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Hydroxyapatite (HA) is a well-known regenerative biomaterial. However, the slow degradation rate of HA is still an obstacle in clinical applications. In this study, we concentrated on investigating the degradation behavior of the calcium-rich HA foams, which had a demonstrated effect on blood differentiation in previous studies. The HA foams were processed by an emulsion method and were infiltrated with calcium nitrate to create a calcium carbonate second phase, heterogeneously distributed on and under the surface of the foam. During the 28-day solubility test, the calcium carbonate phase contributed to enhanced Ca2+ ion release into the saline compared to phase pure HA foams. Both types of foams were biocompatible as demonstrated by human endothelial cell culture on their surface. The release of calcium ions, the degradation behavior, and the endothelial cell differentiation behavior suggest this biphasic ceramic is a candidate for bone marrow in vitro culture and a possible bone substitute material.

Long-term in vitro expansion of hematopoietic stem cells (HSCs), while maintaining their functionality and multilineage differentiation potential, is still challenging. In this study, three-dimensional (3D) high-porosity hydroxyapatite (HA) foams have been designed to closely mimic the chemistry and physical structure of cancellous bone. Furthermore, calcium oxide was distributed in the HA ceramics to provide surface calcium ion release, hypothesizing that a local surface calcium gradient supports HSC localization and maintenance. Primary human HSCs and osteoblasts were cocultured for 6 weeks. Controls were cultured in two-dimensional dishes, while scaffold cultures were performed with calcium nitrate-infiltrated HA scaffolds and untreated HA scaffolds. Cells were analyzed for surface markers by flow cytometry, metabolic activity, and hematopoietic multilineage differentiation potential. The release of calcium into culture medium was also determined. The implementation of HA scaffolds had a positive effect on erythrocyte colony formation capacity of HSCs, with an increased osteoblast fraction observed when compared to control cultures without scaffolds. The presentation of scaffolds did not affect metabolic turnover when compared to control cultures. In conclusion, 3D open-porous HA scaffolds provide a bone-like structure and enable the long-term maintenance of primary HSCs.

Ceramic scaffolds are being developed to control both proliferation and differentiation of hematopoietic stem cells into desired cell products in bioreactors. These scaffolds mimic important aspects of the microenvironment or “niche” inside bone marrow. In particular, hematopoietic stem cell fate is thought to be effected by the architecture of trabecular bone and the presence of calcium. Here we report the effects of ceramics processing on the phase distribution and microstructure of biphasic ceramics used to culture hematopoietic stem cells. Processing of biphasic ceramics by powder mixing resulted in tetracalcium phosphate on the sintered surface. This correlated with observed surface deposits, weight gain, and the release of calcium ions in saline over 28 days. In contrast, impregnation of partially sintered hydroxyapatite with calcium nitrate resulted in calcium carbonate on the sintered surface. Impregnation correlated with the release of calcium ions into the saline, surface pitting, and weight loss.

Silver (Ag)-copper (Cu) bimetallic nanoparticles (NPs) were synthesized by the reduction of silver nitrate and copper (II) acetate monohydrate using ethylene glycol in a microwave (MW) heating system with controlled reaction times ranging from 5 min to 30 min. The molar ratio Ag/Cu was varied from 1:1 to 1:3. The effect of reaction conditions on the bimetallic NPs structures and compositions were characterized by x-ray photoelectron spectroscopy, x-ray diffraction and transmission electron microscopy. The average particle size was approximately 150 nm. The surface plasmon resonance (SPR) of Ag-Cu bimetallic NPs was investigated by monitoring the SPR band peak behavior via UV/Vis spectrophotometry. The resonance peak positions and peak widths varied due to the different structures of the bimetallic NPs created under the synthesis conditions. In the MW heating method, the reduction of Cu was increased and Cu was inhomogeneously deposited over the Ag cores. As the composition of Cu becoming higher in the Ag-Cu bimetallic NPs, the absorption between 400 nm to 600 nm was greatly enhanced.

