UCLA

Chronic wounds affect many patients in the United States every year and generally coincide with other cardiovascular diseases, such as diabetes and foot ulcers. Current treatments for chronic wounds are lacking effectiveness and in the case of surgical intervention cause pain to patients. Therefore, new therapies are emerging that involve the use of hydrogels to promote natural healing by the body. Hydrogels (used as a biomaterial scaffold) have emerged as an option to treat chronic wounds, however, these scaffolds are implanted into the body and may not actually mimic the native tissue. Typically, scaffolds are completely rigid, whereas the human body is dynamic, with forces pushing and pulling constantly on tissues and cells. This thesis explored the creation of a dynamic scaffold for the repair of chronic wounds.

This work focused on creating a scaffold from modified hyaluronic acid polymer building blocks that could form after injection into the body, thus decreasing the need for surgical intervention. The scaffold contained differing ratios of cross-linkable and non-cross-linkable microspheres (or building blocks). The cross-linkable spheres form the porous network of the scaffold, while the non-cross-linkable spheres are able to move around and introduce dynamic forces into the system. In addition to the scaffold creation, a large portion of this work included optimizing the fabrication of these polymer building blocks (or microspheres). The microspheres were created using both inverse suspension and microfluidic setups. The goal was to create uniform spheres to eliminate the possible effect differing geometries could have on the scaffolds. The observable difference in the scaffolds was thus the amount of cross-linked spheres and non-cross-linked spheres.

After fabrication of the microspheres, a scaffold was created by mixing the microspheres together with a cross-linker and characterized through Rheometry, and microscopy. After analysis, the time and minimum amount of cross-linkable spheres required for gelation to occur in the scaffolds was determined to be 1 hour and 30 minutes and 50% respectively. Additionally, it was observed that after decreasing the amount of cross-linkable spheres below 80%, the overall scaffold strength and modulus significantly decreased. Lastly, it was observed that the void space or free space in the scaffolds did not significantly change between any of the scaffold conditions. Following physical characterization, the scaffolds were cultured with human dermal fibroblasts to determine how the dynamic scaffold would interact with the cells. For all the dynamic scaffolds, as well as the control scaffold (a completely cross-linked porous microsphere scaffold) there was an increase of proliferation and spreading over the 7-day trial. Although there was improvement in all the conditions, there was no statistical difference seen between the conditions. Thus, it was concluded that all these scaffolds are biocompatible and can improve cell growth; however, at the moment it cannot be stated that a dynamic scaffold has improvement over the traditionally cross-linked scaffold.