R.V. Ramanujan

Thermoresponsive magnetic composite nanomaterials for multimodal cancer therapy

The synthesis, characterization and property evaluation of drug-loaded polymer-coated magnetic nanoparticles (MNPs) relevant to multimodal cancer therapy has been studied. The hyperthermia and controlled drug release characteristics of these particles was examined. Magnetite (Fe(3)O(4))-poly-n-(isopropylacrylamide) (PNIPAM) composite MNPs were synthesized in a core-shell morphology by dispersion polymerization of n-(isopropylacrylamide) chains in the presence of a magnetite ferrofluid. These core-shell composite particles, with a core diameter of approximately 13nm, were loaded with the anti-cancer drug doxorubicin (dox), and the resulting composite nanoparticles (CNPs) exhibit thermoresponsive properties. The magnetic properties of the composite particles are close to those of the uncoated magnetic particles. In an alternating magnetic field (AMF), composite particles loaded with 4.15 wt.% dox exhibit excellent heating properties as well as simultaneous drug release. Drug release testing confirmed that release was much higher above the lower critical solution temperature (LCST) of the CNP, with a release of up to 78.1% of bound dox in 29h. Controlled drug release testing of the particles reveals that the thermoresponsive property can act as an on/off switch by blocking drug release below the LCST. Our work suggests that these dox-loaded polymer-coated MNPs show excellent in vitro hyperthermia and drug release behavior, with the ability to release drugs in the presence of AMF, and the potential to act as agents for combined targeting, hyperthermia and controlled drug release treatment of cancer.

Thermoresponsive core–shell magnetic nanoparticles for combined modalities of cancer therapy

Thermoresponsive polymer-coated magnetic nanoparticles loaded with anti-cancer drugs are of considerable interest for novel multi-modal cancer therapies. Such nanoparticles can be used for magnetic drug targeting followed by simultaneous hyperthermia and drug release. Gamma-Fe(2)O(3) iron oxide magnetic nanoparticles (MNP) with average sizes of 14, 19 and 43 nm were synthesized by high temperature decomposition. Composite magnetic nanoparticles (CNP) of 43 nm MNP coated with the thermoresponsive polymer poly-n-isopropylacrylamide (PNIPAM) were prepared by dispersion polymerization of n-isopropylacrylamide monomer in the presence of the MNP. In vitro drug release of doxorubicin-(dox) loaded dehydrated CNP at temperatures below and above the lower critical solution temperature of PNIPAM (34 degrees C) revealed a weak dependence of drug release on swelling behavior. The particles displayed Fickian diffusion release kinetics; the maximum dox release at 42 degrees C after 101 h was 41%. In vitro simultaneous hyperthermia and drug release of therapeutically relevant quantities of dox was achieved, 14.7% of loaded dox was released in 47 min at hyperthermia temperatures. In vivo magnetic targeting of dox-loaded CNP to hepatocellular carcinoma (HCC) in a buffalo rat model was studied by magnetic resonance imaging (MRI) and histology. In summary, the good in vitro and in vivo performance of the doxorubicin-loaded thermoresponsive polymer-coated magnetic nanoparticles suggests considerable promise for applications in multi-modal treatment of cancer.

Modeling the performance of magnetic nanoparticles in multimodal cancer therapy

Composite magnetic nanoparticles (MNPs) consisting of an MNP core and drug loaded polymer shell can increase the efficacy of cancer therapy by overcoming several limitations of conventional hyperthermia and chemotherapy. Multimodal therapy consisting of simultaneous hyperthermia and chemotherapy can increase therapeutic efficiency compared to individual applications of these modalities. Factors influencing power output in an alternating magnetic field (AMF) for superparamagnetic γ-Fe2O3 and Fe3O4 iron oxide MNP were studied. The optimum MNP properties for in vivo magnetic hyperthermia were identified. For a 375 kHz AMF, 23 nm γ-Fe2O3 MNP and 12 nm Fe3O4 MNP produce maximum heating, heat generation is dependent primarily on Neel relaxation and is insensitive to polymer shell thickness. The heating of tumors by uniformly distributed magnetic clusters of optimized iron oxide MNP was modeled. The MNP mass required to heat tumors to hyperthermia temperatures was calculated, the Fe3O4 MNP concentration in the t...

Morphing Soft Magnetic Composites

Magnet filler-polymer matrix composites (Magpol) are an emerging class of morphing materials. Applications of Magpol can include artificial muscles, drug delivery, adaptive optics and self healing structures. Advantages of Magpol include remote contactless actuation, several actuation modes, high actuation strain and strain rate, self-sensing and quick response. The actuation modes of Magpol, its dynamic properties, work output and transduction characteristics are described. Analogies between Magpol actuation and phase transformations are presented. As an illustration of Magpol actuation, a proof of concept artificial muscle is presented. Current applications and future prospects are described.