The accumulation of bacteria in surface-attached biofilms can be detrimental to human health, dental hygiene, and many industrial processes. Natural biofilms are soft and often transparent, and they have heterogeneous biological composition and structure over micro- and macroscales. As a result, it is challenging to quantify the spatial distribution and overall intensity of biofilms. In this work, a new method was developed to enhance the visibility and quantification of bacterial biofilms. First, broad-spectrum biomolecular staining was used to enhance the visibility of the cells, nucleic acids, and proteins that make up biofilms. Then, an image analysis algorithm was developed to objectively and quantitatively measure biofilm accumulation from digital photographs and results were compared to independent measurements of cell density. This new method was used to quantify the growth intensity of Pseudomonas putida biofilms as they grew over time. This method is simple and fast, and can quantify biofilm growth over a large area with approximately the same precision as the more laborious cell counting method. Stained and processed images facilitate assessment of spatial heterogeneity of a biofilm across a surface. This new approach to biofilm analysis could be applied in studies of natural, industrial, and environmental biofilms. Graphical abstract A novel photographic method was developed to quantify bacterial biofilms. Broad spectrum biomolecular staining enhanced the visibility of the biofilms. Image analysis objectively and quantitatively measured biofilm accumulation from digital photographs. When compared to independent measurements of cell density the new method accurately quantified growth of Pseudomonas putida biofilms as they grew over time. The graph shows a comparison of biofilm quantification from cell density and image analysis. Error bars show standard deviation from three independent samples. Inset photographs show effect of staining Electronic supplementary material The online version of this article (doi:10.1007/s00216-015-9195-z) contains supplementary material, which is available to authorized users.

Soluble polymers are frequently used in freeze casting of ceramics to improve the structural integrity of the unfired ceramics. This study examined the effect of the molecular weight of polyethylene glycol (PEG) on the sintered microstructure of freeze-cast porous alumina ceramics. Increasing the molecular weight was shown to reduce the measured pore size from 10 μm to 5.5 μm, with the observed trend being qualitatively consistent with the effects of molecular weight on the diffusivity of PEG and constitutional supercooling.

Foamed hydroxyapatite offers a three-dimensional scaffold for the development of bone constructs, mimicking perfectly the in vivo bone structure. In vivo, calcium release at the surface is assumed to provide a locally increased gradient supporting the maintenance of the hematopoietic stem cells niche. We fabricated hydroxyapatite scaffolds with high surface calcium concentration by infiltration, and used human umbilical vein endothelial cells (HUVECs) as a model to study the effects on hematopoietic lineage direction. HUVECs are umbilical vein-derived and thus possess progenitor characteristics, with a prospective potential to give rise to hematopoietic lineages. HUVECs were cultured for long term on three-dimensional porous hydroxyapatite scaffolds, which were either infiltrated biphasic foams or untreated. Controls were cultured in two-dimensional dishes. The release of calcium into culture medium was determined, and cells were analyzed for typical hematopoietic and endothelial gene expressions, surface markers by flow cytometry, and hematopoietic potential using colony-forming unit assays. Our results indicate that the biphasic foams promoted a hematopoietic lineage direction of HUVECs, suggesting an improved in vivo-like scaffold for hematopoietic bone tissue engineering.

Hydroxyapatite pellets, partially densified in a low-temperature heat treatment, were infiltrated with calcium nitrate solution followed by in-situ precipitation of Ca(OH)2 and CaCO3. The infiltrated bodies were then densified to high relative density and the calcium carbonate transformed to calcium oxide during sintering and resulted in biphasic hydroxyapatite-CaO ceramics. This work investigated the influence of the infiltration on surface morphology, weight change, and microstructural-level degradation caused by exposure to saline at pH = 7.4 and a temperature of 20 °C. The CaO rendered the materials more susceptible to degradation, and released calcium into the saline faster than single phase, calcium deficient hydroxyapatite (HA) that were used as a control. In consequence, these ceramics could be used to release calcium into the culture microenvironments of bone tissue or bone marrow cells next to a scaffold surface.

An emulsion casting method was chosen for the processing of highly porous hydroxyapatite (HAp) foams to be used for the in vitro culturing of primary human liver cells. The volume fraction of heptane added to the aqueous dispersion of HAp particles could be varied to achieve a wide range of porosities (10–90 vol.-%) and pore morphologies. The emulsion derived open foam has a distinctive morphology, including a continuous large pore phase and solid struts containing smaller isolated pores. The effect of the heptane content of the slip on this sintered structure was quantified using linear intercept measurement parameters. Additionally, macropores necessary for perfusion were created using polymer tubes placed in the casting mould. When the tube spacing approached the pore size in the foam, the pore morphology was strongly affected.

