Continuous microalgae cultivation in a photobioreactor.

New biomass sources for alternative fuels has become a subject of increasing importance as the nation strives to resolve the economic and strategic impacts of limited fossil fuel resources on our national security, environment, and global climate. Algae are among the most promising non-food-crop-based biomass feedstocks. However, there are currently no commercially viable microalgae-based production systems for biofuel production that have been developed, as limitations include less-than optimal oil content, growth rates, and cultivation techniques. While batch studies are critical for determining basic growth phases and characteristics of the algal species, steady-state studies are necessary to better understand and measure the specific growth parameters. This study evaluated the effects of dilution rate on microalgal biomass productivity, lipid content, and fatty acid profile under steady-state conditions with continuous illumination and carbon dioxide supplemention for two types of algae. Continuous cultures were conducted for more that 3 months. Our results show that the productivity of Chlorella minutissima varied from 39 to 137 mg/L/day (dry mass) when the dilution rate varied from 0.08 to 0.64 day(-1). The biomass productivity of C. minutissima reached a maximum value (137 mg/L/day) at a dilution rate of 0.33 day(-1), while the productivity of Dunaliella tertiolecta varied from 46 to 91 mg/L/day at a dilution rate of 0.17 to 0.74 day(-1). The biomass productivity of D. tertiolecta reached a maximum value of 91 mg/L/day at a dilution rate of 0.42 day(-1). Moreover, the lipid content had no significant change with various dilution rates.

Culture of microalgae Chlorella minutissima for biodiesel feedstock production.

Microalgae are among the most promising of non-food based biomass fuel feedstock alternatives. Algal biofuels production is challenged by limited oil content, growth rate, and economical cultivation. To develop the optimum cultivation conditions for increasing biofuels feedstock production, the effect of light source, light intensity, photoperiod, and nitrogen starvation on the growth rate, cell density, and lipid content of Chlorella minutissima were studied. The fatty acid content and composition of Chlorella minutissima were also investigated under the above conditions. Fluorescent lights were more effective than red or white light-emitting diodes for algal growth. Increasing light intensity resulted in more rapid algal growth, while increasing the period of light also significantly increased biomass productivity. Our results showed that the lipid and triacylglycerol content were increased under N starvation conditions. Thus, a two-phase strategy with an initial nutrient-sufficient reactor followed by a nutrient deprivation strategy could likely balance the desire for rapid and high biomass generation (124 mg/L) with a high oil content (50%) of Chlorella minutissima to maximize the total amount of oil produced for biodiesel production. Moreover, methyl palmitate (C16:0), methyl oleate (C18:1), methyl linoleate (C18:2), and methyl linolenate (C18:3) are the major components of Chlorella minutissima derived FAME, and choice of light source, intensity, and N starvation impacted the FAME composition of Chlorella minutissima. The optimized cultivation conditions resulted in higher growth rate, cell density, and oil content, making Chlorella minutissima a potentially suitable organism for biodiesel feedstock production.

Patterned immobilization of antibodies in mechanically induced cracks.

A new approach of chemically immobilizing antibody within a pattern based on thin-film cracking is presented. An adjustable pattern width is achieved with resolutions varied from nano- to microscale by using loading stress on thin-film coated elastomer substrate in both one and two dimensions. By introduction of solution or chemical vapor deposition approaches, antibodies were covalently immobilized in the channels. To demonstrate the bioactivity, specificity, and response rate of antibody patterned structure, scanning electron microscopy was used to enumerating bacteria. The chemically coupled antibody is found to retain its specificity when incubated with different bacteria solutions. Trichloro(1H,1H,2H,2H-perfluoroctyl)silane coating on nonsensing regions exhibits a distinguished bacteria-resistant function that is beneficial for providing a low intrinsic background signal in detection. This technique shows a great potential for applications in the fields of sensing and tissue engineering.

Functionalization of AlN surface and effect of spacer density on Escherichia coli pili-antibody molecular recognition.

