In vitro dynamic bladder models for studying urinary tract infections: a narrative review

Experimental models of the bladder are key to studying the pathogenic mechanism of catheter-related bacterial biofilm infection. Although numerous studies have reported multiple models, these model designs were heterogeneous. This study aimed to review the status quo and explore the problems associated with in vitro dynamic bladder models for studying urinary tract infections (UTIs). The PubMed and SinoMed databases were searched from their inception to February 2020. Studies regarding in vitro bladder models related to UTIs were reviewed based on a bibliometric evaluation of their basic characteristics and model analysis. A total of 74 papers and 44 bladder models were included in this study. The results were as follows: (I) urine transmission devices: 10 studies applied the gravity effect of culture media, while the others used peristaltic pumps, and 11 of them combined stirring or rotating forces. The flow rates in all studies ranged from 15 µL/min to 50 mL/min. (II) Bladder model: two studies reported on simulating the bladder using plastic bags, while the others reported on glass cylinders or fermenters with a capacity of 200 to 700 mL. E. coli and P. mirabilis were the main bacterial strains. (III) Infection carrier: six studies reported planktonic bacteria as their infection carrier, while 45 studies reported silica gel, rubber, polyurethane, silicone, polytetrafluoroethylene, or perfusion bag. (IV) Infection medium: 25 studies reported the culture medium. Thirty-two studies reported artificial urine, while 17 studies reported human urine. (V) Research analysis: 45 studies investigated the bacterial biofilm formation in the bladder model. Thirty-six studies compared the effects of various drug coatings, diverse material surfaces, or different materials. Only five studies compared distinct bladder models. The included studies' main defects were the single simulation of bladder urodynamics, divers parameter settings, and non-standard experimental modeling. Our analysis showed for the first time that in vitro dynamic bladder models could provide new ideas for exploring the mechanism and prevention of bacterial biofilm infection in urinary implanted biomaterials. Due to the limitations of the included studies, more high-quality studies are needed to verify the conclusions above further.