Photoreversible Covalent Hydrogels for Soft-Matter Additive Manufacturing
Christopher P. Kabb,† Christopher S. O’Bryan,§ Christopher C. Deng,† Thomas E. Angelini,§, ‡,⊥ and Brent S. Sumerlin*,†
†George & Josephine Butler Polymer Research Laboratory, Center for Macromolecular Science & Engineering, Department of Chemistry, University of Florida, Gainesville, FL 32611, USA.
§Department of Mechanical and Aerospace Engineering, University of Florida, Gainesville, FL 32611, USA.
‡J. Crayton Pruitt Family Department of Biomedical Engineering, University of Florida, Gainesville, FL 32611, USA.
⊥Institute for Cell and Regenerative Medicine, University of Florida, Gainesville, FL 32611, USA.
Reversible-covalent chemistry provides access to robust materials with the ability to be degraded and reformed upon exposure
to an appropriate stimulus. Photoresponsive units are attractive for this purpose, as the spatial and temporal application of light is easily controlled.
Coumarin derivatives undergo a [2+2] cycloaddition upon exposure to long-wave UV irradiation (365 nm), and this process can be
reversed using short-wave UV light (254 nm). Therefore, polymers crosslinked by coumarin groups are excellent candidates as reversiblecovalent
gels. In this work, copolymerization of coumarin-containing monomers with the hydrophilic comonomer N,N-dimethylacrylamide
yielded water-soluble, linear polymers that could be cured with long-wave UV light into free-standing hydrogels, even in the absence of a photoinitiator.
Importantly, the gels were reverted back to soluble copolymers upon short-wave UV irradiation. This process could be cycled,
allowing for recycling and remolding of the hydrogel into additional shapes. Further, this hydrogel can be imprinted with patterns through a
mask-based, post-gelation photoetching method. Traditional limitations of this technique, such as the requirement for uniform etching in one
direction, have been overcome by combining these materials with a soft-matter additive manufacturing methodology. In a representative
application of this approach, we printed solid structures in which the interior coumarin-crosslinked gel is surrounded by a nondegradable gel.
Upon exposure to short-wave UV irradiation, the coumarin-crosslinked gel was reverted to soluble prepolymers that were washed away to
yield hollow hydrogel objects.
Fabrication of Triboluminescence Sensors via Additive Manufacturing
Tawakalt Mayowa Akintola, Jolie Breaux Frketic, Roy Madhuparna, Phong Tran, Tarik Dickens
Department of Industrial and Manufacturing Engineering, FAMU-FSU College of Engineering, 2525 Pottsdamer St., Tallahassee, Florida 32310 United States
High-Performance Materials Institute, 2005 Levy Ave, Tallahassee, Florida 32310 United States
In this presentation, functional 3D printing parts were produced using ZnS:Mn powder/Polystyrene (PS) composites. ZnS:Mn is a triboluminescence (TL) material which produces light emission under mechanical loads such as impact, stress, and fracture.
By combining TL materials with additive manufacturing, we can achieve unique TL structures that once restrained by conventional methods. Additionally, 3D printing of TL materials will allow us to strategically embed functionalized material for self-sensing in applications for damage detection and monitoring. The processing-performance relationship has been investigated by TGA, DSC and SEM to understand the effect of TL crystal sizes and distribution on the performance of TL printed parts.
Flexural testing beams were 3D printed and their fracture/deformation energy emission was estimated via J-integral
analysis of three-point bend test.
Interfacial Dynamics in Additively Manufactured Polymer Matrix Composites
Kyle J. Johnson, Andrew Abbott, Lutz Wiegart, Jeff Baur, Hilmar Koerner
UES Inc., University of Dayton Research Institute, Brookhaven National Laboratory (NSLS II), Air Force Research Laboratory
Additive manufacturing (AM) is pervasive across many disciplines at the Air Force Research Laboratory (AFRL). AFRL is investing in these novel manufacturing processes because of their appeal in rapid prototyping, part reduction and the ability to manufacture complex parts using design and topology optimization. Before AM is robust enough for metals, polymers, ceramics and composite manufacturing, morphology/processing/performance relationships have to be established. The presentation will give a brief overview of the different AM areas that AFRL is working on with focus on AM for polymer matrix composites. The road to road interface in additively manufactured composite parts is crucial for part performance. As an example, weakness and anisotropy at this interface have been key areas of study in the pursuit of more robust additively manufactured parts. Here, the dynamics and morphology at road-to-road interfaces were explored in an epoxy/nanoclay composite ink using X-Ray photon correlation spectroscopy (XPCS). We observe a time scale associated with equilibrium dynamics, and observe substantially faster dynamics perpendicular to the road-to-road interface than parallel. This anisotropy in dynamics is shown to pass through a maximum both into the recently printed and previously printed road. The behavior is discussed relative to the alignment of the composite particles during shear of the ink through the extrusion head. The ultimate goal of this research is to use the in-situ data to calibrate more conventional techniques that can be implemented within an AM machine and use this to advance close-loop feedback control in AM processes in the future.