The immobilization of antibodies to sensor surfaces is critical in biochemical sensor development. In this study, Jeffamine spacers were employed to tether Escherichia coli K99 pilus antibody to AlN/sapphire surfaces which may allow the antibody to freely reorient and potentially improving the antigen capture efficiency. Spacer density was one of the key parameters to be optimized in studying its effect on the immobilization of antibody. The spacer density was controlled by functionalizing AlN/sapphire surfaces with a mixed (3-glycidyloxypropyl)trimethoxysilane (GPTMS) and trichloro(1H,1H,2H,2H-perfluoroctyl)silane (FAS) self-assembled monolayer (SAM) through a step-wise method. Contact angle measurement and X-ray photoelectron spectroscopy (XPS) were used to characterize the surface coverage of GPTMS and surface chemical composition. Compared to spacer fully covered samples, the capture efficiency was improved by approximately 28% with optimal Jeffamine ED 600 spacer density, which depends on the spacer properties such as the number of monomer units and its size.

Effect of surface modification of siliconeon Staphylococcus epidermidis adhesion and colonization.

Cerebrospinal fluid (CSF) shunts for the treatment of hydrocephalus are generally made of silicone rubber. The growth of bacterial colonies on the silicone surface leads to frequent CSF shunt complications. A systematic study of the effect of the surface modification of silicone on Staphylococcus epidermidis adhesion and colonization was performed for different incubation times by means of colony counting and scanning electron microscopy (SEM). Silicone was modified with different biopolymers and silanes, including heparin, hyaluronan, octadecyltrichlorosilane (OTS), and fluoroalkylsilane (FAS) to provide a stable and biocompatible surface with different surface functional groups and degrees of hydrophobicity. The modified silicone surfaces were studied by using contact angle measurements, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). After 4 and 8 h of incubation, the FAS- and OTS-coated silicone and the hyaluronan coated OTS/silicone surfaces showed significantly reduced bacterial adhesion and colonization compared to blank silicone by both quantification methods. However, the heparin coated OTS/silicone showed significantly increased bacterial adhesion. These results indicate that the nature of the surface functional group and surface roughness determine the extent of bacterial adhesion and colonization. However, the degree of hydrophobicity of the surface did not appear to play a determining role in bacterial adhesion and colonization.

Effect of cast molded rifampicin/silicone on Staphylococcus epidermidis biofilm formation.

Infection is one of the most common catheter-related complications, especially in shunt systems used to treat hydrocephalus. Staphylococcus epidermidis is directly related to biomaterial infections owing to its ability to form a biofilm on implanted materials. In this study, scanning electron microscopy (SEM) and atomic force microscopy (AFM) were employed to investigate the effect of the antibiotic rifampicin on the colonization and growth of S. epidermidis 35984 on the surface of silicone. A cast molding method was used to load rifampicin into the silicone precursor before it was cured. Bacteria with a diameter of 800-1000 nm and height of 200-500 nm were found to be embedded in the biofilm. Compact multilayer biofilm structures were found on silicone surfaces upon incubation for 4 and 24 h. On the other hand, sparser biofilm structures were observed on rifampicin-loaded surfaces after incubation for the same duration. Deformation of bacteria was observed by AFM. Moreover, different bacterial colony structures on the surfaces of silicone and rifampicin-loaded silicone were observed by AFM and SEM.

Immobilization of polysaccharides on a fluorinated silicon surface.

A self-assembled monolayer (SAM) of fluoroalkyl silane (FAS) was deposited on a silicon surface by chemical vapor deposition (CVD) at room temperature under 1.01x10(5)Pa nitrogen. Using this new approach, the quality and reproducibility of the SAM are better than those prepared either in solution or by vapor phase deposition, and the deposition process is simpler. In this modified CVD process, the silane monomers, instead of the oligomeric species, are the primary reactants. Full coverage of the silicon surface by FAS molecules was achieved within 5 min. Heparin and hyaluronan, two naturally occurring biocompatible polysaccharides, were successfully covalently attached on the FAS SAM/Si surface by photo-immobilization. Atomic force microscopy (AFM) revealed the morphologic changes after the immobilization of heparin and hyaluronan, and X-ray photoelectron spectroscopy (XPS) confirmed the change in chemical compositions. Such combination of coatings is expected to enhance the stability and biocompatibility of the base material.

Effect of surface proteins on Staphylococcus epidermidis adhesion and colonization on silicone.

