly of casein–myricetin nanomicelles

In order to expand the application in the medical field and enhance pharmacological effects, casein–myricetin nanomicelles were prepared by the self‐assembly method and characterised by ultraviolet–visible spectroscopy and Fourier transform infrared spectroscopy. The parameters in self‐assembly were optimised according to the factors of particle size, encapsulation yield, and drug loading. The result showed a pH of 5.5, a casein concentration of 2 mg/ml, a mass ratio of casein to myricetin of 8:1, ultrasonic power of 300 W, ultrasonic time of 5 min and ethanol volume of 7 ml were the optimal conditions. The situ cycle intestinal perfusion methods indicated that casein–myricetin nanomicelles can be more easily absorbed by small intestine than myricetin standard sample. Therefore, casein micelles are effective for improving the water solubility of myricetin.Inspec keywords: encapsulation, nanoparticles, nanomedicine, drugs, nanofabrication, biomedical materials, solubility, molecular biophysics, ultraviolet spectra, drug delivery systems, particle size, pH, visible spectra, colloids, self‐assembly, Fourier transform infrared spectraOther keywords: casein–myricetin nanomicelles, self‐assembly method, ultraviolet–visible spectroscopy, casein concentration, myricetin standard sample, casein micelles, medical field, pharmacological effects, Fourier transform infrared spectroscopy, particle size, pH, ultrasonic power, ethanol volume, water solubility, power 300.0 W, time 5.0 min     

Collagen-hydroxyapatite composite enhances regeneration of calvaria bone defects in young rats but postpones the regeneration of calvaria bone in aged rats

The potential differences in bone repair of calvaria defects treated with a collagen sponge (HELISTAT) or a collagen-hydroxyapatite composite (HEALOS) in young and aged rats were evaluated at 8 weeks after surgery. A histomorphometric analysis of new bone formation and an evaluation of angiogenesis, mast cell, and eosinophil local infiltration were performed. Evaluation showed that HELISTAT induced a similar amount of new bone in both young and aged rats. However this occurred to a lesser degree than in young rats treated with HEALOS. The largest number of blood vessels was present in the defects of aged rats treated with HEALOS, and the number of mast cells was highest in the defects treated with HELISTAT in both young and aged rats. Eosinophils were present to the greatest extent in defects treated with HEALOS in comparison to defects treated with HELISTAT in both young and aged rats. Collagen-hydroxyapatite composite (HEALOS) enhances calvarial bone repair more than collagen sponge alone (HELISTAT) in young rats but not in aged rats at 8 weeks after surgery. HEALOS appears to induce a more intense inflammatory response than HELISTAT especially in aged rats.     

Titanium oxide nanotubes for bone regeneration

Titanium oxide nanotubes with Ca ions on their surfaces were prepared as 2 mm cylindrical inserts and placed into surgically created bone defects in the femurs of Wistar rats. On day 3, fibroblast-like cells were present on the surface of the nanotube inserts and fibers were observed by scanning electron microscopy (SEM). On day 7, cells with alkaline phosphatase activity were present and identified as osteoblasts by SEM and transmission electron microscopy. New bone matrices were observed in and around the porous nanotube inserts by light microscopy. Compared with clinically used hydroxyapatite and tricalcium phosphate, beta-titanium oxide nanotubes promote faster acquisition and development of osteoblasts and bone tissues and have better bone regenerating ability after one week.     

Porous ceramic bone scaffolds for vascularized bone tissue regeneration

Hydroxyapatite scaffolds with a multi modal porosity designed for use in tissue engineering of vascularized bone graft substitutes were prepared by three dimensional printing. Depending on the ratio of coarse (mean particle size 50 microm) to fine powder (mean particle size 4 microm) in the powder granulate and the sintering temperature total porosity was varied from 30% to 64%. While macroscopic pore channels with a diameter of 1 mm were created by CAD design, porosity structure in the sintered solid phase was governed by the granulate structure of the printing powder. Scaffolds sintered at 1,250 degrees C were characterized by a bimodal pore structure with intragranular pores of 0.3-0.4 microm and intergranular pores of 20 microm whereas scaffolds sintered at 1,400 degrees C exhibit a monomodal porosity with a maximum of pore size distribution at 10-20 microm. For in-vivo testing, matrices were implanted subcutaneously in four male Lewis rats. Scaffolds with 50% porosity and an average pore size of approximately 18 microm were successfully transferred to rats and vascularized within 4 weeks.     