This study examined the effect of polyvinyl alcohol (PVA) on the microstructure and permeability of freeze-cast porous alumina. The PVA addition was shown to have a significant effect on the pore size, with the trends in microstructure morphology and scale being qualitatively consistent with the effects of PVA addition on constitutional supercooling. The measured Darcian permeabilities were between 10−10 m2 and 10−12 m2. The permeability decreased as the PVA content increased and a significant fraction of the flow could be attributed to inertial effects.

Suspensions of ZnO nanoparticles in water were prepared with the two-step powder dispersion process using several methods of ultrasonication. The dispersion of ZnO was found to proceed by a fragmentation process, with minimum achievable particle size in the range 50 to 300 nm. This is consistent with other oxide nanopowder systems, in which most primary particulates still remain in hardened aggregates that cannot be further reduced. A submersible accelerometer probe was developed and used to measure the relative ultrasonic energy field in the liquid for the various ultrasonication methods. Oscillation at the expected frequencies was identified in each case, with strong variability at different locations in the liquid volume.

Aqueous zinc oxide (ZnO) suspensions were prepared using a two-step preparation method in which an aggregated nanocrystalline ZnO powder was dispersed in water using a polyelectrolyte. The fluid showed anomalously high thermal conductivity when compared with the Maxwell and Hamilton-Crosser predictions. However, analysis of the particle size distribution showed that the fluid contained aggregated 20 nm crystallites of ZnO with a high volume fraction of particles larger than 100 nm. Sedimentation experiments revealed that particles settled out of the stationary fluid over times ranging from 0.1 hours to well over 10,000 hours. The size of the particles remaining in suspension agreed well with predictions made using Stoke's law, suggesting flocculation was not occurring in the fluids. Finally, a new concept of nanofluid stability is introduced based on the height of the fluid, sedimentation, Brownian motion and the kinetic energy of the particles.

Freeze casting has been used to process a range of ceramics with oriented pore structures, and soluble polymers are often used to improve the strength of the material before sintering. This study examined the effect of polyethylene glycol (PEG) on the three distinct microstructural scales, which include the colony size, the pore size, and the secondary dendrite spacing. The results showed that the trends in pore size and secondary dendrite spacing were consistent with the effect of constitutional supercooling on the growth of ice crystals. In contrast, the effect of PEG on colony size appeared to be more pronounced and may reflect preferential adsorption on the prism faces of the growing ice crystals. For both alumina and PEG content, the observed effects were very much dependent on the temperature of the chill surface used in casting.

Liver cell culture within three-dimensional structures provides an improved culture system for various applications in basic research, pharmacological screening, and implantable or extracorporeal liver support. Biodegradable calcium-based scaffolds in such systems could enhance liver cell functionality by providing endothelial and hepatic cell support through locally elevated calcium levels, increased surface area for cell attachment, and allowing three-dimensional tissue restructuring. Open-porous hydroxyapatite scaffolds were fabricated and seeded with primary adult human liver cells, which were embedded within or without gels of extracellular matrix protein collagen-1 or hyaluronan. Metabolic functions were assessed after 5, 15, and 28 days. Longer-term cultures exhibited highest cell numbers and liver specific gene expression when cultured on hydroxyapatite scaffolds in collagen-1. Endothelial gene expression was induced in cells cultured on scaffolds without extracellular matrix proteins. Hydroxyapatite induced gene expression for cytokeratin-19 when cells were cultured in collagen-1 gel while culture in hyaluronan increased cytokeratin-19 gene expression independent of the use of scaffold in long-term culture. The implementation of hydroxyapatite composites with extracellular matrices affected liver cell cultures and cell differentiation depending on the type of matrix protein and the presence of a scaffold. The hydroxyapatite scaffolds enable scale-up of hepatic three-dimensional culture models for regenerative medicine applications.

Recent studies have compared particle-size analysis methods for soils containing fine clay particles. The results showed significant differences between the techniques. This study consisted of a series of hydrometer experiments designed to give greater understanding of the behavior of kaolinite clay during the ASTM 422-63 hydrometer test. The results were consistent with the aggregation of fine clay particles, possibly due to the known hydrolysis behavior of the sodium polyphosphate dispersants used in the experiment. To avoid a serious underestimation of the fraction of submicron clay particles in soils, dispersants that do not suffer from time-dependent hydrolysis should be evaluated for the hydrometer test.

