Magnetic cristobalite (?): a possible new magnetic phase produced by the thermal decomposition of nontronite.

Prolonged heat treatment (> 1 hour) of nontronite (an iron-rich smectite clay) at 900 degrees to 1000 degrees C produces a phase with some unusual magnetic properties. This new phase has a Curie temperature of 200 degrees to 220 degrees C, extremely high remanent coercivities in excess of 800 milliteslas, and a room-temperature coercivity dependent on the magnitude of the applied field during previous thermomagnetic cycling from above 220 degrees C. X-ray and magnetic analyses suggest that an iron-substituted cristobalite could be responsible, in part, for these observations. Formation of this magnetic cristobalite, however, may require topotactic growth from a smectite precursor.

Magnetodendrimers allow endosomal magnetic labeling and in vivo tracking of stem cells.

Magnetic resonance (MR) tracking of magnetically labeled stem and progenitor cells is an emerging technology, leading to an urgent need for magnetic probes that can make cells highly magnetic during their normal expansion in culture. We have developed magnetodendrimers as a versatile class of magnetic tags that can efficiently label mammalian cells, including human neural stem cells (NSCs) and mesenchymal stem cells (MSCs), through a nonspecific membrane adsorption process with subsequent intracellular (non-nuclear) localization in endosomes. The superparamagnetic iron oxide nanocomposites have been optimized to exhibit superior magnetic properties and to induce sufficient MR cell contrast at incubated doses as low as 1 microg iron/ml culture medium. When containing between 9 and 14 pg iron/cell, labeled cells exhibit an ex vivo nuclear magnetic resonance (NMR) relaxation rate (1/T2) as high as 24-39 s-1/mM iron. Labeled cells are unaffected in their viability and proliferating capacity, and labeled human NSCs differentiate normally into neurons. Furthermore, we show here that NSC-derived (and LacZ-transfected), magnetically labeled oligodendroglial progenitors can be readily detected in vivo at least as long as six weeks after transplantation, with an excellent correlation between the obtained MR contrast and staining for beta-galactosidase expression. The availability of magnetodendrimers opens up the possibility of MR tracking of a wide variety of (stem) cell transplants.

Magnetic material in the human hippocampus.

Magnetic analyses of hippocampal material from deceased normal and epileptic subjects, and from the surgically removed epileptogenic zone of a living patient have been carried out. All had magnetic characteristics similar to those reported for other parts of the brain [6]. These characteristics along with low temperature analysis indicate that the magnetic material is present in a wide range of grain sizes. The low temperature analysis also revealed the presence of magnetite through manifestation of its low temperature transition. The wide range of grain sizes is similar to magnetite produced extracellularly by the GS-15 strain of bacteria and unlike that found in magnetotactic bacteria MV-1, which has a restricted grain size range. Optical microscopy of slices revealed rare 5-10 micron clusters of finer opaque particles, which were demonstrated with Magnetic Force Microscopy to be magnetic. One of these was shown with EDAX to contain AI, Ca, Fe, and K, with approximate weight percentages of 55, 19, 19, and 5, respectively.

A new intraurethral sphincter prosthesis with a self contained urinary pump.

An intraurethral sphincter prosthesis with a self contained urinary pump for the management of atonic bladder in women was developed and tested. The prosthesis is comprised of a short, self retaining silicone catheter in which there is a valve and pump. Available in a range of lengths and diameters according to urethral size, its insertion is similar to that of a urethral catheter. The prosthesis is secured by a novel fixation method that has soft expandable silicone fins at the bladder neck and a flexible flange at the external meatus. It is activated by a small hand-held control device. To urinate, the activator is placed on the lower abdomen area and the "on" button is pressed, providing energy to the pump by a magnetic coupling method. Once activated, the valve opens and the pump rotates at a high speed, drawing urine from the bladder and pushing it forward, allowing the patient to "void" with a urine flow of 10 to 12 cc/sec. When the bladder is completely evacuated, the pumping ceases and the valve closes, restoring continence. The device was evaluated clinically in 17 women. Fifteen of the patients had a range of use of 2 weeks to 16 months during which they were dry and had complete bladder emptying. Two patients did not tolerate the device because of uninhibited detrusor contractions and, in both cases, it was removed without complication after 5 days.

Magnetic properties of uncultivated magnetotactic bacteria and their contribution to a stratified estuary iron cycle.

Of the two nanocrystal (magnetosome) compositions biosynthesized by magnetotactic bacteria (MTB), the magnetic properties of magnetite magnetosomes have been extensively studied using widely available cultures, while those of greigite magnetosomes remain poorly known. Here we have collected uncultivated magnetite- and greigite-producing MTB to determine their magnetic coercivity distribution and ferromagnetic resonance (FMR) spectra and to assess the MTB-associated iron flux. We find that compared with magnetite-producing MTB cultures, FMR spectra of uncultivated MTB are characterized by a wider empirical parameter range, thus complicating the use of FMR for fossilized magnetosome (magnetofossil) detection. Furthermore, in stark contrast to putative Neogene greigite magnetofossil records, the coercivity distributions for greigite-producing MTB are fundamentally left-skewed with a lower median. Lastly, a comparison between the MTB-associated iron flux in the investigated estuary and the pyritic-Fe flux in the Black Sea suggests MTB play an important, but heretofore overlooked role in euxinic marine system iron cycle.

