Impacts of hydrous manganese oxide on the retention and lability of dissolved organic matter.

Minerals constitute a primary ecosystem control on organic C decomposition in soils, and therefore on greenhouse gas fluxes to the atmosphere. Secondary minerals, in particular, Fe and Al (oxyhydr)oxides-collectively referred to as "oxides" hereafter-are prominent protectors of organic C against microbial decomposition through sorption and complexation reactions. However, the impacts of Mn oxides on organic C retention and lability in soils are poorly understood. Here we show that hydrous Mn oxide (HMO), a poorly crystalline δ-MnO2, has a greater maximum sorption capacity for dissolved organic matter (DOM) derived from a deciduous forest composite Oi, Oe, and Oa horizon leachate ("O horizon leachate" hereafter) than does goethite under acidic (pH 5) conditions. Nonetheless, goethite has a stronger sorption capacity for DOM at low initial C:(Mn or Fe) molar ratios compared to HMO, probably due to ligand exchange with carboxylate groups as revealed by attenuated total reflectance-Fourier transform infrared spectroscopy. X-ray photoelectron spectroscopy and scanning transmission X-ray microscopy-near-edge X-ray absorption fine structure spectroscopy coupled with Mn mass balance calculations reveal that DOM sorption onto HMO induces partial Mn reductive dissolution and Mn reduction of the residual HMO. X-ray photoelectron spectroscopy further shows increasing Mn(II) concentrations are correlated with increasing oxidized C (C=O) content (r = 0.78, P < 0.0006) on the DOM-HMO complexes. We posit that DOM is the more probable reductant of HMO, as Mn(II)-induced HMO dissolution does not alter the Mn speciation of the residual HMO at pH 5. At a lower C loading (2 × 102 µg C m-2), DOM desorption-assessed by 0.1 M NaH2PO4 extraction-is lower for HMO than for goethite, whereas the extent of desorption is the same at a higher C loading (4 × 102 µg C m-2). No significant differences are observed in the impacts of HMO and goethite on the biodegradability of the DOM remaining in solution after DOM sorption reaches steady state. Overall, HMO shows a relatively strong capacity to sorb DOM and resist phosphate-induced desorption, but DOM-HMO complexes may be more vulnerable to reductive dissolution than DOM-goethite complexes.

Gas-cluster ion sputtering: Effect on organic layer morphology.

Analysis of the surface of thin Irganox 1010 films before and after sputtering with an argon gas-cluster ion beam was performed with AFM and XPS to determine the effect that Zalar rotation has on the chemistry and morphology of the surface. The analysis is based on the change in roughness of the surface by comparing the same location on the surface before and after sputtering. The ion beam used was an Arn+ of size n = 1000 and energy 4 keV. The XPS analysis agreed with previous results in which the ion beam did not cause measurable accumulation of damaged material. Based on the AFM results, the Irganox 1010 surface became rougher as a result of ion sputtering, and the degree of roughening was quantified, as was the sputter rate. Furthermore, Zalar rotation during ion sputtering did not have a significant effect on surface roughening, surprisingly.

Electrospun polycaprolactone scaffolds with tailored porosity using two approaches for enhanced cellular infiltration.

The impact of mat porosity of polycaprolactone (PCL) electrospun fibers on the infiltration of neuron-like PC12 cells was evaluated using two different approaches. In the first method, bi-component aligned fiber mats were fabricated via the co-electrospinning of PCL with polyethylene oxide (PEO). Variation of the PEO flow rate, followed by selective removal of PEO from the PCL/PEO mesh, allowed for control of the porosity of the resulting scaffold. In the second method, aligned fiber mats were fabricated from various concentrations of PCL solutions to generate fibers with diameters between 0.13 ± 0.06 and 9.10 ± 4.1 µm. Of the approaches examined, the variation of PCL fiber diameter was found to be the better method for increasing the infiltration of PC12 cells, with the optimal infiltration into the ca. 1.5-mm-thick meshes observed for the mats with the largest fiber diameters, and hence largest pore sizes.

DC magnetron sputtered polyaniline-HCl thin films for chemical sensing applications.

