As a first-semester freshman in the Fall of 2022, I enrolled in the First-Year Engineering Program’s Honors Research Experience course, where fellow first-year engineering student Taylor Norris and I began a research project in Dr. Jin-Woo Kim’s Bio/Nano Technology Lab. Our project involved developing a composite membrane using polycaprolactone (PCL), a synthetic polymer, and cellulose nanocrystals (CNCs), naturally occurring biopolymers, to be used as a cardiovascular cell scaffold. Guided by post-doctoral researcher Dr. Joseph Batta-Mpouma, we hypothesized that this PCL/CNC composite material would overcome the mechanical and physicochemical limitations of PCL alone for the stress-intensive cardiovascular system, eventually providing an alternative treatment for cardiovascular disease. During the Fall 2022 and Spring 2023 semesters, Taylor and I empirically established a mixing protocol to achieve relatively homogenous solutions of PCL and CNCs at different concentrations of CNCs, used a spin coater to cast these solutions into flat, even films, and used a Discovery Hybrid Rheometer-2 (DHR-2) to mechanically characterize these films. After the conclusion of the Honors Research Experience course in the Spring 2023 semester, I chose to continue working on this project, now supported by an Honors College Research Grant. During Spring 2024, my first funded semester of research, Dr. Batta-Mpouma and I made significant strides toward the conclusion of this work.
Our initial findings, which were unexpected, revealed that as the concentration of CNCs in the film increased beyond a certain threshold (0.02 w/v%), the mechanical strength decreased. We attributed this result to the centripetal forces present in the spin coating process, which pushed the CNCs to the edges of the film, weakening its center. To address this, I proposed a different method that I had come across in the literature – the doctor blade method. This method, which I implemented this semester, involved casting the films using a doctor blade, thereby eliminating the presence of the centripetal forces and preserving the homogenous dispersal of CNCs throughout the films. After casting the films, I stretched them using the DHR-2, pictured below.
Here, I am locking the DHR-2’s forceps with the film in place. After I finish locking the forceps, the DHR-2 will stretch the film and output its mechanical properties.
This mechanical characterization revealed that the films were much more mechanically strong than before, but the data still showed a decrease in mechanical strength beyond the same 0.02 w/v% threshold. This result prompted Dr. Batta-Mpouma and I to consider the effect of the films’ thicknesses on their mechanical properties. Because the doctor blade is operated manually, I could adjust the casting gap to allow for the casting of thicker films. After casting these thicker films, I stretched them using the DHR-2, and I found that the thicker films did not exhibit the same decrease in mechanical strength beyond the 0.02 w/v% threshold. This confirmed our hypothesis that the films’ thicknesses affected their mechanical properties and that increasing the concentration of CNCs increased the mechanical strength of the composite membrane.
After the mechanical characterization, Dr. Batta-Mpouma trained me to use atomic force microscopy (AFM) to evaluate the surface properties of the films, especially the surface roughness. Using capillary force lithography, I transferred patterns onto the films. For each ratio of PCL to CNC and thickness, I created one completely flat film and another patterned with nanogrooves. Then, I used the AFM to image these films and to evaluate their surface roughness. I found that as the concentration of CNCs in the film increased, the surface roughness also increased. This indicated that adding CNCs to the films provides more attachment sites for cells, effectively increasing the cell affinity of the films. This result is promising and further confirms our hypothesis that a PCL/CNC composite material is better suited for the cardiovascular system than PCL alone. This semester, I have presented my research on two separate occasions. In February, I traveled to Little Rock, where I presented a poster to state legislators. Then, in April, I presented a 15-minute oral presentation at the American Institute of Chemical Engineers Mid-America Regional Conference hosted on our campus. I always enjoy presenting my findings, as it allows me to gain an outside perspective on my work.
Looking ahead, our research will focus on determining the contact angle of each ratio and thickness of films, which will indicate their hydrophobic or hydrophilic nature. We anticipate that as the concentration of CNCs is increased, the films will become more hydrophilic, thereby increasing their cell affinity. Additionally, we plan to conduct a thermogravimetric analysis to measure the degradation of the films over time, providing crucial information about their longevity as a biomedical tool. We aim to compile all these results in the early part of the Fall 2024 semester, the second funded semester of this research project. Subsequently, I will draft an article detailing this project and our results, with the hope of publishing it before the end of the Fall 2024 semester.
Throughout this semester, participating in this Honors College Research Grant-funded research project has greatly enhanced my engineering education. During this project, I encountered many challenges, as noted previously. To overcome them, I had to think outside the box and not be afraid to be wrong. Sharing my research with others has also improved my confidence and stimulated my interest in research. Overall, this grant, and undergraduate research as a whole, has been a cornerstone of my education so far, and I am excited to continue in the world of research in the future.