Concluding Remarks

Shear-thinning hydrogels change from a gel to a liquid state under high enough shear stress, such as the shear stresses that occur during injection. Thus, these systems offer a non-invasive route for otherwise invasive treatments. In the future, fiber-hydrogel composites can be manufactured as a biomaterial for interfacial tissue repair and guest-host hydrogels as an ideal shear-thinning, injectable biomaterial. First, the respective injection forces of fiber-hydrogel composites and non-fibrous hydrogel composites must be examined to ensure clinical injectability of the material into patients. Moreover, the electrospinning technique has gained momentum as a simple technique to create fibrous structures that mimic the fibrous nature of the extracellular matrix. Combining electrospun fibers within a shear-thinning hydrogel has the potential to provide cells with essential physical cues while retaining injectability. Thus arises the question: how is the injection force affected by including fibers within guest-host hydrogels? This study assesses the impact of electrospun PCL (polycaprolactone) fiber inclusions in a shear-thinning hydrogel composed of the guest, adamantine-modified hyaluronic acid (Ad-HA), and the host, cyclodextrin-modified hyaluronic acid (Cd-HA). Injection force was measured using a syringe pump and load cell. Specifically, the average normalized break force, or force needed to overcome static friction, and the average normalized glide force, or the force sustaining extrusion, were quantified for guest-host hydrogels with and without fiber inclusion. The difference in break force between both inclusive and non-inclusive hydrogels was not statistically significant. In addition, no momentary increases in the glide force, likely due to the extrusion of the fiber fragment itself, were observed. Ultimately, comparable average break and glide forces between the inclusive and non-inclusive trials, as well as reduced force fluctuations after the break point of the hydrogel, highlight the limited impedance of fibers during hydrogel injection. Further studies manipulating hydrogel weight percent, hydrogel percent functionalization, and fiber fragment size are required to provide insight into the spectrum of injectable biomaterials, a prerequisite to their clinical implementation.