The posters presented in September during Photopolymerization Fundamentals 2023 in Boulder, Colorado, represented researchers and experts in the field of photopolymerization willing to share recent research and results with an audience of industry and academic professionals. The posters focused on presenting recent advancements, critical achievements and research outcomes in the field of photopolymerization, including research findings and developments relevant to product development. Short summaries of research related to medical and biomedical applications in the field of photopolymerization are provided here, but are only a small portion of the total posters presented. Additional information on posters, presentations and exhibitors can be found at www.radtech.org/pf2023.
Effective Zwitterionic Hydrogel Coatings for Biomaterials
George C. Barrera, Adreann Peel, Ryan Horne, Nir Ben-Shlomo, C. Allan Guymon, University of Iowa
Biomedical implants can have life-altering impacts on the patients who receive them. Implants that interface sensitive tissues and organs face repulsion of the body, known as the foreign body response (FBR). Many implants and biomaterials incorporate polydimethylsiloxane (PDMS), a chemically inert elastomer that is durable and reliable. However, PDMS is subject to FBR. Zwitterionic thin film coatings are a promising solution to recognition by the body. Chemical alteration of PDMS surface allows the attachment of zwitterionic thin films that greatly reduce cell and protein adhesion. Using two photoinitiators, we photograft to the surface of PDMS while building a hydrophilic film (30 µm) that creates a lubricious layer with high water content, significantly reducing the coefficient of friction and reducing cell adhesion compared to PDMS. By introducing a secondary network into the system, enhanced mechanical properties are obtained while retaining the same lubricity and antifouling properties of a single network system. These systems reduce swelling of single network hydrogels, decreasing the variability of coating thickness. These coatings have been shown to greatly reduce the inflammation that follows the surgery.
Characterization of the Interface Between Photopolymerized Soft Hydrogels and Stiff 3D-Printed Materials for Osteochondral Tissue Engineering
Kiera J. Croland, Jian Wei Tay, Andrew N. Sias, Robert R. McLeod, Stephanie J. Bryant, University of Colorado Boulder
Cartilage damage due to degenerative disease or trauma results in a repair tissue with weakened mechanical properties that eventually leads to osteoarthritis. To address this clinical problem, this research investigates a tissue engineering approach based on a composite material consisting of a stiff structure printed by projection microstereolithography infilled with a soft photopolymerizable biomimetic hydrogel. The soft hydrogel serves as the cellular niche, while the 3D-printed structure provides mechanical support. Previous work applied grayscale light patterning for spatial control of cross-link density in the 3D-printed material to create an integration layer and reduce interfacial failure. This layer in the 3D-printed structure is loosely cross-linked to allow for diffusion of the soft hydrogel precursors into the stiff material. However, a consequence of this integration layer is variable swelling of the soft hydrogel. This work aims to investigate this interaction between the stiff 3D-printed structure and the soft infilled hydrogel. The specific aims of this study are to quantify the spatial differences in hydrogel swelling near the interface using two techniques: (1) particle image velocimetry (PIV) and (2) hologram patterning into hydrogels. Ultimately, this work aims to improve material design for cartilage repair.
Digital Light Processing of Stiff Yet Tough Single Network Hydrogels
Abhishek P. Dhand1, Matthew D. Davidson2, Hannah M. Zlotnick2, Jason A. Burdick1,2
1 Department of Bioengineering, University of Pennsylvania 2 BioFrontiers Institute and Department of Chemical and Biological Engineering, University of Colorado
Although hydrogels have been promising polymeric materials for biomedical applications, most single network hydrogels fail to recapitulate high strength and toughness of native tissues. Conventional strategies to enhance stiffness of hydrogels through increased number of cross-links often result in embrittlement of the hydrogel. To resolve the stiffness-toughness conflict, hydrogels with high degree of polymer chain entanglements have been developed. However, these tough gels are fabricated in the form of bulk discs that do not mimic the physiologically relevant tissue architecture. Digital Light Processing (DLP) relies on rapid light-based cross-linking of liquid precursors to form complex 3D structures in a bottom-up manner. Here, we implement an acrylamide-based resin towards DLP-based 3D printing of hydrogels followed by post-curing to achieve complete conversion of monomers left unreacted during DLP. These 3D-printed single network hydrogels can be utilized to design acellular scaffolds for use in tissue engineering or for in vitro disease modeling.
Sonication Labile Peg Based Polymer Hydrogels
Meagan N. Arguien, Christopher N. Bowman, University of Colorado Boulder
In the growing field of polymers, the development of materials that are responsive to external stimuli has gained momentum, especially with the interest in enabling transitions of mechanical or chemical properties to allow a single polymer to be used where previously multiple may have been required. This work uses phthalaldehyde functionalized polyethylene glycol (PEG) macromers, photopolymerized through either a thiol-ene or acrylate reaction to synthesize hydrogels that respond to mechanical triggers. The phthalaldehyde mechanophore linkage has been shown to be sonication labile when incorporated into a polymer backbone. This work characterizes the mechanical properties of cross-linked PEG-phthalaldehyde hydrogels as sonication is applied, illustrating the degradation profile of these hydrogels and degradation into smaller molecular weight byproducts that are water soluble. The use of mechanical triggers, such as sonication or ultrasound, was leveraged to degrade polymers in optically dense or thermally sensitive environments while maintaining the spatial – temporal control characteristic of photo triggered degradation.
Photoinduced Maleimide Crosslinking Enables Topological Control Over Hydrogel Network Architecture
Bruce E. Kirkpatrick, Grace K. Hach, Benjamin R. Nelson, Nathaniel P. Skillin, Joshua S. Lee, Lea P. Hibbard, Violeta Salazar, Connor E. Miksch, Tessa N. Fox, Joshua T. Kamps, Jasmine Sinha, Sean P. Keyser, Laura J. Macdougall, Benjamin D. Fairbanks, Christopher N. Bowman, Kristi S. Anseth, University of Colorado, Boulder
Photocross-linked networks are typically formed by either step- or chain-growth polymerizations, imbuing the underlying polymer architecture with distinct physical characteristics and mechanical properties. To complement these material chemistries, we introduce a new photochemical approach for controlling network topology over a spectrum of those achieved with step- and chain-growth reactions. Using UV light-induced maleimide dimerization and maleimide-styrene alternating copolymerization, we synthesize a gradient of hydrogel network topologies by controlling the ratio of maleimide to styrene, generating soft materials with moduli that vary over an order of magnitude at fixed initial polymer content. We find that preferential reactivity of the maleimide-styrene alternating copolymerization enables fabrication of off-stoichiometry networks with pendant functional groups, allowing for versatile post-gelation modifications, including bulk stiffening and labeling, as well as photopatterning. Results demonstrate tunable topology of the network-forming photochemistry, which can be performed with or without photoinitiator, to regulate mechanical properties, swelling and diffusion of encapsulated cargo.
