3-D Printing Materials
Additive manufacturing is the act of synthesizing three-dimensional objects through successively forming layers of material from a computer model. It enables rapid prototyping and design optimizations that are unable to be produced through conventional manufacturing techniques. Additive manufacturing comes in many forms depending on the desired printing speed, resolution, material used, and quality of the final part. Stereolithography (SLA) is the oldest and one of the most commonly implemented 3D printing methods. In SLA a moveable build platform is placed in a bath of photo-curable pre-polymer resin. The platform is positioned so that a thin layer of resin is over the build platform. A laser or projector then selectively cures the thin layer into the desired shape. The build platform is then moved to flow another thin layer of resin on top of the initial cured layer. This process is repeated until the final three dimensional part is formed. The part is then removed from the resin bath, cleaned, and post-cured. The entire fabrication process may take between several hours to several days depending on the part size, complexity, and photopolymer resin used. The vast majority of photopolymer resins are hybrid acrylate-epoxide systems. This combines the rapid rate of acrylate polymerization with the low cure stress of epoxides. However, neither acrylates nor epoxides have high toughness. The resultant materials are typically brittle. The inability to produce highly tough photopolymers for SLA printing combined with the mechanical anisotropy found in most 3D printed parts has limited the proliferation of additive manufacturing systems in industries where toughness is critical.
Industrial and final-part applications requiring high mechanical strength, mechanical isotropy, and complex part geometries.
Flexible, Softening Bioelectronics
The thiol-ene reaction mechanism provides a versatile chemical toolbox for solvent-free polymerization of organic materials with applications spanning the oil and gas, semiconductor, and flexible electronics industries. However, given the flexibility of the resulting thioether linkage formed during the polymerization of a thiol and an alkene, these materials typically exhibit low glass transition temperatures (Tg). This leads to materials that exhibit rubber-like properties (high gas permeability, elevated coefficient of thermal expansion, etc.) at high temperatures. In this work, synthesis of monomers with stiff intra-thiol linkages, the bulk thiol-maleimide reaction, and post-polymerization oxidation of the thioether linkage are all explored as mechanisms for the rational design and engineering of high-Tg thiol-ene networks, with a primary focus on flexible bioelectronics such as intracortical microelectrode arrays.
Shape Memory Polymers
“Shape memory polymers (SMPs) are stimuli-responsive “smart” polymers that can remember a primary (permanent) shape after having been stabilized in a secondary (temporary) shape by heating.
The shape memory effect (SME) is a result of the structure and morphology of the polymer together with the applied processing and programming procedure. In general, an SMP consists of cross-links or netpoints, which determine the permanent shape. This is because the polymer is required to remain in a stable network structure so as to recover to its permanent shape. On the other hand, an SMP consists of switching segments which are used to create and maintain the temporary shape.
On the basis of the nature of their network structure, SMPs can be subdivided into physically and chemically cross-linked. Thus, SMPs may be thermoplastic as well as thermoset. Further separation can be made according to the thermal transition Ttrans of the particular switching segment on which the triggering of the SME is based. Either the transition temperature Ttrans is the glass transition temperature Tg or the melting temperature Tm.
The permanent shape of the polymer is set during the processing. The programming of an SMP from the permanent shape into a temporary shape typically consists of heating up, deforming and cooling the sample. When heated above the transition temperature Ttrans, the viscoelasticity of the SMP increases. Thus, the sample can easily be deformed into the desired temporary shape through application of an external force. The new shape can then be fixed by cooling the polymer below Tg or Tc, respectively.Subsequently, the remaining stress can be released and the polymer remains stable in that new shape until the SME is triggered by re-heating the sample above Ttrans.Hence, the polymer almost recovers its permanent shape. No recovery to the temporary shape can be observed on subsequent cooling, thus the described effect is termed one-way SME.
The thermally induced SME may either be triggered via direct or indirect heating. In the case of the latter, the polymer is doped with suitable fillers, which enable selective heating of the polymer by electric current, magnetic fields or irradiation with light.
