| With recent advances in tissue engineering and microfluidics, it is now possible to engineer physiologically relevant in vitro 3D tissue-like structures by tuning the geometry and dynamics of microfluidic environments for multicellular culture. This capability offers an entirely new way of studying how host tissues interact with drugs, pathogens, and biomaterials. In this investigation, a multi-channel microfluidic device was designed and used to visualize in real-time the effects of Staphylococcus epidermidis phenotypes on the development of osteoblast cells and bone tissue-like structures. Soft lithography, based on poly(dimethylsiloxane), was used to fabricate the microfluidic device for cross-contamination free, high-throughput co-culture of the host cells and the bacteria. In the absence of bacteria, osteoblasts formed a confluent layer on the bottom surface of the channel within 2 days, gradually migrated to the side and top surfaces between 3 to 4 days, and formed calcified 3D tissue-like structures in 8 to 12 days. The timing and concentration of antibiotic delivery were controlled to produce several phenotypes of S. epidermidis: (1) actively proliferating bacteria, (2) slow-growing bacteria, (3) dormant, sessile biofilm colonies, and (4) dead bacteria. With the actively proliferating and slow-growing bacteria, osteoblasts became severely damaged within a few days. In contrast, the sessile biofilm colonies and dead bacteria did not interfere with the formation of 3D tissue-like structures. These results suggested that: (1) metabolically active, planktonic bacteria were most likely responsible for the observed virulence of S. epidermidis and (2) dormant, sessile biofilm bacteria and osteoblasts did not compete for the surface required for their adhesion and growth. With these findings, the microfluidic approach is presented as a viable method for further development of in vitro 3D tissue models that can be used to systematically correlate: (1) progression of wound healing, (2) pathogenesis of biofilm development, and (3) the efficacy of novel anti-biofilm drugs and biomaterials aimed at treating biofilm-related infection of orthopaedic implants. |