Additive Manufacturing for the Future Warfighter
Jaret C. Riddick
Army Research Labs
Army Research Lab is conducting research to enable the use of additive manufacturing to reduce the logistical burden of the future Warfighter. ARL researchers are investigating additive manufacturing to establish research prototypes such as mission-matched UAS concepts built on-demand at the point-of-need and multifunctional components for maintenance-free air vehicle platforms.
Dielectric and magnetic properties of nanoparticle loaded polystyrene as a printable, low-k hybrid material
Faheem Muhammed,1 Subramanian Ramakrishnan1, Parth Vakil2, Geoffrey Strouse2
1 -Department of Chemical Engineering, Florida A&M University, Tallahassee FL, 32301
2 - Department of Chemistry, Florida State University, Tallahassee, FL, 32301
The development and miniaturization of electronics has increased the need for low-k dielectric materials for use in interconnect shielding. The primary goal of this work was to systematically modify the printed material to strike the balance between magnetic (permeability) and dielectric properties that provides maximal electronic shielding. The key in these applications is maximizing particle loadings in a polymer matrix while maintaining low dielectric constants and losses. Magnetic nanoparticles were dispersed in low-k thermoplastics and the dielectric properties were systematically studied as a function of particle type, concentration (0 to 13 volume percent), and surface coating. By varying the volume percentage of filler in the matrix, it is shown that one can increase the magnetic properties of the materials while minimizing unwanted contributions to the dielectric constant and dielectric loss. The well dispersed nanoparticle systems were successfully modeled through the Maxwell-Garnett (MG) theory thus giving one a predictive ability for the dielectric properties. High-precision (100 μm resolution) additive manufacturing, combined with these materials, has demonstrated further reductions to the dielectric constant by controlled incorporation of air (k=1) in the system. The volume fraction of air present was tuned through topological optimization, computer aided structural design, and printing parameters. By treating the nanocomposite as a continuous matrix, and air as the filler, the MG theory was extended to the manufactured composites.
Advances in Nano-Scale 3D Printing by Multi-Photon Lithography
Stephen M. Kuebler
Department of Chemistry and CREOL, The College of Optics and Photonics, University of Central Florida
Multi-Photon Lithography is an emerging technique for creating functional nano-scale 3D structures and devices. The method relies on the combination of chemical and optical nonlinearity to achieve strong spatial confinement of the writing beam within a photoactive medium. In this presentation we will briefly discuss how the technique works and how it has been used to create optically functional photonic crystals and other nanophotonic devices.
Direct Digital Manufacturing Processes for Electronics and Biology
This talk will cover 3D printing and supplemental processes to enable a more complete device. Printed structures are typically a single material and tools that have multi-material capabilities typically print one type of material. Functional devices are comprised of diverse materials with diverse properties. To accommodate this, nScrypt has developed a system with multiple tools and processes integrated on a single platform. This enables printing functional devices such as RF antenna systems, as opposed to printed antennas. This also enables biological prints and multiple processes will be required to reach the holy grail of a printed organ. In electronics and biology, functioning parts are not single material and multi-material requires multi-processes. These processes include heat, cooling, milling, polishing, pick and place and a wide variety of printing techniques. Examples of printed electronic structures will be covered and demonstrated. In addition, the transition from electronics to biology and the similarities in printing.
Mechanical Instabilities in Contracting 3D Printed Microtissues
Thomas E. Angelini
University of Florida
Living cells are often dispersed in extracellular matrix (ECM) gels like collagen and Matrigel as minimal tissue models. Generally, large-scale contraction of these constructs is observed, in which the degree of contraction and compaction of the entire system correlates with cell density and ECM concentration. The freedom to perform diverse mechanical experiments on these contracting constructs is limited by the challenges of handling and supporting these delicate samples. Here, we present a method to create simple cell-ECM constructs that can be manipulated with significantly reduced experimental limitations. We 3D print mixtures of cells and ECM (collagen-I) into a 3D growth medium made from jammed microgels. With this approach, we design microtissues with controlled dimensions, composition, and material properties. We also control the elastic modulus and yield stress of the jammed microgel medium that envelops these microtissues. Similar to well-established bulk contraction assays, our 3D printed tissues contract. By contrast, the ability to create high aspect ratio objects with controlled composition and boundary conditions allows us to drive these microtissues into different regimes of physical instability. For example, a contracting tissue can be made to buckle as a whole or break up into pieces, depending on composition, size, and shape. These new instabilities may be employed in tissue engineering applications to anticipate the physical evolution of tissue constructs under the forces generated by the cells within.
3D Bioprinting and Efforts to Biofabricate Bioficial Organs
Stuart K. Williams, Ph.D.
Director, Bioficial Organs Program
University of Louisville
The disparity between available donor organs and patients in need of a transplant has been the impetus to create human tissues and organs for transplantation. Efforts to biofabricate replacement organs has evolved over several decades and has included advancements in cell biology, tissue culture, tissue engineering and regenerative medicine. Further evolution toward a totally biologic organ replacement has included the technology known as 3D Bioprinting. Progress toward the fabrication of a Total Bioficial Heart using 3D Bioprinting will be discussed including the source of autologous cells to create components of the heart. Examples of other Bioficial Organs that are being 3D Bioprinted and the clinical readiness of this technology will also be presented. Finally, we are now exploring the use of regenerative medicine and 3D Bioprinting in space with a hope to bring these technologies to support long-term space exploration.