Shunt infections are one of the most serious complications in shunt implant surgery. Previous studies have suggested that cerebrospinal fluid (CSF) proteins could affect bacterial adhesion and subsequent shunt infection. A systematic study using immobilized protein on the surface of silane-modified silicone was conducted to determine how these modifications influenced Staphylococcus epidermidis adhesion and colonization. A comparison was also made with silicone having physically adsorbed protein. A colony-counting adhesion assay and scanning electron microscopy (SEM) were used to provide quantitative analysis of bacterial adhesion and semi-quantitative analysis of bacterial colonization, respectively. In order to determine the appropriate silanization process for effective protein immobilization, the effect of bovine serum albumin (BSA) immobilized on n-3-(trimethoxysilyl)propyl-ethylenediamine (AEAPS)/silicone, aminopropyltriethoxysilane (APTMS)/silicone, 3-(glycidyloxypropyl)trimethoxysilane (GPTMS)/silicone, and octadecyltrichlorosilane (OTS)/silicone on bacterial adhesion was investigated. Upon identifying that OTS is the most effective silane, different types of proteins, including: BSA, human serum albumin (HSA), gamma-globulin, and fibrinogen were immobilized on OTS/silicone by a photo-immobilization method. Immobilized protein on modified silicone surfaces was found to be stable in saline for 30 days, while physically adsorbed protein showed instability within hours as determined by contact angle measurements and X-ray photoelectron spectroscopy (XPS). For HSA/OTS/silicone, BSA/OTS/silicone, gamma-globulin/OTS/silicone, fibrinogen/OTS/silicon, and physically absorbed BSA on silicone, the contact angles were 78.5 degrees, 80.7 degrees, 78.9 degrees, 81.3 degrees, and 96.5 degrees; and the amount of nitrogen content was found to be 4.6%, 5.0%, 5.6%, 7.2%, and 3.2%, respectively. All protein immobilized on OTS/silicone surfaces significantly reduced bacterial adhesion by around 75% compared to untreated silicone, while physically adsorbed BSA on silicone reduced by only 29.4%, as determined by colony-counting adhesion assay. However, there was no significant difference on bacterial adhesion among the different types of proteins immobilized on OTS/silicone. Minimizing bacterial adhesion and colonization can be attributed to the increased concentration of -NH2 group, and stability and more hydrophilic nature of the protein/OTS/silicone surfaces.

In vitro haemocompatibility and stability of two types of heparin-immobilized silicon surfaces.

Heparin was covalently immobilized onto a silicon surface by two different methods, carbodiimide-based immobilization and photo-immobilization. In the former method, a (3-aminopropyl) trimethoxysilane (APTMS) self-assembled monolayer (SAM) or multilayer was first coated onto the silicon surface as the bridging layer, and heparin was then attached to the surface in the presence of water-soluble carbodiimide. In the latter method, an octadecyltrichlorosilane (OTS) SAM was coated on the silicon surface as the bridging layer, and heparin was modified by attaching photosensitive aryl azide groups. Upon UV illumination, the modified heparin was then covalently immobilized onto the surface. The hydrophilicity of the silicon surface changed after each coating step, and heparin aggregates on APTMS SAM and OTS SAM were observed by atomic force microscopy (AFM). In vitro haemocompatibility assays demonstrated that the deposition of APTMS SAM, APTMS multilayer and OTS SAM enhanced the silicon's haemocompatibility, which was further enhanced by the heparin immobilization. There is no evident distinction regarding the haemocompatibility between the heparin-immobilized surfaces by both methods. However, heparin on silicon with APTMS SAM and multilayer as the bridging layers is very unstable when tested in vitro with a saline solution at 37 degrees C, due to the instability of APTMS SAM and multilayer on silicon. Meanwhile, photo-immobilized heparin on silicon with OTS SAM as the bridging layer showed superb stability.

Effect of chain lengths of PEO-PPO-PEO on small unilamellar liposome morphology and stability: an AFM investigation.

