Author: Lillian Hutchinson | Major: Chemical Engineering | Semester: Spring 2025

My name is Lillian Hutchinson, and I am part of the College of Engineering. I am majoring in chemical engineering with a minor in mathematics. I work within Dr. Younghye Song’s lab in the biomedical engineering department. I have completed my second semester of research on my project titled “Adipose-Derived Stem Cell Secretome in 3D Hydrogels for Peripheral Nerve Repair”.
Peripheral nerve injury (PNI) results from damage or trauma to the nerve or surrounding areas and can be permanently debilitating. The autograft is the current gold standard for PNI treatment which is when the damaged nerve is replaced with a nerve from a donor site. The issues with autografts include damage to the donor site, difference in nerve shapes/sizes, and the need for a second surgery. Further work regarding tissue engineered grafts for peripheral nerve repair is needed.
My project seeks to develop a tissue engineered nerve graft from a collagen I hydrogel that elicits a proneural regenerative response. In order to do this I am changing the microarchitecture of the hydrogels to see if the cellular response varies with different collagen fiber orientation and thickness. I am using adipose-derived stem cells within the hydrogel because they have been shown to increase tissue remodeling and secrete matrix metalloproteinases (MMPs) and their inhibitors, TIMPs. MMPs are enzymes that naturally degrade collagen. MMP-2 and 9 have been previously shown to increase neural regeneration, while MMP-14 has been shown to increase MMP-2 expression; therefore, these are secretomes of interest. However, the over expression of MMPs can cause damage to the tissue, so the ratio of MMPs to TIMPs is very important. TIMP-1 has been shown to inhibit MMP-2, 9, and 14, so it is of interest to this study.
To change the microenvironment of the hydrogels, I used a temperature dependent casting method to vary the fiber thickness of the gels. Warm-casting is when the hydrogels are allowed to polymerize at 37°C for 30 minutes while cold-casting is when the gels begin at 4°C then temperature is increased to 22°C and 37°C in a stepwise fashion for 10 minutes each step. Warm-cast gels are characterized as having thinner collagen fibers that form a thick mesh in contrast to the thick collagen fibers of cold-cast gels. The microenvironment was further modified by stretching the hydrogels. By casting the gels in a custom made stretching device, the collagen fibers form in an alignment. I made four combinations of microenvironments: warm-cast non-stretched, warm-cast stretched, cold-cast non-stretched, and cold-cast stretched.
To test the neuroregenerative potential of the hydrogels I measured the MMP-2, 9, and 14 expression in comparison to the TIMP-1 expression. I began quantifying protein expression using Western Blot analysis, but due to the long experiment time and need to improve the protocol, I pivoted to ELISA and dot blot testing. I gathered preliminary data that suggests that the cold-cast stretched hydrogel expresses the most MMPs while the warm-cast non-stretched gel expresses the least. However, the MMP to TIMP ratio with the most potential seems to be the warm-cast stretched gel. I had the opportunity to attend the regional American Institute for Chemical Engineering (AIChE) conference and present a poster over this work. This upcoming
semester I will continue ELISA and dot blot testing to finalize my results and confirm with quantitative data what microenvironment has the best MMP to TIMP ratio.