Highly Aligned Electrospun Fibers and Mats

Current scaffold designs and materials do not provide all of the appropriate cues necessary to mimic in-vivo conditions for tissue engineering and stem cell engineering applications. It has been hypothesized that many biomaterials, such as bone, muscle, brain and heart tissue exhibit piezoelectric and ferroelectric properties. Typical cell seeding environments incorporate biochemical cues and more recently mechanical stimuli, however, electrical cues have just recently been incorporated in standard in-vitro examinations. In order to develop their potential further, novel scaffolds are required to provide adequate cues in the in-vitro environment to direct stem cells to differentiate down controlled pathways or develop novel tissue constructs. This invention is for a scaffold that provides for such cues by mimicking the native biological environment, including biochemical, topographical, mechanical and electrical cues.

NASA's miniaturized electrosprayer offers a new technology that may support the next generation of portable and/or of precise electrosprayers. Developed for applying water to plants in space where gravimetric methods do not apply, this sprayer may also enable the delivery of a precise liquid for terrestrial uses without relying on pressurized air. Electrospraying (aka electrostatic spraying) is a technique where droplets are charged to enhance surface adhesion and coverage efficiency. Various electrospray variants are used in a host of industries to coat auto parts, apply pesticides and nutrients to crops, and more. Commercially-available electrosprayers are generally large, air-assisted devices that traverse up to 20 feet in the air and require large amounts of liquid and electrical power. NASA's miniaturized electrosprayer system does not require compressed air, uses far less liquid, and concentrates the mist in an area less than 2 feet away. The system only needs enough power to charge the droplets at the spray nozzle, so it may use small batteries (e.g., AAA batteries). The new electrosprayer implements a unique nozzle design that imparts a high charge-to-mass ratio on the spray and increases coverage efficiency. Thus, the miniaturized electrosprayer can be placed inside a portable, handheld sprayer or be used as a stationary device for a wide range of uses, particularly when spraying expensive chemicals (e.g., plant nutrients) and when precise, efficient spraying is required (e.g., industrial coatings, disinfectants, etc.).

Carbon nanotubes (CNTs) show promise for multifunctional materials for a range of applications due to their outstanding combination of mechanical, electrical and thermal properties. However, these promising mechanical properties have not translated well to CNT nanocomposites fabricated by conventional methods due to the weak load transfer between tubes or tube bundles. In this invention, the carbon nanotube forms such as sheets and yarns were modified by in-situ polymerization with polyaniline, a -conjugated conductive polymer. The resulting CNT nanocomposites were subsequently post-processed to improve mechanical properties by hot pressing and carbonization. A significant improvement of mechanical properties of the polyaniline/carbon nanotube nanocomposites was achieved through a combination of stretching, polymerization, hot pressing, and carbonization.

NASA GRC has developed several different 3D printing techniques to fabricate polymer aerogel structures; different techniques are suitable for different polymer aerogel formulations. In general, the methods entail forming a first liquid comprising a polymer precursor and cross-linker, forming a second liquid comprising a catalyst for reacting a polymer precursor to form a polymer, then 3D printing the aerogel structure with a mixture of the two liquids onto or into a medium. Specifically, NASA's polymer aerogel 3D printing techniques include: direct syringe printing, dual-syringe printing with static mixing head, direct syringe printing of photocurable formulations, and a unique rapid prototyping method involving a sacrificial bath. The direct syringe process relies upon gelation to occur once the gel is extruded from the print head to the substrate. In the dual-syringe printing process, one syringe contains polyamic acid and the other contains a catalyst. These are mixed in a static mixing head to allow for curing/gelation upon extrusion. For direct syringe printing of photocurable polymer aerogel formulations, a UV pen and array follow the printed gel during extrusion to induce gelation. Finally, the rapid prototyping method uses a bath of highly viscosity, low shear gel that provides a low drag, flexible yet supportive medium in which to print the polymer aerogel. In other embodiments, a bath of polyamic acid is used while cross-linkers and catalysts are introduced via printing, or vice versa (polyamic acid is introduced via printing into a bath of cross-linkers and catalysts). In addition to complex geometries, these layered 3D printing processes allow for the fabrication of chemically-bonded (cross-linked) structures composed of layers of different polymer aerogel formulations (i.e., fabrication of structures with tailored chemistries / properties). Previously, joining different polymer aerogel formulations into a single structure required the fabrication of different formulations using individual molds and joining them using an adhesive, potentially introducing weak fracture points.

Researchers at NASA's Glenn Research Center have developed an approach to significantly improve the mechanical properties and durability of aerogels without adversely affecting their desirable properties. This approach involves coating conformally and cross-linking the individual skeletal aerogel nanoparticles with engineering polymers such as isocyanates, epoxies, polyimides, and polystyrene. The mechanism of cross-linking has been carefully investigated and is made possible by two reactions: a reaction between the cross-linker and the surface of the aerogel framework and a reaction propagated by the cross-linker with itself. By tailoring the aerogel surface chemistry, Glenn's approach accommodates a variety of different polymer cross-linkers, including isocyanates, acrylates, epoxies, polyimides, and polystyreneenabling customization for specific mission requirements. For example, polystyrene cross-linked aerogels are extremely hydrophobic, while polyimide versions can be used at higher temperatures. Recent work has led to the development of strong aerogels with better elastic properties, maintaining their shape even after repeated compression cycling. By tailoring the internal structure of the silica gels in combination with a polymer conformal coating, the aerogels may be dried at the ambient condition without supercritical fluid extraction.