Effect of particle size on microstructure and strength of porous spinel ceramics prepared by pore-forming <Emphasis Type="Italic">in situ</Emphasis> technique

The porous spinel ceramics were prepared from magnesite and bauxite by the pore-forming in situ technique. The characterization of porous spinel ceramics was determined by X-ray diffractometer (XRD), scanning electron microscopy(SEM), mercury porosimetry measurement etc and the effects of particle size on microstructure and strength were investigated. It was found that particle size affects strongly on the microstructure and strength. With decreasing particle size, the pore size distribution occurs from multi-peak mode to bi-peak mode, and lastly to mono-peak mode; the porosity decreases but strength increases. The most apposite mode is the specimens from the grinded powder with a particle size of 6·53 μm, which has a high apparent porosity (40%), a high compressive strength (75·6 MPa), a small average pore size (2·53 μm) and a homogeneous pore size distribution.     

Preparation of 3-D regenerated fibroin scaffolds with freeze drying method and freeze drying/foaming technique

Although three-dimensional fibroin scaffolds have been prepared with freeze drying method, the porosity and pore sizes still can not satisfy the requirement of tissue engineering. In this article, fibroin porous scaffold with high porosity and > 100μm diameter interconnected pores was firstly prepared with freeze drying method through adjusting fibroin concentration. The morphology of different scaffolds lyophilized from different fibroin concentration was observed by SEM. A novel freeze drying improved method, freeze drying/foaming technique, was also devised to prepare fibroin scaffolds at different fibroin concentrations. Using the said method, the porosity and pore size of fibroin scaffolds prepared from 12% concentration were 85.8 ± 4% and 109 ± 20 μm respectively with yield strength up to 450 ± 6 KPa while the porosity and pore size of fibroin scaffolds prepared from 8% concentration were 96.9 ± 3.6% and 120 ± 30 μm respectively with yield strength up to 30 ± 1 KPa. The freeze drying/foaming technique produced scaffolds with a useful combination of high yield strength, interconnected pores, and pore sizes greater than 100 μm in diameter. Through adjusting fibroin concentration and thawing time, the porosity, pore sizes and mechanical properties could be controlled to satisfy the different requirements of tissue engineering. The results suggested that fibroin scaffolds prepared with the above methods could be formed for utility in biomaterial application.     

Synthesis of porous oxide ceramics using a soft responsive scaffold

Ceramic materials have significant utility. Developing synthetic protocols that are facile and provide low energy alternatives to traditional methods remains a major driver in materials synthesis. We present here the adaptation of a method recently developed in our group for the synthesis of porous silica using a non-ionic emulsion template. The silicate materials are porous on both the nanometre and micrometre length scales and surface-to-volume ratios may be readily modified by altering the volume fraction of the emulsion template. Switching the silica precursor for an alumina or titania precursor resulted in the formation of porous alumina and titania materials which were prepared as thin films or monoliths. The pores formed in the amorphous alumina materials were ~0.8 μm and ~50 nm, with a primary particle size of 50–100 nm. The titania materials had pores on one length scale only: ~0.8 μm, with a smaller primary particle size of 20–60 nm. As-synthesized materials were investigated using scanning electron microscopy and X-ray diffraction.     

Biocompatibility and biodegradation of poly(hydroxybutyrate)/poly(ethylene glycol) blend films

Using chloroform as co-solvent, a series of poly(3-hydroxybutyrate) (PHB) and polyethylene glycol (PEG) blend materials with different ratio ranging from 80 : 20 (wt %) to 20 : 80 (wt %) were prepared by solution blend. The blood-compatibility was evaluated by means of platelet clotting time test and exploring its morphological changes. The results showed that PEG played an important role in resisting platelet adhesion. With the increased addition of PEG, the clotting times became longer and the number of platelet adhesion decreased apparently. All platelets were in discrete state, no pseudopodium had been found and no collective phenomenon had been happened. The cell-compatibility was evaluated via Chinese Hamster Lung (CHL) fibroblast cultivation in vitro. The cells cultured on the matrix spread and proliferated well. With the increase of PEG content in the blend films, the number of live cells became more and more. These results indicated that PHB exhibited satisfying cell-compatibility and the addition of PEG also could improve the cell-compatibility of PHB. The biodegradation experiment indicated that the degradation of PHB/PEG was accelerated by enzyme in vitro and the blending of PEG was favorable to degradation.     