Thin films of conducting polymers exhibit unique chemical and physical properties that render them integral parts in microelectronics, energy storage devices, and chemical sensors. Overall, polyaniline (PAni) doped in acidic media has shown metal-like electronic conductivity, though exact physical and chemical properties are dependent on the polymer structure and dopant type. Difficulties arising from poor processability render production of doped PAni thin films particularly challenging. In this contribution, DC magnetron sputtering, a physical vapor deposition technique, is applied to the preparation of conductive thin films of PAni doped with hydrochloric acid (PAni-HCl) in an effort to circumvent issues associated with conventional thin film preparation methods. Samples manufactured by the sputtering method are analyzed along with samples prepared by conventional drop-casting. Physical characterization (atomic force microscopy, AFM) confirm the presence of PAni-HCl and show that films exhibit a reduced roughness and potentially pinhole-free coverage of the substrate. Spectroscopic evidence (UV-vis, FT-IR, and X-ray photoelectron spectroscopy (XPS)) suggests that structural changes and loss of conductivity, not uncommon during PAni processing, does occur during the preparation process. Finally, the applicability of sputtered films to gas-phase sensing of NH(3) was investigated with surface plasmon resonance (SPR) spectroscopy and compared to previous contributions. In summary, sputtered PAni-HCl films exhibit quantifiable, reversible behavior upon exposure to NH(3) with a calculated LOD (by method) approaching 0.4 ppm NH(3) in dry air.

Quantification and molecular characterization of organo-mineral associations as influenced by redox oscillations.

Organo-mineral association is one of the most important stabilization mechanisms of soil organic matter. However, few studies have been conducted to assess the retention, transformation, and transportation of colloids (1-1000 nm) and associated organic carbon (OC) in soil. Given the particularly significant role that wetland soils play in carbon storage and cycling, we quantified the dynamics of organo-mineral association within colloidal size range by conducting three consecutive 35-day redox (reduction-oxidation) oscillation experiments using a wetland soil. Molecular compositions of natural nanoparticle (NNP, 2.3-100 nm), fine colloid (100-450 nm), and particulate (450-1000 nm) fractions were measured using isotope ratio mass spectrometry (IRMS) and x-ray photoelectron spectroscopy (XPS). Results showed that NNP and fine colloids constituted up to 8.94 ± 0.50% and 22.19 ± 7.52% of bulk C concentration (2.3-1000 nm), respectively; indicating substantial contributions of these two fractions to the operationally defined "dissolved" (<450 nm) fraction. There was significant enrichment in heavier δ13C isotopes (p < 0.001) with size: NNP (-29.64 ± 0.32‰) < fine colloid (-28.81 ± 0.31‰) < particulate (-28.34 ± 0.25‰) fractions. NNP had the highest percentages of carbonyl/carboxyl C (C=O); while fine colloid and particulate fractions contained more reduced aromatic or aliphatic C (C-C, C=C, C-H). OC became more enriched (‰) in microbial-derived C (higher δ13C) with increasing particle size as well as with repeated redox oscillations. Our findings clearly demonstrate limitations of using the operationally defined "dissolved" fraction (<450 nm) to assess C cycling in ecosystems such as wetlands. Increase in colloid and OC concentrations and presence of more microbial-derived C in larger size fractions additionally imply that redox oscillations promote the formation of molecularly diverse sub-colloid sized organo-mineral associations. Being a composite unit of soil microaggregates, organic-mineral associations can thus influence the overall stability of OC in wetland soils that undergo frequent redox oscillations.

Neurite outgrowth on well-characterized surfaces: preparation and characterization of chemically and spatially controlled fibronectin and RGD substrates with good bioactivity.

