Suprabha Nayar

Bactericidal effect of iron oxide nanoparticles on Staphylococcus aureus

In order to study the effects of iron oxide (IO) nanoparticles on Staphylococcus aureus, IO nanoparticles were synthesized via a novel matrix-mediated method using polyvinyl alcohol (PVA). The IO nanoparticles were characterized by transmission electron microscopy and dynamic light scattering. Further, S. aureus were grown in the presence of three different IO nanoparticle concentrations for four, 12, and 24 hours. Live/dead assays were performed and the results provide evidence that IO/PVA nanoparticles inhibited S. aureus growth at the highest concentration (3 mg/mL) at all time points.

Mesenchymal cell response to nanosized biphasic calcium phosphate composites

Biphasic calcium phosphate nanoparticles comprising both hydroxyapatite (HA) and beta polymorph of tricalcium phosphate (beta-TCP) have been synthesized together by a polymer matrix mediated process. The process, based on in situ mineralization of poly (vinyl alcohol), exerts a good control over the morphological features of biphasic nanoparticles. By controlling the reaction chemistry (Ca:P ratios), nanobioceramic particles having three different HA/beta-TCP ratios of 50:50, 55:45 and 60:40 respectively. As the two constituents of biphasic system (HA and beta-TCP) facilitate series of signaling cascades in osteoblast division and differentiation, the adhesion and differentiation properties of mesenchymal cells (MSCs) derived from bone marrow has been studied.

Composition dependent structural modulations in transparent poly(vinyl alcohol) hydrogels.

Transparent and stable Poly(vinyl alcohol) hydrogels were synthesized from polymer aqueous solution without resorting to a mixed solvent such as dimethyl sulfoxide and water. Contrary to the reported methods involving hydrogen bond induced physical crosslinking by repeated freeze-thawing at -20 degrees C, the present process demonstrates the gelation taking place at relatively higher temperature, i.e. 0 degrees C. While maintaining transparency in all the synthesized hydrogels, the present paper reports systematic structural and morphological variations in the hydrogels as a function of polymer concentration.

Biomimetic synthesis of superparamagnetic iron oxide particles in proteins

Matrix-mediated in situ synthesis of monodispersed magnetite and maghemite nanoparticles (2-16 nm) was carried out using the cavities present in gels of globular proteins such as egg white and bovine serum albumin. Under stringent conditions, spatial-charge-distribution-assisted molecular recognition of proteins for inorganic ions led to the site- and polymorph-specific synthesis of superparamagnetic iron oxide particles. A transformation from magnetite to maghemite as a nucleating phase could be observed by partially denaturing the egg white protein, signifying the delicate role of quaternary structure of proteins under different reaction conditions, in determining the size and shape of the polymorph.

Comparison study of ferrofluid and powder iron oxide nanoparticle permeability across the blood–brain barrier

In the present study, the permeability of 11 different iron oxide nanoparticle (IONP) samples (eight fluids and three powders) was determined using an in vitro blood–brain barrier model. Importantly, the results showed that the ferrofluid formulations were statistically more permeable than the IONP powder formulations at the blood–brain barrier, suggesting a role for the presently studied in situ synthesized ferrofluid formulations using poly(vinyl) alcohol, bovine serum albumin, collagen, glutamic acid, graphene, and their combinations as materials which can cross the blood–brain barrier to deliver drugs or have other neurological therapeutic efficacy. Conversely, the results showed the least permeability across the blood–brain barrier for the IONP with collagen formulation, suggesting a role as a magnetic resonance imaging contrast agent but limiting IONP passage across the blood–brain barrier. Further analysis of the data yielded several trends of note, with little correlation between permeability and fluid zeta potential, but a larger correlation between permeability and fluid particle size (with the smaller particle sizes having larger permeability). Such results lay the foundation for simple modification of iron oxide nanoparticle formulations to either promote or inhibit passage across the blood–brain barrier, and deserve further investigation for a wide range of applications.

Microwave irradiation enhances kinetics of the biomimetic process of hydroxyapatite nanocomposites

In situ synthesized hydroxyapatite-poly(vinyl) alcohol nanocomposite was subjected to microwave irradiation, post synthesis. Interestingly, the aging time of 1 week required for the normal biomimetic process was reduced to 1 h post microwave irradiation, as characterized by x-ray powder diffraction and transmission electron microscopy. The surface topography shows the tendency of tubules to cross-link with the help of microwave energy. The microwave energy seems to provide a directional pull to the polymer chains which could have led to an enhancement of the kinetics of phase formation.