Preparation,mechanical properties and in vitro degradability of wollastonite/tricalcium phosphate macroporous scaffolds from nanocomposite powders

A new class of scaffolds with a gain size of 200 nm was prepared from wollastonite/tricalcium phosphate (WT) nanocomposite powders (termed “nano-sintered scaffolds”) through a two-step chemical precipitation and porogen burnout techniques. For a comparison, WT scaffolds with a grain size of 2 μm were also fabricated from submicron composite powders (termed “submicron-sintered scaffolds”) under the same condition. The resultant scaffolds showed porosities between 50 ± 1.0% and 65 ± 1.0% with a pore size ranging from 100 μm to 300 μm. The WT nano-sintered scaffolds exhibited compressive strength and elastic modulus values that were about twice that of their submicron-sintered counterparts. The in vitro degradation tests demonstrated that the degradability could be regulated by the grain size of bioceramics. The decreased specific surface area of pores in the nano-sintered scaffolds led to their reduced degradation rate. The mechanical properties of the nano-sintered scaffolds exhibited less strength loss during the degradation process. The WT macroporous nano-sintered scaffolds are a promising and potential candidate for bone reconstruction applications.     

Fabrication and characterization of porous poly(lactic-<Emphasis Type="Italic">co</Emphasis>-glycolic acid) (PLGA) microspheres for use as a drug delivery system

In this work, Simvastatin (SIM) loaded porous poly(lactic-co-glycolic acid) (PLGA) microspheres were fabricated using the W/O/W1/W2 double emulsion and solvent evaporation method. The optimal conditions for fabricating porous PLGA microspheres were determined to be 20% distilled water (v/v), 10% PLGA (m/v), and a 4:1 ratio of internal polyvinyl alcohol (PVA) to dichloromethane (DCM). The pores size distribution of porous PLGA microspheres was varied from 0.01 to 40 μm, while their particle displayed a bimodal size distribution that had two diameter peaks at around 100 μm and 500 μm. The SIM encapsulation efficacy was found to be very high with a yield near 80% and the porous PLGA microspheres showed the excellent biocompatibility. In addition, the drug release profile was found to be significantly different from a temporal basis. Base on the combined results of this study, SIM loaded PLGA microspheres holds great promise for use in biomedical applications, especially in drug delivery system or tissue regeneration.     

Degradation behavior of hydrophilized PLGA scaffolds prepared by melt-molding particulate-leaching method: Comparison with control hydrophobic one

Porous PLGA/PVA scaffolds as hydrophilized PLGA scaffolds for tissue engineering applications were fabricated by a novel melt-molding particulate leaching method (non-solvent method). The prepared scaffolds exhibited highly porous and open-cellular pore structures with almost same surface and interior porosities (pore size, 200–300 μ m; porosity, about 90%). The in vitro degradation behavior of the PLGA and PLGA/PVA scaffolds was compared at 37^∘C in PBS (pH 7.4) with and without the solution change everyday to see the effect of solution pH as well as scaffold hydrophilicity on the degradation behavior. The changes in dimension, molecular weight, mechanical properties (maximum load and modulus), and morphology of the scaffolds were examined with degradation time. The degradation behavior of the PLGA and PLGA/PVA scaffolds was further investigated in vivousing a rat model (subcutaneously implantation). It was observed that both PLGA and PLGA/PVA scaffolds in decreasing pH condition (PBS no change) showed faster degradation than those in constant pH condition (PBS change everyday), owing to the enhanced intramolecular depolymerization by the increment of chain hydrophilicity caused by carboxylate groups as well as the autocatalysis of carboxylic acids accumulated in the solution by the cleavage of PLGA backbone ester bonds. The scaffolds in vivo condition also showed faster degradation than those in vitro, probably due to the aid of foreign body giant cells or enzymes. The PLGA/PVA scaffold showed slightly faster degradation than the PLGA scaffold for both in vitro and in vivo conditions. Author to whom all correspondence should be addressed.     

Preparation of porous hydroxyapatite with interconnected pore architecture

Since pore connectivity has significant effects on the biological behaviors of biomedical porous hydroxyapatite (PHA), the preparation of PHA with interconnected pore architecture is of great practical significance. In the present study, PHA with highly interconnected architecture was prepared via a simple burnout route with rod-like urea as the porogen. Microscopy and porosimetry data showed that the as-prepared PHA had open and interconnected pore structure with the average fenestration size of about 120 μm. Open pores occupied up to 98% of the total porosity. The compressive strength and modulus of the as-prepared PHA were respectively 1.3–7.6 MPa and 4.0–10.4 GPa.     

