Microneedles fabricated with two-photon polymerization:
Credit: Royal Society of Chemistry

I first covered ACerS member Roger Narayan’s work in the field of two-photon polymerization a little more than a year ago in a story for ACerS’ membership magazine, the Bulletin. For several years, Narayan, a professor in the Joint Biomedical Engineering Department that is connected with NC State’s College of Engineering and the University of North Carolina at Chapel Hill, has been examining the use of this rapid prototyping approach using ceramic–polymer hybrid materials to create patient-specific microscale medical prostheses, scaffolds for tissue engineering and microscale medical devices.

One of set of applications he has been working on, in particular, is using two-photon polymerization to create arrays of fine microneedles. (Conceptually, Narayan’s polymerization process is like a 3D inkjet process that builds up structures on the nanoscale.)

Recently, Narayan coauthored a paper on the novel use of microneedles to deliver quantum dots into the skin. “Our findings are significant, in part, because this technology will potentially enable researchers to deliver quantum dots, suspended in solution, to deeper layers of skin. That could be useful for the diagnosis and treatment of skin cancers, among other conditions,” Narayan says in a news release from NCSU.

QDs, sometimes called “artificial atoms,” are semiconductor materials that fall into the category of nanocrystals, and they contain a variable number of electrons that occupy well-defined, discrete quantum states.

This groups is attracted to the use of QDs because of their ability to serve as fluorophores and also work as drug delivery vehicles. QD-based fluorescent probes can be engineered to be superior to organic dye fluorophore by being brighter and having better photostability (can fluoresce after one hour of continuous excitation), signal-to-noise ratio, emission ranges and flourescent lifetimes. Researchers report they can use their intense fluorescence to track individual molecules.

 

Sample quantum dot with bio coating. Credit: Histesh R. Patel

At this point, Narayan and the other researchers just are using the microneedles on pig skin and can capture images of the quantum dots entering the skin using multiphoton microscopy. Although this work is still preliminary, these images allow the researchers to verify the basic effectiveness of the microneedles as a delivery mechanism for quantum dots.

The hope is that multiphoton microscopy will have clinical applications using real-time imaging materials such as the quantum dots for faster diagnosis of cancers or other medical problems.

In the journal Science, a new device is described that fashions nanowires into a transistor small enough to probe the interior of cells.

A Harvard press release reports that the new device is smaller than many viruses and about one-hundredth the width of the probes now used to take cellular measurements, which can be nearly as large as the cells themselves. Being so thin, these transistors are less likely to damage cells upon insertion.

“Our use of these nanoscale field-effect transistors represents the first totally new approach to intracellular studies in decades, as well as the first measurement of the inside of a cell with a semiconductor device,” says senior author Charles Lieber. “The nanoFETs are the first new electrical measurement tool for intracellular studies since the 1960s, during which time electronics have advanced considerably.”

Lieber says nanoFETs could be used to measure ion flux or electrical signals in cells, particularly neurons. The devices could also be fitted with receptors or ligands to probe for the presence of individual biochemicals within a cell.

Lieber and colleagues found that by coating the structures with the same material cell membranes are made of (phospholipid bilayer) the devices are easily pulled into a cell via membrane fusion, a process related to that used to engulf viruses and bacteria.

Lieber and his coauthors found that introducing two 120º angles into a nanowire creates a single V-shaped 60º angle, perfect for a two-pronged nanoFET with a sensor at the tip of the V. The two arms can then be connected to wires to create a current through the nanoscale transistor.

A bone allograft being placed into position.

The University of the Basque Country (Universidad del País Vasco) reports that one of its Ph.D. students has developed a new porous, biodegradable nanocompound support for the regeneration of bone tissue. According to UPV, Beatriz Olalde, in her doctoral thesis, reported on her approach that combines polylactic acid, hydroxyapatite and carbon nanotubes to form a material that could be used instead of bone grafts. Her material interacts chemically and electrically with bone cells and adjoining tissue to speed bone replacement and recovery.

Olalde

Each of the components in Olalde’s foam-like material plays a specific role. The polylactic acid forms a basic biodegradable scaffold. Hydroxyapatite – a benign, bone-like bioceramic substance that is very compatible with tissues – is added attract cell growth and provide a source of calcium. The CNTs are added to provide strength. The CNTs also provide a material that reacts with an external electric field in a way that stimulates cell growth.

The desire for materials like Olalde’s (alloplastic grafts) stems from problems the medical profession faces when, due to events like large scale physical trauma or tumor removal, a patient loses a significant section of bone. Bone has the ability to regenerate itself to a large extent, but that requires time and support for the injured area.

