Narayan Bhattarai

Chitosan-based hydrogels for controlled, localized drug delivery.

Hydrogels are high-water content materials prepared from cross-linked polymers that are able to provide sustained, local delivery of a variety of therapeutic agents. Use of the natural polymer, chitosan, as the scaffold material in hydrogels has been highly pursued thanks to the polymers biocompatibility, low toxicity, and biodegradability. The advanced development of chitosan hydrogels has led to new drug delivery systems that release their payloads under varying environmental stimuli. In addition, thermosensitive hydrogel variants have been developed to form a chitosan hydrogel in situ, precluding the need for surgical implantation. The development of these intelligent drug delivery devices requires a foundation in the chemical and physical characteristics of chitosan-based hydrogels, as well as the therapeutics to be delivered. In this review, we investigate the newest developments in chitosan hydrogel preparation and define the design parameters in the development of physically and chemically cross-linked hydrogels.

Specific targeting of brain tumors with an optical/magnetic resonance imaging nanoprobe across the blood-brain barrier.

Nanoparticle-based platforms have drawn considerable attention for their potential effect on oncology and other biomedical fields. However, their in vivo application is challenged by insufficient accumulation and retention within tumors due to limited specificity to the target, and an inability to traverse biological barriers. Here, we present a nanoprobe that shows an ability to cross the blood-brain barrier and specifically target brain tumors in a genetically engineered mouse model, as established through in vivo magnetic resonance and biophotonic imaging, and histologic and biodistribution analyses. The nanoprobe is comprised of an iron oxide nanoparticle coated with biocompatible polyethylene glycol-grafted chitosan copolymer, to which a tumor-targeting agent, chlorotoxin, and a near-IR fluorophore are conjugated. The nanoprobe shows an innocuous toxicity profile and sustained retention in tumors. With the versatile affinity of the targeting ligand and the flexible conjugation chemistry for alternative diagnostic and therapeutic agents, this nanoparticle platform can be potentially used for the diagnosis and treatment of a variety of tumor types.

PEG-mediated synthesis of highly dispersive multifunctional superparamagnetic nanoparticles: their physicochemical properties and function in vivo.

Multifunctional superparamagnetic nanoparticles have been developed for a wide range of applications in nanomedicine, such as serving as tumor-targeted drug carriers and molecular imaging agents. To function in vivo, the development of these novel materials must overcome several challenging requirements including biocompatibility, stability in physiological solutions, nontoxicity, and the ability to traverse biological barriers. Here we report a PEG-mediated synthesis process to produce well-dispersed, ultrafine, and highly stable iron oxide nanoparticles for in vivo applications. Utilizing a biocompatible PEG coating bearing amine functional groups, the produced nanoparticles serve as an effective platform with the ability to incorporate a variety of targeting, therapeutic, or imaging ligands. In this study, we demonstrated tumor-specific accumulation of these nanoparticles through both magnetic resonance and optical imaging after conjugation with chlorotoxin, a peptide with high affinity toward tumors of the neuroectodermal origin, and Cy5.5, a near-infrared fluorescent dye. Furthermore, we performed preliminary biodistribution and toxicity assessments of these nanoparticles in wild-type mice through histological analysis of clearance organs and hematology assay, and the results demonstrated the relative biocompatibility of these nanoparticles.

Chlorotoxin Labeled Magnetic Nanovectors for Targeted Gene Delivery to Glioma

Glioma accounts for 80% of brain tumors and currently remains one of the most lethal forms of cancers. Gene therapy could potentially improve the dismal prognosis of patients with glioma, but this treatment modality has not yet reached the bedside from the laboratory due to the lack of safe and effective gene delivery vehicles. In this study we investigate targeted gene delivery to C6 glioma cells in a xenograft mouse model using chlorotoxin (CTX) labeled nanoparticles. The developed nanovector consists of an iron oxide nanoparticle core, coated with a copolymer of chitosan, polyethylene glycol (PEG), and polyethylenimine (PEI). Green fluorescent protein (GFP) encoding DNA was bound to these nanoparticles, and CTX was then attached using a short PEG linker. Nanoparticles without CTX were also prepared as a control. Mice bearing C6 xenograft tumors were injected intravenously with the DNA-bound nanoparticles. Nanoparticle accumulation in the tumor site was monitored using magnetic resonance imaging and analyzed by histology, and GFP gene expression was monitored through Xenogen IVIS fluorescence imaging and confocal fluorescence microscopy. Interestingly, the CTX did not affect the accumulation of nanoparticles at the tumor site but specifically enhanced their uptake into cancer cells as evidenced by higher gene expression. These results indicate that this targeted gene delivery system may potentially improve treatment outcome of gene therapy for glioma and other deadly cancers.