Study of axonal growth and ligand-receptor interactions requires specificity and careful characterization of the biomaterial substrates to which the neurons bind. It would be impossible to predict the effects of important variables such as composition, surface density, spatial distribution, and conformation of the ligands on axonal growth of a neuron without highly specific surface characterization. Here, we compare two methods of surface modification (hereafter referred to as "Heterobifunctional Crosslinker" and "Pluronics" methods) used for immobilization of fibronectin (FN) and FN-derived, RGD-containing peptides to the substrates. We also characterized their performance in neurite outgrowth experiments. Various surface analytical techniques such as contact angle measurement, XPS, and time-of-flight secondary ion mass spectrometry (TOF-SIMS) were used for the analysis of the substrates at each step of the two different chemistries involved. FN-patterned surfaces were created by micro-contact printing methods and confirmed by imaging TOF-SIMS, and AFM techniques. After immobilization of FN and/or FN-derived RGD-containing peptide, including the formation of micron-scale patterns of FN, the modified surfaces were plated with neurons from postnatal rat dorsal root ganglia (DRG) and incubated in serum-free medium. Both the peptide- and/or protein-modified substrates supported significantly greater neurite outgrowth than controls, and outgrowth on both substrate chemistries was inhibited by the addition of soluble RGD peptide. Patterned FN surfaces were successful in spatially controlling the neuron attachment and outgrowth.

ToF-SIMS imaging of molecular-level alteration mechanisms in Le Bonheur de vivre by Henri Matisse.

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) has recently been shown to be a valuable tool for cultural heritage studies, especially when used in conjunction with established analytical techniques in the field. The ability of ToF-SIMS to simultaneously image inorganic and organic species within a paint cross section at micrometer-level spatial resolution makes it a uniquely qualified analytical technique to aid in further understanding the processes of pigment and binder alteration, as well as pigment-binder interactions. In this study, ToF-SIMS was used to detect and image both molecular and elemental species related to CdS pigment and binding medium alteration on the painting Le Bonheur de vivre (1905-1906, The Barnes Foundation) by Henri Matisse. Three categories of inorganic and organic components were found throughout Le Bonheur de vivre and co-localized in cross-sectional samples using high spatial resolution ToF-SIMS analysis: (1) species relating to the preparation and photo-induced oxidation of CdS yellow pigments (2) varying amounts of long-chain fatty acids present in both the paint and primary ground layer and (3) specific amino acid fragments, possibly relating to the painting's complex restoration history. ToF-SIMS's ability to discern both organic and inorganic species via cross-sectional imaging was used to compare samples collected from Le Bonheur de vivre to artificially aged reference paints in an effort to gather mechanistic information relating to alteration processes that have been previously explored using µXANES, SR-µXRF, SEM-EDX, and SR-FTIR. The relatively high sensitivity offered by ToF-SIMS imaging coupled to the high spatial resolution allowed for the positive identification of degradation products (such as cadmium oxalate) in specific paint regions that have before been unobserved. The imaging of organic materials has provided an insight into the extent of destruction of the original binding medium, as well as identifying unexpected organic materials in specific paint layers.

Recurrence risk after organ transplantation in patients with a history of Hodgkin disease or non-Hodgkin lymphoma.

This study defines the incidence and recurrence risk of Hodgkin disease (HD) and non-Hodgkin lymphoma (NHL) after organ transplant. Patients from the United States with a history of HD or NHL before organ transplantation reported to the Israel Penn International Transplant Tumor Registry from 1968 to 2001 were analyzed. A total of 91 patients underwent organ transplantation with a lymphoma history: HD (38 patients) and NHL (53 patients). Median disease-free interval pretransplant was 99 (range 0-459.1) months, and median follow-up posttransplant was 25.7 (0.4-131.1) months. Ten patients were excluded from further analysis because of lack of follow-up information (n=9) or they never achieved remission (n=1). Recurrence incidence was 8 of 81 patients (10%) (HD=3/34 [9%] vs. NHL=5/47 [11%]). Gender, race, allograft type and source, age at lymphoma diagnosis, and immunosuppression did not influence recurrence. Patients with less than a 2-year period between diagnosis and transplant seem to be at increased risk of relapse. Median disease-free interval before transplant was longer for patients without recurrence (115 vs. 30.2 months, P=0.24), but was not statistically significant. Median time to recurrence posttransplant was 18.7 (range 1.9-82.2) months (HD=3.7 vs. NHL 23.6 months, P=0.10). Survival after recurrence was poor (HD [1/3] and NHL [1/5], median survival 6.8 [range 0-22.1] months). There is no difference in recurrence rates for HD and NHL. The outcome for recurrent lymphoma is poor. The low risk of recurrence (10%) indicates that preexisting HD and NHL need not be an absolute contraindication to transplantation.

Donors with central nervous system malignancies: are they truly safe?

