Evaluation of bacterial adhesion strength on phospholipid copolymer films with antibacterial ability using microfluidic shear devices†
Biomimetic phospholipid copolymer films are known to possess antifouling properties against protein adsorption and biofilm formation. However, the interactions between bacterial cells and material surfaces are not fully understood. This work investigated the bacterial adhesion strength of phospholipid copolymer films using a shear stress-tunable microfluidic device. The copolymer, comprising 2-methacryloyloxyethyl phosphorylcholine (MPC), 3-methacryloxypropyl trimethoxysilane (MPTMSi), and 3-(methacryloyloxy) propyl-tris(trimethylsilyloxy) silane (MPTSSi), formed crosslinked films on glass substrates; the thickness of the coating film was controlled by the polymer concentration during dip-coating. Polymer films with two typical thicknesses, 20 and 40 nm (denoted as C-20 and C-40, respectively), were prepared on the bottom wall of the microfluidic device. After seeding S. aureus in the microfluidic device, several shear stresses were applied to evaluate the adhesion strength of the polymer films. S. aureus was found to have weaker adhesion strength on the C-40 surface than on the C-20 surface; numerous bacterial cells detached from the C-40 surface on application of identical shear stress. To mimic the presence of plasma protein, fibrinogen (Fg) was introduced into the device before performing the bacterial adhesion assay. The results showed that the adsorption of Fg promoted S. aureus adhesion and strong interactions under shear stress. However, the adhesion strength of S. aureus did not affect the Fg adsorption for both the C-20 and C-40 surfaces. Using the shear stress-tunable microfluidic device, we found that the adhesion of S. aureus on the thicker and softer phospholipid copolymer was weak, and the cells easily detached under high shear stress.