BME Student Seminar (Zoom): Ryan Donahue and Alicja Jagiello
Department of Biomedical Engineering
Ryan Donahue is advised by Kyriacos Athanasiou
Alicja Jagiello is advised by Elliot Botvinick
Zoom: https://uci.zoom.us/s/97629106431 Password: 198Sem
Ryan Donahue: Tissue engineering of temporomandibular joint disc implants toward clinical translation
Abstract: The temporomandibular joint (TMJ) is a ginglymoarthrodial joint central to everyday functions such as mastication and speech. Of crucial importance is the TMJ disc, which is a fibrocartilaginous structure that distributes large stresses during joint articulation. When function is impaired due to trauma or age-related degeneration, abnormal loading occurs and leads to temporomandibular disorders (TMDs), of which 25% of the general population has symptoms. Specifically, a subset of TMDs include disc displacement proceeded by disc perforation and osteoarthritic changes. Tissue engineering is poised to provide future therapeutics that repair or regenerate the TMJ disc.
Encouraged by previous successes in healing focal disc thinning defects, this work started by extending previously optimized tissue engineering techniques to focal disc perforation defects (3mm diameter). When comparing implant-treated discs to empty defects after 24 weeks, mechanically robust healing occurred; implant-treated groups had repair tissue that was 3.4 times stronger, 8.9 times more resilient and 6.2 times tougher. Additionally, repair tissue of implant-treated groups had more collagen type I and less collagen type III (indicative of scar tissue), compared to empty defects.
To scale-up and improve tissue engineering methods in anticipation of performing additional in vivo work, a number of studies investigated 1) the optimal donor age for costal chondrocytes; 2) the duration of the self-assembling process, which yields maximal tensile properties; and 3) the application of fluid-induced shear (FIS) stress, a mechanical stimulus, to further improve functional properties and flatness of implants. Among neonatal, juvenile and adult cells, juvenile-aged cells balanced among the minor differences in aggregate modulus, total collagen and collagen subtypes. Self-assembly for 56 days increased Young’s modulus by 5.6 times those values at day 7, and 42 days was carried forward to balance with the typical self-assembly timeline (28 days). Finally, the application of FIS stress yielded flat constructs with increased aggregate and shear moduli by 2.3 and 2.7 times those of controls. Moving forward, these parameters were used to tissue-engineer neocartilage implants for large perforation defects.
Finally, large disc perforations (6mm diameter) were examined. After eight weeks, implant-treated discs completely filled with repair tissue, while empty defects displayed through-and-through holes. Specifically, all implant-treated repair tissue tensile metrics and defect perimeter were significantly different than those of empty defects. From focal to large perforations, self-assembled, tissue-engineered cartilage implantation results in significantly improved mechanical healing of TMJ disc defects.
Alicja Jagiello: Dermal fibroblasts and human breast cancer cells differentially stiffen their local matrix
Abstract: Bulk ECM stiffness measurements are often used in research on cell mechanobiology. However, past studies by our group have shown that peri-cellular stiffness can span few orders of magnitude and diverges from the bulk properties. Using optical tweezers active microrheology (AMR), we are able to describe stiffness landscape around individual cells. In this study, we show how different cell lines cultured in 1.0 and 1.5 mg/ml type 1 collagen (T1C) create disparate patterns of peri-cellular stiffness. We found that dermal fibroblasts (DFs) increase peri-cellular stiffness, when embedded in 1.0 mg/ml T1C hydrogels, but do not alter stiffness in 1.5 mg/ml T1C hydrogels. In contrast, invasive human breast cancer MDA-MB-231 cells (MDAs) do not significantly change the stiffness of T1C hydrogels, as compared to cell-free controls. Results indicate that while MDAs adapt to the bulk ECM stiffness, DFs regulate local stiffness to levels they intrinsically “favor." Moreover, both cell lines were subjected to three different treatments that were previously shown to regulate their migration, proliferation and contractility. In response to each treatment, cells established dissimilar stiffness patterns. Peri-cellular stiffness magnitude and extent of anisotropy varied with the cell line, T1C concentration and treatment. In summary, we demonstrate that AMR can reveal mechanical properties of the local ECM, which are known to affect cell behavior at the macro-scale, but are obscured by bulk stiffness measurements.