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Biomaterials

Biomaterials - Poster Session E

O15 - Evaluating PEGDA's Influence on Brain-Mimetic Bioink Mechanics for 3D-Bioprinting Applications

Saturday, October 11, 2025
10:00 AM - 11:00 AM PDT
Location: Exhibit Hall F, G & H

Introduction: : Understanding and treating neurological disorders, such as Alzheimer’s and stroke, remains a significant challenge, in part due to the complexity of the brain and the blood-brain barrier (BBB). The BBB regulates the passage of substances from the bloodstream to the central nervous system (CNS), which, while critical for maintaining homeostasis, also restricts delivery of many potential therapeutics to the brain. To address this challenge, physiologically relevant models of the BBB are needed to better study drug transport and tissue-specific responses.

Three-dimensional (3D) bioprinting is a promising approach to fabricate such models that accurately replicate the organization, cellular heterogeneity, and mechanical properties of the native brain environment. The stiffness of brain tissue varies across pathological states, including cancers like glioblastoma. Therefore, creating hydrogels with tunable viscoelastic properties is essential to accurately mimic the appropriate brain environment. However, the effectiveness of this approach hinges on the development of bioinks that are not only biologically relevant but also mechanically suitable for extrusion printing. Accordingly, we investigated how the inclusion of polyethylene glycol diacrylate (PEGDA) in a composite, photopolymerized bioink formulation impacts the material’s viscoelastic properties and printability. PEGDA was selected due to its biocompatibility and diacrylate groups, allowing it to act as a secondary crosslinker to enhance network integrity and improve shape fidelity during and after printing. Specifically, we used rheological assessments, including amplitude and temperature sweeps, to evaluate the effect of PEGDA on the mechanical performance of the hydrogel.

Materials and

Methods: : The bioink consists of a hydrogel composed of methacrylated hyaluronic acid (HAMA), methacrylated gelatin (GelMA), and polyethylene glycol diacrylate (PEGDA); lithium phenyl (2,3,6-trimethylbenzoyl) phosphinate (LAP) is incorporated into the gel to enable crosslinking upon exposure to UV light at 365 nm. HAMA was synthesized using in-house protocols. GelMA, PEGDA, and LAP were purchased commercially. All tested hydrogel formulations included 2 wt/v% HAMA. GelMA concentration was varied between 2 wt/v% and 10 wt/v%. PEGDA was included in some hydrogel formulations at a concentration of 1.95 wt/v% and excluded from others. LAP was included at a concentration of 0.2 wt/v% for cured hydrogel formulations and not included for the uncured hydrogel precursor. Four hydrogel compositions were used for rheology experiments, including H2G2, H2G2P, H2G10, and H2G10P, where H2 represents 2 wt/v% HAMA, G2 represents 2 wt/v% GelMA, G10 represents 10 wt/v% GelMA, and P represents the inclusion of PEGDA at 1.95 wt/v%.

Rheological behavior was assessed through amplitude sweeps and temperature sweeps to determine the effect of PEGDA on the printability of the bioink. A TA Instruments Discovery Hybrid Rheometer with an 8 mm parallel plate geometry was used for all tests. Amplitude sweeps were conducted on cured hydrogels at 1 Hz frequency across a range of 0.1%-50% strain. Temperature sweeps were conducted on uncured hydrogel precursor at 1 Hz frequency, 1% strain, and across a temperature range of 20-40 °C, with a ramp rate of 1 °C/min.

Results, Conclusions, and Discussions:: As seen in Fig. 1, PEGDA did not greatly impact the viscous flow or yield behavior of the hydrogels. The yield strain is approximately 102% for both the H2G2 and H2G2P formulations, and the storage modulus consistently increases for both the H2G10 and H2G10P formulations. The linear viscoelastic region (LVER) of each hydrogel composition also did not vary substantially between formulations with and without PEGDA. However, increasing the concentration of GelMA from 2 wt/v% to 10 wt/v% did lead to changes in the stiffness of the gel; the G10 hydrogels exhibited higher and continuously increasing storage moduli, indicating greater stiffness than the softer G2 hydrogels.

As seen in Fig. 2, the inclusion of PEGDA in the hydrogel formulation did not greatly impact the behavior of the gel across the tested temperature range. In each formulation, the storage modulus, G’, and the loss modulus, G’’, approach or converge in the approximate range of 30-40 °C. This indicates that the bioink exhibits fluid-like behavior at these temperatures, which is optimal for 3D-bioprinting. Additionally, this temperature range encompasses normal physiological temperature, which would support the health of cells seeded within the hydrogel during printing.

It was hypothesized that the inclusion of PEGDA in the hydrogels would affect the mechanical properties of the bioink through increasing crosslinking density; however, these effects were not observed. These results suggest that the inclusion of PEGDA in this bioink formulation had a limited impact on the viscoelastic behavior of the gel within the tested range. While PEGDA contributes to crosslinking, its influence on key mechanical properties such as storage modulus, yield strain, and temperature stability appears to be minimal in comparison to the effects observed with varying GelMA concentration, indicating that mechanical customization of the bioink may be more effectively achieved by modulating GelMA content rather than PEGDA. Future work will focus on evaluating how UV photopolymerization conditions affect cell viability and oxidative stress within printed constructs. Understanding the cellular response to different crosslinking parameters will be essential for balancing mechanical performance with biocompatibility in the development of functional BBB models.

Acknowledgements and/or References (Optional): : Funding is gratefully acknowledged from the University of Oklahoma Undergraduate Research Opportunities Program.