Characterization of extracellular minerals produced during dissimilatory Fe(III) and U(VI) reduction at 100 degrees C by Pyrobaculum islandicum.

In order to gain insight into the significance of biotic metal reduction and mineral formation in hyperthermophilic environments, metal mineralization as a result of the dissimilatory reduction of poorly crystalline Fe(III) oxide, and U(VI) reduction at 100 degrees C by Pyrobaculum islandicum was investigated. When P. islandicum was grown in a medium with poorly crystalline Fe(III) oxide as an electron acceptor and hydrogen as an electron donor, the Fe(III) oxide was reduced to an extracellular, ultrafine-grained magnetite with characteristics similar to that found in some hot environments and that was previously thought to be of abiotic origin. Furthermore, cell suspensions of P. islandicum rapidly reduced the soluble and oxidized form of uranium, U(VI), to extracellular precipitates of the highly insoluble U(IV) mineral, uraninite (UO(2)). The reduction of U(VI) was dependent on the presence of hydrogen as the electron donor. These findings suggest that microbes may play a key role in metal deposition in hyperthermophilic environments and provide a plausible explanation for such phenomena as magnetite accumulation and formation of uranium deposits at ca. 100 degrees C.

Alloplastic implants for orbital wall reconstruction.

Nonabsorbable alloplastic implants for orbital wall reconstruction have been widely accepted by surgeons because of their ready availability, stability, and biocompatability. Many complications have arisen with this class of implants because the lack of host tissue integration allows for implant migration, implant extrusion, recurrent hemorrhage, and infection. Porous polyethylene implants provide a welcome alternative as they have the unique properly of supporting tissue ingrowth in vivo. Their semirigid structure provides structural stability when used around the orbit, and their malleability allows for easy contouring. This paper presents our surgical approach to reconstructing orbital defects with porous polyethylene implants, including orbital floor, and superior, medial, and lateral wall defects, and discusses the advantages/disadvantages of other nonabsorbable alloplasts.

Transconjunctival versus transcutaneous approach in upper and lower blepharoplasty.

In this article, we review the traditional transcutaneous upper lid blepharoplasty technique and contrast it to the newly described transconjunctival upper lid blepharoplasty technique that has limited indications. The technique and application of the skin-muscle flap transcutaneous lower lid blepharoplasty and the transconjunctival lower lid blepharoplasty are also discussed. We prefer the transconjunctival lower lid blepharoplasty as it circumvents the risk of lower eyelid retraction associated with the transcutaneous approach. We also discuss application of adjunctive procedures to the transconjunctival approach to enhance cosmetic results.

Hypokalemic familial periodic paralysis: a case report.

The perioperative management of patients with hypokalemic familial periodic paralysis is well known and has been described previously. This disease does not preclude surgery as long as the surgical team is aware of the diagnosis preoperatively. We describe herein a patient with familial periodic paralysis diagnosed the first time 1 day after undergoing surgery.

Malignant melanoma: primary presentation in bone marrow and lymph node.

We describe an unusual presentation of malignant melanoma with simultaneous lymph node and bone marrow metastasis. In addition the disease was associated with immune-mediated thrombocytopenia. A brief remission was obtained with combination chemotherapy.

Relaxometry and magnetometry of the MR contrast agent MION-46L.

MION-46L is an ultrasmall monocrystalline superparamagnetic (SPM) iron oxide that is of current interest as an MR contrast agent. It is believed to consist primarily of small maghemite or magnetite crystals that possess a SPM moment, but the exact magnetic properties and related mechanisms of T(1) and T(2) proton relaxation enhancement are not well understood. We have obtained a comprehensive data set consisting of magnetization curves, EPR spectra, and 1/T(1) and 1/T(2) nuclear magnetic relaxation dispersion (NMRD) profiles for this contrast agent. The magnetization curves show a primary curvature consistent with a SPM moment of 10,300 Bohr magnetons (BM) per particle. In addition, there is a secondary high-field curvature that is consistent with a smaller SPM moment of 1600 BM, which may be responsible for the observed high-field increase in 1/T(2). Finally, there appear to be a considerable number of paramagnetic ions present that are needed to account for the high-field increase in magnetization, and that can provide an alternative explanation for the magnitude of the low-field T(1) plateau. This "three-phase model" appears to be successful in explaining in a self-consistent and quantitative manner the combined results of the magnetometry, relaxometry, and EPR studies. Magn Reson Med 42:379-384, 1999. Published 1999 Wiley-Liss, Inc.