(601g) In Vitro Biologics Recovery Tissue Platform with Collagen and Crosslinking Hyaluronic Acid Hydrogels

Collagen and hyaluronic acid (HA) are major components of the extracellular matrix of many native tissues. Hydrogels composed of collagen and HA are capable of mimicking various natural tissue material properties. Although the use of collagen and HA are common in the tissue engineering community, the physical and mechanical properties of these materials are variable and poorly understood. Neither alone creates an elastic network similar to tissues. Collagen I networks have mechanical integrity, whereas HA alone is a viscoelastic liquid and does not. Therefore, chemical modifications of HA are common to impart structural integrity and elasticity. In the current study, we examined the rheological and mechanical properties and colocalization of hybrid collagen I and aldehyde/hydrazide-crosslinked HA (HAX) hydrogels for tissue engineering applications. We then created in vitro models of large molecule diffusion and recovery through these hybrid ColHAX hydrogels.

Hydrogel formulations with collagen at 2, 4, and 6 mg/mL and HAX at 20, 30, and 40 mg/mL were combined to form hybrid ColHAX gels. Hydrogel concentrations are denoted by CyHAXz, where y and z indicate the concentration of collagen and HAX in mg/mL respectively. The storage moduli of the ColHAX gels increased from 540 to 1900 Pa with increasing collagen concentration and increased from 100 to 3000 Pa with increasing HAX concentration (Figure 1A). The pore size of the hybrid ColHAX gels were smaller than that of collagen or HAX alone. The swelling capacity increases with increased concentration of HAX, and the swelling capacity of C6HAX30 is higher than that of both C2HAX30 and C6HAX30. The degree of colocalization of collagen and HA, represented by R_{colocalization}, is significant in C6HAX30 and C4HAX20 gels, which are both when the ratio of collagen to HAX is 1:5 (Figure 1B). The release of BSA, lysozyme, and β-lactoglobulin out of the ColHAX gels are impacted by both the hydrogel microstructure and the properties of the released proteins (Figure 2). C2HAX30 and C4HAX30 gels have the same recovery of all proteins; however, C6HAX30 gels release the lowest % of BSA and the highest % of β-lactoglobulin compared to gels with the same concentration of HAX (Figure 2A). At C6HAX30, colocalization of collagen and HA are impacting the microstructure and thus affecting diffusion. C4 gels demonstrate the highest % release compared to gels with the same concentration of collagen, and C4HAX30 releases more BSA and β-lactoglobulin than C4HAX40 (Figure 2B).

Results from this study demonstrate that ColHAX hybrid gels show promise as tissue engineered materials. These hydrogels have a wide range of mechanical and rheological properties and microstructures that impact diffusion and recovery of model proteins. Overall, this study delineates design rules for formulating ColHAX hydrogels that are tailored for in vitro tissue models. These gels can then be used as tissue platforms for drug diffusion and recovery.