BACKGROUND: In an era of organ shortage, the use of expanded or marginal donors has been attempted to increase transplantation rates and diminish waiting list mortality. One strategy is the use of organs from patients with a history of or active central nervous system (CNS) tumor. METHODS: Sixty-two recipients were identified as the recipients of organs from donors with a history of or active CNS malignancy. Patient demographics, donor tumor management, incidence of tumor transmission, and patient survival were examined. RESULTS: Of the organs recovered and transplanted from donors with astrocytoma, 14 were associated with at least one risk factor including high-grade tumor (n=4), prior surgery (n=5), radiation therapy (n=4), and systemic chemotherapy (n=4). One tumor transmission was identified at 20 months posttransplant with the patient expiring from metastatic disease. Twenty-six organs were transplanted from glioblastoma patients with 15 demonstrating risk factors including high-grade tumor (n=9) and prior surgery (n=10). Eight transmissions were identified with a range of 2 to 15 months posttransplant, with seven patients dying as the result of metastatic disease. Seven organs were used from donors with a medulloblastoma. Three transmissions were identified at a range of 5 to 7 months, all associated with ventriculoperitoneal shunts. Two medulloblastoma recipients died as the result of metastatic disease, whereas the third is alive with diffuse disease. The rate of donor tumor transmission, in the absence of risk factors, was 7%, whereas in the presence of one or more risk factor this rate dramatically rose to 53% (P<0.01). CONCLUSIONS: Organs from donors with CNS tumors can be used with a low risk of donor tumor transmission in the absence of the following risk factors: high-grade tumors, ventriculoperitoneal or ventriculoatrial shunts, prior craniotomy, and systemic chemotherapy.

MALToma: a Helicobacter pylori-associated malignancy in transplant patients: a report from the Israel Penn International Transplant Tumor Registry with a review of published literature.

BACKGROUND: Mucosa-associated lymphoid tissue lymphoma (MALToma) is a Helicobacter pylori-related tumor of B-cell origin, the malignant potential for which remains to be defined in immunosuppressed patients. METHODS: Review of the Israel Penn International Transplant Tumor Registry identified six cases of gastric MALToma. Patient demographics, management, and outcomes were compared and published literature was reviewed. RESULTS: MALToma developed in six transplant recipients (three kidney, two heart, one kidney-pancreas). All were treated with immunosuppression minimization and therapy for H. pylori, resulting in disease regression in five patients. One patient developed progression to high-grade MALToma despite documented H. pylori eradication, required surgery and chemotherapy, and died, with significant disease at autopsy. CONCLUSIONS: Treatment of MALToma with immunosuppression minimization and anti-H. pylori therapy results in a majority of patients becoming disease free. Observation of malignant degeneration into an aggressive, high-grade lymphoma in one patient indicates the malignant potential. Diligent follow-up of these patients with endoscopy and biopsy is therefore indicated.

Experience with 274 cardiac transplant recipients with posttransplant lymphoproliferative disorder: a report from the Israel Penn International Transplant Tumor Registry.

BACKGROUND: Posttransplant lymphoproliferative disorder (PTLD) is a life-threatening complication that occurs in a small but significant minority of solid organ transplant recipients. Published experiences with PTLD in cardiac transplant recipients are limited to relatively small single-center reports. METHODS: This report presents experience with 274 cases of PTLD in cardiac transplant recipients reported to the Israel Penn International Transplant Tumor Registry (IPITTR). RESULTS: PTLD carried an ominous prognosis: Kaplan Meier survival after PTLD diagnosis was 45%, 33%, 30%, and 13%, respectively, at 1, 3, 5, and 10 years. Common causes of death included: PTLD, cardiovascular collapse, and infection; all occurred at a median of less than 6 months. Risk of death from cardiovascular collapse secondary to immunosuppression withdrawal was substantial (28%), indicating that a fine balance exists between death from PTLD and from sudden cardiac death due to acute rejection. PTLD therapy in the majority of patients consisted of combination therapy (49%). Survival in patients receiving immunosuppression minimization (ISM) alone was 32%, with ISM plus other therapy was 27%, and with other therapies not containing ISM was 11% (P < 0.01). CONCLUSION: PTLD in cardiac transplant recipients is associated with low long-term survival rates. Analysis of PTLD therapies and outcomes suggest that immunosuppression minimization, when applied, improves survival. However, risk of sudden death may mitigate the positive effect of ISM. This observation has important implications for ISM in PTLD therapy in cardiac transplant recipients. Carefully designed prospective studies are needed to evaluate the positive and negative effects of ISM in cardiac transplant recipients with PTLD.

