Biology subjects

Sumey, J. L.

Publications and source records attributed to Sumey, J. L..

3 recordsLinked to original sources

bioRxiv2023

Packed hydrogel microfibers as a granular medium

Particle-based (granular) hydrogels are an attractive class of biomaterials due to their unique properties and array of applications in the biomedical space - serving as platforms for extrusion printing and injecting as well as permissive materials for 3D cell culture. Physical properties of particle-based hydrogels are governed in part by contact forces between particles, which are limited to interactions with neighboring particles. Secondary annealing mechanisms are often used to increase mechanical properties and serve to link particles across the granular material volume. Here, we present a novel particle-based hydrogel where each "particle" is a discrete electrospun hydrogel microfiber that has been segmented to a length of 93 {+/-} 51 m, with a diameter of 1.6 {+/-} 0.3 m. The fibers are flexible and have aspect ratios that are greater than one order of magnitude larger than most traditional hydrogel microparticles. This enables long-range entanglements of discrete fibers following packing into a bulk material, yielding unique properties. Without crosslinking, these packed hydrogel microfiber materials are mechanically robust, they can stretch without breaking when strained, and they exhibit stress relaxation under constant strain. As a cell culture scaffold, shear-induced alignment of the individual fibers within 3D printed filaments confers contact guidance cues to cells and promotes anisotropic cellular morphologies. Packed hydrogel microfibers can also be used as 3D cell culture environments, with cells able to spread due to the permissive nature of the scaffold. Overall, this work introduces a particle-based material system comprised of individual hydrogel microfibers that allows unique properties to be engineered into biomaterials that might be used in extrusion processes and cell cultures and, ultimately, in tissue engineering and regenerative medicine applications.

bioengineering↗

bioRxiv2023

Serial passaging affects stromal cell mechanosensitivity on hyaluronic acid hydrogels

There is tremendous interest in developing hydrogels as tunable in vitro cell culture platforms to study cell response to mechanical cues in a controlled manner. However, little is known about how common cell culture techniques, such as serial expansion on tissue culture plastic, affect subsequent cell behavior when cultured on hydrogels. In this work we leverage a methacrylated hyaluronic acid hydrogel platform to study stromal cell mechanotransduction. Hydrogels are first formed through thiol-Michael addition to model normal soft tissue (e.g., lung) stiffness (E ~ 1 kPa). Secondary crosslinking via radical photopolymerization of unconsumed methacrylates allows matching of early- (E ~ 6 kPa) and late-stage fibrotic tissue (E ~ 50 kPa). Early passage (P1) primary human mesenchymal stromal cells (hMSCs) display increased spreading, myocardin-related transcription factor-A (MRTF-A) nuclear localization, and focal adhesion size with increasing hydrogel stiffness. However, late passage (P5) hMSCs show reduced sensitivity to substrate mechanics with lower MRTF-A nuclear translocation and smaller focal adhesions on stiffer hydrogels compared to early passage hMSCs. Similar trends are observed in an immortalized human lung fibroblast line. Overall, this work highlights the implications of standard cell culture practices on investigating cell response to mechanical signals using in vitro hydrogel models.

bioengineering↗

bioRxiv2022

Hydrogel mechanics regulate fibroblast DNA methylation and chromatin condensation

Cellular mechanotransduction plays a central role in fibroblast activation during fibrotic disease progression, leading to increased tissue stiffness and reduced organ function. While the role of epigenetics in disease mechanotransduction has begun to be appreciated, there is little known about how substrate mechanics, particularly the timing of mechanical inputs, regulate epigenetic changes such as DNA methylation and chromatin reorganization during fibroblast activation. In this work, we engineered a hyaluronic acid hydrogel platform with independently tunable stiffness and viscoelasticity to model normal (storage modulus, G [~] 0.5 kPa, loss modulus, G [~] 0.05 kPa) to increasingly fibrotic (G [~] 3.5 and 8 kPa, G [~] 0.05 kPa) lung mechanics. Human lung fibroblasts exhibited increased spreading and nuclear localization of myocardin-related transcription factor A (MRTF-A) with increasing substrate stiffness within 1 day, with these trends holding steady for longer cultures. However, fibroblasts displayed time-dependent changes in global DNA methylation and chromatin organization. Fibroblasts initially displayed increased DNA methylation and chromatin decondensation on stiffer hydrogels, but both of these measures decreased with longer culture times. To investigate how culture time affected the responsiveness of fibroblast nuclear remodeling to mechanical signals, we engineered hydrogels amenable to in situ secondary crosslinking, enabling a transition from a compliant substrate mimicking normal tissue to a stiffer substrate resembling fibrotic tissue. When stiffening was initiated after only 1 day of culture, fibroblasts rapidly responded and displayed increased DNA methylation and chromatin decondensation, similar to fibroblasts on static stiffer hydrogels. Conversely, when fibroblasts experienced later stiffening at day 7, they showed no changes in DNA methylation and chromatin condensation, suggesting the induction of a persistent fibroblast phenotype. These results highlight the time-dependent nuclear changes associated with fibroblast activation in response to dynamic mechanical perturbations and may provide mechanisms to target for controlling fibroblast activation.

bioengineering↗