A cartilage tissue engineering approach combining starch-polycaprolactone fibre mesh scaffolds with bovine articular chondrocytes

In the present work we originally tested the suitability of corn starch-polycaprolactone (SPCL) scaffolds for pursuing a cartilage tissue engineering approach. Bovine articular chondrocytes were seeded on SPCL scaffolds under dynamic conditions using spinner flasks (total of 4 scaffolds per spinner flask using cell suspensions of 0.5 × 10⁶ cells/ml) and cultured under orbital agitation for a total of 6 weeks. Poly(glycolic acid) (PGA) non-woven scaffolds and bovine native articular cartilage were used as standard controls for the conducted experiments. PGA is a kind of standard in tissue engineering approaches and it was used as a control in that sense. The tissue engineered constructs were characterized at different time periods by scanning electron microscopy (SEM), hematoxylin-eosin (H&E) and toluidine blue stainings, immunolocalisation of collagen types I and II, and dimethylmethylene blue (DMB) assay for glycosaminoglycans (GAG) quantification assay. SEM results for SPCL constructs showed that the chondrocytes presented normal morphological features, with extensive cells presence at the surface of the support structures, and penetrating the scaffolds pores. These observations were further corroborated by H&E staining. Toluidine blue and immunohistochemistry exhibited extracellular matrix deposition throughout the 3D structure. Glycosaminoglycans, and collagen types I and II were detected. However, stronger staining for collagen type II was observed when compared to collagen type I. The PGA constructs presented similar features to SPCL at the end of the 6 weeks. PGA constructs exhibited higher amounts of matrix glycosaminoglycans when compared to the SPCL scaffolds. However, we also observed a lack of tissue in the central area of the PGA scaffolds. Reasons for these occurrences may include inefficient cells penetration, necrosis due to high cell densities, or necrosis related with acidic by-products degradation. Such situation was not detected in the SPCL scaffolds, indicating the much better biocompatibility of the starch based scaffolds.     

An evaluation of human articular cartilage on femoral head

In this study, we investigated stress relaxation behavior of the human articular cartilage on femoral head. Articular cartilage is a white dense connective tissue that covers the bone ends within diarthrodial joints and works as a weight-transmitting and energy-absorbing material. Human articular cartilage on femoral head was used as test material. Relaxation tests were carried out by using the indentation technique via Instron Universal Testing Machine. Test materials were investigated in an isotonic salt solution at 37 °C. To keep the temperature constant, two vessels being in each other were utilized. Thus, hot water was circulated in the outer vessel and isotonic salt solution was kept in the inner vessel. Experimental results showed that there is a remarkable difference between normal and degenerated cartilage for the same age and sex. It was observed that the relaxation percent of normal cartilage as a function of relaxation time is much higher than that of degenerated cartilage.     

Influence of dynamic load on friction behavior of human articular cartilage,stainless steel and polyvinyl alcohol hydrogel as artificial cartilage

Many biomaterials are being developed to be used for cartilage substitution and hemiarthroplasty implants. The lubrication property is a key feature of the artificial cartilage. The frictional behavior of human articular cartilage, stainless steel and polyvinyl alcohol (PVA) hydrogel were investigated under cartilage-on-PVA hydrogel contact, cartilage-on-cartilage contact and cartilage-on-stainless steel contact using pin-on-plate method. Tests under static load, cyclic load and 1 min load change were used to evaluate friction variations in reciprocating motion. The results showed that the lubrication property of cartilage-on-PVA hydrogel contact and cartilage-on-stainless steel contact were restored in both 1 min load change and cyclic load tests. The friction coefficient of PVA hydrogel decreased from 0.178 to 0.076 in 60 min, which was almost one-third of the value under static load in continuous sliding tests. In each test, the friction coefficient of cartilage-on-cartilage contact maintained far lower value than other contacts. It is indicated that a key feature of artificial cartilage is the biphasic lubrication properties.     