Incidental diagnosis of gastric cancer in transplant recipients improves patient survival.

BACKGROUND: Gastric cancer in the United States is often diagnosed at advanced stages, resulting in dismal outcomes. In the immunosuppressed transplant recipient population, little is known about the clinical staging and outcome of these compromised patients. METHODS: All US cases reported to the Israel Penn International Transplant Tumor Registry were retrospectively examined for patient demographics, immunosuppressive therapy, tumor characteristics, therapeutic modalities, and mortality. Statistical analysis was performed with Students t test, chi-square analysis, and log-rank analysis by the method of Kaplan-Meier. RESULTS: Gastric cancer was identified in 34 recipients: 28 (82%) were male; 24 (71%) were white. Mean age at diagnosis was 58 +/- 11 years. Twenty-four (71%) patients received kidney transplants, 7 (21%) received heart transplants, and 3 (9%) received liver transplants. Fifty percent received induction therapy, whereas 94% were maintained on calcineurin inhibitors and corticosteroids. Thirty-five percent of patients were diagnosed during evaluation for gastrointestinal symptoms, with the remaining cases discovered incidentally during endoscopy (53%) or during computed tomography (12%) performed for other reasons. Stage varied at presentation as follows: stage I (n = 6), stage II (n = 11), stage III (n = 13), and stage IV (n = 4). Incidental diagnoses resulted in a lower stage malignancy (P <.001) and greater 1-year and 5-year survivals (P <.05) compared with those patients whose were diagnosed after being evaluated of gastrointestinal symptoms. CONCLUSION: In the United States, because gastric cancer in the transplant recipient is frequently identified at an earlier stage (50% were stages I and II) than in the general population, survivals are equivalent despite continued administration of immunosuppression. This early identification may be attributed to more frequent presymptom diagnosis and staging, resulting from incidental detection of these malignancies during posttransplant upper endoscopy or computed tomography. Early detection has resulted in a 29% 5-year survival for the entire transplant recipient group compared with a 5% to 15% 5-year survival in the general population.

Donor transmitted malignancies.

Early experiences in transplantation, which pre-dated brain death laws, utilized organs from donors with active malignancies. The use of organs from such donors occasionally resulted in the transmission of malignancy from the donor to an unknowing recipient. Over a period of three decades, Israel Penn, M. D. catalogued some two hundred and fifty cases of organs transplanted from donors with a history of malignancy; carefully examining each reported case for tumor histology, donor risk factors, method of tumor presentation and recipient outcome. Some recipients never developed malignancies, while others were less fortunate, developing cancers that were suspicious for donor origin. The evolution of transplantation has resulted in improved patient survival, which in turn has led to an increased demand for organ transplantation. Unfortunately, the supply of organs available for transplantation has failed to keep pace with the demand, with the worldwide deficit growing annually. In an effort to bridge the widening gap, utilization of older and more marginal donors has been suggested. However, use of older donors is accompanied by the likelihood that a significant proportion may have undiagnosed malignancies. Multiple transplant programs have considered the use of donors with tumors of non-malignant or even low-grade malignant histology, most often involving the central nervous system (CNS). According to a survey from the United Network for Organ Sharing (UNOS), central nervous system malignancies are among the most commonly identified malignancies found in potential donors. This study examines the distribution of potential donor transmitted malignancies reported to the Israel Penn International Transplant Tumor Registry. The incidence of tumor transmission is examined in the overall group as well as among individual histologies. We also seek to identify specific factors associated with the risk of malignancy transmission from donor to recipient, in an effort to minimize future transmission of donor tumors to unwitting recipients. The study is based on voluntary registry data, which some argue can be criticized for a lack of true incidence data. In reality, however, this data may provide a more accurate insight since it is based on transmissions from high-risk donors rather than from the general population.

Posttransplant malignancy.