Recently, the effect of solid inclusions on the sintering of ceramic powders has been explained in terms of a back-stress that opposes densification. Several analyses have been proposed to describe this problem. However, little quantitative information exists concerning the effect of reinforcement on microstructural evolution. This study compares the microstructural development of zirconia and mullite matrices in the presence of alumina platelets. The effect of platelet loading on density is similar for both composites. Quantitative stereological examinations reveal that the average grain size and pore size are finer for the zirconia-matrix composite. The platelet loading does not have any noticeable effect on the average grain size of the matrix in either composite. However, the average pore size increases as the volume fraction of platelets increases for both materials. Contiguity measurements have detected some aggregation of platelets in the zirconia-matrix composite.

Fine-grained materials containing both α L '-Ca 2 SiO 4 and β-Ca 2 SiO 4 were fabricated as an analogue to tetragonal zirconia polycrystals (TZP) with the use of barium to stabilize the high-temperature polymorphs of Ca 2 SiO 4 . The microstructure of dense α L '-Ca 2 SiO 4 exhibited none of the twinning or residual strain previously observed in fine-grained β-Ca 2 SiO 4 and there was no evidence of barium-rich grain boundary phases. Materials fired in the α region exhibited large grain sizes. Stress-induced α L ' → β transformation was observed on ground surfaces but not on fracture surfaces

A process has been developed to produce high surface area Ca2SiO4 and Sr2SiO4 powders using colloidal silica for the silicon precursor. This method was relatively straightforward and avoided the use of precipitation techniques and unstable alkoxides. Calcium carbonate and strontium carbonate were identified as intermediate compounds, and the silicates appeared to form by a low-temperature solid-state reaction. The effect of resin content and calcination conditions on the phase distribution and physical properties of the powders was examined. Finally, the sodium content of the colloidal silica was found to have a significant effect on the phase stability of β-Ca2SiO4 after calcination at 1400°C.

The crystallography, microstructures, and phase transformation mechanisms in dicalcium silicate (Ca2SiO4) were studied by TEM. Three types of superlattice structures were observed in the α′L and β phases. Almost all β grains were twinned and strained. Symmetry-related domain structures inherited from previous high-temperature transformations were observed in β grains. Both the α→α′H and α′L→β transformations were considered to be ferroelastic, and spontaneous strains were calculated. In terms of the crystal structures, the major driving force for the β→γ transformation is proposed to be strains and cation charge repulsions in the β structure. This mechanism can be displacive, but it needs to overcome a comparatively high energy barrier.

Fine-grained β-Ca2SiO4 containing small amounts of sodium was fabricated as an analogue to tetragonal zirconia polycrystals (TZP) in order to study the stress-induced β→γ transformation. This avoided the problems associated with the fabrication and evaluation of composites containing β-Ca2SiO4. The microstructure of dense β-Ca2SiO4 exhibited severe intergranular strains and twin-terminating microcracks as seen by TEM. The β-phase twin widths were quantitatively correlated with grain sizes giving an average ratio of 0.04. Stress-induced transformation was observed on ground surfaces but not on fracture surfaces. The stress–strain behavior and the mechanical properties were consistent with stress-induced microcracking and microcrack coalescence. The elastic modulus of fully dense β phase was estimated to be 123 GPa.

This study investigated the microstructural characteristics of directionally solidified freeze-dried silica sols. Porous structures were formed by depositing silica sol on silicon (100) single crystals. The deposited sols were unidirectionaly solidified by placing the silicon substrate on a copper block immersed in liquid nitrogen and then subsequently freeze-dried. Freeze drying removal of ice crystals created three-dimensional pore channels ranging from 3 to10 micrometers in diameter aggregated in grain like colonies 50–100 micrometers in diameter. Pore size, spacing, colony size and microstructure were determined using optical microscopy (OM) and scanning electron microscopy (SEM) while the structure of the amorphous SiO2 was characterized by X-ray diffraction (XRD). The microstructure results are compared and contrasted with silica aerogel obtained through conventional processing using supercritical CO2.

Single phase, pure monocalcium aluminate (CaAl2O4) powders are chemically synthesized at temperatures as low as 900°C. The powders have a specific surface area of approximately 10 m2/g. The hydration kinetics of CaAl2O4 and the morphology of the hydrates are analyzed using electron microscopy techniques