Recent investigations have shown the importance of scaffold pore size on the realisation of tissue engineered cartilage which promotes cell adhesion, proliferation and differentiation. The objective of this study was to investigate the influence of pore size on the mechanical properties, the permeability and the porosity of hyaluronan-collagen scaffolds. Hyaluronan-collagen scaffolds with three different mean pore sizes (302.5, 402.5 and 525 microm) have been produced according to a standardised protocol. The maximum stress at rupture, the Young's Moduli, permeability and porosity of the scaffolds were investigated. The permeability was determined both empirically and mathematically. Increased pore sizes indicated a larger stress at rupture as well as increased Young's Moduli. Porosity and permeability were raised by increasing pore sizes. The mathematically calculated permeability showed the same trend. The results indicate a higher mechanical stability for scaffolds with larger pores. The experimental and mathematical experiments both show increased permeability and fluid mobility for larger pores in scaffolds. Morphological changes resulting from the alteration of pore size led to non-correlation between the calculated and the experimental permeability. 相似文献
Hierarchical channel or well-connected small and large pore networks show multiple advantages for application in catalysis or adsorbent in aqueous condition. Micro- and mesopores provide size or shape selectivity for a guest molecule, while additional macropores reduce transport limitations. In this study, we proposed a novel method to prepare bimodal porous aluminas, which have meso- and macropores with narrow pore size distribution and well defined pore channels. The framework of the porous alumina is prepared via a chemical templating method using alkyl carboxylates. Polystyrene (PS) beads are employed as a physical template for macropores. We examined polydiallyldimethylammonium chloride (PDDA)-treated aluminas as organic adsorbent in aqueous solution. Above 90% of the anionic dye (acid red 44) is removed within 10 min, and the adsorption rate of PDDA/P4 (supported on the bimodal porous alumina) is faster than that of PDDA/P2 (supported on the unimodal porous alumina) because macropore of P4 have reduced transport limitation and enhanced the accessibility to the active site of cationic charge. 相似文献
This paper reports a novel method for producing porous Ti scaffolds with a gradient in porosity and pore size using the freeze casting method, in which TiH2/camphene slurries with various TiH2 contents (40, 25, and 10 vol.%) were cast sequentially into a mold, followed by freeze drying and heat-treatment in a vacuum at 1300 °C for 3 h. This simple sequential freeze casting method produced good bonding between the layers with different porosities of 35, 53, and 75 vol.% obtained using the TiH2 contents of 40, 25 and 10 vol.%, respectively. In addition, the pore size could be increased significantly by increasing the freezing time. The pore sizes obtained in the regions produced using 40, 25, and 10 vol.% TiH2 after freezing for 7 days were 96, 166, and 270 μm, respectively. 相似文献
Highly porous Al2O3 scaffolds were prepared from natural cellulosic sponges via pyrolysis and Al-vapour phase infiltration. Subsequent oxidation and sintering in air resulted in porous Al2O3 ceramics with an open cellular morphology and a total porosity of 95%. The Al2O3-sponges were immersed in highly supersaturated simulated body fluid (5 × SBF) solutions with different Mg2+ and HCO3− concentrations. After soaking of the porous Al2O3 sponges for 4 days a homogeneous calcium phosphate layer with a thickness of approximately 2 μm and a Ca : P ratio of 1.62 (apatite) was found. 相似文献
Bioceramic materials are used for the reconstruction or replacement of the damaged parts of the human body. In this study an improved procedure is described for producing ceramic scaffolds with controlled porosity. Bioinert alumina ceramic was used to make porous scaffolds by using indirect fused deposition modeling (FDM), a commercially available rapid prototyping (RP) technique. Porous alumina samples were coated with hydroxyapatite (HAp) to increase the biocompatibility of the scaffolds. Initial biological responses of the porous alumina scaffolds were assessed in vitro using rat pituitary tumor cells (PR1). Both porous alumina and HAp coated alumina ceramics provided favorable sites for cell attachments in a physiological solution at 37 °C, which suggests that these materials would promote good bonding while used as bone implants in vivo. Based on these preliminary studies, similar tests were performed with human osteosarcoma cells. Cell proliferation studies show that both the ceramic materials can potentially provide a non-toxic surface for bone bonding when implanted in vivo. 相似文献
Alumina-based macro-porous ceramic foams were successfully coated with MCM-41 meso-porous materials using an in-situ one step hydrothermal synthesis. Low H2O/NaOH ratio in the starting mixture leads to a not uniform deposition of the meso-porous materials. Using higher H2O/NaOH ratio and two cycles of deposition, a CF with a continuous and thick layer of well-ordered MCM-41 material coating was produced. 相似文献