The morphology and stability of small unilamellar egg yolk phosphatidylcholine (EggPC) liposomes modified with the Pluronic copolymer (poly (oxyethylene)-poly (oxypropylene)-poly (oxyethylene) (PEO-PPO-PEO)) with different compositions on mica surface have been investigated using atomic force microscopy. Morphology studies reveal significant morphological changes of liposomes upon incorporating the Pluronic copolymer. Bilayers are observed for Pluronic with small hydrophilic (PEO) chain lengths such as L81 [(PEO)2(PPO)40(PEO)2] and L121 [(PEO)4(PPO)60(PEO)4]; bilayer and vesicle coexistence is observed for P85 [(PEO)26(PPO)39.5(PEO)26] and F87 [(PEO)61.1(PPO)39.7(PEO)61.1]; and stable vesicles are observed for F88 [(PEO)103.5(PPO)39.2(PEO)103.5], F127 [(PEO)100(PPO)65(PEO)100], and F108 [(PEO)132.6(PPO)50.3(PEO)132.6]. The micromechanical properties of Pluronic-modified EggPC vesicles were studied by analyzing AFM approaching force curve. The bending modulus (k(c)) of the Pluronic-modified EggPC vesicles increased several-fold compared with that of the pure EggPC vesicles. The significant difference is due to the enhanced rigidity of the EggPC vesicles as a result of the incorporation of PPO molecules and PEO chains. Based on the analysis of onset point by AFM and diameters of vesicles by light scattering, it was concluded that the favorable model to describe the polymer-bilayer interaction is the membrane-spanning model.

In vitro stability study of organosilane self-assemble monolayers and multilayers.

The stability of self-assembled monolayers (SAMs) and multilayers formed on silicon surface by amino-terminated silanes and SAMs formed by alkyl and glycidyl terminated silanes were investigated in vitro with saline solution at 37 degrees C for up to 10 days. FTIR and XPS results indicated that amino-terminated SAMs and multilayers are very unstable if the alkyl chain is short ((CH2)3), while stable if the alkyl chain is long ((CH2)11). On the other hand, alkyl-terminated SAMs are very stable regardless of the alkyl chain length, and glycidyl terminated SAM retained approximately 77% of the organosilane molecules after 10 days. Hydrogen bonding between the organosilane monomer and silicon surface and among the organosilane monomers is believed to contribute to the instability of the SAM and multilayer formed by amino-terminated silane with a short alkyl chain ((CH2)3). Therefore, the widely used (3-aminopropyl) trimethoxysilane (APTMS) SAM and multilayer may not be suitable for implantable biomedical applications.

Tunneling holes in microparticles to facilitate the transport of lithium ions for high volumetric density batteries.

Microscale materials generally have a higher tap density than that of random nanoparticles. Therefore, microparticles have been attracting much attention for application as high volumetric density electrodes for lithium ion batteries. However, microparticles have much longer electrolyte diffusion and Li-ion migration length and less accessibility to the electrolyte than that of nanoparticles. Therefore, it will be interesting to tunnel-holes in the high volumetric density microparticles to facilitate the reversible storage of lithium ions. Here, tunnel-like holes were generated in microparticles to dramatically increase the accessibility of the active materials to facilitate the lithium ion transfer. A plausible formation mechanism to explain the generation of tunnel-like holes was proposed based on time-course experiments and intensive characterization. Impressively, the as-prepared microbeads with tunnels demonstrated dramatically improved performance compared to the solid microbeads without tunnels in lithium ion storage. The microparticles with tunnels could achieve comparable electrochemical performances to those nanoparticles reported in the literature, suggesting that microparticles, properly tuned, could be promising candidates as negative electrodes for lithium-ion batteries and worthy of further studies. We also directly measured the volumetric density of the microparticles. We would like to highlight that a superior volumetric capacity of 514 mA h cm(-3) has been achieved. We hope to promote more frequent use of the unit mA h cm(-3) in addition to the conventional unit mA h g(-1) in the battery community.

Electrocatalysis of lithium polysulfides: current collectors as electrodes in Li/S battery configuration.

