Skip to main content
2024 BMES Annual Meeting Main banner
Icon Legend
This session is not in your schedule.
This session is in your schedule. Click again to remove it.
Back

Biomaterials

Biomaterials - Poster Session E

Poster C6 - Tuning the Bulk Mechanics of Fiber-enhanced Microporous (FEMP) Scaffolds to Promote Vascularization

Saturday, October 26, 2024
10:00 AM – 11:00 AM EST
Location: Exhibit Hall E, F & G

Introduction:  Loss of large volumes of tissue due to ischemic injury, surgical resection, or other causes can reduce the ability of impacted tissues to heal (1). To facilitate tissue regrowth in these spaces, we propose injecting a highly porous fiber-enhanced microporous (FEMP) scaffold into the site of tissue loss to facilitate the ingrowth of new tissue and support angiogenesis, the formation of blood vessels which deliver oxygen and nutrients to cells (2). Previously, norbornene-modified hyaluronic acid (NorHA) microgel scaffolds have been shown to induce vascularization when co-cultured with human umbilical vein endothelial cells (HUVECs) and mesenchymal stromal cells (MSCs) (3). In FEMP scaffolds, electrospun fibers are incorporated into highly porous granular scaffolds based on spherical microgels. The nanofibers strengthen the porous scaffolds by establishing long-range interactions, as opposed to interactions with only neighboring particles, and increasing the number of crosslinks (3). Clinical applications of FEMP scaffolds will require mechanical tunability to cater to vascularizing cells in specific physiological microenvironments. Both porosity and particle weight percentages influence scaffold stiffness (2). We aim to leverage the ability to perturb both porosity and particle weight percentages to fabricate three-dimensional (3D) FEMP scaffolds with tunable mechanical properties, and will compare the approach in both poly(ethylene glycol)- (PEG) and NorHA-based systems to confirm design principles.

Materials and

Methods:  FEMP scaffolds were generated by photo-crosslinking NorHA nanofibers, NorHA microgels, and gelatin type B microgels. The nanofibers were electrospun from a solution of 3.5 weight% NorHA (15% modification), 50 mg/mL dithiothreitol (DTT), I2959 photoinitiator, and polyethylene oxide, then hydrated, homogenized, and filtered. NorHA microgels were generated by adding 3 weight% NorHA to photoinitiator lithium phenyl-2,4,6-trimethylbenzoylphos-phinate (LAP) and DTT, then adding light mineral oil with 2% Span80, homogenizing, photo-crosslinking, and washing with hexane, isopropanol, and phosphate buffered saline (PBS) (3). Gelatin type B microgels were synthesized by homogenizing melted gelatin type B and light mineral oil with 2% Span80, washing with 2% Pluronic F-127 in 1X PBS then 1X PBS, and filtering.
Acrylated and thiolated PEG (PEG-AC/SH) microgels were generated by bulk emulsification (4). 6 weight% 4-arm PEG-AC and 4 weight% 4-arm PEG-SH solutions in 1X Dulbecco’s phosphate buffered saline (DBPS) were combined in equal ratios, loaded into a syringe pump, and infused directly into an oil-base solution undergoing homogenization. The oil-base solution was composed of light mineral oil, 1% Span80, and 0.5% triethanolamine. The emulsion was homogenized for an hour after the end of the infusion, allowing the microgels to crosslink via Michael addition before washing with isopropanol and 1X DPBS.
In both the NorHA and PEG systems, porosity was controlled by incorporating sacrificial gelatin microgels at 0%, 25%, and 50% (Fig. 1A) (3). Confocal images with high molecular weight FITC-dextran in the interstitial space were analyzed for porosity in FIJI (Fig. 1B). Mechanical properties were determined through shear rheology.

Results, Conclusions, and Discussions: Preliminary research on the porosity of PEG-AC/SH microgels has indicated that increasing the ratio of gelatin microgels in PEG-based microgel scaffolds increases their void fraction (Fig. 1). When 0% gelatin microgels were included, the scaffolds were formed entirely of PEG-AC/SH particles and had a porosity of ~25%. By adding sacrificial gelatin particles, so that the ratio of PEG-AC/SH particles to gelatin was 75:25, the porosity increased by ~25%, as expected. By changing the ratio to 50:50, the porosity increased by ~25% again. These findings are in line with previous work done with NorHA microparticle scaffolds (3). We have found that porosity can be tuned in PEG- and NorHA-based microparticle systems to specific void fractions through the use of sacrificial gelatin microgels (Fig. 1).
Electrospun nanofibers are being used to stabilize highly porosity scaffolds. Ongoing work is utilizing shear rheological measurements of FEMP scaffolds to characterize the mechanical properties of the FEMP scaffolds as well as determine the vascularization responses of endothelial cells incorporated in FEMP scaffolds with different mechanical properties. Bulk moduli of the system will be measured across three porosities and three particle weight percentages. We anticipate that scaffold stiffness will increase with polymer weight percent, based on prior research (2). Moreover, previous experiments have shown that increased porosity correlates with decreased scaffold stiffness (5). Knowledge of these relationships will be integrated into vascular remodeling studies of co-cultured scaffolds. Optimal scaffolds will be determined based on endothelial cell responses in developing networks using metrics of proliferation and network morphology. The formation of endothelial cell networks will also be studied by modifying hydrogels with peptides to support adhesion (RGD) or mimic VEGF (QK). FEMP scaffolds are an exciting new technology in the realm of granular materials that could promote regrowth in damaged tissues.

Acknowledgements (Optional):  I would like to thank Remington Martinez, Natasha Claxton, and Chris Highley for their support and expertise, as well as the organizers of the UVA Dean’s Undergraduate Engineering Summer Fellowship Program for supporting this research.