In the past few decades, great advances have been made in the field of solid-organ transplantation. A greater understanding of immune system function, the development of modern immunosuppression, and advancements in surgical technique have led to marked improvements in both recipient and graft survivals, as well as recipients' quality of life. However, improved survival rates have also led to prolonged exposure to chronic immunosuppression, which increases the risk for the development of posttransplant malignancies. In addition, older transplant candidates are being considered, carrying with them the increased likelihood of preexisting malignancy. Consequently, the potential risk of posttransplant malignancy must be considered. Moreover, as long-term transplant survivors continue to age, posttransplant malignancies will be seen more frequently. This review presents the more commonly encountered posttransplant malignancies and the measures that are currently being utilized to prevent and treat them.

Immobilized laminin concentration gradients on electrospun fiber scaffolds for controlled neurite outgrowth.

Neuronal process growth is guided by extrinsic environmental cues such as extracellular matrix (ECM) proteins. Recent reports have described that the growth cone extension is superior across gradients of the ECM protein laminin compared to growth across uniformly distributed laminin. In this work, the authors have prepared gradients of laminin on aligned electrospun nanofibers for use as substrates for neuronal growth. The substrates therefore presented both topographical and chemical guidance cues. Step gradients were prepared by the controlled robotic immersion of plasma-treated polycaprolactone fibers reacted with N-hydroxysuccinimide into the protein solution. The gradients were analyzed using x-ray photoelectron spectroscopy and confocal laser scanning microscopy. Gradients with a dynamic range of protein concentrations were successfully generated and neurite outgrowth was evaluated using neuronlike pheochromocytoma cell line 12 (PC12) cells. After 10 days of culture, PC12 neurite lengths varied from 32.7 ± 14.2 µm to 76.3 ± 9.1 µm across the protein concentration gradient. Neurite lengths at the highest concentration end of the gradient were significantly longer than neurite lengths observed for cells cultured on samples with uniform protein coverage. Gradients were prepared both in the fiber direction and transverse to the fiber direction. Neurites preferentially aligned with the fiber direction in both cases indicating that fiber alignment has a more dominant role in controlling neurite orientation, compared to the chemical gradient.

On-Surface Cross Coupling Methods for the Construction of Modified Electrode Assemblies with Tailored Morphologies.

Controlling the molecular topology of electrode-catalyst interfaces is a critical factor in engineering devices with specific electron transport kinetics and catalytic efficiencies. As such, the development of rational methods for the modular construction of tailorable electrode surfaces with robust molecular wires (MWs) exhibiting well-defined molecular topologies, conductivities and morphologies is critical to the evolution and implementation of electrochemical arrays for sensing and catalysis. In response to this need, we have established modular on-surface Sonogashira and Glaser cross-coupling processes to synthetically install arrays of ferrocene-capped MWs onto electrochemically functionalized surfaces. These methods are of comparable convenience and efficiency to more commonly employed Huisgen methods. Furthermore, unlike the Huisgen reaction, this new surface functionalization chemistry generates modified electrodes that do not contain unwanted ancillary metal binding sites, while allowing the bridge between the ferrocenyl moiety and electrode surface to be synthetically tailored. Electrochemical and surface analytical characterization of these platforms demonstrate that the linker topology and connectivity influences the ferrocene redox potential and the kinetics of charge transport at the interface.

Quantification of protein incorporated into electrospun polycaprolactone tissue engineering scaffolds.

The surface modification of synthetic tissue engineering scaffolds is essential to improving their hydrophilicity and cellular compatibility. Plasma treatment is an effective way to increase the hydrophilicity of a surface, but the incorporation of biomolecules is also important to control cellular adhesion and differentiation, among many other outcomes. In this work, oriented polycaprolactone (PCL) electrospun fibers were modified by air-plasma treatment, followed by the covalent attachment of laminin. The amount of protein incorporated onto the fiber surface was controlled by varying the reaction time and the protein solution concentration. The protein concentration and coverage were quantified using X-ray photoelectron spectroscopy (XPS), solid-state ultraviolet-visible spectroscopy (UV-vis) and two fluorescence-based assays. XPS results showed a nearly linear increase in protein coverage with increasing protein soaking solution concentration until a monolayer was formed. Results from XPS and the NanoOrange fluorescence assay revealed multilayer protein coverage at protein solution concentrations between 25 and 50 µg/mL, whereas the UV-vis assay demonstrated multilayer coverage at lower protein solution concentrations. The effect of protein concentration on the neurite outgrowth of neuron-like PC12 cells was evaluated, and outgrowth rates were found to be positively correlated to increasing protein concentration.