SMPs have advantages compared to other shape memory materials, such as alloys. Particular highlights are their ability to sustain high elastic deformation (strains >200%) and their tailorable switching temperature. Besides that, SMPs are characterized by low density, low cost, easy processability, and high shape recoverability as well as by potential biocompatibility and biodegradability.
There are manifold areas for potential application of SMPs, ranging from biomedical over aerospace to textile applications.
Proposed biomedical applications for SMPs are diverse and comprise drug delivery systems, flexible, softening bioelectronics, as well as temperature and pressure sensors. Beyond that, they may be used as devices for minimal invasive surgery such as blood clot removal devices, vascular stents, orthopedics, orthodontics and sutures for wound closure
SMPs are also attractive for aerospace applications due to their light weight. Applied as deployable hinges or booms they are space saving upon transportation into space and allow self-unfolding of different devices such as solar arrays or antennas.
Textile industry is another emerging field for potential shape memory applications. Incorporated as fibers into textiles, SMPs may yield smart functionalities, such as moisture/temperature management, controlled release of drugs and odor, wound monitoring, smart wetting properties, protection against extreme climatic conditions and wrinkle-free fabrics.”
Reference: Ecker, M. Development, Characterization and Durability of Switchable Information Carriers based on Shape Memory Polymers. Dissertation, Freie Universität Berlin, Berlin, 2015.
Environmentally benign approach for carbon fiber production Carbon fibers are predominantly made from polyacrylonitrile (PAN) based precursors which are solution spun using hazardous solvent that is not a green technology. Use of melt processable precursors has long been pursued as a solution for the problem. A successful preparation of carbon fiber is achieved by melt spinning of acrylonitrile-co-1-vinylimidazole (AN/VIM) copolymer. A carbon fiber prepared from the copolymer yielded a high tensile strength (TS) of 1.9 GPa with Young’s modulus (YM) of 196 GPa.
These thin filaments, a tenth the thickness of a human hair, are now available in a wide range of useful forms. The fibers are bundled, woven and shaped into tubes and sheets (up to ½” thick) for construction purposes, supplied as cloth for molding, or just regular thread for filament winding. Carbon fiber has gone to the moon on spacecraft, but it is also used widely in aircraft components and structures, where its superior strength to weight ratio far exceeds that of any metal. 30% of all carbon fiber is used in the aerospace industry. From helicopters to gliders, fighter jets to microlights, carbon fiber is playing its part, increasing range and simplifying maintenance. The applications in the military are very wide ranging – from planes and missiles to protective helmets, providing strengthening and weight reduction across all military equipment. It takes energy to move weight – whether it is a soldier’s personal gear or a field hospital, and weight saved means more weight moved per gallon of gas. Carbon fiber offers several advantages over other materials in the medical field, including the fact that it is ‘radiolucent’ – transparent to X-rays and shows as black on X-ray images. It is used widely in imaging equipment structures to support limbs being X-rayed or treated with radiation. The use of carbon fiber to strengthen of damaged cruciate ligaments in the knee is being researched, but probably the most well known medical use is that of prosthetics – artificial limbs.
We are trying to develop new cellular-engineering technologies to facilitate the application of gene editing to complex systemic diseases. We want to genetically engineer robust disease prevention. One such application is the selective depletion of disease-causing proteins. Diseases including allergies and asthma, autoimmune diseases, and neurodegenerative conditions like Alzheimer’s Disease are mediated largely by specific circulating proteins, namely IgE antibodies, IgG antibodies, and amyloid-beta proteins. We seek to genetically engineer cells to internalize and destroy pathogenic antibodies and proteins. We believe our work here has the potential to lay the foundation for a revolution in how we approach a multitude of diseases ranging from allergy and asthma to autoimmune disorders to neurodegenerative disorders.
Autoimmune and neurodegenerative diseases