Controlling ferrofluid permeability across the blood-brain barrier model

In the present study, an in vitro blood–brain barrier model was developed using murine brain endothelioma cells (b.End3 cells). Confirmation of the blood–brain barrier model was completed by examining the permeability of FITCDextran at increasing exposure times up to 96 h in serum-free medium and comparing such values with values from the literature. After such confirmation, the permeability of five novel ferrofluid (FF) nanoparticle samples, GGB (ferrofluids synthesized using glycine, glutamic acid and BSA), GGC (glycine, glutamic acid and collagen), GGP (glycine, glutamic acid and PVA), BPC (BSA, PEG and collagen) and CPB (collagen, PVA and BSA), was determined using this blood–brain barrier model. All of the five FF samples were characterized by zeta potential to determine their charge as well as TEM and dynamic light scattering for determining their hydrodynamic diameter. Results showed that FF coated with collagen passed more easily through the blood–brain barrier than FF coated with glycine and glutamic acid based on an increase of 4.5% in permeability. Through such experiments, diverse magnetic nanomaterials (such as FF) were identified for: (1) MRI use since they were less permeable to penetrate the blood–brain barrier to avoid neural tissue toxicity (e.g. GGB) or (2) brain drug delivery since they were more permeable to the blood–brain barrier (e.g. CPB).

Biomimetic matrix mediated room temperature synthesis and characterization of nano-hydroxyapatite towards targeted drug delivery

The nucleation and growth of hydroxyapatite is closely associated with the extracellular matrix environment. Bovine serum albumin, collagen and polyvinyl alcohol were used to mimic the extracellular matrix. An attempt to understand the role of these matrices on the synthesis and function of hydroxyapatite has been made. XRD, FT-IR, XPS, TG-DTA, SEM and TEM confirmed the formation of hydroxyapatite synthesized by the biomimetic route. Further, the role of the organic matrix in controlling the nucleation and growth of hydroxyapatite particles at the nano level is understood by in-depth analysis of the XPS spectra. The in vitro release of the anti-cancer drug methotrexate in aqueous solution was studied, and the in vitro release profile was assayed by elution in phosphate buffered saline with pH 7.4 and pH 5 at 37 °C. The percentage of loading and release profiles of the drug were evaluated. The results show that the use of the matrix increased the drug release efficiency from 44.5% to 66% at pH 7.4 and 78% to 98.92% at pH 5. These results suggest that the synthesized hydroxyapatite can be used as a pH responsive vehicle for delivering drugs. Further, the release profile was predicted by the Higuchi and Peppas models. The results suggest that the release mechanism is governed by Fickian diffusion for the initial 8 h followed by anomalous transport for longer times. The cytocompatibility of the materials was evaluated by in vitro cytotoxicity tests. Both MTT and live/dead assay observations indicated that the material had no adverse impact on cell proliferation. The results imply that these composites are bioactive with good cytocompatibility. Although all the matrices showed good results, the one with polyvinyl alcohol exhibited higher biocompatibility and drug release efficiency. A plausible explanation is proposed for the enhanced drug delivery efficiency of these materials.

Comparative Study of Biomimetic Iron Oxides Synthesized Using Microwave Induced and Conventional Method

Aqueous ferrofluids having high steric stability were prepared biomimetically by chemical co-precipitation of iron salts in poly (vinyl) alcohol. Both conventional and microwave heating modes were used for the synthesis of the fluids; the bottleneck of conventional heating being low saturation magnetization. The uniqueness of this work lies in the fact that for the same initial constituents, microwave irradiation enhances saturation magnetization without compensating stability. Superparamagnetic iron oxide nanoparticles with a narrow size distribution were formed, and structural investigations of the dried fluid revealed that microwave irradiation increased the polydispersity and the average particle size of the nanocomposites which led to a loss of long-range ordering. X-ray diffraction patterns of the synthesized ferrofluids showed an increase in crystallinity for the microwave irradiated sample. All these structural rearrangements affected the saturation magnetization (Ms) which more than doubled from 12.97 to 27.07 kAm-1 with microwave irradiation.

Colloidal graphite/graphene nanostructures using collagen showing enhanced thermal conductivity

In the present study, the exfoliation of natural graphite (GR) directly to colloidal GR/graphene (G) nanostructures using collagen (CL) was studied as a safe and scalable process, akin to numerous natural processes and hence can be termed “biomimetic”. Although the exfoliation and functionalization takes place in just 1 day, it takes about 7 days for the nano GR/G flakes to stabilize. The predominantly aromatic residues of the triple helical CL forms its own special micro and nanoarchitecture in acetic acid dispersions. This, with the help of hydrophobic and electrostatic forces, interacts with GR and breaks it down to nanostructures, forming a stable colloidal dispersion. Surface enhanced Raman spectroscopy, X-ray diffraction, photoluminescence, fluorescence, and X-ray photoelectron spectroscopy of the colloid show the interaction between GR and CL on day 1 and 7. Differential interference contrast images in the liquid state clearly reveal how the GR flakes are entrapped in the CL fibrils, with a corresponding fluorescence image showing the intercalation of CL within GR. Atomic force microscopy of graphene-collagen coated on glass substrates shows an average flake size of 350 nm, and the hexagonal diffraction pattern and thickness contours of the G flakes from transmission electron microscopy confirm ≤ five layers of G. Thermal conductivity of the colloid shows an approximate 17% enhancement for a volume fraction of less than approximately 0.00005 of G. Thus, through the use of CL, this new material and process may improve the use of G in terms of biocompatibility for numerous medical applications that currently employ G, such as internally controlled drug-delivery assisted thermal ablation of carcinoma cells.