Lithium Sulfur (Li/S) chemistries are amongst the most promising next-generation battery technologies due to their high theoretical energy density. However, the detrimental effects of their intermediate byproducts, polysulfides (PS), have to be resolved to realize these theoretical performance limits. Confined approaches on using porous carbons to entrap PS have yielded limited success. In this study, we deviate from the prevalent approach by introducing catalysis concept in Li/S battery configuration. Engineered current collectors were found to be catalytically active towards PS, thereby eliminating the need for carbon matrix and their processing obligatory binders, additives and solvents. We reveal substantial enhancement in electrochemical performance and corroborate our findings using a detailed experimental parametric study involving variation of several kinetic parameters such as surface area, temperature, current rate and concentration of PS. The resultant novel battery configuration delivered a discharge capacity of 700 mAh g(-1) with the two dimensional (2D) planar Ni current collectors and an enhancement in the capacity up to 900 mAh g(-1) has been realized using the engineered three dimensional (3D) current collectors. The battery capacity has been tested for stability over 100 cycles of charge-discharge.

Mechanical properties and stability measurement of cholesterol-containing liposome on mica by atomic force microscopy.

The micromechanical properties of pure and cholesterol modified egg yolk phosphatidylcholine (EggPC) vesicles prepared by sonication were studied by atomic force microscopy (AFM) on mica surface. The force curves between an AFM tip and an unruptured vesicle were obtained by contact mode. During approach, two repulsion regions with two breaks were observed. The slopes of the two repulsive force regimes for the pure EggPC vesicles are determined to be several times lower than that of EggPC/cholesterol vesicles. The elastic properties from force plot analysis based on the Hertzian model showed that Young's modulus (E) and the bending modulus (kc) of cholesterol-modified vesicles increased several-fold compared with pure EggPC vesicles. The significant difference is attributed to the enhanced rigidity of the EggPC vesicles as a result of the incorporation of cholesterol molecules. The behavior of cholesterol-modified vesicles upon adsorption is different from that in solution as revealed by mechanical properties. The results indicate that AFM can provide a direct method to measure the mechanical properties of adsorbed small liposomes and to detect the stability change of liposomes.

Hollow cocoon-like hematite mesoparticles of nanoparticle aggregates: structural evolution and superior performances in lithium ion batteries.

We report the facile, fast, and template-free preparation of hollow α-Fe2O3 with unique cocoon-like structure by a one-pot hydrothermal method without any surfactants in a short reaction time of 3 h only. In contrast, typical hydrothermal methods to prepare inorganic hollow structures require 24 h or a few days. Templates and/or surfactants are typically used. The hollow α-Fe2O3 nanococoon was thoroughly characterized by field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). Ex situ analysis of a series of samples prepared at different reaction times clearly revealed the structural evolution and possible formation mechanism. Superior electrochemical performance in terms of cyclability, specific capacity, and high rate was achieved, which could be attributed to its unique hollow cocoon-like structure. Structural stability was revealed by analyzing the samples after 120 charge-discharge cycles. The unusual structural stability of the hollow α-Fe2O3 nanococoons after 120 cycles, which is rarely observed for transition metal oxides of particle aggregates, will guarantee further research investigation. Experimental evidence further demonstrated that hollow nanococoons exceed solid nanococoons in reversible lithium-ion storage.

Effect of nutrients on growth and lipid accumulation in the green algae Dunaliella tertiolecta.

Production of biofuel from algae is dependent on the microalgal biomass production rate and lipid content. Both biomass production and lipid accumulation are limited by several factors, of which nutrients play a key role. In this research, the marine microalgae Dunaliella tertiolecta was used as a model organism and a profile of its nutritional requirements was determined. Inorganic phosphate PO4(3-) and trace elements: cobalt (Co2+), iron (Fe3+), molybdenum (Mo2+) and manganese (Mn2+) were identified as required for algae optimum growth. Inorganic nitrogen in the form of nitrate NO3- instead of ammonium (NH4+) was required for maximal biomass production. Lipids accumulated under nitrogen starvation growth condition and this was time-dependent. Results of this research can be applied to maximize production of microalgal lipids in optimally designed photobioreactors.

Nanoscale investigation on E. coli adhesion to modified silicone surfaces.

Bacterial infection is a major challenge in biomaterials development. The adhesion of microorganisms to the material surface is the first step in infectious conditions and this quickly leads to the formation of biofilms on a material surface. A unique attribute of atomic force microscopy (AFM) is that it reveals not only the morphology of cells and the surface roughness of the substrate, but it can also quantify the adhesion force between bacteria and surfaces. We have shown that fluoroalkylsilane (FAS) and octadecyltrichlorosilane (OTS)-coated silicone samples exhibit greater potential for reducing E. coli JM 109 adhesion than heparin- and hyaluronan-modified samples. The force curves obtained from AFM can be used as a primary indicator in predicting bacterial adhesion.