Effects of exogenous glycosaminoglycans on human chondrocytes cultivated on type II collagen scaffolds

Cartilage extracellular matrix (ECM) is composed primarily of type II collagen (COL II) and large, networks of proteoglycans (PGs) that contain glycosaminoglycans such as hyaluronic acid (HA) and chondroitin sulfate (CS). Since cartilage shows little tendency for self-repair, injuries are kept unhealed for years and can eventually lead to further degeneration. During the past decades, many investigations have pursued techniques to stimulate articular cartilage repair or regeneration. The current study assessed the effects of exogenous glycosaminoglycans (GAGs) including CS-A, CS-B, CS-C, heparan sulfate and HA, administration on human chondrocytes in terms of proliferation and matrix synthesis, while the cells were seeded and grown on the genipin-crosslinked collagen type II (COL II) scaffold. DNA content was measured by Hoechst dye intercalation, matrix deposition was evaluated by DMMB dye. Expression of collagen II and aggrecan mRNAs was assessed by RT-PCR, followed by gel electrophoresis. In a 28-day in vitro culture, administration of 5 μg/ml CS-A, 50 μg/ml CS-B, 50 μg/ml CS-C, 5 μg/ml HS, and 500 kDa HA led to significant increase in biosynthesis rate of PGs. Gene expression of aggrecan and collagen II were upregulated by CS-A, CS-C and HA. These results showed considerable relevance of GAGs to the issue of in vitro/ex vivo neo-cartilage synthesis for tissue engineering and regenerative medical applications.     

软骨细胞在聚乳酸支架中的体外生长行为

采用明胶和氯化钠颗粒作为致孔剂,使用溶剂浇铸／颗粒沥滤法制备了高孔隙率、孔间连通和高机械性能的聚乳酸支架,采用软骨细胞体外培养研究了这两种多孔支架对细胞生长性能的影响．结果表明,软骨细胞在以明胶颗粒为致孔剂制备的多孔支架中的相对数量和GAG的分泌量更多,细胞的活性更高。     

Effect of poly(<Emphasis Type="SmallCaps">L</Emphasis>-lactide) surface topography on the morphology of in vitro cultured human articular chondrocytes

Human articular chondrocytes were cultured in vitro on poly(L-lactic) acid, PLLA, substrates. Influence of the surface topography on cell morphology was found. Different surface microtopographies were obtained on PLLA by crystallizing at 120 °C after nucleation treatments that include isothermal stages at temperatures just below (55 °C) and just above (75 °C) the glass transition temperature (T _g = 65 °C). Isothermal crystallization from the melt gave rise to big spherulites (approx. 50 μm diameter) with approx. 1 μm depth. Crystallization after nucleation treatments results in smaller (approx. 5 μm)—difficult to distinguish—spherulites. Cell viability was excellent and not affected by the surface roughness. Cell population on the nucleated samples resembles the result of culture on the reference tissue culture polystyrene (TCPS). However, cells cultured on big spherulites (PLLA isothermally crystallized without nucleation treatment) show a peculiar morphology, with a more isolated disposition and growth oriented in a characteristic direction.     

Description of depth-dependent nonlinear viscoelastic behavior for articular cartilage in unconfined compression

An optimized digital image correlation (DIC) technique was applied to investigate the depth-dependent nonlinear viscoelastic properties of articular cartilage and simultaneously the biphasic nonlinear viscoelastic relaxation model of cartilage was proposed and validated. The stress relaxation tests were performed with different strain levels and it is found that the initial stress and relaxed stress at any time increase with increasing strain levels. The depth-dependent strain of cartilage was obtained by analyzing the images acquired using the optimized DIC technique and moreover the inhomogeneous relaxation modulus distributions within the tissues were determined at different relaxation time points under strain of 11.35, 19.35 and 30% respectively. The strain rate dependent nonlinear stress and strain curves were obtained for articular cartilage through uniaxial compression tests. It is noted that the Young's modulus exhibits a slight increase near the cartilage surface, and then increases fast with depth and both the magnitude and the variation of the Young's modulus are affected by increasing strain rates. A biphasic nonlinear viscoelastic relaxation model was proposed to predict the depth-dependent relaxation behavior of cartilage under unconfined compression and the results show that there are good agreements between the experimental data and predictions.     

纳米氧化亚铜的制备方法研究

氧化亚铜是一种新型的无机材料,因其独特的性质而在诸多领域有着广泛的应用.总结了各种制备纳米氧化亚铜的方法,论述了各种方法的原理,并比较了各自的优缺点.     