基于遗传算法的飞机复合材料结构装配压紧力大小与布局的优化基于遗传算法的飞机复合材料结构装配压紧力大小与布局的优化

针对飞机复合材料结构装配时出现间隙的问题,考虑用压紧力消除间隙可能引起层合板产生损伤,提出了基于遗传算法的压紧力大小和布局的优化算法。结合有限元分析方法,考虑压紧机构之间的干涉问题,以复合材料分层损伤为约束条件,以间隙消除率为优化目标,建立了压紧力大小和布局的优化模型。以复合材料翼盒为例,建立基于内聚力单元的有限元模型,使用上述方法优化复合材料壁板上的压紧力大小和布局。将优化后得到的压紧力方案在有限元模型上进行验算,计算间隙消除率并分析应力应变状态和分层损伤情况。结果表明,优化后的方案能够在不使壁板产生分层损伤的前提下提高间隙消除率,并且能够使壁板的应力和应变分布趋于均匀。当装配间隙的初始值为0.2~0.8 mm时,优化后的方案使间隙消除率提高至77.4%~100%,比优化前的方案提高了19.2%~177.8%。      

Novel 3D porous multi-phase composite scaffolds based on PCL,thermoplastic zein and ha prepared via supercritical CO2 foaming for bone regeneration

The aim of this study was the design of novel biodegradable porous scaffolds for bone tissue engineering (bTE) via supercritical CO₂ (scCO₂) foaming process. The porous scaffolds were prepared from a poly(ε-caprolactone)-thermoplastic zein multi-phase blend w/o interdispersed hydroxyapatite particles (HA) and the porous structure achieved via the scCO₂ foaming technology. The control of scaffolds porosity was obtained by modulating materials formulation and foaming temperature (T_F). The scaffolds were subjected to morphological, micro-structural and biodegradation analyses, as well as in vitro biocompatibility tests. Results demonstrated that both HA concentration and T_F significantly affected the micro-structural features of the scaffolds. In particular, scaffolds with porosity and pore size distribution, mechanical properties and biodegradability adequate for bTE were designed and produced by selecting a T_F equal to 100 °C for all the compositions used. The biocompatibility of these scaffolds was assessed in vitro by using osteoblast-like MG63 and human mesenchymal stem cells (hMSCs).     

Hierarchically engineered fibrous scaffolds for bone regeneration

Surface properties of biomaterials play a major role in the governing of cell functionalities. It is well known that mechanical, chemical and nanotopographic cues, for example, influence cell proliferation and differentiation. Here, we present a novel coating protocol to produce hierarchically engineered fibrous scaffolds with tailorable surface characteristics, which mimic bone extracellular matrix. Based on the sol–gel method and a succession of surface treatments, hollow electrospun polylactic acid fibres were coated with a silicon–calcium–phosphate bioactive organic–inorganic glass. Compared with pure polymeric fibres that showed a completely smooth surface, the coated fibres exhibited a nanostructured topography and greater roughness. They also showed improved hydrophilic properties and a Young''s modulus sixfold higher than non-coated ones, while remaining fully flexible and easy to handle. Rat mesenchymal stem cells cultured on these fibres showed great cellular spreading and interactions with the material. This protocol can be transferred to other structures and glasses, allowing the fabrication of various materials with well-defined features. This novel approach represents therefore a valuable improvement in the production of artificial matrices able to direct stem cell fate through physical and chemical interactions.     

Amperometric immunosensors based on protein A coupled polyaniline-perfluorosulfonated ionomer composite electrodes

A very sensitive immunosensor based on polyaniline/ Nafion/protein A (PA/NF/PrA) composite electrodes has been developed for the amperometric immunoanalysis with urease-labeled immunoreagents. The use of urease conjugated goat anti-RIgG (GaRIgG-Ur) as the labeled antibody and urea as the substrate with an amperometric detection at -200 mV (vs Ag/AgCl) resulted in a dynamic range of 50-2000 ng mL-1 and a low detection limit of 10 ng/mL (64 pM) for the immunoanalysis of rabbit immunoglobulin G (RIgG). Because of the special affinity between protein A and RIgG, the PA/NF/PrA electrode can be regenerated repetitively by changing the pH of the buffer solutions. Characteristics of the PA/NF/PrA/RIgG immunosensor and optimal conditions for the competitive immunoanalysis of RIgG with FIA were studied.     

High strength bioactive glass-ceramic scaffolds for bone regeneration

This research work is focused on the preparation of macroporous glass-ceramic scaffolds with high mechanical strength, equivalent with cancellous bone. The scaffolds were prepared using an open-cells polyurethane sponge as a template and glass powders belonging to the system SiO₂–P₂O₅–CaO–MgO–Na₂O–K₂O. The glass, named as CEL2, was synthesized by a conventional melting-quenching route, ground and sieved to obtain powders of specific size. A slurry of CEL2 powders, polyvinyl alcohol (PVA) as a binder and water was prepared in order to coat, by a process of impregnation, the polymeric template. A thermal treatment was then used to remove the sponge and to sinter the glass powders, in order to obtain a replica of the template structure. The scaffolds were characterized by means of X-ray diffraction analysis, morphological observations, density measurements, volumetric shrinkage, image analysis, capillarity tests, mechanical tests and in vitro bioactivity evaluation.     

