6 well plates

The substrates used to support the different droplets include polyethylene terephthalate (PET) films, purchased from Goodfellow Corporation (Coraopolis, PA USA), petri dishes, purchased from USA Scientific (Ocala, FL USA), 6-well plates, purchased from USA Scientific (Ocala, FL USA), and silicon wafers, purchased from University Wafer (South Boston, MA USA).

The fabricated devices were sterilized by placing in 70% ethanol for 15 minutes and washing with deionized water. The devices were then dried and exposed to UV for 45 mins. In order to enhance cell adhesion, the microchannels were flushed with a 1:50 (v/v) solution of 0.1% fibronectin (Sigma Aldrich) in PBS (Gibco™) using a syringe pump (New Era). The devices were then incubated overnight at 4°C to coat the PC membrane surface with fibronectin. The microchannels were then washed with PBS three times to remove unattached residues. The cells were introduced into the microchannel at a density of 7.5 million/ml in DMEM at a flow rate 0.5 μl/min. The flow was then stopped for 10 mins during which the cells settled down into the PDMS microwells. Excess cells in the microchannels were removed by washing with DMEM. The devices were then placed in 6-well plates (USA Scientific) and submerged in DMEM. The media could diffuse to the cells through the nanochannels in the PC membrane. The well plates were placed inside an incubator (at 37°C with 5% CO2) for 36 hours to allow for cell adhesion and spreading before carrying out the electroporation experiments. DMEM in each well was replenished every 12 hours.

Staphylococcus aureus (methicillin resistant, ATCC 43300), Staphylococcus epidermidis (ATCC 49134) and Escherichia coli (ATCC 25922), were purchased from the American Type Culture Collection (ATCC, Manassas, VA USA. Human fetal osteoblasts (HfOB 1.19) were also purchased from the ATCC (Manassas, VA USA). The substratum biomaterials used to grow biofilms included polyethylene terephthalate (PET) films, purchased from Goodfellow Corporation (Coraopolis, PA USA), 6-well plates, purchased from USA Scientific (Ocala, FL USA) and silicon wafers, purchased from University Wafer (South Boston, MA USA).