Synthesis and characterization of silicalite powders and membranes with micro–meso bimodal pores

Silicalite sols containing silicalite agglomerates of 150–380 nm in size were synthesized by hydrothermal synthesis for 0.5–3 days. Silicalite powders and supported silicalite membranes containing micro-meso bimodal pores were prepared by the sol–gel method using these silicalite sols. The silicalite powders contain intracrystalline zeolitic pores (0.54 nm) and intercrystalline mesopores of about 3–4 nm in diameter. For the silicalite powders the mesopore size decreases and mesopore surface area increases with increasing silicalite agglomerate size as a result of a change of the shape of silicalite agglomerates from round to more faceted one. Continuous silicalite thin films of thicknesses ranging from 3 μm to 12 μm were made on α-alumina by the sol–gel dip-coating method. The supported silicalite membranes also contain both zeolitic pores and mesoporous intercrystalline pores. The single gas He permeance of the 3 μm thick α-alumina supported silicalite membrane was found to be from 2.7 × 10⁻⁶ to 3.3 × 10⁻⁶ mol/m² s Pa. These bimodal pore zeolite powders offer the potential as catalysts and sorbents with improved efficiency. The bimodal pore zeolite membrane can be used as support for zeolite and other membranes and as compact packed-bed reactor for chemical reaction.     

聚合物泡孔材料为模板的溶胶-凝胶法

采用浓乳液聚合方法制备出多孔聚合物结构材料作为模板,通过溶胶-凝胶法,将异丙醇钛的异丙醇溶液多次浸泡聚合物泡孔材料制备出了尺寸为毫米级的多孔氧化钛陶瓷材料.考察了多孔性的聚合物模板的孔径对所制备陶瓷孔径的影响,以及不同聚合物模板体系对陶瓷结构的影响,并采用扫描电子显微镜对所制备的陶瓷材料进行了形态表征.结果表明,通过调节浓乳液体系分散相的体积分数以及改变聚合物模板体系均可以有效地调节所制备的多孔陶瓷的形态结构.     

High-porosity NiTi superelastic alloys fabricated by low-pressure sintering using titanium hydride as pore-forming agent

Porous NiTi shape memory alloys (SMAs) were successfully fabricated by low-pressure sintering (LPS), and the pore features have been controlled by adjusting the processing parameters. The porous NiTi SMAs with high porosity (45%) and large pore size (200–350 μm) can be prepared by LPS using TiH_1.5 as pore-forming agent. These alloys exhibit isotropic pore structure with three-dimensional interconnected pores. The porous NiTi SMA produced by LPS exhibits superelasticity and mechanical properties superior to that by conventional sintering.     

Microstructural characterisation of metallurgical grade porous silicon nanosponge particles

Porous silicon finds numerous applications in the areas of bio-technology, drug delivery, energetic materials and catalysis. Recent studies by Vesta Sciences have led to the development of porous silicon nanosponge particles from metallurgical grade silicon powder through their own patented chemical etching process (Irish patent no. IE20060360). This discovery paves the way for a more economical production method for porous silicon. The study presented here studies the structural morphology of the porous silicon nanosponge particles using high resolution electron microscopy techniques combined with porisometry type measurements, where appropriate. The related surface pore structure is examined in detail using Scanning Electron Microscopy and Transmission Electron Microscopy techniques while the internal pore structure is explored using Focused Ion Beam milling and ultramicrotomed cross-sections. Three samples of the silicon particles were analysed for this study which include the starting metallurgical grade silicon powder and two samples that have been chemically etched. Analysis of the etched samples indicates a disordered pore structure with pore diameters ranging up to 15 nm on porous silicon particles ranging up to 5 μm in size. Crystallographic orientation did not appear to affect the surface pore opening diameter. Internal pore data indicated pore depths of up to 1 μm dependant on the particle size and etching conditions applied.     

Photoluminescence Properties of the Zn<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Y<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O Tubes Prepared by Polycarbonate Templates

We have prepared Zn_1−x Y _x O (x=0 and 0.01) tubes to study its structural and photoluminescent properties. A pore wetting process of porous polycarbonate templates with the liquid precursor and following thermal treatment were utilized for preparing the Zn_1−x Y _x O tube structure. Using the polycarbonate template with pore size of about 2 μm diameter, the Zn_1−x Y _x O tubes were obtained. Photoluminescence (PL) spectroscopy was used to measure optical emissions from 350 to 650 nm with a He-Cd laser. The results of the PL spectra show that the Zn_1−x Y _x O tubes have evident emission peaks at the UV (about 380 nm) and visible (around 500 to 650 nm) region. The emission peak at the UV region was slightly shifted to higher wavelengths with increasing Y content. Meanwhile, the green and yellow emission peaks intensity increases as Y content increases. These results are explained by the structure tuning and oxygen deficiency with the introduction of Y.     

