Saturday, July 05, 2008
Fabrication and characterization of a boehmite nanoparticle
W. J. Ng Æ S. Ramakrishna
Abstract
fiber membrane with sorptive characteristics intended for
removal of heavy metals was investigated. The electrospun
fiber membrane was impregnated with nano-boehmite
particles. The latter had been selected to increase surface
area of the active component. Cd (II) was chosen as the
challenge bivalent cation. The sorption capacity of the
nano-boehmite was studied as a function of pH and time.
Electrospinning was used to prepare the composite submicron
fiber membrane impregnated with boehmite
nanoparticles. The later was blended with the polymer to
produce a homogenous mixture before electrospinning.
Two polymers, the hydrophobic/PCL/and hydrophilic/
Nylon-6/, were chosen to serve as the support for the
boehmite. The nanoparticles and resulting composite
membranes were characterized using SEM, TEM, and
XRD techniques. XRD data confirmed the presence of
nano-boehmite particles in the nanofibers membrane. The
membranes so prepared were challenged with aqueous
solutions of Cd in batch isotherm tests. Atomic absorption
spectroscopy results show sorption of Cd (II) by boehmite
impregnated electospun membrane was possible and a
capacity of 0.20 mg/g was achieved.
Reference:
 | Garudadhwaj Hota Email: garud31@yahoo.com Email: garud@nitrkl.ac.in |
References
http://www.springerlink.com/content/4u5m58862368u14v/fulltext.pdf
Nanofibers and their applications in tissue engineering
Int J Nanomedicine. 2006 March; 1(1): 15–30. | PMCID: PMC2426767 |
Developing scaffolds that mimic the architecture of tissue at the nanoscale is one of the major challenges in the field of tissue engineering. The development of nanofibers has greatly enhanced the scope for fabricating scaffolds that can potentially meet this challenge. Currently, there are three techniques available for the synthesis of nanofibers: electrospinning, self-assembly, and phase separation. Of these techniques, electrospinning is the most widely studied technique and has also demonstrated the most promising results in terms of tissue engineering applications. The availability of a wide range of natural and synthetic biomaterials has broadened the scope for development of nanofibrous scaffolds, especially using the electrospinning technique. The three dimensional synthetic biodegradable scaffolds designed using nanofibers serve as an excellent framework for cell adhesion, proliferation, and differentiation. Therefore, nanofibers, irrespective of their method of synthesis, have been used as scaffolds for musculoskeletal tissue engineering (including bone, cartilage, ligament, and skeletal muscle), skin tissue engineering, vascular tissue engineering, neural tissue engineering, and as carriers for the controlled delivery of drugs, proteins, and DNA. This review summarizes the currently available techniques for nanofiber synthesis and discusses the use of nanofibers in tissue engineering and drug delivery applications.
In a more recent study, Malker et al determined the bioactivity of the PA self-assemblies by incorporating bioactive sequences within the PA. Their results indicated that the formation of the triple-helix for such a PA (ie, containing a bioactive sequence) produced an ordered structure of the bioactive sequence on the exterior of the triple helix that led to a favorable cell response (ie, cell adhesion, spreading, and proliferation) because of the similarity of the self-assembled triple helix to natural ECM. The results of this study and another previous study by Fields et al indicated that these PA structures have potential to be used as surface coatings for biomaterials to improve biocompatibility (Fields et al 1998; Malkar et al 2003).
Based on prior knowledge of PA self-assembling systems (Berndt et al 1995; Stupp et al 1997; Fields et al 1998; Yu et al 1998; Malkar et al 2003), Stupp et al designed di- and tri-block PAs that self-assembled into a rod-like architecture. By engineering the peptide head group of the PA, the authors developed a new technique for the self-assembly of PAs into nanofibers using pH control (Hartgerink et al 2001).
The synthesis of the PA involved the following salient features (Hartgerink et al 2001).
- Incorporation of phosphoserin residue to enable enhanced hydroxyapatite (HA) mineralization.
- Incorporation of RGD (Arg-Gly-Asp) peptide to increase integrin-mediated cell adhesion.
- Incorporation of four consecutive cystine residues, which form inter-molecular disulfide bonds that polymerize to provide improved structural stability.
- Incorporation of a flexible linker region consisting of three glycine residues to provide flexibility to the head group.
