Mechanochemical Control of Stem Cell Biology in Development and Disease: Experimental and Theoretical Models

Whether a stem cell remains or egresses away from its physiological niche is a function of mechanical and soluble factors in a time-dependent manner, which implicates a `memory\u27 of prior mechanochemical conditioning. Virtually every organ in the body contains resident stem or progenitor cells that contribute to organ homeostasis or repair. The wound healing process in higher vertebrate animals is spatiotemporally complex and usually leads to scarring. Limitations for the use of stem cells as regenerative therapy include the lack of expansion capabilities in vitro as well as materials issues that complicate traditional biochemical protocols. A minimal `scar in a dish\u27 model is developed to clarify the kinetics of tension-sensitive proteins in mesenchymal stem cells (MSCs), which possess plasticity to mechanochemical changes of the microenvironment that are typical of scars. The organization and expression of such proteins implicates transcription factors that ultimately steer cell fate. In contrast to classic mechano-transducers of matrix mechanics such as actin assembly-dependent serum response factor (SRF) signaling, a novel mechano-repressive role of NKX2.5 is implicated in maintaining intracellular tension in long-term stem cell cultures on stiff matrices via nucleo-cytoplasmic shuttling — ultimately setting up a \u27mechanical memory\u27. Core gene circuits with known roles in stem cell mechanobiology are modeled based on the \u27use it or lose it\u27 concept: tension inhibits turnover of structural proteins such as extracellular collagens, cytoskeletal myosins and nucleoskeletal lamins. This theoretical approach is tested in a variety of processes in vitro and in vivo that involve forces including cardiac development, osteogenic commitment of MSCs, and fibrosis therapy. With the sophistication of the science and technology of biomaterials relevant to stem cell biology and medicine, matrix mechanics can thus be rigorously combined with biochemical instructions in order to maximize therapeutic utility of stem cells

Antimicrobial efficacy testing of antibiotic-containing biodegradable nanopolymers against biofilm and planktonic cells.

Cystic fibrosis and rampant urogenital infections, caused by increasingly resistant microbial biofilms, call for more creative anti-infective systems. This study investigated the in vitro efficacy of levofloxacin (LEV)–loaded poly(D,L-lactide-co-glycolide) (PLGA) and poly-ε-caprolactone (PCL) nanopolymers against optimally-grown biofilms of Escherichia coli K12 W3110 and Pseudomonas aeruginosa PA01. High-throughput biofilm production and antimicrobial susceptibility testing were conducted in the Calgary Biofilm Device (CBD). Rich Luria-Bertani medium provided maximal accumulation of biofilm biomass, with optimum times (24 and 48 h, respectively) and temperatures (30 C and 21 C, respectively) found under dynamic culture conditions. For both pathogens, minimum inhibitory concentrations (MIC) of 2.8 µg/mL and 16.5 µg/mL total LEV load were found for LEV-PLGA and LEV-PCL, respectively. Minimum biofilm eradication concentrations (MBECs) improved at least 2-fold with increase in exposure time (48 hours) achieving LEV-PLGA MBECs of 1.4 and 0.2 µg/mL and LEV-PCL MBECs of 16.5 and 8.2 µg/mL for E. coli and P. aeruginosa, respectively. With efficient use of drug-encapsulated nanopolymers, bactericidal dosages are sufficiently lowered and dosing intervals can be extended due to the sustained drug release feature afforded by these efficacious nanocarriers.Bachelor of Engineering (Chemical and Biomolecular Engineering