Fabrication of porous poly(L-lactide) (PLLA) scaffolds for tissue engineering using liquid–liquid phase separation and freeze extraction

PLLA scaffolds were successfully fabricated using liquid–liquid phase separation with freeze extraction techniques. The effects of different processing conditions, such as method of cooling (direct quenching and pre-quenching), freezing temperature (−80°C and −196°C) and polymer concentration (3, 5 and 7 wt%) were investigated in relations to the scaffold morphology. SEM micrographs of scaffolds showed interconnected porous network with pore size ranging from 20 to 60 μm. The scaffolds had porosity values ranging from 80 to 90%. Changes to the interconnected network, porosity and pore size were observed when the method of cooling and polymer concentration was changed. Direct quenching to −80°C gave a more porous interconnected microstructure with uniform pore size compared to samples prepared using pre-quenching method. Larger pores were observed for samples quenched at −80°C compared to −196°C. Scaffolds prepared using direct quenching to −196°C had higher elastic modulus and compressive stress compared to those quenched to −80°C. The compressive elastic modulus ranged from 4 to 7 MPa and compressive stress at 10% strain was from 0.13 to 0.18 MPa.     

Preparation of an electrodeposited hydroxyapatite coating on titanium substrate suitable for in-vivo applications

In this paper the porous hydroxyapatite coating on Ti implant materials was prepared by the process of electrodeposition, hydrothermal and sinter. The surface morphology, bond strength and thickness of HA coatings were investigated by SEM, AFM, and its biocompatibility was evaluated by cytotoxicity experiments and implant experiments, respectively. Results showed that (1) The HA coatings was 50 μm thickness and adhered on the Ti substrate strongly, which bond strength reached 38MPa. AFM analysis showed that the HA coating was porous structure, in which the mean pore size was 236.5 μm, (2) Cytotoxicity experiments and implant experiments showed that HA-coated Ti implant materials has little cytotoxicity in vitro and little inflammatory reaction in vivo, and there were no statistically disparity between HA-coated Ti implant and titanium implant materials of clinical application (p > 0.05), which demonstrated that HA-coated Ti has a good biocompatibility.     

Fabrication and characterization of chitosan microcarrier for hepatocyte culture

Using chitosan as raw materials, a suitable size (300–500 μm) of porous microcarrier was fabricated by suspension crosslinking and lyophilizing method, which made the carrier has an average pore size of 50 μm and 86% porosity. The microcarrier was modified with lactose and maltose respectively. Various factors that influenced the preparation of microcarrier were studied and the reaction conditions were optimized. Rat hepatocytes cultured on modified microcarrier retained a spherical shape which is similar to those in vivo and formed aggregates. The metabolic activities of cells on lactose-modified were higher than those on maltose-modified microcarrier. The highest albumin secretion reached 54.8 μg/10⁶ cells/d, and the highest urea synthesis reached 4.65 μmol/10⁶cells/d, which may be promoted by the formation of cellular aggregates. In conclusion, lactose-modified porous microcarrier is promising scaffold for hepatocytes culture.     

Cancellous bone from porous T{i}6Al4V by multiple coating technique

A highly porous T{i}6Al4V with interconnected porous structure has been developed in our previous study. By using a so-called “Multiple coating” technique, the porous T{i}6Al4V can be tailored to resemble cancellous bone in terms of porous structure and mechanical properties. A thin layer of T{i}6Al4V slurry was coated on the struts of base porous T{i}6Al4V to improve the pore structure. After two additional coating, pore sizes ranged from 100 μm to 700 μm, and the porosity was decreased from ∼90% to ∼ 75%, while the compressive strength was increased from 10.3 ± 3.3 MPa to 59.4 ± 20.3 MPa and the Young's modulus increased from 0.8 ± 0.3 GPa to 1.8 ± 0.3 GPa. The pore size and porosity are similar to that of cancellous bone, meanwhile the compressive strength is higher than that of cancellous bone, and the Young's modulus is between that of cancellous bone and cortical bone. Porosity, pore size and mechanical properties can be controlled by the parameters in such multiple coating processes. Therefore the porous T{i}6Al4V with the characteristics of cancellous bone is expected to be a promising biomaterial for biomedical applications. Author to whom all correspondence should be addressed.     