Typically, bone grafts have been used either from the patient (an autograft), a living donor or a cadaver (allografts). But often a patient isn’t capable of providing the graft and donated bone raises complications due to tissue rejection issues, contamination, etc.

According to Olalde, trials involving both in vitro and in vivo experiments have shown satisfactory results. She says the foam displayed good mechanical properties and bone support. In in vivo trials, bone growth was observed after three weeks, and after 16 weeks this new bone showed mechanical, histomorphometric and densitometric properties similar to those of intact, healthy bone tissue.

Olalde has published before about polylactic acid and carbon nanotubes, and has collaborated with the University of Aberdeen, Scotland, and the Institute of Biomechanics of Valencia (IBV). She was awarded her Ph.D. and is currently working as a researcher in the Department of Biomaterials and Nanotechnologies Unit Tecnalia Health.

Samples of textures achieved with laser-engineered bioceramic coatings. These coatings
can provide a 3D topographic cue and appropriate chemistry suitable for load bearing
implant applications. Credit: Narendra Dohotre.

Surfaces of artificial implants that mimic natural structures are expected to improve biocompatibility by enhancing the connection between the living bone and the surface. The challenge is to create such multiscaled surfaces with common production facilities. Particular laser process parameters may be one way to the desired surface structure.

Anil Kumar Kurella and Narendra Dahotre from the Department of Materials Science and Engineering at the University of Tennessee now report calcium phosphate CaP–TiO₂ coatings with multiscale features on Ti alloys via laser surface engineering for enhanced biocompatibility. The authors have deposited a layer of CaP tribasic material onto a Ti alloy surface by air spraying. Laser processing at multiple speeds on these surfaces generates coatings of different morphology and chemistry.

Scanning electron microscopy shows the porous nature of the laser-processed surfaces. The nature of porosity varies with processing speeds: At lower speeds TiO₂ is the abundant phase, while at medium and higher speeds CaTiO₃ and CaP are the preferred phases. CaP–TiO₂ features self-assembled into circular rings; CaTiO₃ evolved into star-shaped features at the center of these circular rings.

The authors correlate the different morphologies arising from the different processing speeds with biomimetic precipitation of hydroxyapatite on these multiscaled features, an indirect indication of the biocompatibility of the modified surface. For medium processing conditions, Kurella and Dahotre suggest surfaces with multiscale features, similar to those seen in natural environments. In comparison, a lower processing speed results primarily in porous surfaces of cuboid features and star-shape particles inside. Faster laser-processing conditions produce a mix of reacted and unreacted zones. The latter two are unlike natural structures, this has a negative influence on biocompatibility.

The study shows that a simple modulation of the laser process parameters can improve biocompatibility of artificial implants.

Editor’s note: Martin Grolms is a writer for Material Views

Ultrasensitive Nanomechanical Transducers Based on Nonlinear Resonance, one of ORNL’s 2010 R&D 100 award winners. (Credit: ORNL.)

R&D Magazine awarded DOE and other federal labs with 50 of its R&D 100 Awards. The awards, sometimes referred to as the “Academy Awards of Science,” are presented to those labs and companies that have been a major contributor to the development of “one of the 100 most technologically significant new products of 2010.”

“The large number of winners from the Department of Energy’s national labs every year is a clear sign that our labs are doing some of the most innovative research in the world. This work benefits us all by enhancing America’s competitiveness, ensuring our security, providing new energy solutions, and expanding the frontiers of our knowledge. Our national labs are truly national treasures, and it is wonderful to see their work recognized once again,” says Energy Secretary Steven Chu.

U.S. federal labs have a history of being highly recognized for technological developments and materials innovation through these awards. Here are the labs that are winners this year:

• Ames National Lab
• Argonne National Lab
• Idaho National Lab
• Lawrence Berkeley National Lab
• Lawrence Livermore National Lab
• Los Alamos National Lab
• NASA Glenn Research Center
• National Energy Technology Lab
• National Renewable Energy Lab
• Oak Ridge National Lab
• Pacific Northwest National Lab
• Sandia National Lab
• Army Engineer R&D Center

The biggest winner is the Lawrence Livermore National Lab which is recognized with 10 awards.

ACerS Corporate Member Toyota Central R&D Labs was also recognized by R&D Magazine for their Permanently Engaged Gear Starting Mechanism for Stop and Start System (Mechanical Devices).

All of the award winners can be seen here.