纳米级铁酸盐粉体材料合成的进展

本文综述了具有尖晶石结构的纳有铁酸盐（ＭＦｅ２Ｏ４,Ｍ＝Ｍｎ,Ｚｎ,Ｃｏ,Ｎｉ,Ｃｕ等）的合成方法,其中包括：共沉淀法,水热法,溶胶－凝胶法,微乳液法,冲击波法以及本文作者最近发展的共沉淀催化相转化法等。这些方法合成的铁酸盐的粒径一般小于１００ｎｍ,是当今合成的纳米级铁酸盐粉体的有效方法。     

Zone-dependent mechanical properties of human articular cartilage obtained by indentation measurements

Emerging 3D printing technology permits innovative approaches to manufacture cartilage scaffolds associated with layer-by-layer mechanical property adaptation. However, information about gradients of mechanical properties in human articular cartilage is limited. In this study, we quantified a zone-dependent change of local elastic modulus of human femoral condyle cartilage by using an instrumented indentation technique. From the cartilage superficial zone towards the calcified layer, a gradient of elastic modulus values between 0.020?±?0.003?MPa and 6.44?±?1.02?MPa was measured. To validate the tissue quality, the histological tissue composition was visualized by glycosaminoglycan and collagen staining. This work aims to introduce a new protocol to investigate the zone-dependent mechanical properties of graded structures, such as human articular cartilage. From this knowledge, better cartilage repair strategies could be tailored in the future.     

纳米NiO的制备及其赝电容特性研究

运用沉淀转化法制备Ni(OH)2超微粉末,并通过热处理得到纳米NiO.利用TEM,TG,XRD,循环伏安和恒流充放电测试对样品进行了分析和表征.结果表明,实验制备的NiO粒径为10nm左右, 在-0.05～0.35V(vs SCE)的电位范围内表现出典型的法拉第赝电容行为, 在电流密度为2mA*cm-2时, 其比容达到243F·g-1.     

Fracture behavior of human molars

Despite the durability of human teeth, which are able to withstand repeated loading while maintaining form and function, they are still susceptible to fracture. We focus here on longitudinal fracture in molar teeth??channel-like cracks that run along the enamel sidewall of the tooth between the gum line (cemento-enamel junction??CEJ) and the occlusal surface. Such fractures can often be painful and necessitate costly restorative work. The following study describes fracture experiments made on molar teeth of humans in which the molars are placed under axial compressive load using a hard indenting plate in order to induce longitudinal cracks in the enamel. Observed damage modes include fractures originating in the occlusal region (??radial-median cracks??) and fractures emanating from the margin of the enamel in the region of the CEJ (??margin cracks??), as well as ??spalling?? of enamel (the linking of longitudinal cracks). The loading conditions that govern fracture behavior in enamel are reported and observations made of the evolution of fracture as the load is increased. Relatively low loads were required to induce observable crack initiation??approximately 100?N for radial-median cracks and 200?N for margin cracks??both of which are less than the reported maximum biting force on a single molar tooth of several hundred Newtons. Unstable crack growth was observed to take place soon after and occurred at loads lower than those calculated by the current fracture models. Multiple cracks were observed on a single cusp, their interactions influencing crack growth behavior. The majority of the teeth tested in this study were noted to exhibit margin cracks prior to compression testing, which were apparently formed during the functional lifetime of the tooth. Such teeth were still able to withstand additional loading prior to catastrophic fracture, highlighting the remarkable damage containment capabilities of the natural tooth structure.     

制备条件对纳米NiO微粉的影响

用化学沉淀法制备了纳米立方NiO的微粉 ,研究了介质 pH、不同沉淀剂和热处理温度对纳米NiO粒子大小和聚结状态的影响。用NaOH作沉淀剂 ,控制介质 pH为 9～10 ,经 2 70～ 30 0℃热处理 4h ,制备得到粒子尺寸约 5nm ,在水中易重新分散的纳米NiO微粉     

Thermo-mechanical coupling effect on fatigue behavior of cement asphalt mortar

This contribution first presents a fatigue model to elaborate fatigue behavior of materials subjected to thermal mechanical effect. To calibrate the presented model, a valid experiment is then conducted on cement asphalt mortar. The model can be further extended to other materials and valid experimental data from literature is utilized for verification. Results suggested the model is sufficient to describe thermo-mechanical fatigue behavior of cement-based materials, under the condition that no phase or morphological change occurred in the fatigue temperature range. Finally, the developed model is applied to predict fatigue life of one current track.     