The aim of this work is to demonstrate that the structural and fluidic properties of polymer foam tissue scaffolds, post-fabrication but prior to the introduction of cells, can be engineered via exposure to high power ultrasound. Our analysis is supported by measurements of fluid uptake during insonification and imaging of the scaffold microstructure via X-ray computed tomography, scanning electron microscopy and acoustic microscopy. The ultrasonic treatment is performed with a frequency of 30 kHz, average intensities up to 80,000 Wm? 2 and exposure times up to 20 h. The treatment is found to increase the mean pore size by over 10%. More striking is the improvement in fluid uptake: for scaffolds with only 40% water uptake via standard immersion techniques, we can routinely achieve full saturation of the scaffold over approximately one hour of exposure. These desirable modifications occur with negligible loss of scaffold integrity and mass, and are optimized when the ultrasound treatment is coupled to a pre-wetting stage with ethanol. Our findings suggest that high power ultrasound is highly targeted towards flow obstructions in the scaffold architecture, thereby providing an efficient means to promote pore interconnectivity and fluid transport in thick foam tissue scaffolds. 相似文献
An easy, fast and inexpensive method to determine the mean pore size of a microfiltration ceramic membrane is offered by the
wicking technique combined with electrical resistance measurements. Mean pore size is derived from the measured rates of capillary
rise of different liquids of known surface tension through the ceramic membrane, via the Washburn equation. We used low-energy
liquids for which the contact angle θ ≈ 0, such as hydrocarbons, and we determined the tortuosity of the membrane pores from
electrical resistance measurements so that the mean pore radius was the only unknown in the Washburn equation. The mean pore
diameter of the ceramic membrane was also determined from Mercury Intrusion Porosimetry (MIP) for comparison. It was found
to be in very good agreement with that afforded by the wicking technique.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
Aluminium oxide is relatively cheap material, abundant almosteverywhere and therefore it is widely used for thermal sprayapplications. Various alumina based powder containing 13 wt. Titania, two different 40 wt.% Zirconia and three differentcompositions of alumina-zirconia-chromia were deposited byatmospheric plasma spraying (APS) and high power plasma spraying(HPPS). The coatings obtained were evaluated by optical microscopy,microhardness measurements, X-ray diffraction and porositymeasurements. Moreover, abrasion and friction wear resistance wereevaluated by using Pin-on-Disc machine. Microhardness values of APScoatings are relatively high as compared to HPPS coatings except inalumina-zirconia-chromia coatings. HPPS have higher hardness values.APS coatings are much coarser and show higher porosity values thanHPPS coatings. The best wear/friction behaviour exhibited coatingAl2O3-40 wt.% ZrO2 that deposited from agglomerated andsintered powder type. 相似文献
While conventional Gibson–Ashby models provide a general insight into how elastic modulus and yield strength degrade with increasing overall porosity in materials, very limited work has investigated the effects of pore size and distribution on the mechanical properties of metals. One key question is whether and how pores can be utilized for improved mechanical properties rather than being eliminated or minimized for full densification. To fill in this gap, austenitic stainless steel 316L samples with intentional pores of varying diameters and distributions were fabricated by spark plasma sintering using starting powders with different morphologies. Characterization of pore features was not limited to the total volume percentage but also addressed the pore size, shape, interpore spacing, and pore surface area. The mechanical properties of those samples were investigated at multiple length scales to investigate the effect of pore characteristics, including macro-scale compression testing, Vickers micro-indentation, nanoindentation, and nanoscratch. Results suggested incorporating submicron pores improved both the yield strength and strength to weight ratio. The sample containing submicron pores represented an outlier in the classical Hall–Petch relation between yield strength and grain size, and it achieved a yield strength of 482 MPa, compressive strength of?~?1.4GPa at a strain of 0.3 without fracture, and a specific yield strength of 67.7 MPa cm3/g. The mechanism was attributed to local stiffening and (Cr, Mn)-rich precipitates surrounding the submicron pores. It was discovered, for the first time, the specific yield strength and the pore diameter followed a Hall–Petch type correlation.
Cryochemically prepared alumina and yttria-doped alumina powders and their sulphate precursors were examined in the SEM and TEM. The TEM examination revealed a typical chained agglomerate structure with subnamometre-sized porosity within the agglomerates and micrometre-sized porosity between the agglomerates. The SEM examination showed that the sulphate solutions had separated into water channels and immiscible hydrates upon freezing. The water channels had ovulated and spheroidized as they were freezing. This morphology was maintained through vacuum drying and calcining. 相似文献
A transient nonlinear finite-element program has been used to calculate the electric field distribution as a function of time for a spherical cell with a pore in a conducting medium during application of a subnanosecond rise time “step” wave, including the effects of dipolar saturation in the water-based cytoplasm and cell medium. The time-dependent pressure on the pore wall has been computed as a function of time as the system polarizes from the change of the energy in the electric field to the left (inside the pore) and to the right (inside the membrane) of the pore wall. The computations suggest that dipolar saturation, while significant, has little effect on the time-dependent electric field distribution but a substantial effect on the field-induced pore wall pressure. Also, the effect of pore size on both the computed electric field and field-induced pressure was studied. As the pore size increases, a collapse in both the electric field and field-induced pressure has been noticed. This suggests that as the pore size increases, the driving force for further opening the pore is not electrical. 相似文献