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    Biomaterials

    (C-115) 3D Printing Of Collagen-FiberNetwork (CFN) Inspired Hydrogels

    Friday, October 13, 2023
    9:30 AM – 10:30 AM PDT
    Location: Exhibit Hall - Row C - Poster # 115
    Introduction::

    Several studies have  investigated the utility of tissue-inspired constructions that are architecturally and functionally similar to their biological counterparts, such as heart valve (HV) prosthetics. However, for these devices, mimicking the morphological complexities of  the CFN remains a challenge. We believe the CFN is essential in creating devices that match the native valve, because the CFN is the primary stress-bearing element as it delivers  stiffness and strength , as well as how cusps attach to the heart and large vessels. Furthermore, since the CFN drives the gross functional mechanics of the valves,  we anticipated that the mechanical properties of CFN-patterned hydrogels would also differ under varying patterns. The purpose of this preliminary study was to test for the size, length, shape, and number of connecting structures embedded in a 3D printed hydrogel coupon at the same length scale as a HV (12x5x1mm) to determine their influence on the hydrogel’s mechanical properties.  These connecting structures were inspired from the circumferential collagen fibers in a HV and the length scale was determined as such to test for the 3D printer’s capability to print at fine resolutions (50 um). 



    Materials and Methods:: We explored challenges of printing CFN-inspired patterns onto hydrogels to determine feasibility and the impact that patterns have on hydrogel mechanics.  Three hydrogel coupons were created using a computer aided design (CAD) program (2). The designs consist of two main sections: the ends of the coupons and the middle structure connecting the two ends. The ends of the coupons were implemented to mimic the ends of a valve leaflet that are attached to the walls of the heart, while the middle structure represents collagen fibers along the circumferential axis of a HV that allow for load transfer to the walls (1). Additionally, one coupon consisted of a uniform structure that served as a control. The stems within the middle section connecting the two ends varied in size, length, shape, and number to investigate their ability to transfer load. We then printed these coupons using the Cell-ink Polyethylene Glycol Diacrylate (PEGDA) Start (< 2 kDa ) on the LumenX bioprinter. When initial right angled stems tore upon removal after 3D printing, stems connecting to the ends were redesigned with fillets to reduce stress concentration. Testing for 30°,45° and 60° fillets was conducted to  determine which held up best. Furthermore, hydrogel composites were created using 1% w/v Irgacure (Ig) 2959 in 100% ethanol, ultra pure water (UPW), and PEGDA 6 kDa in the Cell-ink PEGDA Start (3). This solution was then crosslinked under UV light. Samples were then tested using uniaxial tensile protocols to determine their stress-strain response.

    Results, Conclusions, and Discussions:: The number of stems within each coupon was reduced in order to increase the width of each stem. This allowed for  incorporation of fillets in a way that would allow for improved and equal distribution of stress throughout each coupon. Unreliable structural integrity caused by the stems connecting at right angles led to implementation of 45° angled fillets (1) allowing for more structurally durable coupons that were less prone to breakage (2). Mechanical testing conducted on the solid coupon without pattern had higher young’s modulus than coupons with stems as part of the CFN pattern. The designs with stems sustained higher strain due to having lower Young’s moduli. This result indicated patterned coupons were more flexible. An interesting finding was that implementation of the stems sometimes led to failure at one of the stems, which prevented failure across the entire coupon as would occur in a control. Furthermore in the process of creating the composites we found that pouring the softer prepolymer solution over the coupons within a mould was superior to injecting the prepolymer solution into an enclosed space. Future work includes refining the methods for preparing and mechanically testing the composites, as well as building on preliminary tests to incorporate aligned carbon nanotubes into the hydrogels.

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