The preparation of nanofibers involved reduction of cystine residues of the PA to free thiol groups using dithiotheritol followed by acidification below pH 4 to cause self-assembly of the PAs into cylindrical micelles/nanofibers. The resulting nanofibers had a hydrophobic core of alkyl residues and a hydrophilic exterior lined by peptide residues. Their results indicated that the nanofibers produced by self-assembly were approximately 5–8 nm in diameter and several microns in length (see Figure 2). Hartgerink et al further investigated the mineralization potential of these nanofibers. The authors observed the formation of HA crystals that were oriented along the length of the nanofibers. This nanoscale orientation resembles the orientation of HA crystals in mineralized ECM and collagen fibers of bone tissue. Since the mineralized, self-assembled nanofibers were similar to the lowest level of the hierarchical structure of bone tissue, the authors believe that the nanofibers show potential to be used as primary building blocks for the engineering of bone or other mineralization tissue (Hartgerink et al 2001).
 | Figure 2 Transmission electron micrograph (TEM) of nanofibers formed from peptide amphiphile molecules (N terminus – C10H19O and Peptide – CCCCGG GS(PO4)RGD) that self-assembled by drying directly onto a TEM grid without adjusted pH (negatively (more ...) |
In another study, Hartgerink et al (2002) investigated the effect of variations in the molecular structure of the PAs on the self-assembled nanofibers. It was observed that modifications in the alkyl chain length of the PA alter the pH sensitivity of nanofibers, which affects self-assembly. Modification of the C- terminal region (ie, the region that is expressed on the surface of the nanofibers after self-assembly) led to changes in length and stiffness of the nanofibers. Replacement of cystine residues by alanine did not affect the self-assembly of the PAs into nanofibers. These results suggested that the self-assembled nanofibers show potential for development as novel biomaterials (Hartgerink et al 2002; Hwang et al 2002). This study also introduced three different methods of forming self-assembled PAs, including pH-controlled self-assembly, drying on surface-induced self-assembly, and divalent-ion-induced self-assembly. The study demonstrated that PAs can be self-assembled reversibly into nanofibers that result in the formation of gels through pH changes. These PA nanofibers can also be reversibly polymerized to improve their stability. The reversibility of these two procedures makes the self-assembly technique attractive as it enables the fabrication of remarkably versatile materials. In addition, this technique produces a good yield of nanofibers with low polydispersity.
Therefore, the self-assembly technique, by virtue of the modifications possible in the structure of the PA, enables a variety of self-assemblies including layered and lamellar structures, and by virtue of the aforementioned reversibilities lends flexibility to the system. Thus, the self-assembly technique shows good potential for further exploration with the goal of designing novel scaffolds for tissue engineering applications.
Reference: http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=2426767Monday, June 30, 2008
Functional Self-Assembled Nanofibers by Electrospinning
A. Greiner1 and J. H. Wendorff1
| (1) | Department of Chemistry and Center of Material Science, Philipps-University, 35032 Marburg, Germany |
Abstract Electrospinning constitutes a unique technique for the production of nanofibers
with diameters down to the range of a few nanometers. In strong contrast to conventional
fiber producing techniques, it relies on self-assembly processes driven by the Coulomb interactions
between charged elements of the fluids to be spun to nanofibers. The transition
from a macroscopic fluid object such as a droplet emerging from a die to solid nanofibers
is controlled by a set of complex physical instability processes. They give rise to extremely
high extensional deformations and strain rates during fiber formation causing among
others a high orientational order in the nanofibers as well as enhanced mechanical properties.
Electrospinning is predominantly applied to polymer based materials including
natural and synthetic polymers, but, more recently, its use has been extended towards
the production of metal, ceramic and glass nanofibers exploiting precursor routes. The
nanofibers can be functionalized during electrospinning by introducing pores, fractal
surfaces, by incorporating functional elements such as catalysts, quantum dots, drugs,
enzymes or even bacteria. The production of individual fibers, random nonwovens, or
orientationally highly ordered nonwovens is achieved by an appropriate selection of electrode
configurations. Broad areas of application exist in Material and Life Sciences for
such nanofibers, including not only optoelectronics, sensorics, catalysis, textiles, high efficiency
filters, fiber reinforcement but also tissue engineering, drug delivery, and wound
healing. The basic electrospinning process has more recently been extended towards compound
co-electrospinning and precision deposition electrospinning to further broaden
accessible fiber architectures and potential areas of application.
Keywords Co-electrospinning · Electrospinning · Fiber architectures · Functions and applications · Nanofibers · Nonwovens · Precision electrospinning
Paper Reference: http://www.springerlink.com/content/v80076257623ul64/fulltext.pdf
Fabrics made of functional nanofibers that would decompose toxic industrial chemicals into harmless byproducts.
Cornell fiber scientist Juan Hinestroza is working with the
Potential applications include safety gear for
Hinestroza, assistant professor of fiber science in the
about $875,000 will go directly to Hinestoza's work. Both grants are multi-university collaborative efforts funded through the U.S. Defense Threat Reduction Agency.