Chitosan effect on the mesophase behavior of phosphatidylcholine supramolecular systems

Two distinct supramolecular self assemblies of phosphatidylcholine and chitosan, namely liposomes and their precursory organogel, have been investigated by means of SAXS, Light Scattering and Polarized Optical Microscopy. The main goal was the evaluation of the chitosan effect on the self assemblies phase transition behavior upon heating. A distinct smectic organization was observed for the organogel prepared in the presence of chitosan, if compared to that prepared only with phosphatidylcholine. In addition, the phosphatidylcholine–chitosan organogel showed unchanged optical properties upon heating and after 24 h, indicating increased stability when compared to the organogel prepared without chitosan. For the liposomes containing chitosan, the thermotropic behavior features a lamellar pattern that is preserved under heating, until at least 81 °C. A phase transition temperature has been determined around 64 °C, which was clearly higher than that observed for liposomes prepared without chitosan. The bilayer repeat distance typical of the liposomes increases slowly by increasing the temperature and stacking fluctuations of the bilayers are delayed due to enhancement of the membrane rigidity.     

PN-junction diode behavior based on polyaniline nanotubes field effect transistor

Polyaniline (PANI) nanotubes configured as a field effect transistor (FET) exhibits a p–n junction diode behavior. The forward-bias current can be modulated by a gate voltage; turning on at negative gate voltage and turning off at positive gate voltage. An energy band diagram model has been proposed to explain the rectifying effect of the PANI nanotubes FET (PNT-FET). All the four different forward bias conduction mechanisms of a typical p–n junction diode can be identified for this PNT-FET using a semi-log graph to confirm this resemblance.     

Phase morphology effect on elevated temperature mechanical behavior of nanostructures

A devitrification procedure by annealing was applied to a multicomponent Fe-based metallic glass in order to obtain nanocrystalline materials. Phase composition and phase morphology were strongly dependent on the annealing conditions. An elevated temperature mechanical behavior of nanostructures was evaluated by tensile testing. A strong effect of phase morphology on the mechanical response of the material was revealed. A most attractive combination of strength and plasticity was observed in the nanostructure with approximately equal grain sizes of crystallized phases.     

Surface effect on the elastic behavior of static bending nanowires

The surface effect from surface stress and surface elasticity on the elastic behavior of nanowires in static bending is incorporated into Euler-Bernoulli beam theory via the Young-Laplace equation. Explicit solutions are presented to study the dependence of the surface effect on the overall Young's modulus of nanowires for three different boundary conditions: cantilever, simply supported, and fixed-fixed. The solutions indicate that the cantilever nanowires behave as softer materials when deflected while the other structures behave like stiffer materials as the nanowire cross-sectional size decreases for positive surface stresses. These solutions agree with size dependent nanowire overall Young's moduli observed from static bending tests by other researchers. This study also discusses possible reasons for variations of nanowire overall Young's moduli observed.     

Viscoelastic behavior of nano-hydroxyapatite reinforced poly(vinyl alcohol) gel biocomposites as an articular cartilage

Nanohydroxyapatite reinforced poly(vinyl alcohol) gel (nano-HA/PVA gel) composites has been proposed as an articular cartilage repair biomaterial. In this paper, nano-HA/PVA gel composites were prepared by in situ synthesis nano-HA particles in PVA solution and accompanied with freeze/thaw method. The influence of nano-HA content, PVA concentration, test frequency and freeze/thaw cycle times on the viscoelastic behavior of nano-HA/PVA gel composites were evaluated using dynamic mechanical thermal analysis (DMTA). The results showed that both storage modulus and loss modulus firstly increased and then presented decreasing trend with the rise of nano-HA content. Their maximum values were obtained while nano-HA content was 6%. Furthermore, the G′ and G″ of the composites improve with the increase of PVA concentrations and freeze/thaw cycle times. This effect was more distinct at low freeze/thaw cycles. The phase angle (tan δ) of the pure PVA gel is larger than that of the nano-HA/PVA composites at the test frequency spectra, but all the phase angle values of the tested composites were close to that of nature bone.