Optimizing material and flow properties of guest-host hydrogels for injectable cell delivery

Abstract

Event Abstract Back to Event Optimizing material and flow properties of guest-host hydrogels for injectable cell delivery Minna H. Chen1, Christopher B. Highley1, Christopher B. Rodell1*, Ann Gaffey2*, Chantel Venkataraman2*, Pavan Atluri2 and Jason A. Burdick1* 1 University of Pennsylvania, Department of Bioengineering, United States 2 University of Pennsylvania, Division of Cardiovascular Surgery, Department of Surgery, United States Introduction: Cell delivery by direct injection is plagued by low (<10%) retention of cells at the injection site. The use of biomaterial carriers can improve cell retention, and shear-thinning hydrogels are particularly advantageous as cells can be encapsulated within hydrogels and then delivered via syringes and catheters in a minimally invasive approach. Toward this, we recently developed a class of shear-thinning hyaluronic acid (HA) hydrogels assembled via guest (adamantane, Ad) and host (cyclodextrin, CD) modifications[1]. However, it is important to understand how material formulations and injection parameters influence potentially damaging shear forces on cells. Materials and Methods: HA was modified with either Ad or CD and combined to form shear-thinning, injectable hydrogels upon mixing. Using rheology, mechanical properties of gel formulations at differing concentrations (2.5-7.5 wt%) and modifications (20-50%) were measured. Within these gels, 5µm polystyrene beads were embedded and injection parameters (i.e., flow rate, needle gauge) investigated; bead velocity during injection was determined (Trackpy). 3T3 fibroblast cells were similarly encapsulated and injected and live/dead staining was used to quantify cell viability and distribution. Finally, endothelial progenitor cells (EPCs) were encapsulated in one formulation and injected into the border zone region of an acute myocardial infarction (AMI) in a rat[2]. After 4 weeks, ventricular remodeling and functional outcomes were evaluated using immunostaining, histology, and echocardiography. Results and Discussion: Upon mixing, Ad-HA and CD-HA formed injectable, shear-thinning hydrogels that were used to encapsulate cells (Fig. 1A). Variations in gel formation and injection parameters, such as flow rate, resulted in parabolic flow velocity profiles at low flow rates (0.1 mL/h, Fig. 1B) and more plug-like flow profiles at high flow rates (5 mL/h, Fig. 1C). Live/dead staining of 3T3 cells after injection (Fig. 1D, 1E) showed higher viability in middle regions of the extruded gel for low flow rates. A plug-like flow profile showed higher overall viability compared to a parabolic flow profile, demonstrating an ability to enhance cell viability necessary for in vivo efficacy. Injection of EPCs encapsulated in gel in a rat model of AMI resulted in enhanced cell engraftment and vasculogenesis compared to injection of EPCs alone (15.3 ± 5.8 vessels per high power field compared to 5.0 ± 2.1 vessels per high power field, p < 0.001). Decreased myocardial scar fraction (9.9 ± 5.6 versus 27.0 ± 7.6, p < 0.0001) and increased ejection fraction (68.9 ± 12.0 versus 57.3 ± 10.7, p < 0.03) were also observed after injection of cells in gel compared to cells alone. Conclusion: We developed an injectable, shear-thinning hydrogel system for cell delivery that could be tuned to enhance cell viability after injection. In vitro assessments of cell viability show that material and flow properties affect cell viability. Delivery of cells using one formulation showed positive results for recovery after AMI in a rat model, and due to the tunable nature of the gels, this system is broadly applicable in the field of injectable cellular therapeutics. This work was funded in part by NIH T32-AR007132 (to MHC), R01 HL111090 (to JAB), TSFRE Nina Starr Braunwald Research Fellowship (to ACG), AHA predoctoral fellowship (to CBR), and AATS David C. Sabiston Research Scholarship and AHA Scientist Development Grant 13SDG17230005 (to PA).