"These nanostructures could be used in creating advanced air filtration and personal protection systems against airborne chemical threats and can find many applications in buildings, airplanes as well as personal respirators," Hinestroza said.
The first project, in collaboration with
"Understanding how these charges are injected into the fibers and how they are dissipated under different environmental conditions can open an avenue to significant improvements in air filtration technology," Hinestroza said.
The position and distribution of the electrical charges on the nanofibers will be fed into computerized fluid dynamics algorithms developed by Andrey Kutznetsov of NC State to predict the trajectory of the nanoparticles challenging the filter. Hinestroza and NC State's Warren Jasper pioneered work in this area a couple of years ago.
The second project, in collaboration with the University of California-Los Angeles (UCLA), will study the incorporation of a new type of molecules -- called metal organic polyhedra and metal organic frameworks -- onto polymeric nanofibers to trap dangerous gases as toxic industrial chemicals and chemical warfare agents, then decompose them into substances that are less harmful to humans and capture them for further decontamination. The synthesis of these molecules was pioneered by Omar Yaghi of UCLA.
This project will also look into the potential toxicity of these nanofiber-nanoparticle systems to humans in collaboration with Andre Nel from
Hinestroza's research group specializes in understanding and manipulating nanoscale phenomena in fiber and polymer science. Related Information: Hinestroza Research Group
By Sheri Hall assistant communications director for the
Cornell Chronicle: Susan Lang (607) 255-3613 ssl4@cornell.edu, Media Contact: Press Relations Office (607) 255-6074 pressoffice@cornell.edu
Friday, June 27, 2008
On The Boil: New Nano Technique Significantly Boosts Boiling Efficiency
ScienceDaily (June 27, 2008) — Whoever penned the old adage “a watched pot never boils” surely never tried to heat up water in a pot lined with copper nanorods.
A new study from researchers at Rensselaer Polytechnic Institute shows that by adding an invisible layer of the nanomaterials to the bottom of a metal vessel, an order of magnitude less energy is required to bring water to boil. This increase in efficiency could have a big impact on cooling computer chips, improving heat transfer systems, and reducing costs for industrial boiling applications.
“Like so many other nanotechnology and nanomaterials breakthroughs, our discovery was completely unexpected,” said Nikhil A. Koratkar, associate professor in the Department of Mechanical, Aerospace, and Nuclear Engineering at
Bringing water to a boil, and the related phase change that transforms the liquid into vapor, requires an interface between the water and air. In the example of a pot of water, two such interfaces exist: at the top where the water meets air, and at the bottom where the water meets tiny pockets of air trapped in the microscale texture and imperfections on the surface of the pot. Even though most of the water inside of the pot has reached 100 degrees Celsius and is at boiling temperature, it cannot boil because it is surrounded by other water molecules and there is no interface — i.e., no air — present to facilitate a phase change.
Bubbles are typically formed when air is trapped inside a microscale cavity on the metal surface of a vessel, and vapor pressure forces the bubble to the top of the vessel. As this bubble nucleation takes place, water floods the microscale cavity, which in turn prevents any further nucleation from occurring at that specific site.
Koratkar and his team found that by depositing a layer of copper nanorods on the surface of a copper vessel, the nanoscale pockets of air trapped within the forest of nanorods “feed” nanobubbles into the microscale cavities of the vessel surface and help to prevent them from getting flooded with water. This synergistic coupling effect promotes robust boiling and stable bubble nucleation, with large numbers of tiny, frequently occurring bubbles.
“By themselves, the nanoscale and microscale textures are not able to facilitate good boiling, as the nanoscale pockets are simply too small and the microscale cavities are quickly flooded by water and therefore single-use,” Koratkar said. “But working together, the multiscale effect allows for significantly improved boiling. We observed a 30-fold increase in active bubble nucleation site density — a fancy term for the number of bubbles created — on the surface treated with copper nanotubes, over the nontreated surface.”
Boiling is ultimately a vehicle for heat transfer, in that it moves energy from a heat source to the bottom of a vessel and into the contained liquid, which then boils, and turns into vapor that eventually releases the heat into the atmosphere. This new discovery allows this process to become significantly more efficient, which could translate into considerable efficiency gains and cost savings if incorporated into a wide range of industrial equipment that relies on boiling to create heat or steam.
“If you can boil water using 30 times less energy, that’s 30 times less energy you have to pay for,” he said.