Non-equilibrium cation distribution and enhanced spin disorder in hollow CoFe2O4 nanoparticles.

We present magnetic properties of hollow and solid CoFe(2)O(4) nanoparticles that were obtained by annealing of Co(33)Fe(67)/CoFe(2)O(4) (core/shell) nanoparticles. Hollow nanoparticles were polycrystalline whereas the solid nanoparticles were mostly single crystal. Electronic structure studies were performed by photoemission which revealed that particles with hollow morphology have a higher degree of inversion compared to solid nanoparticles and the bulk counterpart. Electronic structure and the magnetic measurements show that particles have uncompensated spins. Quantitative comparison of saturation magnetization (M(S )), assuming bulk Néel type spin structure with cationic distribution, calculated from quantitative XPS analysis, is presented. The thickness of uncompensated spins is calculated to be significantly large for particles with hollow morphology compared to solid nanoparticles. Both morphologies show a lack of saturation up to 7 T. Moreover magnetic irreversibility exists up to 7 T of cooling fields for the entire temperature range (10-300 K). These effects are due to the large bulk anisotropy constant of CoFe(2)O(4) which is the highest among the cubic spinel ferrites. The effect of the uncompensated spins for hollow nanoparticles was investigated by cooling the sample in large fields of up to 9 T. The magnitude of horizontal shift resulting from the unidirectional anisotropy was more than three times larger than that of solid nanoparticles. As an indication signature of uncompensated spin structure, 11% vertical shift for hollow nanoparticles is observed, whereas solid nanoparticles do not show a similar shift. Deconvolution of the hysteresis response recorded at 300 K reveals the presence of a significant paramagnetic component for particles with hollow morphology which further confirms enhanced spin disorder.

Optimization of protein patterns for neuronal cell culture applications.

In the present study, we fabricated two-component extracellular matrix protein patterned substrates with fibronectin (FN) and laminin (LN) because of our interest in the mechanism of axonal regeneration and injury in the central and peripheral nervous systems. The authors investigated how the patterning order and method of attachment affected the spatial distribution and biological activity of the immobilized proteins. Micro-contact printing (µCP) techniques in concert with reactive surface chemistry were used to modify glass substrates with one- and two-component films of FN and LN, including micrometer-scale patterns of FN and LN. The composition and spatial distributions of both proteins on the patterned surfaces were characterized by x ray photoelectron spectroscopy, epi-fluorescence microscopy, atomic force microscopy, and time-of-flight secondary-ion mass spectrometry. The authors also characterized the biological activity of the top-most protein layer in a two-layer protein system as well as the ability of the top-most protein layer to mask the biological activity of an underlying protein layer using a fluorescence-based enzyme-linked immunosorbent assay. The order of protein deposition significantly affected the relative biological activity of the upper-most and underlying immobilized proteins. As a result of these optimization studies, maximum biological activity per surface protein was achieved by first immobilizing FN from solution, followed by µCP of LN on the FN. Addition of µCP LN films was able to mask ∼84% of the underlying FN activity, whereas µCP FN films were only able to mask ∼27% of the underlying LN activity.

Coaxial electrospun poly(methyl methacrylate)-polyacrylonitrile nanofibers: atomic force microscopy and compositional characterization.

Poly(methyl methacrylate) (PMMA)-polyacrylonitrile (PAN) fibers were prepared using a conventional single-nozzle electrospinning technique. The as-spun fibers exhibited core-shell morphology as verified by transmission electron microscopy (TEM) and atomic force microscopy (AFM). AFM-phase and modulus mapping images of the fiber cross-section and X-ray photoelectron spectroscopy (XPS) analysis indicated that PAN formed the shell and PMMA formed the core material. XPS, thermogravimetric analysis (TGA), and elemental analysis were used to determine fiber compositional information. Soaking the fibers in solvent demonstrated removal of the core material, generating hollow PAN fibers.