Joseph DeSimone Image Map
Jul 072015
 
150320HRTumblestonCover
Fig. 1. Science cover feature. CLIP was revealed on March 16, 2015 by Prof. DeSimone at TED2015 in Vancouver and in a paper published in Science.

Additive manufacturing (AM), commonly referred to as 3D printing, has soared in popularity in recent years in both academia and industry. In the past several decades, the technology has evolved to include many platforms that enable the regeneration of a 3D object from a computer aided design (CAD) file using a variety of materials. Typically, a CAD file is processed into a series of 2D cross sections of defined thickness that are sequentially directed to a printer, enabling the generation of a 3D object in layer-by-layer manner. The stereolithography apparatus (SLA) is one method of 3D printing that uses selective exposure of UV light to polymerize a photo-active resin one layer at a time. SLA, along with other AM platforms, enables the fabrication of geometries that are otherwise considered unmanufacturable. However, despite increasing popularity and potential, 3D printing has not developed beyond the realm of rapid prototyping given various limitations associated with layer-by-layer printing, the most notable being print speed, typically on the order of a few millimeters per hour. This slow production rate is not viable on a commercial scale. Further, layer-by-layer produced parts exhibit inherent structural weakness along the axis of printing due to a lack of significant chemical association between layers. CAD file conversion to a series of 2D slices imparts a “stair-casing” effect on angled structures, which has several drawbacks. “Stair-casing” results in a non-ideal surface finish that is merely an approximation of the original design and further represents a physical manifestation of the anisotropy of the final part. This effect can be mediated through the use of finer slicing, though at the expense of longer print times. Due to the deficiencies associated with layer-by-layer 3D printing, AM has been restricted to rapid prototyping, and its full potential in manufacturing has yet to be realized.

Fig. 2.  Comparison between traditional SLA and CLIP.

Continuous Liquid Interface Production (CLIP) is a recently developed AM platform that utilizes the selective exposure of UV light to initiate photopolymerization and solidify a part, similar to SLA. Free radical photopolymerization, used in the fabrication of thin films, is commonly conducted in an oxygen-free environment to avoid O2 inhibition. The free radical photopolymerization mechanism is inhibited in the presence of atmospheric oxygen and results in an incomplete cure as well as other consequences such as slow polymerization rates, long induction (onset of reaction) periods, low conversion, short polymer kinetic chain lengths, and tacky surface properties. Oxygen can quench either the excited-state photoinitiator or form a stable peroxy radical upon interaction with a free radical of a propagating chain. CLIP, however, turns O2 inhibition into an advantage by exposing the photopolymerizable resin via an oxygen-permeable build window, resulting in the formation of a dead zone at the surface of the window, or a region of uncured liquid resin beneath the growing part. The dead zone is present throughout the fabrication process and represents the liquid interface of the CLIP platform. The dead zone is the defining difference between CLIP and traditional SLA. As shown in Figure 2, the presence of the liquid interface allows for part production, resin renewal, and build elevator movement to occur in a single step, as opposed to the discrete steps of SLA.

Fig. 3. CLIP Microneedles for Transdermal Drug Delivery. CLIP enables microneedles to be fabricated quickly with unprecedented control over size, shape and spacing. Novel geometries may afford improved penetration into the skin.

The DeSimone lab is exploring the potential for CLIP to be used in the fabrication of very small defined structures for medical applications. Significant opportunity exists in personalized medicine to create tailored devices to meet an individual patient’s needs within an office setting or operating room. We are examining the incorporation of drugs, vaccines, and other agents, as well as the release properties of devices made using CLIP. We are also developing new materials to be used with CLIP. While standard 3D printing resins work with CLIP, the continuous nature of the new technology allows for the development of new chemistries with better mechanical and stability properties than traditional 3D printing resins.

 July 7, 2015
Apr 172015
 
Developed in the DeSimone lab in 2004, the PRINT® technology is central to both our life science and materials science research. A powerful nano-molding technique, PRINT enables the fabrication of particles with precise control over the shape, size, composition, and surface functionality. Figures 2 and 3 below illustrate the breadth of shapes, sizes, and compositions possible for nanoparticle fabrication using PRINT.

The PRINT Process

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Figure 1. A unique liquid fluoropolymer (green) is poured on the surface of the master template (gray) and photochemically cross linked. The template is then peeled away to generate a precise mold with micro- or nanoscale cavities. A pre-particle solution (red) is distributed evenly in the mold, which then solidifies. Particles are removed from the mold by bringing the mold in contact with a harvesting film (yellow). Dissolution of the film yields free-flowing particles in solution, enabling them to be easily handled, chemically modified, and analyzed.

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Figure 2. Micron-sized PRINT particles.
print_figure3Figure 3. Nano-sized PRINT particles.
 April 17, 2015
Apr 162015
 

batteries2014Humankind’s reliance on fossil fuels over the past two centuries has enabled unprecedented population growth and urbanization, with concomitant advances in technology and quality of life. Yet the extreme costs to the health of our planet through depletion and use of these resources — no longer a distant possibility but a present reality — have generated significant research investment into alternative energy solutions. At the heart of these alternative energy solutions is the notion of sustainability, and ideally, the use of renewable energy that produces little to no emissions.

In particular, rechargeable lithium-ion batteries are playing a continuing key role in today’s emerging sustainable energy landscape. They are not only used to power consumer electronics and zero-emission electric vehicles, but are also currently gaining traction in aircraft and smart-grid applications. However, safety concerns regarding these systems continue to persist because the electrolyte component currently used in commercial batteries contains a flammable mixture of organic solvents. These materials pose a high risk of spontaneous ignition under most operating conditions, which necessitates the development of radically new electrolytes with improved safety.

The DeSimone laboratory is developing next-generation polymeric electrolytes for lithium-ion batteries that demonstrate high thermal and electrochemical stability and ionic conductivity (Wong et al., Proc. Nat. Acad. Sci., 2014, 111(9), 3327-3331). Specifically, the team’s strategy is to accomplish this through the creative design of novel polymers and conductive elastomers based on perfluoropolyethers (PFPEs). Due to the inherent nonflammability, chemical resistivity, and oxidative stability of PFPEs, we have had early success in engineering both liquid and solid-state electrolytes for lithium-ion and lithium-air batteries with properties that make them immediately relevant to zero-emission vehicles and smart-grid energy storage systems. Further research will continue to improve the energy density and cycling efficiencies of these batteries, enabling more prominent use of lithium-ion batteries in applications that traditionally employ fossil fuels. Environmental and safety impact serves as a primary touchstone in our work.

 April 16, 2015
Mar 162015
 

150320HRTumblestonCoverA new 3D printing technology, called Continuous Liquid Interface Production (CLIP), was revealed on March 16 by Prof. DeSimone simultaneously at TED2015 in Vancouver and in a paper published in Science. The technology was developed at Carbon3D, Inc., a company co-founded by DeSimone, Alex Ermoshkin, and Prof. Ed Samulski. The paper’s authors include DeSimone group graduate students, Rima Janusziewicz and Ashley Johnson.

Read UNC’s news release

Read the Science paper

Watch CLIP in action

Watch Prof. DeSimone at TED2015

 March 16, 2015