The team’s discovery could also revolutionize the process of cooling computer chips. As the physical size of chips has shrunk significantly over the past two decades, it has become increasingly critical to develop ways to cool hot spots and transfer lingering heat away from the chip. This challenge has grown more prevalent in recent years, and threatens to bottleneck the semiconductor industry’s ability to develop smaller and more powerful chips.
Boiling is a potential heat transfer technique that can be used to cool chips, Koratkar said, so depositing copper nanorods onto the copper interconnects of chips could lead to new innovations in heat transfer and dissipation for semiconductors.
“Since computer interconnects are already made of copper, it should be easy and inexpensive to treat those components with a layer of copper nanorods,” Koratkar said, noting that his group plans to further pursue this possibility.
Along with Koratkar, co-authors of the paper include Rensselaer MANE Associate Professor Yoav Peles; Rensselaer mechanical engineering graduate student Zuankai Wang;
The research was funded by the National Science Foundation.
Journal reference:
1. Li et al. Nanostructured Copper Interfaces for Enhanced Boiling. Small, 2008; NA DOI: 10.1002/smll.200700991
Adapted from materials provided by Rensselaer Polytechnic Institute.
Wednesday, June 18, 2008
Nanotechnology, Biomolecules And Light Unite To 'Cook' Cancer Cells
Nanotechnology, Biomolecules And Light Unite To 'Cook' Cancer Cells
ScienceDaily (Jun. 17, 2008) — Researchers are testing a new way to kill cancer cells selectively by attaching cancer-seeking antibodies to tiny carbon tubes that heat up when exposed to near-infrared light.
Biomedical scientists at UT Southwestern Medical Center and nanotechnology experts from UT Dallas describe their experiments in a study available online and in an upcoming print issue of Proceedings of the National Academy of Sciences.
Scientists are able to use biological molecules called monoclonal antibodies that bind to cancer cells. Monoclonal antibodies can work alone or can be attached to powerful anti-cancer drugs, radionuclides or toxins to deliver a deadly payload to cancer cells.
In this study, the researchers used monoclonal antibodies that targeted specific sites on lymphoma cells to coat tiny structures called carbon nanotubes. Carbon nanotubes are very small cylinders of graphite carbon that heat up when exposed to near-infrared light. This type of light, invisible to the human eye, is used in TV remote controls to switch channels and is detected by night-vision goggles. Near-infrared light can penetrate human tissue up to about 1½ inches.
In cultures of cancerous lymphoma cells, the antibody-coated nanotubes attached to the cells' surfaces. When the targeted cells were then exposed to near-infrared light, the nanotubes heated up, generating enough heat to essentially "cook" the cells and kill them. Nanotubes coated with an unrelated antibody neither bound to nor killed the tumor cells.
"Using near-infrared light for the induction of hyperthermia is particularly attractive because living tissues do not strongly absorb radiation in this range," said Dr. Ellen Vitetta, director of the
"Demonstrating this specific killing was the objective of this study. We have worked with targeted therapies for many years, and even when this degree of specificity can be demonstrated in a laboratory dish, there are many hurdles to translating these new therapies into clinical studies. We're just beginning to test this in mice, and although there is no guarantee it will work, we are optimistic."
The use of carbon nanotubes to destroy cancer cells with heat is being explored by several research groups, but the new study is the first to show that both the antibody and the carbon nanotubes retained their physical properties and their functional abilities -- binding to and killing only the targeted cells. This was true even when the antibody-nanotube complex was placed in a setting designed to mimic conditions inside the human body.
Biomedical applications of nanoparticles are increasingly attracting the attention of basic and clinical scientists. There are, however, challenges to successfully developing nanomedical reagents. One is the potential that a new nanomaterial may damage healthy cells and organisms. This requires that the effects of nanomedical reagents on cells and organisms be thoroughly studied to determine whether the reagents are inherently toxic.
"There are rational approaches to detecting and minimizing the potential for nonspecific toxicity of the nanoparticles developed in our studies," said Dr. Rockford Draper, leader of the team from UT Dallas and a professor of molecular and cell biology.
Other researchers from UT Southwestern involved in the research were lead authors Pavitra Chakravarty, a graduate student in biomedical engineering, and Dr. Radu
The research was supported by the
Dr. Vitetta is a co-inventor on a patent describing the techniques outlined in the study.
Journal reference:
1. Chakravarty et al. Thermal ablation of tumor cells with antibody-functionalized single-walled carbon nanotubes. Proceedings of the National Academy of Sciences, Published online on June 16, 2008 DOI: 10.1073/pnas.0803557105
Adapted from materials provided by UT Southwestern Medical Center.
WEB Reference: http://www.sciencedaily.com/releases/2008/06/080616170807.htm