基于装配顺序的飞机装配容差信息建模

论文提出了基于装配顺序的装配容差信息建模方法,以装配仿真路径规划的装配顺序为基础,提取装配体中各零件的特征约束关系及相关的关键特征,进而获取组成环容差信息,建立装配容差信息模型。该模型考虑了装配顺序对装配误差累积过程的影响,减少了人工容差信息建模繁琐的交互操作,提高了装配容差信息的建模质量。基于DELMIA平台开发了飞机装配仿真系统。该系统已在工程上成功应用,提高了飞机装配仿真的效率,减少了飞机实际装配生产中的出错率。     

Drug-loaded porous spherical hydroxyapatite granules for bone regeneration

Porous spherical hydroxyapatite (HAp) granules, which are not only can be used for bone void filler, but also drug delivery systems, were prepared using a liquid nitrogen method. Various pore and channel structures of spherical granules were obtained by adjusting the ratio of water to HAp powder and the amount of sodium chloride (NaCl). By using the water to powder ratio at 2.0 ml/g and the amount of NaCl at 15 wt% by powder, the spherical granules have optimal pore volume, micro-channel structure and strength to handle as well as the ability to work as a drug delivery system. When the NaCl content was 15 wt%, the micro-channel structure was changed, but the pore volume was maintained. For the drug release test, dexamathasone (Dex) was loaded as a model drug on the prepared HAp granules by the immersion method, and the drug release behavior was curved by a UV/vis spectrophotometer. As a result, different drug release behavior was observed according to micro-channel structural differences. Therefore, it was concluded that the NACl could be applied as the pore and micro-channel structure control agent. Porous spherical HAp granules, which were fabricated by a liquid nitrogen method, show potential as bone void filler with the ability of controlled drug release.     

Development of magnesium calcium phosphate biocement for bone regeneration

Magnesium calcium phosphate biocement (MCPB) with rapid-setting characteristics was fabricated by using the mixed powders of magnesium oxide (MgO) and calcium dihydrogen phosphate (Ca(H₂PO₄)₂·H₂O). The results revealed that the MCPB hardened after mixing the powders with water for about 7 min, and the compressive strength reached 43 MPa after setting for 1 h, indicating that the MCPB had a short setting time and high initial mechanical strength. After the acid–base reaction of MCPB containing MgO and Ca(H₂PO₄)₂·H₂O in a molar ratio of 2 : 1, the final hydrated products were Mg₃(PO₄)₂ and Ca₃(PO₄)₂. The MCPB was degradable in Tris–HCl solution and the degradation ratio was obviously higher than calcium phosphate biocement (CPB) because of its fast dissolution. The attachment and proliferation of the MG₆₃ cells on the MCPB were significantly enhanced in comparison with CPB, and the alkaline phosphatase activity of MG₆₃ cells on the MCPB was significantly higher than on the CPB at 7 and 14 days. The MG₆₃ cells with normal phenotype spread well on the MCPB surfaces, and were attached in close proximity to the substrate, as seen by scanning electron microscopy (SEM). The results demonstrated that the MCPB had a good ability to support cell attachment, proliferation and differentiation, and exhibited good cytocompatibility.     

Encapsulation of apatite particles for improvement in bone regeneration

The layering of fluorapatite on hydroxyapatite bodies provides a means of decreasing the solubility of hydroxyapatite, providing fluoride for possible stimulation of bone formation and delaying the release of calcium and phosphate from the more soluble hydroxyapatite. The purpose of this work was to encapsulate hydroxyapatite particles with fluorapatite spanning a thickness more than several crystallites deep. A three-step procedure was employed. Hydroxyapatite powder was immersed in an electrolyte solution until an equilibrium was established between the solid and the dissolved calcium at pH 4.67 and 37 °C. Equilibrium was determined by measurement of dissolved calcium with a calcium-specific ion-specific electrode. A 5×10^–2 M ammonium fluoride added to the suspension resulted in a rapid decrease of both calcium and fluoride in the solution. Analysis with X-ray diffraction indicated that a fluoride rich layer containing calcium fluoride deposited onto the particle surface. Scanning electron microscopy revealed submicron spherical precipitate clusters on the hydroxyapatite particles. These clusters transformed to fluorapatite by soaking in a 0.1 M K₂HPO₄ solution at pH 8 and 70 °C. A total time of 10 h was necessary for complete transformation of CaF_{_2} into fluorapatite.