Functionalized Nanoparticles with Long-Term Stability in Biological Media†

Nanoparticles have been extensively studied in recent years due to their unique optical, magnetic, or chemical properties.[1-4] While many synthetic methods have been investigated, an effective way to produce ultrafine and monodisperse nanoparticles with controllable sizes is thermal decomposition of precursors in organic solvents at high temperature.[5,6] In this approach, nanoparticles are stabilized by hydrophobic coatings and as a result, the as-synthesized nanoparticles can not be dispersed in aqueous solutions. In biomedical applications, nanoparticles have to be hydrophilic and maintain a superior stability in biological media. For advanced biomedical applications of nanoparticles (e.g., in vivo diagnostics and therapy), additional requirements such as minimization of non-specific uptake by reticulo-endothelial systems (RES) must be imposed in order to achieve long blood circulation time and high diagnostic or therapeutic efficiency.[7] In addition, the surface of the nanoparticle should possess functional groups for further conjugation of targeting ligand or therapeutic agents. Commonly used modification strategies for coating hydrophobic nanoparticles with hydrophilic polymers include ligand exchange,[8] micelle encapsulation,[9] and covalent bonding.[10] [11] Particularly, hydrophilic poly(ethylene glycol) (PEG) have been the focus of research as an effective coating materials for nanoparticles[2,12-15] due to its ability to resist protein fouling and provide steric hindrance preventing nanoparticle from aggregation.[12,16,17] Typical examples include coating PEG on hydrophobic nanoparticles via ligand exchange in which dopamine linked PEG replaces oleylamine & oleic acid on the particle[18] and coating PEG on iron oxide nanoparticles in situ via covalent bonding during the aqueous co-precipitation process.[10] Despite the advances made with those methods, the challenge remains in producing a highly stable polymeric coating on nanoparticles and retaining the long-term stability of functionalized nanoparticles in biological-relevant media.

Controlled synthesis and structural stability of alginate-based nanofibers

Electrospinning has emerged as a unique and versatile technique for the fabrication of nanofibrous structures with well-defined architecture to mimic the native extracellular matrix for tissue engineering applications. In this study, natural polymer alginate-based nanofibers were fabricated by electrospinning blend solutions of alginate and polyethylene oxide (PEO). To obtain better fibrous morphology and structural uniformity, the influence of alginate/PEO ratio and surfactants on the electrospun products were investigated. This study elucidated that polymer solution viscosity is a key factor that regulates the electrospinnability of the solution and the structure of the electrospun product. The sustained structural integrity of nanofibers in aqueous environments as well as simulated body fluid, which is essential for tissue engineering applications, was improved by crosslinking. This study also revealed that the polymer solution properties and thus the solution spinnability changed over storage time in the ambient environment, which can be a major source in causing the problem of reproducibility or resulting in differed structures when the solution is electrospun at different times. In light of the general biocompatibility of alginate, the technical approaches introduced and the underlying mechanisms revealed in this study may be of benefit to the production of alginate-based nanofibrous matrices for a wide range of tissue engineering applications.

Vanadium pentoxide nanofibers by electrospinning

New vanadate fibers with nano- to submicron diameter were prepared by electrospinning using vanadium sol and poly(vinylacetate) (PVAC) solutions followed by thermal treatment. The PVAC has been applied as structure directing template for the synthesis of vanadium oxide fibers. The fibers were characterized by SEM, AFM, XRD and IR spectra.

The photoluminescence properties of zinc oxide nanofibres prepared by electrospinning

The morphology and optical properties of zinc oxide fibres with diameters in the nanometre to micrometre range are reported. The PVA/zinc acetate organic/inorganic hybrid nanofibres were successfully prepared by electrospinning using polyvinyl alcohol (PVA) and zinc acetate. Pure zinc oxide fibres were obtained by high-temperature calcination of the hybrid fibres in air. The nanofibres were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), x-ray diffractometry (XRD) and Raman spectroscopy. The photoluminescence spectra under excitation at 325 nm showed an ultraviolet emission at 3.13 eV and a green emission at 2.21 eV. These nanofibres could be used as light emitting devices in nanoscale optoelectronic applications.

Preparation and morphology of niobium oxide fibres by electrospinning

Abstract Niobium oxide/poly(vinylacetate) composite nanofibres have been prepared by electrospinning method. Pure ceramic niobium oxide fibres were obtained by high temperature calcination of the organic–inorganic composite nanofibres. The materials have been characterised by scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD) and infra-red (IR) spectroscopy. It has been observed that both the morphology and the crystallinity of the fibres depend on the calcination temperature.

Rapid Pharmacokinetic and Biodistribution Studies Using Cholorotoxin-Conjugated Iron Oxide Nanoparticles: A Novel Non-Radioactive Method

Background Recent advances in nanotechnology have led to the development of biocompatible nanoparticles for in vivo molecular imaging and targeted therapy. Many nanoparticles have undesirable tissue distribution or unacceptably low serum half-lives. Pharmacokinetic (PK) and biodistribution studies can help inform decisions determining particle size, coatings, or other features early in nanoparticle development. Unfortunately, these studies are rarely done in a timely fashion because many nanotechnology labs lack the resources and expertise to synthesize radioactive nanoparticles and evaluate them in mice. Methodology/Principal Findings To address this problem, we developed an economical, radioactivity-free method for assessing serum half-life and tissue distribution of nanoparticles in mice. Iron oxide nanoparticles coated with chitosan and polyethylene glycol that utilize chlorotoxin as a targeting molecule have a serum half-life of 7–8 hours and the particles remain stable for extended periods of time in physiologic fluids and in vivo. Nanoparticles preferentially distribute to spleen and liver, presumably due to reticuloendothelial uptake. Other organs have very low levels of nanoparticles, which is ideal for imaging most cancers in the future. No acute toxicity was attributed to the nanoparticles. Conclusions/Significance We report here a simple near-infrared fluorescence based methodology to assess PK properties of nanoparticles in order to integrate pharmacokinetic data into early nanoparticle design and synthesis. The nanoparticles tested demonstrate properties that are excellent for future clinical imaging strategies and potentially suitable for targeted therapy.