Session: 04-26-01: Nanoengineered, Nano Modified, Hierarchical, Multi-Scale Materials and Structures

Paper Number: 164092

Fabrication of Patterned Hydrogels With Controlled Mechanical Properties Using Chemically Modified RLPs 

Introduction: Hydrogels are polymeric materials that have gained significant attention due to their unique properties, such as biocompatibility, high water content, and tunable mechanical properties. These properties make hydrogels promising candidates for providing a microenvironment to many different cells with opportunities to capture features of the extracellular matrix (ECM). Among different materials that have been investigated for biomedical applications, resilin-like polypeptides (RLPs) are a class of elastomeric proteins that exhibit remarkable mechanical properties, such as high resilience, extensibility, and fatigue resistance. Owing to these unique features, RLPs are promising building blocks for manufacturing hydrogels that can mimic some important properties of native tissues, including cell binding, viscoelasticity, and microstructure. RLPs contain amino acid sequences that facilitate binding to the cell surfaces, while their elastin-like domains enable them to withstand mechanical forces and maintain their structural integrity over time. By photopolymerizing chemically modified RLPs under specific conditions, it is possible to create hydrogels with regions of varying mechanical properties and microstructures, providing additional control over their properties.

Our study develops a novel method for creating  hydrogels with tunable mechanical properties through photopolymerization. To achieve this, we used RLPs that were chemically modified with photoreactive groups. We then subjected the RLP solutions to two different photopolymerization methods: conventional UV photopolymerization and DMD photopolymerization. The conventional method involved exposing the hydrogel to uniform UV light, while DMD allowed for precise control of the light pattern, resulting in complex 3D patterns and tunable mechanical properties. The resulting hydrogels were characterized using various techniques such as NMR, mass spectrometry, scanning electron microscopy, confocal microscopy, and atomic force microscopy. Our study provides insight into the potential of RLP hydrogels for use in various biomedical applications, and our approach offers a new way to control the mechanical properties of hydrogels.

Results and Discussion: While the conventional method of photopolymerizing RLP hydrogels results in a homogeneous distribution of mechanical properties, the DMD polymerization technique offers significant advantages. By utilizing a projection system that controls the UV light pattern used to activate the photoinitiator, DMD allows for the precise creation of complex, three-dimensional patterns with high resolution and reproducibility. Moreover, the ability to achieve spatially distinct crosslink densities enables tunable mechanical properties of the hydrogel.

Our AFM studies revealed some interesting findings regarding the mechanical properties of hydrogels. Specifically, we observed that the hydrogel without a crosslinker exhibited a lower Young's modulus in the center of the DMD-illuminated region than at the edges. Our data demonstrated that the Young's modulus of the DMD crosslinked region was higher than that of the background crosslinked region.   We hypothesize that this may be due to the fact that the AFM probe detected more signals from the glass substrate at the edges. In contrast, the hydrogel prepared in the presence of a crosslinker exhibited two distinct regions: a DMD crosslinked region where light directly shone, and a background crosslinked region where polymerization occurred due to the propagation of light-activated free radicals. These observations provide insights into the spatially varying mechanical properties of hydrogels and offer new opportunities for tuning these properties using advanced techniques. Confocal microscopy images provided additional evidence that the hydrogel fabricated by conventional UV source was homogeneous and uniform throughout the hydrogel matrix. In contrast, the DMD photopolymerized hydrogel showed two distinct regions with different fluorescence intensities, further indicating the presence of two different types of crosslinking within the hydrogel matrix. These findings are consistent with our AFM results, which showed that the DMD crosslinked region had a higher Young’s modulus than the background crosslinked region..

The cryo-SEM images of the hydrogels made by the conventional and DMD light sources provide further evidence of the distinct differences between these two techniques. The conventional hydrogel, which appears to be the same throughout the sample, with no noticeable variation in morphology. In contrast, the DMD hydrogel with two distinct regions, one where the light directly shone, resulting in a higher degree of crosslinking, and another where polymerization occurred due to the migration of light-activated free radicals, resulting in a lower degree of crosslinking. These distinct regions are likely responsible for the observed differences in mechanical properties between the DMD crosslinked and background crosslinked regions, as noted in our AFM studies. Overall, the combination of cryo-SEM and confocal microscopy images provided valuable insights into the microstructure and mechanical properties of the RLP-based hydrogels fabricated by conventional UV polymerization and DMD photopolymerization

 

Conclusion: In conclusion, our study has shown that Digital Micromirror Device (DMD) polymerization can be used to create hydrogels with spatially varying mechanical properties. By leveraging the precise control over the UV light pattern provided by DMD, we were able to create hydrogels with distinct regions of crosslinking, resulting in differences in mechanical properties that were not achievable using conventional photopolymerization techniques. Our AFM, confocal, and cryo-SEM studies further supported these findings, providing evidence of the distinct mechanical and morphological properties of the DMD hydrogel. These results have important implications for a wide range of biomedical applications, from tissue engineering to drug delivery, where precise control over the mechanical properties of hydrogels is critical for their efficacy. Future research will continue to explore the potential of DMD polymerization for creating hydrogels with even more complex and tunable properties, further expanding the range of potential applications for these materials.

 

 

 

Presenting Author: Sambeeta Das University of Delaware

Presenting Author Biography: Dr. Sambeeta Das is an Assistant Professor of Mechanical Engineering at the
University of Delaware where she established the Soft Microrobots for Tissue Engineering
(SMT) lab in 2019. Before joining University of Delaware, she was a postdoctoral researcher at the University of Pennsylvania where she worked with Dean Vijay Kumar in the
GRASP Lab. She earned her Ph.D. at the Pennsylvania State University in 2016, carrying out
her thesis work with Prof. Ayusman Sen. She received her M.S. with distinction from the
University of London and her bachelor’s in physics from Presidency College, India.

Authors:

Ramadan Abouomar University of Delaware
Zameer Shah University of Delaware
Davis P. Rivas University of Delaware
Sudipta Mallick University of Delaware
Luisa Palmese University of Delaware
Sai S. Patkar University of Delaware
Kristi L. Kiick University of Delaware
Sambeeta Das University of Delaware