Preparation and characterisation of controlled porosity alginate hydrogels made via a simultaneous micelle templating and internal gelation process

Controlled porosity alginate hydrogel monoliths were synthesised by simultaneous micelle templating (MT) and an internal gelation reaction. In water, the self assembling surfactant, cetyltrimethylammonium bromide (CTAB) formed non-spherical micelles that were used as a template for pore formation. The porous microstructure was assessed by mercury intrusion porosimetry (MIP), helium pycnometry, X-ray microtomography (XMT) and scanning electron microscopy (SEM), respectively. The MT hydrogels displayed relatively monodisperse pore size distributions (with pore sizes ranging from 32.5 μm to 164.0 μm), high total pore volumes (4.5–20.3 cm³/g) and high degrees of porosity (83–97%). Some control over pore size distributions was achieved by varying the surfactant concentration; higher surfactant concentrations, led to smaller pores with lower total pore volumes. Uniaxial compression testing revealed that hydrogels made via MT are stable in cell culture media for 28 days. Fourier transform infrared (FTIR) spectroscopy data, suggested that all surfactant could be removed from the final product by washing with ethanol and water, making these hydrogels potentially suitable for tissue engineering (TE) applications.     

A sol–gel-derived α-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> crystal interlayer modified 316L porous stainless steel to support TiO<Subscript>2</Subscript>, SiO<Subscript>2</Subscript>, and TiO<Subscript>2</Subscript>–SiO<Subscript>2</Subscript> hybrid membranes

A homogeneous α-Al₂O₃ crystal membrane was fabricated by the sol–gel technique on 316L porous stainless steel (PSS) substrate with an average pore size of 1.0 μm. The preparation process was optimized by carefully choosing the binder, the concentrations of the casting solutions and the sintering temperatures of the membranes. Compared to methylcellulose and polyethylene glycol 20000, polyvinyl alcohol 1750 was found to be the most effective binder to fabricate a homogeneously structured Al₂O₃ membrane without defects. The concentration to prepare an uniform coverage membrane with a thickness of ~10 μm was 0.032 mol/L. When sintered at 1000 °C, γ-Al₂O₃ membrane with ~3 μm grains was obtained. When sintered at 1200 °C, γ-Al₂O₃ completely transformed into α-Al₂O₃ and the grains grew to ~5 μm. Accordingly, the process was applied to a bigger pore-sized PSS with an average pore size of 1.5 μm to fabricate an α-Al₂O₃ intermediate layer to initially modify its surface. A single α-Al₂O₃ crystal layer with a thickness of ~5 μm and an average pore size of 0.7 μm was achieved. Subsequently, TiO₂, SiO₂, and TiO₂–SiO₂ hybrid membranes were tried on the modified PSS. Defect-free microfiltration membranes with average pore sizes of ~0.3 μm were readily fabricated. The results indicate that the sol–gel method is promising to initially modify the PSS substrates and the sol–gel-derived α-Al₂O₃ crystal layer is an appropriate intermediate layer to modify the PSS and to support smaller grain-sized top membranes.     

The preparation and properties of monodisperse core-shell silica magnetic microspheres

The monodisperse core-shell silica magnetic microspheres (MMS) were synthesized by sol–gel method gelling in the emulsion. Optical microscope (OM), field emission scanning electron microscope (FESEM), nitrogen adsorption and desorption Brunauer Emmett Teller Procedure (BET) isotherms and Barrett-Joyner-Halenda (BJH) pore size distribution measurements, X-ray diffraction (XRD), energy dispersive spectrometer (EDS) and vibrating sample magnetometer (VSM) were used to characterize the appearance, size distribution, phase, specific surface area, chemical composition and magnetic property of silica MMS. The results showed that silica MMS prepared through sol–gel method with acid-alkali two-step catalyze and gelling in emulsion exhibited the superior core-shell structure and size distribution of the microspheres concentrated in about 20 μm. The main phase of microspheres was amorphous silica and spinel ferroferric oxide. Meanwhile, the microspheres remained the superparamagnetic behavior and could be used as biomaterials. This work is supported by both National Science Foundation 50572072 and Science & Technology Commission of Shanghai Municipality (STCSM) 0452nm059.