Surfactant-Directed Synthesis of Branched Bismuth Telluride/Sulfide Core/Shell Nanorods†

Branched core/shell bismuth telluride/bismuth sulfide nanorod heterostructures are prepared by using a biomimetic surfactant, L-glutathionic acid. Trigonal nanocrystals of bismuth telluride are encapsulated by nanoscopic shells of orthorhombic bismuth sulfide. Crystallographic twinning causes shell branching. Such heteronanostructures are attractive for thermoelectric power generation and cooling applications.

Magnetic nanoparticle-loaded polymer nanospheres as magnetic hyperthermia agents

Uniform magnetic nanoparticle-loaded polymer nanospheres with different loading contents of manganese ferrite nanoparticles were successfully synthesized using a flexible emulsion process. The MnFe2O4-loaded polymer nanospheres displayed an excellent dispersibility in both water and phosphate buffer saline. The effect of loading ratio and size of MnFe2O4 nanoparticles within the nanospheres on the specific absorption rate (SAR) under an alternating magnetic field was investigated. Our results indicate that a large size (here 18 nm) and a low loading ratio are preferable for a high SAR. For a smaller particle size (6 nm), the low loading ratio did not result in an enhancement of the SAR value, while a very low SAR value is expected for 6 nm. In addition, the SAR of low-content MnFe2O4 (18 nm)-loaded polymer nanospheres in the agarose gel which is simulated for in vivo environment is the highest among the samples and does not change substantially in physiological environments. This differs largely from the behaviour of singly dispersed nanoparticles. Our results have paved the way for the design of MnFe2O4-loaded polymer nanospheres as magnetic hyperthermia agents for in vivo bio-applications.

Template assisted assembly of cobalt nanobowl arrays

3-D interconnected networks of magnetic cobalt nanobowls with a wall size of <100 nm dimension have been fabricated. A novel technique was used to overcome the problem of volume shrinkage usually observed in such structures when formed by chemical conversion route. Cobalt particles were formed in the interstitial spaces of 3-D closed packed polystyrene (PS) colloidal template by borohydride reduction of a cobalt salt. Template removal was carried out by annealing either at 500 °C for 3 h in nitrogen or at 400 °C for 4 h in air, followed by toluene etching. The presence of an oxygen atmosphere during annealing was found to be imperative to obtain metallic cobalt. Magnetic measurements on cobalt nanobowl arrays showed enhanced coercivity in comparison to spherical particles due to shape effects.

Influence of La and Ce additions on the magnetocaloric effect of Fe–B–Cr-based amorphous alloys.

The magnetic entropy change (ΔSM), temperature of peak ΔSM (Tpk) and refrigerant capacity (RC) in Fe(RE)80B12Cr8 (RE=La, Ce, or Gd) alloys were studied. Increasing La, Ce, and Gd content led to relatively constant, decrease, and increase in Tpk, respectively. Both the phenomenologically constructed universal curve for ΔSM and field dependence power laws demonstrated that these alloys exhibited similar critical exponents at Curie temperature. With 5% Ce added to Fe80B12Cr8, Tpk could be tuned near room temperature with relatively constant peak ΔSM. Fe79B12Cr8La1 exhibited enhanced RC compared to Gd5Si2Ge1.9Fe0.1. The tunable Tpk and enhanced RC are needed in active magnetic regenerators.

Design parameters for magneto-elastic soft actuators

Novel soft actuators can be designed from ferrogels by combining the elastic behavior of a polymer matrix with the magnetic properties of a magnetic filler. A thorough understanding of the mechanical behavior of ferrogel actuation is essential for optimizing actuator performance. For actuation by linear magnetostriction, the influence of geometrical parameters on the onset and magnitude of hysteretic loss, the range for the continuous deformation ratio, the rate of change of the deformation ratio with respect to the field strength, and the saturation elongation were modeled. These results demonstrate that geometrical design parameters such as specimen length, aspect ratio, and distance from the magnetic field source can be used to tune the performance of ferrogels.

Hot hardness and indentation creep studies of a Fe-28Al-3Cr-0.2C alloy

The hot hardness behaviour of a Fe‐28Al‐3Cr‐0.2C (at.%) alloy was evaluated from room temperature to 1273 K. Indentation creep measurements were also carried out in the temperature range of 843‐963 K. The hardness‐temperature plot of this alloy showed five distinct regions. The mechanism of deformation operating in each of these regions has been suggested. Indentation creep measurements showed that the stress exponent (n) obtained from the hardness‐time plots was weakly temperature dependent. The activation energy for high temperature creep was found to be in good agreement with that for self-diffusion of pure iron and in excellent agreement with previous studies. These values of n and activation energy were found to be consistent with dislocation climb as the rate controlling creep mechanism.