Performance of heterogeneous ZrO2 supported metaloxide catalysts for brown grease esterification and sulfur removal.

In order to achieve a viable biodiesel industry, new catalyst technology is needed which can process a variety of less expensive waste oils, such as yellow grease and brown grease. However, for these catalysts to be effective for biodiesel production using these feedstocks, they must be able to tolerate higher concentrations of free fatty acids (FFA), water, and sulfur. We have developed a class of zirconia supported metaloxide catalysts that achieve high FAME yields through esterification of FFAs while simultaneously performing desulfurization and de-metallization functions. In fact, methanolysis, with the zirconia supported catalysts, was more effective for desulfurization than an acid washing process. In addition, using zirconia supported catalysts to convert waste grease, high in sulfur content, resulted in a FAME product that could meet the in-use ASTM diesel fuel sulfur specification (<500 ppm). Possible mechanisms of desulfurization and de-metallization by methanolysis were proposed to explain this activity.

Influence of silicone surface roughness and hydrophobicity on adhesion and colonization of Staphylococcus epidermidis.

Bacterial adhesion and colonization are complicated processes that depend on many factors, including surface chemistry, hydrophobicity, and surface roughness. The contribution of each of these factors has not been fully elucidated because most previous studies used different polymeric surfaces to achieve differences in properties. The objective of this study was to modify hydrophobicity and roughness on one polymeric surface, eliminating the confounding contribution of surface chemistry. Mechanically assembled monolayer (MAM) preparation methods (both one- and two-dimensional) were used to impart different degrees of hydrophobicity on fluoroalkylsilane (FAS)-coated silicone. Surface roughness was varied by casting the silicone to templates prepared with different abrasives. Surface hydrophobicity was determined by contact angle measurement, whereas surface roughness was determined by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Bacterial adhesion and colonization were analyzed using a direct colony-counting method and SEM images. Hydrophobicity increased as a function of stretched length or width (Deltax or Deltay); it reached a maximum at Deltax = 60% with one-dimensional MAM and decreased as Deltax further increased to 80 and 100%. The same trend was observed for the two-dimensional MAM. After 12-h incubation, all the FAS/silicone surfaces had significantly reduced adherence of Staphylococcus epidermidis by 42-89%, compared to untreated silicone, and the degree of which is inversely related to surface hydrophobicity. On the other hand, surface roughness had a significant effect on bacterial adhesion and colonization only when the root-mean-square roughness was higher than 200 nm.

The effect of self-assembled layers on the release behavior of rifampicin-loaded silicone.

Providing a long period of sustained antibiotic release is one of the important challenges in the development of clinical shunts for long-term implantation. A cast-molding approach was used to load rifampicin into the silicone precursor before curing. Sustained in vitro release from rifampicin-loaded silicone for upwards of 110 days at a level of approximately 2-4 microg/cm2 per day was achieved. Quantitative comparisons of Staphylococcus epidermidis adhesion on untreated and rifampicin-loaded silicone surfaces were carried out to demonstrate the effect of rifampicin to discourage the bacterial adhesion. It was shown that the fresh 8.3% rifampicin-loaded silicone decreased bacterial adherence by 99.8%. Bacterial adherence on rifampicin-loaded silicone surfaces after 90 days release (eluted silicone) was decreased by 94.8%. A new approach was used to tune the initial burst effect and prolong long lasting release by introducing self-assembled perfluorodecyltrichlorosilane (FAS) and octadecyltrichlorosilane (OTS) layers. FAS layered structures can tune the burst effect and prolong the subsequent continuous release to achieve the long-term delivery. Significant decreases in initial burst effect (70.3% for multi-FAS layers and 39.7% for FAS monolayer) and enhanced long-term release (approx. 10 microg/cm2 per day for FAS monolayer for 110 days and approx. 15 microg/cm2 per day for multi-FAS layers for 60 days) were observed.