Browsing by Author "Cox, Lewis M."

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Pericellular Matrix Formation and Atomic Force Microscopy of Single Primary Human Chondrocytes Cultured in Alginate Microgels
(Wiley, 2023-09) Fredrikson, Jacob P.; Brahmachary, Priyanka P.; June, Ronald K.; Cox, Lewis M.; Chang, Connie B.
One of the main components of articular cartilage is the chondrocyte's pericellular matrix (PCM), which is critical for regulating mechanotransduction, biochemical cues, and healthy cartilage development. Here, individual primary human chondrocytes (PHC) are encapsulated and cultured in 50 µm diameter alginate microgels using drop-based microfluidics. This unique culturing method enables PCM formation and manipulation of individual cells. Over ten days, matrix formation is observed using autofluorescence imaging, and the elastic moduli of isolated cells are measured using AFM. Matrix production and elastic modulus increase are observed for the chondrons cultured in microgels. Furthermore, the elastic modulus of cells grown in microgels increases ≈ten-fold over ten days, nearly reaching the elastic modulus of in vivo PCM. The AFM data is further analyzed using a Gaussian mixture model and shows that the population of PHCs grown in microgels exhibit two distinct populations with elastic moduli averaging 9.0 and 38.0 kPa. Overall, this work shows that microgels provide an excellent culture platform for the growth and isolation of PHCs, enabling PCM formation that is mechanically similar to native PCM. The microgel culture platform presented here has the potential to revolutionize cartilage regeneration procedures through the inclusion of in vitro developed PCM.
Through-Thickness Modulus Gradient and Pattern Fidelity of UV-Cured Thiol-Acrylate Films
(American Chemical Society, 2024-08) Darabi, Amir; Cox, Lewis M.
The utilization of photopolymers in diverse applications such as microfluidic devices, gas inhibitors, and biomimetic tissues has surged due to advancements in digital light processing technologies that now support multimaterial platforms, facilitating micrometer-scale control over material heterogeneity. However, significant knowledge gaps remain in our understanding of spatiotemporal evolution within these multimaterial actinic films and layers. To help bridge these gaps, a thiol-acrylate system is employed for photopatterning, and atomic force microscopy is leveraged to map through-thickness modulus profiles at various UV exposure levels, in both flood and masked curing setups. This approach enables the evolution of material properties to be tracked through the film thickness for incremental light exposure durations and across different photopatterned feature sizes. The results illustrate complicated modulus profiles that highlight the complex interplay among light exposure parameters, polymerization kinetics, oxygen inhibition, and light scattering.
Tunable Surfaces and Films from Thioester Containing Microparticles
(American Chemical Society, 2022-06) Martinez, Alina M.; Cox, Lewis M.; Darabi, Amir; Bongiardina, Nicholas J.; Nowman, Christopher N.
Reported here, thioester containing microparticles were designed with 40% excess thiol to enable thiol–thioester exchange to facilitate the formation of cohesive films from the particles. A thiol-Michael dispersion polymerization was used to generate thioester containing microparticles with a diameter of 4.0 ± 0.4 μm. The particles were then swollen with a base at varying concentrations to activate the thiol–thioester exchange and subsequently compressed between two glass slides. Resultant films were characterized over time with profilometry and atomic force microscopy (AFM) to infer particle coalescence at different catalyst loadings and times. Tensile tests were performed confirming the structural integrity of the particle-based films. Furthermore, microparticles were welded to a nondynamic network demonstrating feasibility in potential applications to generate materials containing differing mechanical properties. Being able to control the functionality of particles, and thus mechanical properties of the resultant films, is also important for applications in coatings, adhesives, and 3D printing where spatial patterning or selective material property control is needed.